Investigation of thermo-mechanically induced stress in a PQFP 160 using finite element techniques

The authors use finite element (FE) techniques to illustrate how thermomechanical stresses are built up within a plastic IC package, due to encapsulation. Plane strain is chosen as the most suitable 2D FE model for the thermomechanical stress analysis of plastic packages. The compressive stress on the die is separated into direct and bending components of stress. This is used to show that the molding compound induces over half of the encapsulation stress into the die. An explanation of the compressive stress distribution throughout the die is presented. The encapsulation stress on the die can be eliminated by isolating the die from the package with a side buffer of soft material