3D stacking of Co- and Ni-based microbumps

In this paper,the wettability, quality of joint formation and electrical yield of daisy chains in 3D stacks when using Cobalt and Nickel as UBM with different finish layers such as immersion Au, ELD NiB, ELD Cu and SAM are investigated. The performance of the stacks are characterized by cross-section SEM images, EDS analysis and electrical resistance measurement of the daisy chains.