Solder flux compatible with flip-chip underfill material

摘要

An epoxy-based soldering flux is used to solder a flip-chip IC device to a metallic bond site on a substrate material. The soldering flux is composed of a thermosetting epoxy resin and a cross-linking agent with inherent flux activity. When heated the cross-linking agent cleans the metal oxides from the metal surfaces on the chip and then reacts with the epoxy resin to form a thermosetting epoxy residue. The flux residue left on the board after soldering does not inhibit the flow of an underfill encapsulant. The underfill binds to the thermosetting residue of the flux which increases adhesion strength preventing delamination of the chip during thermal cycling.