CA1333578C - Production of metallic patterns - Google Patents
Production of metallic patternsInfo
- Publication number
- CA1333578C CA1333578C CA 568036 CA568036A CA1333578C CA 1333578 C CA1333578 C CA 1333578C CA 568036 CA568036 CA 568036 CA 568036 A CA568036 A CA 568036A CA 1333578 C CA1333578 C CA 1333578C
- Authority
- CA
- Canada
- Prior art keywords
- electrodeposited film
- resist
- photoresist
- areas
- resin
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
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Classifications
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
- G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K3/00—Apparatus or processes for manufacturing printed circuits
- H05K3/02—Apparatus or processes for manufacturing printed circuits in which the conductive material is applied to the surface of the insulating support and is thereafter removed from such areas of the surface which are not intended for current conducting or shielding
- H05K3/06—Apparatus or processes for manufacturing printed circuits in which the conductive material is applied to the surface of the insulating support and is thereafter removed from such areas of the surface which are not intended for current conducting or shielding the conductive material being removed chemically or electrolytically, e.g. by photo-etch process
- H05K3/061—Etching masks
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K2203/00—Indexing scheme relating to apparatus or processes for manufacturing printed circuits covered by H05K3/00
- H05K2203/05—Patterning and lithography; Masks; Details of resist
- H05K2203/0562—Details of resist
- H05K2203/0582—Coating by resist, i.e. resist used as mask for application of insulating coating or of second resist
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K2203/00—Indexing scheme relating to apparatus or processes for manufacturing printed circuits covered by H05K3/00
- H05K2203/05—Patterning and lithography; Masks; Details of resist
- H05K2203/0562—Details of resist
- H05K2203/0585—Second resist used as mask for selective stripping of first resist
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K2203/00—Indexing scheme relating to apparatus or processes for manufacturing printed circuits covered by H05K3/00
- H05K2203/07—Treatments involving liquids, e.g. plating, rinsing
- H05K2203/0779—Treatments involving liquids, e.g. plating, rinsing characterised by the specific liquids involved
- H05K2203/0783—Using solvent, e.g. for cleaning; Regulating solvent content of pastes or coatings for adjusting the viscosity
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K2203/00—Indexing scheme relating to apparatus or processes for manufacturing printed circuits covered by H05K3/00
- H05K2203/13—Moulding and encapsulation; Deposition techniques; Protective layers
- H05K2203/1333—Deposition techniques, e.g. coating
- H05K2203/135—Electrophoretic deposition of insulating material
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K3/00—Apparatus or processes for manufacturing printed circuits
- H05K3/0011—Working of insulating substrates or insulating layers
- H05K3/0017—Etching of the substrate by chemical or physical means
- H05K3/0023—Etching of the substrate by chemical or physical means by exposure and development of a photosensitive insulating layer
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K3/00—Apparatus or processes for manufacturing printed circuits
- H05K3/22—Secondary treatment of printed circuits
- H05K3/28—Applying non-metallic protective coatings
Abstract
A method of making a metallic pattern on a substrate surface, the substrate surface comprising bare metal in predetermined areas and metal coated by a first resist in remaining areas which method comprises: (i) protecting the bare metal by electrodepositing a resinous film thereon; (ii) removing the first resist from said remaining areas using a solvent which does not remove the electrodeposited film; (iii) etching the metal exposed in (ii) using an etchant which does not remove the electrodeposited film; (iv) forming a layer of a second resist in a predetermined pattern over the electrodeposited film, thereby leaving areas of the electrodeposited film uncovered by the resist; and (v) removing the uncovered areas of the electro-deposited film by treatment with a solvent therefor. The method is useful in the production of printed circuit boards.
Description
-PRODUCTION OF METALLIC PATTERNS
The present invention relates to the production of metallic patterns such as printed circuits and the like.
There are numerous methods used for the manufacture of printed circuit boards, although some of the steps used are common to the various methods.
In the case of single sided printed circuit boards, the hoard, comprising a copper-clad plastics laminate, has holes drilled where desired, a resist is coated on the copper in a pre-determinated pattern, using screen printing or photoimaging techniques, to give a board having hare copper in some areas and copper coated by the resist in remaining areas, the bare copper is then plated with a tin-lead alloy, the resist is then removed, the copper thereby exposed is etched using an etchant which does not remove the tin-lead alloy, which is finally removed using a tin-lead alloy stripper.
In the case of douhle sided, plated through hole printed circuit boards, the procedure is similar, but with the following additional steps:
after the holes are drilled the board is subjected to electroless copper deposition to deposit copper on the surface of the holes (as well as over all the copper); and after applying the resist in a predetermined pattern the board is subjected to copper electroplating to deposit copper on the bare copper parts including the surface of the holes.
-The copper patterns produced in these known processes are conventionally further processed to render predetermined areas thereof available for the application of solder, whereby components such as resistors and capacitors can be connected to the electrical circuit, and to render other predetermined areas thereof unavailable for such treatment. This is achieved by forming on the copper pattern a layer of a solder mask, which can be a photocured or heat-cured resinous film, in predetermined areas of the copper pattern, leaving remaining areas of the pattern bare and available for connection to various components. This further processing produces, in effect, a further copper pattern by masking predetermined areas of the pattern originally produced.
Disadvantages of the known processes are the high cost of the tin-lead alloy stripper and the necessary subsequent cleaning; and the tin-lead alloy slipper (usually a mixture of hydrogen peroxide and sulphuric acid) is aggressive to the boards themselves and to personnel and equipment used in carrying out the stripping.
We have now found that the copper left bare after applying the resist can be protected by electrodeposition of an electrodepositable resin which is not removed by the etching process and which can be left in place on the copper during subsequent processing to produce a desired metallic pattern.
Electrodepositable resins have been known for many years and are commonly used for coating metal articles e.g. painting car ~ 3 ~ ` 1 333 578 bodies and accessories, steel girders, and household items such as washing machines. In all these uses the resin is electrodeposited and then cured. There has been a proposal in Russian Patent Specification No. 293312 to use an electrodepositable resin to protect exposed copper during the manufacture of a printed circuit board, the resin being thermally cured after electrodeposition.
The cured resin is subsequently removed by treatment with a strongly alkaline solution at 7û to 80C. These are harsh conditions which can damage the base laminate of a circuit board.
We have found that the electrodeposited resin can be left in place while the board is coated with a further resist, such as a solder mask, in a predetermined pattern, which coating is conventionally used to treat boards made by conventional processes such as those described above to shield areas of the metallic pattern which are not to be soldered to other components, followed by removal of electrodeposited resin only from areas where bare copper is required for subsequent application of solder for the connection of components to the printed circuit. Thus, such a process avoids the necessity to remove all of the electrodeposited resin. When the solder mask is a photosensitive material applied to the hoard in a predetermined pattern by an imaging process, the electrodeposited resin can be removed from the required areas by the solvent treatment used for image development, thereby avoiding the necessity for a separate 4 ` 1333578 28377-2 step to remove the electrodeposited resin in the manufacturing process. Furthermore, the electrodeposited resin remaining beneath the solder mask serves to facilitate good adhesion between the underlying copper and the solder mask.
Accordingly, the present invention provides a method of making a metallic pattern on a substrate surface, said substrate surface comprising bare metal in predetermined areas and metal coated by a first resist in remaining areas which method comprises (i) protecting the bare metal by electrodepositing a resinous film thereon, (ii) removing the first resist from said remaining areas using a solvent which does not remove the electrodeposited film, (iii) etching the metal exposed in (ii) using an etchant which does not remove the electrodeposited film, (iv) forming a layer of a second resist in a predetermined pattern over the electrodeposited film, thereby leaving areas of the electrodeposited film uncovered by the resist, and (v) removing the uncovered areas of the electrodeposited film by treatment with a solvent therefor.
The resist present as a coating on the initial substrate may be an epoxide resin applied by a screen printing process and then cured. Preferably, the resist is a photoresist coated in selected areas by applying it uniformly to the substrate, which is usually a copper-clad laminate, subjecting it to actinic radiation `~ -in a predetermined pattern and then removing exposed or unexposed areas according to whether the photoresist is positive or negative respectively. Positive and negative photoresists for use in making printed circuit boards are well known materials and any of them may be used. They can be strippable under aqueous conditions or by means of an organic solvent. A layer of another metal such as nickel may be deposited on bare copper areas before electrodeposition in stage (i).
