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Thin Film Solid-Liquid Interdiffusion Bonding of Bi2Te2.55Se0.45 Thermoelectrical Material with Cu/Ag Electrode
Date Issued
2011
Date
2011
Author(s)
Lin, Che-Wei
Abstract
Thermoelectrical materials is one of the renewable energy resourses which has been largely developed recently. It is a material which can transform heat energy to electrical energy reversibly.This materials have two major application:thermal energy and thermoelectric refrigeration. As there are more and more studies dedicate to this field, the energy transform efficiency of thermoelectrical materials has been gradually enhanced. Since thermoelectrical device usually operates in high temperature envi-ronment,the conventional jointing method (ex.soldering、brazing) have faced a lot of challenges. Therefore, this study uses Bi2Te2.55Se0.45 thermoelectrical material, adopts Ag/Sn thin films as the solid-liquid interdiffusion bonding materials joints with Cu/Ag electrode, and tries to make a use of the special feature of this technique : jointing in a relative low temperatures; operating in a relative high temperatures. The intermetallic compounds (IMCs) between the substrates can form in a relative low temperatures but,once formed, they are stable in much higher temperatures. This investigation includes the interfacial reaction between Bi2Te2.55Se0.45 and nickel and between Ag/Sn thin films and Cu/Ag substrate, calculating the kinectic of intermetallic compounds and analysising the shear stress of devices jointing in different parameters.
The results show that electroplating a tin layer between Bi2Te2.55Se0.45 and nickel layer can dramatically enhance the shear strength of this interface. This tin layer form Sn(Te,Se) with Bi2Te2.55Se0.45 and form Ni3Sn4 with nickel. At the temperature above 250°C,3 minute will be enough to exhaust the 4μm tin layer between two substrates. The intermetallic compounds formed at the interface between Cu/Ag/Sn and Ag/Ni/Sn/Bi2Te2.55Se0.45 are Ag3Sn、Cu6Sn5 and Cu3Sn. At 250°C、275°C, as the jointing increase, Ag3Sn and Cu3Sn will consume Cu6Sn5 and get thicker gradually, Cu6Sn5 will be exhausted rapidly. At 300°C、325°C, since there are no Cu6Sn5 anymore, as the jointing increase, Cu3Sn will start to consume Ag3Sn. Sound shear strength of 21.7 MPa have been obtained under bonding condition at 250°C for 60 minute. At 250°C,the average shear strengths can maintain over 19 MPa. Heating at the temperature above 325°C caused the tin buffer layer between Bi2Te2.55Se0.45 and nickel lost its functionality, and the shear strength drastically droped off to 6.2 MPa.
The results show that electroplating a tin layer between Bi2Te2.55Se0.45 and nickel layer can dramatically enhance the shear strength of this interface. This tin layer form Sn(Te,Se) with Bi2Te2.55Se0.45 and form Ni3Sn4 with nickel. At the temperature above 250°C,3 minute will be enough to exhaust the 4μm tin layer between two substrates. The intermetallic compounds formed at the interface between Cu/Ag/Sn and Ag/Ni/Sn/Bi2Te2.55Se0.45 are Ag3Sn、Cu6Sn5 and Cu3Sn. At 250°C、275°C, as the jointing increase, Ag3Sn and Cu3Sn will consume Cu6Sn5 and get thicker gradually, Cu6Sn5 will be exhausted rapidly. At 300°C、325°C, since there are no Cu6Sn5 anymore, as the jointing increase, Cu3Sn will start to consume Ag3Sn. Sound shear strength of 21.7 MPa have been obtained under bonding condition at 250°C for 60 minute. At 250°C,the average shear strengths can maintain over 19 MPa. Heating at the temperature above 325°C caused the tin buffer layer between Bi2Te2.55Se0.45 and nickel lost its functionality, and the shear strength drastically droped off to 6.2 MPa.
Subjects
thermoelectrical material
solid-liquid interdiffusion bonding
intermetallic compound
interfacial reaction
bonding strength
SDGs
Type
thesis
File(s)
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Name
ntu-100-R98527029-1.pdf
Size
23.54 KB
Format
Adobe PDF
Checksum
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