BLM structure for application to copper pad

A microelectronic element, comprising:

• a continuous cheesed metal contact pad having a contact surface and including a plurality of dielectric-filled openings exposed at the contact surface and spaced apart from peripheral boundaries of the contact surface, the dielectric-filled openings surrounded in the plane of the contact surface by the metal of the contact pad, said contact pad having a composition including copper exposed at said contact surface;
• a passivation layer overlying said major surface of said substrate, said passivation layer exposing at least a portion of said contact surface;
• and
• an underbump metallization (“UBM”) including a plurality of metal layers arranged in a stack overlying said contact surface and at least a portion of said passivation layer, said UBM including:
• (a) a lower layer including an alloy including titanium (Ti) and nickel (Ni) in contact with said contact surface wherein a weight percentage of titanium in the alloy is substantially greater than a weight percentage of nickel in the alloy;
• and
• (b) an upper layer overlying said lower layer, said upper layer consisting essentially of copper;
• and
• a conductive bump including a fusible metal metallurgically bonded to the upper layer of the UBM.