Wettability and thermal performance of Ga_62.5In_21.5Sn₁₆ liquid metal alloy on W-coated Cu substrates with varying film thickness

The Ga_62.5In_21.5Sn₁₆ liquid metal alloy (LMA) has been considered as a promising thermal interface material for electronics cooling. In this work, the Cu substrates were deposited with tungsten (W) films or copper (Cu) films of various thicknesses to form different morphology and composition. The surface morphology and wettability of the filmed Cu substrates were investigated by the scanning electron microscope and drop shape analyzer, respectively. Thermal performances of the Ga_62.5In_21.5Sn₁₆ sandwiched between filmed Cu substrates were studied using the laser flash analyzer. It was observed that the rough Cu substrate becomes smooth after being deposited with metal film. A decrease in surface roughness leads to the decrease in the contact angle of Ga_62.5In_21.5Sn₁₆ droplet on filmed Cu substrate and the thermal resistance of Ga_62.5In_21.5Sn₁₆ sandwiched between filmed Cu substrates. The wettability and thermal performance are strongly dependent on the surface composition. Thermal performance of the Ga_62.5In_21.5Sn₁₆ sandwiched between the W-coated Cu substrates initially varies dramatically with W film thickness, and then changes slowly beyond a critical film thickness of ∼60 nm. This trend originates from the changing of surface composition arising from the thickening of W films.