Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,...
Reexamination Certificate
2001-09-05
2003-11-11
Goodrow, John (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
C430S058400, C430S058550, C430S318000, C347S238000
Reexamination Certificate
active
06645685
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for producing a printed wiring board utilizing an electrophotographic method, particularly to a process for producing a printed wiring board utilizing a wiring board provided thereon a photoconductive layer in which its chargeability is changed by light exposure, and comprising an electrostatic image forming step containing at least image pattern exposure by UV light and a charging step subsequent thereto, a resist forming step by toner development, an alkali dissolution step of the photoconductive layer, and an etching step of a metal conductive layer.
2. Prior Art
In a conventional preparation of a printed wiring board, a printed circuit has generally been prepared onto an insulating substrate by the following steps. That is, laminating a photosensitive film onto a copper-clad laminated board wherein an insulating substrate is coated with a copper film, superposing a negative thereon, followed by exposure, development, removal of unnecessary portion of the copper film other than a circuit pattern, and finally, exfoliating the photosensitive layer. However, in this method using a photosensitive layer, since a thickness of the photosensitive film is generally as thick as about 50 &mgr;m, a circuit pattern formed by exposure and development is not sharp, and it is difficult to laminate the photosensitive film uniformly on a copper film surface.
In order to improve resolution, etc. of the photosensitive film, there is disclosed a method of forming a photosensitive resist on a substrate by electrode position as is disclosed in Japanese Provisional Patent Publications No. 262855/1987, No. 4672/1989, etc. However, a photo resist for electrode position has generally a problem of low sensitivity. Particularly, it is difficult to irradiate inside the through holes, and in case of positive method where irradiated portion becomes soluble for a dissolving solution, it requires energy around several hundreds mJ/cm
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in order to give sufficient solubility. Therefore, it has been improper to use laser and the like for irradiation.
Further, as a preparation method for a printed wiring board other than that utilizing the photosensitive resist, there is disclosed a method of utilizing an electrophotographic method in West German Patents No. 2526720 and No. 3210577, Japanese Provisional Patent Publications No. 2437/1977, No. 48736/1982 and No. 168462/1984. In Japanese Provisional Patent Publication No. 129689/1988, there is disclosed a preparation method for a printed wiring board utilizing an electrophotographic material having specific sensitivity for wavelength of lasers. An example of using the electrophotographic method by directly drawing an image to be formed by laser on a substrate has already been applied for an electrophotographic material used in electrophotographic lithographic printing plate, etc. and a method has been now in a practical use that utilizes a laser scanning exposure, based on data directly sent from a computer without using a photomask, to form a high density image.
In a printed wiring board prepared by utilizing the electrophotographic method (hereinafter referred to as “electrophotographic printed wiring board”), different from a photosensitive dry film resist or a liquid photo resist, it is possible to set a thickness of a resist small, thereby it is advantageous in coating and drying conditions, alkali developing condition, in keeping the etching factor of circuit patterns large enough after etching, so that it is excellent in reproducibility of fine lines and productivity. In addition, since it is a liquid resist, it is possible for a resist film to comply with unevenness of a substrate, thereby decreasing defects such as open circuit or leaching, etc. Further, there has been an increasing expectation for a practical use, since it is excellent in many properties such as maintenance of alkali developing solution, handling of a substrate after coating, ability for perfect protection of through holes, etc. as compared with other resist materials.
Preparation of the electrophotographic printed wiring board is carried out as follows. On the surface of a photoconductive layer of a wiring board in which a photoconductive layer was coated on a conductive support comprising an insulating substrate and provided thereon, a metal conductive layer, charging and exposure according to a wiring pattern are carried out to form an electrostatic latent image corresponding to an exposed portion. To this electrostatic latent image, toner developing treatment is carried out to obtain a toner image, and using this toner image as a resist, a portion of the photoconductive layer other than the toner image is removed by dissolution to prepare a resist image comprising the toner image and the photoconductive layer. Removal of unnecessary portion of the metal conductive layer by dissolution and succeeding processes for preparation of the printed wiring board can be carried out in the same manner as conventional methods.
In a method of preparing an electrophotographic printed wiring board wherein a wiring pattern is formed on both surfaces of the insulating substrate, as disclosed in Japanese Provisional Patent Publication No. 209606/1998, at least a metal conductive layer and a photoconductive layer are provided in this order on both surfaces of an insulating substrate, the obtained board is mounted on a flat table of an exposing device, adjusted to a proper place (positioning), then charging is conducted. Then, exposure is carried out on one surface of a photoconductive layer to form an electrostatic latent image. After turning over the board, positioning and charging are conducted again, followed by exposure on the other surface of the photoconductive layer to form an electrostatic latent image. After that, toner developing treatment and succeeding processes are conducted in the same manner as the above, to prepare a printed wiring board with circuit patterns formed on both surfaces.
However, according to this method, there is a problem that when the board on the flat table is turned over after exposure, the surface having the electrostatic latent image initially formed by exposure and charging makes a mechanically strong contact with the flat table of the exposing device, and electric charge distribution of the contacted surface is disturbed. Similarly, even after the electrostatic latent images are formed on the both surfaces, there is a problem such that the electrostatic latent image is distorted by contacting with a conveying member for transport to the toner developing process. Since an image quality of the toner image is largely dependent on the electric charge distribution of the electrostatic latent image, distortion of the electrostatic latent image produced is reflected on the toner image as it is, resulting a problem of shortcircuiting, breakage or open circuit, etc.
In addition, this direct circuit drawing method by laser using electrophotographic method requires an exposure dose as low as 1 to 50 &mgr;J/cm
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, it is possible to use as laser a semiconductor laser which is less expensive and requires less power output. However, since its photoconductive layer has high photosensitivity for wavelength of 500 to 900 nm, there are problems that red laser diode sensor used for positioning of the printed wiring board during an image forming process causes an image fog at the photoconductive layer and that it is impossible to carry out the succeeding processes under visible light where the process are done efficiently from charging of the photoconductive layer, image-exposing, and until toner developing of the electrostatic latent image.
Further, a charge transfer material generally used for an organic electrophotographic material inherently has a function to transport a photo-carrier (a hole or an electron) generated from a charge generating material that has absorbed a visible light or infrared rays according to an electric field applied on the photoconductive layer. Generally, the charge g
Horiuchi Tamotsu
Hyodo Kenji
Irisawa Munetoshi
Miura Hidetoshi
Natsuka Masanori
Manelli Denison & Selter PLLC
Mitsubishi Paper Mills Limited
White, Jr. Paul E.
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