Direct Observation of Crystal Facet Transformation During Gold-Tin Alloy Electroplating
Keywords:Gold, Tin, Eutectic, Intermetallic compounds, Electroplating
Gold-Tin alloys are commonly used as solder materials in semiconductor industries. In this work, Au-Sn alloys have been electroplated with different bath conditions. For the first time, Au-Sn alloy single crystals have been observed. There are two kinds of single crystals were grown with the compositions of Au4Sn and Au2Sn, different from literature-stated Au5Sn and AuSn. The effects of bath composition and plating factors on crsytal facet development of Au-Sn deposits have been investigated. SEM/EDX analysis showed that only Au4Sn and Au2Sn phases are single crystals among all plated deposits. The growth of either Au4Sn or Au2Sn phases showed preferred orientation with plating conditions. We report on quantitative SEM/EDX characterizations used to study the facet transformation behavior of Au-Sn alloy at the nanometer scale. We have obtained direct evidence that the single crystals and crystal facet transformation of Au4Sn and Au2Sn does exist in Au-Sn alloy, and high Sn content enhanced the crystal growth through a spiral-like growth mechanism.