Patent ID: 7780063

Claim:
A method comprising the steps of: providing a mask having a plurality of through holes and a silicon mold having a plurality of cavities; aligning said through holes and said cavities; dispensing preformed conductive balls into said aligned through holes and cavities, said preformed conductive balls having a diameter e, substantially one preformed conductive ball to each aligned through hole and cavity, said cavities of said mold comprising pits having an opening diameter ranging from about e to about 2e and having tapered side walls with a tapered side wall angle controlled such that upon removal of said mask from said mold, said preformed conductive balls extend beyond said outer surface of said mold and are immobile in said mold, said mask with said holes and said cavities in said mold being configured and dimensioned such that: said preformed conductive balls are one of substantially flush with, and recessed below, an outer surface of said mask under conditions of said alignment of said through holes and said cavities; and upon removal of said mask from said mold, said preformed conductive balls extend beyond an outer surface of said mold; removing said mask from said mold so that said preformed conductive balls extend beyond said outer surface of said mold; aligning said preformed conductive balls with pads of a semiconductor device; and transferring said preformed conductive balls to said pads by fluxless reflow in a formic acid environment.