A Novel Method for the Production of Microwires by Alexander Michael Couch B.S., United States Naval Academy (2017) Submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of

Master of Science in Mechanical Engineering at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY

February 2019

Massachusetts Institute of Technology 2019. All rights reserved.

redacted A u th o r ...... Signature .. Department of Mechanical Engineering 1, y.- january 14, 2019 Certified by...... Signature redacted ...... Kasey Russell Principal Member of the Technical Staff, The Charles Stark Draper Laboratory

Certified by.....SignatureC ertified by ...... redacted Thesis...... Supervisor .. . Irmgard Bischofberger Assistant Professor of Mechanical Engineering Signature redacted Thesis Supervisor A ccepted by ...... MASSACHUSES INSTITUTE I Nicblas Hadjiconstantinou OF TECHNOWOGY Chairman, Department Committee on Graduate Theses FEB 252019

LIBRARIES ARCHIVES A Novel Method for the Production of Microwires by Alexander Michael Couch

Submitted to the Department of Mechanical Engineering on January 14, 2019, in partial fulfillment of the requirements for the degree of Master of Science in Mechanical Engineering

Abstract Radio frequency (RF) systems such as cell phones and GPS can perform better and last longer if we can reduce electrical heat loss in the wires. This is typically done in power systems by twisting or weaving the wires, following one of several patterns. Though, at radio frequencies, wire dimensions must scale down by as much as 1000 times in order to achieve the same effects. This project decomposes the problem into two main categories; the manufacturing of micron scale wires and the manipulation of these wires in order to form a twisted bundle. This project aims to produce twisted bundles of wire that have an AC resistance value at GHz frequencies approaching a fundamental limit in which electrical resistance is independent of frequency. This thesis focuses specifically on the first major problem: producing micron scale wires of considerable length. In order to accomplish this, I have developed a bottom-up approach to the manufacturing of microwires. Rather than reducing the diameter of a wire by drawing through successive dies, I have instead formed a wire by metalizing a small nanofiber core to reach the target diameter. Initially, I designed a mechanical system to harvest Nomex nanofibers 200-400 nm in diameter that have been electrospun onto a spinning drum. Next, I designed a system to concentrically coat the harvested nanofibers with a conductive seed layer via sputter deposition. Finally, I have designed a reel to reel system in order to electroplate over a segment of seeded nanofiber in order to achieve the target diameter. This now allows for the creation of microwires of considerable length for use in high frequency applications.

Thesis Supervisor: Kasey Russell Title: Principal Member of the Technical Staff, The Charles Stark Draper Laboratory

Thesis Supervisor: Irmgard Bischofberger Title: Assistant Professor of Mechanical Engineering

2 Acknowledgments

This thesis was prepared at The Charles Stark Draper Laboratory and was funded by the Air Force Research Laboratory (AFRL) and the Defense Advanced Research Projects Agency (DARPA) under Contract No. FA8650-15-C-7543. Draper Labora- tory was instrumental in providing me with both the guidance and funding necessary for a meaningful graduate experience. Every person in the A2P program has pro- vided me with assistance and without them, I would not have been able to contribute meaningful research and write a coherent thesis. Specifically, I would like to thank Kasey Russell, my thesis co-supervisor, for being so supportive and helping me find a project that is both interesting to me and can contribute to the program as a whole. I would also like to thank David Carter, who has been instrumental in helping with my research and the logistics regarding the Draper Fellow Program. Peter Lewis has also greatly helped in my research, helping with SEM imaging and using the Focused Ion Beam at MIT, as well as many other small things. Heena Mutha has also greatly helped, working closely with me on electroplating and providing guidance in an area I had never previously worked in. I would like to thank Irmgard Bischofberger, who served as my thesis co-supervisor and included me in her lab group at MIT over the past two years. Irmgard, through her leadership and passion for research, has cultivated an innovative and welcoming research group culture, and I learned a lot both from her and from the other members of our lab group. Through group presentations of my progress, both Irmgard and my fellow group members have been able to provide meaningful feedback and have thus been instrumental in my work. I am incredibly grateful that the Navy allowed me the opportunity to pursue my Master's Degree through the Immediate Graduate Education Program. Graduate school has provided me with an opportunity to better myself academically and has also allowed me to learn more about myself. I would also like to thank my friends and family for their tremendous support throughout my time here. Without them, I would not be where I am today.

3 Contents

1 Introduction 11 1.1 Motivations for the Production of Microwires ...... 11 1.2 Current Methods for the Fabrication of M icrow ires ...... 13 1.2.1 The Wollaston Process ...... 14 1.2.2 Taylor-wire Process ...... 15 1.2.3 Further Developments of the Taylor-wire Process ...... 16 1.2.4 Other Methods for Creating Fine Wires ...... 17 1.3 A Proposal for a New Method of Creating Fine Wires ...... 18 1.3.1 Electrospinning ...... 18 1.3.2 Sputter Deposition ...... 22 1.3.3 Electroplating ...... 25

2 Nanofiber Harvesting 27 2.1 Challenges Associated with Small Diameter Fibers ...... 27 2.2 Initial Harvesting Efforts ...... 30 2.3 Fluidic Tensioning of Nanofibers ...... 31 2.4 Mechanical Spooling System ...... 32

3 Sputtering a Conductive Seed Layer onto a Nanofiber 36 3.1 Sputtering System and Requirements ...... 36 3.2 Fiber Sputtering Assembly Design ...... 37 3.3 Sputtering Results ...... 39

4 4 Electroplating Over a Conductive Nanofiber 41 4.1 Initial Electroplating Efforts ...... 41 4.2 Contactless Electroplating in a Reel-to-Reel System 44 4.3 Reel-to-Reel Electroplating ...... 47 4.4 Proof of Concept for Reel-to-Reel Electroplating 52

5 Conclusions 54 5.1 Thesis Summary ...... 54 5.2 Future Work...... 55

A Bill of Materials and Engineering Drawings for Mechanical Spool Design. 57

B Bill of Materials and Engineering Drawings for Fiber Sputtering Assembly 65

C Bill of Materials and Engineering Drawings for Electroplating As- sembly 72

5 List of Figures

1-1 Graph showing the effect of frequency on skin depth for a copper wire in the G H z range...... 12 1-2 Schematic demonstrating typical wire drawing equipment. The wire is pulled from a coil onto a rotating bull block, passing through a die and is reduced in diam eter [4]...... 13 1-3 Taylor-wire drawing cylinder. f, 2mm diameter holes used for drawing. c, steel rod used to hold the copper cylinder in position. a, copper cylinder containing holes used for drawing [7]...... 15 1-4 Taylor-Ulitovski process in progress at Microfir Tehnologii Industriale Ltd. Shown is a glass tube with a drop of metal alloy heated by a high frequency inductor. This glass tube with molten metal is then drawn through an orifice to create a glass coated microwire [15]...... 17 1-5 Schematic illustration of the electrospinning process. The illustration also shows a typical SEM image of the nonwoven mats often formed and a drawing of the Taylor cone [22] ...... 19 1-6 Plexiglas disk with copper wires used by P. Katta et al to collect aligned nanofibers formed via electrospinning. [23]...... 20

6 1-7 Top: Image of equipment used to electrospin fibers with the metallic needle appearing in the top left of the image and the grounded col- lector appearing in the center of the image [25]. Bottom: Functional schematic illustrating how electrospinning is implemented. The left of the image represents the metallic tip where the fiber originates. This metallic tip is able to move laterally along the length of the grounded and spinning collector, allowing for the collection of a continuous fiber. 21 1-8 Aligned Nomex fibers on the spoked-drum collector...... 22 1-9 Schematic of a simplified DC sputtering system [291. Shown is a target (cathode) from which metal atoms are ejected, the substrate (anode), a pump to evacuate the chamber, and an argon feed...... 23 1-10 Image of the KDF 900 series system [30]. This system is an example of a DC Magnetron sputtering system and is used in this research. . . 24 1-11 Schematic demonstrating the establishment of a charge on a metal when placed into an electrolyte solution [32]...... 25 1-12 Schematic demonstrating the main components of a DC electroplating system [32]...... 26

2-1 Graph demonstrating the scaling issues associated with Nomex fibers of small diameters. Shown are the forces generated by gravity on a Nomex fiber of density 0.90 g/cm 3, the forces generated by office air disturbance at a speed of 0.1 m/s, and the electrostatic force between two fibers spaced apart by 1 cm...... 28 2-2 Frame containing ~ 200-400 nanometer diameter Nomex fibers. .. . 29 2-3 Nano Universal Testing Machine used to determine the force at which Nom ex nanofibers fail...... 29 2-4 Initial spooling efforts showing a schematic of the initial design (left) and a view of the overall setup (right)...... 30

7 2-5 Controlling tension during spooling of bare Nomex nanofiber. a, Schematic illustration of our tensioning process utilizing hydrophilic interactions between the nanofiber and a water meniscus to provide controllable sub-micronewton forces to tension the nanofiber during spooling. b, Image of Nomex nanofiber in contact with water meniscus during spool- ing. c, Image of Nomex nanofiber wound around target spool. .... 31 2-6 SEM image of harvested nomex fiber on initial solid spool...... 32 2-7 The initial SolidWorks design (left) and the first build (right) of the mechanical spooling system to be used for nanofiber harvesting. Also shown in the image is a large fiber used for initial tests...... 33 2-8 Image showing the Nomex nanofiber spanning the distance between the electrospinning collector and the secondary spool...... 34 2-9 ~ 1.2 meter length of Nomex nanofiber harvested using the mechanical spooling system ...... 35

3-1 SolidWorks model of the fiber sputtering assembly...... 38 3-2 Fiber sputtering assembly pictured after a sputtering run...... 39 3-3 SEM image showing the sputtered fiber after being cross sectioned by a focused ion beam (left) and a zoomed in image of the same fiber in order to determine the thickness of the seed layer (right)...... 40

4-1 A schematic representation of the plating process claimed in the 1974 patent [34]. Shown in this image is a pair of wire pushing rollers push- ing the wire through various baths and processes in order to create a continuous electroplating line...... 42 4-2 Electroplating bath set up. A syringe pump circulates electroplating solution as it passes through a water bath to raise the temperature and provide more concentric plating. The wires are plated where there is an exposed meniscus of electrolyte providing isolation and mechanical support for the wire as it is plated...... 43

