Effect of Au and Ni/Au coatings on the electrolytic migration of Cu-conductors, and effect of Au coatings on joint strength of BGA for Sn-0.7Cu and In-48Sn solder after reflow

• Main Authors: Guh-Yaw Jang, 張顧耀
• Other Authors: Jing-Chie Lin
• Format: Others
• Language: en_US
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/58856788558324436154

碩士 === 國立中央大學 === 機械工程研究所 === 90 === Effects of Au and Ni/Au coatings on the electrolytic migration of copper conductors have been studied. The migration of the copper conductors in dionized water, 0.01M NaCl and (NH4)2SO4 solutions at a bias of 5V was inhibited by coating a layer of Au in thickness of 0.1 ~ 1.0 μm. When Au-coated copper conductors are under a lower bias (e.g. < 0.5VSCE), heat treatment (at 250 ℃ for 300 seconds) enhances the migration resistance. To the opposite, under a higher bias (e.g. > 1.4VSCE), heat treatment diminishes the migration resistance for the specimen coated with only 0.1 μm Au, but causes no influence with the thickness of Au-coats greater than 0.5 μm. The migration inhibition is more efficient with increasing thickness of the Au-coats from 0.1 to 1.0 μm in the case of Ni/Au-coated copper conductors. However, it is less efficient when the Ni/Au-coated conductors have been heat-treated at 250 ℃ for 300 seconds. Electrochemical polarization such as potentiodynamic and potentiostatic experiments were conducted. The ESCA analysis for the anode indicates that gold is un-reactive for Au-coated copper conductors and Ni/Au-coated copper conductors in the 0.01M (NH4)2SO4 solution. Effect of Au coatings on joint strength of ball grid array (BGA) estimated by conducting the shear test of the soldered system where Sn-37Pb, Sn-0.7Cu and In-48Sn solders have been reflowed, respectively, onto the Au-deposited Ni/Cu pads. The thickness of Au-deposits is ranging from 0.1 to 1.2 µm and that for Ni-coat is 5µm. The Sn-37Pb alloy had a slight decrement in ball shear strength with increasing the thickness of gold coat from 0.1 μm to 1.0 μm. The strength however was degraded drastically while the gold coat is 1.2 μm. On the other hand, the two lead free systems had a slight increment in ball shear strength with increasing the thickness of gold coat.