Pre-applied underfill adhesives for flip chip attachment

As flip chip attachment becomes a more prevalent method of IC packaging, new classes of materials are being developed to simplify the process of mounting and underfilling these components. Specifically, materials that can be pre-applied to either the chip or the substrate are attractive alternatives to the current capillary underfills. We will describe our materials development of both liquid no-flow underfills and wafer-applied underfill (WAU) film adhesives for flip chip attachment. For any pre-applied approach, voids can be problematic if the materials are inherently volatile or the substrates exhibit excessive outgassing. Our studies in identification and elimination of volatiles from various classes of circuit boards and compounds used in the underfills will be disclosed.