中文摘要：

本研究主旨在探討時效處理以及高溫環境對電子構裝用Sn-3.5Ag無鉛銲錫之潛變及低週疲勞性質影響。實驗結果顯示，經過 長時間以及高溫時效處理的Sn-3.5Ag擠製材，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擠製材，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擠製材，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擠製材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。另外，經過高溫時效處 理的Sn-3.5Ag鑄造材，其抗拉強度比自然時效300天要來得低，主要是因為富錫相粗大所造成；而在高溫環境下的Sn-3.5Ag 鑄造材，抗拉強度也比在室溫環境下來得低，主要是因為熱活化機制造成材質軟化所致。利用Coffin-Manson關係式來描述 Sn-3.5Ag鑄造材在經過時效處理後或者是在高溫環境下的低週疲勞行為都有相當不錯的結果。在高應變振幅下，經過高溫 時效處理的Sn-3.5Ag鑄造材，其低週壽命要比經過自然時效處理的合金來得低，主要是因為粗大化的富錫相及介金屬化合物 會加速微小孔洞的成長；在低應變振幅下，富錫相及介金屬化合物的尺寸大小對經過不同時效處理的Sn-3.5Ag鑄造材低週疲 勞壽命影響相對較小。Sn-3.5Ag鑄造材在高溫環境下的低週疲勞壽命都比室溫下來得低，主要是由熱活化機制助誘之裂縫生 成機制所造成，然而微結構粗大化並非造成高溫環境下低週疲勞壽命縮短的主要因素。

 

Abstract：

The purpose of this study is to investigate the effects of aging treatment and environmental temperature on the creep and low-cycle fatigue (LCF) properties of Sn-3.5Ag lead-free solders. Experimental results show that the ultimate tensile strength (UTS) of an extruded Sn-3.5Ag 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 ��-Sn phases and Ag3Sn IMCs in the microstructure. In addition, the UTS of the extruded Sn-3.5Ag solder aged at 150oC for 3 days was lower 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 the extruded 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 the 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.

Experimental results also show that the reduction of UTS of a cast Sn-3.5Ag at high-temperature-aged conditions was due to coarsening of ��-Sn phases. However, the UTS of the cast Sn-3.5Ag was reduced at high temperatures due to a thermally activated softening process. The LCF properties of the cast Sn-3.5Ag solder at variously aged conditions or different testing temperatures could be well described by a Coffin-Manson relation. Coarsening of �� -Sn phases and IMCs would accelerate the growth of microvoids at a higher strain amplitude leading to a shorter LCF life for high-temperature-aged specimens. However, a smaller effect of the size of ��-Sn phase and IMC was exerted on the LCF life at a low strain amplitude for variously aged conditions. For a given aged condition tested at high temperatures, the in-situ aging and coarsening effect was not the controlling factor for the reduction of LCF strength at high temperatures. A thermally activated fatigue deformation and cracking mechanism was responsible for the high-temperature LCF behavior resulting in a decrease in LCF strength with an increase in testing temperature.