Estimate the thermomechanical fatigue life of two chip scale packages

In this paper, two three dimensional finite element models were developed to numerically compute the stress, total strain, plastic strain and the cumulative plastic strain of the solder joints in a microBGA and a chip scale package (CSP) under temperature cycling. These stress and strain values, along with the results of solder fatigue tests, were then used to predict the solder joint lifetime through either strain-based approaches such as Coffin-Manson and modified Coffin-Manson equations or stress-based approach (S-N curve). Particular attention was given to the complex temperature profile of the thermal loading. The estimated fatigue life for both packages is extremely high, indicating that the packages are well designed for thermomechanical reliability.