| abstract |
A thin, uniform, high viscosity, uncured and unreinforced film (30) is disclosed. The film (30) comprises: (a) 0.5 to 50%, by weight of the film (30), of a polymeric or polymer forming matrix material; (b) 0.01 to 10%, by weight of the film (30), of a curing agent that is soluble in the matrix material at a temperature no greater than 100 °C; and (c)50 to 80%, by volume of the film (30), of a substantially spherical and inert filler that has a maximum particle size no greater than 30 νm. The film (30) exhibits certain kinetic properties that permit it to cure very quickly and in a manner that does not produce void causing volatiles. The film (30) can be placed between a silicon chip (40) and a printed board (10) in a flip-chip assembly process and cured to form an underfill (70). The curing step can be conducted during the same heat cycle used to form the solder joints (75' and 75') in the flip-chip process. Underfilled assemblies (60) created using said film (30) exhibit a thermal cycle resistance that is 250% greater than the obtained using traditional low viscosity underfill materials. |