A new and improved process for bonding solder bumps on an IC chip to a BT
substrate in "flip chip" packaging technology. In one embodiment, the
process includes providing a resilient chip holder on a pressure head and
pressing the solder bumps on the inverted IC chip against bond pads on the
BT substrate to bond the lead solder bumps to the BT substrate. In another
embodiment, the solder bumps of the inverted IC chip are pressed against
the BT substrate as the BT substrate is subjected to ultrasonic vibration
to bond the solder bumps to the BT substrate. This generates
friction-induced small heat affected zones (HAZ) on the substrate and
enhances breaking of the tin oxide layer on the solder bumps and bonding
of the solder bumps with the substrate.
