Characterization of Intermetallic Compound Formation and Growth Kinetics in Lead-Free Solder SAC305

摘要

This paper describes the experimental techniques necessary for studying intermetallic layer formation and growth throughout the melting and solidification, and thermal aging of the solder alloy. To observe intermetallic compound (IMC) growth during the liquid state of soldering, an experimental setup that quickly raises the temperature, followed by fast cooling (comparable to the actual joint conditions) was required. Temperatures at increments of 25°C above the soldering temperature and times of two, five and eight seconds for growth were carefully controlled. Thermal aging was performed for 20, 50, and 100 hours at 70, 100, and 130°C. The copper substrate/solder alloy interface was examined using light microscopy and SEM-EDS in the as soldered condition and after thermal aging. As expected, intermetallic phases such as Cu_6Sn_5, Cu_3Sn, and Ag_3Sn were observed, with Cu_6Sn_5 being the major phase in as-soldered and thermally aged conditions. Statistical analysis was performed in the IMC thickness data obtained from the long profile analysis. Using Arrhenius analysis, the activation energy for IMC growth was calculated to be approximately 8kCal/mol in the as-soldered condition, and 20kcal/mol for thermal aging, in agreement with reported values in literature, that are in the range of 18 to 27kcal/mol for thermally aged specimens.