Evaluation of Bondability and Reliability of Single Crystal Copper Wire Bonding

Copper-based interconnect is an emerging trend in microelectronics packaging. Some studies have shown that copper wires may serve as a viable, cost-effective alternative to gold in some high-end, ball and wedge bonding applications. This study is intended to evaluate the bondability and reliability of single crystal copper wire bonding. After annealing, the copper wires are bonded on gold (1~2 micron thick) and aluminum (2 micron thick) surfaces without gas protection. The bondability of single crystal copper wire is evaluated and compared with gold and aluminum wires. The intermetallic compounds (IMCs) between copper and gold and between copper and aluminum are identified on the fractured surfaces by EDAX. After thermal aging, wire pull and ball shear tests are performed and the test results are compared with those without thermal aging. From the present study, it is found that single crystal copper wires can be bonded on the gold pad and the aluminum pad by thermosonic ball bonding and wedge bonding without gas protection. Cu3Au and AuCu IMCs are found at the copper/gold interface while CuAl2 is found at the copper/aluminum interface. After thermal aging, Kirkendall voids are discovered at the Cu/Au interface.