Combined Moisture and Thermal Stresses Failure Mode in a PLCC

Abstract

A finite element analysis has been conducted to provide a new explanation for PLCC cracking during soldering and develop a working model for the cracking phenomena. The model shows that cracking is due to strong moisture, temperature and material properties gradients that are developed in the body of the PLCC and that the moisture is not accumulated in a free state under the pad. Instead it is distributed in three distinct regions in the PLCC encapsulation. The results of this model indicate high stress at points where cracks were reported to occur.