Behavior of delaminated plastic IC packages subjected to encapsulation cooling, moisture absorption, and wave soldering

Plastic IC packaging subjected to moisture is vulnerable to delamination and cracking during the solder reflow process. Modeling the response of the delaminated plastic package is an essential step to fundamentally understand failure mechanisms and mechanics involved in the cooling, moisture absorption, and solder reflow process. A nonlinear finite element model was developed for predicting the deformation, stress, and fracture behavior of delaminated plastic packages induced by mechanical and hygro-thermal loads. The model consists of a sequentially coupled hygro-thermo-mechanical analysis considering moisture absorption, evaporation and interface contact and fracture analysis. A Lagrange Multiplier method was utilized to model the delamination interface condition. A general contact model was adopted which can handle complex contact conditions, such as arbitrary slippage and discontinuous curvature. A thermal contact was utilized to model the contact along delamination surfaces. Mixed mode fracture modes were elaborated. The model was verified by comparing existing analytical results with the predictions in the case of pulsed heating of the IC chip. Packaging responses and failure mechanisms due to encapsulation cooling, moisture absorption and evaporation, wave soldering, and interfacial moisture pressure loading are investigated, with consideration of temperature-dependent material properties change around the glass transition temperature for both die attach and molding compound. Packaging deformation and stress, crack tip driving force, doming of the delamination, and delamination growth stability as a function of time are discussed