Sn-Ag-Cu無鉛銲錫添加稀土元素 高溫慢速拉伸性質之研究

Abstract

本研究主要利用高溫拉伸試驗測試無鉛銲錫的機械性質，以及觀察材料內部的潛變特徵，無鉛銲錫的材料主要為Sn-3wt％Ag-0.5wt％Cu，另外添加0.05wt％Ce、0.5wt％Ce與0.2wt％Zn，比較不同合金的特性；溫度的範圍介在30℃-150℃之間，而應變速率則為1×10-3mm/sec與1×10-4mm/sec。無鉛銲料為電子產業的開發重點，未來隨著環保意識的抬頭，有毒物質的禁用是不可避免的。在電子產品輕薄化的前提之下，熱應力的累積以及機械力的作用，將造成更大的影響，高溫低應力的環境將使材料更易發生潛變破壞。實驗的過程將分成兩個主軸進行，第一部份為拉伸破斷的微結構觀察，第二部份為拉伸試驗所得到之結果分析。 研究結果顯示，在高溫拉伸的環境下，Sn-Ag-Cu合金生成的介金屬化合物，易成為微裂縫和孔洞的源頭，裂縫發生在三粒界交叉處，視為潛變的重要特徵。藉由微結構之觀察，添加0.05wt％Ce可以細化晶粒，並抑制介金屬化合物(Ag3Sn和Cu6Sn5)的成長，同時偏析在樹枝狀晶粒間的稀土析出物，具有強化材料的作用，提升材料的抗潛變能力；添加0.5wt％Ce的Sn-Ag-Cu合金易生成過大的稀土析出物CeSn3，此介金屬化合物析出在晶界處，易造成應力過度集中，加速材料的破壞，故添加過量稀土造成不良的影響。另外添加0.2wt％Zn有效抑制稀土析出物的產生，並具有細化晶粒的效果。透過拉伸試驗之結果，同樣的銲錫材料，隨著測試溫度的上升和應變速率的減緩，抗拉強度呈現下降的趨勢；而低溫下添加其他元素對機械性質的影響要高於高溫下的作業環境，添加微量稀土可提升其抗拉強度，過量則會使抗拉強度下降，再添加Zn則使強度上升近未添加稀土的母合金強度，但不如添加微量稀土的母合金強度；固定應變速率下，合金的伸長量在30℃-150℃維持穩定，不會有明顯的變化。

The tensile properties of Sn-3wt％Ag-0.5wt％Cu-0.05 wt％Ce, Sn-3wt％Ag-0.5wt％Cu-0.05 wt％Ce and Sn-3wt％Ag-0.5wt％Cu-0.05 wt％Ce-0.2wt％Zn were investigated and compared with those of a Sn-Ag-Cu solder. The tensile strength of each solder decreases with increasing test temperature, and decreasing strain rate.The ductility of each lead-free solder keeps stable value in the strain rate from 1×10-4mm/s to 1×10-3mm/s and in the test temperature ranging from 30℃ to 150℃. Coarsing β-Sn grains and dendrite grains are formed in Sn-3Ag-0.5Cu, especially bigger Ag3Sn and Cu6Sn5 intermetallic compounds(IMCs) were found in Sn-3Ag-0.5Cu alloy.With addition of different content rare earth(Ce) element the dendrite grains were refined, at the same time, Ag3Sn and Cu6Sn5 intermetallics were finer according to the adsorption affection of the active rare earth elements.It was found easier formation and faster growth of voids at the coarsing IMCs by the lower tensile rate at a higher temperature.Voids and cavities were observed along grain boundaries in Sn-3Ag-0.5Cu-0.5Ce.More coursing rare earth IMCs had the same affection, they would resulted in excess stress concentration, the crack and cavity might be nucleated near the impurity particles along the grain boundaries. Adding adequate Ce could improved mechanical properties, the tensile strength were enhanced, but excess adding brought negative affection.In addition, the alloy with the addition of trace Zn, it restricted the growth of Ce IMCs. The mechanical properties were also enhanced. All these results indicated that adding trace rare earth element and Zn was an efficient way to develop tensile properties for the new solders.