Influence of cure dependency of molding compound properties on warpage and stress distribution during and after the encapsulation of electronics components

Commercial FEM software codes do not directly support the cure dependency of polymers behavior. In electronics packaging, for example, cure shrinkage of the molding compound is consequently treated as a surplus to thermal contraction and its changes in visco-elastic behavior during curing are usually ignored. This give rise to inaccurate results and may cause difficulties even in recognizing factors important for further optimization. This work introduces a cure dependent visco-elastic material model being implemented into ANSYS by USERMAT, the user material subroutine. The results obtained when simulating the warpage of bi-material strips during and after curing with the full scale material model were compared to those obtained with simplified material models. Varying the geometric configuration different changes in the deformation results have been found caused by cure dependency anywhere between -10%, 0%, and +20%. Hence, correct results can only be achieved in general case with models accounting for cure dependency directly.