A comparison of copper and gold wire bonding on integrated circuit devices

Abstract

A comparative approach was used to develop new copper wire bond technology using the current standard production gold wire process as a baseline. Characterizations were made in the areas of assembly processes and material selection, electrical and thermal performance, intermetallic formation on Al and Al alloy bond pads, and reliability testing. It was demonstrated that copper wire bond strength tested with wire-pull and ball-shear methods can be maintained at higher levels than comparable gold wire bonds. Die shear strengths were degraded by temperature cycling, but not by high-temperature storage. AC/DC parameter characterizations across temperature and power supply exhibited identical performances on copper and gold devices. Input impedance, capacitance, and ESD (electrostatic discharge) showed no deviations between Au and Cu wire bonded devices selected for this investigation. The lower resistivity of Cu wire offers the potential for increased device power ratings. The thermal transient response showed negligible differences between Au and Cu wire bonded devices. The difference in intermetallic growth rates between Au and Cu wire processed devices suggest that Cu wire bonded devices will have greater reliability than Au wire bonded devices. The reliability data indicate that copper wire bonding is at least equal to conventional gold wire bonding. It is concluded that a copper ball bond assembly process can be developed for mass production which will equal and potentially surpass the performance and reliability of the present gold ball bond assembly process. >