Analysis and Experimental Test of Electrical Characteristics on Bonding Wire

electronics

Article Analysis and Experimental Test of Electrical Characteristics on Bonding Wire

Wenchao Tian, Hao Cui * and Wenbo Yu

School of Electro-Mechanical Engineering, Xidian University, Number 2 Taibai South Road, Xi’an 710071, China; [email protected] (W.T.); [email protected] (W.Y.) * Correspondence: [email protected]; Tel.: +86-29-8820-2954

Received: 20 February 2019; Accepted: 23 March 2019; Published: 26 March 2019

Abstract: In this paper, electrical characteristic analysis and corresponding experimental tests on gold bonding wire are presented. Firstly, according to EIA (Electronic Industries Association)/JEDEC97 standards, this paper establishes the electromagnetic structure model of gold bonding wire. The parameters, including flat length ratio, diameter, span and bonding height, were analyzed. In addition, the influence of three kinds of loops of bonding wire is discussed in relation to the S parameters. An equivalent circuit model of bonding wire is proposed. The effect of bonding wire on signal transmission was analyzed by eye diagram as well. Secondly, gold bonding wire design and measurement experiments were implemented based on radio frequency (RF) circuit theory analysis and test methods. Meanwhile, the original measurement data was compared with the simulation model data and the error was analyzed. At last, the data of five frequency points were processed to eliminate the fixture error as much as possible based on port embedding theory. The measurement results using port extension method were compared with the original measurement data and electromagnetic field simulation data, which proved the correctness of the simulation results and design rules.

Keywords: bonding wire; S parameters; electromagnetic simulation; port embedding

1. Introduction Electronic packaging is the connection between the chip and the external pin. It is an important part for maintaining the electrical, thermal and mechanical properties of the device. Electronic components are developing towards being small volume, high power, high frequency and highly reliable, which requires higher packaging techniques. However, packaging technology has gradually become a bottleneck in the development of semiconductor industry. Although there are advanced package forms such as ﬂip-chip, tape automated bonding, and wafer level package, more than 90% of the device packages are still using wire bonding (WB). Therefore, WB is the dominant form of electronic packaging for its mature technology, low cost and high reliability [1]. Precious metal bonding wires are key materials in electronic packaging including gold bonding wire, copper bonding wire, sliver bonding wire and composite metal bonding wire. Currently, semiconductor packaging is using gold wire bonding as the main connection from the chip to the lead frame or substrate. The high price of gold wire has led to the development of bonding wire made from copper silver and palladium-coated-copper as lower cost alternatives. So far, gold wire accounts for the highest proportion of bonding wire in high-end electronic products because of its stable chemical properties, good ductility and excellent weldability. According to authoritative prediction and a realistic encapsulation of the industry situation, WB will still be the main interconnection method of electronic products until 2020 and will continue developing [2].

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In the package structures, bonding wire can be used as signal transmission line, power, grounding and so on. With the improvement of the transmission signal frequency (currently the system operating frequency up to GHz), bonding wire is no longer a simple transmission line. Moreover, it performs like radio frequency (RF) in a variety of ways, such as crosstalk, coupling, distortion, parasitism, ground bounce, interference and other electromagnetic phenomena [3]. Therefore, how to solve the electrical problems and improve the signal transmission quality of the gold bonding wire in circuit design, analysis and testing have become research hotspots. At present, research on the electrical properties in WB packaging is mainly focused on the following aspects: (1) the process and geometric parameters of bonding wire such as bonding process, bonding wire loop parameters, materials and so forth [4–7]; (2) the wiring form of bonding wire including wire spacing, signal pin distribution, interconnection etc., [8–11]; (3) the overall package design such as grounding copper cover, through silicon vias (TSV) technology, and the redistribution layer (RDL) of flip chip or the like [12–15]. Zhang analyzed the influence of bonding wire on parasitic parameters under different span and arch height. The larger the span and arch height, the greater the influence on the circuit characteristics by simulation [16]. Lu investigated the relationship between materials with different dielectric constants and return losses, but the geometric parameters of bonding wire were not taken into consideration, unfortunately [17]. Liang studied the height arch of single gold bonding wire and the results showed that the lower the arch height of bonding gold wire the better in the case of single gold and the same span. But the value of high arches in the simulation cannot guarantee the welding stability of flat bonding gold because of the characteristics of bonding process [18]. Owing to the diversity of the IC products and package types, there are still no satisfactory results on effects such as wire loops, geometric parameters, electromagnetic models, overall package design and other factors on comprehensive IC electromagnetic properties. In this paper, the electromagnetic properties of bonding wire are studied. The transmission performance of bonding wire is analyzed based on the electromagnetic field model. The design rule is derived from the simulation result. Furthermore, the WB and measurement experiments are designed. The experimental data and simulation data are compared. The error is also analyzed. Finally, the correctness of the simulation is proved by comparison with other experiments, which provides the theoretical basis for the bonding wire selection and design in high frequency.

2. Bonding Wire Model Figure1 shows the package structure of a ball grid array (BGA) composed of a BGA solder ball, PCB board, lead frame, chip, gold bonding wires, epoxy resin encapsulation and so on. In addition, bonding wire can be used as signal transmission line, power, and grounding. In low frequency signal, the bonding wire is equivalent to a line without resistance, capacitor, or inductive transmission. However, in high frequency, the electrical properties of bonding wire have an important influence on the performance of the whole structure and even the circuit. On the one hand, the influence of the parasitic parameters of the bonding wire on the circuit cannot be ignored. At the same time, the inductance, resistance and capacitance (RLC) parameters of bonding wire are constantly changing because of the skin effect with frequency. On the other hand, the cumulative effect of many bonding wires greatly influences the signal transmission capacity, especially in high frequency system. Once the poor WB transmission performance affects the signal transmission and cause large signal loss, it may easily lead to signal crosstalk and other serious signal integrity problems. Electronics 2019, 8, x FOR PEER REVIEW 3 of 22

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Figure 1. Wire bonding (WB) package structure.

2.1. Geometric Parameters S-loop wire is the most common bonding wire. S-loop wire that has a longer flat distance then breaks is mainly used in twoFigure conditions: 1. Wire bondingwhen the (WB) actual package loop structure. length of wire is too long, or the welding wire arc height shouldFigure be under1. Wire controlbonding in (WB) some package devices. structure. S-loop can prevent the sweep and sag2.1. problem Geometric when Parameters epoxy compound flows during the transfer injection molding process because of 2.1. Geometric Parameters its strongS-loop stability wire is and the stiffness. most common The geometric bonding parameters wire. S-loop of wire the S-loop that has wire a longer are shown flat distance in Figure then 2 (dbreaks is theS-loop is diameter, mainly wire usedis L the is in themost two span, common conditions: L1 is the bonding when flat distance the wire. actual S-loop of loopS-loop wire length wire, that of H1 has wire is a the islonger too bonding long, flat ordistance height the welding of then the archbreakswire and arc is H2 heightmainly is the shouldused connection in be two under height). conditions: control inwhen some the devices. actual loop S-loop length can preventof wire theis too sweep long, and or the sag weldingproblemIn this wire when section, arc epoxy height the compound shouldinfluence be flowsunderof the during control geometrical the in some transfer parameters devices. injection S-loop on molding the can scattering prevent process theparameters because sweep ofand itsis discussed.sagstrong problem stability The when four and epoxy geometric stiffness. compound Theparameters geometric flows factors during parameters are th ethe transfer ofratio the of S-loopinjection the L1/L, wire molding the are diameter shown process in d, Figure becausethe span2 (d of isL anditsthe strong diameter,the bonding stability L is theheightand span, stiffness. H1. L1 Finally, is The the flatgeometric by distance comparin parameters of S-loopg the wire,scatteringof the H1 S-loop is parameters, the wire bonding are shownthe height transmission in of Figure the arch 2 characteristics(dand is the H2 isdiameter, the connectionof Q-loop, L is the S-loop height).span, L1and is M-loop the flat aredistance analyzed of S-loop and derived. wire, H1 is the bonding height of the arch and H2 is the connection height). In this section, the influence of the geometrical parameters on the scattering parameters is discussed. The four geometric parameters factors are the ratio of the L1/L, the diameter d, the span L and the bonding height H1. Finally, by comparing the scattering parameters, the transmission characteristics of Q-loop, S-loop and M-loop are analyzed and derived.

Figure 2. S-loop wire geometric parameters. Figure 2. S-loop wire geometric parameters. In this section, the inﬂuence of the geometrical parameters on the scattering parameters is 2.2.discussed. Simulation The Model four geometricof Single Gold parameters Bonding Wire factors are the ratio of the L1/L, the diameter d, the span L andThe the simulation bonding model height of H1. single Finally, bonding by comparing wire (as shown the scattering in Figure 3 parameters, was composed the using transmission S-loop wire,characteristics microstrip of lines, Q-loop, chips, S-loop substrate and M-loop and ground. are analyzed In practice, and derived.the bonding wire was embedded in a plastic body. The plastic materialFigure was 2. not S-loop taken wire into geometric consideration parameters. in order to simplify this model. In actual2.2. Simulation work conditions, Model of Singlebonding Gold wire Bonding usually Wire connects the chip I/O pin to the other chip pins or the 2.2. Simulation Model of Single Gold Bonding Wire externalThe PCB simulation board. modelTherefore, of single the bondingtwo ends wire of (asthe shownbonding in Figurewires 3were was composedconnected usingto different S-loop materials.wire,The microstrip simulation This meant lines, model that chips, theof substratesingle dielectric bonding and constant ground. wire and (as In shownthe practice, dielectric in Figure the thickness bonding 3 was composed wirewere wasdifferent. embeddedusing AsS-loop the in simulationwire,a plastic microstrip body. frequency The lines, plastic ischips, up materialto substrate GHz waslevel, and not Rogersground. taken RO4350B intoIn practice, consideration was the chosen bonding in orderas thewire tosubstrate was simplify embedded in this order model. in to a reduceplasticIn actual body.substrate work The conditions, dielectric plastic material loss. bonding The was materials wire not taken usually of eaintoch connects considerationpart in thethe chipsimulation in I/O order pin modelto to simplify the are other shown this chip model. in pins Table In or 1.actualthe The external ambientwork conditions, PCB temperature board. bonding Therefore, can be wire maintained the usually two ends connect at a of constant thes the bonding chip and I/O the wires pin loss to werefactor the connectedother of materials chip topins differentignored or the asexternalmaterials. well. PCB This board. meant Therefore, that the dielectric the two constantends of andthe thebonding dielectric wires thickness were connected were different. to different As the materials.simulation This frequency meant that is up the to dielectric GHz level, constant Rogers and RO4350B the dielectric was chosen thickness as the were substrate different. in order As the to simulationreduce substrate frequency dielectric is up loss. to GHz The materialslevel, Rogers of each RO4350B part in thewas simulation chosen as model the substrate are shown in inorder Table to1. reduceThe ambient substrate temperature dielectric loss. can The be maintained materials of at ea ach constant part in the and simulation the loss factor model of are materials shown in ignored Table 1.as The well. ambient temperature can be maintained at a constant and the loss factor of materials ignored as well.

