Intermetallic Compounds Formation And Reliability On Bonding Joints Of Copper Wire And Gold Wire With Aluminum Alloy Pad

Copper wire ball bonding is a new technology which is expected to replace the traditional gold wire ball bonding and is of great significance in reducing the cost and improving the reliability of microelectronic components. The process and mechanism of ball bonding were studied in this paper, specifically, intermetallic compounds (IMC) formation and reliability on copper wire and aluminum alloy pad bonding joint during thermal Aging were analyzed in detail. As a contrast object, gold wire ball bonding technology was also studied.The whole process of copper wire ball bonding and gold wire ball bonding were compared and analyzed, and a central composite design of experiment (DOE) approach was applied to optimize the parameters of free air ball formation process and bonding process, separately. Research on interface shows the joint begins at the bond periphery, then the center area of the joint, and at last the achievement of connection of the whole joint. Friction-based model was founded to explain the above phenomena.A reliability experiment of thermal aging was carried out for the two types of joints, Scanning Electron Microscopy, Energy Dispersive X-ray Spectrometer and Micro X-Ray Diffractomer were adopted to investigate the interfacial evolution behavior of joints, and kinetics model of IMC formation was established. The results show that IMC growth follows the parabolic law as a function of aging time at certain aging temperature, IMC growth is more sensitive to the aging temperature than the aging time, the activation energy of Cu-Al IMC growth is 97.1kJ/mol and the major forming Cu-Al IMC are CuAl2 and Cu9Al4, the activation energy of Au-Al IMC growth is 40.1kJ/mol and the main Au-Al IMC are Au4Al and Au5Al2, with Au2Al and AuAl at the interfacial periphery of joints, the rate of Cu-Al IMC growth is about 1000 times slower than that of Au-Al IMC, and Kirkendall voids and cracks are easily appeared during thermal aging in gold ball bonds while voids and cracks are absent in copper ball bonds even after aging at 200℃for 2900 hours and 250℃for 169 hours. The essential factors for different growth rate of IMC were analysed as well.