An assessment of mechanical reliability of a die-bonded chip package during chip encapsulation and accelerated thermal cycling

Abstract

Thermo-mechanical stresses induced during encapsulation and accelerated thermal cycling (ATC) of a chip solder die bonded to a card consisting of a thermal carrier and a thick heat sink has been analyzed using a two-dimensional linear elastic finite element (FE) model. The FE model is first verified against the displacement fields measured using laser moire interferometry. A parametric study of the effect of encapsulant thickness, Young's modulus, coefficient of thermal expansion, and chip size, on die and encapsulant stresses has been carried out. Potential for die and encapsulant cracking, and delamination at the die/encapsulant interfaces have been assessed. The results are useful in selecting a suitable encapsulant material to minimize the risk of die cracking. Thermo-mechanical strain induced in the solder bond during ATC has also been computed using an elasto-plastic FE analysis. Number of ATC cycles to failure of the solder bond have been estimated by combining FE results with Coffin-Manson equation for solder. >