單側Ni與Co擴散阻障層對Sn–3.5Ag/Cu接點界面反應之影響

Effect of Single-Sided Ni and Co Diffusion Barriers on the Interfacial Reactions of Sn–3.5Ag Solder with Cu Substrate

隨著高密度與高可靠度電子封裝技術的快速發展，Sn–Ag無鉛銲料已成為主流材料，其中Sn–3.5Ag錫銲料因具有優異的機械強度與導電特性而被廣泛應用，然而，銲料與金屬基材間的界面反應會形成金屬間化合物（IMC），其成長與剝離現象將顯著影響銲點的機械與熱穩定性，尤其在長時間環境中更為關鍵。本研究針對Sn–3.5Ag錫銲料與三種不同金屬基材（Cu/Cu、Ni/Cu、Co/Cu）之界面反應行為進行系統性探討，並設計對稱式焊接結構以排除重力因素干擾，分析IMC成分、形貌演化與Cu擴散機制之差異。實驗結果顯示，Cu基材生成Cu₆Sn₅及Cu₃Sn，老化後出現IMC剝離與內聚失效；Ni/Cu結構形成穩定的(Cu,Ni)₆Sn₅層，有效抑制Cu擴散並提升界面穩定性；而Co/Cu結構則生成CoSn₃與(Co,Cu)₆Sn₅，雖具一定阻隔效果，但仍有Cu擴散行為。整體而言，Ni作為阻障層展現最佳界面穩定性與潛在可靠度，為提升無鉛銲料接合品質提供重要設計依據。

With the advancement of high-density and high-reliability electronic packaging technologies, lead-free Sn–Ag solders have become mainstream, among which Sn–3.5Ag is widely adopted due to its excellent mechanical strength and electrical conductivity. However, the formation and evolution of intermetallic compounds (IMCs) at the solder–substrate interface significantly affect joint reliability, particularly under long-term service conditions. This study systematically investigates the interfacial reaction behavior between Sn–3.5Ag solder and three different metal substrates (Cu, Ni/Cu, and Co/Cu), using a symmetrical soldering structure to eliminate gravitational effects and clarify the diffusion mechanisms. Microstructural analysis reveals that Cu promotes the rapid formation of Cu₆Sn₅and Cu₃Sn IMCs, which exhibit spalling and cohesive failure after aging. The Ni/Cu substrate forms a stable (Cu,Ni)₆Sn₅layer that effectively suppresses Cu diffusion and enhances interfacial stability. The Co/Cu substrate forms CoSn₃and (Co,Cu)₆Sn₅IMCs, offering partial barrier performance but allowing some Cu migration. Overall, Ni demonstrates superior capability as a diffusion barrier, improving the structural reliability of Sn–3.5Ag solder joints and providing valuable guidance for material selection in advanced electronic packaging.