Gold wire weakening in the thermosonic bonding of the first bond

Factors that are likely to weaken gold wire during thermosonic wirebonding of the first bond on the die pad are studied. The studies show that weakening is due mainly to the golf club ball formation, grain growth of wire, neckdown formation, tie-bar severance, and the wire-scratching phenomenon. Golf club ball formation can be eliminated by long tail length and wire grain size after recrystallization, can be reduced by low current supplied and short spark time during the EFO excitation. Neckdown and tie-bar severance can be removed by introducing reverse loop and ensuring no indexing problem during the wirebonding process. Wire scratching and dragging due to inside chamfer can be eliminated when the capillary for bonding is not too worn out