8 4-3 SEM images of gold plated Nomex wire of ~ 5 pm diameter. Left: Image of a wire plated at 8 mA/cm 2 current density for 15 minutes. Right: Cross section of wire prepared by focused ion beam milling showing the Nomex core surrounded by a ~ 2.5 micron thick layer of electroplated gold...... 44 4-4 Reel-to-reel contactless electroplating concept. A metal anode and cathode in two separate streams of conductive saline and gold plat- ing solution are bridged by the nanowire, completing the circuit and allowing for electroplating...... 45 4-5 Contactless electroplating test. A metal anode and cathode in two sep- arate drops of gold plating solution and conductive saline are bridged by a 1 mil copper wire, completing the circuit and allowing for electro- plating...... 46

4-6 SEM images obtained at 2.2 mA/cm 2 (top left), 4.3 mA/cm 2 (top right), 6.5 mA/cm 2 (bottom left), and 8.6 mA/cm 2 (bottom right) over 30 m inutes...... 46 4-7 Early flow system design integrating a peristaltic pump ...... 48 4-8 Mechanism for how the peristaltic pump creates pulsations [35]. . .. 49 4-9 Reel-to-reel electroplating assembly consisting of two heavily geared stepper motors to drive the wire and one heavily geared stepper motor to drive the linear stage...... 50 4-10 Images of the assembled spooling system for plating. Left: Image of the system showing both spools, the cathode rod, the anode rod, and the wire between spools. Right: Image showing the liquid bridge in which the wire passes through...... 51 4-11 Image of the full plating system, including the mechanical spooling system and the flow system...... 51

9 4-12 Schematic image demonstrating what a wire would look like throughout the plating process. Left: Image of the wire where plating initially begins. Middle Left: Image of wire where plating transitions from rough to relatively smooth. Middle Right: Image of wire where gold plating can be seen. Right: Image of wire at the end of plating where the transition from smooth plating and back to bare copper can be seen. 52 4-13 Optical image showing the cross section of the 1.5 mil diameter copper wire coated by a layer of plated gold...... 53

5-1 Image showing data collected during electroplating of the 1.5 mil bare copper wire. The arrow in the image shows an abrupt transition in which the voltage rapidly increases...... 55

10 Chapter 1

Introduction

The first portion of this chapter will outline the motivations for a new method for the production of microwires. Although it is currently possible to create wires of a relatively small diameter, these methods are both time consuming and incredibly expensive. As such, this thesis will explore other possibilities in a unique way. The rest of this chapter will feature background information on each of the processes used in this research.

1.1 Motivations for the Production of Microwires

Radio Frequency (RF) systems such as cell phones and GPS perform better and last longer if the electrical heat loss in the wires is reduced. This is done in power systems by braiding the wires, creating what is known as a Litz bundle. At high frequencies, alternating current does not penetrate deeply into a wire, but rather flows near the surface due to an increased resistance in the center of the wire [1, p. 120-121]. When operating, the conductor can approximately be considered to be replaced by its outer shell, of thickness known as the skin depth [1, p. 122j. By braiding wires, each individual wire spends an equal amount of time on the inside of the bundle, where resistances are higher, and on the outside of the bundle, where resistances are lower. This allows for the reduction in the skin effect for the bundle as a whole [2]. However, at RF, each individual wire will experience the skin effect unless wire dimensions are

11 -1

scaled down (1000x). Figure 1-1 demonstrates the effect of frequency on skin depth for a copper wire.

10-4-

0f.

as -o c 10-6

106 10 109 1010 Frequency (Hz)

Figure 1-1: Graph showing the effect of frequency on skin depth for a copper wire in the GHz range.

At frequencies in the range of 1 GHz and above, the skin depth rapidly decreases to a thickness less than that of the radius of most commercial wires. This project as a whole aims to produce braided Litz bundles that have an AC resistance value at GHz frequencies approaching a fundamental limit in which electrical resistance is independent of frequency. To do this, sub-micron wires must be produced and braided. This project decomposes the challenges of fabricating RF Litz wire into three component challenges: fabricating sub-micron diameter wires with centimeter- scale and meter-scale length; optionally attaching anchors to the ends of the wires to enable manipulation; and manipulating the wires into twisted or braided structures. This thesis will focus specifically on the creation of meter-scale length wires that are on the scale of one micrometer in diameter. To achieve wires of the necessary diameter and strength, a novel process has been developed that begins with a strong nanometer-scale diameter polymer wire scaffold fabricated by electrospinning. The fiber is then conformally coated with a layer of gold (20-40 nm) in order to make the fiber conductive. Finally, the fiber is drawn through an electrochemical bath in order

12 to electroplate the fiber to a goal diameter of one micrometer.

1.2 Current Methods for the Fabrication of Microwires

Wire is most commonly made by drawing, through the forcing of metal through a die by means of a tensile force applied at the exit of the die [3]. Wire drawing begins with a wire rod, a small rod that has been reduced in diameter by hot-rolling. This wire rod then receives a surface treatment, depending on the metal. The end of the wire rod is then reduced in diameter, by means of a metallurgical process, passed through the die, and connected to a drawing block, as shown in Figure 1-2 [4].

Die Wire

Coil Bull block Side view of Top view bull block

Figure 1-2: Schematic demonstrating typical wire drawing equipment. The wire is pulled from a coil onto a rotating bull block, passing through a die and is reduced in diameter [4].

For coarse wires of larger diameters, a single draw block is used. For finer wires, a larger number of draw blocks are used, with the wire passing through a number of dies until it reaches its final diameter in one continuous operation. For fine wires "reductions per pass of 15 to 25 percent are used, while for coarse wires the reduction per pass may be 20 to 50 percent [4]". Drawing through dies becomes less practical as the required diameter decreases below 50 pum. In principle, it is possible to draw ductile metals to a diameter of 5

13 ,um to 10 pm, though the process requires many drawing and annealing stages. As a result, manufacturing smaller wires by drawing is extremely labor intensive, and therefore expensive [3,4]. However, there are other methods which rely on producing microwire in one operation directly from the melt that have been used successfully to produce a wide variety of metals and alloys in sizes ranging from more than 100 pm down to around 1 pm [5]. These methods, as well as several others, will be reviewed below.

1.2.1 The Wollaston Process

In 1813, William Hyde Wollaston published a paper titled "A Method of drawing extremely fine wires [6]." In this paper, Wollaston discusses his process for drawing extremely fine wire of both gold and platinum. To begin, Wollaston notes that it is possible to draw silver wires as small as 1/500th of an inch in thickness, beginning with a rod 3 inches in diameter. He then proposes that at any stage of this process, a hole can be drilled through the silver rod longitudinally, having its diameter one-tenth part of that of the rod, and if a wire of pure gold is inserted to fill the hole, that by continuing to draw the rod, the gold within it will be reduced in diameter in exactly the same proportion to the silver. Then, to remove the silver, Wollaston placed the wire for a few minutes in warm nitrous acid, which dissolves the silver without danger of doing anything to the gold [6]. After some time, Wollaston found that it was too difficult to drill a central hole all the way through a silver rod, and thus wondered if platinum could be used in a similar process. Because of the infusability of platinum, Wollaston surmised that he would be able to coat it with silver, rather than trying to drill though silver. To this end, Wollaston formed a cylindrical mold 1/3 of an inch in diameter, fixed a platinum wire in the center, and then filled the mould with silver. With this process, Wollaston was able to obtain wires of platinum as small as 1/18000 of an inch (1.4 pm) as well as short, interrupted segments of platinum as small as 1/30000 of an inch (850 nm) [6].

14 1.2.2 Taylor-wire Process

In 1924, G.F. Taylor first reported a method for drawing wire directly from melt in his paper titled "A Method of Drawing Metallic Filaments and a Discussion of their properties and uses [7]". The process, which is now known as the "Taylor-wire process," consists of filling a glass tube with the desired metal, placing the glass tube in a heated cylinder or flame, and drawing it out to the desired diameter [8]. To begin the Taylor-wire process, a glass tube having a 2 mm inner diameter is closed at one end, then a bit of the metal to be drawn is dropped into the tube. The end of the tube is then heated until the metal melts and the glass softens. At this stage, the softened end of the glass tube is drawn out to a diameter of about 0.5 mm to 1 mm and a foot or more in length. Next, the tubes are drawn down further by passing the tubes through holes in a heated copper cylinder, a schematic of which is shown in Figure 1-3 [7,8].

Sa 0 0 fO 0 0

Fig. 1

Figure 1-3: Taylor-wire drawing cylinder. f, 2mm diameter holes used for drawing. c, steel rod used to hold the copper cylinder in position. a, copper cylinder containing holes used for drawing [7].

Toward one end of the cylinder is a row of holes f, each 2 mm in diameter. The copper cylinder is held in position at the other end by a smaller steel rod c. Finally, the copper cylinder is heated to be bright red at the end nearest the supporting rod a, in order to create a heat distribution across the rest of the cylinder. Depending on the temperature required for drawing, one of the holes in the cylinder is selected to be used for drawing. The glass covered wire is then passed through the hole, grabbed by a pair of forceps, and drawn out as fine as desired. The size of the wire is determined by wall thickness of the glass, the rate at which it is fed into the heated cylinder, and the rate at which it is drawn out. With this process, Taylor claims to have produced

15 wires as fine as 1 pm [7].

1.2.3 Further Developments of the Taylor-wire Process

By the 1950s and 1960s, a growing interest in the development of microwires was being shown, mainly due to potential applications in small electrical components [5]. In 1957, A. V. Ulitovsky filed a patent in the USSR for the production of microwires with diameters that range from 2 to 20 pm on a commercial scale [9]. A number of later patents disclosed that the process being used was a modified Taylor-wire process [5]. One such patent, filed by Baikov, showed that the method involved feeding a glass tube, closed at one end and containing a metal wire, continuously into an high frequency inductively heated zone [10]. The metal in this zone would then melt, softening the glass around it. The softened glass and molten metal was then drawn and wound onto a take up drum. By varying the take up speed, feed rate, cooling rate, and initial glass thickness, the diameter of the final wire and thickness of the coating can be controlled [5]. Over time, a number of other patents and studies were published further refining the process [11-14]. Today, Microfir Tehnologii Industriale Ltd. is an example of a company using the Taylor-Ulitovski process [15]. This process can be seen in Figure 1-4.

16 A

Drop ofmetlallk

Figure 1-4: Taylor-Ulitovski process in progress at Microfir Tehnologii Industriale Ltd. Shown is a glass tube with a drop of metal alloy heated by a high frequency inductor. This glass tube with molten metal is then drawn through an orifice to create a glass coated microwire [15].

1.2.4 Other Methods for Creating Fine Wires

In addition to drawing processes, several methods have been developed to prepare microwire by ejecting molten metal through a fine orifice into gaseous or liquid envi- ronments. Under certain conditions (high ejection velocity, use of gas or liquid with a high cooling rate, surface tension of the melt, viscosity, etc.), it is possible to maintain a stable stream of melt, which will then solidify into a solid filament. These methods have been used to create wires ranging from ~ 13 pm to 3 pm [5,16-18]. Today, most methods for creating fine microwires involve the use of drawing in order to achieve a suitable diameter [3]. But, all of these methods are time consuming, expensive, and are limited by how small a diameter they can obtain.

