Protection of copper from intermetallic copper-tin formation for flipchip bumping applications
Original Publication Date: 2002-Apr-10
Included in the Prior Art Database: 2002-Apr-10
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A process to minimize/eliminate copper-tin intermetallic formation, during electroplated flip chip bump processing, is described. An area is defined for the electrolytic or electroless deposition of nickel by photolithography method. Nickel is deposited in such a way that it wraps around the copper underbump metallurgy. It eliminates the possibility of direct contact of tin with copper during the high temperature reflow process and hence reduces the copper-tin intermetallic formation which is considered as a major cause of bump failure. Since no electroplated copper is exposed , this process also enhances the selectivity of the etching of the sputtered bus layer vs.plated copper, as the etchant exposed to copper and nickel.