. . "More particularly, FIG. 14a is a plan view of the substrate surface; FIG. 14b is a cross-sectional view thereof; FIG. 14c is a plan view of the substrate surface after it has been hardened with resin impregnated therein; FIG. 14d is a cross-sectional view of the resin impregnated substrate; and FIG. 14e is a cross-sectional view of a substrate of a three layer structure hardened with resin impregn" . .