To satisfactorily joint a semiconductor device mounting board with a solder, by a method wherein at least a part forsolder joining the semiconductor device mounting board of a base material in which fibers or particles of a low expansion coefficient are compounded with a high heat conductivity metal is coated with an Ni alloy layer.

SiC fibers (diameter of 0.3 μm and length of 90 μm), AlN fibers (diameter of 1 μm and length of 30 μm), or carbon fibers (diameter of 10 μm and length of 200 μm) are formed as a porous fiber perform of 50 volume %. The perform is set in a pressurizing casting device having a cavity of the same shape as the porous fiber perform, an Al-13 wt.% Si alloy molten metal is injected to the cavity, thereby manufacturing a composite base material 1 by pressurizing and casting. Furthermore, the composite base material 1 is dipped in an alkaline liquid at 50°C for 40 sec. to degrease and each, and next a zincate processing dissolution in nitric acid and a zincate processing are sequentially performed, and next various coated layers are plated so that the outermost layer is an Ni alloy layer 2, thereby attaining a heat sink.