The resinous film electrodeposited in stage (i) comprises an electrodepositable resin, which may be anodically depositable or cathodically depositable. Anodically depositable resins are preferred if acidic etchants are to be used, and cathodic types are preferred if alkaline etchants are to be used.
A particularly preferred combination is the use of a photoresist which is strippable under aqueous conditions in step (ii) and an electrodepositable resin which is strippable by means of an organic solvent in step (v).
Any of the large number of electrodepositable resins may be used, including acrylic resins; adducts of epoxide resins with amines, polycarboxylic acids or their anhydrides, or aminocarboyxlic, mercaptocarboxylic or aminosulphonic acids; polyurethanes; polyesters;
and reaction products of phenolic hydroxyl group-containing resins with an aldehyde and an amine or amino- or mercapto- carboyxlic or aminosulphonic acid. Suitable acrylic resins include copolymers - 6 - ` 1333578 of at least one acrylic ester such as an alkyl or hydroxyalkyl acrylate or methacrylate with an ethylenically unsaturated monomer containing a salt-forming group, such as an acyrlic monomer containing a carboxyl or tertiary amino group and, optionally, another ethylenically unsaturated monomer. Suitable epoxide resin adducts include those of diglycidyl ethers of dihydric alcohols or bisphenols with a primary or secondary amine, usually a monoamine such as ethanolamine, 1-amino-2-propanol, diethanolamine or diethylamine, a polycarboxylic acid such as glutaric or adipic acid, a polycarboxylic acid anhydride such as maleic or succinic anhydride, an aminocarboxylic acid such as o-, m- or p-aminobenzoic acid or a mercaptocarboxylic acid. Suitable polyurethanes include adducts of hydroxyl-terminated polyurethanes with polycarboxylic acid anhydrides. Suitable polyesters include carboxyl-terminated polyesters derived from polyhydric alcohols such as ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol or butane-1,4-diol with polycarboxylic acids such as glutaric, adipic, maleic, tetrahydrophthalic and phthalic acids or esterifying derivatives thereof. Suitable reaction products of phenolic hydroyxl-containing resins include reaction products of phenol-terminated adducts of diglycidyl ethers with bisphenols, with aldehydes such as formaldehyde or benzaldehyde and amines such as ethanolamine, diethanolamine or ethylene diamine, aminocarboxylic acids such as glycine, sarcosine or aspartic acid, or mercaptocarboxylic acids ~ 7 ~ 1333578 such as thioglycolic or 3-mercaptopropionic acid.
Preferred electrodepositable resins are copolymers of at least one monoacrylic ester, particularly selected from methyl acrylate, ethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, butyl acrylate, ethylhexyl acrylate and the corresponding methacrylates, with at least one monoacrylic monomer containing a carboxyl or tertiary amino group, particularly acrylic acid, methacrylic acid or dimethylaminoethyl methacrylate and, optionally, with a further vinyl monomer such as styrene.
Other preferred electrodepositable resins are adducts of a diglycidyl ether of a bisphenol, particularly, bisphenol A, which may have been advanced, with a monoamine, particularly diethanolamine.
Electrodeposition of the resinous film may be carried out using conventional procedures for resinous materials. Thus the electrodepositable resin, optionally together with a heat-activated curing agent therefor and conventional additives such as pigments, dyes, fillers and plasticizers, can be dissolved or dispersed in an aqueous medium, which may contain a minor amount of an organic solvent, together with an acid or base to at least partially neutralise salt-forming groups on the resin. The aqueous electrodeposition medium generally contains from 2 to 60o~ preferably from 5 to 25o~ by weight of the resin.
The amount of resinous film which is electrodeposited needs to be sufficient to cover the exposed metal completely and protect - 8 - 1~33578 it during removal of the first resist and during etching of the metal thereby exposed.
Electrodeposition for only a few minutes, usually one minute, at a voltage of up to 200 volts is sufficient in most cases. Voltages as low as 2 volts may be used in some cases, especially if the size of the electrode on which the resin film is deposited is small in relation to the other electrode. For example, a cathodically depositable resin may be deposited on a small cathode in a tank where the whole of the tank is the anode, at voltages of 2 volts or 5 volts.
We have found that the adhesion of the resin film may be improved if it is deposited in two steps, first at a low voltage and then at a higher voltage. For example, a good coating can be obtained by electrodepositing the resin at 2 volts for 2 minutes, followed by deposition at 5 volts for up to 5 minutes.
An aqueous solvent may be used to remove the resist in step (ii). It is possible to use a combination of a photoresist and an electrodepositable resin which are both strippable under acidic aqueous conditions or both strippable under basic aqueous conditions provided that the photoresist is strippable under milder conditions than are needed to remove the electrodeposited resin, e.g. a more dilute solution of acid or base.
When an organic solvent is used to remove the resist in step (ii), a suitable solvent which does not dissolve the electro-deposited resin can be found by routine experimentation. Both this solvent and the solvent used to remove the electrodeposited resin in step (v) can be selected from hydrocarbons such as toluene and xylene, halohydrocarbons such as 1,1,1-trichloroethane and dichloromethane, hydroxylic solvents such as 2-n-butoxyethanol, 2-ethoxyethanol and diethylene glycol monobutyl ether, esters such as 2-ethoxyethyl acetate, propylene carbonate and butyrolactone, ketones such as acetone, methyl ethyl ketone and cyclohexanone and ethers such as tetrahydrofuran. Where, for example, the electrodeposited resin is derived from an epoxy resin and the resist is an acrylic material, the resist can be removed in step (ii) using a halohydrocarbon solvent and the electrodeposited resin can be removed in step (v) using a ketone.
The electrodeposited resin is preferahly dried, for example by heating at a temperature up to 110C, before carrying out the etching step (iii), more preferably before removing the resist in step (ii).
In step (iii) of the process of the invention, the metal exposed by removal of the resist, usually copper, may be removed by any well known etchant such as ferric chloride, hydrogen peroxide/
ph~ r ic acid, ~mm~n;l~ persulphate, or cupric ~hlor;~.
At the end of step (iii), the substrate has a surface comprising predetermined areas of metal covered by the electro-deposited resin and predetermined areas from which the metal has been removed by the etching process. Where the initial substrate is a copper-clad plastics laminate, at the end of step (iii) the _ 10 - 1333~78 surface comprises predetermined areas of copper covered by the electrodeposited resin and areas in which the laminate base is devoid of copper.
After the etching, a layer of a resist to act, for example, as a solder mask is formed in a predetermined pattern over the electrodeposited film and, usually, also over areas etched in step (iii). It will be appreciated that it is not strictly necessary to have solder mask in areas which are devoid of metal after step (iii). However, in practice, it is usually more convenient to have the solder mask in these areas. The pattern formation of step (iv) can be effected by applying a curable, preferably photocurable, resin composition directly in a predetermined pattern using a screen printing technique and curing the composition, preferably by irradiating the screen printed layer. Photocurable resin compositions which can be applied by screen printing are well known to those skilled in the art of making printed circuit boards. The photocurable resins can be, for example, resins containing polymerisahle acrylate or methacrylate ester groups used together with free radical-generating photoinitiators therefor, epoxy resins used together with cationic photoinitiators therefor such as onium salts, and resins containing directly activated photosensitive groups such as cinnamate, chalcone, phenylpentadienone and similar groups.
Preferably, step (iv) is effected hy (a) applying a layer of a photoresist over the electrodeposited film, 13335~8 (b) irradiating the photoresist layer in a predetermined pattern, thereby effecting a difference in solubility between exposed and unexposed parts of the layer, and (c) removing more soluble areas of the irradiated layer by treatment with a solvent.
In step (iv) (a), the photoresist is usually applied over substantially all of the surface of the substrate, that is over areas etched in step (iii) as well as over the electrodeposited film.
Positive and negative photoresists are suitable. They may be liquid polymerisable photoresists or solid photoresists which may be applied to the substrate as preformed films, as powders which are melted to form liquid layers and then cooled to form films, or as solutions in solvents, which are then evaporated to form photoresist films.
