GB2193727A - Producing a printed circuit board - Google Patents

Abstract

A printed circuit board 3 having a desired wiring pattern is produced by a process which includes the step of depositing a photosensitive resist film on the surface of a copper plated laminated insulating plate by electro- deposition from a coating bath 9 comprising a water soluble or water dispersible light hardening plastics. During deposition the bath may be agitated by air from pipe 11. The electro-deposition bath 8 may be incorporated in a series of automatic processing tanks 12 having automatic transfer apparatus 13. The process is applicable to boards having throughholes and allows the entire surface to be plated without loss of material. <IMAGE>

Description

SPECIFICATION Printed circuit board FIELD OF THE INVENTION The present invention relates to a method of producing a print circuit board, and more particularly to that for producing a photosensitive resist film on a surface copper film of a copper plated laminated insulating plate for a print circuit board.

BACKGROUND OF THE INVENTION Conventionally, a method of producing a print circuit board described below is well used. That is, a photosensitive resist film is produced on a surface copper film of a copper plated laminated plate, and a development is conducted to the laminated plate to which a light exposure of a desired pattern is conducted, thereby obtaining a resist film pattern.

Thereafter, an etching is executed to the surface copper film with the resist film pattern as a mask, thereby obtaining a desired wiring pattern.

As a prior art method of producing a photosensitive resist film on a surface copper film of a copper plated laminated plate, there is a method of coating a liquid resist material by dipping, rollar coating, or an eccentric coating, or a method of laminating a film type photosensitive film which is also called a dry film resist (for example, liston film made by Dupon Corporation) with the use of an exclusive pasting machine.

Fig. 3 shows a construction of a general dry film resist. A protection film 2 is coated over the surface of a dry film 1.

Fig. 4 is a diagram for exemplifying the mechanism of pasting a dry film, in more detail, pasting a first and a second dry film la and 1b to the both surface of the copper plated laminated plate 3, respectively.

A first and a second protection film 2a and 2b are stripped off from a first and a second dry film 1a and 1b which are supplied from a first and a second dry film supply roller 4a and 4b, respectively. These protection films 2a and 2b are wound around a first and a second protection film winding roller 5a and 5b, respectively. Then, the first and the second dry film 1a and 1b obtained by the stripping off of the protection film 2a and 2b are pasted to the front and the rear surface of the copper plated laminated plate 3 which passes through between a first and a second heating and pressing roller 6a and 6b. Besides, the reference numeral 7a designates a guide roller for guiding the first dry film 1a.

The reference numeral 7b designates a guide roller for guiding the second dry film 1b and stripping off the second protection film 2b.

In this prior art method of producing a print circuit board a dry film which is produced separately from the copper plated laminated plate is pasted to the copper plated laminated plate as described above, and there arises loss of dry films in the width direction and the length direction thereof dependent on the relationship between the width of the dry film and the size of the copper plated laminated plate.

Furthermore, two operators are required because the side for throwing into the copper plated laminated plate and the side for receiving the copper plated laminated plate on which the dry film is pasted confront with each other. Although an automatic laminator can be used, this device is expensive. Furthermore, if there are flaws on the surface of the copper film, the dry film is not sufficiently coated over the flaws, thereby resulting in a breaking of a wire or a short circuiting at the pattern etching.

Furthermore, methods of producing a print circuit board having throughholes described below are also well used. That is, first of all, throughholes are apertured on the copper coated laminated plate, a plating (usually a copper plating) is executed thereto, plastics which are hardened by such as heating for embedding the throughholes is embedded therein, a photosensitive resist film pattern is produced on the surface copper film of the copper plated laminated plate similarly as described above, an etching is executed to the surface copper film with the resist pattern as a mask, and thereafter the plastics embedded in the throughhole is removed thereby to obtain a desired wiring pattern.Another method is that in which the throughholes apertured on the copper plated laminated plate are coated over by a photosensitive resist film, a pattern of photosensitive resist film is produced similarly as described above, and an etching is executed to the surface of the copper film with the resist film as a mask, whereby a desired wiring pattern is obtained.

