GB2193730A

GB2193730A - Production of printed circuit boards

Info

Publication number: GB2193730A
Application number: GB08715744A
Authority: GB
Inventors: Toshiaki Ishimaru; Nobuyuki Hayashi; Haruo Akahoshi; Kanji Murakami; Motoyo Wajima
Original assignee: Hitachi Chemical Co Ltd; Hitachi Ltd
Current assignee: Hitachi Ltd; Showa Denko Materials Co ltd
Priority date: 1986-07-11
Filing date: 1987-07-03
Publication date: 1988-02-17
Anticipated expiration: 2007-07-03
Also published as: GB2193730B; JPH0344432B2; KR900003848B1; JPS6318692A; DE3722749C2; KR880002416A; GB8715744D0; DE3722749A1

Description

1 GB2193730A 1

SPECIFICATION

Production of printed circuit boards The present invention relates to a process for producing a printed circuit board. More particu- 5 larly, the present invention relates to a process for producing a printed circuit board wherein a circuit pattern is formed on a substrate by means of electroless plating using a photoresist.

Printed circuit boards have been mostly produced according to a process wherein a copper- clad laminated board is subjected to etching to remove the copper of the portions other than those to later become a printed circuit (this process is called an etched foil process). Meanwhile, 10 a process wherein no copper-clad laminated board is used and an insulating laminated board is subjected to electroless copper plating to directly form a circuit pattern thereon (this process is called an additive process) is drawing attention recently because the process involves no disad vantage of removing unnecessary copper portions and gives a low production cost. In the additive process, however, since the copper precipitation rate in electroless copper plating is 15 very slow, the insulating laminated board must be immersed in a plating bath of high alkalinity (ordinarily of pH 11 to 13.5) at high temperatures (ordinarily 600 to 80'C) for a long time (ordinarily 5 to 60 hours). Hence, there becomes necessary a resist for electroless plating which can withstand severe conditions such as mentioned above.

Such a resist has been formed by screen-printing an ink composed mainly of an epoxy resin 20 and a curing agent on a substrate and heat-curing and printed ink. However, since the dimen sional precision of printed lines has a limitation, the production of a printed circuit board having a high density pattern has been difficult according to the additive process. Photoresists are suitable in formation of a high density pattern, and photoresists to be used in the additive process are proposed in, for example, Japanese Patent Application Kokai (Laid-Open) Nos. 25 43468/1975, 770/1979, 199341/1983, 12434/1984, 56344/1986 and 101532/1985. How ever, the photoresists hitherto proposed or already put into market have had a drawback in that when such a photoresist is used in the photoadditive process to mass- produce a printed circuit board, part of the photoresist composition dissolves slowly in the electroless plating solution, gradually contaminating the plating solution and reducing the properties of the copper to be 30 precipitated by means of electroless plating. This reduction in copper properties is detrimental to the reliability of the printed circuit board formed and, accordingly, the plating soluble once used cannot be reused making mass production difficult.

OBJECT OF THE INVENTION 35 An object of the present invention is to provide a process for producing a printed circuit board of high precision having a copper plating of good properties, by means of the photoaddi tive method. Another object of the present invention is to provide a process for mass-producing such a printed circuit board.

40 CONSTITUTION OF THE INVENTION The present invention relates to a process for producing a printed circuit board, which comprises:

(1) a step of forming, on the surface of a substrate (on the required portions of which, copper is to be precipitated by means of electroless plating), a layer of a photosensitive resin 45 composition containi ' ng (A) 100 parts by weight of a photopolymerizable mixed component comprising (a) 5 to 99% by weight of at least one kind of unsaturated compound having at least one terminal methacryloyl group and no nitrogen atom bonding directly with at least one hydrogen atom within the moleculae and (b) 95 to 1 % by weight of at least one kind of unsaturated compound having at least one terminal acryloyl group and no nitrogen atom bonding 50 directly with at least one hydrogen atom within the molecule, (B) 0 to 400 parts by weight of a linear high molecular compound having no nitrogen atom bonding directly with at least one hydrogen atom within the molecule, and (C) 0.5 to 20 parts by weight of a sensitizing agent or/(and) a sensitizing system, both capable of forming a free radical upon irradiation with an actinic ray, 55 (2) a step of subjecting the layer of the photosensitive resin composition to irradiation with an imagerial actinic ray and then to development to form a negative pattern of the photosensi tive resin composition on the surface of the substrate, and (3) a step of subjecting the substrate to electroless copper plating using the negative pattern of the photosensitive resin composition as a plating resist to form a circuit pattern on the 60 surface of the substrate.

