Temperature Cycling Failures of a FC/WB Stacked Die SiP with F2F Micro-bump Interconnections

A FC/WB stacked die system-in-package (SiP) with face-to-face micro-bump interconnections was evaluated for reliable low-cost process. An electroless Ni/Pd/Au pad finish was deposited for both flip chip and wire bond processes. An unexpected premature failure was observed in the package after temperature cycling test. Detachment of the electroless Ni-based pad finish at the bottom micro-bump interconnections resulting in direct contact of the solder material with Al metallization of the bottom die was observed after planar lapping and cross-sectioning. The failure mechanism is discussed in this paper.