Li-Ling Liao

Interfacial reactions between PbTe-based thermoelectric materials and Cu and Ag bonding materials

The development of reliable bonding materials for PbTe-based thermoelectric modules that can undergo long-term operations at high temperature is carried out. Two cost-effective materials, Cu and Ag, are isothermally hot-pressed to PbTe-based thermoelectric materials at 550 °C for 3 h under a pressure of 40 MPa by the rapid hot-pressing method. Scanning electron microscopy, electron probe micro-analysis, and X-ray diffraction analysis are employed to identify intermetallic compounds, chemical reactions, and microstructure evolution after the initial assembly and subsequent isothermal aging at 400 °C and 550 °C. We find that Cu diffuses faster than Ag in PbTe. Neither Cu nor Ag is a good bonding material because they both react vigorously with Pb0.6Sn0.4Te. In order to be able to use Cu electrodes, it would be necessary to insert a diffusion barrier to prevent Cu diffusion into PbTe.

Through-Silicon Hole Interposers for 3-D IC Integration

In this investigation, a system-in-package (SiP) that consists of a very low-cost interposer with through-silicon holes (TSHs) and with chips on its top and bottom sides (a real 3-D IC integration) is studied. Emphasis is placed on the fabrication of a test vehicle to demonstrate the feasibility of this SiP technology. The design, materials, and process of the top chip, bottom chip, TSH interposer, and final assembly will be presented. Shock and thermal cycling tests will be performed to demonstrate the integrity of the SiP structure.

Assembly of N type Bi2(Te, Se)3 thermoelectric modules by low temperature bonding

Abstract Solid liquid interdiffusion technique is employed to attach N type Bi2(Te0·92Se0·08)3 thermoelectric material to alumina substrate. The surface finishes of the bonding surfaces for Bi2(Te0·92Se0·08)3 and alumina are Ni and Ag respectively. The bonding layer is pure Sn. The growth kinetic of intermetallic compounds and their microstructure evolution during aging at 200°C was established. The success of this bonding technique provides a cost effective way to assemble thermoelectric modules at a low temperature for higher temperature applications.

Low-cost TSH (through-silicon hole) interposers for 3D IC integration

In this investigation, a SiP (system-in-package) which consists of a very low-cost interposer with through-silicon holes (TSHs) and with chips on its top- and bottom-side (a real 3D IC integration) is studied. Emphasis is placed on the fabrication of a test vehicle to demonstrate the feasibility of this SiP technology. The design, materials, and process of the top-chip, bottom-chip, TSH interposer, and final assembly will be presented. Shock and thermal cycling tests will be preformed to demonstrate the integrity of the SiP structure.

Development of interconnection materials for Bi 2 Te 3 and PbTe thermoelectric module by using SLID technique

In this study, low-temperature Bi2Te3 and mid-temperature PbTe thermoelectric modules are assembled by the technique of Solid Liquid Interdiffusion (SLID). Scanning electron microscope is carried out for issues relating to factors limiting the reliability, growth of intermetallic compounds, and thermal stability. For low-temperature thermoelectric module, N-type Bi2Te3 is bonded to alumina substrates by using a Ni/Sn/Ag system. During bonding and subsequent aging reaction at 200 °C, Sn reacts with Ag to form Ag3Sn, and Ni reacts with Sn to form Ni3Sn4. This reaction process takes less than 72 h to exhaust the entire Sn layer to produce a bonding that can withstand temperature as high as 480 °C. The interfacial reaction, Ni penetration depth, and IMC kinetics between Ni and Bi2Te3 at 200, 250, and 300 °C are also investigated in detail. For mid-temperature thermoelectric module, N-type PbTe is bonded to alumina substrates by using a Ag/In/Ag system. During assembly at 190 °C, all Ag/In/Ag joint are transformed into Ag2In, which has the melting temperature above 670 °C, in less than 2 minutes. Furthermore, this Ag-In joint has passed high temperature storage test at 400 °C for 1000 h. The success of solid liquid interdiffusion technique and related contact materials provide a cost effective way to assemble thermoelectric modules for power generating or cooling applications which require long term operations at high temperatures.

Capacitor discharge sintering with silver-nickel nano-composite in the interconnection of thermoelectric generators

This paper presents a capacitor discharge sintering process with a homemade silver-nickel paste for thermoelectric element interconnections. The paste is a 75 nm silver/nickel composite mixture. Without using any specific atmosphere control, the capacitor discharge is capable of nanoparticle sintering with time-efficient process at room temperature. A 0.01 F capacitor is serially connected to the sample and charged to 10 V (0.5 Joule) for the sintering process. To evaluate the conductivity of the sintered composite, the conductive material is screen-printed on an Al2O3 ceramic substrate; it forms a rectangular tunnel to bridge two silver electrodes. After sintering process, the resistance of the screened conductive pass-way is dropped from 9.47 Ω to 0.35 Ω. The bonding strength and high temperature resistance test results of the sintered composite is also presented in this paper. Without generating a lot of heat, the sintering process can be applicable to flexible electronics.