Scanning white light interferometry in quality control of single-point tape automated bonding

We report on applying a scanning white light interferometry (SWLI) for quality control of aluminum lead single-point tape automated bonding (spTAB). A spTAB process was used to connect Al leads on a thin polyimide flex to Al bond pads on a flexible Al-polyimide cable. In the experiment three different bonding process parameters, i.e. bond force, ultrasonic power, and ultrasonic treatment time were varied in order to maximize the pull force. A custom built scanning white-light interferometer was used to measure the bond height in order to correlate this parameter with the tensile bond force. This force was obtained in a destructive way by a consecutive pull test. All bonds with a height within (7.22 ± 1.80 μm), possessed a tensile strength exceeding 85 mN. This was verified by a separate validation measurement where the pull force of bonds complying with the height requirement was recorded. Based on the 3D observations the conditions for an acceptable bond quality were revisited and refined.