Thermocompression Bondability of Thick-film Gold-A Comparison to Thin-Film Gold

The thermocompression bondability of beam-leaded devices to thick-film Au was studied. The objective was to find a range of bonding parameters, i.e., a bondability window, which would result in acceptable initial bondability. The thick films were either as-fired or mechanically burnished prior to bonding. Both typos of thick films were compared to thin films by bonding all three types under identical conditions. Quantitative Auger electron spectroscopy (AES), optical microscopy, and scanning electron microscopy (SEM) were used to analyze the bonding surfaces. The results showed that it was possible to get acceptable initial bondability to the thick-film Au but that the bondability window was significantly smaller than that for thin-film Au. This large difference in bondability was thought to be due, at least in part, to the observations that the thick films were less dense, rougher, and had more surface contaminants. To a lesser degree, burnished thick films were more bondable than as-fired thick films. This difference was thought to be due to the same factors.