<p>To fulfill the requirements for dependable low-temperature soldering of high-temperature lead-free materials and to inhibit the transformation of Cu₆Sn₅ to Cu₃Sn during transient liquid phase diffusion bonding (TLPB) and aging processes, along with minimizing joint porosity, Cu particles were initially coated with a Ni layer through electroless plating, followed by Sn layer deposition via stannous sulfamate electroplating to achieve Cu@Ni@Sn core-shell structured powder. The study explored the oxidation resistance of Cu@Ni@Sn powder and examined the formation rate and activation energy of Cu₃Sn in both Cu@Sn and Cu@Ni@Sn TLPB joints, clarifying the Ni coating’s role in restricting element migration and phase transformation. The Cu@Ni@Sn TLPB joint displayed a three-dimensional network of intermetallic compounds enveloping Cu particles. This joint demonstrated thermal endurance of at least 400&#xa0;°C, room temperature shear strength exceeding 80&#xa0;MPa, and shear strength of no less than 28&#xa0;MPa after aging at 250&#xa0;°C for 336&#xa0;h, representing a 20% improvement compared to the Cu@Sn system. Joint porosity was lowered from 10% in the Cu@Sn system to 5% in the Cu@Ni@Sn system, surpassing both high-lead and nano-sintered Ag systems. The findings illustrate that the introduction of a Ni coating successfully restricted Cu diffusion, suppressed Cu₆Sn₅ phase transformation, decreased void formation, and improved the high-temperature oxidation resistance of Cu@Ni@Sn powder. After undergoing reflow at 250&#xa0;°C, the Cu@Ni@Sn joint exhibited thermal conductivity of 156 W/m·K and electrical resistivity of 4.2 μΩ·cm, surpassing those observed in the Cu@Sn system, Cu₆Sn₅, and Cu₃Sn. These results imply that Cu@Ni@Sn TLPB joints fulfill the criteria for high-performance interconnections, presenting a viable replacement for high-lead and sintered nano-Ag soldering materials, making them a favorable candidate for high-temperature, high-reliability interconnect applications in power modules.</p>