17 1.3 A Proposal for a New Method of Creating Fine Wires

As an alternative to the wire manufacturing methods previously discussed, I have worked to develop a bottom-up approach to manufacturing microwires. In this sense, a bottom-up approach means that I will start from a very fine nanofiber, and then metalize it to obtain the target diameter. I first harvest a continuous segment of a Nomex nanofiber, formed via electrospinning. Next, I sputter coat the Nomex fiber with a seed layer in order make the fiber conductive. Finally, I develop an electroplat- ing line in order to metalize the conductive fiber. Subsections 1.3.1-1.3.3 will discuss the underlying ideas behind electrospinning, sputter coating, and electroplating.

1.3.1 Electrospinning

Electrospinning is a technique that allows for the fabrication of continuous fibers with diameters down to only a few nanometers [19]. In the electrospinning process, a polymer solution is held at the end of a capillary spinning tip by surface tension. Next, a large charge is induced at the liquid surface by means of an electric field. As the charge at the surface increases, repulsive forces cause the hemispherical surface to transition into a conical shape known as the Taylor cone [20]. At a critical point, in which the repulsive force overcomes the surface tension force, a stream of liquid is ejected from the tip of the Taylor cone. The ejected polymer solution jet undergoes an instability and elongation process, which allows the jet to become very long and thin [21]. During this time, the solvent evaporates and leaves behind a charged polymer fiber. The trajectory of the charged polymer fiber can then be manipulated using an electric field [19]. In this way, continuous fibers can be laid onto the grounded collector. A schematic of the apparatus used in the electrospinning process is shown in Figure 1-5 [22]. The apparatus consists of three major components: a high-voltage power supply, a metallic needle, and a grounded collector. The metallic needle is

18 connected to a syringe in which the polymer solution is held. Thus, a syringe pump can be used to feed the solution through the needle at a controllable rate. When the high voltage is applied across the metallic needle and the grounded collector, a long and thin charged polymer will be laid onto the grounded collector. The fiber is often deposited in a randomly oriented, nonwoven mat, as seen in the inset of Figure 1-5.

Polymer Solution

M* P

Syringe Driver

High Voltage Fiber Formation Supply

Figure 1-5: Schematic illustration of the electrospinning process. The illustration also shows a typical SEM image of the nonwoven mats often formed and a drawing of the Taylor cone [22].

Although electrospinning often results in the formation of randomly oriented non- woven mats, researchers have also explored the possibility of electrospinning aligned nanofibers, as they have potential applications in systems that require highly ordered architectures. In a 2004 paper, P. Katta et al explored this possibility by substituting the grounded platform with a copper wire-framed drum [23]. This copper wire-framed drum consists of two circular nonconducting Plexiglas disks connected together by a series of copper wires. This drum can be seen in Figure 1-6.

19 Figure 1-6: Plexiglas disk with copper wires used by P. Katta et al to collect aligned nanofibers formed via electrospinning. [23].

The set up created by P. Katta et al placed the copper wire drum 15 centimeters below the needle, and rotated the drum at a speed of 1 rpm. Initially, the nanofibers were collected at the copper wire closest to the needle, then as the drum rotates, the next copper wire attracts the nanofibers allowing for the fibers to be laid perpendic- ular to the copper wires and onto the drum. Through these experiments, P. Katta et al were able to demonstrate good alignment up to approximately 15 minutes of electrospinning [23]. In a similar manner, our collaborators Aykut Aydin and Professor Roy Gordon at Harvard University have developed a process for the alignment of small diameter nomex fibers spaced evenly on a rotating drum collector [24]. Figure 1-7 shows an image of the equipment used to electrospin fibers as well as a functional schematic illustrating how electrospinning is implemented.

20 -j

2000-2500 rpm C

+

Figure 1-7: Top: Image of equipment used to electrospin fibers with the metallic needle appearing in the top left of the image and the grounded collector appearing in the center of the image [25]. Bottom: Functional schematic illustrating how elec- trospinning is implemented. The left of the image represents the metallic tip where the fiber originates. This metallic tip is able to move laterally along the length of the grounded and spinning collector, allowing for the collection of a continuous fiber.

The electrospinning tip moves laterally along the length of the grounded and spinning collector, allowing for the collection of a continuous fiber. By using this system, as well as controlling a series of other parameters, Aykut Aydin has been able to achieve aligned fibers along the length of the spoked drum collector, as seen in Figure 1-8.

21 Figure 1-8: Aligned Nomex fibers on the spoked-drum collector.

In Figure 1-8, the region on the right end of the drum corresponds to the initiation of the spinning where randomly aligned fibers are collected. The metallic tip was then scanned along the spoked-drum to produce aligned fibers along the rest of the collector. These aligned fibers can be seen faintly in the picture. The rotating drum is 180 mm in length and 90 mm is diameter. In this thesis, these Nomex fibers, which range from 200 to 400 nm in diameter, will be used as the core of the microwires. The fibers will be coated with a thin conducting seed layer and then metalized via electroplating, resulting in a bottom-up approach to fabricating wires.

1.3.2 Sputter Deposition

Sputtering is the process which removes atoms from the surface of solids through the bombardment of high energy particles. This process leads to surface erosion and the modification of the surface morphology [26, p. 180]. Sputtering is used for many indispensable processes in modern technology, such as the removal of surface layers, surface analysis, depth profiling, and the deposition of thin films [27]. One of the largest applications of sputtering, including in this thesis, is the de- position of thin films onto a variety of substrates, both large and small [26, p. 203].

22 This process involves bombarding a target surface, resulting in the ejection of atoms onto a substrate. The composition and properties of the deposited films depend on the deposition process, such as short or long pulsed or continuous sputtering of the substrate and the residual gas pressure during deposition [28]. This is particularly useful, as sputtering allows for the deposition of films having the same composition as the target source [26, p. 180]. Figure 1-9 depicts a simplified sputtering system capable of depositing metal films.

Subsrate E

- voc

Argon Fed + Target

To Pump Figure 1-9: Schematic of a simplified DC sputtering system [29]. Shown is a target (cathode) from which metal atoms are ejected, the substrate (anode), a pump to evacuate the chamber, and an argon feed.

Inside a simple sputtering system, such as the one shown in Figure 1-9, is a pair of parallel metal electrodes. One of these electrodes is known as the target and acts as the cathode. The target will be bombarded with gas ions which will cause atoms to be ejected. In this system, the cathode is connected to the negative terminal of a DC power supply. Opposite the target is the substrate or anode. The chamber is then evacuated in order to create a vacuum. Next, a working gas is introduced. This working gas serves as the medium in which an electrical discharge is initiated and sustained. After reaching a high enough voltage, a visible glow discharge is maintained between the electrodes. Once this happens, current will begin to flow and metal from the target deposits on the substrate [26-28, p.145-1461. On a smaller scale, positive gas ions in the discharge strike the target. This bom-

23 bardment will transfer momentum and cause the physical ejection of atoms. These atoms will then pass through the discharge region to deposit onto the anode, allowing for the creation of a thin film [26, 28, p. 146].

7 I~7 KDFrn' 954i

Figure 1-10: Image of the KDF 900 series system [30]. This system is an example of a DC Magnetron sputtering system and is used in this research.

In this thesis, I will utilize the KDF 900 series system, as seen in Figure 1-10. The KDF 900 series system is an example of a cathodic sputtering system. In a cathodic sputtering system, the bombardment of the target is by positive ions derived from an electrical discharge in a gas [31]. More specifically, the KDF 900 series system is a DC magnetron sputtering system. Magnetron is the most widely used variant of DC sputtering, as it is capable of high deposition rates, whereas diode sputtering suffers from very low deposition rates [31]. The magnetron uses the principle of ap- plying a specially shaped magnetic field to a diode sputtering target. In a magnetron sputtering system, the electrons generated at the cathode become trapped in a lo- calized region due to the generated magnetic field [31]. Because of this, there is a much higher chance for these electrons to experience an ionizing collision with a gas atom, leading to more positive gas ions striking the target [31]. Examples of appli- cations of DC magnetron sputtering includes metalizing for microelectronic circuits, electrical resistance films, magnetic films, optical storage devices, and bonding lay- ers [31]. Additionally, DC magnetron sputtering can be used for general metallurgical films [26, p. 222-223]. In this thesis, I will make use of this application in order to apply a thin conductive layer onto a nonconductive Nomex nanofiber.

24 1.3.3 Electroplating

Electroplating is a process in which an electric current is passed through an electrolyte solution in order to reduce dissolved metal ions so that they form a solid metal coating on an electrode. Though there are several forms of electroplating, I will mainly discuss electrolytic metal deposition, as this is the process I will be using in this thesis. The core principle of the electrodeposition of a metal is shown in Figure 1-11. When a metal is placed in an electrolyte solution, a dissolution takes place whereby metal atoms leave the metal lattice of the solid to form positive ions in the electrolyte. As a result, an opposite charge develops on the metal. This electrostatic charge has the opposite effect and attracts the positively charged metal ions back to the negatively charged metal. After some time, the system will come to equilibrium, resulting in an equal number of ions leaving the metal lattice and rejoining the metal lattice [32,33].

C+- +

Figure 1-11: Schematic demonstrating the establishment of a charge on a metal when placed into an electrolyte solution [32].

If instead the metal is connected to an electron source or sink, a reaction will take place moving the system out of equilibrium. If the metal is attached to an electron source, more electrons will flow into the metal, resulting in the attraction of more positive metal ions in the solution. Similarly, if the metal is attached to an

25 electron sink, more electrons will leave the metal, resulting in the repulsion or more metal ions in the solution. The former system results in a cathodic system in which electrodeposition will take place, while the later results in an anodic system in which dissolution takes place. This cathodic system is the basis of electroplating [32,331. A DC electroplating system can be seen in Figure 1-12. Two electrodes are im- mersed in an electrolyte solution and are connected together with a power source. The cathode is a conductive solid and will be plated on. The anode is the material from which the positive metal ions will be removed. Applying a voltage potential, as shown in the figure, will upset the equilibrium of the system and drive a reaction. The negative charge on the cathode results in the positive metal ions in the solution being attracted, leading to the deposition of metal onto the cathode surface. The positive charge on the anode results in the repulsion of positive metal ions taken from its own metal lattice. In another type of electroplating system, the anode is instead a permanent anode that will not dissolve. In this system, positive metal ions are added to the electrolyte bath. As a result, the positive metal ions are taken from the bath, rather than from a solid, and deposited onto the cathode [32,33].

