Introduction

1. LEAD-FREE AND MIXED ASSEMBLY SOLDER JOINT RELIABILITY TRENDSby Jean-Paul Clech, EPSI Inc.Montclair, NJ, USATel: +1 (973)746-3796, fax: +1 (973)655-0815E-mail: jpclech@aol.com, URL: http://jpclech.comPresented atIPC / SMEMA Council APEX Conference Anaheim, CA, February 26, 2004

2. Introduction • Objective: Compare lead-free vs. SnPb solder joint reliability over a wide range of circumstances • Preliminary study limited to thermal cycling data • Where are we on the learning curve?

3. SAC Test Data • Coffin-Manson approach: • Correlation coefficient: R2 ~ 0.6 • Not much data for Dg < 1%

4. First Order Correlation of SAC Test Data • First-order correlation obtained by: • Scaling characteristic life for solder joint crack area • Using characteristic life for population of critical solder joints • Do not use for life predictions or AF calculations • Dwell time, frequency effects etc… not included

5. Correlation of SAC Test Data: Sorted by Board Finish • First-order correlation does not show significant board finish effect • Slide # 4 data re-plotted by board finish type

6. Correlation of SAC Test Data: Sorted by Alloy

7. SAC versus SnPb Test Data Correlation (Leadless Assemblies) • Difference in slopes suggests opposite reliability under low and high stress conditions • Do not use for life predictions or AF calculations • Dwell time, frequency effects etc… not included

8. SAC vs. SnPb: Creep Rate Comparison ~ 25°C ~ 75°C • Under high stress conditions, SAC creeps as fast as SnPb regardless of temperature ~ 125°C

9. SAC vs. SnPb: Creep Rate Comparison (2) -55°C ~ 25°C ~ 125°C 75°C

10. Sn0.7Cu vs. SnPb Correlations based on Bare Flip-Chip Thermal Cycling Data (references in paper) Fatigue Testing Data at 20C (ITRI Pub. # 656 ). • Compared to SnPb, SnCu fatigue trend appears opposite that of SnAg / SAC trend

11. SAC vs. SnPb: Alloy 42 TSOPs • Alloy 42 TSOPs assembled with SAC have shorter test lives than when assembled with SnPb • Sn2Bi finish provides for 31% life improvement over SnPb finish

12. SAC vs. SnPb: Summary • Reversed trends under high vs. low to medium stress conditions • Situation requires accurate life prediction models or acceleration factors for reliability assessment under service conditions. • Need to consider data over a wide range of conditions before conclusions can be drawn. • Lack of data at cyclic strain ranges < 1%

13. Mixed Assembly Test Results • Leadless SMT: with or without Pb contaminant • SnPb balls: SAC or SnPb paste • SAC balls: SAC or SnPb paste

14. Leadless SMT with Pb Contamination • -55 to 125°C and -40 to 125°C data • Pb contamination (< 1% wt.) is from component (R1206) or board finish (HASL SnPb). 1

15. Area Array Assemblies with SnPb Paste SAC Balls vs. SnPb Balls • “Backward compatibility”: mixed record. • Limited data under 0/100°C conditions

16. Area Array Assemblies with SAC Balls SAC Paste vs. SnPb Paste • Under stated conditions, assemblies with SAC paste have similar or longer life than with SnPb paste.

17. Area Array Assemblies with SnPb Balls SAC Paste vs. SnPb Paste • “Forward compatibility”: opposite trends depending on thermal cycling conditions (-40/125°C vs. 0/100°C) • Test conditions matter, possible issue under milder conditions

18. Lead-free Assembly Reliability - Conclusions • Lead-free assembly reliability is dependent on package, assembly and test conditions • Reliability rank-ordering is strongly dependent on test conditions: • SnPb test standards may have to be optimized for Pb-free assemblies • Need accurate life prediction model(s) and acceleration factors to extrapolate to use conditions • Mixed assemblies • Both “backward” and “forward” compatibility situations require further attention.

19. Speaker’s Bio • Jean-Paul Clech is the founder of EPSI Inc. in Montclair, New-Jersey. His activities at EPSI include technical consulting with clients across the electronics industry, software development and professional training. He is the principal developer of the Solder Reliability Solutions model and application software. His research interests cover multi-disciplinary aspects of electronics packaging, Surface Mount Technology (SMT) and circuit board assemblies, with emphasis on materials characterization and the application of materials and mechanical engineering fundamentals to sound product design. He has consulted on the physical design of small and large circuit boards and is constantly challenged by design and reliability problems brought about by emerging packaging and soldering technologies, and the application of SMT in harsh environments. His current research interests are in the areas of flip-chip assemblies, chip scale packages, mechanical flexing and vibration of board assemblies, lead-free material properties and lead-free reliability assessment. • Jean-Paul previously was a member of the technical staff at AT&T Bell Laboratories and manager of electronic packaging at a European super-computer start-up. He was trained as a metallurgist and received the "Diplôme d’ Ingénieur" degree (Materials Science major) from Ecole Centrale de Paris, France. He then received the M.S. and Ph.D. degrees in mechanical engineering from Northwestern University, Evanston, Illinois, where he worked on the mechanics and failures of hip and knee joint replacements. His interest in soldering and solder fatigue started during a post-doctoral assignment in the Materials Science department at Northwestern. He is a recognized expert in the field of surface mount assembly quality and reliability and has assisted law firms as an expert witness on packaging, board and soldering related issues. Jean-Paul is an active member of ASME, IEEE, IMAPS, SMTA and TMS, has published over thirty five papers and a book chapter, and has chaired numerous workshops and technical sessions at international conferences. He has been an invited speaker, lecturer and seminar leader at corporations, universities and R&D institutions in Asia, Europe and North America. • Contact information: • Home page URL: http://jpclech.com • E-mail: jpclech@aol.com • Tel.: +1 (973)746-3796; fax: +1 (973)655-0815