Radiation imagery chemistry: process – composition – or product th – Registration or layout process other than color proofing
Reexamination Certificate
1999-12-03
2002-09-03
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Registration or layout process other than color proofing
C430S054000, C430S103000, C430S131000, C355S117000, C347S238000, C399S402000, C399S031000
Reexamination Certificate
active
06444379
ABSTRACT:
TECHNICAL FIELD
This invention relates to a process for making a printed wiring board which comprises preparing a printed wiring board utilizing an electrophotographic method using a material to be developed having a metal conductive layer and a photoconductive layer in this order on at least one surface of an insulating substrate and a preparation device thereof.
BACKGROUND ART
A method for making a printed wiring board is roughly classified into two methods of the subtractive method and the additive method. The subtractive method is a method of forming a resist layer on a laminated board to which a conductive layer such as copper, etc. is provided on an insulating substrate, and removing the conductive layer not covered by the resist layer by etching. The additive method is a method of forming a conductive layer only at a wiring pattern portion on an insulating substrate. In addition the above, it has been proposed a wiring transfer method in which a resist image is provided by a plate resist on a conductive substrate, metal plating is applied to the conductive substrate other than the resist image to form a metal wiring pattern, and then, the resist image is removed, only the metal wiring pattern is transferred to the insulating material.
Moreover, according to the recent trend of making light, thin, short and compact, or variety of electronic devices, in a printed wiring board, it is required to make it with high density and within a short period of time. Also, application of an electrophotographic material as a resist material has been investigated. Heretofore, in an electrophotographic material to be used in an electronic photography lithographic printing plate, etc., drawing an image at an infrared region has been already carried out, and it has been practically carried out that an image data are directly sent from a computer by a scanning exposure of a laser beam without using a photomask to form an image with a high density.
Also, not only the above-mentioned scanning exposure, but also a light-sensitive electrophotographic printing material is high sensitivity in a surface exposure using a photomask, so that it is not necessary to use the conventionally used expensive ultra-high pressure or high-pressure mercury lamp for printing a resist or an expensive UV exposure device such as a metal halide lamp, etc., and there is a merit of capable of using a simple and easy, and cheap visible light exposure device.
Also, in a photopolymer which is the conventional resist, an exposed portion of a photopolymer layer provided with a certain film thickness is cured or solubilized to form a wiring pattern. However, in this case, if light to be irradiated through a photomask is scattered light, light is spread in the photopolymer-layer, and in this case, a line width of an origin of the photomask cannot be reproduced accurately. Also, when dry resist film is used, resolution becomes worse due to spread of light still more in a scattered light since a polyester film exists between the photomask and the resist. This phenomenon becomes more significant when a wiring pattern becomes finer, and thus, light to be irradiated is required to be parallel light. As an exposure device therefor, there are a device in which light is tried to be parallel light by elongating the distance between a light source and an exposure surface, or a device in which a parabolic mirror is provided at the back surface of a light source and a light buffle is provided at an exposure surface side of the light source so that only the parallel light reflected from the back surface is irradiated to the exposure surface or the like. In either of the method, not only the device becomes complicated and a large-sized, but also utilization factor of light is lowered. On the other hand, as is clear from the explanation mentioned below, in the resist using the electrophotographic method, presence or absence of electric charge on the surface of a photoconductive layer contributes to resolution so that it is not so required to consider lowering in resolution by spreading light in the photoconductive layer. Accordingly, as an exposure device, that using a scattered light can be used and there is a merit of constituting an inexpensive and a small sized exposure system.
In the preparation method of a resist layer utilizing an electrophotographic method, a photoconductive layer is provided on a metal conductive layer of an insulating substrate on which a metal conductive layer is provided on the insulating substrate, and after uniformly charging the surface of the photoconductive layer in a dark place, an electrostatic latent image corresponding to a wiring pattern is formed by exposure. The electrostatic latent image is subjected to toner developing treatment and fixing, and by using the toner image as a resist, the photoconductive layer of the toner image unformed portion is dissolved and removed to prepare a resist image of a metal conductive layer comprising the toner image and the photoconductive layer. Dissolution and removal of the unnecessary portion of the metal conductive layer and the subsequent preparation step of the printed wiring board can be carried out in the same manner as in the conventional procedure.
A method of toner developing treatment can be roughly classified to a positive development method using a toner having a charge in an opposite polarity to an electrostatic latent image by exposing a non-image portion, and a reverse development method using a toner having a charge with the same polarity as that of an electrostatic latent image by exposing an image portion.
The preparation method of a printed wiring board by the electrophotographic method using the positive development method has been proposed in Japanese Patent Publication No. 35518/1989, and the preparation method of a printed wiring board by the electrophotographic method using the reverse development method has been proposed in Japanese Provisional Patent Publication No. 112627/1994.
At present, in a progress of high density preparation of a printed wiring board, a printed wiring board having a lot of conductive fine pores-called through holes provided to respective substrate with a multi-layered structure has been prepared. In this case, circuits formed on the both surfaces of the substrate are connected by the through holes. Thus, not only precision of the circuit itself formed on the substrate but also precision of formed positions of the circuits on the both surfaces relative to the through holes as a standard, i.e., positional precision prior to formation of the resist film are required.
Also, at the time of forming a wiring pattern, it is important to completely protect the metal conductive layer in the through hole by using a resist. That is, in the electrophotographic method, in the toner developing treatment step, it is necessary to form a toner image throughout the whole surfaces in the through holes.
When the electrophotographic method by the reverse developing method is used, procedure is carried out that the surface of a photoconductive layer is charged in a dark place and forming an electrostatic latent image is formed by vanishing a charge at the exposed portion by exposing an image portion, and then, fine toner particles having the same polarity as those of the charged electric charge are adhered to the exposed portion, i.e., to a portion at which the electric charge is vanished. At this time, a conductive member called a developing electrode is provided opposed to the surface of an electrostatic latent image, and a bias voltage with the same polarity is applied to the electrode whereby adhesion of the toner particles to the exposed portion is promoted and a toner image with a high image quality can be obtained.
A toner attached amount at the toner developing treatment is markedly dependent on a toner concentration, a developing time as well as the state of an electric field at around the exposed portion of a material to be developed. That is, as the electric field is stronger, adhesion of the toner can be carried out rapidly,
Hyodo Kenji
Kaneda Yasuo
Takase Masanori
Chacko-Davis Daborah
Huff Mark F.
Manelli Denison & Selter PLLC
Mitsubishi Paper Mills Limited
White, Jr. Paul E.
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