本研究目的為藉由觀察通電對鍍錫銅線之微結構影響，探討其機械性質與電性變化之機制。鍍錫銅線施以9.7-14.6 × 103 A/cm2 (1.6A-2.4A)之電流密度達4至36小時，再進行機械性質與電性的量測，並觀察其微結構。研究結果顯示，通電後鍍錫銅線的電阻率並沒有明顯的變化；但是中央銅線的部份硬度值上升，而鍍錫銅線的伸長率與韌性大幅下降，其下降幅度高達35%。在銅/錫界面生成Cu6Sn5與Cu3Sn兩種介金屬化合物(Intermetallic compound, IMC)，同時存在一些孔洞；通電後並沒有觀察到明顯的相轉變或生成新的相。兩種界金屬化合物的厚度都隨著電流密度的提高與通電時間的增長而逐漸增厚；隨著電流密度增加，介金屬化合物的成長機制由擴散控制(Diffusion control)轉變為反應控制(Reaction control)；中央銅線的銅晶粒的尺寸則有縮小與雙晶增加的趨勢。綜上所述，鍍錫銅線機械性質的改變，是界面介金屬化合物增厚、銅晶粒細化與雙晶增加的共同影響所致。此外，拉伸破斷面分析顯示有兩種破斷模式；模式一是破斷於銅、錫與界面，模式二則是在有界金屬化合物的銅/錫界面。而隨著界面介金屬化合物厚度的增長，會發生模式一轉變為模式二的情形。

This study discussed the mechanism of properties change on Sn-coated Cu wires after current stressing through the investigation of microstructure and mechanical properties. The Sn-coated Cu wires were cut into 60 cm long and subjected to 9.7-14.6 × 103 A/cm2 direct current for 4-36 hours. The results show that the resistivity almost remained the same while the micro-hardness of Cu kept increasing with the increase of current density and current stressing time. By contrast, the elongation and tensile toughness showed a dramatically decrease after current stressing. The intermetallic compounds formed at the Cu/Sn interface were identified as Cu6Sn5 and Cu3Sn, which grew thicker with higher current density and longer current stressing time. In addition, the growth kinetics of IMCs changed from diffusion control to reaction control as the current density increased. EBSD analysis indicated that the grain size of Cu decreased, and the twin fraction increased after current stressing. It can be summarized that the variations in the mechanical properties of Sn-coated Cu wires were ascribed to the increase in interfacial IMCs, Cu grain refinement and the increase in twin fraction of Cu grains. On the other hand, the fracture mode of Sn-coated Cu wires would transfer from mode 1 to mode 2 as the interfacial IMCs grew thicker. Mode 1 indicated that the fracture occurred at Cu, Sn, Cu/intermetallic interface and initiated at the Cu/intermetallic interface, while mode 2 initiated within the interfacial IMCs.

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