Herein, a printing embedding or a roll coater method are used for embedding plastics into holes such as throughholes.

Fig. 5 shows the manner that the throughholes are embedded by the conventional roll coater method. The reference numeral 3 designates a copper plated laminated plate, the numerals 15 designate throughholes provided on the laminated plate 3, and the numeral 16 designates plastics to be embedded into the throughholes 15.

The plastics 16 is coated over the laminated plate 3 by a plating roller 14a and an auxiliary roller 14b of the roll coater, and at the same time it is pushed into the throughholes 15 of the laminated plate 3. The plastics 16 is dried to be hardened, and thereafter only the plastics at the surface of the laminated plate 3 is removed. Thus, the throughholes 15 are embedded, and thereafter a photosensitive resist film is produced on the surface of the copper film similarly as described above, and a desired wiring pattern is produced.However, in such a case where throughholes are provided on the copper plated laminated plate, there are disadvantages that a process of embedding the throughholes and that of drying the throughhole embedding plastics are required because the holes are previously embedded by plastics and a dry film separately produced from a laminated plate is pasted on the laminated plate.

SUMMARY OF THE INVENTION An object of the present invention is to provide an improved method of producing a print circuit board capable of producing a photosensitive resist film to be produced on an entire surface of the copper plated laminated plate without any loss of material.

A second object of the present invention is to provide an improved method of producing a a print circuit board which requires no expensive equipment and no extra man hands and capable of incorporated in an automatic processing line.

A third object of the present invention is to provide an improved method of producing a print circuit board which has only a simplified process and which is applicable to a copper plated laminated plate having throughholes.

Other objects and advantages of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific embodiment are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

According to the present invention, there is provided a method of producing a print circuit board having a desired wiring pattern which is produced with the use of a photosensitive resist film produced on a surface of a copper plated laminated insulating plate, which comprises: a process of precipitating plastics described later on the surface of said insulating plate by sinking said insulating plate in an electrodeposition coating bath including watersoluble or water-dispersible light hardening plastics as principal constituents by a DC current dissolution method, thereby producing a photosensitive resist film on the surface of said insulating plate.

l BRIEF DESCRIPTION OF THE DRA WINGS Figure 1 is a cross-sectional view for exemplifying a method of producing a print circuit board as an embodiment of the present invention; Figure 2 is a side view for exemplifying an application in which an electrodeposition coating bath of the present embodiment is incorporated in an automatic processing line; Figure 3 is a side view showing a construction of a conventional dry film resist; Figure 4 is a side view for exemplifying the mechanism for coating a dry film on a copper plated laminated plate; and Figure 5 is a cross-sectional view for exemplifying a process of the conventional roll coater method for embedding throughholes of a print circuit board.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 shows a method for producing a print circuit board according to an embodiment of the present invention. In Fig. 1, the reference numeral 8 designates an electrodeposition coating bath as an electrolyser. The reference numeral 9 designates electrodeposition paint contained in the bath 8 for sinking the copper plated laminated plate 3. This electrodeposition paint 9 includes water-soluble or waterdispersible light hardening plastics as a principal constituent. The reference numeral 10 designates a negative electrode consisting of stainless steel sank in the coating bath 8 confronting a copper plated laminated plate 3.

The reference numeral 11 designates an air blowing pipe for stiring the liquid.

The method of this embodiment will be described in detail below. When a DC voltage of about 200 V is applied to between the copper plated laminated plate 3 and the negative electrode 10, light hardening plastics which is charged minus with resolved or diversed in the electrodeposition paint 9 is electrodeposited on the surface of the copper plated laminated plate 3. The current value of this electrodeposition coating is reduced with the increase in the thickness of the plastic film, and when the thickness reaches a predetermined thickness, dehydration is conducted.

Thereafter, the copper plated laminated plate 3 is pulled up and the plastics is dried by heating, whereby a photosensitive resist film is obtained.

In this method, it is possible to obtain a uniform photosensitive resist film with no loss of material. It is also possible to automate the production of the photosensitive resist film easily, thereby resulting in an effective utilization of the factor space is enabled.

