High-strength and high-conductivity Cu-Cu bonding fabricated by resistance micro-welding with amorphous Ni-P coatings and multi-pulse discharging

Fabricating high-quality bonding with a wide operating temperature range while minimizing thermal damage to substrates during welding is critical for the reliability of circuit interconnections but also challenging. A method was proposed to resolve this challenge by resistance micro-welding with amorphous Ni-P coatings and multi -pulse discharging. With this technology, high-strength, and high-conductivity Cu-Cu joints were prepared while keeping the Cu solid. The Ni-P coatings evolved into a purified faying interface dominated by Ni-alloy crystals, contributing to superior mechanical and electrical properties and enabling joints to work at low and high temperatures. Further investigation revealed that the discharging-induced electromigration of nickel ions resulted in the accelerated growth of Ni-alloy grains on the anode-side Cu substrate and the concentration of P in Ni-P near the cathode side. The liquid P-rich Ni-P was squeezed out by electrode force, and the Ni-alloy grains were retained, which finally formed the purified interface.