Solder flux compatible with flip-chip underfill material
AssigneeNorthrop Grumman Corporation
InventorKenneth J. Kirsten
Life of this patent
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Abstract
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.
Claims11
A method of electrically connecting an electrical component having a plurality of spaced apart electrical component electrical terminations to a substrate having a plurality of spaced apart substrate electrical terminations corresponding to the terminations of said electrical component to form a plurality of spaced apart electrical connections and then interfilling said electrical and substrate components with an encapsulant composition sandwiched therebetween to encase said spaced apart electrical connections comprising:
- a) forming spaced apart electrical connections of said spaced apart component electrical terminations to said corresponding spaced apart substrate electrical terminations with solder at reflow soldering temperature utilizing an epoxy-based fluxing agent that leaves an epoxy-based fluxing agent residue that is partially cured on said spaced apart electrical connections and leaves open space between the spaced apart electrical connections with epoxy-based fluxing agent residue thereon;
- b) filling said open space between said spaced apart electrical connections with partially cured epoxy-based fluxing agent residue thereon with an epoxy underfill encapsulant that co-cures with the epoxy-based fluxing agent residue;
- and then
- c) co-curing said epoxy underfill encapsulant and epoxy-based fluxing agent residue to form a bond at the interface of said epoxy based underfill encapsulant and epoxy-based fluxing agent residue.
Dependencies are inferred from the claim text.