Effects of number of reflows on the mechanical and electrical properties of BGA package

Mechanical and electrical properties of the Sn–37Pb/Cu joints were investigated in terms of the effect of intermetallic compound (IMC) layer growth. A layer of continuous scallop-shaped Cu6Sn5 IMC was formed at the interface between the solder and substrate after 1 reflow, while Cu3Sn IMC layer was formed after 3 reflows. The thickness of the total IMC layer increased as a function of cubic root of reflow time. The shear force of the solder joints did not vary much with the number of reflows. Only ductile failure mode was observed regardless of the number of reflows, and explaining well the shear force variations. The electrical resistivity of the BGA package was measured to investigate the relation between the microstructural variation and electrical properties of the solder joints. The electrical resistivity increased with the number of reflows.