Reliability of WLP Structures Fabricated with ALX Dielectric Polymer

For wafer level packaging (WLP) applications, BCB, polyimides, epoxies, and PBO are the predominant spin-on dielectric materials used for repassivation, redistribution, and stress buffering. Each of these materials has their respective strengths and weaknesses in process and in reliability. Asahi Glass Co., LTD has developed a new spin-on dielectric polymer (ALX) designed for WLP applications that provides a unique set of material properties coupled with a low curing temperature. We have previously presented process evaluation and optimization data on ALX polymer material, which showed an application process similar to BCB with wide process latitude. In this paper we present the results of a study done to evaluate the performance of ALX polymers in WLP test structures fabricated at RTI International. Typical solder bumped repassivation and bump-onpolymer test structures have been fabricated using ALX and BCB and evaluated through bump shear tests. We have also evaluated the adhesion of ALX to typical materials encountered in WLP structures through shear testing free-standing polymer

structures.