Accurate thermal cycle lifetime estimation for BGA memory components with lead-free solder joints

The paper reports the results of a systematic improvement project on the thermal cycle (TC) lifetime prediction of BGA memory modules with SnAg1.0Cu0.5 and SnAg1.0Cu0.5Ni0.05 solder alloys. The pre-existing lifetime modeling scheme allowed predictions with an inaccuracy factor of about 1.6^plusmn1 on average while in TC experiments, the characteristic lifetime, N₆₃, showed a standard deviation of about 0.3 N₆₃ when tests were repeated for the same product. After analyzing the weaknesses of the pre-existing scheme, improvements were introduced to the geometric, the material, and the load models. Afterwards, the creep strain energy density accumulated in the critical layers of the solder joints during one steady state TC was computed. Correlating it to the N₆₃, the coefficients of the lifetime model have been determined. Based on this, the TC lifetime expectancy of BGA memory systems has been predicted for different product configurations (two packages, two solder alloys, two PCBs) exposed to several thermal cycle profiles. Comparing all estimates to test results, the prediction inaccuracy has been shown to be reduced down to the level of 1.3^plusmn1-N₆₃ on average. This meets the range of experimental standard deviation.