Patent ID: 6906417

Claim:
A flip-chip assembly comprising: a semiconductor device including an active surface having a plurality of contact pads thereon, each contact pad having a layer of solder on at least a portion of a surface thereof; a substrate including a surface having a plurality of contacts thereon, at least one contact of said plurality of contacts having a layer of solder on at least a portion thereof; and a plurality of balls bonded to said plurality of contact pads on said active surface of said semiconductor device and bonded to said at least one contact of said plurality of contacts on said surface of said substrate, at least one of said plurality of balls including a core material and an outer layer of solder wettable material, the solder wettable material solder wettable without solder flux and bonded solely by said layer of solder on a portion of the surface of the contact pad of the plurality of contact pads of said semiconductor device and the layer of solder on a portion of the at least one contact of the plurality of contacts on the surface of the substrate, said core material having a diameter in a range of approximately 50 microns to approximately less than 100 microns, said outer layer including an outer layer having a thickness in a range of 0.5 to 10 microns, and said core material having a greater rigidity and a higher melting temperature than the material comprising said outer layer.