Electroless Ni/Pd/Au plating for semiconductor package substrates-effect of gold plating combinations on gold wire bonding reliability

In order to investigate the root causes of the good wire bonding reliability in electroless Ni/Pd/Au plating (ENEPIGEG), the wire bonding reliability of the combinations with electrolytic and electroless processes were evaluated. The reliability of ENEPIGEG and electrolytic Ni (SB-Watt)/IGEG were equivalent to that of the conventional electrolytic Ni (SB-Watt)/electrolytic Au and were excellent. The reliability of electrolytic Ni (SB-Watt)/IGEG was higher than that of EN/Electrolytic Au after heat treatment. We found that the grain size of the gold deposit coordinated with the grain size of the underplated Ni deposit with the epitaxial crystal growth. The large grain size of the gold deposit decreased the grain boundary of the gold deposit and reduced the grain boundary diffusion from the underplated metals onto the gold plating. We concluded that the wire bonding reliability after heat treatment depended on the diffusion behavior of the underplated metals and the grain size of the gold deposit.