R A V

Cathode AA Anode

Cations

Electrolyte

Figure 1-12: Schematic demonstrating the main components of a DC electroplating system [321.

In this thesis, I will utilize electroplating to form the bulk of the wire around the nanofiber core.

26 Chapter 2

Nanofiber Harvesting

In this chapter, I will describe the challenges associated with and the methods used to harvest small diameter nanofibers formed via electrospinning. The scale of these nanofibers range from 200-400 nm, and as such present challenges that call for un- conventional solutions.

2.1 Challenges Associated with Small Diameter Fibers

In Wollaston's 1813 paper "A method of drawing extremely fine Wires," Wollaston describes some challenges of working with small diameter wires. In this paper he states, "when the diameter [of a wire] is not less than 1/2000 or 1/3000 of an inch (12.7 um to 8.5 um), the difficulty of seeing and applying them in short pieces is not considerable; but when their diameter is farther reduced, and their length as much as an inch or more, the slightest current of air is sufficient to defeat all attempts to lay hold of an object so difficult to see, and so impossible to feel [6]." Just as Wollaston found, working with fibers at a scale of 200-400 nm presents many challenges, as the fibers cannot be seen unless under perfect lighting conditions, and are also at a scale in which gravity is not the dominating force. Figure 2-1 demonstrates how at such small scales, electrostatic forces and wind currents cause a much greater effect on a Nomex fiber.

27 10- 106

E 8 10A z-2 10-70 E1crsttc(1kot m 0 10-1

-Electrostatic (11kV at 1 cm) 10-1- Office Air Disturbance (0. 1 mn/s) Gravity (Nomex, 0.9 g/cm3

...... I . . . 10-12 10- 1 101 102 Fiber Radius ( ym)

Figure 2-1: Graph demonstrating the scaling issues associated with Nomex fibers of small diameters. Shown are the forces generated by gravity on a Nomex fiber of density 0.90 g/cm3 , the forces generated by office air disturbance at a speed of 0.1 m/s, and the electrostatic force between two fibers spaced apart by 1 cm.

Figure 2-1 shows the forces generated by gravity on a Nomex fiber of density 0.90 g/cm 3, the forces generated by office air disturbance at a speed of 0.1 m/s, and the electrostatic force between two fibers spaced apart by 1 cm. As seen above, both electrostatic forces and office air disturbances will dominate a fiber of radius less than roughly 8 pm. At the scale of the Nomex fibers, ranging from 200-400 nm, gravity is hardly even noticed. Instead, the fibers will sway in the air in any direction, and will be strongly attracted to anything carrying a static charge. In addition to these challenges, the fibers also present the problem that they fail under tension at extremely low loads. In order to determine the loads at which the fibers fail, a frame of fibers, as seen in Figure 2-2, was sent off to the Wan Lab at Northeastern University. These fibers were loaded into a universal testing machine (UTM) for nanomechanical characterization. This machine, seen in Figure 2-3, offers nanomechanical characterization by utilizing a nanomechanical actuating transducer head to produce tensile force.

28 Figure 2-2: Frame containing - 200-400 nanometer diameter Nomex fibers.

Probe Load Cell

Vertical (Z-axis) Horizontal Stage (X-Y) Stage

Figure 2-3: Nano Universal Testing Machine used to determine the force at which Nomex nanofibers fail.

The Wan Lab utilized this Nano UTM to determine the tensile force at which the fibers failed. After performing a number of these tests, the Wan Lab showed that these fibers will break at a tensile force of 60-80 pN. This low tensile strength will, therefore, present additional challenges for harvesting.

29 2.2 Initial Harvesting Efforts

As in commercial wire manufacturing, using a spooled process offers great potential for economies of scale. As such, the initial efforts of fiber harvesting focused on a reel-to-reel process for the spooling of bare Nomex nanofiber. In this first iteration, I made use of a custom rotation stage to rotate the electrospinning collector at a fixed rate while manually removing one end of the Nomex nanofiber, attaching it to a second, smaller spool, and spooling onto the secondary spool. The initial design can be seen in Figure 2-4 which shows a schematic of the initial design (left) and a view of the overall setup (right).

Espinning TargtSpool

Nanofiber

Target spool

E-spinning Collector Fixed Rotation Stage

Figure 2-4: Initial spooling efforts showing a schematic of the initial design (left) and a view of the overall setup (right).

With this method, I was able to successfully spool 0.9 meters of ~ 300 nm diameter Nomex fiber onto the secondary spool, though not without difficulty. With this simple set up, static electricity and ambient wind in the room proved to be a very difficult problem to overcome. With the low tensile strength of the nanofiber, it is incredibly difficult to reliably tension the fiber between spools without breaking it. As a result, the fiber must be held loose between the two spools, though this introduces its own problems, as the ambient wind in the room blows the fiber in any which direction. This leads to an unreliable collection in which I could not control where on the target spool the fiber would go. In addition, the fiber would blow near the 3D printed plastic part,

30 which held a high static charge that would introduce additional problems. Though difficult, these first efforts gave me the confidence that I could iterate on this design to produce a reliable spooling method.

2.3 Fluidic Tensioning of Nanofibers

To further improve the spooling process, I developed a method to controllably tension the wire during spooling. As I have discussed previously, nanofibers are extremely sensitive to disturbances from typical laboratory phenomena. As such, it is important to maintain tension on the nanofiber during spooling in order to control the spooling process. Though, with a breaking strength on the order of 50 pN, the fibers can not easily be mechanically tensioned. Instead, I have chosen to utilize surface interactions with water to provide a controllable force at the appropriate scale, as seen in Figure 2-5. a

Nanofiber contacting meniscus

Target spool

Vial of water on vertical stage E-spinning Collector 0! Figure 2-5: Controlling tension during spooling of bare Nomex nanofiber. a, Schematic illustration of our tensioning process utilizing hydrophilic interactions be- tween the nanofiber and a water meniscus to provide controllable sub-micronewton forces to tension the nanofiber during spooling. b, Image of Nomex nanofiber in contact with water meniscus during spooling. c, Image of Nomex nanofiber wound around target spool.

31 With this method, the fiber can be spooled in a much more reliable fashion, leading to a controlled capture onto the target spool. The reason that this is so vital is because the Nomex fiber tends to stick very strongly to itself, which will introduce difficulties in further processes. In addition, as seen in Figure 2-5, I changed the design of the target spool from a solid drum to a spoked drum, looking very similar to the electrospinning collector. After the initial spooling test in which 0.9 m of nanofiber was collected onto the target spool, it could no longer be seen with the naked eye. Only after imaging the target spool with an SEM, as seen in Figure 2-6, could we manage to see the fiber. As seen in the image, the diameter of the fiber is on the order of the surface defects present on the solid spool. For these reasons, a spoked drum must be used for future processing.

Figure 2-6: SEM image of harvested nomex fiber on initial solid spool.

2.4 Mechanical Spooling System

In order to scale up the efficiency and repeatability of harvesting fibers, it is impor- tant to create a mechanized system capable of automating the reel-to-reel harvesting of nanofibers. Because of this, I have created a reel-to-reel spooling system which consists of three independent stepper motors. One stepper motor is used to rotate the electrospinning collector, another is used to rotate the secondary spool, and the third is used to translate a stage which holds a vial of water, used for tensioning the

32 .1

nanofiber. The original SolidWorks design (left) and the first build (right) can be seen in Figure 2-7.

Linear Target Stage Spool

E-spinning Collector

Figure 2-7: The initial SolidWorks design (left) and the first build (right) of the mechanical spooling system to be used for nanofiber harvesting. Also shown in the image is a large fiber used for initial tests.

The motor rotating the electrospinning collector and the motor rotating the sec- ondary spool are synced as to provide the same tangential velocity at the edge of the spools. The third stepper motor is used to move a linear stage. Seated on this stage is a small glass vial containing water so as to create a meniscus at the opening. Utilizing the principles discussed prior, the nanofiber is laid onto the meniscus to provide proper tensioning. The nanofiber is intentionally not put under mechanical tension, but rather held loose between the electrospinning collector and the small spool. This is done to allow the surface interactions to tension the fiber and because it is extremely difficult to provide the mechanical precision necessary to not break the fiber. This glass vial is placed onto the linear stage, as the tensioning at the surface will allow for us to guide the collection of the fiber onto the target spool. An Arduino Uno and two Adafruit motor shields are used to drive the motors independently at their specific RPM. A bill of materials, as well as engineering drawings, are included in Appendix A. After testing the system with a large diameter wire, the set up was brought to Harvard University where Aykut Aydin does the electrospinning. The electrospinning

33 collector was first loaded into the system. Next, I manually removed a length of fiber from the electrospinning collector and attached it to a small piece of carbon tape on the secondary spool. After ensuring the nanofiber was contacting the meniscus of water, a power source was connected to the Arduino and spooling was started. An image showing the nanofiber spanning the distance between the electrospinning collector and secondary spool can be seen in Figure 2-8. w

Figure 2-8: Image showing the Nomex nanofiber spanning the distance between the electrospinning collector and the secondary spool.

Using this mechanized spooling system, I have been able to reliably harvest meter long lengths of Nomex nanofiber. Figure 2-9 shows the secondary spool and ~ 1.2 meters of Nomex nanofiber after one successful run.

34 -1

Figure 2-9: - 1.2 meter length of Nomex nanofiber harvested using the mechanical spooling system.

Having developed a method to reliably harvest Nomex nanofibers of a diameter of 200-400 nm, the next step is to develop a means of making the fibers conductive so that they may be electroplated on, thereby forming a microwire with a bottom-up approach.

35 Chapter 3

Sputtering a Conductive Seed Layer onto a Nanofiber

In this chapter, I will describe the method and design I have chosen to form a con- ductive seed layer on a harvested nanofiber. This method will utilize sputtering to form a conductive seed layer on fibers which have been harvested, as described in the previous chapter. Sputtering onto these nanofibers presents challenges, mainly resulting from size limitations in the sputtering chamber and due to the fact that sputtered particles only come from one direction.

3.1 Sputtering System and Requirements

As mentioned in Chapter 1, the sputtering system used in this thesis work is a KDF 900 series machine. One such machine was shown in Figure 1-10. The 900 series KDF system is utilized as it is capable of producing nearly uniform thin films for many application critical devices. The KDF system features horizontal cathode and substrate orientation, with the target located above the substrate. As a result, sput- tering in this system yields a top-down metal deposition. The KDF system features a 13" x 13" pallet capable of housing many different wafer sizes, including up to four 6 inch wafers at the same time. In addition, the KDF system is capable of holding substrates up to 1.5" thick. These limits, as well the fact that the KDF operates

36 under vacuum, must be considered when designing a system for sputtering on the harvested nanofibers.

