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    Sac+mn or ce presentation Sac+mn or ce presentation Presentation Transcript

    • Achieving High Reliability Low Cost Lead-Free SAC Solder Joints Via Mn Or Ce Doping Dr. Weiping Liu1, Dr. Ning-Cheng Lee1, Adriana Porras2, Dr. Min Ding2, Anthony Gallagher3, Austin Huang4, Scott Chen4, and Jeffrey ChangBing Lee5 1 Indium Corporation; 2 Freescale Semiconductor 3 Motorola Inc; 4 Advanced Semiconductor Engineering Group; 5 IST-Integrated Service Technology Inc1
    • Introduction • SAC with high Ag good in thermal fatigue performance, but poor in drop test performance • SAC with low Ag OK in drop test, but poor in thermal fatigue performance • A Pb-free alloy with improved drop test performance, and good in thermal fatigue performance badly needed. • SAC105+Mn or Ce studied here2
    • Experimental Design • New Alloys – SAC105+0.05Mn (SACM) – SAC105+0.02Ce (SACC) • DOE for JEDEC drop test & TCT Package Daisy TFBGA244 12X12 Ball/pitch ( mm) 0.3/0.5 0.3/0.5 0.3/0.5 0.3/0.5 0.3/0.5 0.3/0.5 Solder ball SnPb SAC105 SAC305 SACM SACM SACC Surface finish of substrate NiAu NiAu NiAu NiAu OSP NiAu Solder paste SnPb SAC305 SAC305 SAC305 SAC305 SAC305 Reflow profile 220C 245C 245C 245C 245C 245C PCB High Tg FR4/8 layer/NVIP/NSMD/OSP (ENIG, ImAg)3
    • Test Design 1500G • JEDEC Drop Test (JESD22-B111) – Fail when > 1000 ohms • Dynamic Bending Test – Board strain at 1st fail – Dye & pry • Thermal Cycling Test – - 40C/125C – 42 min/cycle, ramp 11 min, dwell 10 min – Fail when > 20% Resistance increase • Cyclic Bending Test – 1 Hz/2mm – Paste SAC387 – Fail when > 1000 ohms4
    • JEDEC Drop Test Results SACM, SACC ≥ SnPb, 105 > 305 ReliaSofts Weibull++ 6.0 - www.Weibull.com Probability - Weibull 6.0 3.0 2.0 1.6 1.4 1.2 1.0 0.9 0.8 0.7 0.6 0.5 β 99.00 Weibull SAC105 90.00 W2 RRX - SRM F=10 / S=5 SnPb SAC305 300 η W2 RRX - SRM 150C/0 hr F=10 / S=5 SACCe 150C/100 hrs 50.00 W2 RRX - SRM Mn 150C/250 hrs 200 TCT 250 cycles F=10 / S=5C-Life in Drop Test SACMn Unreliability, F(t) W2 RRX - SRM Ce F=11 / S=4 SnPb 100 105 W2 RRX - SRM 10.00 F=10 / S=5 305 0 SnPb SAC105 SAC305 SACM SACC 5.00 CK Company 2009/2/23 09:4 1.005 1.00 10.00 Time, (t) 100.00 500.00
    • Dynamic Bending Test Result SACM ≥ SACC > 105 > 305 Failure Criteria: 0.5% strain level Package TFBGA ( Bravo) ball/pitch ( mm) 0.3/0.5 0.3/0.5 0.3/0.5 0.3/0.5 surface finish (substrate) NiAu NiAu NiAu NiAu solder ball SAC105 SAC305 SAC105Mn SAC105Ce Solder paste SAC387 reflow profile Linear ramp profile, peak 235C PCB (FR4/8 layer/NVIP/SMD) 80 80 80 80 Thermal aging 150C/0hr Failure Criteria( Strain ) 0.5049% 0.2406% 0.7490% 0.6963% Thermal aging 150C/250hr Failure Criteria( Strain ) 0.0999% 0.1493% 0.3550% 0.2968% *SACM is SAC105 + Mn dopant SACC is SAC105 + Ce dopant 0.8% 150C/0 hr 150C/250 hrs 0.6% Strain to failure 0.4% 0.2%6 0.0% SAC105 SAC305 SACM SACC
    • TCT (-40C/125C) Test Results TFBGA on PCB (OSP) SACC, SACM, -305 > SAC105 > SnPb ReliaSofts Weibull++ 6.0 www.Weibull.com Probability - Weibull 6.0 3.0 2.0 1.6 1.4 1.2 1.0 0.9 0.8 0.7 0.6 0.5 β 99.00 Weibull 150C/250 hr SAC105 90.00 Aging 105 W2 RRX - SRM M F=13 / S=2 SAC305 η W2 RRX - SRM M 2500 F=15 / S=0 150C/0 hr SACCe 50.00 2000 150C/100 hrs 150C/250 hrs SnPb W2 RRX - SRM M F=15 / S=0 SACMn 305 Unreliability, F(t)C-Life in TCT 1500 W2 RRX - SRM M F=14 / S=0 1000 Mn SnPb W2 RRX - SRM M 10.00 F=14 / S=1 500 Ce 5.00 0 SnPb SAC105 SAC305 SACM SACC CK Company 2009/2/16 17:54 1.00 100.00 1000.00 5000.007 Time, (t)
