Patent ID: 6994243

Claim:
A process of capping a Pb-rich ball with at least one layer of low melting point metal, said process comprising the steps of: (a) forming said Pb-rich ball on a substrate; (b) placing a mask over said Pb-rich ball such that a portion of said Pb-rich ball is exposed; (c) depositing at least one layer of a low melting point metal over said Pb-rich ball through said mask, such that at least a portion of said Pb-rich ball has a capping layer of said low melting point metal; (d) heating said Pb-rich ball and said capping layer of said low melting point metal to form a eutectic alloy having a Pb-rich core and a cap region of said low melting point metal; (e) annealing said eutectic alloy such that one of said low melting point metal from said cap region is diffused into said Pb-rich core and Pb from said Pb-rich core is diffused into low melting point metal from said cap region, wherein the melting point of said low melting point metal is lower than the melting point of Pb.