Gold-to-aluminum bonding for TAB applications

In thermocompression bonding used in tape automated bonding (TAB) technology, the gold-to-aluminum interface is one of the most difficult bonds that can be formed, because a thin aluminum oxide layer inhibits bonding at low temperatures. The usual bonding temperature is, therefore, expected to be higher than 500°C. This results in extensive growth of intermetallics. In an effort to reduce the bonding temperature of a TAB application, a laser-processed gold-plated balltape was used for thermocompression bonding to aluminum. The effects of hardness, thickness, and morphology of the gold layer on thermocompression bonding have been investigated. As a result, an improved gold layer surface morphology has been developed by controlling the plating rate. The new bumped tape structure was bonded at temperatures from 500°C down to as low as 350°C