The pro cess for producing a printed circuit board according to the present invention is explained in detail below.

The process for producing a printed circuit board according to the present invention comprises - a step of forming a layer of photosensitive resin composition on the surface of a substrate, on 65 2 GB2193730A 2 the required portions of which copper is to be precipitated by means of electroless plating.

As the substrate, there can be used, for example, laminated boards such at a paper-phenolic resin laminated board and a glass-epoxy resin laminated board, as well as metal core-containing substrates such as an iro-porcelain enamel substrate and a substrate consisting of a metal sheet (e.g. an aluminum sheet) and epoxy resin insulating layers formed on the both surfaces of said 5 metal sheet. It is possible that these substrates be subjected to perforation and then immersed in a solution containing a plating catalyst to allow the plating catalyst to adhere to the inner walls of the through-holes formed. As such a plating catalyst solution, there can be used, for example' HS-10113, a sensitizer manufactured by Hitachi Chemical Co., Ltd. Preferably, an adhe- sive layer is formed on the surface of the substrate in order to make easier, for example, 10 adhesion of the plating catalyst or of the copper to be precipitated later by means of electroless plating.

As the adhesive, there can be used those known as an adhesive for the additive method, such as a phenol-modified nitrile rubber adhesive and the like. It is possible that the adhesive contains a compound which acts as a plating catalyst. For easier adhesion of the plating catalyst or of 15 the copper to be precipitated later by means of electroless plating, it is preferable to roughen the surface of the adhesive layer before said surface is subjected to an electroless plating treatment. This surface roughening can be conducted by immersing the substrate having the adhesive layer in, for example, an acidic solution containing sodium bichromate, chromic acid or the like. As well known, the surface roughening step can be before formation of a layer of a 20 photosensitive resin composition which is described later or after formation of a resist pattern, as long as the roughening step is before a step of the electroless copper plating.

As the substrate, there can also be used copper-clad substrates prepared by attaching a copper foil to the both surfaces of, for example, a laminate board (e.g. a paper-phenolic resin laminated board, a glass-epoxy resin laminated board) or of a metal core- containing substrate 25 [e.g. an iron-porcelain enamel substrate, a substrate consisting of a metal sheet (e.g. an aluminum sheet) and epoxy resin insulating layers formed on the both surfaces of said metal sheet]. It is possible that these substrates by subjected to perforation and then immersed in a solution containing a plating catalyst to allow the plating catalyst to adhere to the inner walls of the through-holes formed. It is also possible that the surface of the copper foil attached be 30 subjected to etching with an aqueous acidic solution containing an oxidizing agent such as cupric chloride or the like, in order to improve adhesion between the copper and a plating resist to be formed thereon later. When a copper-clad substrate is used, a negative pattern of a photosensi tive resin composition which is described later is formed as a plating resist on the copper foil of the substrate; a circuit pattern is formed on the portions of the substrate other than the negative 35 pattern by means of electroless copper plating; the plating resist is removed and the copper foil between the lines of the circuit pattern is removed by etching; thereby, a printed circuit board can be obtained. Alternatively, the copper foil of the substrate is subjected to etching to form a circuit pattern; then, a negative pattern of a photosensitive resin composition which is described below is formed on the portions of the board other than the through-holes and the land 40 portions; the through-holes and the land portions having no negative pattern are subjected to electroless copper plating to form a final circuit pattern; thereby, a printed circuit board can be obtained.

