Popcorn cracking in a plastic ball grid array package

The preconditioning testing (85/spl deg/C/85% RH or 6O% RH/168 hrs) for a plastic ball grid array (PBGA) package was carried out. The use of a substrate with relatively high rigidity at temperatures higher than 200/spl deg/C resulted in improvement of the popcorn cracking resistance during IR reflow. This result was reasonably explained to be due to the relatively large compressive stress between chip and substrate induced by its high rigidity. Further improvement was observed by increasing the thickness of the solder resist (SR) or the Ag-filled die attach (DA) layer.