Impact of residue on Al/Si pads on gold bonding

Gold wire bonds on Al/Si bonding pads were evaluated for bondability and bond reliability as a function of bonding pad over- and under-etch. Glass residues affect the bonds when the bonding pad is under-etched. When pads are over-etched, residues deposited form the plasma affect the bonds. Bondability to pads with various layers of residue was evaluated by visual inspection of the bonds, by pull-testing the bonds, and by measuring the electrical resistance of the bonds. Reliability was evaluated by monitoring electrical resistance of the bonds as a function of bake-time. It was discovered that bonds to under-etched pads do not stick and have low reliability. A small amount of over-etching was observed to improve the reliability of the bonds, but extended over-etching decreased the lifetime slightly