Patent ID: 7754343

Claim:
A Pb-free electrical interconnect structure comprising: a body having a composition off an eutectic composition in a ternary alloy system, the ternary alloy system comprising the Sn—Ag—Cu system; a first joint having a ternary composition off the eutectic in the ternary alloy system, the first joint composition being distinct from the body composition; and a second joint having a ternary composition off the eutectic in the ternary alloy system, the second joint composition being distinct from the body composition and the first joint composition, wherein a composition of the interconnect structure varies smoothly from the first joint composition to the body composition and from the body composition to the second joint composition, said varying smoothly comprising a composition gradient of at least a constituent of the ternary alloy system and wherein the composition of the body is significantly richer in Ag than a binary Sn—Ag eutectic composition and comprises substantially no Cu, the ternary composition of the first joint is significantly richer in Ag and Cu than a ternary Sn—Ag—Cu eutectic composition, and the ternary composition of the second joint is significantly poorer in Aq and Cu than a ternary Sn—Aq—Cu eutectic composition.