PURPOSE: To prevent the generation of Al film blister in a baking process and enhance the yield rate and the reliability in said process, by spouting pure water, etc., intermittently through nozzle holes which are formed circumferentially and at fixed spaces from each other at the tip of a nozzle to be inserted into the captioned tube body.

CONSTITUTION: At the tip of a nozzle 21 to be inserted into a tube body, for instance, 16 holes 23 of 1mm are circumferentially formed with the space of about 1mm from each other and pure water 20 is spouted intermittently through the holes 23. For instance, first the pure water 20 is spouted for 10sec, then stopped for 2.5sec, further it is spouted for 10sec, and then stopped for 2.5sec. Such intermittent spouting of pure water is repeated and thus lacquer trimming is carried out for 60sec in total. By doing this, an excess lacquer film 8 can be removed and the blisters of Al film in the baking process can be eliminated.