3.2 Fiber Sputtering Assembly Design

Initial brainstorming about how to sputter onto the Nomex nanofiber focused on a reel-to-reel system, similar to the one described in the previous chapter. As the idea was looked into farther, it became clear that there would be many challenges that would need to be overcome in order to make a reel-to-reel sputtering process viable. The biggest challenge is designing a system in which the fiber could be tensioned reliably in a mechanical spooling system. Because the KDF operates under vacuum, the same fluidic tensioning method used previously can not be used. The only other possible method would be to mechanically tension the fiber, but that is not feasible considering the precision required at the scale of these forces. In addition, the space available in the KDF system at 13" x 13" x 1.5" and the fact that the sputtered material is transferred vertically from the top limit the design space for this problem. After deciding not to utilize a spooling system to sputter coat the nanofibers, the next design critical limitation was considered. In the KDF system, this limitation arises due to sputtered material only transferring from one direction. The design must also be limited to 1.5" in height and should utilize a wafer design, as the KDF features convenient wafer to pallet loading. A SolidWorks model of the initial design is shown in Figure 3-1. Shown in this figure is the secondary spool, containing the harvested Nomex nanofibers, coupled to a geared Pololu DC micromotor. Six 3V coin cell batteries are used to power this motor and a switch is used to initiate the system. A bill of materials and engineering drawings can be seen in Appendix B.

37 Coin Cell Battery

Secondary Toggle Spool Switch

Polol[)C Assembly Cover

Figure 3-1: SolidWorks model of the fiber sputtering assembly.

This design was chosen as the rotation of the secondary spool will allow each segment of the Nomex nanofiber to be coated on the top and bottom, resulting in conformal coating. In addition, the design is featured on a standard 6" wafer and has a height of just under 1". Finally, the design features an assembly cover to shield the assembly components from sputtered material. In building and assembling this design, the materials and epoxy used must be KDF compatible. To this end, the entire assembly was machined from 6061 aluminum. In addition, the battery clips and wiring are isolated from the aluminum base through the use of GI, a high-pressure fiberglass laminate. Finally, the battery clips are epoxied down to the base using Armstrong C7 with activator W. Another important consideration in this design is whether or not it will cause virtual leaks. A virtual leak occurs when there exists a small pocket of gas that is trapped in the chamber with a limited release path. A good example of a virtual leak that could occur in this system would be a small pocket of gas trapped in the small area above and around the screws that connect the base plate to the assembly cover. Taking this into consideration, drill holes were tapped slightly deeper to allow for a

38 perpendicular hole to be machined into their path thereby providing a release path. The final build, pictured after a sputtering run, can be seen in Figure 3-2.

Figure 3-2: Fiber sputtering assembly pictured after a sputtering run.

3.3 Sputtering Results

After the assembly of the fiber sputtering design, the system was then placed into the KDF and sputtered on. Initially, 100 angstroms of titanium were sputtered onto the nomex nanofibers in order to create a strong adhesion layer. Next, 200 angstroms of copper were sputtered to create a 30 nm total seed layer. The results of this sputtering run can be seen in Figure 3-3.

39 Figure 3-3: SEM image showing the sputtered fiber after being cross sectioned by a focused ion beam (left) and a zoomed in image of the same fiber in order to determine the thickness of the seed layer (right).

In the left image, the sputtered fiber is imaged using an SEM. The cross section of interest is created by using a focused ion beam. In order to prevent the fiber from being displaced by the ion beam, it is anchored down by sputtering a small layer of platinum, which can be seen covering the fiber. The right image, then, shows a much closer image of the cross section of interest. In this image it is possible to see that the Nomex core is - 307 nm in diameter and the sputter coated seed layer is roughly conformal and ranges from ~ 26 to 32 nm in thickness. Other images show similar results, meaning that this design can be used to deposit nearly concentric seed layers on harvested nanofibers. In the following chapter, these seeded nanofibers will be electroplated on to achieve the target wire diameter. Although successful, there is one drawback to this design which must be addressed. Because the nanofiber is spooled onto a drum with spokes, there are small segments of the fiber which cannot be sputtered on. It is the hope that the continuous seed layer on the outer portion of the fiber contacting each spoke will allow for electroplating in a relatively concentric fashion.

40 Chapter 4

Electroplating Over a Conductive Nanofiber

In this chapter, I will describe the progress made in the metalization of the Nomex wire. Initially, efforts of metalization were done on small centimeter scale segments of sputter coated nanofibers. After showing initial electroplating efforts were successful, the focus then shifted to electroplating in a reel-to-reel fashion.

4.1 Initial Electroplating Efforts

Electroplating, most typically, is done in a very large bath that is both heated and agitated in which static objects are plated on, though there have been efforts to plate on wire in a reel-to-reel manner. Figure 4-1 shows a schematic for a reel-to-reel plating line from a 1974 patent [34]. In this system, wire is drawn off a substrate reel via wire pushing rollers, then passes through various baths to clean, plate, and anneal the wire.

41 WATER RINSE

10 11 2 16 18 20

1 4 1411 14MI 1433

SUBSTRATE ELECTRO- -COPPER ANNEALING CUT AND REEL CLEANER PLATING FURNACE PACKAGE WIRE PUSHING ACID MAGNETIC TEST ROLLERS ETCHANT PLATING

Figure 4-1: A schematic representation of the plating process claimed in the 1974 patent [34]. Shown in this image is a pair of wire pushing rollers pushing the wire through various baths and processes in order to create a continuous electroplating line.

As discussed in previous chapters, typical reel-to-reel efforts that rely on mechan- ical tensioning, like the one shown above, are extremely difficult to implement at the scale of the Nomex nanofibers. As a result, conventional electroplating methods on fibers drawn through a bath and tensioned mechanically cannot be used. Rather, an unconventional method of achieving this tensioning must be utilized. Looking forward to the end goal of a reel-to-reel plating line, the first idea stemmed from the fluidic tensioning as discussed in Chapter 2. Initially, I wondered whether or not a wire could be electroplated on while contacting a meniscus of plating solution, rather than being submerged in a bath. This idea quickly evolved into placing the wire in a small fluidic channel to ensure that the wire would be completely submerged during the plating process. In addition, this fluidic channel could also be used to fluidicly tension the wire in a reel-to-reel process in order to allow for reliable collection on the secondary spool. The first iteration of design can be seen in Figure 4-2.

42 Water Bath Nomex w Syringe Pump T=95 OC ---

44A Wir frame menisc

Circulating fluid "ater batH

Figure 4-2: Electroplating bath set up. A syringe pump circulates electroplating solution as it passes through a water bath to raise the temperature and provide more concentric plating. The wires are plated where there is an exposed meniscus of electrolyte providing isolation and mechanical support for the wire as it is plated.

Figure 4-2 shows the first design in which plating in a fluidic channel was tested.

In this iteration, centimeter scale length Nomex fibers which had previously been sputter coated were brought into contact with a fluidic channel, labeled as the plating meniscus in the rightmost image. The schematic illustration at the top shows a syringe pump used to circulate plating solution, a water bath used to heat the plating solution, the wire frame which is then connected to the potentiostat and acts as the cathode, and a platinum wire entering through the bottom of the tubing into the solution and acting as the anode. The syringe pump is used as a means to agitate the solution so as to prevent gold ions from depleting locally. By tuning the fluid flow rate, the bath temperature, and the time for plating, I have successfully demonstrated electroplating gold films concentrically onto sputter coated polymer nanofiber scaffolds. Figure 4-3 shows an SEM image of one successful electroplating run.

43 DRAPER

Figure 4-3: SEM images of gold plated Nomex wire of ~ 5 pm diameter. Left: Image of a wire plated at 8 mA/cm 2 current density for 15 minutes. Right: Cross section of wire prepared by focused ion beam milling showing the Nomex core surrounded by a ~ 2.5 micron thick layer of electroplated gold.

In the above images, a - 40 pm segment of electroplated nanofiber can be seen on the left, while a cross section prepared by focus ion beam milling can be seen on the right. In the cross sectioned image, the nanofiber core can clearly be seen surrounded by a concentric gold coating. With this process, we were able to coat a ~

2.5 pm thick layer of gold onto a conductive fiber at a current density of 8 mA/cm 2 . With these successes, the next steps involve creating a scalable and manufacturable approach, namely, a reel-to-reel elecroplating process.

4.2 Contactless Electroplating in a Reel-to-Reel Sys-

tem

Initially, I electroplated the polymer nanofibers on metal frames by making an elec- trical connection to the frame (cathode), and a platinum wire in solution (anode). However, as I extended the system capabilities to reel-to-reel processing I had to look towards better solutions for applying a potential across the wire without making rigid electrical connection. As such, I have developed a contactless electroplating system shown in Figure 4-4. In this modified configuration, we create an electrochemical cell

44 across two platinum wires dipped in two separate solutions: the gold electroplating solution and a conductive saline solution respectively. The nanowire bridges the two completing the circuit and allowing current to pass through the loop. This should allow us to electroplating onto the wire at a fixed current and a voltage between the cell anode and cathode.

Cathode (V-)

S=I Anode (V+) Pt electrodes 1MKCI

Nomex Au plated

Figure 4-4: Reel-to-reel contactless electroplating concept. A metal anode and cath- ode in two separate streams of conductive saline and gold plating solution are bridged by the nanowire, completing the circuit and allowing for electroplating.

In order to test the feasibility of this contactless plating, we first attempted to plate using an extremely simple system as shown in Figure 4-5. This system consists of two droplets, one of gold electroplating solution, and one of 3.5 M KCl solution. Spanning these two solutions is a 1 mil Copper wire. One platinum wire is placed in the electroplating solution and acts as the anode. The second platinum wire is placed in the salt solution and acts as the cathode.

45 I

Figure 4-5: Contactless electroplating test. A metal anode and cathode in two sepa- rate drops of gold plating solution and conductive saline are bridged by a 1 mil copper wire, completing the circuit and allowing for electroplating.

This concept was tested over a range of 2.2-8.6 mA/cm 2 (2-8 A/ft 2 ), as recom- mended by Transene, the company from which we have acquired the electroplating solution. Images of plating at 2.2, 4.3, 6.5, and 8.6 mA/cm 2 over a period of 30 minutes can be seen in Figure 4-6.

Figure 4-6: SEM images obtained at 2.2 mA/cm 2 (top left), 4.3 mA/cm 2 (top right), 6.5 mA/cm 2 (bottom left), and 8.6 mA/cm 2 (bottom right) over 30 minutes.