Even for a copper plated laminated plate having throughholes a uniform photosensitive resist film can be obtained because the throughholes are embedded by the plastics. In this case it is possible to remove the process of drying the plastics embedding the throughholes.

Fig. 2 shows an application in which the electrolyser of the above-described embodiment is incorporated in an automatic processing line. In Fig. 2 the electrodeposition coating bath 8 is incorporated in a series of automatic processing tanks 12. The reference numeral 13 designates an automatic transfer apparatus for transferring the copper plated laminated plate 3 to a predetermined position, that is, above the electrodiposition coating bath 8 at a predetermined timing.

Next, the electrodeposition paint used in the method of the present invention will be described. In the present invention it is possible to use anionic electrodeposition paint and cationic electrodeposition paint recited in the U.S.P. 3,954,587.

An example of anionic electrodeposition paint One comprising water soluble or water diversible light hardening composition including component selected from (1) to (5) described below including water soluble or water dispersible polymerized unsaturated resin having an acid value of 20 to 300, an unsaturation eqivalent of about 150 to about 3000, and a number-average molecular weight of larger than about 300 and non water soluble photopolymerization initiator such as benzoin as principal constituents.

(1) A component including polymerized unsaturated resin obtained by adding reaction product of a compound including a polymerized unsaturated bond and a hydroxyl group in a molecule and a diisocyanate series compound to high acid value acrylic resin including a hydroxyl group in a skeleton or a component co-using these and ethylenic unsaturated compound having more than one polymerized unsaturated resin in a molecule as principal constituents.

(2) A component including mixture of polymerized unsaturated resin obtained by adding a,fl-ethylenic unsaturated dibasic acids or their anhydride to unsaturated bonds in a fatty acid chain in an esterified product of epoxy resin having an epoxy group and unsaturated fatty acid, and an ethylenic unsaturated compound having more than one polymerized unsaturated bond in a molecule as principal constituents.

(3) A component including mixture of polymerized unsaturated resin comprising unsaturated fatty acid denatured high acid value alkyd resin and ethylenic unsaturated compound having more than one polymerized unsaturated bond in a molecule as principal constituents.

(4) A component including mixture of polymerized unsaturated resin comprising maleic oil and ethylenic unsaturated compound having more than one polymerized unsaturated bond in a molecule as principal constituents.

(5) A component including polymerized unsaturated resin obtained by adding a compound including a polymerized unsaturated bond and a glycidyl group in a molecule to a high acid value acrylic resin, or one co-using these and ethylenic unsaturated compound having more than one polymerized unsaturated bond in a molecule as principal constituents.

An example of cationic electrodeposition paint One comprising water soluble or water dispersible light hardening compound including water soluble or water dispersible polymirized unsaturated resin including an ethylenic unsaturated group and an amino group in a resin skeleton selected from (6) to (8) described below and non water soluble photopolymerization initiator as principal constituents.

(6) Resin obtained by adding ethylenic unsaturated group including isocyanate compound to a hydroxyl group of a compound which is obtained by adding primary or secondary amine to epoxy compound.

As the above-described epoxy compound, copolymerized resin obtained by copolymerizing vinyl monomer such as bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, aliphatic epoxy resin, nobolac type epoxy resin, styrene, methyl acrylate (methacrylate), 2-hydroxyethyl acrylate (methacrylate) and glycidyl group including unsaturated monomer such as glycidyl acrylate (methacrylate) can be used.

As the above-described amine, monoethyl amine, monobutyl amine, diethyl amine, dibutyl amine, monoethyl monoethanol amine, or diethanol amine can be used.

As ethylenic unsaturated group including isocyanate compound, compound obtained by adding hydroxyl group including unsaturated monomer such as 2-hydroxyethyl acrylate, 2hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, or 2-hydroxypropyl methacrylate to an isocyanate group of diisocyanate compound such as tolylene diisocyanate, isoboron diisocyanate, xylylene diisocyanate, or 1,6hexane diisocyanate, or isocyanic ethyl methacrylate can be used.

(7) Resin obtained by adding compound including an ethylenic unsaturated group and a carboxyl group such as acrylic acid to the remaining epoxy group therein in resin including an epoxy group obtained by reacting a portion of a epoxy group of epoxy resin with secondary amine, and tertiary amine.