Thus negative photoresists suitable for use in step (iv) (a) include well known photocurable resin compositions such as those comprisiing resins contalning directly activated photosensitive groups, for example those having azido, coumarin, stilbene, maleimido, pyridinone or anthracene groups or, preferably, those containing alpha, beta-ethylenically unsaturated ester or ketone groups having aromaticity or ethylenic unsaturation in conjugation with the alpha, beta-unsaturation, such as cinnamate, sorbate, chalcone, phenyl-substituted propenone and phenyl-substituted pentadienone groups.
Resins containing such photosensitive groups are described in United States Patent 4 572 890.
Other photocurable resin compositions suitable for use as the photoresist in step (iv) (a) include those comprising a cationically polymerisable material, particularly an epoxide resin or a vinyl ether, together with a cationic photoinitiator therefor, particularly a metallocenium salt, an onium salt or an aromatic iodosyl salt. Photocurable compositions of this type are also described in United States Patent 4 572 890 and in EP-A-0094915.
Further photocurable resin compositions suitable for use as the photoresist in step (iv) (a) include those comprising a free-radical-polymerisable unsaturated material, particularly an acrylate or methacrylate, together with a free radical-generating photoinitiator therefor. Many acrylic, that is acrylate or methacrylate group-containing, photocurable compositions of this type are available commercially.
Other negative photoresists suitable for use in step (iv) (a) include those comprising a substance, or mixture of substances, containing an acrylate or methacrylate group and a directly activated photosensitive group such as hereinbefore described, together with a free radical-generating photoinitiator for the acrylate or methacrylate group. Such photoresists are described in United States Patents 4 413 052 and 4 416 975 and in European Patent Publication EP-A-O 207 893.
Positive photoresists suitable for use as the photoresist in step (iv) (a) include those comprising polyoxymethylene polymers described in United States Patent No. 3 991 033; the o-nitrocarbinol esters described in United States Patent No. 3 849 137; the o-nitrophenyl acetals, their polyesters, and end-capped derivatives described in United States Patent No. 4 086 210; sulphonate esters of aromatic alcohols containing a carbonyl group in a position alpha or beta to the sulphonate ester group, or N-sulphonyloxy derivatives of an aromatic amide or imide, such as esters and imides described in United States Patent 4 618 564; aromatic oxime sulphonates, such as those described in EP-A-0199672; quinone diazides such as quinone-diazide-modified phenolic resins; and resins containing benzoin groups in the chain, such as those described in United States Patent No. 4 368 253.
The photoresist may include conventional photosensitisers and non-photosensitive film-forming polymers such as those used in conventional photoresists.
Preferred photoresists for use ln step (iv) (a) are negative photoresists, particularly useful such resists being those which are suitable as solder masks.
Irradiation of the photoresist layer in a predetermined pattern in step (iv) (b) may be achieved by exposure through an image-bearing transparency consisting of substantially opaque and substantially transparent areas, or by means of a computer-controlled laser beam. Electromagnetic radiation having a wavelength of 200-600 nm is generally used, and suitable sources include carbon arcs, mercury vapour arcs, fluorescent lamps with phosphors emitting ultra violet light, argon and xenon glow lamps, tungsten lamps, and photographic flood lamps; of these, mercury vapour arcs and metal halide lamps are the most suitable. The exposure time required depends on such factors as the nature and thickness of the components of the photoresist layer, the type of radiation source, and its distance from the solder mask. Suitable exposure times can readily be found by routine experimentation.
Removal of more soluble areas of the irradiated layer in step (iv) (c) is effected by treatment with a solvent chosen according to the nature of the photoresist, and may be water, an aqueous or aqueous organic solution of an acid or base or an organic solvent or mixture of solvents. Suitable acid solutions include those of acetic, lactic, glycolic or toluene-p-sulphonic acids, while suitable basic solutions include those of sodium or potassium hydroxide or carbonate. Suitable organic solvents include hydrocarbons such as toluene and xylene, halohydrocarbons such as 1,1,1-trichloro-ethane and dichloromethane, hydroxylic solvents such as ethanol, 2-n-butoxyethanol and 2-ethoxyethanol, esters such as 2-ethoxyethyl acetate, ketones such as cyclohexanone, acetone and methyl ethyl ketone and ethers such as tetrahydrofuran.
When the photoresist used in step (iv) (a) is a negative photoresist, areas not exposed to radiation in step (iv) (b) are removed by treatment with solvent in step (iv) (c). When a :` 1333578 positive photoresist is used in step (iv) (a), usually areasexposed to radiation in step (iv) (b) are removed in step (iv) (c), although if an image reversal process is used, for instance with a quinone diazide photoresist, the areas initially exposed to radiation are subsequently rendered less soluhle than the other areas so that it is the areas not exposed in step (iv) (b) which are removed in (iv) (c).
The solvent used to remove uncovered areas of the electro-deposited film in step (v) can be selected from the same group of solvents hereinbefore specified for removal of the photoresist in step (iv) (c). The removal of the uncovered electrodeposited film can be effected in a separate step from (iv) (c) using, for example, a different solvent from that used in (iv) (c). In preferred embodiments of the process of the invention, the removal (v) of the electrodeposited film is effected by the solvent treatment (iv) (c).
A suitable solvent can he found by routine experimentation.
In particularly preferred embodiments of the process of the invention, in which the first resist is removed by aqueous solvents, the second resist is removed by means of an organic solvent, and the electrodeposited film is removed by means of an organic solvent used to remove the second resist.
The process of the invention is very useful in the production of multilayer printed circuit boards, particularly those havinq plated through holes or vias.
The invention is illustrated by the following Examples, in which parts and percentages are by weight unless stated otherwise.
The resins used in the Examples are prepared as follows:
Resin I
A monomer mixture consisting of styrene (47.5 parts), 2-ethyl-hexylacrylate (25 parts), 2-hydroxyethyl methacrylate (20 parts) and dimethylaminoethylmethacrylate (7.5 parts) with azobis(isobutyro-nitrile) (1.5 parts) is added dropwise over 2 hours to 2-n-butoxy-ethanol (50 parts) stirred under nitrogen at 100C. The reaction mixture is maintained at 100C for a further 1 hour and a further charge of azobis(isobutyronitrile) (0.5 pts) and 2-n-butoxyethanol added. This procedure is repeated twice more and the reaction mixture held at 100C for a further 1 hour and then cooled.
The amine value of the resulting solution is 0.28 eq/kg and the molecular weight of the copolymer is 10,416.
Resin II
A monomer mixture consisting of styrene (60 parts) 2-ethyl-hexyl acrylate (27.5 parts), 2-hydroxyethyl methacrylate (7.5 parts) and 2-(dimethylamino)ethyl methacrylate (5 parts) with azobis(iso-butyronitrile) (1.5 parts) is added dropwise over 2 hours to 2-n-butoxyethanol (50 parts) stirred at 120C. The reaction mixture is maintained at 12nC for a further 1 hour and a further charge of azobis(isobutyronitrile) (0.5 part) and 2-n-butoxyethanol (5.5 parts) added. This procedure is repeated twice more and the reaction mixture is held at 120C for a further 1 hour and then cooled. The amine value of the resulting solution is 0.19 eq/kg and the molecular weight of the copolymer is 10,279.
Resin III
A monomer mixture consisting of methyl methacrylate (20 parts), n-butyl acrylate (22.5 parts), 2-hydroxyethyl methacrylate (5 parts) and methacrylic acid (2.5 parts) with 1-tert.-dodecyl mercaptan (0.015 part) and azobis(isobutyronitrile (0.75 part) is added dropwise over 2 hours to 2-n-butoxyethanol (50 parts) stirred at 100C. The reaction mixture is maintained at 100C for a further hour and a further charge of azobis(iso-butyronitrile (0.25 part) added. The mixture is held at 100C
for a further 3 hours and then evpaporated under reduced pressure for 30 minutes to remove volatiles before cooling. The acid value of the resulting solution is 0.30 eq/kg and the molecular weight of the copolymer is 10,048.
Resin IV
An epoxide resin prepared by advancing a diglycidyl ether of bisphenol A by reaction with bisphenol A (epoxide content 1.55 mol/kg, 100 parts) is heated to 140C together with 2-n-butoxyethanol (47.3 parts) to form a solution. To this is added diethanolamine (16.7 parts) and the mixture is maintained at 140C until the epoxide content is zero. The solution is cooled - 18 - 1 3 3 3 ~ 7 8 to 7noc and aqueous 75o lactic acid is added (9.6 parts), followed by water (15.7 parts). The resin solution is then cooled.
