The reliability of Sn-Ag-Cu (SAC)-based solder alloys has been extensively investigated after the prohibition of lead in the electronics industry owing to their toxicity. Low-temperature solder (LTS) alloys have recently received considerable attention because of their low cost and reduced defects in complex assemblies. The shear and fatigue properties of individual solder joints were tested using an Instron micromechanical testing system in this research. Two novel solder alloys (Sn-58Bi-0.5Sb-0.15Ni and Sn-42Bi) with low melting temperatures were examined and compared with Sn-3.5Ag and Sn-3.0Ag-0.8Cu-3.0Bi. The surface finish was electroless nickel-immersion gold (ENIG) during the test. Shear testing was conducted at three strain rates, and the shear strength of each solder alloy was measured. A constant strain rate was used for the cyclic fatigue experiments. The fatigue life of each alloy was determined for various stress amplitudes. The failure mechanism in shear and fatigue tests was characterized using scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS). The results revealed that Sn-3.0Ag-0.8Cu-3.0Bi had superior shear and fatigue properties compared to other alloys but was more susceptible to brittle failure. The shear strain rate affected the failure modes of Sn-3.0Ag-0.8Cu-3.0Bi, Sn-58Bi-0.5Sb-0.15Ni, and Sn-42Bi; however, Sn-3.5Ag was found to be insensitive. Several failure modes were detected for Sn-3.5Ag in both shear strength and fatigue tests.

This work reports on employing X-ray computed tomography (XCT) and optical microscopy to investigate the causal relationships between printing parameters, pore properties, and porosity in 316L stainless steel samples additively manufactured by Laser Powder Bed Fusion (LPBF). The porosity is very similar for both investigation methods. XCT provides more accurate results for large lack of fusion pores, while optical results are more accurate for small keyhole pores. These results were employed to develop mathematical models to determine how printing parameters influence pore properties and overall porosity. The developed optical and XCT mathematical models reveal that power is the most significant factor affecting pore properties and overall porosity. Pore number and mean diameter decrease and sphericity increases with increasing power. Overall porosity is negatively correlated with power, indicating that the higher the power, the lower the overall porosity. Attention should also be paid to the quadratic effects of power, velocity and hatch spacing on porosity, revealing an inverse change in porosity after a certain threshold. Power interacts with velocity and hatch spacing, suggesting that changes in power affect the influence of velocity and hatch spacing on porosity, and vice versa. The interaction of velocity and hatch spacing is not significant. Both models successfully predicted optimal printing parameter sets as validated by experimental measurements.