Numerical Simulation of Creep Strain of PBGA Solders under Thermal Cycling

An octant 3D finite element (FE) model of plastic ball grid array (PBGA) assembly system was developed according to actual package product. The FE method was used to study the creep strain and reliabilities of solder joints under four thermal cycles. The distribution of the creep strain of solder joints under temperature loading was analyzed, and the reason of which was investigated. 95.5Sn-3.8Ag-0.7Cu and 63Sn-37Pb were taken as two kinds of solder to be compared in this study. The creep strain, low cycle fatigue life and reliability of both solders were evaluated. Results showed that for the whole joints array, the creep strain was much larger around the die, the reason of which might be attributed to the larger thermal expansion mismatches between the die and other components in this area. Comparing the reliability of the two kinds joints in this paper: 63Sn-37Pb joints creep more seriously in the cycling process. And 95.5Sn-3.8Ag-0.7Cu joints had longer fatigue life, which showed a higher reliability under thermal cycling.