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

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