Development of Printed Circuit Board Technology Embedding Active and Passive Devices for e-Function Module Noboru Fujimaki Kiyoshi Koike Kazuhiro Takami Sigeyuki Ogata Hiroshi Iinaga
Background shortening of signal wirings between circuits, reduction of damping resistors and elimination of characteristic Higher functionality of today’s portable devices impedance controls. Embedded component module demands smaller, lighter and thinner electronic boards have been adopted for higher functionality of components. Looking at the evolution of package video cameras and miniaturizing wireless communication miniaturization from the flat structure (System in Package: devices. It is expected the use will spread to a wider SiP) -> silicon chip stack structure (Chip on Chip: CoC) -> range of areas including automotive, consumer products, package stack structure (Package on Package: PoP) -> Si industrial equipment and infrastructure equipment. To through chip contact structure, the technology has gone meet these needs, a technology to package and embed from two-dimensional to three-dimensional packaging the various components and LSI will be required. This achieving high density packages. The trends in printed article discusses the method of embedding components, circuit boards and their packaging are shown in Figure 1. soldering technology, production method, reliability and Among the printed circuit boards, the three-dimensional case examples of the embedded component module integrated printed circuit board (hereafter referred to as board. “embedded component module board”) is attracting great attention. Integrating components into embedded component module boards Component embedding enables passive components (1) Embedding active components to be positioned directly beneath the LSI mounted There are two methods of embedding active on the surface providing electrical benefits such as components. One is to embed the components in bear
Packaging Micro packages trends Fine pitch BGA packages High density Bare chips surface packages W-CSP packages Function modules Flip-chip Embedded passive AD/ CR CR packages components CPU DAC CR CR e-Function modules CR CR ASIC RAM Embedded XTAL Flex-rigid boards ISB boards components MID Automotive modules Buildup boards (3D Molded Interconnect Circuit-board Devices) RF modules trends Analog mixed SiP ZigBee Modules Hiper VIA boards Embedded component module board AD/ CPU DAC Image sensor modules
ASIC RAM Digital SiP ASIC ASIC CPU Flash ASIC CPU SD CPU ASIC CPU SiP Trends RAM
SiP (CoC) PoP SiP SiP (flat) (Silicon chip stack) (Package stack) (Si through chip contact) 3-dimentional LSI
2003 2004 2005 2006 2007 2010 Figure 1. Trends in Printed circuit Boards and Packaging
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R08fig01 Special Edition on Component Technologies Supporting Innovative Design chip form, and the other is to process components Component thickness is an obstacle when it comes into a package prior to embedding. Considering the achieving thinner devices. Manufacturers are working to stability of quality and yield, we have decided on the develop components that are both large capacity and low latter method utilizing W-CSP (Wafer-Level Chip Size profile. Currently it is possible to manufacture 1005-sized Package). Inspection guarantees the quality of W-CSP, components comparable in thickness with 0603-sized and achieving KGD (Known Good Die) will not be an components. issue. Soldering technology for embedded (2) Embedding passive components Passive components (C, R, L) can be embedded component module boards either by building them in during the manufacturing In order to simultaneously mount W-CSP and chip process of the board or embedding commercially available components, reflow soldering using lead-free solder was chip components. Guaranteeing the properties with the employed. The benefits of this soldering method are given former method is difficult. Additionally, required properties below. cannot be obtained due to manufacturing constraints. It is an extension of an existing process and does not For example, a required capacitance can be achieved by require a new facility. expanding the area of the layered stack or increasing the It can utilize exiting components. number of stacked layers, however that would stray from LSI and passive components can be mounted the purpose of miniaturizing and thinning. In comparison, simultaneously. the latter method ensures reliability using general-purpose Our component mounting technology was acquired components that have guaranteed properties and are with the cooperation of Nagano OKI. An integrated line available commercially. We have chosen to use the latter consisting of solder printing machine, mounter, reflow method. oven and inspection machine was built and a production