Resin V
This denotes a liquid epoxide resin based on bisphenol A
having an epoxide content of 5 . 3 mol/kg.
Resin VI
This denotes 3,4-epoxycyclohexylmethyl-3',4'-epoxy-cyclohexane carboxylate.
The RISTON~ and VACRE ~ photoresists used in the Examples are acrylic photoresists available from Du Pont (UK) Ltd., Riston Division, Wedgwood Way, Stevenage, Hertfordshire SG1 4QN, England, as is the VACRE ~ developer.
The aqueous solution of Robertsons Aqueous Film Stripper 279H used in the Examples is obtained by diluting with water the aqueous 70o solution of ethanolamine available from Robertsons Chemicals Ltd., Shepherds Grove Industrial Estate West, Stanton, Bury St. Edmunds, Suffolk IP31 2AR, England.
-A copper clad laminate coated with a RIST0 ~aqueous developable negative photoresist, which has been imaged and developed to form a pattern ln the RIST0~ photoresist, is used as the cathode in an electrodeposition bath equipped with a stainless steel anode. The electrodeposition bath contains the following solution:-Resin I 100 pts Aqueous 20o lactic acid 6.7 pts Water 493.3 pts A voltage of 2 volts is applied for 2 minutes and then avoltage of 5 volts is applied for 4 minutes. The laminate is removed from the bath, rinsed with water and dried at 110C for 5 minutes.
The electrodeposited resin fills the areas where there is no photoresist and the copper is exposed. The laminate is then immersed in a bath of CANNING 1887 DRY FILM STRIPPER, available from W. Canning Materials Ltd., Birmingham, B18 6AS, at 50C. This treatment removes the photoresist leaving the electrodeposited film. The exposed copper is etched away in an ammoniacal cupric chloride bath, after which the plate is washed in water and dried, to leave a clear pattern, in copper covered with the electrodeposited film, on the laminate base. A VACREL~film photoresist solder mask is applied over the surface bearing the copper pattern using a dry film laminator.
The solder mask film is irradiated through an image-bearing transparency - 2G _ using a lamp emitting radiation in the range 350-450nm for 90 seconds. The laminate is immersed in proprietary VACREL developer to remove the areas of the solder mask not irradiated in the imagewise exposure and also remove the electrodeposited film in these areas so that solder can now be applied to the bare copper.
In areas which have been irradiated the electrodeposited film is -not effected and so provides a good bond between the copper tracks and the solder mask.
A copper-clad laminate coated with a RISTON aqueous-developable negative photoresist, which has been imaged and developed to form a pattern in the photoresist, is used as the cathode in an electrodeposition bath equipped with a stainless steel anode.
The electrodeposition bath contains the following solution:-Resin II 100 parts Aqueous 20o lactic acid 6.7 parts Water 493.3 parts A voltage of 80 volts is applied for one minute and the laminate is then removed from the bath, rinsed with water and dried at 110C for 5 minutes. The electrodeposited resin film - 21 - 1333~78 coats the areas where there is no photoresist and the copper is exposed. The laminate is then immersed in a bath of a 10o aqueous solution of ROBERTSONS 279 H DRY ~ILM STRIPPER, at 50C. This treatment removes the photoresist leaving the electrodeposited film. The exposed copper is etched away in an aqueous solution of sulphuric acid and ammonium persulphate at 50C, after which the plate is washed in water and dried, to leave a clear pattern, in copper covered with the electrodeposited film, on the laminate base. A second RISTO ~film photoresist is applied over the surface bearing the copper pattern using a dry film laminator. The photoresist film is irradiated through an image-bearing transparency using a 5kW metal halide lamp at a distance of 75 cm for 15 seconds. The laminate is immersed in a mixture of sodium carbonate (0.5 part), 2-n-butoxyethanol (4 parts) and water (95.5 parts) to remove the areas of the photoresist not irradiated in the imagewise exposure. The electrodeposited resin thereby exposed is removed by immersion in a bath of 1,1,1-trichloroethane with gentle rubbing. In areas which have been irradiated, the electrodeposited film is not affected and so provides a good bond between the copper tracks and the photoresist.
- 22 - ~ 1 333 5 78 A copper-clad laminate coated with a RISTO~ aqueous developable negative photoresist, which has been imaged and developed to form a pattern in the photoresist, is used as the anode in an electrodeposition bath equipped with a stainless steel cathode. The electrodeposition bath contains the following solution:-Resin III 10û parts Aqueous 20o potassium hydroxide 5 parts Water 395 parts A voltage of 40 volts is applied for one minute and thelaminate is then removed from the bath, rinsed with water and dried at 110C for 5 minutes. The electrodeposited resin film coats the areas where there is no photoresist and the copper is exposed. The laminate is then immersed in a bath of a 10o aqueous solution of ROBERTSONS 279H DRY FILM STRIPPER, at 50C. This treatment removes the photoresist leaving the electrodeposited film. The exposed copper is etched away in an aqueous solution of sulphuric acid and ammonium persulphate at 5noc, after which the plate is washed in water and dried, to leave a clear pattern, in copper covered with the electrodeposited film, on the laminate base. A second RISTO ~film photoresist is applied over the surface -bearing the copper pattern using a dry film laminator.
The photoresist film is irradiated through an image-bearing transparency using a 5kW metal halide lamp at a distance of 75 cm for 15 seconds. The laminate is immersed in 1,1,1-trichloroethane to remove the areas of the photoresist not irradiated by the imagewise exposure and the electrodeposited resin thereby exposed in these areas. In areas which have been irradiated, the electrodeposited film is not affected and so provides a good bond between the copper tracks and the photoresist.
Example 2 is repeated, using a solution of Resin IV
(100 parts) in water (566.6 parts) in the electrodeposition bath instead of the Resin II solution, applying the voltage of 80 volts for 2 seconds instead of one minute, and removing both the unirradiated areas of the second photoresist and the electrodeposited resin beneath those areas by immersion in 1,1,1-trichloroethane. In the areas which have been irradiated, the electrodeposited film is not affected and so provides a good bond between the copper tracks and the second photoresist.
A copper-clad laminate coated with a RIST0 ~aqueous developable photoresist, which has been imaged and developed to form a pattern in the photoresist, is used as the cathode in an ` 1333578 electrodeposition bath equipped with a stainless steel anode. The electrodeposition bath contains the following solution:-Resin II 100 parts Aqueous 20o lactic acid 6. 7 parts Water 493.3 parts A voltage of 70 volts is applied for one minute and thelaminate is then removed from the bath, rinsed with water and dried at 110C for 5 minutes. The electrodeposited resin film coats the areas where there is no photoresist and the copper is exposed. The laminate is then immersed in a bath of a 10o aqueous solution of ROBERTSONS 279H DRY FILM STRIPPER, at 50C.
This treatment removes the photoresist leaving the electrodeposited film. The exposed copper is etched away in an aqueous solution of sulphuric acid and ammonium persulphate at 50C, after which the plate is washed with water and dried, to leave a clear pattern, in copper covered with the electrodeposited film, on the laminate base. A layer of a phenylpentadienone solder mask is applied over the surface bearing the copper pattern.
The solder mask is irradiated through an image-bearing transparency using a 5kW metal halide lamp at a distance of 75 cm for 2 minutes. The laminate is immersed in a mixture of 1~33578 propylene carbonate (50 parts), gamma-butyrolactone (20 parts) and butyl digol (diethylene glycol monobutyl ether; 30 parts) to remove the areas of the photoresist not irradiated in the image-wise exposure and the electrodeposited resin thereby exposed in those areas. In areas which have been irradiated, the electro-deposited film is not affected and so provides a good bond bet-ween the copper tracks and the solder mask.
A copper-clad laminate coated with a RIST0 ~aqueous-developable photoresist, which has been imaged and developed to form a pattern in the photoresist, is used as the cathode in an electrodeposition bath equipped with a stainless steel anode.
