NOVEL STRUCTURE OF UBM AND SOLDER BUMPS AND METHODS OF FABRICATION

Methods and UBM structures having bilayer or trilayer UBM layers that include a thin TiW adhesion layer and a thick Ni-based barrier layer thereover both deposited under sputtering operating conditions that provide the resultant bilayer or trilayer UBM layers with minimal composite stresses. The Ni-based barrier layer may be pure Ni or a Ni alloy. These UBM layers may be patterned to fabricate bilayer or trilayer UBM capture pads, followed by joining a lead-free solder thereto for providing lead-free solder joints that maintain reliability after multiple reflows. Optionally, the top layer of the trilayer UBM structures may include soluble or insoluble metals for doping the lead-free solder connections.