PURPOSE: To make it possible to improve the flatness of metal foil as the outermost layer by reducing the amount of shrinkage by cooling of insulating material in through holes after lamination by a method wherein the insulating material, which is prepared by adding inorganic particles and coupling agent in insulating resin, is filled in the through holes of metal board and the metal foil is laminated through insulating layer to the surface of the metal board.
CONSTITUTION: A large number of through holes, the diameter of each of which is normally about 0.3-7mm, are provided on metal board. Each through hole is filled with material, which is prepared by mixing coupling agent, inorganic particles and insulating resin with one another. The preferable loading of the coupling agent is 5wt.% or more of the whole insulating material filled in the through hole. The preferable inorganic particle diameter is 100μm or less in mean particle diameter. As a result, the surface flatness of the top face part of the insulating material filled in the through hole and the adhesion of through hole plating provided in the through hole are improved.
SAHODA HIROSHI
NAGAMATSU KEIJI
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