The electrodeposition bath contains the following solution:-Resin II 100 parts Aqueous 20o lactic acid 6. 7 parts Water 493.3 parts A voltage of 70 volts is applied for one minute and the laminate is then removed from the bath, rinsed with water and dried at 110C for 5 minutes. The electrodeposited resin film coats the areas where there is no photoresist and the copper is exposed. The laminate is then immersed in a bath of a 1noo aqueous solution of ROBERTSnNS 279H DRY FILM STRIPPER, at 50C. This -treatment removes the photoresist leaving the electrodeposited film. The exposed copper is etched away in an aqueous solution of sulphuric acid and ammonium persulphate at 50UC, after which the plate is washed with water and dried, to leave a clear pattern, in copper covered with the electrodeposited film, on the laminate base. A mixture of Resin V (1 part), Resin VI (1 part) and triphenyl sulphonium hexafluoroantimonate (0.1 part) is screen printed onto selected areas of the copper covered with the electrodeposited film on the laminate base. This is then flood irradiated using a ~kW metal halide lamp at a distance of 75 cm for 5 minutes, converting the screen-printed resin composition from a liquid into a tack-free coating. Immersion in 1,1,1-trichloroethane removes the exposed electrodeposited resin.
In the areas protected by the screen-printed resin, the electro-deposited film is not affected and so provides a good bond between the copper tracks and the screen-printed resin composition.
The present invention relates to the production of metallic patterns such as printed circuits and the like.
There are numerous methods used for the manufacture of printed circuit boards, although some of the steps used are common to the various methods.
In the case of single sided printed circuit boards, the hoard, comprising a copper-clad plastics laminate, has holes drilled where desired, a resist is coated on the copper in a pre-determinated pattern, using screen printing or photoimaging techniques, to give a board having hare copper in some areas and copper coated by the resist in remaining areas, the bare copper is then plated with a tin-lead alloy, the resist is then removed, the copper thereby exposed is etched using an etchant which does not remove the tin-lead alloy, which is finally removed using a tin-lead alloy stripper.
In the case of douhle sided, plated through hole printed circuit boards, the procedure is similar, but with the following additional steps:
after the holes are drilled the board is subjected to electroless copper deposition to deposit copper on the surface of the holes (as well as over all the copper); and after applying the resist in a predetermined pattern the board is subjected to copper electroplating to deposit copper on the bare copper parts including the surface of the holes.
-The copper patterns produced in these known processes are conventionally further processed to render predetermined areas thereof available for the application of solder, whereby components such as resistors and capacitors can be connected to the electrical circuit, and to render other predetermined areas thereof unavailable for such treatment. This is achieved by forming on the copper pattern a layer of a solder mask, which can be a photocured or heat-cured resinous film, in predetermined areas of the copper pattern, leaving remaining areas of the pattern bare and available for connection to various components. This further processing produces, in effect, a further copper pattern by masking predetermined areas of the pattern originally produced.
Disadvantages of the known processes are the high cost of the tin-lead alloy stripper and the necessary subsequent cleaning; and the tin-lead alloy slipper (usually a mixture of hydrogen peroxide and sulphuric acid) is aggressive to the boards themselves and to personnel and equipment used in carrying out the stripping.
We have now found that the copper left bare after applying the resist can be protected by electrodeposition of an electrodepositable resin which is not removed by the etching process and which can be left in place on the copper during subsequent processing to produce a desired metallic pattern.
Electrodepositable resins have been known for many years and are commonly used for coating metal articles e.g. painting car ~ 3 ~ ` 1 333 578 bodies and accessories, steel girders, and household items such as washing machines. In all these uses the resin is electrodeposited and then cured. There has been a proposal in Russian Patent Specification No. 293312 to use an electrodepositable resin to protect exposed copper during the manufacture of a printed circuit board, the resin being thermally cured after electrodeposition.
The cured resin is subsequently removed by treatment with a strongly alkaline solution at 7û to 80C. These are harsh conditions which can damage the base laminate of a circuit board.
We have found that the electrodeposited resin can be left in place while the board is coated with a further resist, such as a solder mask, in a predetermined pattern, which coating is conventionally used to treat boards made by conventional processes such as those described above to shield areas of the metallic pattern which are not to be soldered to other components, followed by removal of electrodeposited resin only from areas where bare copper is required for subsequent application of solder for the connection of components to the printed circuit. Thus, such a process avoids the necessity to remove all of the electrodeposited resin. When the solder mask is a photosensitive material applied to the hoard in a predetermined pattern by an imaging process, the electrodeposited resin can be removed from the required areas by the solvent treatment used for image development, thereby avoiding the necessity for a separate 4 ` 1333578 28377-2 step to remove the electrodeposited resin in the manufacturing process. Furthermore, the electrodeposited resin remaining beneath the solder mask serves to facilitate good adhesion between the underlying copper and the solder mask.
Accordingly, the present invention provides a method of making a metallic pattern on a substrate surface, said substrate surface comprising bare metal in predetermined areas and metal coated by a first resist in remaining areas which method comprises (i) protecting the bare metal by electrodepositing a resinous film thereon, (ii) removing the first resist from said remaining areas using a solvent which does not remove the electrodeposited film, (iii) etching the metal exposed in (ii) using an etchant which does not remove the electrodeposited film, (iv) forming a layer of a second resist in a predetermined pattern over the electrodeposited film, thereby leaving areas of the electrodeposited film uncovered by the resist, and (v) removing the uncovered areas of the electrodeposited film by treatment with a solvent therefor.
The resist present as a coating on the initial substrate may be an epoxide resin applied by a screen printing process and then cured. Preferably, the resist is a photoresist coated in selected areas by applying it uniformly to the substrate, which is usually a copper-clad laminate, subjecting it to actinic radiation `~ -in a predetermined pattern and then removing exposed or unexposed areas according to whether the photoresist is positive or negative respectively. Positive and negative photoresists for use in making printed circuit boards are well known materials and any of them may be used. They can be strippable under aqueous conditions or by means of an organic solvent. A layer of another metal such as nickel may be deposited on bare copper areas before electrodeposition in stage (i).
The resinous film electrodeposited in stage (i) comprises an electrodepositable resin, which may be anodically depositable or cathodically depositable. Anodically depositable resins are preferred if acidic etchants are to be used, and cathodic types are preferred if alkaline etchants are to be used.
A particularly preferred combination is the use of a photoresist which is strippable under aqueous conditions in step (ii) and an electrodepositable resin which is strippable by means of an organic solvent in step (v).
Any of the large number of electrodepositable resins may be used, including acrylic resins; adducts of epoxide resins with amines, polycarboxylic acids or their anhydrides, or aminocarboyxlic, mercaptocarboxylic or aminosulphonic acids; polyurethanes; polyesters;
and reaction products of phenolic hydroxyl group-containing resins with an aldehyde and an amine or amino- or mercapto- carboyxlic or aminosulphonic acid. Suitable acrylic resins include copolymers - 6 - ` 1333578 of at least one acrylic ester such as an alkyl or hydroxyalkyl acrylate or methacrylate with an ethylenically unsaturated monomer containing a salt-forming group, such as an acyrlic monomer containing a carboxyl or tertiary amino group and, optionally, another ethylenically unsaturated monomer. Suitable epoxide resin adducts include those of diglycidyl ethers of dihydric alcohols or bisphenols with a primary or secondary amine, usually a monoamine such as ethanolamine, 1-amino-2-propanol, diethanolamine or diethylamine, a polycarboxylic acid such as glutaric or adipic acid, a polycarboxylic acid anhydride such as maleic or succinic anhydride, an aminocarboxylic acid such as o-, m- or p-aminobenzoic acid or a mercaptocarboxylic acid. Suitable polyurethanes include adducts of hydroxyl-terminated polyurethanes with polycarboxylic acid anhydrides. Suitable polyesters include carboxyl-terminated polyesters derived from polyhydric alcohols such as ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol or butane-1,4-diol with polycarboxylic acids such as glutaric, adipic, maleic, tetrahydrophthalic and phthalic acids or esterifying derivatives thereof. Suitable reaction products of phenolic hydroyxl-containing resins include reaction products of phenol-terminated adducts of diglycidyl ethers with bisphenols, with aldehydes such as formaldehyde or benzaldehyde and amines such as ethanolamine, diethanolamine or ethylene diamine, aminocarboxylic acids such as glycine, sarcosine or aspartic acid, or mercaptocarboxylic acids ~ 7 ~ 1333578 such as thioglycolic or 3-mercaptopropionic acid.
