Power Cycling Simulation And Solder Joint Life Prediction For Chip Scale Package

The integrity of solder joints is a major reliability concern in modern microelectronic package structures. Temperature fluctuations caused by power transients or environmental changes commonly experienced in external applications results in thermal expansion mismatch between the various package materials causing the plastic strain deformation of the solder interconnects. Compared to the amount of analysis in the industry on reliability effects of passive thermal cycling, the work done with power cycling is very limited. With the same temperature on package, solder ball and PCB board, thermal cycling simulation ignores the thermal gradients in the whole assembly. Power cycling simulates the actual heating of chip. Power is uniformly applied on the die. The heating of the electronics packages is defined by power on and the cooling is defined by power off.In this paper a method is introduced for analyzing the effect of power cycling on the solder interconnects of a CSP assembly. The method consists of 1) a transient thermal simulation with die power cycling and 2) a thermal-mechanical analysis of the assembly, where the thermal analysis results provide the nodal loading conditions.A unified viscoplastic constitutive relation, the Anand model, was applied to represent the nonlinear deformation behavior of 63Sn37Pb solder. Three-dimensional nonlinear finite element modeling was used to analyze stress-strain response of 63Sn37Pb solder joint under power cycling loading conditions. Number of cycles to failure was calculated depending on life prediction equation. And life prediction results was studied for coarse vs. detailed model of non-critical joints. The paper discusses the analysis methodology and results as implemented using the ANSYS finite element simulation software tool.