Lead-free 95.5Sn-3.8Ag-0.7Cu solder joint reliability analysis for micro-BGA assembly

Abstract

A design-for-reliability methodology was applied to a micro-BGA assembly with lead-free, 95.5Sn-3.8Ag-0.7Cu solder joints. A rate dependent viscoplastic Anand model was curve fitted from a series of constant strain rate tensile test and creep test results. The material parameters for the viscoplastic Anand model for 95.5Sn-3.8Ag-0.7Cu solder was implemented in finite element analysis. Low cycle isothermal fatigue test was conducted over three frequencies of 1 Hz, 0.01 Hz and 0.001 Hz; three temperatures of 25/spl deg/C, 75/spl deg/C and 125/spl deg/C; and four total strain range values of 2, 3.5, 5, and 7.5% respectively. A micro-BGA assembly with lead-free, 95.5Sn-3.8Ag-0.7Cu solder joints was subjected to (-55 to 125/spl deg/C) thermal cycling test and the Weibull distribution was obtained. FEA modeling and simulation was employed to predict the fatigue life cycles of the micro-BGA package and compared to the MTTF life cycles.