    • CBT Test Results TFBGA on PCB (OSP) 305 > 105, SACM, SACC > SnPb SAC305 exhibited the Mn highest value in TS, YS, 105 Youngs modulus, and elongation (%). All LF are better than SnPb SnPb. as reflowed Ce 3058
    • Effect of Surface Finish Package: NiAu ≥ OSP (in general) 300 10000 150C/0 hr 150C/100 hrs JDT TCT 150C/0 hr CBT 150C/250 hrs 150C/100 hrs 7500 150C/250 hrs TCT 250 cycles C-Life in Bending TestC-Life of Drop Test 200 TCT 250 cycles 5000 100 2500 0 0 NiAu BGA SACM OSP BGA SACM NiAu BGA SACM OSP BGA PCB: Weak trend ImAg > OSP > ENIG (in general) 300 16000 150C/0 hr 150C/0 hr 150C/100 hrs JDT TCT CBT 150C/100 hrs C-Life of Bending Test (cycles) 150C/250 hrs 12000 150C/250 hrs C-Life of Drop Test 200 TCT 250 cycles TCT 250 cycles 8000 100 PCB: 4000 No obvious trend. 0 0 OSP ENIG ImAg OSP ENIG ImAg OSP ENIG ImAg OSP ENIG ImAg 9 PCB PCB SACM PCB PCB PCB SACC PCB PCB PCB SACM PCB PCB PCB SACC PCB
    • Results SACM and SACC displayed (a) thinner and smoother interfacial IMC layers (b) finer IMC particles within bulk solder10
    • Mn & Ce Suppressed IMC Growth On package side On PCB side 12 8 SnPb/NiAu 10 SAC105/NiAuIMC Thickness (microns 6 IMC Thickness (microns 8 SAC305/NiAu SACM/NiAu 6 SACM/OSP 4 SACC/NiAu 4 2 SnP b/NiA u B GA SA C105/NiA u B GA 2 SA C305/NiA u B GA SA CM /NiA u B GA SA CM /OSP B GA SA CC/NiA u B GA 0 0 0 400 800 1200 0 400 800 1200 150C Aging Hrs 150C Time (hrs)11
    • 150CMn & Ce suppressedcoarsening of IMC rodsat interface12
    • Microstructure of solder joints of TFBGA (NiAu) on PCB (OSP) after TCT 15Vicker Hardness Number 10 Mn suppressed coarsening of IMC particles, thus maintained hardness of joint 5 SAC105 SACM 0 0 100 200 30013 150C Aging Time (hrs)
    • Mn & Ce suppressed IMC coarsening uponthermal aging, hence stabilized microstructure. IMC particle coarsened14
    • Mn & Ce stabilized grain size upon thermal aging,presumably through stabilizing IMC particles.Grain boundary fading away Grain size stabilized Grain size stabilized15
    • Discussion • Drop Test – Both SACM and SACC exhibit finer and thinner IMC structure at interface. – Inclusion of dopants in IMC may also alter the crystallinity, hence reduce the brittleness of IMC layer. • TCT Test – A stable and fine IMC structure may be the primary contributing factor, and the stabilized grain structure resulted may be the secondary cause for SACM and SACC to exhibit a high TCT reliability.16
    • Conclusion • The Mn or Ce doped low cost SAC105 alloys – Achieved a higher drop test and dynamic bending test reliability than SAC105 and SAC305, and exceeded SnPb for some test conditions. – Matched high Ag SAC in thermal cycling performance • The mechanism for high drop performance and high thermal cycling reliability can be attributed to – A stabilized microstructure, with uniform distribution of fine IMC particles, presumably through the inclusion of Mn or Ce in the IMC. – A thinner IMC layer • The cyclic bending results showed SAC305 being the best, and all lead-free alloys are equal or superior to SnPb. • NiAu is preferred over OSP for BGA packages if assembled on PCB (OSP). • Weak trend on preference of PCB finishes: ImAg > OSP > ENIG17