Design optimization of a laser bond tool

This study is concerned with the design of a laser bond tool operating at a laser power of less than 8 W, having a life of more than 25000 bonds and meeting the laser safety requirements of the manufacturing environment. The finite-element method (FEM) was used to predict temperature and stress profiles during the bonding process. Laser tool optimization involves selection of wall and cap thicknesses to provide a fast temperature rise of the tool-wire interface while maintaining stresses at a safe level. For the range of wall and cap thicknesses considered, it was found that there is a critical wall thickness above which the stresses induced in the tool are not conducive to tool cracking. Larger wall thickness, however, was found to adversely affect the transient thermal energy transmitted to the wire: Capping thickness was found to be a minor contributor to the stresses induced in the tool. A tool having a capping thickness of 260 /spl mu/m and wall thickness of 250 /spl mu/m was recommended.