Underfill method

摘要

A process for selectively depositing a filled underfill material (14) onto a die surface without covering solder bumps (12) present on the die (10). The process entails microjetting a polymer matrix material, a filler material, and optionally a fluxing material (22) onto the die surface. Together, the polymer matrix and filler materials define the filled underfill material (14) in which the filler material is dispersed to reduce the coefficient of thermal expansion of the underfill material (14). The resulting underfill material (14) surrounds but does not cover the solder bumps (12). The die (10) is then placed on a substrate (16) on which a second underfill material (26) is present, forming a composite underfill layer (24) that completely fills the space between the die (10) and substrate (16) and forms a fillet (28) on a peripheral wall (30) of the die (10).