摘 要 本研究主旨在探討時效處理對電子構裝用Sn-3.5Ag無鉛銲錫之耐久機械性質影響。不同時效處理會造成Sn-3.5Ag微結構及潛變性質的改變，利用掃描式電子顯微鏡(SEM)來觀察此款無鉛銲錫之潛變破壞特徵。實驗結果顯示，經過長時間以及高溫時效處理的Sn-3.5Ag合金，其抗拉強度比自然時效30天處理要來得低，主要是因為富錫相與介金屬化合物粗大所造成。在兩個高溫時效條件的比較中，時效處理150oC三天的抗拉強度比120oC三天還要低，起因於較粗大的介金屬化合物。經過不同時效處理的Sn-3.5Ag合金，其潛變機制主要是差排潛變伴隨散佈顆粒強化的機制。而經過長時間自然時效或高溫時效處理的Sn-3.5Ag合金，其抗潛變能力比經過短時間自然時效處理的合金要來得低。利用Monkman-Grant 關係式來描述在不同時效處理下的Sn-3.5Ag合金之潛變行為有相當不錯的結果。在高應力下，介金屬化合物的粗大會加速微小孔洞的成長，因而縮短潛變壽命；在低應力下，介金屬化合物的尺寸大小對潛變壽命的影響相對較小。 ABSTRACT The purpose of this study is to investigate the mechanical properties and creep behavior of extruded Sn-3.5Ag lead-free solder at differently aged conditions. Various aging treatments could cause changes in microstructure and mechanical properties. Fractography analysis with scanning electron microscopy (SEM) was conducted to study the creep fracture behavior in terms of microstructural change. Experimental results show that the ultimate tensile strength (UTS) was reduced after a long-time natural aging or artificial aging at high temperatures, as compared to that of a short-time natural aging. This was due to coarsening of the ?-Sn phases and Ag3Sn IMCs in the microstructure. In addition, the UTS of Sn-3.5Ag solder aged at 150oC for 3 days was smaller than that aged at 120oC for 3 days due to a greater extent of coarsening of Ag3Sn IMCs. The values of stress exponent, n = 6 ~ 8, for the extruded Sn-3.5Ag solder at the four given aging conditions implied a creep mechanism involving dislocation creep and dispersion-particle-strengthening mechanism. The creep resistance for Sn-3.5Ag solder aged at room temperature (RT) for 600 days, 120oC for 3 days, or 150oC for 3 days was each worse than that after natural aging at RT for 30 days. The creep rupture times at all given aged conditions could be well described by a Monkman-Grant relation. Coarsening of Ag3Sn IMCs would accelerate the growth of microvoids at higher applied stresses leading to a much shorter creep rupture time for high-temperature aged specimens.