Preferred electrodepositable resins are copolymers of at least one monoacrylic ester, particularly selected from methyl acrylate, ethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, butyl acrylate, ethylhexyl acrylate and the corresponding methacrylates, with at least one monoacrylic monomer containing a carboxyl or tertiary amino group, particularly acrylic acid, methacrylic acid or dimethylaminoethyl methacrylate and, optionally, with a further vinyl monomer such as styrene.
Other preferred electrodepositable resins are adducts of a diglycidyl ether of a bisphenol, particularly, bisphenol A, which may have been advanced, with a monoamine, particularly diethanolamine.
Electrodeposition of the resinous film may be carried out using conventional procedures for resinous materials. Thus the electrodepositable resin, optionally together with a heat-activated curing agent therefor and conventional additives such as pigments, dyes, fillers and plasticizers, can be dissolved or dispersed in an aqueous medium, which may contain a minor amount of an organic solvent, together with an acid or base to at least partially neutralise salt-forming groups on the resin. The aqueous electrodeposition medium generally contains from 2 to 60o~ preferably from 5 to 25o~ by weight of the resin.
The amount of resinous film which is electrodeposited needs to be sufficient to cover the exposed metal completely and protect - 8 - 1~33578 it during removal of the first resist and during etching of the metal thereby exposed.
Electrodeposition for only a few minutes, usually one minute, at a voltage of up to 200 volts is sufficient in most cases. Voltages as low as 2 volts may be used in some cases, especially if the size of the electrode on which the resin film is deposited is small in relation to the other electrode. For example, a cathodically depositable resin may be deposited on a small cathode in a tank where the whole of the tank is the anode, at voltages of 2 volts or 5 volts.
We have found that the adhesion of the resin film may be improved if it is deposited in two steps, first at a low voltage and then at a higher voltage. For example, a good coating can be obtained by electrodepositing the resin at 2 volts for 2 minutes, followed by deposition at 5 volts for up to 5 minutes.
An aqueous solvent may be used to remove the resist in step (ii). It is possible to use a combination of a photoresist and an electrodepositable resin which are both strippable under acidic aqueous conditions or both strippable under basic aqueous conditions provided that the photoresist is strippable under milder conditions than are needed to remove the electrodeposited resin, e.g. a more dilute solution of acid or base.
When an organic solvent is used to remove the resist in step (ii), a suitable solvent which does not dissolve the electro-deposited resin can be found by routine experimentation. Both this solvent and the solvent used to remove the electrodeposited resin in step (v) can be selected from hydrocarbons such as toluene and xylene, halohydrocarbons such as 1,1,1-trichloroethane and dichloromethane, hydroxylic solvents such as 2-n-butoxyethanol, 2-ethoxyethanol and diethylene glycol monobutyl ether, esters such as 2-ethoxyethyl acetate, propylene carbonate and butyrolactone, ketones such as acetone, methyl ethyl ketone and cyclohexanone and ethers such as tetrahydrofuran. Where, for example, the electrodeposited resin is derived from an epoxy resin and the resist is an acrylic material, the resist can be removed in step (ii) using a halohydrocarbon solvent and the electrodeposited resin can be removed in step (v) using a ketone.
The electrodeposited resin is preferahly dried, for example by heating at a temperature up to 110C, before carrying out the etching step (iii), more preferably before removing the resist in step (ii).
In step (iii) of the process of the invention, the metal exposed by removal of the resist, usually copper, may be removed by any well known etchant such as ferric chloride, hydrogen peroxide/
ph~ r ic acid, ~mm~n;l~ persulphate, or cupric ~hlor;~.
At the end of step (iii), the substrate has a surface comprising predetermined areas of metal covered by the electro-deposited resin and predetermined areas from which the metal has been removed by the etching process. Where the initial substrate is a copper-clad plastics laminate, at the end of step (iii) the _ 10 - 1333~78 surface comprises predetermined areas of copper covered by the electrodeposited resin and areas in which the laminate base is devoid of copper.
After the etching, a layer of a resist to act, for example, as a solder mask is formed in a predetermined pattern over the electrodeposited film and, usually, also over areas etched in step (iii). It will be appreciated that it is not strictly necessary to have solder mask in areas which are devoid of metal after step (iii). However, in practice, it is usually more convenient to have the solder mask in these areas. The pattern formation of step (iv) can be effected by applying a curable, preferably photocurable, resin composition directly in a predetermined pattern using a screen printing technique and curing the composition, preferably by irradiating the screen printed layer. Photocurable resin compositions which can be applied by screen printing are well known to those skilled in the art of making printed circuit boards. The photocurable resins can be, for example, resins containing polymerisahle acrylate or methacrylate ester groups used together with free radical-generating photoinitiators therefor, epoxy resins used together with cationic photoinitiators therefor such as onium salts, and resins containing directly activated photosensitive groups such as cinnamate, chalcone, phenylpentadienone and similar groups.
Preferably, step (iv) is effected hy (a) applying a layer of a photoresist over the electrodeposited film, 13335~8 (b) irradiating the photoresist layer in a predetermined pattern, thereby effecting a difference in solubility between exposed and unexposed parts of the layer, and (c) removing more soluble areas of the irradiated layer by treatment with a solvent.
In step (iv) (a), the photoresist is usually applied over substantially all of the surface of the substrate, that is over areas etched in step (iii) as well as over the electrodeposited film.
Positive and negative photoresists are suitable. They may be liquid polymerisable photoresists or solid photoresists which may be applied to the substrate as preformed films, as powders which are melted to form liquid layers and then cooled to form films, or as solutions in solvents, which are then evaporated to form photoresist films.
Thus negative photoresists suitable for use in step (iv) (a) include well known photocurable resin compositions such as those comprisiing resins contalning directly activated photosensitive groups, for example those having azido, coumarin, stilbene, maleimido, pyridinone or anthracene groups or, preferably, those containing alpha, beta-ethylenically unsaturated ester or ketone groups having aromaticity or ethylenic unsaturation in conjugation with the alpha, beta-unsaturation, such as cinnamate, sorbate, chalcone, phenyl-substituted propenone and phenyl-substituted pentadienone groups.
Resins containing such photosensitive groups are described in United States Patent 4 572 890.
Other photocurable resin compositions suitable for use as the photoresist in step (iv) (a) include those comprising a cationically polymerisable material, particularly an epoxide resin or a vinyl ether, together with a cationic photoinitiator therefor, particularly a metallocenium salt, an onium salt or an aromatic iodosyl salt. Photocurable compositions of this type are also described in United States Patent 4 572 890 and in EP-A-0094915.
Further photocurable resin compositions suitable for use as the photoresist in step (iv) (a) include those comprising a free-radical-polymerisable unsaturated material, particularly an acrylate or methacrylate, together with a free radical-generating photoinitiator therefor. Many acrylic, that is acrylate or methacrylate group-containing, photocurable compositions of this type are available commercially.
Other negative photoresists suitable for use in step (iv) (a) include those comprising a substance, or mixture of substances, containing an acrylate or methacrylate group and a directly activated photosensitive group such as hereinbefore described, together with a free radical-generating photoinitiator for the acrylate or methacrylate group. Such photoresists are described in United States Patents 4 413 052 and 4 416 975 and in European Patent Publication EP-A-O 207 893.
Positive photoresists suitable for use as the photoresist in step (iv) (a) include those comprising polyoxymethylene polymers described in United States Patent No. 3 991 033; the o-nitrocarbinol esters described in United States Patent No. 3 849 137; the o-nitrophenyl acetals, their polyesters, and end-capped derivatives described in United States Patent No. 4 086 210; sulphonate esters of aromatic alcohols containing a carbonyl group in a position alpha or beta to the sulphonate ester group, or N-sulphonyloxy derivatives of an aromatic amide or imide, such as esters and imides described in United States Patent 4 618 564; aromatic oxime sulphonates, such as those described in EP-A-0199672; quinone diazides such as quinone-diazide-modified phenolic resins; and resins containing benzoin groups in the chain, such as those described in United States Patent No. 4 368 253.
The photoresist may include conventional photosensitisers and non-photosensitive film-forming polymers such as those used in conventional photoresists.