The photosensitive resin composition used in the present invention comprises, as an essential component, a photopolymerizable mixed component comprising (a) 5 to 99% by weight of at 45 least one kind of unsaturated compound having at least one terminal methacryloyl group and no nitrogen atom bondirig directly with at least one hydrogen atom within the molecule and (b) 95 to 1% by weight of at least one kind of unsaturated compound having at least one terminal acryloyl group and no nitrogen atom bonding directly with at least one hydrogen atom within the molecule. As the unsaturated compound (a) having at least one terminal methacryloyl group and 50 no nitrogen atom bonding directly with at least one hydrogen atom within the molecule, there can be mentioned, for example, methacrylic acid esters of polyalcohols such as trimethylolpro pane, trimethylolethane, pentaerythritol, dipentaerythritol, 1,6- hexanediol, propylene glycol, tetrae thylene glycol, dibromoneopentyl glycol and the like; dicyclopentenyloxyethyl methacrylate; tet rahydrofurfuryl methacrylate; benzyl methacrylate; and so forth. 55 As the unsaturated compound (b) having at least one terminal acryloyl group and no nitrogen atom bonding directly with at least one hydrogen atom within the molecule, there can be mentioned, for example, acrylic acid esters of polyalcohols such as trimethylolpropane, trimethy lolethane, petaerythritol, dipentaerythritol, 1,6-hexanediol, propylene glycol, tetaethylene glycol, dibromonoeopentyl glycol and the like; dicyclopentenyloxyethyl acrylate; tetrahydrofurfuryl acry- 60 late; benzyl acrylate; and so forth.

The in-depth investigation by the present inventors revealed that the presence of at least one nitrogen atom in the unsaturated compounds (a) and (b) reduces in many cases the chemical and physical properties of the copper precipitated and the presence of particularly a group containing at least nitrogen atom bonding directly with at least one hydrogen atom, such as a primary or 65 3 GB2193730A 3 secondary amino group, an amido group, an urethane group or the like significantly reduces the chemical and physical properties of the copper precipitated. Further, the presence of a group containing at least oxygen atom bonding directly with a hydrogen atom, such as a hydroxyl group, a carboxyl group or the like is not desirable, either, in many cases. Particularly preferable examples of the unsaturated compound (a) include trimethylolpropane trimethacrylate, trimethylo- 5 [ethane trimethacrylate, pentaerythritol tetramethacrylate, pentaerythritol hexamethacrylate and 1,6-hexanediol dimethacrylate. It was also revealed that although the reason is not clear, the contamination of the plating bath is reduced and the properties of the copper precipitated ore improved remarkably by using, as the photopolymerizable component, its mixture with a metha- crylate type unsaturated compound or a methacrylate type unsaturated compound alone in 10 comparison with the use of an acrylate type unsaturated compound alone.

In amounts of the unsaturated compound (a) and the unsaturated compound (b) in the photo- - polymerizable component are determined to be 5 to 99% by weight and 95 to 1% by weight, respectively, in view of the photosensitivity of the photosensitive resin composition and the chemical and physical properties of the copper precipitated by electroless plating. Preferably, the 15 amount of the compound (a) is 20 to 95% by weight and the amount of the compound (b) is to 5% by weight.

The photosensitive resin composition used in the present invention comprises 0 to 400 parts by weight, based on'100 parts by weight of the total of the unsaturated compounds (a) and (b), of a linear high molecular compound having no nitrogen atom bonding directly with at least one 20 hydrogen atom within the molecule. When the amount of the linear high molecular compound exceeds 400 parts by weight, the photosensitive resin composition has a reduced photosensitiv ity and has no practical applicability. As the linear high molecular compound having no nitrogen atom bonding directly with at least one hydrogen atom, there can be mentioned, for example, vinyl type high molecular compounds obtained by polymerizing or copolymerizing vinyl type 25 monomers such as methyl methacrylate, ethyl acrylate, tetrahydrofurfuryl methacrylate, metha crylic acid, 2-hydroxyethyl methacrylate, benzyl methacrylate, styrene, vinyltoluene, vinyl acetate, butadiene and the like, as well as polyester type high molecular compounds obtained by con densing a dihydric alcohol (e.g. ethylene glycol, dipropylene glycol, 1,6- hexanediol etc.,) and a dicarboxylic acid (e.g. maleic acid and phthalic acid etc.,). Use of a linear high molecular 30 compound having at least one tetrahydrofurfuryl group as the side chain is preferable because it enhances the properties of the copper precipitated.

