TCT Reliability of Organic Passivation Layer for WLCSP

Wafer level chip scale packages (WLCSP) have been increasingly used in portable electronic products such as mobile phones. Solder bumps with redistribution layer (RDL) are typical interconnect technology for WLCSP applications. One of the major concerns in joint reliability is the failure by temperature cyclic stresses. In addition, in terms of heat tolerance or device yields, process temperature of RDL dielectric is limited around 200deg.C in some packaging applications. According to our board level reliability test for temperature cycle test (TCT), photosensitive polyimide (PI) which is 200deg.C curable material has lower fail rate than polybenzoxazole (PBO) by TCT. In this study, we compared the actual board level test and Finite Element Analysis (FEA) during temperature cycle test, and correlated the mechanical and fatigue properties of passivation layer material with TCT reliability.