After gathering microstructural evidence that a practical highly-conductive, high-temperature lead-free solder may be produced through liquid-phase diffusion bonding of gas-atomized Cu-10Ni, wt.%, powder with SN100C (Sn-0.7Cu-0.05Ni+0.01Ge) commercial solder powder, research was completed on the solder’s thermal and mechanical properties. Our results indicated that moderate reflow temperatures (250˚C) produced a transformed microstructure that should have stability approaching 400˚C. New tests were performed on the solder joint microstructure, including: DSC to help determine the maximum service temperature, TMA to determine CTE, four-point probe measurements of electrical conductivity, and asymmetric four-point bend testing of shear strength at temperatures up to 250°C. These results suggest that this composite solder could be a superior “drop-in” replacement for the currently used Pb-based high-temperature solders and, certainly, for Au-20Sn, the primary Pb-free alternative. Support from the Iowa State Research Foundation and Nihon Superior Co.. Ltd., through Ames Lab (DE-AC02-07CH11358) is gratefully acknowledged.