Interfacial Reactions of Pure Sn on Ni-coated Anisotropic Bi2Te3 Substrate and Ni Foil

• Main Authors: Yu-Chen Tseng, 曾宥蓁
• Other Authors: 陳志銘
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/05405484261403234368

碩士 === 國立中興大學 === 化學工程學系所 === 104 === Thermoelectric (TE) materials are functional semiconductors that have numerous applications for our current society suffering from energy shortage because they can convert heat to electricity. Bismuth telluride (Bi2Te3) is a well-known TE material for its high conversion efficiency at room temperature. Much effort has been devoted for improving the figure-of-merit of TE materials, but only few studies exploited the solder joint reactions in TE module which can provide fundamental information for assessing the reliability of packaging process In this research, we utilized zone-melted Bi2Te3 substrates that the bulk p-type and n-type Bi2Te3 substrates was electroplated with a nickel layer as a diffusion barrier layer to join with pure Sn solder in a direction perpendicular or parallel to layer direction of substrate. The results of solid - solid reaction at 200° C show that the morphology and thickness of grown Ni3Sn4 in both directions were similar. However, the Ni layer on n-type Bi2Te3 was quickly consumed because the Ni diffuses into the substrate to form NiTe phase during the long-term aging time. In contrast, the Ni layer on p-type Bi2Te3 was shown as a great diffusion barrier layer. Furthermore, the source of Ni also plays an important role. Ni foil and electroplated Ni shows considerably different results for the interfacial reaction. The preferential orientation of the resulting Ni grains were {0 0 1} and {1 1 1} for electroplated Ni and Ni foil, respectively. The Sn trends to react with Ni foil through diffusion-limited reaction and thus form elongated Ni3Sn4 grains. In contrast, the ripening-limited reaction occurred for electroplated Ni, resulting in large grains. The experimental data from this study show that the electroplated Ni possesses great advantages serve as a diffusion barrier layer.