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Figure 3. Single bonding wire simulation model. Figure 3. Single bonding wire simulation model. Figure Table3. Single 1. Modelbonding material wire simulation parameters. model. Table 1. Model material parameters. NameTable 1. ModelMaterial material parameters.Dielectric Constant NameS-loop wire Material Gold Dielectric 0.99996 Constant Name Material Dielectric Constant S-loopMicrostrip wire Copper Gold 0.99991 0.99996 MicrostripS-loopChip wire GoldCopperSilicon 0.99996 11.9 0.99991 MicrostripChipSubstrate RogersCopper Silicon RO4350B 0.99991 3.66 11.9 SubstrateGroundChip RogersSiliconCopper RO4350B 0.99991 11.9 3.66 GroundSubstrate Rogers Copper RO4350B 3.66 0.99991 Ground Copper 0.99991 2.3. Solve Setting 2.3. Solve Setting 2.3. SolveThe Setting bonding wire models with different geometric parameters were established by using HFSS (HighThe Frequency bonding Structure wire models Simulator) with different electromagne geometrictic parametersfield simulation were software. established After by usingadding HFSS the The bonding wire models with different geometric parameters were established by using HFSS (Highradiation Frequency boundary Structure condition Simulator) and the port electromagnetic excitation, the ﬁeld corresponding simulation analysis software. was After set to adding solve thethe (High Frequency Structure Simulator) electromagnetic field simulation software. After adding the radiationfrequency boundary of the simulation. condition The and return the port loss excitation, (S11) and the insertion corresponding loss (S21) analysis of different was set geometric to solve radiation boundary condition and the port excitation, the corresponding analysis was set to solve the theparameters frequency models of the were simulation. obtained The after return simulation loss (S11). The and HFSS insertion simulation loss (S21) model of differentis shown geometric in Figure frequency of the simulation. The return loss (S11) and insertion loss (S21) of different geometric parameters4. The total port models excitations were obtained were set after respectively simulation. on Thethe two HFSS sides simulation of the bonding model wire. is shown The insimulation Figure4. parameters models were obtained after simulation. The HFSS simulation model is shown in Figure Thefrequency total port was excitations from 1MHz were to 20 set GHz respectively and the onlogari thethmic two sides scale of was the bondingused to solve wire. the The step. simulation In this 4. The total port excitations were set respectively on the two sides of the bonding wire. The simulation frequencypaper, skin was effect from can 1MHz be ignored to 20 GHzas a andsecondary the logarithmic factor. The scale electrical was used performance to solve the of the step. bonding In this frequency was from 1MHz to 20 GHz and the logarithmic scale was used to solve the step. In this paper,wire was skin obtained effect can and be analyzed ignored as by a using secondary the terminal-driven factor. The electrical solution. performance of the bonding wire paper, skin effect can be ignored as a secondary factor. The electrical performance of the bonding was obtained and analyzed by using the terminal-driven solution. wire was obtained and analyzed by using the terminal-driven solution.

Figure 4. HFSS simulation model.

3. Frequency Domain SimulationFigure 4. HFSS simulation model. 3.1. Influence of Flat Length Ratio on S Parameter of Bonding Wire 3.3.1. Frequency Influence Domainof Flat Length Simulation Ratio on S Parameter of Bonding Wire S-loop wire is the most common bonding wire. Due to its flat length, S-loop wire can withstand 3.1. InfluenceS-loop wireof Flat is Lengththe most Rati commono on S Parameter bonding of wire. Bonding Due Wire to its flat length, S-loop wire can withstand the impact from the epoxy compound in plastic molding process and prevent the gold bonding wire the impact from the epoxy compound in plastic molding process and prevent the gold bonding wire fromS-loop having wire a horizontal is the most sweep common and bonding vertical sagwire. problem. Due to its However, flat length, too S-loop long a wire length can of withstand flat length from having a horizontal sweep and vertical sag problem. However, too long a length of flat length thewire impact will bring from seriousthe epoxy signal compound crosstalk in andplastic coupling molding problems. process and According prevent to the the gold Kulicke bonding and wire Soffa wire will bring serious signal crosstalk and coupling problems. According to the Kulicke and Soffa frompackage having model a horizontal library in sweep Cadence and APD, vertical WL_LH3_SPXX sag problem. series However, of models too long were aselected length of for flat modeling length package model library in Cadence APD, WL_LH3_SPXX series of models were selected for modeling wireand simulation.will bring serious The value signal after crosstalk SP is the and ratio coupling of the flatproblems. length According with span, to that the is, Kulicke the value and of Soffa L1/L and simulation. The value after SP is the ratio of the flat length with span, that is, the value of L1/L package(as shown model in Figure library5). in According Cadence APD, to the WL_LH3_SPXX standard, there areseries six of sizes models in total: were 00, selected 12, 20, 40,for 60modeling and 70. (as shown in Figure 5). According to the standard, there are six sizes in total: 00, 12, 20, 40, 60 and 70. and simulation. The value after SP is the ratio of the flat length with span, that is, the value of L1/L (as shown in Figure 5). According to the standard, there are six sizes in total: 00, 12, 20, 40, 60 and 70.

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Figure 5. Three S-loop wires with different ﬂat lengths. Figure 5. Three S-loop wires with different flat lengths. According to the geometric relationship shown in Figure5, the parameters of the model were According to the geometric relationship shown in Figure 5, the parameters of the model were selected (L = 4500 µm, H1 = 250 µm, H2 = 254 µm, d = 25 µm). The ratios of the ﬂat length to the span selected (L = 4500 μm, H1 = 250 μm, H2 = 254 μm, d = 25 μm). The ratios of the flat length to the span L are 0, 12%, 20%, 40%, 60% and 70%, respectively through changing the length of L1, while sweep L are 0, 12%, 20%, 40%, 60% and 70%, respectively through changing the length of L1, while sweep frequency ranges from 1 MHz to 20 GHz. The results of S11 and S21 with the ratio and frequency of frequency ranges from 1 MHz to 20 GHz. The results of S11 and S21 with the ratio and frequency of the bonding wire are shown in Figure6a,b respectively. the bonding wire are shown in Figure 6a and 6b respectively.

Figure 6. (a) S11 of bonding wire with different flat length; (b) S21 of bonding wire with different Figure 6. (a) S11 of bonding wire with different flat length; (b) S21 of bonding wire with different flat Figureflat length. 6. (a) S11 of bonding wire with different flat length; (b) S21 of bonding wire with different flat length. In order to get a clear graph and accurate data, the S11 log coordinate was set from 1 to 20 GHz. In order to get a clear graph and accurate data, the S11 log coordinate was set from 1 to 20 GHz. The returnIn order loss to describes get a clear the graph signal and reflection accurate performance data, the S11 of log the coordinate transmission was line. set Thefrom smaller 1 to 20 return GHz. The return loss describes the signal reflection performance of the transmission line. The smaller Theloss meansreturn lessloss signaldescribes loss andthe signal better signalreflection integrity performance performance. of the From transmission Figure6, itline. can beThe seen smaller that return loss means less signal loss and better signal integrity performance. From Figure 6, it can be returnthe loss loss increases means with less thesignal frequency. loss and In better addition, signal the integrity SP12 bonding performance. wire has aFrom higher Figure cutoff 6, frequency, it can be seen that the loss increases with the frequency. In addition, the SP12 bonding wire has a higher cutoff whichseen that demonstrates the loss increases that it with can work the frequency. in a higher In frequency addition, band.the SP12 Compared bondingwith wire SP70has a bonding higher cutoff wire, frequency, which demonstrates that it can work in a higher frequency band. Compared with SP70 frequency,the working which frequency demonstrates increases th byat 16%it can (0.64 work GHz). in a Figurehigher7 frshowsequency S21 band. (insertion Compared loss) parameters. with SP70 bonding wire, the working frequency increases by 16% (0.64 GHz). Figure 7 shows S21 (insertion loss) Thebonding abscissa wire, is the set working from 0.1 frequency to 20 GHz. increases It can by be 16 found% (0.64 that GHz). the Figure insertion 7 shows loss also S21 (insertion increases withloss) parameters. The abscissa is set from 0.1 to 20 GHz. It can be found that the insertion loss also increases parameters.frequency, which The abscissa suggests is set the from ratio 0.1 of to the 20 signal GHz. powerIt can be delivered found that to the the insertion terminal loss prior also to increases insertion with frequency, which suggests the ratio of the signal power delivered to the terminal prior to versuswith frequency, the signal which power suggests delivered the to theratio terminal of the aftersignal insertion power isdelivered constantly to decreasing.the terminal The prior value to insertion versus the signal power delivered to the terminal after insertion is constantly decreasing. insertionof the minimum versus the point signal of S21 power and delivered its corresponding to the terminal frequency after under insertion thecondition is constantly of different decreasing. flat The value of the minimum point of S21 and its corresponding frequency under the condition of Thelength value are selectedof the minimum in Table2. point The minimum of S21 and point its indicatescorresponding the signal frequency transmission under is the the condition worst when of different flat length are selected in Table 2. The minimum point indicates the signal transmission is differentthe ratio offlat the length passing are andselected input in signal Table reaches2. The minimum the minimum. point It indicates is easy to the get signal from Tabletransmission2 that the is the worst when the ratio of the passing and input signal reaches the minimum. It is easy to get from theminimum worst when values the of ratio S21 in of SP12 the passing are larger and than input that signal in other reaches cases. the At minimum. 17.38 GHz, It theis easy modulus to get of from S21 Table 2 that the minimum values of S21 in SP12 are larger than that in other cases. At 17.38 GHz, the Tablereaches 2 that 8.71, the which minimum increases values by 13.9%of S21 comparedin SP12 are with larger SP70. than According that in other to thecases. definition At 17.38 of GHz, S21, the modulus of S21 reaches 8.71, which increases by 13.9% compared with SP70. According to the modulusratio of passing of S21 signal reaches with 8.71, incoming which signalincreases is 36.69% by 13.9% after calculation.compared with SP70. According to the definition of S21, the ratio of passing signal with incoming signal is 36.69% after calculation. Table 2. Comparison of S21 extremum under different flat length. Table 2. Comparison of S21 extremum under different flat length. Ratio of Flat Length to Span SP00 SP12 SP20 SP40 SP60 SP70 Ratio of Flat Length to Span SP00 SP12 SP20 SP40 SP60 SP70 Ratio of Flat Length to Span − SP00− SP12− SP20− SP40 − SP60 − SP70 MinMin S21 (InsertionS21 (Insertion Loss)/dB Loss)/dB 9.10 −9.108.71 −8.719.34 −9.34 9.58−9.58 9.82−9.82 9.92−9.92 CorrespondingMin S21 (Insertion frequency/GHz Loss)/dB 17.63−9.10 17.38 −8.71 17.58 −9.34 17.58 −9.58 17.48−9.82 17.48−9.92 PassingCorresponding signal/incoming frequency/GHz signal/% 35.07 17. 36.6963 17.38 34.12 17.58 33.19 17.58 32.2817.48 31.9217.48 Passing signal/incoming signal/% 35.07 36.69 34.12 33.19 32.28 31.92

