THERMO-MECHANICAL ANALYSIS OF A CHIP SCALE PACKAGE (CSP) USING LEAD FREE AND LEAD CONTAINING SOLDER MATERIALS

This work is intended to provide a quantitative estimation of the accumulated inelastic strain of two different lead free solder alloys, namely, Sn3.5Ag and Sn3.8Ag0.5Cu. The eutectic Sn37Pb solder is also considered to establish a baseline. Thermomechanical stress and strain analysis was conducted on a Chip Scale Package (CSP). The solder joint fatigue was modeled for two typical temperature cycling loadings (from -40 to 125oC and from 0 to 100oC) in order to study the influence of acceleration factors on the reliability of different solder joints. A viscoplastic constitutive model is used to analyze the thermally induced inelastic deformation. The trends obtained from modeling results have a good agreement with the experimental data found in literature. Results also indicate that these lead free alloys can be used as alternative solder to improve the resistance to fatigue when compared with standards lead containing solder.