Critical Barriers Associated with Copper Bonding Wire. William (Bud) Crockett Jr.

Transcription

1 Critical Barriers Associated with Copper Bonding Wire William (Bud) Crockett Jr. May 2015

2 1980s, wire bonding was supposed to be replaced by tape automated bonding (TAB)

3 In Global Electronics the most emphasized precious metal is Gold Vehicles Mobile phones PCs LCD TVs etc. Electronic devices Ag Rh Ru Precious metal Pt Pd Au Electrical properties, high corrosion resistance

4 Question is how to cut the device cost while using Gold (Au) metal? 1 2 Reduce the thickness of Au plating on the substrate Use alternative metals instead of Au wire Reduce the material cost of PKG Target is to optimize the combination between the Surface finish material and Wire bond material

5 Bonding Wire Transition Gold => Copper

6 Copper vs. Gold

7 Challenges of Bare Copper Wire Challenges of Bare Copper Wire Copper Wire is Hard Die pad crack Al pad splash Narrow process windows (Short tail, fish tail, lifted bonds) FAB (Forming Gas N2H2) Capillary life Reliability (PCT/HAST Failures, Oxidation)

8 Au/Cu/PCC Hardness & Compression Comparisons PCC PCC

9 Cu Wire Bonding Process Window Comparison High First Bond Second Bond Bonding Parameters Cu Au High Parameters Narrow Range Cu Wire Parameters Narrow Range Low Parameter Range Low Parameters Wide Range Std Parameters Wide Range 1) Copper wire is harder than Gold wire 2) Copper processes have work hardening issues

10 Existing Common problem in Cu bonding Short tail / No tail issue High High Parameters Bonding Parameters Cu Low Parameters Optimum Parameters Low Parameter Range

11 More Common problems in Cu bonding High High Parameters Aluminum splashing shorting to adjacent pad Bonding Parameters Low Cu Low Parameters Optimum Parameters Parameter Range Lifted Metal 1) Lifted metal occurs at lower side of optimum parameters

12 How to Achieve Process Window Closer to Au Wire and Solve Oxidation Issues?

13 Palladium Coated Copper Wire (PCC)

14 (Gen I) Palladium Coated Wire: CLR-1 Copper bonding wire, Long life & Robust stitch bond 4N Bare Cu wire Thin Coated layer CLR-1 φ20um Comparison with Bare Copper wire Advantage Disadvantage Longer Spool Lengths (1km 5km/spool) Wider 2 nd bond window/higher 2 nd bond pull Price is higher than bare copper Chemical Stability (Au relative value 1.0, bare Cu 0.2, Better HAST (BGA) PdCu 0.4 in HVM) Longer shelf life; 6 months after FAB is harder (possible pad damage) manufacturing date, 1 month after opening Capillary Life package (bare Cu 1-week after opening)

15 Storage Resistance Comparisons Copper Wire **No Packing, stored in open environment (office)

16 Manufacturing Process Comparison Copper Wire

17 (Gen II) Palladium Coated wire: CLR-1A 4N Bare Cu wire CLR-1 (Gen I) Pd Coated layer + Thin Au layer Compare with CLR-1 (Gen I) Advantage Disadvantage Wider 2 nd bond window/higher 2 nd bond pull Slightly softer FAB Reduce capillary drag Fine pitch applications SSB bonding **Same Cost as CLR-1 (Gen I) New Qualification PCN

18 PCC Wire (FAB Schematic Image)

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20 FAB EPMA Mapping FAB make Wire: PCC 1, PCC 2 φ20um FAB: φ38um Bonder: UTC-3000 EFO: 80mA, 0.12ms Gas: N 2 +5%H 2, 0.5L/min Measurement count n=3 Molded by epoxy resin Polish and buff PCC EPMA-1600 SHIMADZU PCC 1 PCC 2 1) Pd remains more on the FAB surface of PCC 1 than that of PCC 2 wire type 2) Pd element diffused in FAB which makes it harder. Pad damage risk 3) Pd element on perimeter of ball more effective for retarding Halogen attack??

21 Reliability

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24 PCC Comparisons HTS 220deg C, QFP, Halogen resin Failure ratio (%) Failure=initial resistannce 20%up K&S MaxumPlus Bonder:K&S Maxum Plus Forming Gas :N2-5%H2, 0.5l/min Die-Pad :Al-0.5%Cu (t=0.8um) (Hitachi 6mm Al-Cu0.5%) Capillary :SPT SI E-ZS36 (H:25, T:130, CD:38, FA:8, OR:30) Wire Dia.:20um FAB Dia.:40um Squashed Ball Dia.:50um CLR-1A TD PCC CLR-1 PCC 1 Wire PCC E (ref) Time(h)

