Lasersonic bonding of TAB components to epoxy-glass circuit boards

The lasersonic bonding process is an alternative to soldering for the attachment of tape automated bonding (TAB) and other fine-pitch, surface-mounted components to epoxy-glass circuit cards. In this process, a special laser-assisted wire bonder attaches gold-plated TAB component leads to bare copper pads on the card. No solder or flux is required, and leads with very fine widths and spacings can be attached. Bonding is effected by the simultaneous application of heat and ultrasonic energy through a bonding tip held with force against the component lead. Laser energy is transmitted through a fiber optic cable into the hollow tip to supply heat to the bonding tip. Leads are attached one at a time at a speed of 6-8 per second. Details of the equipment used, bonding process conditions, and reliability test results are presented. A thermocouple sensor and feedback control system for the bonding process were designed, and observations regarding the performance of the tip and optical fiber are presented.