The Characterization of Intermetallic Growth in Copper and Gold Ball Bonded on Thicker Aluminum

Wire bonding has been the most popular interconnection method in semiconductor device packaging. Recently, due to the increasing demand for enhancing the reliability of the device, fine wire diameter and more function property, attention has been focused on failure solution of wire bonding. Au-Al intermetalic compound formation and associated Kirkendall voids have resulted in wire bond failures. 2N gold alloy wire (Purity: 99%) is recommended to replace 4 N gold wire (Purity: 99.99%) for improving 1st bond failure. Due to palladium-rich layer formation at the gold ball and intermetallic compound, the Pd barrier layer restrain the gold atom not continued move to Al metallization side to avoid crack propagation. However, the gold wire with Pd element cannot overcome the crack propagation or void formation. Slower intermetallic compound property of Cu wire is investigated with thicker Al metalization. This paper describes the characteristics of Cu-Al amd Au-Al intermetallic compounds and characterizes the difference in the intermetallic compound growth between Au-Al and Cu-Al for thicker Al metallization (~5um)