| 摘要 |
PROBLEM TO BE SOLVED: To improve a dimensional stability of a cover lay film after a releasing material is stripped by heat-treating the film at a temperature within a pecified range for a period of time within a specified range after it is attached with the releasing material. SOLUTION: A preliminarily prepared thermosetting adhesive solution is applied onto an electric insulated film. Next, a solvent is dried and removed to half-harden an adhesive. Thereafter, a releasing material film is attached under pressure to the adhesive applied surface of the film by means of a hot roll to obtain a cover layer film Then, the cover layer film is heat-treated at 30-70 deg.C, preferably 40-60 deg.C, for 1 to 48 hours. If the heat treatment temperature is lower than 30 deg.C, enough dimensional stability cannot be obtained. If the temperature exceeds 70 deg.C, a dimensional stability in the width direction is not good enough and a stripping withstanding strength and a solder heat resisting property are deteriorated and, consequently, the workability is degraded.
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