Mechanical property of Cu-Sn-Ni intermetallics in the full intermetallic micro-joints formed with transient liquid phase soldering

Abstract

A structure of Cu/IMCs/Ni micro-joint has been prepared from Cu/Sn (1.5µm)/Ni sandwich layers through the transient liquid phase soldering at 240 °C and 290 °C. On the result of microstructural observation, two layers can be distinguished as the thick (Cu, Ni)6Sn5 layer beneath the upper layer of thin (Cu, Ni)3Sn layer, to constitute the IMCs interlayer in micro-joint formed at 240 °C with dwell time of 15 min. Whereas, the IMCs interlayer in micro-joints after 5∼25 min dwelling at 290 °C is much more uniform and homogenous. The creep properties of IMCs have been evaluated at room temperature with the condition of 2000 µN loading for 30 s. Also, the reduced Young's modulus and hardness of (Cu, Ni)6Sn5 and (Cu, Ni)3Sn have been measured by nanoindentation with the application of displacement-controlled multiple loading method, which are respectively higher than the common value of Cu6Sn5 and Cu3Sn. With the focus ion beam micro-milling, Cu-Sn-Ni IMCs micro-cantilevers have been fabricated with the size about 1 µm×1 µm×3 µm in the sample formed at 290 °C. Afterwards, an in-situ micro-compression test has been conducted, the fracture strength was calculated to be 2.46 GPa.