Copper wire bond reliability evaluation using a modular test chip

The use of copper wire for wire bonding integrated circuits (ICs) has increased significantly in recent years, driven mainly by the dramatic increase in the cost of gold. The technical advantages and limitations, particularly with respect to reliability, of copper for wire bonding, compared with gold, have been widely reported. This paper describes reliability studies comparing on copper, palladium coated copper and gold wires using a dedicated test vehicle comprising a modular test chip with multiple daisy chains and corrosion sensors in a BGA package. The reliability tests were High Temperature Storage (HTS), 1000 hours at 150°C, Thermal cycling (TC) from 1000 cycles from -40°C to + 125°C, Temperature Humidity Bias (THB), 1000 hours at 85°C/85% RH, 20 V applied, and unbiased HAST. It was found that performance was strongly dependent on the wire type and mold compound. Copper wires with one mold compound having a higher chlorine level (12mmm), showed high leakage currents and rates of failure during THB. Both copper and palladium coated copper wires with a different mold compound showed high rates of failure during thermal cycling.