Combined vibration and thermal cycling fatigue analysis for SAC305 lead free solder assemblies

In this paper, a combined random vibration and thermal cycling fatigue time-to-failure (TTF) prediction analysis will be reported. The combined random vibration and thermal cycling (TC) loading profile employed in the study is a thermal cycle loading of -40°C to +125°C (1 hour cycle with 15 minutes dwell) with random vibration of 7.5GRMS. Random vibration is applied concurrently at the extreme temperature during dwell periods for 15 minutes. The test vehicle used has six (6) Plastic Ball Grid Array (PBGA) packages mounted on the PCB with 12 mounting holes. Full model was adopted for this work. The 3D model consists of a PCB with edge connector, 1936 solder joints per package, BT substrate, silicon die and mold compound. A global model with solder cuboids and a local “submodel” with fine mesh was analyzed separately for temperature cycling analysis. A stress versus failure cycles (S-N) curve was formulated by performing a SN curve test on SAC305 test specimens. Combined loading test with TC from -40°C to +125°C and random vibration of 7.5 GRMS was conducted. Correlation between the experimental test results and the combined loading life prediction results are made in this paper.