Improving solder wetting of micro bumps on metal pads using metallic or organic pad coatings

In this paper the passivation effect of thin electroless metallic layers such as Au, NiB or Immersion Sn or thin organic layers such as Self Assembled Monolayer (SAM) on Cu, Co and Ni UBM microbumps is studied during Thermo-Compression-Bonding (TCB) and after anneal with conditions that were identified to be equal to 10 years working device at 80°C on an electrical test vehicle. Characterization with X-section SEM is done to look at the wettability and joint formation and electrical resistance measurement are performed to determine the yield.