Improvement of High-Temperature Reliability of Ball Bond Using Platinum-Modified Gold Alloy Wires

For superior Au/Al ball-bond reliability, we have developed the 3N (>99.9 wt% Au), 2N5 (>99.5 wt% Au) and 2N (>99 wt% Au) Au alloy bonding wires which contain less than 0.1, 0.5 and 1 wt% Pt, respectively. In the thermal aging test of squashed balls (40 μm in diameter), which consists of storage in air at 250°C and evaluation with wire pull and ball shear, it has been found that there are interesting differences in the ball-bond degradation as a function of wire type. Even the samples bonded using the 3N wire with a very small amount of Pt show superior ball-bond reliability compared with those using a 4N (>99.99 wt% Au) wire without any addition of Pt. The ball-bond degradation in the thermal aging test is reduced significantly with increasing Pt content of a wire. From microstructural analysis of the aged 2N ball bonds, the Pt-containing layer, which seems to play a crucial role in improvement of the ball-bond reliability, have been found in the upper part of intermetallic compounds.