When the layer of the photosensitive resin composition is formed on a substrate by attaching a photosensitive element, as described later, the amount of the linear high molecular compound having no nitrogen atom bonding directly with at least one hydrogen atom within the molecule is 35 preferred to be 20 to 400 parts by weight based on 100 parts by weight of the photopolymeri zab(e component (A), from the standpoint of film formability.

The photosensitive resin composition used in the present invention comprises 0.5 to 20 parts by weight, based on 100 parts by weight of the photopolymerizable component (A), of a sensitizing agent or (and) a sensitizing system, both capable of forming a free radical upon 40 irradiation with an actinic ray. When the amount of the sensitizing agent or (and) the sensitizing system is less than 0.5 part by weight, the photosensitive resin composition has a low photo sensitivity When the amount exceeds 20 parts by weight, the negative pattern formed has a poor shape.

As the sensitizing agent, there can be used, for example, substituted or unsubstituted polynu- 45 clear quinones such as 2-ethylanthraquinone, 2-t-butylanthraquinone, octamethylantrhaquinone, 1,2-benzanthraquinone, 2,3-diphenylanthraquinone and the like; ketoaldonyl compounds such as diacetyl, benzyl and the like; alpha-ketoaldonyl alcohols such as benzoin, pivalone and the like; ethers; alpha-hydrocarbon-substituted aromatic acyloins such as alpha- phenylbenzoin, alpha-alpha diethoxyacetophenor!e and the like; and aromatic ketones such as benzophenone, 4,4'-disdialky50 laminobenzophenone and the like. These compounds can be used alone or in combination. As the sensitizing systern, there can be used, for example, a combination of (a) a dimer of a 2,4,5 triarylimidazole and (b) 2-mercaptobenzoquinazole, leuco crystal violet or tris(4-diethylamino-2methylphenyl) methane. Also, it is possible to add to one of the above mentioned sensitizing agents such a substance as has no photoinitiatability by itself but can enhance the photoinitiata- 55 bility of the sensitizing agent. For example, a tertiary amine such as triethanolamine or the like can be added to benzophenone to improve the photoinitiatability of benzophenone.

The photosensitive resin composition used in the present invention can further comprise other secondary components. The secondary components include a thermal polymerization inhibitor, a dye, a pigment, a coatability improver, etc. The selection of the secondary components is made 60 under the same consideration as in ordinary photosensitive resin compositions.

The process for producing a printed circuit board according to the present invention necessa- rily comprises a step of forming a layer of the above explained photosensitive resin composition on the surface of a substrate, on the required portions of which copper is to be precipitated by means of electroless plating. This step can be conducted according to an ordinary method. It is 65 4 GB2193730A 4 conducted, for example, by uniformly dissolving or dispersing a photosensitive resin composition of the present invention in a solvent such as methyl ethyl ketone, toluene, methylene chloride or the like, coating the resulting solution on the surface of an insulating substrate on which copper is to be precipitated by means of electroless plating, according to the dip coating method, the few coating method or the like, and drying the coated substrate to remove the solvent. Alterna- 5 tively, the above step can be conducted without coating a solution of a photosensitive resin composition directly on a substrate, that is, by coating the solution on a base film according to a known method such as the knife coating method, the roll coating method or the like, drying the coated film to prepare a photosensitive element consisting of a base film and a layer of a photosensitive resin composition formed thereon, and then attaching the photosensitive element 10 to the surface of an insulating substrate on which copper is to be precipitated by means of electroless plating, under heating and pressure according to a known method. As the base film there can be used known films such as a polyester film a polypropylene film, a polyimide film a polystyrene film and the like. Use of a photosensitive element in forming a layer of a photosensi tive resin composition is preferred because it can provide a uniform layer of a photosensitive 15 resin composition and moreover enables use of an adhesive of low solvent resistance.

