Effect of Surface Roughness and Electroless Ni–P Plating on the Bonding Strength of Bi–Te-based Thermoelectric Modules

In this study, electroless-plating of a nickel-phosphor (Ni–P) thin film on surface-controlled thermoelectric elements was developed to significantly increase the bonding strength between Bi–Te materials and copper (Cu) electrodes in thermoelectric modules. Without electroless Ni–P plating, the effect of surface roughness on the bonding strength was negligible. Brittle SnTe intermetallic compounds were formed at the bonding interface of the thermoelectric elements and defects such as pores were generated at the bonding interface owing to poor wettability with the solder. However, defects were not present at the bonding interface of the specimen subjected to electroless Ni–P plating, and the electroless Ni–P plating layer acted as a diffusion barrier toward Sn and Te. The bonding strength was higher when the specimen was subjected to Ni–P plating compared with that without Ni–P plating, and it improved with increasing surface roughness. As electroless Ni–P plating improved the wettability with molten solder, the increase in bonding strength was attributed to the formation of a thicker solder reaction layer below the bonding interface owing to an increase in the bonding interface with the solder at higher surface roughness.

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Effect of Electroless Ni-P Plating on the Bonding Strength of PbTe Thermoelectric Module Using Silver Alloy-Based Brazing

Materials Science Forum ◽

10.4028/www.scientific.net/msf.985.16 ◽

2020 ◽

Vol 985 ◽

pp. 16-22

Author(s):

Sung Hwa Bae ◽

Joon Young Choi ◽

Injoon Son

Keyword(s):

Bonding Strength ◽

Filler Metal ◽

Thermoelectric Module ◽

Bonding Interface ◽

Silver Alloy ◽

Thermoelectric Element ◽

Thermoelectric Modules ◽

High Bonding Strength ◽

Diffusion Barrier Layer ◽

Electroless Ni

This study investigates a brazing method for manufacturing PbTe thermoelectric modules using a Ag-based filler metal with a melting point of about 650 °C. To improve the bonding strength between the Ag-based brazing layer and the PbTe thermoelectric module, an electroless Ni-P plating layer is formed on the surface of the thermoelectric module as a diffusion barrier layer. The bonding strength of the PbTe thermoelectric module manufactured by the electroless Ni-P plating and Ag-based brazing has a high value of approximately 8.3 MPa. No defects such as pores or cracks were observed at the bonding interface between the thermoelectric element and the brazing layer. Furthermore, because of the high bonding strength of the manufactured thermoelectric module, fractures occur inside the thermoelectric element rather than at the bonding interface. Accordingly, the electroless Ni-P plating and Ag-based brazing method proposed in this study is found to be effective in manufacturing PbTe-based thermoelectric modules with high bonding strength.

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Effect of the Electroless Nickel, Electroless Palladium, and Immersion Gold Multilayer as a Diffusion Barrier on the Bonding Strength of BiTe-Based Thermoelectric Modules

Journal of Nanoscience and Nanotechnology ◽

10.1166/jnn.2021.19431 ◽

2021 ◽

Vol 21 (8) ◽

pp. 4498-4502

Author(s):

Yen Ngoc Nguyen ◽

Khanh Quoc Dang ◽

Injoon Son

Keyword(s):

Intermetallic Compounds ◽

Electrochemical Deposition ◽

Barrier Layer ◽

Diffusion Barrier ◽

Bonding Strength ◽

Effective Diffusion ◽

Electroless Nickel ◽

Thermoelectric Modules ◽

Diffusion Barrier Layer ◽

Plating Layer

An effective diffusion barrier layer was coated onto the surface of BiTe-based materials to avoid the formation of brittle intermetallic compounds (IMCs) by the diffusion of the constituents of Sn-based solder alloys into the BiTe-based alloys. In this study, the electrochemical deposition of multi-layers, i.e., electroless nickel/electroless palladium/immersion gold (ENEPIG) was explored to enhance the bonding strength of BiTe materials with Cu electrodes. The thermoelectric modules with the ENEPIG plating layer exhibited high bonding strengths of 8.96 MPa and 7.28 MPa for the n- and p-type, respectively that increased slightly to 9.26 MPa and 7.76 MPa, respectively after the thermoelectric modules were heated at 200 °C for 200 h. These bonding strengths were significantly higher than that of the thermoelectric modules without a plating layer.

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Molecular Dynamics Simulation of Aluminium Thin Film Surface Activated Bonding

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.486.127 ◽

2011 ◽

Vol 486 ◽

pp. 127-130

Author(s):

Chao Cheng Chang

Keyword(s):

Thin Film ◽

Thin Films ◽

Molecular Dynamics ◽

Surface Roughness ◽

Bonding Strength ◽

Film Surface ◽

Dynamics Simulation ◽

Thin Film Surface ◽

Common Neighbour ◽

Eam Potential

This study used molecular dynamics simulations with an embedded-atom method (EAM) potential to investigate the effect of surface roughness on the surface activated bonding (SAB) of aluminium thin films. The simulations started with the bonding process and followed by the tensile test for estimating bonding strength. By averaging the atomic stresses over the entire system, the stress-time curves for the bonded films under a tensile condition were predicted. Moreover, the evolution of the crystal structure in the local atomic order was examined by the common neighbour analysis. The simulated results show that the decrease in the surface roughness of thin film improves the bonding strength. The observed recrystallization processes inside the bonded thin films also reveal that the plastic deformation of the aluminium surface due to atomic attracting force compensates surface roughness.

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