Crystallographic texture of drawn gold bonding wires using electron backscattered diffraction (EBSD)

摘要

Gold ball bonding wire is used as an interconnection between die pads and substrates in over 90% of worldwide semiconductor assemblies. Typical wire thicknesses in consumer applications are 20-25 μm with an increasing trend towards the use of 12-15 μm with an increasing trend towards the use of 12-15 μm wires forecast for the near future. The end of the wire is melted into a ball using an electric arc on a wirebonding machine and the ball is then thermosonically welded to the die pad metallization (which is usually 0.7-1.0 μm thick Al with Cu and/or Si minor additions). The thermosonic welding is performed at frequencies from 60-140 kHz and at temperatures of 150-250 ℃. The melting of the end of the wire results in a temperature gradient along the wire length that causes a variation in properties over a region called the heat-affected zone (HAZ). The region after the HAZ has the normal properties of the wire. After the ball has been bonded, the wire is then formed into a controlled-profile loop that is thermosonically welded to the substrate, thus forming an electrical connection between die and substrate. A significant factor in loop control is the HAZ length that determines where the wire bends and characterization of the HAZ is an essential part of bonding wire development.