1. Field of the Invention
The present invention relates to the art of adhering a thin film to a base plate, and particularly relates to the art in which a dry film consisting of a light-transmissible resin film and a photosensitive resin layer provided on one side of the resin film is stuck under pressure to a base plate such as a printed circuit board and an electronic circuit substrate of silicon, gallium arsenide or the like without leaving an air bubble between the dry film and the base plate and without wrinkling the dry film.
2. Description of the Prior Art
In one conventional apparatus for adhering a dry film to a base plate under pressure, as disclosed in Japanese Patent Publication No. 13341/80, the base plate and a photosensitive resin layer bonded to one side of a light-transmissible resin film are brought into contact with each other while being kept in a vacuum chamber of reduced pressure. Sufficient pressure is thereafter applied to the other side of the resin film to push the film and the layer onto the base plate. Thereafter, heat is applied. In another conventional apparatus the dry film is pressed onto the base plate in the air at atmospheric pressure by a rotating heat and pressure sticking roller. In yet another conventional apparatus as disclosed in the Japanese Patent Application (OPI) No. 121696/83, the end of the base plate and that of the dry film are stuck to each other in the air at atmospheric pressure and the film and the plate are thereafter completely stuck to each other in a vacuum. The dry film consisting of a light-transmissible resin film and a photosensitive resin layer bonded to one side of the film is thus stuck to the base plate, under prescribed pressure and at a prescribed temperature in each of the conventional apparatuses. The photosensitive resin layer is thereafter exposed to light through a pattern mask overlaid on the light-transmissible resin film. The resin film is then removed. The resin layer is then etched so that a desired pattern is made on the base plate.
In the above-mentioned conventional arts, however, an air bubble is likely to be left between the dry film and the base plate at the time the film and the plate are stuck to each other. The air bubble causes defects in the step of exposing the film and layer to light or the step of etching the resin layer, thereby causing problems for the process. If the dry film is entirely or partly stuck to the base plate in air at atmospheric pressure, not only will air bubbles likely be left between the dry film and the base plate but also the film will likely be wrinkled by the pressure of the rotating pressure sticking roller. This is another problem.