3.2. Influence of Diameter on S Parameter of Bonding Wire

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3.2.Electronics Inﬂuence 2019, of8, x Diameter FOR PEER on REVIEW S Parameter of Bonding Wire 6 of 22

ConsideringConsidering thethe densitydensity ofof thethe pins connection, thethe diameter ofof the bonding wirewire isis an important designdesign parameter.parameter. Six Six kinds kinds of of nominal nominal diameters diameters of of bonding bonding wire wire were were selected selected for simulation:for simulation: 15 µ m,15 20μm,µm, 20 25μm,µm, 25 30μm, m, 30 35 m,µm 35 and μm 40andµm. 40 Takingμm. Taking the SP12 the SP12 bonding bonding wire wire as a model,as a model, the span the span of L wasof L 4500was 4500µm and μm theand connection the connection height height of H1 of was H1 250wasµ 250m. Theμm. other The other simulation simulati parameterson parameters were were kept constant,kept constant, while while the diameter the diameter of d was of d chosen was chosen as the as variable. the variable. The sweep The sweep frequency frequency ranges ranges from 1MHz from to1MHz 20 GHz. to 20 TheGHz. results The results of the of S11 the and S11 S21 and with S21 thewith diameter the diameter and frequencyand frequency of the of bondingthe bonding wire wire are shownare shown in Figure in Figure7a,b. 7a,b.

Figure 7. (a) S11 of bonding wire with different diameter; (b) S21 of bonding wire with Figure 7. (a) S11 of bonding wire with different diameter; (b) S21 of bonding wire with different different diameter. diameter. Figure7a is the logarithmic coordinate graph of S11. It can be easily seen that the return loss Figure 7a is the logarithmic coordinate graph of S11. It can be easily seen that the return loss grows with increase of frequency. For example, the bonding wire with a diameter of 40 µm can operate grows with increase of frequency. For example, the bonding wire with a diameter of 40 μm can at the near 5 GHz frequency. Compared with the diameter of 15 µm, the working frequency band operate at the near 5 GHz frequency. Compared with the diameter of 15 μm, the working frequency increased by 17.5% (0.73 GHz,). Figure7b is the logarithmic coordinate graph of S21. With the increase band increased by 17.5% (0.73 GHz,). Figure 7b is the logarithmic coordinate graph of S21. With the of frequency, the insertion loss rises, while the signal transmission performance decreases. The S21 increase of frequency, the insertion loss rises, while the signal transmission performance decreases. extreme points of different diameters were extracted as shown in Table3. When the diameter was The S21 extreme points of different diameters were extracted as shown in Table 3. When the diameter 40 µm (17.18 GHz), S21 had the minimum value of −8.16 dB, and the ratio of passing with incoming was 40 μm (17.18 GHz), S21 had the minimum value of −8.16 dB, and the ratio of passing with signal was 39.06%. Compared with the diameter of 15 µm, the modulus of S21 went up by 1.26 dB incoming signal was 39.06%. Compared with the diameter of 15 μm, the modulus of S21 went up by (about 15.4%). Also, the signal transmission quality increased by 5.26%. 1.26 dB (about 15.4%). Also, the signal transmission quality increased by 5.26%. Table 3. Comparison of S21 extremum under different diameter. Table 3. Comparison of S21 extremum under different diameter. Diameter/µm 15 20 25 30 35 40 Diameter/µm 15 20 25 30 35 40 Min S21 (Insertion Loss)/dB −9.42 −8.87 −8.71 −8.55 −8.37 −8.16 Min S21 (Insertion Loss)/dB −9.42 −8.87 −8.71 −8.55 −8.37 −8.16 Corresponding frequency/GHz 17.53 17.43 17.38 17.38 17.33 17.18 PassingCorresponding signal/incoming frequency/GHz signal/% 33.80 17. 36.0153 17.43 36.67 17.38 37.38 17.38 38.1617.33 39.0617.18 Passing signal/incoming signal/% 33.80 36.01 36.67 37.38 38.16 39.06 3.3. Inﬂuence of Span on S Parameter of Bonding Wire 3.3. Influence of Span on S Parameter of Bonding Wire With the development of the narrow spacing (ﬁne-pinch) and the stacked package, the ratio With the development of the narrow spacing (fine-pinch) and the stacked package, the ratio of of low radian and long span bonding wire are also rising. The span L is the horizontal distance low radian and long span bonding wire are also rising. The span L is the horizontal distance of of interconnection, which is the most important geometric parameter in the bonding wire. While interconnection, which is the most important geometric parameter in the bonding wire. While keeping the other parameters unchanged, the bonding wire span L was selected as a variable. The span keeping the other parameters unchanged, the bonding wire span L was selected as a variable. The scanning ranged from 2000 µm to 4500 µm. In addition, the interval was 500 µm: 2000 µm, 2500 µm, span scanning ranged from 2000 μm to 4500 μm. In addition, the interval was 500 μm: 2000 μm, 2500 3000 µm, 3500 µm, 4000 µm and 4500 µm. The sweep frequency ranged from 1 MHz to 20 GHz. μm, 3000 μm, 3500 μm, 4000 μm and 4500 μm. The sweep frequency ranged from 1 MHz to 20 GHz. The results of S11 and S21 with the span and frequency of the bonding wire are shown in Figure 8a and Figure 8b ranging from 1MHz to 20 GHz.

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The results of S11 and S21 with the span and frequency of the bonding wire are shown in Figure8a,b rangingElectronics from2019, 8 1MHz, x FOR toPEER 20 REVIEW GHz. 7 of 22

Figure 8. (a) S11 of bonding wire with different span; (b) S21 of bonding wire with different span. Figure 8. (a) S11 of bonding wire with different span; (b) S21 of bonding wire with different span. According to the trends of return loss and graph of insertion loss, the transmission quality of the According to the trends of return loss and graph of insertion loss, the transmission quality of the signal decreases with the rise of the span because of the increase of the span and the length of the signal decreases with the rise of the span because of the increase of the span and the length of the bonding wire. Figure8a is the logarithmic graph of return loss S11. Taking half the power point as bonding wire. Figure 8a is the logarithmic graph of return loss S11. Taking half the power point as an example, when the longitudinal coordinate was −3 dB, the horizontal coordinate of span 2500 µm an example, when the longitudinal coordinate was −3 dB, the horizontal coordinate of span 2500 μm bonding wire stood at 7 GHz, while the coordinate of span 5000 µm was 3.65 GHz. The working bonding wire stood at 7 GHz, while the coordinate of span 5000 μm was 3.65 GHz. The working frequency also increased by 91%. In the insertion loss graph, the working band of the bonding wire frequency also increased by 91%. In the insertion loss graph, the working band of the bonding wire with a span of 2500 µm was higher than 3.36GHz in the −3 dB (101%). Figure8b is the insertion loss with a span of 2500 μm was higher than 3.36GHz in the −3 dB (101%). Figure 8b is the insertion loss S21 logarithmic coordinate graph. With the increase of frequency, the insertion loss grows and the S21 logarithmic coordinate graph. With the increase of frequency, the insertion loss grows and the signal transmission performance drops. The S21 extreme points of different spans were extracted signal transmission performance drops. The S21 extreme points of different spans were extracted (as (as shown in Table4). When the span was 2500 µm at 25.12 GHz, the S21 had the minimum value of shown in Table 4). When the span was 2500 μm at 25.12 GHz, the S21 had the minimum value of −8.01 dB, and the ratio of passing with incoming signal was 39.76%. Compared with the case of the −8.01 dB, and the ratio of passing with incoming signal was 39.76%. Compared with the case of the 5000 µm, the modulus of S21 increased by 0.98 dB (about 12.2%). The signal transmission quality grew 5000 μm, the modulus of S21 increased by 0.98 dB (about 12.2%). The signal transmission quality by 4.4%, and the corresponding frequency of the extreme point increased by 10.79 GHz. grew by 4.4%, and the corresponding frequency of the extreme point increased by 10.79 GHz. Table 4. Comparison of S21 extremum under different span. Table 4. Comparison of S21 extremum under different span. Span/µm 2500 3000 3500 4000 4500 5000 Span/µm 2500 3000 3500 4000 4500 5000 − − − − − − MinMin S21 (InsertionS21 (Insertion Loss)/dB Loss)/dB 8.01 −8.018.37 −8.378.69 −8.69 8.71−8.71 8.96−8.96 9.03−9.03 Corresponding frequency/GHz 25.12 22.54 19.82 17.33 15.67 14.33 PassingCorresponding signal/incoming frequency/GHz signal/% 39.76 25. 38.1512 22.54 36.77 19.82 36.69 17.33 35.6515.67 35.3614.33 Passing signal/incoming signal/% 39.76 38.15 36.77 36.69 35.65 35.36 3.4. Inﬂuence of Bonding Height on S Parameter of Bonding Wire 3.4. Influence of Bonding Height on S Parameter of Bonding Wire The height of the bonding wire and the arch has a great inﬂuence on the electrical properties of The height of the bonding wire and the arch has a great influence on the electrical properties of the bonding wire. The signal transmission path also increases because of the rise of the height, which the bonding wire. The signal transmission path also increases because of the rise of the height, which exacerbates the signal transmission loss. Keeping the other parameters unchanged, the bonding height exacerbates the signal transmission loss. Keeping the other parameters unchanged, the bonding of H1 was chosen as the variable. The bonding height scanning ranged from 210 µm to 310 µm, and height of H1 was chosen as the variable. The bonding height scanning ranged from 210 μm to 310 the interval was 20 µm: 210 µm, 230 µm, 250 µm, 270 µm, 290 µm and 310 µm. The sweep frequency μm, and the interval was 20 μm: 210 μm, 230 μm, 250 μm, 270 μm, 290 μm and 310 μm. The sweep ranged from 1 MHz to 20 GHz. The results of S11 and S21 with the bonding height and frequency of frequency ranged from 1 MHz to 20 GHz. The results of S11 and S21 with the bonding height and the bonding wire are shown in Figure9a,b ranging from 1 MHz to 20 GHz. frequency of the bonding wire are shown in Figure 9a,b ranging from 1 MHz to 20 GHz.

