High solder-reflow crack resistant molding compound

A variety of epoxy resins, filler mixtures, and adhesion additives were examined in semiconductor molding compounds for solder-reflow crack resistance (popcorn crack resistance). A limited comparison of molding compound high temperature strength properties and extent of popcorn cracking suggests no strong positive correlation. On the other hand, factors that might have an impact on adhesive properties of the molding compound, such as Low melt viscosity resins and putative adhesion additives appear to have the greatest impact. A molding compound developed with these factors showed no internal or external cracks on 84 Lead QFP´s (29.2×29.2×3.68 mm) after 72 h of 85°C/85% R.H. and one 10-s solder dip at 260°C. Nor were any external cracks observed after 168 h of 85°C/85% R.H. and one solder dip. However, minor internal cracks were observed