Relationship of Cu Oxidation and Hardness towards Cratering in Wirebonding

摘要

Nowadays, copper wire ball bonding is gaining popularity due to its economic advantage and superior electrical performance. However, the idea of replacing gold wire with copper wire in the wire bond process does come with technical challenges. From mechanical point of view, copper is harder than gold. Hence, replacing gold wire with copper wire will introduce hardness related issues which concurrently contributes towards cratering defects. At the same time, copper also shows faster oxidation rate than gold and this native behavior is actually another limitation of utilizing copper wirebonding in semiconductor industries.rnThis paper was carried out in order to know the relationship of copper oxidation and hardness on the detectable oxidation layers on 22μm copper wire ballbond. Transmission Electron Microscopy (TEM) equipped with Energy Dispersive X-ray (EDX) Analysis was used to study the copper oxidation layers. A logarithmic relationship of oxidation and hardness was obtained from Vickers microhardness test results on Free Air Balls (FABs). This relationship was used in tracking cratering defect in wirebonding performance and found out that copper oxidation was not the major factor that caused cratering, but not optimum wirebonding parameters setting was. Therefore, in order to have a thorough look on this matter, wire related reliability tests were also carried out to evaluate Cu wire intermetallic performance.