Underfill preform interposer for joining chip to substrate

Abstract

An apparatus for and method of minimizing the thermo-mechanical fatigue of flip-chip packages. The interposer of the present invention, preferably comprising an organic polymer such as polyimide, contains apertures having conductive plugs inserted therein for joining a chip to a substrate in an electronic module utilizing flip-chip packaging. The interposer is selected to provide optimum spacing between the chip and substrate having a coefficient of thermal expansion adapted to the thermal cycling temperature extremes of the module components. The interposer may comprise an inner core with two adhesive outer layers which may comprise different materials to promote adhesion at their respective interfaces within a module. Conductive plugs are disposed within the apertures of the interposer comprising of a first and second solder or comprising a conductive plug having top and bottom surfaces coated with a conductive adhesive. Preferably, the first solder is disposed within an interior of the apertures and the second solder is disposed within an exterior of the apertures such that the first solder is between a first portion and a second portion of the second solder. Upon reflow, the second solder is reflowed while the first solder remains solid.