Patent ID: 7629246

Claim:
A method for forming a high-strength solder joint between a solder ball and a microelectronic circuit package that contains at least one contact pad at its interconnect face, said method comprising: providing at least one solder ball, said solder ball having a polymeric core surrounded by a metallic shell, containing copper (Cu), that in turn is surrounded by a layer of solder material, containing tin (Sn); positioning the at least one solder ball atop the at least one contact pad of the circuit package, said contact pad containing copper (Cu); and reflowing said solder material between the solder ball and the corresponding contact pad for a preselected temperature range and a preselected time range such that an intermetallic layer, composed of Cu 6 Sn 5 and formed on an outer surface of the contact pad, and an opposed intermetallic layer, composed of Cu 6 Sn 5 and formed on an outer surface of the metallic shell of the solder ball, coalesce and intertwine with one another to form a substantially unitary intermetallic joint therebetween.