Thermosonic gold ball bonding to alternate plating finishes on laminate MCM substrates

As the laminate substrate industry moves from Hot Air Solder Level (HASL) finishes, alternate plating finishes are being proposed such as electroless palladium and immersion gold over electroless nickel. This paper presents results of an evaluation of the thermosonic gold ball wire bondability of immersion gold over electroless nickel. The initial evaluation criteria included bondability (number of missed bonds), wire pull strength, and bond failure mode. Different preconditioning environments such as reflow cycles, high temperature storage and humidity storage on initial bondability were also considered. Rutherford backscattering, Auger spectroscopy and XPS were used to examine the gold and nickel layers. The stability of the bonds was investigated by high temperature storage with periodic electrical resistance and pull strength testing.