裸銅與被覆金之銅線經錫–5銀析鍍後之電解質遷移

Electrolytic Migration of Sn-5Ag Coating on Cu and Cu/Ni/Au Substrates

本文主要探討錫–5銀鍍層在裸銅與被覆鎳／金之銅線兩種基材之電解質遷移。分別在裸銅與被覆鎳／金之銅線的一對電極上鍍錫-5銀鍍層，兩極浸泡在去離子水中施以5V直流偏壓，研究其電解質遷移機理，並研究熱處理（250℃持溫5分鐘）對於遷移性的影響。由陽極動態極化掃瞄分析，配合XPS在電極表面之分析，推測電解質遷移行為之機理。鍍有錫-5銀之裸銅的遷移行為包含銀、錫、銅。經過熱處理後，錫-5銀中的銀與錫形成Ag3Sn之介金屬化合物，降低鍍層中的游離銀濃度，因此抗遷移有明顯改善。鍍有錫-5銀之被覆鎳／金之銅線因為銅被鎳、金有效的覆蓋，遷移機制沒有銅的參與，只有銀、錫發生遷移。經熱處理後，錫-5銀同樣形成Ag3Sn介金屬化合物，降低游離銀濃度，因此鍍有錫-5銀之被覆鎳／金之銅線經熱處理後有最佳的抗電解質遷移能力。

Electrolytic migration for a couple of conductors, made from bare copper and Ni/Audeposited copper electroplated with a coat of Sn-5Ag (5 m in thickness) was investigated. The electrolytic migration was conducted in deionized water at a dc bias of 5V. the effect of heat treatment (at 250℃ for 5 minutes) of the specimens on the electrolytic migration was also explored. On the basis of electrochemical data resulted from potentiodynamic polarization and surface analysis through X-ray photoelectron spectroscopy (XPS), we proposed a mechanism for electrolytic migration. Different behaviors in electrolytic migration for various specimens are realized stemmed from this mechanism. In the system of bare copper coated with Sn-5Ag (denoting as C), silver, copper and tin are responsible for migration. Heat treatment of this system (denoting as C-h) led to consumption of elemental silver and formation of inter-metallic compound Ag3Sn that is less susceptible for migration. In the system of Ni/Au-deposited copper that is further coated with Sn-5Ag (denoting as G), only silver and tin are subject to migration since copper is covered and shielded by its Ni/Au-deposits. Heat treatment of this system (denoting as G-h) also transfers the elemental silver to Ag3Sn, hence retards the migration. The resistance to electrolytic migration increases in the order: C < G < C-h < G-h.