抄録
This work was undertaken to develop reliable ball bonding technique for copper wire.
In this investigation, the effect of the shielding gas on ball formation, ball quality and the bondability of the copper ball was examined.
The shielding gases of only high purity argon and high purity argon containing hydrogen produced spherical copper balls without cellular structure surfaces or necking at the ball-wire interface. Auger and SEM analyses revealed that the copper ball formed in the high purity argon gas containing 10 vol. % hydrogen had a very smooth surface without oxidation. Therefore, this gas was selected for copper ball formation.
The copper balls which were thermosonically bonded to aluminum electrode pads failed at a shear strength level comparable to that of gold. It was found that good stitch bonding of copper wire to unplated copper lead frame fingers could be achieved by preventing them from oxidizing.
Simple thermal aging tests at 300°C verified that the copper/aluminum intermetallic layer grew considerably slow without degradation of mechanical characteristics.
