Methods of ball grid array

A method for making a flip-chip assembly, the method comprising:

• providing a semiconductor device having an active surface having a plurality of bond pads thereon, at least a portion of each bond pad having a layer of solder thereon and a substrate having a surface having a plurality of contacts thereon, at least a portion of each contact having a layer of solder thereon;
• providing a plurality of balls to contact at least one bond pad of said plurality of bond pads on said active surface of said semiconductor device and to contact 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, said at least one ball having a diameter of at least approximately 50 μms, said at least one ball comprised of a rigid non-conductive polymer, said core having a diameter in the range of 80% to 99% of the diameter of said at least one ball, said outer layer comprising one of silver and a silver alloy having a thickness of about 1 μm substantially covering the entire surface of said core;
• and
• bonding at least one ball of said plurality of balls to said at least one bond pad of said plurality of bond pads on said active surface of said semiconductor device and to said at least one contact of said plurality of contacts on said surface of said substrate, said bonding including reflowing the layer of solder on at least a portion of said plurality of bond pads on said active surface of said semiconductor device and reflowing the layer of solder on at least a portion of said plurality of contacts on said surface of said substrate.

A method for preparing a plurality of balls for a flip-chip assembly, the method comprising:

• providing at least one ball of said plurality of balls having a diameter of at least approximately 50 μms comprised of a core material and an outer layer on said core material;
• providing a core material for said at least one ball of said plurality of balls, said core material having a diameter in the range of 80 to 99% of the diameter of said at least one ball;
• and
• providing an outer layer on said core material for said at least one of said plurality of balls, said outer layer comprising a material having a rigidity less than said core material, said outer layer including a solder wettable material having a thickness of 10% to less than 1% of the diameter of said core material, said outer layer comprised of one of silver and a silver alloy covering substantially the entire surface of said core having a thickness of about 1 μm, said core material including a height, said height of said core of said at least one of said plurality of balls being substantially equal.