Stitch Bonding Strength of Cu Wire on AuAg/Pd/Ni Preplated Cu Leadframes: Influence of AuAg Thickness

Abstract

Copper (Cu) wire bonding on the pre-plated leadframes with Ni/Pd/AuAg plating has been applied extensively in the semiconductor industry for the interconnection of integrated-circuit (IC) packaging due to the lower material cost of Cu and its excellent electrical properties. Furthermore, the Cu wire bonding on the preplated leadframe has advantages, such as the tin whisker prevention and the robust package for automotive application. Nevertheless, a stitch bondability of Cu wire-preplated leadframe is facing several challenges, such as the Cu oxidation, the high hardness of Cu wire and the very thin AuAg plating on the leadframes. This paper discusses the effect of AuAg plating thickness in roughened pre-plated leadframe on the stitch bonding of Cu wires with the leadframe. The stitch bonding integrity was assessed using Dage 4000 shear/pull tool at a key wire bond responses of stitch pull at time zero (T0). Results show that the stitch pull strength of the Cu-leadframe stitch bonding increases with the increase thickness of AuAg layer. FESEM images of the stitch bonding between the Cu wires and the pre-plated leadframes of different AuAg plating thickness did not show any defect in microstructures, thus it suggests that the bonding property is determined by diffusion mechanism at the Cu wire/AuAg stitch bonding interface. Finally, a brief discussion is provided on the stitch bondability of high performance Au-flashed palladium-coated copper wires on the pre-plated leadframe with different AuAg thickness.