抄録
Plastic encapsulated semiconductor devices have been accepted for most industrial applications because of their cost advantage and great improvement in moisture induced reliability problems. Since the residual thermal stress is induced after the molding process by the large difference in the thermal expansion coefficient between the plastic resin and the silicon chip, this stress can cause serious reliability problems such as cracks in passivation films and deformation of aluminum metallization. The purpose of this study has been to examine the use of photoelasticity in determining the residual thermal stresses in the encapsulation material of plastic ICs. The method to measure the stress of ICs molded with the transparent resin instead of the conventional opaque encapsulating resin is established by using photoelasticity. The shearing stress parallel to the chip surface shows the maximum value at the chip edge and it becomes smaller toward the center of the chip. On the other hand, the vertical element is tensile at the chip edge and is compressive stress from the appropriate position. The effect of the chip buffer coat is clarified by the method. The package thickness is the most effective upon the thermal stress in the package size. As it is thiner, the stress is smaller.
