(V010T13A056)ANISOTROPIC BEHAVIOR OF SINGLE GRAIN CU_6SN_5 INTERMETALLIC

摘要

Intermetallic (IMC) layers (Cu_6Sn_5 and Cu_3Sn) are an essential component of a solder joint for good metallurgical bonding. However, the mechanical and physical properties of IMC layers differ significantly from the solder and substrate, and excessive IMC layers can lower the reliability of solder joints due to their brittle nature. Moreover, continuous miniaturization of packages and joints has increased the volume fraction of IMCs to a point where smaller joints could be completely composed of IMCs. Further miniaturization of joints may result in statistical grain size effects. One of the most common types of IMCs in microelectronic joints is CueSns, which is formed in a variety of bonding materials with different compositions of Sn, Cu, and Ag. Due to its large percentage of volume in solder joint; to predict the reliability of micro solder joints, it is necessaiy to characterize single crystal Cu_6Sn_5 IMC completely. This study reports the information on grain growth orientation and elastic-plastic properties such as young's modulus, hardness, yield strength and strain hardening exponent of single grain of Cu_6Sn_5 in Sn-3.5Ag/Cu solder alloy system. IMCs materials were grown using reflow process using an experiment in which the time and temperature of reflow process was varied. Electron backscatter diffraction (EBSD) analysis was conducted after the reflow to measure the grain size and determine the preferred grain orientation. It was found that the growth orientation is in the orientation of the c-axis. Nanoindentation was carried out in 4 individual grains with different crystallographic orientation along normal to the growth axis to determine the elastic properties of Cu_6Sn_5 single crystal. Plastic properties were predicted using the nanoindentation results and Dao reverse analysis model. The results indicate that the hardness for Cu_6Sn_5 grains with different orientation along normal to growth axis is statistically indistinguishable. Lower elastic modulus was observed for a grain with [010] direction parallel to the loading direction. Yield strength of a grain with (001) plane parallel to the loading direction was slightly lower than other grain orientations. Overall, the experimental results obtained were found to be within the range shown in the literature.