Popcorning in Fully Populated and Perimeter Plastic Ball Grid Array Packages*

Two types of Plastic ball Grid array packages, a 225‐lead full matrix array and a 256‐lead perimeter array, were subjected to 168 hours of moisture preconditioning at 85°C and 30% relative humidity followed by simulated infra‐red reflow at temperature ramp rates of 1°C/s and 0.67°C/s. The packages were subsequently examined for delamination and cracking using scanning acoustic microscopy and environmental scanning electron microscopy. At the higher ramp rate, delamination and cracking were observed in both package types, originating in the die attach and propagating along the weakest interfaces. At the lower ramp rate, a small amount of delamination was observed. This suggests that there is a critical ramp rate below which popcorn cracking does not occur.