Study of the UBM to copper interface robustness of solder bumps in flip chip packages
Shear tests on SnAg solder bumps were performed with a reduced height to the surface for a high shear force on the under bump metallurgy (UBM) to redistribution layer (RDL) copper interface. By this the failure mechanism of UBMRDL delamination after stress tests simulating several assembly reflows could be reproduced. A design of experiment was done with corner wafers at worst case conditions for topography and interface clean. TEM cross sections confirmed nano scale carbon residues in the interface when reducing the clean efficiency. This results in a mechanically weakened interface with a present electrical contact. The shear test with reduced height is a more severe test beyond the JEDEC test to verify the bump robustness. This is important when existing bump technologies are used for flip chip package solutions with increased solder reflow requirements.
robustness bump flip chip shear test tem ubm delamination