Development of a non-conductive, no-flow wafer level underfill

WLCSP (wafer level chip scale package) has been developed for several years to reduce package size, process cost and to increase product reliability. With the development of high-density, flip chip packages, an underfill process for fine-pitch bump size become more important. WLUF (wafer level underfill) is a technology that applies an underfill material onto a wafer front side and encapsulates the flip chip package without the need for capillarity flow and flux dispensing. Thus, voids from capillarity flow may be avoided and flux-dispensing process is eliminated to prevent potential reliability risks resulting from residual fluxes. In this study, we describe the investigation of a new WLUF technology for fine pitch WLCSP packages and present the lamination and bonding test results using the WLUF materials on our test WLCSP packages.