The process for providing a printed circuit board according to the present invention necessarily comprises a step of subjecting the layer of the photosensitive resin composition to irradiation with an imagerial actinic ray and then to development to form a negative pattern of the photosensitive resin composition on the surface of the substrate, on the required portions of 20 which copper is to be precipitated by means of electroless plating. The irradiation wih an imagerial actinic ray can be conducted by imagerially applying a light emitted from a light source such as an ultrahigh-pressure mercury-vapor lamp, a high-pressure mercuryvapor lamp or the like through a negative mask. Alternatively, it can be conducted by imagerially scanning a laser beam or the like on very small cross-sections. The development can be conducted, for example, 25 by immersing the substrate having the layer of the photosensitive resin composition which has been imagerially irradiated with an actinic ray, in a developing solution such as 1,1,1-trichloroe thane, or by spraying such a developing solution on the substrate.

Reirradiation of the substrate after development with an actinic ray is preferred because it makes the photocure of the photosensitive resin composition more complete, improves its 30 plating resistance and makes the contamination of a plating bath less. The reirradiation with an actinic ray can be conducted to the entire surface of the substrate using a light source such as an ultrahigh-pressure mercury-vapor lamp, a high-pressure mercury-vapor lamp or the like.

The process for producing a printed circuit board according to the present invention necessa- rily comprises a step of subjecting the substrate to electroless copper plating using the negative 35 pattern of the photosensitive resin composition as a plating resist to form a circuit pattern on the surface of the substrate. As the electroless plating solution, there can be used a plating solution containing a copper salt, a complexing agent, a reducing agent and a pH-adjusting agent.

As the copper salt, there can be used, for example, a copper sulfate, a copper nitrate, a 40 copper formate and a cupric chloride. As the complexing agent, there can be used, for example, ethylenediaminetetraacetic acid, N-hydroxyethylethylenediaminetriacetic acid, N,N,N',N'-tetrakis-2 hydroxypropyleihylenediamine and a Rochelle salt. As the reducing agent, formalin is preferred.

As the pH-adjusting agent, an alkali hydroxide such as sodium hydroxide, potassium hydroxide or the like is used ordinarily. In some cases, various other additives are added to the plating 45 solution to increase its stability or to improve the properties of the copper precipitated. In view of the stability of the plating solution and the properties of the copper precipitated, the condi tions of the plating solution are preferred to be such that the plating solution has a copper concentration of 1 to 15 g/l, a pH of 10 to 13.5 and a temperature of 50" to 90'C. In conducting electroless copper plating, adhesion of catalyst and/or activation is naturally con- 50 ducted as necessary.

After the formation of a circuit pattern by electroless plating, the negative pattern of the photosensitive resin composition used as a plating resist can be peeled off or removed, or can be left as it is as a permanent resist.

After the formation of a circuit pattern, the entire surface of the circuit pattern or its required 55 surface portions can- be coated with solder using, for example, a solder leveler or can be subjected to gold plating, tin plating, etc. to protect the copper surface from oxidation and, when that part becomes an electrical connecti6n part, to reduce the contact resistance. After the copper surface has been covered with solder, gold, tin or the like or without applying any treatment to the copper surface, a solder mask can be formed on the required portions of the 60 substrate. The solder mask can also be utilized as a resist for covering only the required portions of the circuit pattern with solder or the like. The solder mask can be formed by printing an epoxy resin-based ink according to the screen printing method and then curing it, or a solder mask of high precision can be formed according to the photographic method. The thus produced printed circuit board can be used in various applications according to known methods. For - GB2193730A 5 example, it can be utilized by fixing electronics components thereto by soldering. Also, the printed circuit board after electroless copper plating can be used as an intermediate layer board for multi-layered printed circuit boards.

WORKING EXAMPLES 5 The present invention is specifically explained below by way of Examples. But the present invention is in no way restricted by these Examples. Parts in the Examples and Comparative Examples refer to parts by weight.

Example 1 10

Trimethylolpropane trimethacrylate 46 parts Trimethylolpropane triacrylate 4 parts Methyl methacrylate-tetrahydrofurfuryl methacrylate (80/20 by weight ratio) copolymer 50 parts 15 Benzophenone 3 parts 4,4-Bis(diethylamino)benzophenone 0.1 part Victoria Pure Blue 0.01 part Methyl ethyl ketone 100 parts 20 Using an apparatus shown in Fig. 1, a photosensitive resin composition solution 10 having the above formulation was uniformly coated on a polyethylene terephthalate film 16 having a thick ness of 25 um. The coated film was dried for about 10 minutes in a hot air convection type drier 11 to 80 to 100'C. The photosensitive resin composition layer after drying had a thick ness of about 35 um. Onto the photosensitive resin composition layer thus formed, there was 25 further attached, as a cover film, a polyethylene film 17 having a thickness of about 25 um, in a manner as shown in Fig. 1, to obtain a photosensitive element.

