Composite copper nickel alloys with improved solderability shelf life

DETAILED DESCRIPTION What is claimed is: 1.
A composite structure having a reduced growth of copper-tin intermetallic compounds, said composite structure comprising: a substrate formed from a copper base alloy; said copper base alloy consisting essentially of 19% to about 28% nickel and the balance essentially copper; a coating covering at least a portion of said substrate; said coating being formed from a tin-containing material; and said nickel in said alloy retarding the growth of said copper-tin intermetallic compounds and diffusion of said copper through said coating and thereby improving the solderability shelf life and contact resistance of said structure.
2.
The composite structure of claim 1 further comprising: said copper alloy consisting essentially of 19% to about 26% nickel and the balance essentially copper.
3.
The composite structure of claim 1 wherein: said copper alloy further includes up to about 25% zinc, whereby said nickel in said alloy retards the growth of copper-zinc-tin intermetallic compounds.
4.
The composite structure of claim 1 further comprising: said tin-containing material being selected from the group consisting of tin and tin alloys.
5.
The composite structure of claim 1 wherein: said tin-containing material comprises a tin solder consisting essentially of about 40% lead and the balance essentially tin.
6.
The composite structure of claim 1 further comprising: said coating comprising a stripe of said tin-containing material plated on at least one surface of said substrate.
7.
The composite structure of claim 1 wherein: said substrate comprises a composite having a core and a cladding material; and said copper base alloy forming one of said core and said cladding material.
8.
An integrated circuit assembly for electrical applications, said assembly comprising: a lead frame formed from a composite structure; said composite structure having a substrate formed from a copper alloy consisting essentially of 19% to about 28% nickel and the balance essentially copper and a coating covering at least a portion of said substrate; said coating being formed from a tin-containing material; and said nickel in said alloy retarding the growth of copper-tin intermetallic compounds and diffusion of said copper through said coating