PURPOSE: To enhance an electronic component case in airtightness by a method wherein the adhesive surface of a lower board as a component part of the electronic component case to an upper board is rendered flat and even so as to enable a joint surface between the upper board and the lower board to be enhanced in adhesion.

CONSTITUTION: Insulating overglaze 6 is applied onto the adhesive surface 2c of a lower board 2 as a component part of an electronic component case A to an upper board 3 to make the adhesive surface 2c flat and smooth, whereby a joint surface between the lower board 2 and the upper board 3 is enhanced in adhesion.