Effect of heat slug and die attach material properties on plastic pin grid array (PPGA) package stress

A three-dimensional finite element model of a plastic pin grid array (PPGA) with an internal heat slug has been developed by using the ANSYS finite element simulation code. The model has been used to study the effects of heat slug as well as die attach material properties on the thermomechanical stresses developed within an electronic package during temperature cycle. Parametric studies have been performed by changing the Young´s modulus and the coefficient of thermal expansion for the die attach and heat slug materials to create a database for the predicted von Mises stresses and the package warpage. This database is then used to obtain empirical correlations for the stress and the package warpage as a function of the Young´s modulus and the coefficient of thermal expansion of the heat slug and die attach materials. These stress correlations would be useful to design engineers in selecting the die attach and heat slug materials to reduce the stresses on the critical devices. In addition to the finite element simulation, the analytical solutions for two elastic layers joined by one bonded joint are also used to predict the maximum shear stress for the joint made of die, die attach, and heat slug when the Young´s modulus and the coefficient of thermal expansion of one of the layers are independently changed