A study of wafer level package board level reliability

Abstract

Board level reliability studies have been performed on wafer level packages (WLP) with various solder ball alloys, underbump metallurgy compositions, and redistribution (RDL) metal thicknesses. All of the WLPs studied pass drop shock with the thicker RDL having the best performance. In contrast to drop shock, , thicker RDL did not significantly improve thermal cycle on board reliability. A WLP with no underbump metallurgy (UBM) passed drop shock, but the temperature cycle performance was marginal. A WLP with Ni-doped alloy and NiCu UBM passed drop shock; however, this Ni-rich joint failed temperature cycle.

Electromigration of solder balls for wafer-level packaging with different under bump metallurgy and redistribution layer thickness

“…This paper describes the impact of such changes on electromigration. Related papers investigate other aspects of board level reliability including drop shock and temperature cycle [1][2]. Fundamentally, EM is the self-diffusion of metal(s) induced by electric current, which can lead to voiding and interconnect failure, and is an area of major reliability concern for interconnects.…”