Electronics 2019, 8, 365 8 of 21 Electronics 2019, 8, x FOR PEER REVIEW 8 of 22

FigureFigure 9. (a()a S11) S11 of ofbonding bonding wire wire with with different different bonding bonding height; height; (b) S21 ( bof) bonding S21 of bonding wire with wire bonding with bondingheight. height. In order to get clear graph and accurate data, the S11 log coordinate was intercepted from three In order to get clear graph and accurate data, the S11 log coordinate was intercepted from three to 10 GHz in Figure9a. With the increase of frequency, the return loss also increased. Furthermore, to 10 GHz in Figure 9a. With the increase of frequency, the return loss also increased. Furthermore, the wire with a smaller bonding height had better electrical performance. For example, when the the wire with a smaller bonding height had better electrical performance. For example, when the longitudinal coordinate was −3 dB, the corresponding abscissa of bonding wire with height 210 µm longitudinal coordinate was −3 dB, the corresponding abscissa of bonding wire with height 210 μm was 4.69 GHz, and the abscissa of bonding wire with 310 µm is 4.40 GHz. Figure9b is the logarithmic was 4.69 GHz, and the abscissa of bonding wire with 310 μm is 4.40 GHz. Figure 9b is the logarithmic coordinate graph of insertion loss S21. The S21 extreme points of different bonding height are extracted coordinate graph of insertion loss S21. The S21 extreme points of different bonding height are in Table5. When the bonding height was 210 µm, the S21 had the minimum value of −8.61 dB extracted in Table 5. When the bonding height was 210 μm, the S21 had the minimum value of −8.61 at 17.58 GHz, and the ratio of passing with incoming signal was 37.11%. Compared with the case dB at 17.58 GHz, and the ratio of passing with incoming signal was 37.11%. Compared with the case of 310 µm, the modulus of S21 increased by 0.41 dB (about 4.8%). The signal transmission quality of 310 μm, the modulus of S21 increased by 0.41 dB (about 4.8%). The signal transmission quality also also rises by 1.71%. Although the increase of bonding height will cause the rise of the whole wire rises by 1.71%. Although the increase of bonding height will cause the rise of the whole wire length length and a decrease in signal quality, the connection height cannot be over reduced. A low height and a decrease in signal quality, the connection height cannot be over reduced. A low height connection will increase stress of bonding wire, making the solder joint unstable and causing other connection will increase stress of bonding wire, making the solder joint unstable and causing other mechanical problems. mechanical problems.

Table 5. Comparison of S21 extremum under different bonding height. Table 5. Comparison of S21 extremum under different bonding height. Bonding Height/µm 210 230 250 270 290 310 Bonding Height/µm 210 230 250 270 290 310 MinMin S21 (InsertionS21 (Insertion Loss)/dB Loss)/dB −8.61 −8.61−8.59 −8.59−8.71 −8.71− 8.79−8.79 −8.88−8.88 −9.02−9.02 Corresponding frequency/GHz 17.58 17.33 17.38 17.28 17.43 17.38 PassingCorresponding signal/incoming frequency/GHz signal/% 37.11 17. 37.2058 17.33 36.69 17.38 36.35 17.28 35.9717.43 35.4017.38 Passing signal/incoming signal/% 37.11 37.20 36.69 36.35 35.97 35.40

3.5. Influence Of Three Loops On S Parameter Of Bonding Wire 3.5. Influence Of Three Loops On S Parameter Of Bonding Wire Q-loop, S-loop and M-loop bond modes are shown in Figure 10. The Q-loop is the most universal Q-loop, S-loop and M-loop bond modes are shown in Figure 10. The Q-loop is the most universal bonding wire form. Compared with the Q-loop, the S-loop has a longer flat distance. The M-loop bonding wire form. Compared with the Q-loop, the S-loop has a longer flat distance. The M-loop bond has the most kinking points. Through the finite element analysis and experimental verification, bond has the most kinking points. Through the finite element analysis and experimental verification, the result shows that the M-loop is 13–75% as good as the S-loop [19], which suggests that the sweep the result shows that the M-loop is 13–75% as good as the S-loop [19], which suggests that the sweep resistance is better than the S-loop relying on bond span and height. This is because the M-loop bond resistance is better than the S-loop relying on bond span and height. This is because the M-loop bond has five kinking nodes. During the transfer molding process, the M-loop bond has higher stiffness has five kinking nodes. During the transfer molding process, the M-loop bond has higher stiffness to to resist the deformation when epoxy compound flows. Keeping the diameter, span and bonding resist the deformation when epoxy compound flows. Keeping the diameter, span and bonding height height unchanged, the S parameters of three kinds of loop wires in 1 MHz–30 GHz are simulated and unchanged, the S parameters of three kinds of loop wires in 1 MHz–30 GHz are simulated and compared. The results of the 1 MHz–20 GHz scan are shown in Figure 11a,b. compared. The results of the 1 MHz–20 GHz scan are shown in Figure 11a,b.

Electronics 2019, 8, 365 9 of 21 Electronics 2019, 8, x FOR PEER REVIEW 9 of 22 Electronics 2019, 8, x FOR PEER REVIEW 9 of 22

Figure 10. Bonding wire loop modes: ( a) Q-loop bonding wire; ( b) S-loop bonding wire; (c) M-loop Figure 10. Bonding wire loop modes: (a) Q-loop bonding wire; (b) S-loop bonding wire; (c) M-loop bonding wire. bonding wire.

Figure 11. (a) S11 of bonding wire with different loop modes; (b) S21 of bonding wire with loop modes. Figure 11. (a) S11 of bonding wire with different loop modes; (b) S21 of bonding wire with loop modes. Figure 11. (a) S11 of bonding wire with different loop modes; (b) S21 of bonding wire with loop modes. The results of the return loss S11 from 1MHz to 1GHz are shown in Figure 11a. As shown in The results of the return loss S11 from 1MHz to 1GHz are shown in Figure 11a. As shown in FigureThe 11 resultsa, the return of the lossreturn S11 loss of threeS11 from different 1MHz loop to modes1GHz are has shown little difference. in Figure 11a. Figure As 11shownb is the in Figure 11a, the return loss S11 of three different loop modes has little difference. Figure 11b is the logarithmicFigure 11a, the coordinate return loss graph S11 of of the three insertion different loss loop S21. modes It can be has seen little that difference. the electrical Figure performance 11b is the logarithmic coordinate graph of the insertion loss S21. It can be seen that the electrical performance oflogarithmic the S-loop coordinate wire is the graph best, of while the insertion the Q type loss is S2 slightly1. It can worse be seen than that that the andelectrical the M performance type is the of the S-loop wire is the best, while the Q type is slightly worse than that and the M type is the worst worstof the inS-loop Figure wire 11 b.is Forthe best, example, while the the working Q type is frequency slightly worse of S type than wire that increases and the byM type 0.32 GHzis the (about worst in Figure 11b. For example, the working frequency of S type wire increases by 0.32 GHz (about 8%) 8%)in Figure compared 11b. For with example, M-loop wirethe working at −3 dB. frequency The S21 extremeof S type points wire increases of different by bonding0.32 GHz height (about were 8%) compared with M-loop wire at −3 dB. The S21 extreme points of different bonding height were extractedcompared in with Table M-loop6. For the wire S type at − bonding3 dB. The wire, S21 S21 extreme has the minimumpoints of different value of −bonding8.71 dB atheight 17.38 GHz,were extracted in Table 6. For the S type bonding wire, S21 has the minimum value of −8.71 dB at 17.38 andextracted the ratio in Table of passing 6. For and the incoming S type bo signalnding is wire, 36.69%. S21 Compared has the minimum with the casevalue of theof − M8.71 type dB wire, at 17.38 the GHz, and the ratio of passing and incoming signal is 36.69%. Compared with the case of the M type modulusGHz, and of the S21 ratio rises of by passing 0.88 dB and (about incoming 10.1%), signal and theis 36.69%. signal transmission Compared with quality the increasescase of the by M 3.54%. type wire, the modulus of S21 rises by 0.88 dB (about 10.1%), and the signal transmission quality increases Therefore,wire, the modulus reasonable of S21 bonding rises by wire 0.88 modes dB (about should 10.1%), be made and accordingthe signal totransmission the process quality and mechanical increases by 3.54%. Therefore, reasonable bonding wire modes should be made according to the process and reliabilityby 3.54%. requirementsTherefore, reasonable comprehensively. bonding wire modes should be made according to the process and mechanical reliability requirements comprehensively. mechanical reliability requirements comprehensively. Table 6. Comparison of S21 extremum under different loop modes. Table 6. Comparison of S21 extremum under different loop modes. Table 6. Comparison of S21 extremum under different loop modes. Bonding Wire Loop M Q S Bonding Wire Loop M Q S Bonding Wire Loop − M − Q − S MinMin S21 (Insertion S21 (Insertion Loss)/dB Loss)/dB 9.59 −9.59 9.29−9.29 −8.718.71 CorrespondingMin S21 frequency/GHz(Insertion Loss)/dB 17.73−9.59 17.68−9.29 − 17.388.71 Corresponding frequency/GHz 17.73 17.68 17.38 PassingCorresponding signal/incoming frequency/GHz signal/% 33.15 17.73 34.32 17.68 17.38 36.69 Passing signal/incoming signal/% 33.15 34.32 36.69 Passing signal/incoming signal/% 33.15 34.32 36.69 3.6. Design Rules 3.6. Design Rules 3.6. Design Rules With the increase of the frequency, the bonding parameters have a great inﬂuence on the With the increase of the frequency, the bonding parameters have a great influence on the characteristicsWith the ofincrease microwave of the transmission. frequency, Therefore,the bonding it isparameters important tohave analyze, a great optimize influence and designon the characteristics of microwave transmission. Therefore, it is important to analyze, optimize and design thecharacteristics parasitic characteristics of microwave oftransmission. high-power Therefore, bonding wiresit is important under high to analyze, frequency. optimize The appropriate and design the parasitic characteristics of high-power bonding wires under high frequency. The appropriate designthe parasitic parameters characteristics should be ofselected high-power according bonding to differentwires under working high frequencyfrequency. bands. The appropriate When the design parameters should be selected according to different working frequency bands. When the workingdesign parameters frequency isshould too high, be theselected transmission according quality to different of the signal working may befrequency very poor. bands. Combined When with the working frequency is too high, the transmission quality of the signal may be very poor. Combined theworking practical frequency project is application, too high, the in ordertransmission to reduce qu theality parasitic of the signal characteristics may be very while poor. improving Combined the with the practical project application, in order to reduce the parasitic characteristics while improving with the practical project application, in order to reduce the parasitic characteristics while improving