(3) Sizes of embedded components Basic Processing of Embedded Component Module Board Sizes of components that can be embedded are 4-layer board example 0402, 0603 and 1005. However, if 0402, 0603 and 1005 Material are mixed in the same layer, internal board thickness will be the same as when 1005 is implemented. The cross- Exposure Etching sectional view of a embedded component module board Mid-layer with 0603 and 1005-sized chips mixed in the same layer inspection is shown in Figure 2. Component Due to recent increase in product applications, 1005- mounting sized components capable of handling capacitance greater than 1μF are increasingly being implemented. Clean
Copper foil Prepreg
Configure
0603 0603 1005 0603 Prepreg Copper foil
0603-sized 1005-sized 0603-sized resistor capacitor capacitor
Laminate
0603 1005 To surface processing
Figure 2. Mixing Chip Components with Different Sizes Figure 3. Embedded Component Module Board Manufacturing
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R08fig02 R08fig03 system was established (line is capable of processing the
same work size as circuit board manufacturing). Mounting Surface-mounted board (312 mounted chips) 24000 400000 density is at the same level as surface mounting. Strain Over-range 22000 380000 20000 Strain Resistance 360000 18000 Manufacturing embedded 16000 340000 ) 14000 320000
component module boards ) 12000 -6 300000 10000 (×10 Resistance ( The manufacturing process of embedded component 8000 280000
module boards (4-layer board example) is shown in Strain 6000 260000 4000 240000 Figure 3. Using a photographic method, copper circuits are 2000 220000 formed on both sides of a 2-layer board. After solder paste 0 -2000 200000 printing, reflow soldering is used to mount components, 2 4 6 8 10 Number of bends which is followed by flux residue cleaning. The mounted Embedded component board (312 mounted chips) board is sandwiched and laminated between the prepregs 24000 400000 Strain Over-range 22000 and copper foils then heat bonded. To avoid stress on the 380000 20000 Strain Resistance 360000 components during pressure bonding, the height of the 18000 components are taken into consideration when selecting 16000 340000 ) 14000 320000 ) the prepreg thickness. Thereafter, the surface processing -6 12000 300000
(×10 10000
is the same as the manufacturing process of a normal Resistance ( 8000 280000 Strain printed circuit board. 6000 260000 4000 We offer one-stop service including miniaturization 240000 2000 220000 suggestions, circuit board design, board fabrication, 0 -2000 200000 component assembly and product inspection based 2 4 6 8 10 12 14 16 18 20 on specification and other information provided by the Number of bends customer. Figure 4. Bending Reliability of Surface-Mounted and Embedded Component Boards Reliability of embedded component module boards Table 1. Reliability Test Results of Embedded (1) Comparing reliability of surface-mounted and Component Module Board embedded component boards Result of the temperature cycle test has revealed the Test Test Condition and Result Remarks Drop test Board dropped on its X, Y and Z-axis. No embedded W-CSP has more than twice the lifespan of a resistance change after 150 drops. surface-mounted board 1). The following describes the Repeated reflow After moisture absorption, reflow profile Cross-section R08fig04 test repeated 20 times. observed with result of the evaluation. No change in resistance. S A T , a n d n o Using an exclusive TEG (Test Element Group), a No blistering or peeling. problems found. T e m p e r a t u r e -65°C (30min) 125°C (30min) board with embedded W-CSP and chip component was cycle test No resistance change after 3,000 cycles. manufactured. The embedded W-CSP was 6mm square, HAST test 110°C, 85%RH, DC25V bias Passed 500 hour test 0.5mm pitch and had 112 terminals. The chip component Static electricity Discharged ten times for max. 8KV at 5s. N o p e e l i n g was a 0603-sized resistor. Temperature was cycled test Resistance and capacitance measured observed with -25°C/9min room temperature 125°C/9min for the IEC-61000-4-2 before and after were found to be within SAT normal values. evaluation. As a result, the time for the 50% failure rate to Vibration test 10 ~ 2000Hz applied for 20 cycles each occur from W-CSP breakdown was more than twice the JIS C 60068-2-6 in X, Y, Z directions. Resistance and (IEC60068-2-6) capacitance measured before and after surface-mounted board. were found to be within normal values. Next, a board with surface-mounted chip resistors and Repair tolerance After mounting BGA to the surface, N o p e e l i n g post-rework connection was verified. . observed with another with embedded components were prepared. They Resistance and capacitance measured SAT before and after were found to be within were subjected to a push-bending test along 18% of their normal values. length. Number of 0603 chip resistors connected in series Bending test Amount of bending changed (5, 10, 20% Reference test of length) and breakage was observed. on each board was 312. Changes in resistance were Breakage occurred after 14 bends at 10%, observed and the result is shown in Figure 4. after 4 bends at 20%.