In Fig. 1, 5 is a delivery roll of a polyethylene terephthalate film; 6, 7 and 8 are rolls; 9 is a knife; 12 is a delivery roll of a polyethylene film; 13 and 14 are foils; and 15 is a wind-up roll of a photosensitive element. 30 Separately, an adhesive (NO. 777, manufactured by ACI Japan K.K.) composed mainly of a phenolic resin modified with an acrylonitrile-butadiene rubber was coated on the both surfaces of a paper phenolic laminated board (LP-461F manufactured by Hitachi Chemical Co., Ltd.) having a thickness of 1.6 mm. The coated board was heated at 160'C for 110 minutes to cure the adhesive, whereby a laminated board having an adhesive layer of about 30 um in thickness was 35 obtained. Then, holes were made with a drill at required places of the board, after which the board was immersed in a surface-roughening solution containing chromic acid anhydride and sulfuric acid to roughen the surface of the adhesive layer. Subsequently, the board was im mersed for 10 minutes in an aqueous acidic solution containing a sensitizing agent (HS 101B manufactured by Hitachi Chemical Co., Ltd.) as a catalyst for chemical plating, was water- 40 washed, was treated with 3.6% (by wt) dilute hydrochloric acid for 5 minutes, was water washed, and was dried at 120'C for 20 minutes. The resulting board was cut into a size of 16 cm x 10 cm to obtain test substrates each of 16 cm x 10 cm.

To the both surfaces of these 30 test substrates was attached the photosensitive element obtained previously, according to an ordinary method. A light emitted from an ultrahigh-pressure 45 mercury-vapor lamp was applied in an amount of 400 MJ/CM2 to each of the resulting sub strates through a test negative mask shown in Fig. 2. In Fig. 2, 21 is the non-transparent portions of the negative mask; 22 is the transparent portions of the negative mask; and the unit of the numerical values is mm. Then, each substrate was heated at 80C for 5 minutes; the substrate was allowed to stand at normal temperature for 20 minutes; the polyester film as a 50 base film was peeled off; the resulting substrate was subjected to development by spraying 1,1,1-trichloroethane; and the substrate was drid at 800C for 10 minutes. Subsequently, an ultraviolet light emitted from a high-pressure mercury-vapor lamp was applied in an amount of 3 J/CM2 to the entire surface of the test substrate. Thus, there were prepared 30 test substrates having a negative pattern of a photosensitive resin composition. 55 These substrates were then immersed in a chemical copper plating solution having a formula- tion shown below, at 70'C for 12 hours to conduct electroless copper plating, whereby copper was precipitated at a thickness of about 30 um on the surface portions of each substrate other than the negative pattern. Simultaneously, a sensitized stainless steel sheet of 16 cm x 10 cm prepared by polishing a stainless steel sheet of the same size with a No. 500 polishing paper 60 and then subjecting the polished stainless steel sheet to a sensitization treatment with a com mercially available catalyst solution (HS 101B manufactured by Hitachi Chemcial Co., Ltd.) was also subjected to electroless copper plating. After the plating, the copper foil formed by the plating was mildly peeled off the stainless steel sheet and cut into a width of 1 cm to obtain 6 test pieces for tensile test. 65 6 GB2193730A 6 Formulation of chemical copper plating solution Copper sulfate pentahydrate 10 g/I Ethylenediaminetetraacetic acid 30 g/I 37% formalin 3 MI/I 5 pH (adjusted by sodium hydroxide) 12.5 Polyethylene glycol (m.w.=600) 20 MI/I 2,2'-Dipyridyl 30 mg/I All the 30 test substrates had a copper plating pattern reproducing the pattern of the negative 10 mask at a high precision. The copper foil formed on the stainless steel sheet was subjected to a tensile test at a tensile rate of 2 mm/min and at a chuck-to-chuck distance of 50 mm using an autograph, DSS-5000 manufactured by Shimadzu Corp., to measure the mechanical properties of the copper. It has good mechanical properties at an elongation of 9.2% and a bending frequency of 6 times. 15 Example 2 The same procedure as in Example 1 was conducted except that 25 parts of

