a tiny amount of phosphorus which lowers the fusing point of nickel and is quite similar to solder bni 6 ni 89 p 11 therefore the joining of the coating treatment material particle 12 with each other and with the heat transfer body 13 is almost as strong as solder the joining strength of the base material according to the present invention is compared with that according to a conventional manufacturing method fig5 a shows a cross sectional view of a specimen obtained by the joining method according to the present invention and fig5 b shows a cross sectional view of a specimen obtained according a conventional method as shown in fig5 b on both end faces of the copper specimen base material 30 copper powder is used as the core material dipping it in conventional plating liquid and obtaining a conventional multi layered porous specimen 31 of 2 mm thickness on the other hand as shown in fig5 a a specimen according to the present invention having 2 mm of porous layer is obtained by changing the thickness of the coating material 11 to 1 5 and 10 u03bcm fig6 shows the results of a tension test using these specimens fig6 is a characteristic figure that shows the relation between joining strength kgf mm 2 and thickness u03bcm of the plating coat in the figure x shows the characteristics of the specimen joined using the joining method according to the present invention and y shows the characteristics of the specimen.