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標題: Synergetic effect of Bi2Te3 alloys and electrodeposition of Ni for interfacial reactions at solder/Ni/Bi2Te3 joints
作者: Chih-Fan Lin
Nga Yu Hau
Yu-Ting Huang
Ya-Huei Chang
Shien-Ping Feng
Chih-Ming Chen
關鍵字: Thermoelectric
Surface modification
Diffusion barrier
摘要: Ni is the most commonly used barrier in thermoelectric solder joints, and its role is to avoid excessive reaction between the bismuth telluride (Bi2Te3) element and the Sn-based solder. This study, for the first time, demonstrates a strong effect of the Bi2Te3 substrate on the electrodeposition of Ni layer, consequently affecting the interfacial reaction with the Sn-4 wt.% Ag-0.5 wt% Cu (SAC405) solder. Two types of Bi2Te3 substrates, prepared using zone-melting and ball-milling/hot-pressing methods, exhibit different crystal structures, and this structural difference significantly affects the microstructures of the Ni diffusion barrier electroplated on the Bi2Te3 substrates and the growth of their intermetallic compound (IMC) at the SAC405/Ni/Bi2Te3 solder joints. The Ni layer electroplated on a zone-melted Bi2Te3 substrate (anisotropic crystal structure) has a small grain size and a high grain-boundary density, and one IMC, (Cu,Ni)6Sn5, is formed at the interface between SAC405 and Ni after joining. The other (Ni,Cu)3Sn4 phase is formed at the (Cu,Ni)6Sn5/Ni interface after thermal aging and grows at a progressively faster rate with increasing aging time. In contrast, the Ni layer electroplated on a ball-milled/hot-pressed Bi2Te3 substrate (isotropic crystal structure) has a large grain size and a low grain-boundary density, and only the (Cu,Ni)6Sn5 phase is formed at the SAC405/Ni interface, with a very sluggish growth rate after joining and thermal aging. Since the IMCs are electrically resistive and mechanically brittle, the latter solder joint with a large-grained Ni layer on a ball-milled/hot-pressed Bi2Te3 substrate appears to have better reliability.
Appears in Collections:化學工程學系所



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