Investigation of Sn Whisker Growth in the Matte Sn/Alloy 42 Substrate Coated Different Metallic Layers

• Main Authors: Meng-Yu Tsou, 鄒孟妤
• Other Authors: Yee-Wen Yen
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/75809384603961882306

碩士 === 國立臺灣科技大學 === 工程技術研究所 === 98 === In this study, the multi-layer structure effect on the Sn whisker growth in the matte Sn/Fe-42 wt% Ni (Alloy 42) systems was investigated. It was expected that the optimal processing parameters to prevent the whisker growth could be found. The Alloy 42 substrates were electroplated with 1.8 ?慆-thick of the Cu layer (CuE), electrolessplated with 0.3 ?慆-thick Cu layer (CuC), and electroplated with 1.8 ?慆-thick Ni layer, respectively. Thus, 4 kinds of multilayer specimens, CuE/Sn/Alloy 42, CuC/Sn/Alloy 42, Ni/Sn/Alloy 42, and Sn/Alloy 42 were prepared. Finally, thermal treatment at 60°C for 500 hours and thermal cycle tests were applied to each specimen. The thermal cycle is one hour from -35 to 85 oC. The results indicate that the Sn layer with the thicker thickness was observed under passing the higher current density. The surface morphology was different at different metallic layers and various current densities. When current density was 5.0ASD, increasing numbers of the thermal cycle produces more thermal stress to induce the Sn whisker formation. The order of the Sn whisker length and density in each specimen is : Sn/Alloy 42 > Sn/CuE/Alloy 42 > Sn/CuC/Alloy 42. The copper layer could eliminate the thermal stress which was generated due to coefficient of thermal expansion (CTE) mismatch between Sn layer and Alloy 42 during thermal cycling. However, no Sn whiskers were formed in the Ni/Sn/Alloy 42 system. Because tin atoms diffusion to nickel layer. The tension stress built up in the tin layer. This tension stress could mitigate thermal stress. At different current density, current density and Sn whisker length were proportional. But current density and the Sn whisker density were inversely proportional. No Sn whiskers were found in each specimen after 60 oC for 500 hours.