Electronics 2019, 8, x FOR PEER REVIEW 10 of 22 the frequency characteristics and electromagnetic properties of bonding wires, the optimization Electronics 2019, 8, 365 10 of 21 measures are obtained from the following five aspects (as shown in Table 7). frequency characteristicsTable and 7. The electromagnetic influence of WB properties parameters of on bonding electrical wires, properties. the optimization measures areFactors obtained from the followingMeasurement five aspects (as shown in Table7). Restriction Flat length changes nonlinearly Flat Through the comparison of the data, it is found that with returnTable loss 7. andThe insertion influence loss. of WB parameters on electrical properties. Length signal quality is the best when the flat ratio of length and The flat length only stands in a (S-loopFactors Measurementspan is 12%, maybe the best L1/L Restriction is 11% or 13% in real specific value, and its signal wire) operation. transmissionFlat length performance changes nonlinearly is good with return loss Through the comparison of the data, it is Flat Length and insertion loss. found that signal quality is the best when the (S-loop wire)The biggerThe flat diameter length only is, standsthe better in a specific value, flat ratio of length and span is 12%, maybe electricaland properties its signal transmission are. performanceExcessive is good increasethe bestin wire L1/L diameter: is 11% or 13% in real operation. Diameter InsertionThe biggerloss diameterand equivalent is, the better electrical1. Aggravate the cost of materials Excessive increase in wire diameter: inductanceproperties decline are. with increasing 2. Decline in toughness Diameter 1. Aggravate the cost of materials diameter.Insertion loss and equivalent inductance decline 2. Decline in toughness The shorterwith increasing loop span diameter. is, the better Too shorter span: electricalThe properties shorter loop are. span is, the better electrical Too shorter span: 1. Increase line tension, Span Shorterproperties loop can are. reduce signal loss 1. Increase line tension, Span 2. Make welding spot unstable and improveShorter loopthe canquality reduce of signal signal loss and improve 2. Make welding spot unstable the quality of signal transmission. 3. Cause wire sag3. Causeand sweep wire sag problem and sweep problem transmission. Too lower height: Too lower height: 1. Stress concentration The lower wire height is, the better electrical Bonding HeightThe lower wire height is, the better 1. Stress concentration2. Phenomenon of expanding under hot properties are. Height electrical properties are. 2. Phenomenoncondition of expanding and shrinking under underhot condition cold condition and shrinking underin cold bonded condit component.ion in bonded component.

3.7.3.7. SPICE SPICE Equivalent Equivalent Circuit Circuit Model Of Bonding Wire AsAs is shown in Figure 12,12, the SPICE (simulation program with with integrated circuit circuit emphasis) emphasis) equivalentequivalent circuit circuit model model of of bonding bonding wire wire consists of of resistance RR,, inductance inductance LL and two different capacitorscapacitors CC11 andand CC22. .The The resistance resistance RR andand the the inductance inductance LL areare related related to to the the parameters parameters of of the bondingbonding wire itself.itself. TheThe twotwo endsends of of bonding bonding wires wires are are connected connected to to different different materials. materials. Therefore, Therefore, the theequivalent equivalent capacitance capacitanceC at C the at the ends ends of the of the bonding bonding wire wire is not is not the same.the same.

I1 R L I2

V1 V2

Port1C1 C2 Port2

FigureFigure 12. 12. TheThe SPICE SPICE equivalent equivalent circuit circuit model model of of bonding bonding wire.

InIn Figure 12,12, There areare fourfour variables;variables; VV11, V2,, II11 andand I2I.2 Based. Based on on Two Two Port Port Network Network Theory, Theory, the the followingfollowing equations equations can can be obtained: ( =⋅ +⋅ VVIZIZ11111212= I1 · Z11 + I2 · Z12  (1)(1) V2 ==⋅I1 · Z21 +⋅+ I2 · Z22 VIZIZ2121222

InIn this this case the relationship between the the port currents, port port voltages voltages and and the the Z-parameter is is given by: given by: V1 V1 Z11 = , Z12 = I1 = I2 = I2 0 I1 0 (2) Z = V2 , Z = V2 21 I1 22 I2 I2=0 I1=0

Electronics 2019, 8, x FOR PEER REVIEW 11 of 22

VV ==11 ZZ11， 12 II12== II2100 (2) VV ==22 ZZ21， 22 II12== II2100

Figure 13 shows the equivalent impedance model of Z11. Taking Z11 as an example, the following Electronicsequations2019 can, 8, 365 be obtained through math deduction. 11 of 21 ωω+−2 RC22 j() LC 1 Figure 13 showsZZs the()ω equivalent== () impedance model of Z11. Taking Z11 as an example, the following(3) 11 11 sj= ω ωω()−+++2 ω equations can be obtained through math deduction.LC12 C C 1 C 2 jRC 12 C

2 Similarly, other parameters can be derived as RCfollows:2ω + j LC2ω − 1 Z (ω) = Z (s)| = (3) 11 11 s=jω (−LC C 2 + C + C + jRC C ) ω 1 2ωωω+−1 2 2 1 2ω RC11 j() LC 1 ZZs()ω == () (4) Similarly, other parameters22 22can besj= derivedω ωω as−+++ follows: 2 ω ()LC12 C C 1 C 2 jRC 12 C RC ω + jLC ω2 − 1 ( ) = ( )| = 1 1 Z22 ω Z22 s s=jω 2 1 (4) ZZZs()ωω== ()= ()ω(−LC1C2ω + C1 + C2 + jRC1C2ω) (5) 12 21 12 sj= ω ωωω−−++2 () jLC12 C RC 12 C j C 1 C 2 1 ( ) = ( ) = ( )| = Based onZ12 theω principleZ21 ω of ZRF12 scircuit,s=jω the two-port S2 parameters can be obtained from (5)the ω[−jLC1C2ω − RC1C2ω + j(C1 + C2)] equivalent two-port Z parameters by means of the following expressions: Based on the principle of RF circuit, the two-port S parameters can be obtained from the equivalent ZZZZ()ωω− ⋅−⋅ ()+  ZZ()ωω () two-port ZS parameters()ω = 11 by means 0 22 of the following 0 12 expressions: 21 11 ()ωω+ ⋅−⋅ ()+ ()ωω () ZZZZ11 0 22 0  ZZ12 21 21⋅+[ZRZ11(ω)−()Z −0] LC·[Z22ωω(2ω) ++ jRCLZ()0]−Z12 +(ω)·Z21(ω) (6) S11(ω) = 02 2 = [Z11(ω)+Z0]·[Z22(ω)+Z0]−Z12(ω)·Z21(ω) −1 22 2 22 2 2 −−++++−+++++RC C Zωω L() C C Z2 Z R j()2 LC C Z ω RC Z RC Z C Z C Z L ω(6) 120 1 2 02·[R+Z0 (1−LC2ω )+ 120j(RC2+L)ω] 10 20 10 20 = 2 2 2 2 2 2 2 − 1 −RC1C2Z0 ω −L(C1+C2)Z0ω +2Z0+R+j(−LC1C2Z0 ω +RC1Z0+RC2Z0+C1Z0 +C2Z0 +L)ω 2Z ()ω ⋅ Z S ()ω = 21 0 21 ()ωω++⋅−⋅2Z21 ()(ω) · Z0 ()ωω () (7) S21(ω) = ZZZZ11 0 22 0 ZZ12 21 (7) [Z11(ω) + Z0] · [Z22(ω) + Z0] − Z12(ω) · Z21(ω)

Figure 13. The equivalent impedance model of Z11. Figure 13. The equivalent impedance model of Z11. In order to compare the data accurately and eliminate the inconsistency of the software, the simulationIn order tools to ofcompare ADS software the data were accurately adopted. and The eliminate diameter, the flat inconsistency length ratio, of span, the software, height and the differentsimulation loops tools of bondingof ADS software wire will were certainly adopted. affect The the resistancediameter, R,flat inductance length ratio, L and span, two height different and capacitorsdifferent loops C1 and of C2bonding in SPICE wire equivalent will certainly circuit affect model. the resistance As previously R, inductance mentioned, L and the two S-loop different wire iscapacitors the best loop C1 and modes. C2 in Meanwhile, SPICE equivalent based oncircuit the designmodel. rules, As previously SP12 bonding mentioned, wire is the appropriate S-loop wire for is thethe model best loop and modes. the parameters Meanwhile, of this based model on the were design selected rules, (L SP12 = 4500 bondingµm, H1 wire = 250 is µappropriatem, H2 = 254 forµ mthe, dmodel = 25 µ mand). Comparedthe parameters with theof this result model file solved were selected by the HFSS (L = electromagnetic4500 μm, H1 = 250 field μ simulationm, H2 = 254 software μm, d = and S parameter curve obtained by the ADS frequency domain simulation solver, the results of the S11 and S21 are shown in Figure 14. As is shown below, the two curves are basically well fitted, which can verify the correctness of the SPICE equivalent circuit model. ElectronicsElectronics 20192019,, 88,, xx FORFOR PEERPEER REVIEWREVIEW 1212 ofof 2222

2525 μμm).m). ComparedCompared withwith thethe resultresult filefile solvedsolved byby thethe HFSSHFSS electromagneticelectromagnetic fielfieldd simulationsimulation softwaresoftware andand SS parameterparameter curvecurve obtainedobtained byby thethe ADSADS frequencfrequencyy domaindomain simulationsimulation solver,solver, thethe resultsresults ofof thethe S11S11 andand S21S21 areare shownshown inin FigureFigure 14.14. AsAs isis shownshown below,below, thethe twotwo curvescurves areare basicallybasically wellwell fitted,fitted, whichwhich Electronics 2019, 8, 365 12 of 21 cancan verifyverify thethe correctnesscorrectness ofof thethe SPICESPICE equivalentequivalent circuitcircuit model.model.