(8) Resin obtained by adding the above-described chemical compound including ethylenic unsaturated group and the carboxyl group to a remaining epoxy group or adding the abovedescirbed ethylenic unsaturated group including isocyanate compound to a hydroxyl group of a compound which is obtained by adding diepoxy compound or multiepoxy compound to one which is obtained by adding primary amine to monoepoxy compound and executing a secondary amidation thereto such that the equivalent weight of the secondary amine and the epoxy group becomes larger than 1 : 2.

As the above-described monoepoxy compound, allyl glycidyl ether, phenyl glycidyl ether, ethylene oxide, propylene oxide, or butylene oxide can be used.

As the diepoxy compound or multiepoxy compound, bisphenol type epoxy resin, aliphatic series epoxy resin, or nobolac type epoxy resin can be used.

An example of the electrodeposition paint A mixture solution of methyl methacrylate of 40 weight portions, butyl acrylate of 40 weight portions, acrylic acid of 20 weight portions, and azobisisobutyronitrile of 2 weight portions is dropped into propyleneglycol monomethyl ether (hydrophilic solvent) of 90 weight portions which is held at 110 C in a nitrogen gas ambient with requiring three hours. After the drop, aging is conducted for one hour, and a mixture solution of azobisdimethylvaleronitrile of 1 weight portion and propyleneglycol monomethyl ether of 10 weight portions is dropped thereinto with requiring one hour, and thereafter aging is conducted for five hours, thereby obtaining high acid value acrylic resin solution (acid value 155).Next, glycidyl methacrylate of 24 weight portions, hydroquinone of 0.12 weight portions, and tetraethylammonium bromide of 0.6 weight portions are added to this solution with blowing air at a temperature of 1 100C for five hours to make them react with each other, thereby obtaining polymerized unsaturated resin solution having an acid value of about 50, an unsaturation equivalent of about 740, a number average moleculer weight of about 20,000. 0.6 equivalents of this polymerized unsaturated resin is neutralized by triethylamine, and thereafter acetylacetone of 6 weight portions and a-hydroxyisobutylphenone of 6 weight portions as photopolimerization initiator are added thereto, and water is added such that the solid component inclusion rate becomes 10 weight %, thereby obtaining electrodeposition paint salt of pH 7.0.

In the above-illustrated embodiment stainless steel is used for the negative electrode 10, but carbon or other conductive material can be used therefore. Furthermore in the embodiment, copper plated laminated plate 3 is used as a positive electrode, but the copper plated laminated plate can be made another negative electrode by changing the polarities of the applied voltages and using electrodeposition paint appropriate thereto.

As evident from the foregoing, according to the present invention, a photosensitive resist film is produced on a surface of a copper plated laminated plate by electrodeposition coating, thereby enabling of producing a uniform photosensitive resist film without any loss of material and of automating the process quite easy. Also in a case where the copper plated laminated plate has throughholes, a uniform photosensitive resist film can be produced with embedding throughholes, thereby enabling of removing the process of embedding the holes by hole embedding plastics.

Claims (5)

1. A method of producing a print circuit board having a desired wiring pattern which is produced with the use of a photosensitive resist film produced on a surface of a copper plated laminated insulating plate, which comprises: a process of precipitating plastics described later on the surface of said insulating plate by sinking said insulating plate in an electrodeposition coating bath including water-soluble or water-dispersible light hardening plastics as principal constituents by a DC current dissolution method, thereby producing a photosensitive resist film on the surface of said insulating plate.

2. A method of producing a print circuit board as defined in Claim 1, wherein said copper plated laminated insulating plate has throughholes.

3. A method of producing a print circuit board as defined in Claim 1, wherein the production of said photosensitive resist film is conducted as one step of an automatic processing in said electrodeposition coating bath which is incorporated in a group of automatic processing tanks.

4. A method of producing a print circuit board substantially as herein described with reference to Fig. 1 or Fig. 2 of the accompanying drawings.

5. A circuit board when produced by the method of any preceding claim.