Copper post solder bumps on substrates

In a method comprising forming a semiconductor flip chip from a wafer having solderable electrical conducting sites and a substrate having electrical connecting pads and electrically conductive posts operatively associated with said pads and extending away from said pads to terminate in distal ends, the steps comprising solder bumping said distal ends through openings in a solder mask by injection molding solder onto said distal ends to produce a solder bumped substrate and soldering said solder bumped substrate to said sites wherein said distal ends extend into said mask through said openings;

• said openings in said mask comprising reservoirs for receiving molten solder wherein said reservoirs and said posts sealingly engage one another toward the proximal ends of the post in a manner to substantially minimize or eliminate leakage of molten solder from said reservoirs, where either said posts taper from their proximal ends toward their distal ends in a narrowing fashion or said reservoirs taper from the point of solder injection toward the other end of said reservoir in a narrowing fashion or, by employing both of said tapered posts and said tapered reservoirs.