46 As seen in the images above, plating at up to - 4.3 mA/cm 2 yields relatively smooth plating, whereas burning begins to occur at 6.5 mA/cm 2 and is extremely bad at 8.6 mA/cm 2. Burning, in this case, occurs when there are not enough metal ions present locally at the cathode. When this happens, hydrogen ions will reduce to hydrogen gas, leading to an increase of hydroxide ions locally. In our case, the increase in the amount of local hydroxide will lead to the precipitation of gold hydroxide. This will lead to bumpy and inconsistent coating, as seen in the bottom left of the figure above, or hardly any coating, as seen in the bottom right of the figure above. Here then, 4.3 mA/cm 2 appears to be the limit at which current can be pushed while still creating a relatively smooth plated surface. Burning, though, can be reduced with agitation, a higher temperature, and a higher gold ion concentration. These factors will be taken into consideration when creating a reel-to-reel electroplating line.

4.3 Reel-to-Reel Electroplating

Initial goals for plating were to demonstrate up to 1 micron of plating over a length of 10 cm of wire. With an advertised deposition rate of 0.25 [tm per minute, plating in a small fluidic channel (0.5 cm in diameter) over a length of 10 cm would take over 80 minutes, assuming that plating actually occurred at the advertised rate. Drawing on the initial electroplating bath set up, which utilized a syringe pump to achieve agitation, it was decided that I would have to transition to a peristaltic pump in order to achieve a closed system for continuous flow in a reel-to-reel system. This is especially important when considering scaling up to larger segments of wire. As such, initial efforts focused on creating a closed loop design integrating a peristaltic pump. Figure 4-7 demonstrates an early flow system design using a peristaltic pump.

47 Flow Opening cell for fluidic channel

Figure 4-7: Early flow system design integrating a peristaltic pump.

Using a peristaltic pump presents issues that are not present when using a syringe pump that must be accounted for. As fluid enters the peristaltic pump, it will become trapped between two rollers. A "pillow" of fluid is followed by a void, where the tubing is occluded by the rollers. These alternating pillows and voids will cause the fluid flow to be pulsated, as seen in Figure 4-8 [35]. This presents problems, as the flow system seen in Figure 4-7 is not truly closed, but rather open to the air at the point in which plating is desired. This will cause visible pulsations, changing the size of the droplet at the opening. These changes in size of the droplet will therefore cause uneven plating as the wire moves through the pulsating droplet.

48 1) Pump head consists of only two parts: the rotor and the housing. The tubing is placed in the tubing bed between the rotor and housing where it is occluded (squeezed).

2) The rollers on the rotor move across the tubing, pushing the fluid. The tubing behind the rollers recovers its shape, creates a vacuum and 0 0 draws fluid in behind it.

3) A "pillow" of fluid is formed between the rollers. This is specific to the ID of the tubing and the geometry of the rotor. Flow rate is determined by multiplying speed by the size of the pillow. This 0 0 pillow stays fairly constant except with very viscous fluids.

Figure 4-8: Mechanism for how the peristaltic pump creates pulsations [35].

With this in mind, the original flow line was designed to reduce pulsation by as much as possible. Several methods were thus used to reduce this pulsation. Soft silicone tubing was used over a portion of the line, as the softer tubing material can help absorb pulsations. Hard and small diameter tubing was also used in order to increase the friction in the flow. This increase in friction raises back pressure, which compresses the pulses together, leading to lower pulsations. Additionally, a flow cell was used as an additional method to absorb pulsations. Finally, a peristaltic pump with six rollers was chosen to further reduce pulsations in the system. After designing a continuous flow system in which the flow channel holds and does not pulse, the next step was to design the mechanical system for the spooling of the wire through an electroplating channel and a saline solution channel. Keeping in mind the slow speeds at which the wire must move to be plated on, a system

49 very similar to the fiber harvesting system was designed, though with heavily geared stepper motors. The SolidWorks design for this model can be seen in Figure 4-9.

Compression Fittings for Tubing Secondary Geared Spool Stepper Motor

Linear Stage

Primary

Figure 4-9: Reel-to-reel electroplating assembly consisting of two heavily geared step- per motors to drive the wire and one heavily geared stepper motor to drive the linear stage.

This design consists of three 100:1 geared stepper motors, two of which drive the primary and secondary spools, while the third drives a linear stage. An Ardruino Uno and two motor shields are used to control these three stepper motors. Seated on the stage is a 3D printed plastic part for housing the four compression fittings and tubing. These compression fittings will each hold teflon tubing that will form the opening for the fluidic channel in the center of the 3D printed part. Additionally, the compression fitting will hold tubing for the inflow and outflow of solution, as well as a 1/4" platinum coated titanium rod. These rods will be used as the anode and cathode for plating. The full design can be more clearly seen in Figure 4-10.

50 Auii pte son Salt soln

PIFFanIod * Pt cathode

W.r, b, dr

Motontzed spooks

Figure 4-10: Images of the assembled spooling system for plating. Left: Image of the system showing both spools, the cathode rod, the anode rod, and the wire between spools. Right: Image showing the liquid bridge in which the wire passes through.

Finally, a full image including the flow lines can be seen in Figure 4-11. In addition, a full bill of materials as well as engineering drawings can be seen in Appendix C.

Gold Plating Solu~ionPeristaltic Pump

3.5M KCI Flow Cell

Figure 4-11: Image of the full plating system, including the mechanical spooling system and the flow system.

51 4.4 Proof of Concept for Reel-to-Reel Electroplating

Given the difficulty of working with Nomex nanofibers, I first wanted to provide a proof of concept of the electroplating line using a larger and easier to work with wire. To this end, I spooled 1.5 mil bare copper wire onto the primary spool to conduct initial tests. In one such test, I plated at a current density of 4.3 mA/cm 2 over a period of 100 minutes. Figure 4-12 shows a schematic of the copper wire moving through the fluidic channels, as well as optical images that demonstrate what the wire looks like throughout the process.

550 000pm 500pgm 500pUm

KCI Solution AuI Plating

Figure 4-12: Schematic image demonstrating what a wire would look like throughout the plating process. Left: Image of the wire where plating initially begins. Middle Left: Image of wire where plating transitions from rough to relatively smooth. Middle Right: Image of wire where gold plating can be seen. Right: Image of wire at the end of plating where the transition from smooth plating and back to bare copper can be seen.

The schematic shows a bare copper wire moving from the right to the left through the TSG gold plating solution and the KCl salt solution. Several focus sections were then imaged optically to determine the success of the plating. The left most image shows the initial section of wire where plating first began. In this image, it can be seen that to the left is the bare copper wire and to the right plating begins, though it is very rough. The next image shows an abrupt transition from rough plating to seemingly smooth plating. The following image shows a full section of plating in which we can only see gold plated wire. The final image to the right then shows the

52 transition back from smooth plating to bare copper, which occurs when plating is stopped. In this test, plating occurred over a segment of copper wire about 6 cm in length. The rough section measured ~ 2.5 cm in length while the smooth section measured ~ 3.5 cm in length. To determine the smoothness of the wire and the plating rate of the reel-to-reel system, the smooth section of the wire from the test mentioned above was mechani- cally cross sectioned via potting and grinding. An image of the potted cross section can be seen in Figure 4-13.

1.5 mil Copper wr %withGold platig

Figure 4-13: Optical image showing the cross section of the 1.5 mil diameter copper wire coated by a layer of plated gold.

The above image shows a mechanical cross section of the 1.5 mil diameter bare copper wire plated with gold. Measuring the plated wire shows that the radius has grown to 22.02 pm (up from 19.05 pm), resulting in a plating thickness of 2.97 Pm. With a wire feed rate of 0.06 cm/min through a fluidic channel of 0.5 cm, we have achieved a plating rate of roughly 0.35 pm/min. Similar results have been achieved at various wire feed rates on the same 1.5 mil bare copper wire. Unfortunately, tests were not able to be conducted on the Nomex nanofiber with a sputtered seed layer. Shortfalls in electroplating as well as questions that will be looked into in the future will be discussed in the following chapter.

53 Chapter 5

Conclusions

As discussed in the beginning of this thesis, RF systems such as cell phones and GPS can perform better and last longer if the electrical heat loss in the wires can be reduced. This is done in power systems by braiding the wires, though to achieve good results at radio frequencies, wire dimensions must scale down (1000x). Though traditional wire manufacturing methods may be possible to create wires at these scales, they are both time consuming and extremely expensive. This thesis thus explores a new method for creating microwires.

5.1 Thesis Summary

In this thesis, I have explored a novel method for the creation of microwires. In order to accomplish this, I have employed a series of processes in order to create a wire using a bottom-up approach. What this means is that, rather than drawing a wire through consecutive dies as is conventionally done, the wire will be built up by metalizing an extremely small diameter nanofiber. This thesis describes a method for harvesting the nanofiber formed via electrospinning, then depositing a small conductive seed layer using sputter deposition, followed by forming the bulk of the wire through electroplating. To do this, I have created a series of assemblies for fiber harvesting, sputter deposition onto the harvested fibers, and a reel to reel electroplating line. Throughout this research I have been able to show reliable fiber harvesting, sputter

54 deposition onto the harvested fibers, and electroplating onto the seeded fibers.

5.2 Future Work

I have shown that electroplating a nanofiber with a conductive seed layer is both possible and repeatable and that the designed reel-to-reel electroplating assembly is capable of electroplating on a wire over a distance. Unfortunately, I have not yet been able to show a successful run demonstrating electroplating on a seeded nanofiber in a reel-to-reel manner over a certain distance. As a result, the next step will be proving that electroplating over a distance is possible on a seeded fiber of this diameter. In addition, electroplating over a distance has given rise to several questions that must be addressed. As seen in Figure 4-12 in Chapter 4, the electroplated layer on the bare copper wire is extremely rough over a small segment, then transitions rapidly to smooth plating. It is believed that the transition occurs at the marked spot as seen in Figure 5-1.

2.4

2.2 - -

2

1.8 -Abrupt ) 1 . -T ra n sit io n () 1.6 - 0 1.4 -

1.2 -

1-

0.8 0 1000 2000 3000 4000 5000 6000 7000 8000 Time (s)

Figure 5-1: Image showing data collected during electroplating of the 1.5 mil bare copper wire. The arrow in the image shows an abrupt transition in which the voltage rapidly increases.

