<p>The reliability of electrical connections is critical in high-current applications, where joint performance directly influences efficiency, safety, and service life. In this study, a comparative investigation of ultrasonic welding (USW) and crimping was conducted for joining 16 mm² copper conductors to silver-coated copper substrates. Mechanical testing, microstructural and compositional analysis (SEM/EDS and XRD), electrical resistance measurements, infrared thermography, and salt spray corrosion evaluations were employed to assess the performance and degradation behavior of both joining methods. Tensile results showed that crimped joints exhibited higher initial strength, whereas USW joints maintained superior interfacial integrity under corrosive conditions. Microhardness measurements indicated lower hardness at the USW interface (65–75 HV) compared to crimped joints (82–88 HV), reflecting differences in bonding mechanisms. SEM/EDS and XRD analyses confirmed metallurgical bonding and enhanced oxidation resistance in USW joints, while crimped joints relied primarily on mechanical interlocking and showed greater susceptibility to interfacial degradation. Electrical measurements revealed that crimped joints generally exhibited lower resistance but higher variability, whereas USW joints demonstrated more stable electrical behavior. Infrared thermography further indicated more uniform and stable thermal responses for USW joints under current loading. Unlike previous comparative studies that mainly emphasize initial mechanical or electrical performance, this work focuses on reliability and degradation behavior by correlating interfacial bonding mechanisms with mechanical, electrical, and thermal stability. The results provide new insight into the long-term performance of high-current copper connections and offer practical guidance for selecting joining technologies in demanding industrial applications.</p>