Development of molding compounds suited for copper leadframes

We conducted various studies on molding compounds for surface mount packages suitable for copper alloy leadframes. First, we examined the adhesion of molding compounds to copper alloys and found that the adhesion strength varies depending upon the kind of copper alloys and the degree of oxidation of their surfaces. It also interested us that the highest adhesion strength was achieved when the oxidation reached a certain degree. In the practical package assembly process we will be able to improve the reliability of packages by controlling heating of leadframes. Then we made a reliability test on packages. As for solder crack resistance, copper alloys are somewhat inferior to Alloy-42. Molding compounds whose adhesion strength to lead frame is higher have higher solder crack resistance. As for temperature cycle performance, copper alloys are obviously inferior to Alloy-42. Molding compounds with lower stress perform better in temperature cycle tests. Therefore, molding compounds with high adhesion and low stress are suitable for copper alloy leadframes. In the future, the more reliable packages shall be developed by improving die-attach paste (silver paste), the shape of leadframes (slit design), etc