Oki Technical Review April 2010/Issue 216 Vol.77 No.1 Special Edition on Component Technologies Supporting Innovative Design
7 700 12 10 600 584 Sample A 8 Sample B 500
10 6 400 4 Concrete floor 300 224 A, B blocks sandwiched between 6 Frequency 200 0 (3 on each side) 1.5t copper clad laminate and secured with tape 100 10 5 Sample A Total weight: 110g 1 2 1 3 13 2 1 -4 Drop height: 1.5m 0 Resistance ( Ω ) Sample B 0.96 0.97 0.98 0.99 1 1.01 1.02 1.03 1.04 Ω Drop angle Sample C Resintance(k ) -8 3 boards dropped in order with one of 3 axis facing down 10 4 Change of resistance (%) 0 500 1000 1500 2000 2500 3000 3500 4000 -12 0 20 40 60 80 100 120 140 160 3 Time (h) Number of drops 1 2 Accuracy of individual parts was No connection failure from ±5%, and after 3,000 cycles, temperature cycle test. resistances were still within accuracy. No connection failure from dropping. (blistering or peeling was not observed)
Figure 5. Result of Drop Test Figure 6. Result of Temperature Cycle Test
The surface-mounted board began to show an increase As shown above, results of the various reliability tests in resistance at the seventh bending and completely broke conducted on the embedded component module board at the tenth. The embedded board showed no change equal or surpass that of the surface-mounted board. This in resistance even after twenty bends. This confirms the confirms that embedding existing components does not embedded board has a higher mounting reliability against degrade connection reliability. bending than the surface-mounted board. It is speculatedR08fig05 that the reliability is higher with the embedded board Actual examples of embeddedR08fig06 because the resins surrounding the component junctions component module boards help to distribute stress. (1) ZigBee®*1) module (2) Reliability test results of the embedded ZigBee module is a type of low power RF module component module board that is capable of linking together with other modules Results of the reliability tests are shown in Table 1. to establish networks. It is expected to be one of the In the drop test, there were no changes in resistance networks in the upcoming ubiquitous society. With the even after 150 drop, and it was confirmed that there use of embedded component technology, the module were no problems with the connection of the internal that was once 52mm×35mm in size has been reduced to components from drop impact. 15mm×15mm (about 1/8 the area). Figure 7 shows the Figure 5 shows the details of drop test. development of the ZigBee wireless network module. To determine if temperature cycling has any effect on the properties of embedded components, the board was (2) Fingerprint authentication module subjected to a cycling test condition of -65°C × 30min The fingerprint authentication module was developed 125°C × 30min. Resistance variation was continuously (for OKI Semiconductor) based on the goal of achieving measured as a sign of change in electrical properties. an ultra-compact, high-speed, high-precision, low-power, high-security, all-in-one module. An ultra-compact size of Result of the temperature cycle test is shown in Figure 6. There were no changes in resistance for 3,000 25mm×23mm was achieved by embedding 0603 passive cycles and problems with electrical properties were not components. Product summary is shown in Figure 8. observed. (3) Compact IP camera Moreover, after the temperature cycle test, chip Through the embedding of passive components, components in the sample board were checked individually the size was reduced from 96mm×50mm down to and resistances were all found to be within the tolerance 64mm×50mm. This is approximately 33% smaller in guaranteed by the component manufacturer. area. Other tests including repeated reflow, HAST, static, Figure 9 shows the example of the developed compact vibration and repair tolerance were performed, but no IP camera. problem with reliability of the embedded component module board could be found.
*1 : ZigBee is a registered trademark of ZigBee Alliance Inc.
Oki Technical Review April 2010/Issue 216 Vol.77 No.1 ZigBee Wireless Network Solution All required elements for the function module provided with one stop. Sensor network application Ultra-compact ZigBee module development
System Conventional module e-Function module ZigBee sensor module technology development technology • Conventional mounting st (dual-side/surface-mount) 1 generation 35 • Passive components (C.R) Antenna nd embedding 2 generation Integration into Sensor • Single-chip LSI sensor module (ZigBee wireless LSI + • Embedded passive components microcomputer) & LSI Power • Component miniaturization 20
52 • Connector elimination & land termination (single-side/surface-mount, 15 ZigBee sensor wireless
30 slimming) • External antenna network technology 15
[mm] Mesh link High density Embedded component Embedded component Star link mounting module board technology module board technology ZigBee technology (Passive components) (LSI, passive components) coordinator Star link Component Semiconductor technology miniaturization technology LSI packaging technology ZigBee (Single-chip) (W-CSP) router ZigBee end device
Figure 7. ZigBee® Module
Fingerprint Authentication Module/ Product Summary Compact IP Camera Fingerprint authentication in a single unit Feature • Downsized 33% from previous version using embedded component technology • Ultra-compact, high-speed, 33% smaller R08fig07 high-precision, ALL IN ONE!
