Investigations on popcorn cracking of T-QFP packages

The paper reports a finite element (FE) study of the "popcorn" effect of a plastic Thin Quad Flat Pack (T-QFP) 176 package, based upon experimental investigations. Delamination of the die-pad/adhesive interface and subsequent occurrence of a kink crack at the lower die-pad edge is shown to be the typical kind of popcorning failure for the thin package after level 1 preconditioning. The elastic stiffness as well as fracture toughness of low-stress molding compounds are shortly characterized in dependence on temperature. Moisture, heat, and vapor pressure induced stresses are calculated by FE-analysis for the uncracked package. The initially delaminated package is studied by means of linear elastic fracture mechanics. Low critical vapor pressure but a sharp pressure induced increase of the vapor volume is observed for different package design. No significant influence of the die size, varied by about 20%, on the package stress could be detected.