1. Field of the Invention
The present invention relates to a substrate holding method for holding a flexible substrate typified by a plastic film on a holding jig and to a method of manufacturing an electronic part by using the substrate holding method.
2. Description of the Related Art
In recent years, as an electronic equipment is becoming mobile and wearable, a smaller and flexible electronic part is demanded. To address such a technical demand, for example, the material of a substrate used for forming an electronic device as a main part of an electronic part is being changed from a material having rigidity typified by a ceramics substrate, an FPC (Flexible Printed Circuit) board, a glass substrate, and the like to a material having flexibility typified by a plastic film. An example of the electronic part accompanying the technical demand is a small solar battery provided in a clock or the like. The electronic part is not easily cracked, is bendable, and can be processed in an arbitrary shape since a flexible substrate is used, so that the electronic part has an advantage from the viewpoint of portability. By using the advantage, development of an active display is also being progressed.
In the case of using a flexible substrate (for example, a plastic film) in order to manufacture an electronic part, for example, a problem occurs in handling of the plastic film from the following two viewpoints. First, since the plastic film generally has low rigidity and a high coefficient of thermal expansion, when heat (concretely, heat cycle) is generated during various processes (for example, in a film forming process) in a process of manufacturing an electronic part, the plastic film is thermally deformed by the influence of the heat. Specifically, the plastic film is contracted or warped. When the plastic film is thermally deformed, the dimensions of the plastic film change, so that it becomes difficult to control the dimensional precision of the electronic part. Second, since the plastic film is generally thin and deflectable, when an external force is applied during a process of manufacturing an electronic part, the plastic film is physically deformed by the influence of the external force. Specifically, the plastic film is broken or a wrinkle occurs. Since the plastic film is physically easily deformed and cannot be conveyed in the manufacturing process, it is difficult to put the plastic film in an electronic parts automatic manufacturing line.
In consideration of the problems, some techniques have been proposed to improve the handling of a plastic film. Concretely, a technique of holding a plastic film by a holding frame by adhering the plastic film to the holding frame by using an adhesive tape in a process of manufacturing an electronic part is known (refer to, for example, Japanese Patent Laid-Open No. 2002-100790). In the technique, particularly, in order to make the plastic film stably held by suppressing thermal deformation of the holding frame, the holding frame having a coefficient of thermal expansion which is less than 10 ppm/° C. is used.
In the case of manufacturing an electronic part by forming an electronic device on a plastic film, naturally, also in the case of using the plastic film, the performance of the electronic part has to be assured to the same degree as that in the case of using a ceramics substrate or the like. In the conventional electronic part manufacturing method, as described above, by adhering the plastic film to the holding frame by using the adhesive tape, the plastic film can be stably held by using the holding frame. On the other hand, since the adhesive is used to make the plastic film held by the holding frame, there is a problem such that the performance of the electronic part tends to deteriorate due to the existence of the adhesive.