• Ultra-compact-size achieved Sensor side by embedding passive components into printed circuit board controller side 25mm×23mm Stacked structure − 25mm×23mm Passive components (0603) embedded component Embedded passive module board component
Figure 8. Fingerprint Authentication Module Board Figure 9. Compact IP Camera
Conclusion
Until now, existing components were not manufactured It is becoming increasingly more difficult to realize with purpose of embedding into printed circuit boards, and new applications using only conventional soldering there have been very few reports confirming the reliability technologies. Therefore, technology to support ultrasonic of embedded components. The results of our reliability R08fig08bonding, ACF, ACP and other various bonding methods R08fig09 tests performed on boards embedded with existing is necessary. Application development using embedded components confirm the technology to be fully viable. component technology has only just begun, however Furthermore, it was demonstrated that the technology market and customer needs are very high. In response, we could be utilized to reduce the size of products. are considering to further advance technical development In order to manufacture embedded component and make improvements to the embedded component module boards requested by customers, a wide variety module boards. of LSI packaging technology is required. Putting existing components into W-CSP is difficult, and there are times when customers directly supply the components.
Oki Technical Review April 2010/Issue 216 Vol.77 No.1 Special Edition on ComponentReferences Technologies Supporting Innovative Design
References Authors
1) Y. Shizuno, “Development of LSI-embedded Board Noboru Fujimaki, Team Leader, Packaging Technology Technology”, OKI Technical Review No. 211, Vol.74 No.3, Department, e-Function Module Division, OKI Printed Circuits pp.62-65,Authors 2007 Co., Ltd. Kiyoshi Koike, Manager, e-Function Module Development Department, e-Function Module Division, OKI Printed Circuits Co., Ltd. Kazuhiro Takami, Packaging Technology Department, e-Function Module Division, OKI Printed Circuits Co., Ltd. Sigeyuki Ogata, Senior Manager, Packaging Technology Department, e-Function Module Division, OKI Printed Circuits Co., Ltd. Hiroshi Iinaga, Senior Manager, e-Function Module Development Department, e-Function Module Division, OKI Printed Circuits Co., Ltd.
Glossary
e-Function module ACF (Anisotropic Conductive Film) e-Function module is a short TAT, high value-added module A film-like insulating resin material containing fine conductive combining "high-density packaging technologies” , "system particles dispersed inside. By applying heat and pressure, technologies" and “component technologies” held by the OKI bonding will take place and at the same time an electrical Group. connection is make through the conductive material between the electrodes while maintaining isolation with the adjacent SiP (System in Package) electrode. SiP is a package containing multiple chips and LSI. From the exterior, it looks like an electronics system on a single chip. ACP (Anisotropic Conductive Paste) A bonding paste with particle-like conductor material CoC(Chip on Chip) dispersed inside. It is transcribed into a printed circuit board CoC is a package with multiple chips stacked inside and using screen-printing then dried. It serves the same function designed to enable complex features. Wiring bonding or as ACF. flip-chip bonding is used between the chips. Prepreg PoP (Package on Package) A sheet of glass fiber pulled and arranged in one direction or PoP is a technology to increase the density by stacking a fabric impregnated with thermosetting resin (mainly epoxy multiple packages. Utilizing BGA (Ball Grid Array), connection resin) then dried. is often made by connecting the interposer electrodes on the bottom package with the solder ball on the top package. VIA VIA is a region for electronically connecting the lower and W-CSP (Wafer-Level Chip Size Package) upper layers in a multi-layer wiring. Conductivity is usually W-CSP is a form of semiconductor component packaging. achieved by drilling a VIA hole in the dielectric then filling the External terminals, resin molding and other processing on the hole with metallic material or metallic plating. bare chips are done at the wafer level before chips are cut out. Internal wiring with bonding wire is not performed, and it is a ZigBee big bear chip package with part of the semiconductor is ZigBee is one of the short-range wireless standards for exposed. consumer electronics. It is slower and has shorter range than the similar Bluetooth technology, but has the advantage of low RF module power and low cost. Two AA-size alkaline batteries can drive a RF is an abbreviation for Radio Frequency and refers to ZigBee device for about two years. high-frequency signals. It is a general term for modules utilizing high-frequency signals.
Oki Technical Review April 2010/Issue 216 Vol.77 No.1