Abstract: A microelectronic assembly (10) incorporating a particulate free underfill material (32 includes a substrate (24) having a plurality of bond pads (26) disposed on a substantially planar die attach region (24), and an integrated circuit die (12) having a die face (16) and a plurality of bond pads (20). The die face (16) is superimposed over the substrate die attach region (24) so that each of the die face bond pads (20) is generally aligned with a corresponding one of the substrate bond pads (26) and such that the die face is spaced apart from the die attach region by a gap not greater than about 20 microns. Each of the die face bond pads (20) is connected to its corresponding one of the substrate bond pads (26) by a solder connection (30). A particulate free polymeric material (32) is disposed in the gap, with the polymeric material substantially encapsulating each of the solder connections.

Abstract: A method for dispensing underfill material between a flip chip bonded to substrate. The method requires an underfill injection port to be drilled through the substrate prior to reflow such that underfill material can be dispensed between the flip chip and substrate through the port. After reflow is completed, a pressurized pump delivers a predetermined amount of underfill under hydraulic pressure through the underfill injection port between the flip chip and substrate. Once injected, the underfill migrates between the flip chip and substrate via capillary action pushing out any air around the joints.

Abstract: A method and apparatus improves a distribution of an underfill material (504) applied between a flip chip die (202) and a circuit board (310) at a flip chip site (302) having a solder mask (308). An aperture (304) is formed (806) in the solder mask (308) by removing a predetermined majority of the solder mask (308) from the circuit board (310) within the flip chip site (302) before mounting the flip chip die (202). Then the flip chip die (202) is mounted (810) to the flip chip site (302). The underfill material (504) is then applied (812, 814, 816) such that the underfill material (504) flows into the aperture (304), thus improving the distribution of the underfill material (504).