Abstract:

This paper presents a strain based fatigue model for Pb-free SAC (Sn3.9Ag0.7Cu) solder interconnects based on the results of a designed experiment. Testing consists of temperature cycling CLCC packages soldered to printed wiring board under a fixed 100oC temperature range with the mid-point temperature varying between 25 and 75oC. In addition, the dwell (hold) time at the maximum temperature is varied between 15 and 75 minutes. The mean cycles to failure (N50) is related to the strain range using a numerical regression program . This strain-range failure model captures the observed transistion point where fatigue life of SnPb solder is greater than Pb-free SAC solder. Further, the model captures the effect of extended dwell and changes in cycle temperature. The model can be used to predict acceleration factors between test and field conditions.

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