Figure 14. Comparison between SPICE and HFSS (a) S11; (b) S21. Figure 14.14. Comparison between SPICESPICE andand HFSSHFSS ((aa)S) S1111;;( (b))S S21.

3.8. Eye Diagram Analysis 3.8.3.8. EyeEye DiagramDiagram AnalysisAnalysis The eye diagram is a very successful and effective way of showing the quality and parametric TheThe eyeeye diagramdiagram isis aa veryvery successfulsuccessful andand effecteffectiveive wayway ofof showingshowing thethe qualityquality andand parametricparametric information in digital transmission. Careful analysis of this visual display can give the user a ﬁrst-order informationinformation inin digitaldigital transmission.transmission. CarefulCareful analysisanalysis ofof thisthis visualvisual displaydisplay cancan givegive thethe useruser aa first-first- approximation of signal-to-noise, clock timing jitter and skew. orderorder approximationapproximation ofof signal-to-nosignal-to-noise,ise, clockclock timingtiming jitterjitter andand skew.skew. SP12 bonding wire (H1 = 250 µm, H2 = 254 µm, d = 25 µm) were selected as an illustration. SP12SP12 bondingbonding wirewire (H1(H1 == 250250 μμm,m, H2H2 == 254254 μμm,m, dd == 2525 μμm)m) werewere selectedselected asas anan illustration.illustration. InIn In order to control variables, H2 is constant in this part. The span scanning ranged from 2000 µm orderorder toto controlcontrol variables,variables, H2H2 isis constantconstant inin thisthis part.part. TheThe spanspan scanningscanning rangedranged fromfrom 20002000 μμmm toto 45004500 to 4500 µm. In addition, the interval was 500 µm: 2000 µm, 2500 µm, 3000 µm, 3500 µm, 4000 µm μμm.m. InIn addition,addition, thethe intervalinterval waswas 500500 μμm:m: 20002000 μμm,m, 25002500 μμm,m, 30003000 μμm,m, 35003500 μμm,m, 40004000 μμmm andand 45004500 and 4500 µm. Meanwhile, L1 varied from different span According to the schematic in Figure 15, the μμm.m. Meanwhile,Meanwhile, L1L1 variedvaried fromfrom differentdifferent spanspan AccordAccordinging toto thethe schematicschematic inin FigureFigure 15,15, thethe excitationexcitation excitation signal was added at the input port as follows, the high level was 1 V, the low level was 0 V, signalsignal waswas addedadded atat thethe inputinput portport asas follows,follows, thethe hihighgh levellevel waswas 11 V,V, thethe lowlow levellevel waswas 00 V,V, thethe risingrising the rising and falling time was set to 50 ps, and the bit rate of the signal was 10 Gbps. In this part, it andand fallingfalling timetime waswas setset toto 5050 ps,ps, andand thethe bitbit raterate ofof thethe signalsignal waswas 1010 Gbps.Gbps. InIn thisthis part,part, itit recognizesrecognizes recognizes a high level to be a logic 1 and a low level as a logic 0. The voltage values of logic 0 and aa highhigh levellevel toto bebe aa logiclogic 11 andand aa lowlow levellevel asas aa logiclogic 0.0. TheThe voltagevoltage valuesvalues ofof logiclogic 00 andand logiclogic 1,1, eyeeye logic 1, eye height and eye width in the eye diagram are shown in Table8. heightheight andand eyeeye widthwidth inin thethe eyeeye diagramdiagram areare shownshown inin TableTable 8.8.

Figure 15. Eye diagram analysis schematic. FigureFigure 15. EyeEye diagram diagram analysis analysis schematic. schematic.

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µ µ µ µ Figure 16. EyeEye diagram diagram with with different different span. span. (a): (2000a) 2000 μm (mb): (2500b) 2500 μm (mc): (3000c) 3000 μm (dm): (3500d) 3500 μm (em): µ µ (4000e) 4000 μm (mf): (4500f) 4500 μm.m. As illustrated in Table8, with the increase of span, logic 1 voltage decreases, logic 0 voltage As illustrated in Table 8, with the increase of span, logic 1 voltage decreases, logic 0 voltage increases, and this will cause signal inconsistency between the input port and the output port and the increases, and this will cause signal inconsistency between the input port and the output port and the increase of the bit error rate. Furthermore, as shown in Figure 16, the problem of unclear trace was increase of the bit error rate. Furthermore, as shown in Figure 16, the problem of unclear trace was aggravated with the increase of span, which will led to inter-symbol interference. aggravated with the increase of span, which will led to inter-symbol interference.

Table 8. Eye diagram characteristics under different span. Table 8. Eye diagram characteristics under different span. Number Span/µm Logical 1 Voltage/V Logical 0 Voltage/V Eye Height/V Eye Width/ps Logical 1 Logical 0 Eye Eye Number Span/µm a 2000Voltage/V 0.473 Voltage/V 0.012 Height/V 0.424 Width/ps 50 b 2500 0.458 0.021 0.392 50 a c2000 3000 0.473 0.450 0.012 0.028 0.3510.424 49.5 50 b d2500 3500 0.458 0.441 0.021 0.032 0.3200.392 49.25 50 c e3000 4000 0.450 0.440 0.028 0.039 0.2940.351 48.75 49.5 f 4500 0.425 0.046 0.261 48 d 3500 0.441 0.032 0.320 49.25 e 4000 0.440 0.039 0.294 48.75 4. Bonding Wire Design and Measurement Experiment f 4500 0.425 0.046 0.261 48 In order to improve the correctness of the bonding wire simulation model, the bonding wire measurement4. Bonding Wire experiments Design and were Measurement designed in this Experiment section. The TPT HB05 type manual bonding machine was usedIn order to bond to improve the gold the wire correctness in the test board.of the Inbond addition,ing wire the simulation vector network model, analyzer the bonding (VNA) wire was usedmeasurement to measure experiments the bonding were wire designed S parameter in this in thesection. experiment. The TPT At HB05 the same type time, manual based bonding on the networkmachine portwas extensionused to bond and the port gold embedding wire in the theory, test board. the S parameters In addition, of the the vector device network under test analyzer (DUT) (VNA) was used to measure the bonding wire S parameter in the experiment. At the same time, based on the network port extension and port embedding theory, the S parameters of the device under test

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(DUT) were derived. With the error analysis, the results were compared with the original weremeasurement derived. With data, the which error proves analysis, the the correctness results were of the compared simulation with results the original and design measurement rules. data, which proves the correctness of the simulation results and design rules. 4.1. Circuit Board Design 4.1. Circuit Board Design In order to reduce the measurement error, it is necessary to shorten the length of the microstrip lineIn and order make to reducethe impedance the measurement matching error, design. it is Si necessarynce the measurement to shorten the frequency length of the band microstrip had reached line andthemake GHz thelevel, impedance a Rogers matching RO4350B design. high-speed Since theplat measuremente was chosen frequencyas substrate band in hadaccordance reached thewith GHzsimulation level, a Rogersmodel. RO4350BThe test board high-speed length plate and width was chosen were as3.5 substrate cm × 5.0 incm. accordance with simulation model.By The using test boardthe empirical length and formula width were of the 3.5 cmcharacteristic× 5.0 cm. impedance for microstrip line, the approximateBy using the calculation empirical of formula characteristic of the characteristic impedance is impedance [20]: for microstrip line, the approximate calculation of characteristic impedance is [20]: =⋅87 5.98H Z0 ln  (8) ε87+ 0.85.98WTH+ Z0 = √ r 1.41· ln  (8) εr + 1.41 0.8W + T In Equation (1), Z0 is the characteristic impedance of the microstrip line. As shown in Equation In Equation (1), Z0 is the characteristic impedance of the microstrip line. As shown in Equation (1), (1), εr is the dielectric constant of the substrate, H is the thickness of the substrate, W is the width of ε is the dielectric constant of the substrate, H is the thickness of the substrate, W is the width of the rthe microstrip line, and the T is the thickness of the microstrip line. The test board was connected microstrip line, and the T is the thickness of the microstrip line. The test board was connected with the with the VNA using the SMA connector. In order to weld with the SMA joint and shorten the VNA using the SMA connector. In order to weld with the SMA joint and shorten the microstrip line, microstrip line, the microstrip line length L was designed as 8 mm. The plate thickness H was 0.508 the microstrip line length L was designed as 8 mm. The plate thickness H was 0.508 mm. A Rogers mm. A Rogers RO4350B was selected as double-layer plate with a dielectric constant of 3.48. Keeping RO4350B was selected as double-layer plate with a dielectric constant of 3.48. Keeping the Z0 as the Z0 as constant 50 Ω based on Equation (1) and Cadence two-dimensional field solver impedance constant 50 Ω based on Equation (1) and Cadence two-dimensional ﬁeld solver impedance design tool, design tool, the rest of design parameters are obtained after adjustment: microstrip width W is 0.85 the rest of design parameters are obtained after adjustment: microstrip width W is 0.85 mm, thickness mm, thickness T is 0.05 mm. The specific microstrip line design parameters are as shown in Figure T is 0.05 mm. The speciﬁc microstrip line design parameters are as shown in Figure 17. 17.

FigureFigure 17. 17.Microstrip Microstrip line line design design parameters. parameters.

