Patent ID: 7331106

Claim:
A method of underfilling a flip chip die, the method comprising the steps of: microjetting a filled underfill material onto a surface of a wafer on which individual dies are delineated and separated by scribe lines, each of the dies having solder bumps associated therewith, the filled underfill material comprising a polymer matrix material and a dispersion of particulate filler material that reduces the coefficient of thermal expansion of the filled underfill material, the filled underfill material being selectively deposited between the solder bumps and not over the solder bumps or the scribe lines; singulating the dies from the wafer along the scribe lines, without cutting through the filled underfill material to prevent underfill debris from separating from the surface of the wafer; depositing an adhesive on a substrate having bond pads on a surface thereof, the adhesive being substantially free of a filler material; registering the solder bumps of one of the dies with the bond pads on the substrate so that the filled underfill material and the adhesive fill a space defined by and between the die and the substrate and the adhesive extends from the substrate past the space and the filled underfill material onto a peripheral wall of the die to form a fillet between the die and the substrate; heating the substrate, the solder bumps, the filled underfill material and the adhesive so that the solder bumps melt and so that the filled underfill material and the adhesive form a composite underfill layer having discrete filled and unfilled portions; and then cooling the molten solder bumps and the composite underfill layer so that the molten solder bumps form solid electrical connections that are metallurgically bonded to the bond pads, the composite underfill layer encapsulates the connections, the unfilled portion of the composite underfill layer defines the fillet that extends onto the peripheral wall of the die, and the space between the die and the substrate is free of voids.