High reliability performance of Ag-cored Au coated wire capable of bonding in gas free condition

The bonding wire that connects electrical signals for semiconductor PKG mainly used Au material, but it is being replaced with relatively cheaper material such as Cu and Ag due to a steady rise in Au prices. However, materials such as Cu or Ag to replace Au have a common problem in that the free air ball is oxidized by reaction with oxygen in the atmosphere when forming the free air ball, and thus a spherical free air ball cannot be formed. And since Cu wire has high hardness, there is a limitation in that it cannot completely replace Au wire due to a problem that may cause damage to the Al pad during bonding. In this study, we developed ACA (Au Coated Ag) bonding wire in which Au is plated on the surface of the Ag core which has similar hardness to that of Au to replace the Au wire. When the ACA is melted in the air atmosphere, Au on the wire surface melts and wraps around the molten Ag core to prevent oxidation and also prevents oxygen adsorption to the molten Ag core. Due to this, high surface tension is maintained and a spherical free air ball is formed even in air atmosphere. In addition, in the high-temperature reliability evaluation conducted by bonding the free air ball of ACA formed in the atmospheric atmosphere to the Al pad, the advantage of not forming Kirkendall voids was confirmed because the IMC growth rate of ACA-Al bond was slower than that of the Au-Al bond. Therefore, it was found that the high temperature reliability of the ACA-Al bond was superior to that of the Au-Al bond.