AA TPT TPT HB05 HB05 type type semi-automatic semi-automatic bonding bonding machine machine works works on on the the basis basis of of thermal thermal compress compress bondingbonding method. method. HighHigh pressurepressure andand highhigh temperaturetemperature causedcaused metal metal plastic plastic deformation deformation in in the the bondingbonding region, region, which which realized realized the the connection connection between between the the pad pad and and the the lead. lead. Therefore, Therefore, the the hot hot pressingpressing bonding bonding method method needs needs the the hot hot pressing pressing area area to to adopt adopt the the same same metallurgy metallurgy material, material, so so that that thethe hot hot pressing pressing bonding bonding process process can can be be completed. completed. The The conventional conventional PCB PCB technique technique is is not not suitable suitable forfor the the bonding. bonding. This This means means that that depositing depositing Sn Sn on on copper copper pads pads as as tin tin does does not not make make the the wire wire pressing pressing successful.successful. Considering Considering about about the the bonding bonding machine machine hot hot press press temperature, temperature, hot hot press press reliability reliability and and cost,cost, bare bare gold gold process process is is the the ﬁnal final choice choice for for the the microstrip microstrip line. line. There There is is no no solder solder layer layer on on the the line, line, whilewhile the the back back of of circuit circuit board board is is deposited deposited with with gold gold as as well well as as ground ground plane. plane. Finally, Finally, the the front front and and backback of of the the test test board board are are shown shown in in Figure Figure 18 18aa,b. and 18b.

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FigureFigure 18. 18. TestTest circuit circuit board: board: ( (aa))) front frontfront ( ((bb))) back. back.back. 4.2. Bonding Wire Shape 4.2.4.2. BondingBonding WireWire ShapeShape The semi-automatic bonding machine (TPT HB05 type) was used to bond on the surface of a TheThe semi-automaticsemi-automatic bondingbonding machmachineine (TPT(TPT HB05HB05 type)type) waswas usedused toto bondbond onon thethe surfacesurface ofof aa gold plated microstrip line. After adjusting the bonding parameters, the bonding wire under the goldgold platedplated microstripmicrostrip line.line. AfterAfter adjustingadjusting thethe bondingbonding parameters,parameters, thethe bondingbonding wirewire underunder thethe requirements of the ball pad was ﬁnally obtained. The TPT HB05 bonding machine and bonding requirementsrequirements ofof thethe ballball padpad waswas finallyfinally obtaobtained.ined. TheThe TPTTPT HB05HB05 bondingbonding machinemachine andand bondingbonding parameter settings are shown in Figure 19a,b. parameterparameter settingssettings areare shownshown inin FigureFigure 19a,b.19a,b.

FigureFigure 19. 19. ((aa)TPT)TPT HB05 HB05 bonding bonding machine machine ( (bb)) Bonding Bonding parameter parameterparameter settings. settings.settings.

TheThe observationobservation ofof of bondingbonding bonding wirewire wire underunder under videovideo video metemete meterrr systemsystem system (VMS)(VMS) (VMS) isis shownshown is shown inin FigureFigure in Figure 20a.20a. The20Thea. µ spanThespan span waswas was 44804480 4480 μμmm bybym measurement. bymeasurement. measurement. ToTo Tomakemake make suresure sure therethere there waswas was nono no falsefalse false welding,welding, welding, thethe the firstfirst ﬁrst andand secondsecond bondingbonding pointpointpoint were werewere checked checkedchecked through throughthrough a microscope. aa microscope.microscope. The The ﬁrstThe andfirstfirst second andand secondsecond bonding bondingbonding point of pointpoint the bonding ofof thethe bondingwirebonding under wirewire the underunder metallographic thethe metallographicmetallographic microscope microscopemicroscope is shown is fromis shownshown Figure fromfrom 20 Figureb–d.Figure 20b–d.20b–d.

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FigureFigure 20. 20.20. (a (()aa )Bonding) BondingBonding wire wirewire under underunder VMS; VMS;VMS; (b ((b) )First) FirstFirst bonding bondingbonding point pointpoint under underunder 10 1010 times timestimes microscope; microscope;microscope; ( c (()cc )First) FirstFirst bondingbonding point pointpoint under underunder 40 4040 times timestimes microscope; microscope;microscope; (d ((dd) )Second) SecondSecond bonding bondingbonding point pointpoint under underunder 20 2020 times timestimes microscope. microscope.microscope.

4.3.S4.3.4.3.S SParameter Parameter Parameter Measurement Measurement Measurement And And And Error Error Error Analysis Analysis Analysis TheThe measurement measurement band bandband is isis determined determineddetermined from from 0.3 0.30.3 MHz MHzMHz to toto 10 1010 GHz GHzGHz using usingusing VNA. VNA. The The test test board board was waswas connectedconnectedconnected to toto the the instrument instrument through through SMA. SMA.SMA. Also, Also,Also, the the S Sparameters parameters of of the the device device were were measured measured after after calibration.calibration.calibration. The TheThe S11, S11,S11, ϑ ϑϑ11,11,11, S21 S21S21 and andand ϑϑ ϑ212121 measured measuredmeasured graphs graphs graphs of of bonding bonding wire wire are are shown shown from from FigureFigure Figure 2121a– 21a–a–d. d.Thed. The The measured measured measured data data data were were were compared compared compared with with with the the the simulation simulation simulation data data data (as (as (as shown shown shown in in Figurein Figure Figure 22 22).). 22).

（a）（a）（b）（b）

（c）（c）（d）（d）

FigureFigure 21. 21. (a ()a Measured) Measured S11 S11 of of circuit-under-test; circuit-under-test; circuit-under-test; (b ( b) Measured) Measured ϑ ϑ1111 of of circuit-under-test; circuit-under-test; (c ()c Measured) Measured S21S21 of ofof circuit-under-test; circuit-under-test;circuit-under-test; (d ((dd) )Measured) MeasuredMeasured ϑ ϑϑ212121 of ofof circuit-under-test. circuit-under-test.circuit-under-test.

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Figure 22. Comparison between simulated and measured values: (a) S11; (b) S21. Figure 22. Comparison between simulated and measured values: (a) S11; (b) S21. It can be seen from Figure 22 that the trend of simulation curve and measured curve are consistent, It can be seen from Figure 22 that the trend of simulation curve and measured curve are that is, the S11 increases and S21 decreases with the rise of the frequency. This means that the signal consistent, that is, the S11 increases and S21 decreases with the rise of the frequency. This means that reflection increases and the passing signal drops. The peak value of the test curve may appear because the signal reflection increases and the passing signal drops. The peak value of the test curve may of the resonance problem of the whole test system. However, there is a certain gap between the appear because of the resonance problem of the whole test system. However, there is a certain gap measured value and the simulation value. The maximum error was about −20 dB in S11 curve, while between the measured value and the simulation value. The maximum error was about −20 dB in S11 −7 dB in S21 curve. The error comes mainly from the following three aspects: curve, while −7 dB in S21 curve. The error comes mainly from the following three aspects: 1. Systematic error of measurement experiment 1. Systematic error of measurement experiment Due to the use of the SMA connector, the error of the measurement system is introduced to Due to the use of the SMA connector, the error of the measurement system is introduced to complete the measurement such as SMA conversion error, reflection/transmission measurement complete the measurement such as SMA conversion error, reflection/transmission measurement circuit error and fixture embedded error, as well as the random error in measurement. circuit error and fixture embedded error, as well as the random error in measurement. 2. Model error 2. Model error For example, the simulation model is not precise enough resulting in less accurate modeling of the For example, the simulation model is not precise enough resulting in less accurate modeling of first and second bonding point; unable to establish completely accurate bonding wire model of actual the first and second bonding point; unable to establish completely accurate bonding wire model of experiment wire; the excitation port of stimulation is inconsistent with the actual measurement port. actual experiment wire; the excitation port of stimulation is inconsistent with the actual measurement port.3. Manufacturing error The dielectric constant of the test plate is not constant resulting in dielectric loss; the actual 3. Manufacturing error impedance is inconsistent with calculation causing impedance mismatch and reflection loss problem. The dielectric constant of the test plate is not constant resulting in dielectric loss; the actual impedance4.4. Port Extension is inconsistent with calculation causing impedance mismatch and reflection loss problem.

4.4. PortBased Extension on network analysis theory, the measured S parameters will inevitably have a fixture effect because the measured parameter is a joint cascading result with DUT and the fixture. The port extensionBased is on to movenetwork the analysis position oftheory, the calibration the measured reference S parameters and compensate will inevitably the transmission have a linefixture loss effectby measuring because the measured electrical delay parame andter loss is a for joint each cascading single port. result That with is DUT to say, and the the fixture fixture. is equivalent The port extensionto a lossless is transmissionto move the position line (or lossyof the transmission calibration reference line) under and certain compensate conditions. the Thetransmission measurement line lossmethod by measuring is also used the to measureelectrical the delay loss and phaseloss for shift each of thesingle transmission port. That line. is to Finally, say, the the fixture reference is equivalentsurface is extendedto a lossless to the transmission actual device line to (or reduce lossy the transmission influence of line) the under fixture certain on the conditions. final measuring The measurementresults. The extension method is reference also used and to measure actual reference the loss inand test phase are shownshift of inthe Figure transmission 23. line. Finally, the reference surface is extended to the actual device to reduce the influence of the fixture on the final measuring results. The extension reference and actual reference in test are shown in Figure 23

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Extension reference Actual reference

Figure 23. ExtensionExtension reference and ac actualtual reference in test.

Based on the RF network theory: " #baSSa" # " # " # b1 1=⋅=[]S a1 1 11S11 S 1212 ⋅ 1 a 1 = [S]originorigin· =  · (9)(9) b2 baSSa2221222 a2 S21 S22 a2

" # '''''" # " # " # 0 baSSa1 0 1 110 120  1 0 b1 =⋅=⋅[]S a1 S11 S12 a 1 0 ='''''[S]extensionextension· 0 = 0 0 · 0 (10)(10) b2 baSSa2 a2 2 21S21 S 2222  2 a2 From the signal ﬂowflow graph in Figure 2424,, the relationshiprelationship betweenbetween normalized reﬂectionreflection wave and incident wave is as follows:

" # " − ϑ # " − ϑ # " # 0 '−jϑj 1 −j j1ϑ ' 0 a1 a a aee 1 ee 1 00 a a 1= ==1 1 = ⋅· 1 1 (11) 0 '−j−ϑ2jϑ −−jϑjϑ2 ' 0 (11) a2 a2e 2 0 e 2 a2 a2 ae2 0 e a2

