New Alternative Metal Coated Silver Bonding Wire for Gas Free Bonding & High Reliability Performance

Abstract

Au Bonding wire, which has been widely used in the semiconductor PKG market, is being converted into Cu Bonding wire due to a sharp increase in Au price. The price of Cu is cheaper than Au and Pd coated wire products with improved reliability and workability have been introduced, bringing a large portion of Au Bonding wire usage. However, the sensitive structure of the PKG still uses Au Bonding wire, because of the problem of pad cratering due to the high workhardening of Cu, so the Au Bonding wire cannot be converted to a cheap Cu Bonding wire despite the high Au price. Recently, Ag alloy Bonding wire has been widely evaluated as a low cost Bonding wire for PKG with sensitive structure. However, like the Cu Bonding wire, a gas kit and an inert gas are required to prevent oxidation when forming a FAB (Free Air Ball, the following notation is unified FAB) for ball Bonding. In addition, the high-humidity reliability level of silver alloy Bonding wire is lower than that of Au Bonding wire. In this study, we evaluated the metal coated silver bonding wire as a next generation low cost bonding wire product to replace Au Bonding wire. In order to improve the disadvantages of the Ag alloy Bonding wire in which the elliptical FAB is formed when the inert gas is not used in the 1st ball Bonding, the noble metal coating is performed on the high purity Ag alloy Bonding wire. Gas free Bonding characteristics and high humidity reliability performance were evaluated according to the kind and thickness of noble metal. In the evaluation of high humidity reliability, metal coated silver Bonding wire showed a high humidity reliability performance more than 2 times compared to the conventional silver alloy Bonding wire. Metal coated silver Bonding wire is expected to be an alternative to the new low cost Bonding wire in the PKG market due to gas free Bonding and improved high humidity reliability performance.