A numerical study of the effects of temperature, moisture and vapour pressure on delamination in a PQFP during solder reflow

Delamination during solder reflow is a critical reliability problem for the plastic IC packages. The main objective of this paper is to investigate the effects of temperature, moisture diffusion and vapour pressure on the likelihood of delamination of the interface between the leadframe pad and the encapsulant. In this paper the entire thermal and moisture history of a plastic IC package is simulated from the start of level 1 moisture preconditioning (85°C/85%RH for 168 hours) to subsequent exposure to a solder reflow process lasting about 5 minutes. The transient development of the strain energy release rate due to thermal stress only G_t, hygrostress only G_h, vapour pressure G_p and combined G_tot are computed and studied by using a new modified crack surface displacement extrapolation method (MCSDEM). Finite element models were constructed for a 160-leaded PQFP. The initial crack length was varied from 0.1mm to 3.5mm in order to study its effect. The results show that for small cracks, the effects of temperature and moisture are dominant while that of vapour pressure is insignificant. For moderate crack lengths, the effect of temperature is greatest. For large crack lengths, the effect of vapour pressure is dominant.