PURPOSE: To prevent the drop of breakdown strength and the increase of water absorption rate by using insulating varnish filled with inorganic matter being gotten by agitating and mixing inorganic matters, where BET specific surface areas and the maximum particle diameters are below specified values, under decompression.
CONSTITUTION: As inorganic matter, where BET specific surface area is 2.0m2/g or order and the maximum particle diameter is 20μm or under is used. And, this inorganic matter is diluted and agitated into two or more times large in volume with a solvent capable of dissolving insulating varnish. Next, the insulating material varnish is added to the inorganic matter diluted with a solvent so as to adjust the viscosity of the whole to 0.01Ps.s or under, and these are agitated and mixed under decompression to make insulating varnish filled with inorganic matter. The insulating material varnish filled with inorganic matter being gotten this way is applied on a copper foil or a metallic plate and is dried, and then it is stacked on the metallic plate or the copper foil. Hereby, a copper-clad laminate with metal-base, which has an insulating layer where inorganic matter is filled by 50-76wt.%, can be gotten.
YAMAGUCHI MASATOSHI
KATO JUNICHI
MIMORI SEIJI
NAGAO KENICHI
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