Formation of diffusion barrier layers for thermoelectric modules via electroless Ni-P plating

In this study, electroless Ni-P plating was applied to thermoelectric elements to create a diffusion barrier layer. To achieve selective Ni-P plating, a surface activation process involving sensitization and activation treatments was applied. This pre-treatment protocol promoted the formation of a uniform Ni-P layer and enabled selective plating through wettability differences, which were regulated using sodium dodecyl sulfate as an anionic surfactant. The deposited Ni-P layer functioned effectively as a diffusion barrier by suppressing the formation of intermetallic compounds between the solder and the thermoelectric elements. The influence of sodium dodecyl sulfate on surface chemistry and wettability was investigated using contact angle measurements and X-ray photoelectron spectroscopy. Additionally, the microstructure and interfacial characteristics of the Ni-P and Cu/Ni-P-plated layers were examined by electron probe microanalysis (EPMA). The EPMA results revealed that the Ni-P layer effectively suppressed Cu diffusion into the thermoelectric elements even after thermal treatment, demonstrating its potential as a reliable diffusion barrier for thermoelectric module applications.