The above figure shows the voltage over time curve generated as the bare copper wire is drawn through the electroplating line. In these experiments, the current is

55 kept constant as to keep the current density over the wire constant. As seen near the middle of the graph, the voltage rapidly increases and almost doubles. This seems to occur when the first plated section of wire reaches the salt solution, which may be more clearly understood by viewing Figure 4-12 in Chapter 4. Though this seems to be the case, it is not yet fully understood. As a result, it would be important that experiments are carried out in the future to understand this further. Finally, upon achieving successful results of electroplating over a length of seeded nanofiber, it will be important to perform mechanical and electrical tests and to com- pare the results to that of conventionally formed wire. For these wires, the most important mechanical tests would be to test for ultimate tensile strength, bending stiffness, and hardness. All of these properties will be vital in determining the feasi- bility of using these wires to create Litz bundles, as discussed previously. Electrically, it will be important to determine the resistivity of the wire. Future work will require measuring these properties and comparing them to a solid gold wire of the same diameter formed by conventional wire drawing.

56 Appendix A

Bill of Materials and Engineering Drawings for Mechanical Spool Design

Bill of Materials Part Part Name Vendor Qty Num- ber 1 V-Slot NEMA 17 Linear Actuator Bundle OpenBuilds 1 (Belt Driven) . 2 T-slot framing 20 mm x 20 mm solid silver McMaster Carr 6 anodized (1 foot length) 3 T-slotted corner brace 20 mm McMaster Carr 8 4 T-slot end-feed fastener McMaster Carr 10 5 Stepper motor - NEMA-17 size - 200 Adafruit 3 steps/rev, 12V 350mA 6 Arduino Uno Arduino 1 7 Adafruit Motor/ Stepper/ Servo Shield for Adafruit 2 Arduino v2 Kit - v2.3 8 Shield stacking headers for Arduino (R3 Adafruit 1 Compatible) 9 TMEZON 12 Volt 2A Power Adapter Sup- Amazon 1 ply AC to DC 2.1mm X 5.5mm Plug 12v 2 Amp Power Supply Wall Plug Extra Long 8 Foot Cord

57 2 1

[4] [20] .1575 .7874

[10] .3937 B B a [67] 2.6378 +

[344.78] C;1 13.5740 00 4.20] .1654

UNLESS OTHERWISE SPECIFIED: NAME DATE

DIMENSIONS ARE IN INCHES DRAWN A TOLERANCES: TITLE: A FRACTIONAL CHECKED ANGULAR:MACHt BEND ENGAPPR. TWO PLACE DECIMAL F THREE PLACE DECIMAL MFG APPR. Linear Slide INTERPRET GEOMETRIC OA. TOLERANCINO PER: Mount COMMENTS: MATERIAL SIZE DWG. NO. REV

FINISH NEXT ASSY USED ON A 1 01 A.O( ) APPLICATION DO NOT SCALE DRAWING SCALE: 1:2 WEIGHT: SHEET 1 OF 1 2 1

+ 2 1

B B

[180] 7.0866

Qi

UNLESS OTHERWISE SPECIFIED: NAME DATE

DIMENSIONS ARE IN INCHES DRAWN TOLERANCES: A CHECKED TITLE. A FRACTIONAL ANGULAR:MAC BEND ENG APPR. TWO PLACE DECIMAL THREE PLACE DECIMAL MPG APPR. T-Slot Framing for

INTERPRET GEOMETRIC Q.A. TOLERANCING PER: Base Width COMMENTS: MATERIAL SIZE DWG. NO. REV

FINISH NEXT ASSY USED ON A 202 A.OC ) APPLICATION DO NOT SCALE DRAWING SCALE: 1:2 WEIGHT: SHEET 1OF 1 2 1 2 1

B B [304.80] 12.0000

UNLESS OTHERWISE SPECIFIED: NAME DATE

DIMENSIONS ARE IN INCHES DRAWN TOLERANCES: CHECKED TITLE: A FRACTIONAL ANOULAR:MACH BEND ENG APPR. TWO PLACE DECIMAL THREE PLACE DECIMAL MFG APPR. I-slot Frami nfor INTERPRET GEOMETRIC Q.A. TOLERANCINO PER: COMMENTS: Base Len g h MATERIAL SIZE DWG. NO. REV FINISH NEXT ASSY USED ON A 103 A0E APPLICATION DO NOT SCALE DRAWING SCALE: 1:2 SHEET 1 OF Ij 2 2 1

B _ __ __

B

[100] 3.9370

UNLESS OTHERWISE SPECIFIED: NAME DATE

DIMENSIONS ARE IN INCHES DRAWN TOLERANCES: A A CHECKE D TITLE: FRACTIONALt I ' ANGULAR:MACH BEND- ENG APP TWO PLACE DECIMAL I-slot Framing THREE PLACE DECIMAL for MFG APP INTERPRET GEOMETRIC MA. TOLERANCING PER: COMMEI NTS: Motor Mounting MATERIAL Aluminum SIZE DWG. NO. REV FINISH NEXT ASSY USED ON A 104 A.0( APPLICATION DO NOT SCALE DRAWING SCALE: 2:1 WEIGHT: SHEET 1OF 1 2 1 2 -~______1

B B [250] , , 9.8425

UNLESS OTHERWISE SPECIFIED: NAME DATE DIMENSIONS ARE IN INCHES DRAWN A TOLERANCES: FRACTIONAL CHECKED TITLE: A ANGULAR: MACH BEND ENG APPR. TWO PLACE DECIMAL THREE PLACE DECIMAL MFG APPR. V-slot Linear Rail INTERPRET GEOMETRIC Q.A. TOLERANCING PER: COMMENTS: MATERIAL Aluminum SIZE DWG. NO. REV FINISH NEXT ASSY USED ON A 1_05 A.0( APPLICATION DO NOT SCALE DRAWING SCALE: 1:2 WEIGHT: SHEET 1OF 1 2 1 __ 2 1

[6.35] .250

B .075m- B [6] .236 - ol .394 .250

M5 x 0.8 T .18 .02 [5] 0.197 SLIP FIT WITH COUPLING FOR 05mm SHAFT (ATTACHED)

UNLESS OTHERWISE SPECIFIED: NAME DATE

mini drum mount shaft DIMENSIONS ARE IN INCHES DRAWN A TOLERANCES: TITLE: A FRACTIONAL CHECKED ANGULAR: MACNT BEND ENG APPR. TWOPLACEDECIMALE Secondary Spool THREE PLACE DECIMAL U MFG APPR. INTERPRET GEOMETRIC G.A. Mounting Shaft TOLERANCING PER: COMMENTS: MATERIAL SIZE DWG. NO. REV FINISH NEXT ASSY USED ON A 106 APPLICATION DO NOT SCALE DRAWING SCALE: 2:1 WEIGHT: SHEET 1OF 1 2 1 2 1

[4] 0.1575 M5xO.8 Machine Threads B B

_ [9.41] -- [9.53]750

[.37[6.5] [5] -- 0.1969 [1.59] [6.35] .10] .2500 .0625 [12.70] .3937 .5000 [6.30 .248C

UNLESS OTHERWISE SPECIFIED: NAME DATE

DIMENSIONS ARE IN INCHES DRAWN A TOLERANCES: A FRACTIONAL CHECKED TITLE: ANGULAR: MACA BEND ENG APPR. TWO PLACE DECIMAL THREE PLACE DECIMAL MFG APPR. Threaded Rod for E- INTERPRET GEOMETRIC Q.A. spinning Drum TOLERANCING PER: COMMENTS: MATERIAL Aluminum SIZE DWG. NO. REV FINISH NEXT ASSY USED ON A 107 A.Oq ) APPLICATION DO NOT SCALE DRAWING SCALE: 5:1 WEIGHT: SHEET 1OF 1 2 1 Appendix B

Bill of Materials and Engineering

Drawings for Fiber Sputtering Assembly

Bill of Materials Part Part Name Description Qty Num- ber 1 210:1 Micro Metal Gearmotor HPCB 6V Pololu 1 2 Pololu Micro Metal Gearmotor Bracket Pololu 1 3 Shaft Coupler 5mm to 5mm Amazon 1 4 Battery Holder Coin 20 mm PC Pin Digikey 6 5 Battery Lithium 3V Coin 20 mm Digikey 6 6 NKK Toggle Switch SPST Panel Mount Digikey 1 7 18-8 Stainless Steel Phillips Flat Head McMaster Carr 2 Screw Passivated, 2-56 Thread Size, 9/16" Long 8 18-8 Stainless Steel Phillips Flat Head McMaster Carr 7 Screw Passivated, 4-40 Thread Size, 1/4" Long

65 2 1

.500 -- .100 .500 ______050 X 45.000 .050 X 45.00

.100 X 45.000 B L.. I'~.JJ B .275- 0.250

.100 00 .200 .700

.065 .250 .100 X 45.00- 2X 0 .089 THRU ALL Tap drill #4-40

UNLESS OTHERWISE SPECIFIED:, NAME DATE

DIMENSIONS ARE IN INCHES DRAWN A TOLERANCES: A FRACTIONALT CHECKED TITLEb ANGULAR: MACH. BEND. ENG A. TWO PLACE DECIMAL THREE PLACE DECIMAL MPG APFR. Switch bracket NTERPET GEOMETRIC Q.A. COMMENTS: MATERIAL Aluminum SIZE ;DWG. NO. REV FINISH NEXT ASSY USED ON A 201 APPUCATION DO NOT SCALE DRAWING SCALE: 1:1 WEIGHT: SHEET 1OF 1 2 1

-Ah 2 1

2X 0 .129 T .262 2X 0 .129 1 .262 0 .225 X 1000 0 .225 X 1000 CSK #4 CSK #4

B B 06.000 2.800- .400 + ~ 700 +

.350.0 2X .129 . 0.225 X 1000 \34 + + CSK #4 .002.5

1.215 2X .096 T .262 0 .129 T .200 .87 - 0 .172 X 100* 0 .225 X 1000 CSK #2 -CK#- UNLESS OTHERWISE SPECFIED: NAME DATE

A DIMENONS ARE ININCHES DRAWN FRACTIONALt CHECKED TITLE: ANGULAR: MACH BEND ENG APPR. THRE PLACE DECIMAL MGAP. -- THREEPLACE DECIMAL IMF PR Base Plate

INTERPRET GEOMETRIC Q A. TOLERANCING PER: MENTS: MATERIALAlumInum SIZE DWG. NO. REV

NEXT ASSY USED ON iN A 202 APPLICATION DO NOT SCALE DRAWING SCALE: 1:2 WEIGHT: SHEET I OF 1 2 1

b. mob- - - 2 1

R.250 2X E .089 1 .100 11 .900

2X 0 .089 T .350 B - 12 tap drill for #4-40 B .AJ~ 11

* .300

.212 .200- R. 0 .113 00 .212 2X d .089 7 .099

R2.850 R3.00 4.0 R2.900

UNLESS OTHERWISE SPECIFIED: NAME DATE DIMENSIONS ARE IN INCHES DRAWN A TOLERANCES: A FRACTIONAL CHECKED TITLE: ANGULAR: MACH BEND I ENG APPR. TWO PLACE DECIMAL I THREE PLACE DECIMAL MPG APPR. Assembly INTERPRET GEOMETRIC Q.A. TOLERANCING PER: ~COMMENTS: Cover MATERIAL SIZE DWG. NO. REV Aluminum NEXT ASSY USED ON A 203 APPLICATION DO NOT SCALE DRAWING iSCALE: 1:2 WEIGHT: SHEET 1OF 1 2 1 2 1

