Solder Joint Fatigue Studies Subjected to Board-level Random Vibration for Automotive Applications

Abstract

In this paper, a simplified methodology is presented for the evaluation of test-to-failure board-level random vibrations using a combination of experimental and finite element modeling techniques in calculating equivalent stresses for SAC305 solder joints experiencing high- and ultra-high-cycle fatigue usually found in the emerging automotive robo-taxi industry. Some partial results that were obtained during this study allow for an investigation of the effects of a printed circuit board geometry on possible failure modes of Pb-free solder joints. These results seem to confirm the findings that have been reported previously by some researchers on the migration of a failure mode from the ductile fracture in the bulk solder to the brittle fracture of the intermetallic compound (IMC) layer due to the positive correlation between the tensile strength of the solder joint and the strain rate which may have occurred from high level of vibration and shock during the test. The generated data points were then compared to the existing S-N (stress-life) fatigue curves for the SAC305 solder joints in order to assess whether these curves can provide adequate results for the test vehicles fatigue life calculations. These preliminary results show that more work is needed in both verifying the effect of a failure mode migration in the solder joints as well as developing additional data points for S-N curve generation. This research is a continuation of the study initiated by the JEDEC JESD22 working group.