A heat dissipation substrate having a metal layer with few defects on the surface is obtained by forming a metal layer by plating on the surface of an alloy composite chiefly comprising a main metal, an added metal, and diamond powder, and applying heat and pressure at or below the melting point of the metal layer and the alloy composite. This makes it possible to obtain a heat dissipation substrate in which Ni plating can be carried out at a soldering void rate of 5% or less, the heat dissipation substrate having a linear expansion coefficient of 6.5-15 ppm/K and a thermal conductivity of 420W/m/K or greater, and the defects on the surface of the metal layer being repaired.