Interfacial reaction and shear strength of ultrasonically-assisted Sn-Ag-Cu solder joint using composite flux

Abstract

Cu modified carbon nanotubes (Cu-CNTs) doped flux were prepared in this paper, the influence of the composite flux on the evolution of microstructure and shear strength of Sn-3.0Ag-0.5Cu (SAC305) solder joints were investigated, the ultrasonic vibration (USV) was applied for the solder joint during reflowing. Experiments were designed to modify the CNTs with Cu nanoparticles through electroless modification process. Transmission electron microscopy (TEM) was utilized to obtain the graph of modified CNTs. Using X-ray photoelectron spectroscopy (XPS) spectra to prove that the CNTs were successfully modified with Cu nanoparticles. Compared with the solder joint without USV, the application of USV on the solder joint would alter the morphologies of interfacial IMC layer and grains, reduce the IMC thickness and grain size by 16.6 % and 65.6 %, respectively. Reflow process was implemented to evaluate the microstructure evolution and interfacial reaction of SAC305 solder joint with different content of Cu-CNTs doped flux with USV. It was found that the presence of Cu-CNTs could reduce the thickness and grain size of interfacial intermetallic compound (IMC) within solder joint by 3.1 % and 5.25 %, respectively. After addition of the Cu-CNTs in the flux, the thickening of IMC layer and the coarsen of interfacial IMC grain were suppressed, the optimal inhibition effect was gained when the content of Cu-CNTs was 0.1 wt.%. The shear test was conducted for the Cu/SAC305/Cu solder joint with flux containing Cu-CNTs under different soldering condition, the results indicated that as the content of the Cu-CNTs in the flux increased, the shear strength was significantly enhanced by up to 16.8 %. Furthermore, the application of USV could enhance the shear strength by up to 14.2 % as well, The fracture type of solder joints without USV treatment also changed from ductile-brittle mixed type to ductile type as the content of Cu-CNTs in the flux increased. While, the fracture type of all the solder joints with USV treatment was ductile type.