B B 2.325

.900

R2.943 45.270 R2.858

.085

UNLESS OTHERWISE SPECIFIED: NAME DATE

DIMENSIONS ARE IN INCHES DRAWN A TOLERANCES: -- -4. FRACTIONALt CHECKED TITLE: ANGULAR: MACH. BEND. ENG APPR. TWO PLACE DECIMAL E A THREE PLACE DECIMAL * MFG APPR. Switch Door INTERPRET GEOMETRIC Q.A. TOLERANCING PER: COMMENTS: IMATERILAIumInUm SIZE DWG. NO. REV

NEXT ASSY USED ON FINISH A, 204 APPLICATION DO NOT SCALE DRAWING SCALE: 2:1 WEIGHT: SHEET 1OF 1 v 2 1 2 1

[6.35] .250

B .075-- B [6] .236 [10] .394 .250

M5 x 0.8 .18 .02 [

0.197 06 -SLIP FIT WITH COUPLING FOR 05mm SHAFT (ATTACHED)

UNLESS OTHERWISE SPECIFIED: NAME DATE mini drum mount shaft DIMENSIONS ARE IN INCHES DRAWN TOLERANCES: FRACTIONAL CHECKED TITLE: A ANOULAR:MACH BEND- ENG APPR. TWO PLACE DECIMAL Secondary Spool THREE PLACE DECIMAL MFG APPR. INTERPRET GEOMETRIC Q.A. Mounting Shaft TOLERANCING PER: COMMENTS: MATERIAL SIZE DWG. NO. REV FINISH NEXT ASSY USED ON A 205 APPLICATION DO NOT SCALE DRAWING SCALE: 2:1 WEIGHT: SHEET 1 OF 1 2 1 2 1

2X 0 .070 THRU ALL Tap drill #2-56

[9] B .354 B

.250 .950

- .300 1- .950

UNLESS OTHERWISE SPECIFIED: NAME DATE DIMENSIONS ARE IN INCHES - DRAWN A TOLERANCES: TITLE: A FRACTINAL CHECKED ANGULAR: MACH BEND - ENGAPPR. TWOPLACEDECIMAL t THREE PLACE DECIMAL MFG APPR. Motor Mount INTERPRET GEOMETRIC Q.A. TOLERANCING PER: COMMENTS: MATERIAL SIZE DWG. NO. REV FINISH NEXT ASSY USED ON A 206 APPLICATION DO NOT SCALE DRAWING ISCALE: 2:1 WEIGHT: SHEET 1OF 1 2 1 Appendix C

Bill of Materials and Engineering

Drawings for Electroplating Assembly

Bill of Materials Part Part Name Description Qty Num- ber 1 Transene Sulfite Gold TSG-250 Transene 1 2 VapLock Solvent Delivery Cap, three 1/4"- Cole Parmer 2 28 ports, GL-45 3 Vaplock Port Plug, 1/4"-28 UNF(M), nat- Cole Parmer 1 ural PTFE; 10/pk 4 Vaplock Tubing Adapter, 1/8" OD x 1/4- Cole Parmer 1 28 UNF(M); 10/pk 5 Tube Made from PTFE 1/4" OD x 1/8" McMaster Carr 1 ID, 1' 6 High-Temperature Silicone Rubber Tub- McMaster Carr 25 ing, Semi-Clear White, Durometer 50A, 1/8" ID, 1/4" GD, 1

72 7 Tube Support for 1/4" OD Plastic Com- McMaster Carr 4 pression Tube Fitting for Water 8 Chemical-Resistant Barbed Tube Fitting McMaster Carr 4 Connector, for 1/8" Tube ID, 150AirF Maximum Temperature 9 Abrasion-Resistant Polyurethane Tubing McMaster Carr 25 for Water, 1/16" ID, 1/8" GD, 1' 10 Chemical-Resistant Barbed Tube Fitting McMaster Carr 8 Reducer, for 1/8" x 1/16" Tube ID, 150AfF Maximum Temperature 11 1/4" diameter x 6" long platinum clad ti- Technic 2 tanium rod, clad with 100 pum of platinum 12 T-slot framing 20 mm x 20 mm solid silver McMaster Carr 6 anodized (1 foot length) 13 V-Slot NEMA 17 Linear Actuator Bundle OpenBuilds 1 (Belt Driven) 14 T-slot framing 20 mm x 20 mm solid silver McMaster Carr 6 anodized (1 foot length) 15 T-slotted corner brace 20 mm McMaster Carr 10 16 T-slot end-feed fastener McMaster Carr 4 17 100:1 Planetary Gearbox Nema 17 Stepper Amazon 3 Motor Low Speed High Torque DIY CNC 18 5mm to 8mm Shaft Rigid Motor Wheel Amazon 3 Coupling Coupler Alumlnum Casing 18 Arduino Uno Arduino 1 19 Adafruit Motor/ Stepper/ Servo Shield for Adafruit 2 Arduino v2 Kit - v2.3

73 20 Shield stacking headers for Arduino (R3 Adafruit Compatible)

74 2 1

[55] [10] 2.1654 .3937 [51 .1969 B [145] 5.7087 [290] f I w 11.4173

A1N -- 5.31] co .2090

UNLESS OTHERWISE SPECIFIED: NAME DATE

DIMENSIONS ARE IN INCHES DRAWN A TOLERANCES: A CHECKED TITLE L i FRACTIONALt AHGULAR:MACHt BEND+ END APPE. TWO PLACE DECIMAL [20] THREE PLACE DECIMAL MG A PPR. Mount for Linear INTERPRET GEOMETRIC Q.A. .7874 TOLERANCINO PER: Slide COMMENTS: MATERIAL Aluminum SIZE DWG. NO. REV FINISH NEXT ASSY USED ON A 301 APPLICATION SCALE: 1:2 WEIGHT: SHEET 1OF 1 2 1

- -0m - 2 1

[6.35] .250'

B .075w - [6] B .236 [10] 394 .250

M5 x 0.8 T .18 .02 [5] 0.197 06-- SLIP FIT WITH COUPLING FOR 05mm SHAFT (ATTACHED)

UNLESS OTHERWISE SPECIFIED: NAME DATE

DIMENSIONS ARE IN INCHES DRAWN A TOLERANCES: A FRACTIONAL CHECKED TITLE: ANGULAR:MACH BEND ENG APPR. TWO PLACE DECIMAL THREE PLACE DECIMAL MPG APPR. Spool Mounting Shaft

INTERPRET GEOMETRIC Q.A. TOLERANCING PER: COMMENTS: MATERIAL SIZE Aluminum DWG. NO. REV FINISH NEXT ASSY USED ON A 3 02 APPLICATION SCALE: 2:1 WEIGHT: SHEET 1 OF 1 2 1 2 1

0 24

02.050 B T 1.500 B

M5

-K! 10

3

I UNLESS OTHERWISE SPECIFIED: NAME DATE DIMENSIONS ARE IN mm DRAWN TOLERANCES: A A FRACTIONAL CHECKED TITLE: ANGULAR:MACH BEND TWO PLACE DECIMAAL ENG APPR. ITHREE PLACE DECIMAL MPG APPR. Spoked Drum INTERPRET GEOMETRIC G.A. TOLERANCIG PER: End COMMENTS: MATERIAL: Aluminum SIZE DWG. NO. REV FINISH NEXT ASSY USED ON A 303 APPLICATION DO NOT SCALE DRAWING SCALE: 2:1 WEIGHT: SHEET 1OF 1 2 1 2 1

B B

[250] I 9.8425

00

UNLESS OTHERWISE SPECIFIED: NAME DATE

DIMENSIONS ARE IN INCHES DRAWN A TOLERANCES: A FRACTIONAL CHECKED TITLE: ANGULAR: MACH BEND ENG APPR. TWO PLACE DECIMAL THREE PLACE DECIMAL MFG APPR. T-slot Framing for INTERPRET GEOMETRIC G.A. TOLERANCING PER: COMMENTS: Base Length MATERLAL SIZE DWG. NO. Aluminum REV FINISH NEXT ASSY USED ON A 304 APPLICATION SCALE: 1:2 WEIGHT: SHEET 1OF 1 2 1 2 1

B B

[210] 8.2677

UNLESS OTHERWISE SPECIFIED: NAME DATE

DIMENSIONS ARE IN INCHES DRAWN A TOLERANCES: A FRACTIONAL CHECKED TITLE: ANGULAR: MACH BEND ENG APPR. TWO PLACE DECIMAL THREE PLACE DECIMAL MFG APPR. T-slot Framin for INTERPRET GEOMETRIC Q.A. TOLERANCING PER: Base Widt COMMENTS: MATERIAL SIZE DWG. NO. REV um FINISH NEXT ASSY USED ON A 305 APPLICATION SCALE: 1:2 WEIGHT: SHEET 1 OF 1 2 1 2 1

B

[70] 2.7559

00

UNLESS OTHERWISE SPECIFIED: NAME DATE

DIMENSIONS ARE IN INCHES DRAWN A TOLERANCES: A FRACTIONALt CHECKED TITLE: ANGULAR: MACH BEND ENG TWO PLACE DECIMAL APPR. THREE PLACE DECIMAL MFG APPR. T-slot Framin for INTERPRET GEOMETRIC G A. TOLERANCING PER: Motor Moun Ting COMMENTS: MATERIAL SIZE DWG. NO. REV Aluminum FINISH NEXT ASSY USED ON A 306 APPLICATION SCALE: 1:1 WEIGHT: SHEET I OF 1 2 1

NNW ______2 1

B B

[205.05] 8.0728

00

UNLESS OTHERWISE SPECIFIED: NAME DATE

DIMENSIONS ARE IN INCHES DRAWN A TOLERANCES: A FRACTIONAL CHECKED TITLE: ANGULAR: MACH BEND TWO PLACE DECIMAL ENG APPR. THREE PLACE DECIMAL MFG APPR. V-slot Linear Rail INTERPRET GEOMETRIC Q.A. TOLERANCING PER: COMMENTS: MATERIAL Aluminum SIZE DWG. NO. REV FINISH NEXT ASSY USED ON A 307 APPLICATION SCALE: 1:2 WEIGHT: SHEET I OF 1 2 1 References

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84