trimethylolpro- pane trimethacrylate and 25 parts of trimethylol propane triacrylate were used in place of 46 parts of trimethylolpropane trimethacrylate and 4 parts of trimethylol propane triacrylate. A copper plating pattern of high precision was obtained. The copper has good mechanical properties at an elongation of 7.5% and a bending frequency of 5 times.

Example 3

The same procedure as in Example 1 was conducted except that 20 parts of trimethylolpro- 25 pane trimethacrylate, 10 parts of 2,2-bis(4-methacryloxydiethoxyphenyl) propane and 20 parts of KAYARADO R-604 (an acrylate monomer manufactured by NIPPON KAYAKU CO., LTD.) were used in place of 46 parts of trimethylolpropane trimethacrylate and 4 parts of trimethylolpropane triacrylate. A copper plating pattern of high precision was obtained. The copper had good mechanical properties at an elongation of 10.1% and a bending frequency of 6 times. 30 Example 4

The same procedure as in Example 1 was conducted except that 30 parts of dipentaerythritol hexamethwrylate, 10 parts of tetrahydrofurfuryl methacrylate and 10 parts of trimethylolethane triacrylate were used in place of 46 parts of trimethylolpropane trimethacrylate and 4 parts of 35 trimethylolpropane triacrylate. A copper plating pattern of high precision was obtained. The copper had good mechanical properties at an elongation of 9.5% and a bending frequency of 6 times.

Example 5 40

TrimethylOlpropane trimethacrylate 20 parts 2,2'bis(4-methacryloxydiethoxyphenyl)propane 5 parts Trimethylolpropane triacrylate 20 parts Methyl methacrylate-styrene-butadiene (65/24/11 by weight ratio) copolymer 55 parts 45 Benzophenone 3 parts 4,4'-bis(diethylamine)benzophenone 0.1 part aF Victoria Pure Blue 0.01 part Toluene 50 parts Methyl ethyl ketone 50 parts 50 The same procedure as in Example 1 was conducted except that a photosensitive resin composition solution having the above formulation was used. A copper plating pattern of high precision was obtained. The copper had good mechanical properties at an elongation of 8.7% and a bending frequqncy of 6 times. 55 Example 6

The same procedure as in Example 5 was conducted except that 55 parts of a methyl methacrylatetetrahydrofurfuryl methacrylate-methacrylic acid-2hydroxyethyl methacrylate (82/15/1/2 by weight ratio) copolymer was used in place of 55 parts of the me1hyl methacry- 60 late-styrene-butadiene copolymer. A copper plating pattern of high precision was obtained. The copper had good mechanical properties at an elongation of 8.2% and a bending frequency of 6 times.

Comparative Example 1 65 7 GB2193730A 7 The same procedure as in Example 1 was conducted except that 50 parts of trimethylolpro- pane triacrylate was used in place of 46 parts of trimethylolpropane trimethacryla ' te and 4 parts of trimethylolpropane triacrylate. The copper formed by means of electroless plating did not have good mechanical properties at an elongation of 3.2% and a bending frequency of 3 times.

5 Comparative Example 2 The same procedure as in Example 1 was conducted except that 50 parts of urethane diacrylate obtained by reacting 1 mole of isophorone diisocyanate with 2 mole of 2-hydroxyethyl acrylate was used in place of 46 parts of trimethylolpropane trimethacrylate and 4 parts of trimethylolpropane triacrylate. The copper formed did not have good mechanical properties at an 10 elongation of 1.5% and a bending frequency of 1 time.

Comparative Example 3 The same procedure as in Example 1 was conducted except that 50 parts of urethane dimethacrylate obtained by reacting 1 mole of tolylene diisocyanate with 2 moles of 2-hydroxye- 15 thyl methacrylate was used in place of 46 parts of trimethylol propane trimethacrylate and 4 parts of trimethylol propane triacrylate. The copper formed did not have good mechanical proper ties at an elongation of 2. 1 % and a bending frequency of 1 time.