25 PCC Comparisons HTS 200deg C, QFP, Green resin 1135h (Next page) X Y 不良数 (Ω20%up) :PCC 1,N2-5%H2,90mA (1.60mil) :PCC 1,N2,90mA (1.69mil) :TD PCC,N2-5%H2,90mA (1.65mil) :TD PCC,N2,90mA (1.69mil) Time(h) 1135h (Next page) Bonder:K&S KnS ICONN Heat Stage Temperature=200 Die-Pad :Al-0.5%Cu-1%Si / SiO2 / Si (Renesas DG001 t=0.8um) Capillary :SPT SU F-ZU34TP (H25,CD38,T80) Wire Dia.:20um FAB Dia.:X=39.5um,Y=36 Squashed Ball Dia.: X=50.5um, Y=50.0, Z=10.0 1st B g Parameter Tip=7.0(mils),CV=0.3(mils/msec) Contact Threshold=70% Constant Current Contact Defect Mode=V Mode USG Current=85(mA) USG Profile=Square USG Bond Time=10(ms) USG Pre Bond=60(mA) Force=15(gf) Force Profiling=On Init l Force=45(gf) Init'l Force time=33(%) Force Ramp Time=10% X-Scrub=3(um), Y-Scrub=0(um) Scrub Cycles=2,Scrub Phase=90(deg) 1st Scrub mode=pre USG

26 HTS 200deg C, QFP, Green resin TD PCC N2 90mA TD PCC N2H2 90mA 1135h PCC 2 N2 90mA PCC 1 N2H2 90mA Observation is no corrosion in 1 st bond cross section

27 UHAST 130deg C 85%rh, QFP, Halogen resin :PCC 1,N2-5%H2,45mA (1.52mil) :PCC 1,N2,45mA (1.61mil) :TD PCC,N2-5%H2,45mA (1.55mil) :TD PCC,N2,45mA (1.67mil) 1085h 不良数 (Ω20%up) h Time(h) Bonder:K&S KnS ICONN Heat Stage Temperature=200 Die-Pad :Al-0.5%Cu-1%Si / SiO2 / Si (Renesas DG001 t=0.8um) Capillary :SPT SU F-ZU34TP (H25,CD38,T80) Wire Dia.:20um FAB Dia.:X=39.5um,Y=36 Squashed Ball Dia.: X=50.5um, Y=50.0, Z=10.0 1st B g Parameter Tip=7.0(mils),CV=0.3(mils/msec) Contact Threshold=70% Constant Current Contact Defect Mode=V Mode USG Current=85(mA) USG Profile=Square USG Bond Time=10(ms) USG Pre Bond=60(mA) Force=15(gf) Force Profiling=On Init l Force=45(gf) Init'l Force time=33(%) Force Ramp Time=10% X-Scrub=3(um), Y-Scrub=0(um) Scrub Cycles=2,Scrub Phase=90(deg) 1st Scrub mode=pre USG

28 UHAST 130deg C 85%rh, QFP, Halogen resin Corrosion? alloy layer? TD PCC N2 45mA TD PCC N2H2 45mA 1085h PCC 1 N2 45mA PCC 1 N2H2 45mA

29 Introduction: Alternative alloy Bonding Wires (Cu & Ag)

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31 FAB Compression Test Comparisons Ag Alloy Au>Ag>Cu>PCC

32 Al Splash Comparisons Ag alloy

33 Crystal Observation (Vertical Section) Ag alloy Heat Affected Zone 4N Au Heat Affected Zone Ultra low Loop & Reverse Bonding is possible for Ag alloy wire

34 Ag Wire Reliability 4N Au 4N Au Ag/Au/Pd Ag/Pd Ag alloy Ag alloy

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36 Reliability Comparisons 4N bare Cu vs. Cu Alloy Cu alloy Cu alloy

37 Wire Types Summary Gold Ag alloy Cu alloy Copper PCC Material Cost High Medium Low Low Medium Forming Gas - N 2 N 2 +H 2 N 2 +H 2 N 2 +H 2 N 2 Chip Damage Low Low Med Med High Process window 1st Process window 2nd HTS 2000+hr Reliability Wide Med Med Med Narrow Wide Med Wide Med Med Poor Excellent Excellent Fair Fair Bonding wires material cost can be summarized as: Cu>>Cu alloy>>pcc>>ag alloy>>au (LGP used $1200)

38 Closing Remarks Alternative (Ag_Cu) alloy wires show good potential as they offers several advantages compared to bare copper and palladium coated copper wires; good bonding performance and superior reliability. Alternative (Ag_Cu) alloy wires may not work for all applications but they can certainly help support many application areas where cost and performance define a product Ag & Cu alloy wire usage is expected to increase in the next few years in both the LED and Semiconductor industry.

39 Thank you Tsutomu Yamashita Tanaka Denshi Kogyo K.K.