On hydro-thermal stresses of plastic IC packages

In this paper, the 3-D deformation of a plastic IC package due to moisture absorption was revealed experimentally with an invented 3-D optical testing system. The result shows that warpage can even be reversed by hygroscopic expansion. Then, a united finite element model was employed to investigate the hygro-thermal stress inside the plastic IC packages. Experimental results were used to adjust/verify the FEM model. Through this FEM/experiment hybrid method, the effect of moisture absorption on the internal stress field of the plastic package was investigated, and peal stress on the solder bump due to moisture absorption was found, which is considered the reason of UBM (under bump metallization) opening. Through this investigation, a reliability problem that is usually unnoticed or underestimated is revealed.