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Relationship of Cu Oxidation and Hardness towards Cratering in Wirebonding
Keywords: Copper Oxidation, Copper Wire, Vickers Hardness, Cratering Impact, Wirebonding
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. This paper was carried out in order to know the relationship of copper oxidation and hardness on the detectable oxidation layers on 22m 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 shown obtained from Vickers microhardness test results on Free Air Balls (FABs). Meanwhile, this relationship was used in tracking cratering defect in wirebonding performance, however an unexpected observation had been found. 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.
Chai Ying Lee, Manufacturing Engineer
Infineon Technologies (M) Sdn Bhd.
Melaka 75710,
Malaysia


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