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Sn-Pd-Ni Electroplating on Bi2Te3-Based Thermoelectric Elements for Direct Thermocompression Bonding and Creation of a Reliable Bonding Interface

Kang Seok Jun, Bae Sung Hwa, Son Injoon

Archives of Metallurgy and Materials

2021

Vol. 66, iss. 4

963--966

The Sn-Ag-Cu-based solder paste screen-printing method has primarily been used to fabricate Bi2Te3-based thermoelectric (TE) modules, as Sn-based solder alloys have a low melting temperature (approximately 220°C) and good wettability with Cu electrodes. However, this process may result in uneven solder thickness when the printing pressure is not constant. Therefore, we suggested a novel direct-bonding method between the Bi2Te3-based TE elements and the Cu electrode by electroplating a 100 μm Sn/ 1.3 μm Pd/ 3.5 μm Ni bonding layer onto the Bi2Te3-based TE elements. It was determined that there is a problem with the amount of precipitation and composition depending on the pH change, and that the results may vary depending on the composition of Pd. Thus, double plating layers were formed, Ni/Pd, which were widely commercialized. The Sn/Pd/Ni electroplating was highly reliable, resulting in a bonding strength of 8 MPa between the thermoelectric and Cu electrode components, while the Pd and Ni electroplated layer acted as a diffusion barrier between the Sn layer and the Bi2Te3 TE. This process of electroplating Sn/Pd/Ni onto the Bi2Te3 TE elements presents a novel method for the fabrication of TE modules without using the conventional Sn-alloy-paste screen-printing method.

Dilatometric Analysis of the Sintering Behavior of Bi2Te3 Thermoelectric Powders

Han Ju-Yeon, Byun Jong Min, Lee Young-In, Choi Byung Joon, Kim Hogyoung, Oh Sung-Tag

Archives of Metallurgy and Materials

2020

Vol. 65, iss. 3

1117--1120

The sintering behavior of p-type bismuth telluride powder is investigated by means of dilatometric analysis. The alloy powders, prepared by ball milling of melt-spun ribbons, exhibit refined and flake shape. Differential thermal analysis reveals that the endothermic peak at about 280°C corresponds to the melting of bismuth, and peaks existing between 410°C and 510°C are presumably due to the oxidation and crystallization of the powder. The shrinkage behavior of ball-milled powders was strongly dependent of heating rate by the thermal effect exerted on specimens. In the case of 2°C/min, the peak temperature for the densification is measured at 406°C, while the peak temperature at a heating rate of 20°C/min is approximately 443°C. The relative density of specimen pressureless-sintered at 500°C exhibited relatively low value, and thus further study is required in order to increase the density of sintered body.