Microstructures and Mechanical Properties of the Sn58wt.%Bi Composite Solders with Sn Decorated MWCNT Particles

The mechanical properties and microstructures of Sn58Bi (in wt.%) composite solders with Sn decorated multiwalled carbon nanotube (Sn MWCNT) particles were investigated. The contents of Sn MWCNT particles were 0, 0.05, 0.1, and 0.2 wt.%. Sn58Bi composite solder pastes were printed on printed circuit board (PCB) substrates and bonded to the substrates using reflow processes (1, 2, 3, 5, and 7 times). This study describes the effect of Sn MWCNTs content and the number of reflow processes on the mechanical properties and microstructures of Sn58Bi composite solders. Mechanical properties were investigated using a low speed ball shear test. In the shear test, the shear strength increased by 7.07%, and the fracture energy increased by 14.4% with 0.1 wt.% of Sn MWCNT particles after 1one reflow. The number of reflows did not significantly affect the shear strength, but the fracture energy increased with increasing content of Sn MWCNT particles. Cross-sectional microstructures and fracture surfaces were observed by scanning electron microscopy (SEM). Sn MWCNT particles in the solder matrix were observed on polished surfaces of SEM images and were also identified by a Raman spectrometer. After the shear test, brittle failure occurred in all joints, indicating no influence of MWCNT particles.