Comparsion of Au/Al and Cu/Al in wirebonding assembly and reliability

The replacement of gold with copper bonding wire has taken a prominent position in the microelectronics packaging industry in recent years. This is largely driven by the increase of gold prices. The hardness, oxidation and electro-chemical potential of copper properties have a significant impact of its wire bonding process and reliability as compared to gold. This paper focuses on the relationship of Au and Cu material properties to wirebonding processes. A higher ultrasonic energy was needed for Cu than Au bonding and this resulted in pad cratering for Cu wire after thermal aging. A drop in stitch strength was observed due to oxidation under thermal aging condition. The resilient of corrosion for Au and Cu wire in moisture, DI water and NaCl conditions were also investigated. The IMC ball coverage appears to have an impact to initiate corrosion with the ingress of electrolyte. For Cu, the galvanic corrosion was suspected for the moisture and DI water soaking with additional pitting corrosion for NaCl condition. This paper provides a good initiation point for further investigation into the mechanisms of corrosion for Cu bonding. The paper summarises the effect of Au and Cu wires in wirebonding process and its reliability relating to its material properties.