Preferred photoresists for use ln step (iv) (a) are negative photoresists, particularly useful such resists being those which are suitable as solder masks.
Irradiation of the photoresist layer in a predetermined pattern in step (iv) (b) may be achieved by exposure through an image-bearing transparency consisting of substantially opaque and substantially transparent areas, or by means of a computer-controlled laser beam. Electromagnetic radiation having a wavelength of 200-600 nm is generally used, and suitable sources include carbon arcs, mercury vapour arcs, fluorescent lamps with phosphors emitting ultra violet light, argon and xenon glow lamps, tungsten lamps, and photographic flood lamps; of these, mercury vapour arcs and metal halide lamps are the most suitable. The exposure time required depends on such factors as the nature and thickness of the components of the photoresist layer, the type of radiation source, and its distance from the solder mask. Suitable exposure times can readily be found by routine experimentation.
Removal of more soluble areas of the irradiated layer in step (iv) (c) is effected by treatment with a solvent chosen according to the nature of the photoresist, and may be water, an aqueous or aqueous organic solution of an acid or base or an organic solvent or mixture of solvents. Suitable acid solutions include those of acetic, lactic, glycolic or toluene-p-sulphonic acids, while suitable basic solutions include those of sodium or potassium hydroxide or carbonate. Suitable organic solvents include hydrocarbons such as toluene and xylene, halohydrocarbons such as 1,1,1-trichloro-ethane and dichloromethane, hydroxylic solvents such as ethanol, 2-n-butoxyethanol and 2-ethoxyethanol, esters such as 2-ethoxyethyl acetate, ketones such as cyclohexanone, acetone and methyl ethyl ketone and ethers such as tetrahydrofuran.
When the photoresist used in step (iv) (a) is a negative photoresist, areas not exposed to radiation in step (iv) (b) are removed by treatment with solvent in step (iv) (c). When a :` 1333578 positive photoresist is used in step (iv) (a), usually areasexposed to radiation in step (iv) (b) are removed in step (iv) (c), although if an image reversal process is used, for instance with a quinone diazide photoresist, the areas initially exposed to radiation are subsequently rendered less soluhle than the other areas so that it is the areas not exposed in step (iv) (b) which are removed in (iv) (c).
The solvent used to remove uncovered areas of the electro-deposited film in step (v) can be selected from the same group of solvents hereinbefore specified for removal of the photoresist in step (iv) (c). The removal of the uncovered electrodeposited film can be effected in a separate step from (iv) (c) using, for example, a different solvent from that used in (iv) (c). In preferred embodiments of the process of the invention, the removal (v) of the electrodeposited film is effected by the solvent treatment (iv) (c).
A suitable solvent can he found by routine experimentation.
In particularly preferred embodiments of the process of the invention, in which the first resist is removed by aqueous solvents, the second resist is removed by means of an organic solvent, and the electrodeposited film is removed by means of an organic solvent used to remove the second resist.
The process of the invention is very useful in the production of multilayer printed circuit boards, particularly those havinq plated through holes or vias.
The invention is illustrated by the following Examples, in which parts and percentages are by weight unless stated otherwise.
The resins used in the Examples are prepared as follows:
Resin I
A monomer mixture consisting of styrene (47.5 parts), 2-ethyl-hexylacrylate (25 parts), 2-hydroxyethyl methacrylate (20 parts) and dimethylaminoethylmethacrylate (7.5 parts) with azobis(isobutyro-nitrile) (1.5 parts) is added dropwise over 2 hours to 2-n-butoxy-ethanol (50 parts) stirred under nitrogen at 100C. The reaction mixture is maintained at 100C for a further 1 hour and a further charge of azobis(isobutyronitrile) (0.5 pts) and 2-n-butoxyethanol added. This procedure is repeated twice more and the reaction mixture held at 100C for a further 1 hour and then cooled.
The amine value of the resulting solution is 0.28 eq/kg and the molecular weight of the copolymer is 10,416.
Resin II
A monomer mixture consisting of styrene (60 parts) 2-ethyl-hexyl acrylate (27.5 parts), 2-hydroxyethyl methacrylate (7.5 parts) and 2-(dimethylamino)ethyl methacrylate (5 parts) with azobis(iso-butyronitrile) (1.5 parts) is added dropwise over 2 hours to 2-n-butoxyethanol (50 parts) stirred at 120C. The reaction mixture is maintained at 12nC for a further 1 hour and a further charge of azobis(isobutyronitrile) (0.5 part) and 2-n-butoxyethanol (5.5 parts) added. This procedure is repeated twice more and the reaction mixture is held at 120C for a further 1 hour and then cooled. The amine value of the resulting solution is 0.19 eq/kg and the molecular weight of the copolymer is 10,279.
Resin III
A monomer mixture consisting of methyl methacrylate (20 parts), n-butyl acrylate (22.5 parts), 2-hydroxyethyl methacrylate (5 parts) and methacrylic acid (2.5 parts) with 1-tert.-dodecyl mercaptan (0.015 part) and azobis(isobutyronitrile (0.75 part) is added dropwise over 2 hours to 2-n-butoxyethanol (50 parts) stirred at 100C. The reaction mixture is maintained at 100C for a further hour and a further charge of azobis(iso-butyronitrile (0.25 part) added. The mixture is held at 100C
for a further 3 hours and then evpaporated under reduced pressure for 30 minutes to remove volatiles before cooling. The acid value of the resulting solution is 0.30 eq/kg and the molecular weight of the copolymer is 10,048.
Resin IV
An epoxide resin prepared by advancing a diglycidyl ether of bisphenol A by reaction with bisphenol A (epoxide content 1.55 mol/kg, 100 parts) is heated to 140C together with 2-n-butoxyethanol (47.3 parts) to form a solution. To this is added diethanolamine (16.7 parts) and the mixture is maintained at 140C until the epoxide content is zero. The solution is cooled - 18 - 1 3 3 3 ~ 7 8 to 7noc and aqueous 75o lactic acid is added (9.6 parts), followed by water (15.7 parts). The resin solution is then cooled.
Resin V
This denotes a liquid epoxide resin based on bisphenol A
having an epoxide content of 5 . 3 mol/kg.
Resin VI
This denotes 3,4-epoxycyclohexylmethyl-3',4'-epoxy-cyclohexane carboxylate.
The RISTON~ and VACRE ~ photoresists used in the Examples are acrylic photoresists available from Du Pont (UK) Ltd., Riston Division, Wedgwood Way, Stevenage, Hertfordshire SG1 4QN, England, as is the VACRE ~ developer.
The aqueous solution of Robertsons Aqueous Film Stripper 279H used in the Examples is obtained by diluting with water the aqueous 70o solution of ethanolamine available from Robertsons Chemicals Ltd., Shepherds Grove Industrial Estate West, Stanton, Bury St. Edmunds, Suffolk IP31 2AR, England.
-A copper clad laminate coated with a RIST0 ~aqueous developable negative photoresist, which has been imaged and developed to form a pattern ln the RIST0~ photoresist, is used as the cathode in an electrodeposition bath equipped with a stainless steel anode. The electrodeposition bath contains the following solution:-Resin I 100 pts Aqueous 20o lactic acid 6.7 pts Water 493.3 pts A voltage of 2 volts is applied for 2 minutes and then avoltage of 5 volts is applied for 4 minutes. The laminate is removed from the bath, rinsed with water and dried at 110C for 5 minutes.
The electrodeposited resin fills the areas where there is no photoresist and the copper is exposed. The laminate is then immersed in a bath of CANNING 1887 DRY FILM STRIPPER, available from W. Canning Materials Ltd., Birmingham, B18 6AS, at 50C. This treatment removes the photoresist leaving the electrodeposited film. The exposed copper is etched away in an ammoniacal cupric chloride bath, after which the plate is washed in water and dried, to leave a clear pattern, in copper covered with the electrodeposited film, on the laminate base. A VACREL~film photoresist solder mask is applied over the surface bearing the copper pattern using a dry film laminator.
The solder mask film is irradiated through an image-bearing transparency - 2G _ using a lamp emitting radiation in the range 350-450nm for 90 seconds. The laminate is immersed in proprietary VACREL developer to remove the areas of the solder mask not irradiated in the imagewise exposure and also remove the electrodeposited film in these areas so that solder can now be applied to the bare copper.