" # " − ϑ # " − ϑ # " # 0 ' −jϑj 1 −jjϑ1 b b bbe1e 1 ee 1 00 b b1 1 1 ====⋅1 = · 1 (12) 0' −−jϑjϑ2 −jjϑϑ2  (12) b2 b2e 2 0 e 2 b2 b2 be2 0 e b2 According to the relationship among the parameters, the scattering matrix of extended surface [S] According to the relationship among the parameters, the scattering matrix of extended surface extension can be obtained after the calculation: [S] extension can be obtained after the calculation: " 0 # " − # " − # " # " − # " # " # b b e jϑ1 − ϑ e jϑ1−−ϑϑ0 b e jϑ1 0 S S a 1 =b' 1 be =j 1 jj11· 1bSSa= · 11 12 · 1 0 1 −jϑ2 1 ee−jϑ2 00111121−jϑ2   b2 b2==e 0 e ⋅=⋅b2 0 e S21 S22 ⋅a2 ' − jϑ −−jjϑϑ   " − # " 2 # " − 22# " 0 # (13) e jϑ1b2 0 be2 S S00eee jϑ1 0bSSa221222a   = · 11 12 · · 1 −jϑ2 −jϑ2 0 (13) 0 e −−ϑϑS21 S22 0 e a2 eejj1100SS a' =⋅⋅⋅11 12 1 "−−jjϑϑ# " # " # ' " # −jϑ1 22−jϑ1 −j2ϑ1 −j(ϑ1+ϑ2) e00ee0 SS21S11 S 2212 e 0 a2 S11e S12e [S]extention = −jϑ · · −jϑ = −j(ϑ +ϑ ) −j2ϑ (14) 0 e 2 S21 S22 0 e 2 S21e 1 2 S22e 2 −−ϑϑ− j2ϑ −+j()ϑϑ jj11 1 12 ee00SS11 12  Se 11 Se 12 []S =⋅⋅ = (14) extention −−jjϑϑ −+j()ϑϑ − ϑ 00ee22SS 12 j2 2 21 22 Se21 Se 22

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Figure 24. Port extension outward and signal flow graph. Figure 24. Port extension outward and signal flow graph. Taking the bonding wire with 4480 µm span as the example, the port extension and data analysis Taking the bonding wire with 4480 μm span as the example, the port extension and data analysis were performed at 2.5 GHz, 3.0 GHz, 3.5 GHz, 4.0 GHz and 4.5 GHz frequency points. After calibration were performed at 2.5 GHz, 3.0 GHz, 3.5 GHz, 4.0 GHz and 4.5 GHz frequency points. After of the VNA, the test circuit board was connected to Port 1, while Port 2 was kept empty. Then the calibration of the VNA, the test circuit board was connected to Port 1, while Port 2 was kept empty. reflection coefficient file was obtained. Furthermore, according to the cascade algorithm and signal Then the reflection coefficient file was obtained. Furthermore, according to the cascade algorithm and flow chart, the port extension file was written in MATLAB. The S parameters of the final bonding wire signal flow chart, the port extension file was written in MATLAB. The S parameters of the final are shown in the Table9 after calculation. bonding wire are shown in the Table 9 after calculation. Table 9. Bonding wire S parameter results file DUT_WireBond.TXT. Table 9. Bonding wire S parameter results file DUT_WireBond.TXT. Frequency/GHz |S | ϑ |S | ϑ 11 11ϑ 21 ϑ 21 Frequency/GHz S 11 11 S 21 21 2.5 6.67 × 10−1 −2.51 × 10 5.51 × 10−2 3.27 × 10 −1 −2 3.0 2.5 6.94 × 6.6710−1 × 10 5.87−2.51× 10× 10 5.515.03 × 10× 10 −2 3.27 × 10−4.62 × 10 3.5 3.0 7.03 × 6.9410−1 × 10−1 2.60 5.87× 10× 102 5.034.16 × 10× −102 −2−4.62 × −108.54 × 10 4.0 3.5 7.10 × 7.0310−1 × 10−1 −4.21 2.60× × 10102 4.164.21 × 10× −102 −2−8.54 × −101.08 × 10 − − 4.5 4.0 7.71 × 7.1010 1 × 10−1 8.59−4.21× 10× 10 4.214.05 × 10× −102 2−1.08 × 101.85 × 102 −1 −2 2 Frequency/GHz4.5 |S12 7.71| × 10 8.59ϑ12 × 10 4.05 ×| S1022| 1.85 × 10 ϑ22 −2S ϑ S −1 ϑ 2.5Frequency/GHz4.65 × 10 12 3.24 ×1210 6.8922× 10 22 −2.69 × 10 3.0 2.5 4.47 × 4.6510−2 × 10−2 −2.89 3.24× ×10 10 6.89×7.23 10×−101 −1−2.69 × 104.17 × 10 −2 −1 2 3.5 3.0 4.32 × 4.4710 × 10−2 −5.69−2.89× ×10 10 7.237.42 × 10× −101 4.17 × 103.28 × 10 4.0 × −2 − × 2 × −1 −8.26 × 10 3.5 4.02 4.3210 × 10−2 6.78−5.69 ×10 10 7.427.38 × 10−101 3.28× 102 4.5 3.65 × 10−2 1.95 × 102 7.94 × 10−1 1.22 × 10 4.0 4.02 × 10−2 −6.78 × 102 7.38 × 10−1 −8.26 × 10 4.5 3.65 × 10−2 1.95 × 102 7.94 × 10−1 1.22 × 10 The data of 5 fixed frequency points are calculated by extending the port, and the calculated dataThe were data compared of 5 fixed with frequency the result points and are original calculated test by data extending without the error port, elimination and the calculated using HFSS data werethree-dimensional compared with electromagnetic the result and field original simulation. test data The without comparison error graph elimination of the threeusing cases HFSS above three- is dimensionalshown in Figure electromagneti 25. c field simulation. The comparison graph of the three cases above is shownFrom in Figure the experimental 25. data, system error can be eliminated to some extent by the port extension method making the measurement result more accurate. From the comparison between the simulation and the experimental data, the trends of S11 and S21 parameters were consistent. There was a deviation in some specific values, and the S parameter error contrast value was extracted in Table 10 among the five fixed points. Due to limited experimental method and inability to establish the precise and accurate bonding wire loop model of experiment wire, even after port extension method and data processing, there was still some deviation between the simulation and measurement values. However, the experimental results have confirmed the results of S parameters simulation for the bonding wire and design rules. The error is also within the reasonable range. Therefore, the correctness of the simulation is proved.

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Figure 25. Comparison of S parameters: (a) S11; (b) S21. Figure 25. Comparison of S parameters: (a) S11; (b) S21. Table 10. Comparison between simulated and measured value with port extension. From the experimental data, system error can be eliminated to some extent by the port extension methodS Parameter making the measurement Max Relative result Error more accura Frequencyte. From Minthe comparison Relative Error between Frequency the simulation and the experimentalS11 data, the 33% trends of S11 2.5and GHz S21 parameters 11% were consistent. 4.0 There GHz was a deviation S21in some specific values, 69% and the S parame 3.5 GHzter error contrast 39% value was extracted 2.5 GHz in Table 10 among the five fixed points. 5. Conclusions Table 10. Comparison between simulated and measured value with port extension. This article adopted the method of electromagnetic field simulation analysis and actual experiment test. In addition,S parameter the electrical Max Relative properties Error of gold Freq bondinguency wire Min in WB Relative package Error were Frequency studied. According to EIA/JEDEC97S11 standard, this paper 33% establishes 2.5 the GHz electromagnetic 11% structure model 4.0 of GHz gold bonding wire. The equivalentS21 circuit model 69% of bonding wire 3.5 wasGHz proposed and 39% discussed. The 2.5 effect GHz of bonding wire on signal transmission was analyzed by an eye diagram as well. Although it was difficult to obtainDue accurate to limited mathematical experimental relations meth betweenod and inability the electrical to establish parameters the precise and geometries and accurate and materials bonding ofwire bonding loop model wire, theof experiment reasonable wi parameterre, even after select port method extension and generalmethodrules and data can beprocessing, obtained there after qualitativewas still analysissome deviation in this paper. between The platform the simula length,tion diameter, and measurement span, bonding values. height parametersHowever, andthe theexperimental influence of results three have kinds confirmed of loops on the the results S parameters of S parameters of bonding simulation wire were for discussed. the bonding The wire results and showeddesign that:rules. (1) The the transmissionerror is also performancewithin the ofreas theonable bonding range. wire withTherefore, high diameter, the correctness short span of andthe archsimulation height is good;proved. (2) the flat length ratio only in a specific value, its signal transmission performance is good; (3) S-type arc signal transmission performance is the best, Q-type the second, M-type the worst.5. Conclusions Furthermore, the design rules were derived from the simulation data. Meanwhile, based on RF circuitThis theoryarticle analysisadopted and the test method method, of gold electromagnetic bonding wire field design simulation and measurement analysis experiments and actual wereexperiment implemented. test. In Theaddition, original the measurement electrical properties data was of compared gold bonding with thewire simulation in WB package model were data andstudied. the error According was analyzed. to EIA/JEDEC97 At last, the standard, data of five this frequency paper establishes points were the processedelectromagnetic to eliminate structure the fixturemodel errorof gold as muchbonding as possiblewire. The based equivalent on port embeddingcircuit model theory. of bonding The measurement wire was proposed results using and portdiscussed. extension The method effect of were bonding compared wire on with signal the transmission original measurement was analyzed data by and an electromagnetic eye diagram as fieldwell. simulationAlthough it data, was whichdifficult proves to obtain the correctnessaccurate mathematical of the simulation relations results between and design the electrical rules. parameters Authorand geometries Contributions: and materialsW.T. guided of otherbonding authors wire, to completethe reasonable this paper. parameter He also supplied select method the latest and supporting general material.rules can H.C. be wroteobtained the paper.after qualitative W.Y. helped toanalysis revise the in grammarthis paper. of literature.The platform length, diameter, span, Acknowledgments:bonding height parametersThis work wasand supportedthe influence by the of Nationalthree kinds Natural of loops Science on Foundation the S parameters of China of (61176130), bonding thewire Natural were Sciencediscussed. Foundation The results of Ningbo showed city that: of China (1) the (2016A610030). transmission performance of the bonding wire Conflictswith high of Interest:diameter,The short authors span declare and noarch conflict height of interest.is good; (2) the flat length ratio only in a specific value, its signal transmission performance is good; (3) S-type arc signal transmission performance is Referencesthe best, Q-type the second, M-type the worst. Furthermore, the design rules were derived from the simulation data. Meanwhile, based on RF circuit theory analysis and test method, gold bonding wire 1. Fischer, A.C.; Korvink, J.G.; Roxhed, N. Unconventional applications of wire bonding create opportunities design and measurement experiments were implemented. The original measurement data was for microsystem integration. J. Micromechan. Microeng. 2013, 23, 905–923. [CrossRef] compared with the simulation model data and the error was analyzed. At last, the data of five frequency points were processed to eliminate the fixture error as much as possible based on port

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