Patent ID: 7696439

Claim:
An interconnect element for conductively interconnecting one or more microelectronic elements, comprising: a dielectric layer; a plurality of wiring patterns consisting essentially of copper and extending along a surface of said dielectric layer; a plurality of conductive posts having first ends adjacent to said wiring patterns and second ends remote therefrom; an etch stop layer consisting essentially of chromium or an alloy of chromium and nickel electrically connecting said first ends of said posts with said wiring patterns, said etch stop layer being resistant to an etchant usable to pattern each of first and second metal layers in accordance with first and second masks, respectively, to form said posts and said wiring patterns, respectively, wherein said etchant includes cupric chloride, wherein lengths of said posts between said first and second ends are much greater than a thickness of said etch stop layer between said posts and said wiring patterns.