Surface roughness, wear and thermal conductivity of ternary electroless Ni–Ag–P coating on copper substrate

Abstract

Thermal testing tool used in electronic industries requires a high thermal conductivity and wear resistant coating to ensure efficient thermal transfer over some period of testing cycles. A study on ternary nickel-silver-phosphorus (Ni–Ag–P) coating was carried out by adding silver sulphate into electroless nickel-phosphorus (Ni–P) bath solution with a target to improve thermal conductivity. The results showed that silver can be co-deposited into Ni–P coating but in limited concentration without causing bath decomposition. Cethyltrimethyl ammonium bromide (CTAB) were added into the bath solution as surfactant to improve the coating surface morphology and roughness. Characterization of coatings were done using atomic force microscope (AFM), scanning electron microscope (SEM), energy dispersive x-ray (EDX), optical microscope, Knoop microhardness tester, pin-on-disc wear tester and hot disk thermal analyser. When the concentration of silver sulphate added was low, coating produced have smoother surface with improved thickness, hardness and wear resistance. Higher concentration of silver sulphate led to bath decomposition thus coatings have rougher surface with reduced thickness, hardness and wear resistance. Thermal conductivity test showed increment in the thermal conductivity value of Ni–P coating from 445.7 W m−1.K to 466.9 W m−1.K with addition of 10 mg l−1 silver sulphate. It is found that co-deposition of silver at low concentration can improve the hardness, wear resistance and thermal conductivity, and as comparable thickness value is possible, ternary Ni–Ag–P showed interesting potential to replace current NiP coating used in thermal testing tool.