Adhesive resins with high adhesive strength and high heat resistance have been studied in developing a novel iron-core printed circuit board with high mechanical strength and high heat radiation capability. A reticular pattern formed on the surface of an adhesive resin composed of nitrile rubber, phenolic resin, and epoxy resin. It caused blisters in the plating or reduced the heat resistance of the printed board. This pattern was formed as a result of phase separation of epoxy resin or phenolic resin from the nitrile rubber. Using a high-molecular-weight epoxy resin led to high adhesive strength and high heat resistance, without phase separation. The relationships between the composition of adhesive resins and their characteristics were discussed on the basis of the state of their surface after being roughened by chemical etching.