A ball grid array for a flip-chip assembly. The ball grid array includes a plurality
of bumps bonded between an active surface of a semiconductor die and a top surface
of a printed circuit board or any type of substrate carrier. The plurality of balls
include at least one bump having a core material and an outer layer. The rigidity
of the core material is greater than that of the material of the outer layer. Additionally,
the melting temperature of the core material is higher than the material of the
outer layer. By this arrangement, the core material with an outer layer provides
bumps that are substantially uniform in height. In addition, the balls only procure
marks or deformation to the core material during burn-in testing and reflow.
