PURPOSE: To reduce the capacity between leads for masking the products subject to strict standard for capacity between leads acceptable by a method wherein cavities not coated with any sealer are made between the leads of leadframe to be mounted between a base and a cap.

CONSTITUTION: In order to coat a low melting point glass 7, the peripheral end part of a base 1 in proper width is coated with the low melting point glass 7 not to coat the part inside the part in proper width coated with the same 7. The proper width to be coated with the low melting point glass 7 shall be the width causing no problem in the sealing strength in practical use while cavities 9 are made between respective leads 3, 3 on the base 1 along the other cavity 4 of base 1. Through these procedures, the air with dielectric constant of 1 can be laid between respective leads 3, 3 to reduce the capacity between the leads 3, 3 compared with the case when the cacities 9 between the leads 3 are filled with the low melting point 7 (with the dielectric constant of around 12W30)