The Ni-P stratum was fabricated upon the Cu substrate via an electroless plating technique, and the microstructure and properties of electroless Ni-P/Sn2.5Ag0.7Cu0.1RE micro-joints under temperature gradient was studied. Research indicates that in the initial stage of thermomigration in micro-solder joints, the intermetallic compound (IMC) in the Ni-P/soldering seam transition area appears as both "needle-shaped" and "block-shaped" (Ni, Cu)