Example 7 20

Pentaerythritol tetramethacrylate, 80 parts Trimethylolpropane triacrylate 20 parts a,ci-dimethoxy-a-phenylacetophenone 3 parts Methyl ethyl ketone 20 parts 25 The above photosensitive resin composition solution was coated on the same 30 test sub- strates as used in Example 1, according to the dip coating method. The coated substrates were dried at 80'C for 10 minutes. The photosensitive resin composition layer after drying had a thickness of about 20 jum. Onto this layer was attached a polyethylene terephthalate film having a thickness of 25 um. Other procedure was conducted in the same manner as in Example 1. A 30 copper plating pattern of high precision was obtained. The copper had good mechanical proper ties at an elongation of 7.4% and a bending frequency of 5 times.

EFFECTS OF THE INVENTION As appreciated from the Examples, the process for producing a printed circuit board according 35 to the present invention can provide a printed circuit board of high precision having a copper plating of good properties, by means of the additive method.

Further, in the process of the present invention, there occurs little contamination of the plating solution, whereby a printed circuit board having the above excellent characteristics can be mass produced. 40 The above are only several Examples of the present invention and can naturally be subjected to various modifications unless such modifications depart from the spirit of the present invention.

BRIEF EXPLANATION OF THE DRAWINGS Fig. 1 is a schematic view of an apparatus for producing photosensitive elements used in the 45 foregoing Examples. Fig. 2 shows a test negative mask used in the Examples. In these figures, the numerals represent the followings.

Delivery roll -of polyethylene terephthalate film 6,7,8 Rolls 50 9 Knife Photosensitive resin composition solution 11 Drier 12 Delivery roll of polyethylene film 13,14 Rolls 55 Wind-up roll of photosensitive element 16 Polyethylene terephthalate film 17 Polyethylene film 21 Non-transparent portions of negative mask 22 Transparent portions of negative mask 60

Claims

1. A process for producing a printed circuit board, which comprises the steps of (1) forming, on the surface of a substrate a layer of photosensitive resin composition which composition comprises 65 8 GB2193730A 8 (i) 100 parts by weight of a photopolymerizable mixture comprising from 5 to 99% by weight of at least one unsaturated compound (a) having at least one terminal methacrylo.Yl group and no direct nitrogen-hydrogen bonds and from 95 to 1% by weight of at least one unsaturated compound (b) having at least one terminal acryloyl group and no direct nitrogen-hydrogen bonds and 5 (ii) 0.5 to 20 parts by weight of a sensitizing agent or system capable of forming a free radical upon actinic irradiation, (2) exposing part of the photosensitive resin composition to actinic irradiation to form an image and developing the image to form a negative plating resist pattern in the photosensitive resin composition on the surface of the substrate, and 10 (3) subjecting the substrate to electroless copper plating to form a circuit pattern on the surface of the substrate.

2. A process according to claim 1 wherein the photosensitive resin composition comprises (iii) up 400 parts by weight of a linear high molecular compound having no direct nitrogen hydrogen bonds. 15

3. A process according to claim 2, wherein the linear high molecular compound (iii) has at least one tetrahydrofurfuryl side chain.

4. A process according to any one of claims 1 to 3 comprising placing a photosensitive element on the surface of the substrate to form the layer of the photosensitive resin compo sition. 20

5. A process according to any preceding claim which comprises, after developing the image, reirradiating the substrate surface with actinic radiation.

6. A process according to any preceding claim wherein the unsaturated compound (a) has no direct oxygen-hydrogen bond.

7. A process according to claiml and substantially as hereinbefore described with reference 25 to the Examples.

8. A printed circuit board produced by a process according to any one of claims 1 to 7.

9. A printed circuit board according to claim 8 and substantially as hereinbefore described with reference to any one-of the Examples.

Published 1988 at The Patent office, State House, 66/71 HigliHolborn, London WC1R 4TP. Further copies maybe obtained from The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Burgess & Son (Abingdon) Ltd. Con. 1/87.