Detailed processes are involved in underfilling flip-chip
assemblies, and a variety of fluid formulations and dispensing
alternatives are available to today's flip-chip process
engineer. In the past few years, flip-chip technology has
migrated from a specialized packaging application to mainstream
production as a key method for improving circuit densities,
reliability and cost in miniaturized electronic products. The
use of underfill encapsulant beneath the flip-chip die is
necessary to significantly increase reliability by reducing the
strain on the solder bumps during thermal cycling imposed by
coefficient of thermal expansion (CTE) differences between the
die and the substrate. By adhering to all surfaces under the
die, the underfill adhesive makes the die-adhesive-substrate
system stiffer. The underfill adhesive also keeps the solder
bump in hydrostatic compression, thereby increasing fatigue
endurance and holding the bump intact under strain. Underfill
encapsulant has been shown to provide an improved de