Laser bumping for flip chip and TAB applications

An important aspect in microelectronics and packaging technologies is single chip bumping. A laser bumping method is suggested both for flip chip and TAB (tape automated bonding) applications. Laser chemical vapor deposition with an organometallic gold compound was used to deposit gold bumps from the vapor phase. With a computer controlled laser deposition system the laser bumping process was performed. The laser deposition was carried out on a gold pad metallization which is used on GaAs devices. Growth rate and bump height were determined as function of deposition time, chip temperature and laser power. The optimal deposition parameters for the laser bumping process were determined. Bump heights of 70 μm were deposited with growth rates up to 6 μm/s. Bump shape, height and morphology were shown with SEM and metallographic cross sections. A good morphology and contact wetting were achieved with a laser power of 1.9 W and a device temperature of 100°. The bondability of the deposited laser bumps were proved. The bonding process with a gold plated copper tape was performed by TAB thermocompression gang bonding and TAB single point bonding. The bond strengths were investigated with pull tests. The bumps were flip chip thermocompression bonded onto a sputtered TiW/Au metallization on a Si-substrate