In areas which have been irradiated the electrodeposited film is -not effected and so provides a good bond between the copper tracks and the solder mask.
A copper-clad laminate coated with a RISTON aqueous-developable negative photoresist, which has been imaged and developed to form a pattern in the photoresist, is used as the cathode in an electrodeposition bath equipped with a stainless steel anode.
The electrodeposition bath contains the following solution:-Resin II 100 parts Aqueous 20o lactic acid 6.7 parts Water 493.3 parts A voltage of 80 volts is applied for one minute and the laminate is then removed from the bath, rinsed with water and dried at 110C for 5 minutes. The electrodeposited resin film - 21 - 1333~78 coats the areas where there is no photoresist and the copper is exposed. The laminate is then immersed in a bath of a 10o aqueous solution of ROBERTSONS 279 H DRY ~ILM STRIPPER, at 50C. This treatment removes the photoresist leaving the electrodeposited film. The exposed copper is etched away in an aqueous solution of sulphuric acid and ammonium persulphate at 50C, after which the plate is washed in water and dried, to leave a clear pattern, in copper covered with the electrodeposited film, on the laminate base. A second RISTO ~film photoresist is applied over the surface bearing the copper pattern using a dry film laminator. The photoresist film is irradiated through an image-bearing transparency using a 5kW metal halide lamp at a distance of 75 cm for 15 seconds. The laminate is immersed in a mixture of sodium carbonate (0.5 part), 2-n-butoxyethanol (4 parts) and water (95.5 parts) to remove the areas of the photoresist not irradiated in the imagewise exposure. The electrodeposited resin thereby exposed is removed by immersion in a bath of 1,1,1-trichloroethane with gentle rubbing. In areas which have been irradiated, the electrodeposited film is not affected and so provides a good bond between the copper tracks and the photoresist.
- 22 - ~ 1 333 5 78 A copper-clad laminate coated with a RISTO~ aqueous developable negative photoresist, which has been imaged and developed to form a pattern in the photoresist, is used as the anode in an electrodeposition bath equipped with a stainless steel cathode. The electrodeposition bath contains the following solution:-Resin III 10û parts Aqueous 20o potassium hydroxide 5 parts Water 395 parts A voltage of 40 volts is applied for one minute and thelaminate is then removed from the bath, rinsed with water and dried at 110C for 5 minutes. The electrodeposited resin film coats the areas where there is no photoresist and the copper is exposed. The laminate is then immersed in a bath of a 10o aqueous solution of ROBERTSONS 279H DRY FILM STRIPPER, at 50C. This treatment removes the photoresist leaving the electrodeposited film. The exposed copper is etched away in an aqueous solution of sulphuric acid and ammonium persulphate at 5noc, after which the plate is washed in water and dried, to leave a clear pattern, in copper covered with the electrodeposited film, on the laminate base. A second RISTO ~film photoresist is applied over the surface -bearing the copper pattern using a dry film laminator.
The photoresist film is irradiated through an image-bearing transparency using a 5kW metal halide lamp at a distance of 75 cm for 15 seconds. The laminate is immersed in 1,1,1-trichloroethane to remove the areas of the photoresist not irradiated by the imagewise exposure and the electrodeposited resin thereby exposed in these areas. In areas which have been irradiated, the electrodeposited film is not affected and so provides a good bond between the copper tracks and the photoresist.
Example 2 is repeated, using a solution of Resin IV
(100 parts) in water (566.6 parts) in the electrodeposition bath instead of the Resin II solution, applying the voltage of 80 volts for 2 seconds instead of one minute, and removing both the unirradiated areas of the second photoresist and the electrodeposited resin beneath those areas by immersion in 1,1,1-trichloroethane. In the areas which have been irradiated, the electrodeposited film is not affected and so provides a good bond between the copper tracks and the second photoresist.
A copper-clad laminate coated with a RIST0 ~aqueous developable photoresist, which has been imaged and developed to form a pattern in the photoresist, is used as the cathode in an ` 1333578 electrodeposition bath equipped with a stainless steel anode. The electrodeposition bath contains the following solution:-Resin II 100 parts Aqueous 20o lactic acid 6. 7 parts Water 493.3 parts A voltage of 70 volts is applied for one minute and thelaminate is then removed from the bath, rinsed with water and dried at 110C for 5 minutes. The electrodeposited resin film coats the areas where there is no photoresist and the copper is exposed. The laminate is then immersed in a bath of a 10o aqueous solution of ROBERTSONS 279H DRY FILM STRIPPER, at 50C.
This treatment removes the photoresist leaving the electrodeposited film. The exposed copper is etched away in an aqueous solution of sulphuric acid and ammonium persulphate at 50C, after which the plate is washed with water and dried, to leave a clear pattern, in copper covered with the electrodeposited film, on the laminate base. A layer of a phenylpentadienone solder mask is applied over the surface bearing the copper pattern.
The solder mask is irradiated through an image-bearing transparency using a 5kW metal halide lamp at a distance of 75 cm for 2 minutes. The laminate is immersed in a mixture of 1~33578 propylene carbonate (50 parts), gamma-butyrolactone (20 parts) and butyl digol (diethylene glycol monobutyl ether; 30 parts) to remove the areas of the photoresist not irradiated in the image-wise exposure and the electrodeposited resin thereby exposed in those areas. In areas which have been irradiated, the electro-deposited film is not affected and so provides a good bond bet-ween the copper tracks and the solder mask.
A copper-clad laminate coated with a RIST0 ~aqueous-developable photoresist, which has been imaged and developed to form a pattern in the photoresist, is used as the cathode in an electrodeposition bath equipped with a stainless steel anode.
The electrodeposition bath contains the following solution:-Resin II 100 parts Aqueous 20o lactic acid 6. 7 parts Water 493.3 parts A voltage of 70 volts is applied for one minute and the laminate is then removed from the bath, rinsed with water and dried at 110C for 5 minutes. The electrodeposited resin film coats the areas where there is no photoresist and the copper is exposed. The laminate is then immersed in a bath of a 1noo aqueous solution of ROBERTSnNS 279H DRY FILM STRIPPER, at 50C. This -treatment removes the photoresist leaving the electrodeposited film. The exposed copper is etched away in an aqueous solution of sulphuric acid and ammonium persulphate at 50UC, after which the plate is washed with water and dried, to leave a clear pattern, in copper covered with the electrodeposited film, on the laminate base. A mixture of Resin V (1 part), Resin VI (1 part) and triphenyl sulphonium hexafluoroantimonate (0.1 part) is screen printed onto selected areas of the copper covered with the electrodeposited film on the laminate base. This is then flood irradiated using a ~kW metal halide lamp at a distance of 75 cm for 5 minutes, converting the screen-printed resin composition from a liquid into a tack-free coating. Immersion in 1,1,1-trichloroethane removes the exposed electrodeposited resin.
In the areas protected by the screen-printed resin, the electro-deposited film is not affected and so provides a good bond between the copper tracks and the screen-printed resin composition.
Claims (20)
1. A method of making a metallic pattern on a substrate surface, said substrate surface comprising bare metal in predetermined areas and metal coated by a first resist in remaining areas which method comprises (i) protecting the bare metal by electrodepositing a resinous film thereon, (ii) removing the first resist from said remaining areas using a solvent which does not remove the electrodeposited film, (iii) etching the metal exposed in (ii) using an etchant which does not remove the electrodeposited film, (iv) forming a layer of a second resist in a predetermined pattern over the electrodeposited film, thereby leaving areas of the electrodeposited film uncovered by the resist, and (v) removing the uncovered areas of the electrodeposited film by treatment with a solvent therefor.
2. A method according to claim 1, in which the first resist is a photoresist.
3. A method according to claim 2, in which the photoresist is strippable under aqueous conditions in step (ii) and the electrodeposited film is strippable by means of an organic solvent in step (v).
27a
27a
4. A method according to claim 1, in which the electrodeposited film comprises an acrylic resin; an adduct of an epoxide resin with an amine, a polycarboxylic acid or an anhydride thereof, an aminocarboxylic, mercaptocarboxylic or aminosulfonic acid; a polyurethane; a polyester; a reaction product of a phenolic hydroxyl group-containing resin with an aldehyde and an amine or an amino-or mercapto-carboxylic or aminosulfonic acid.
5. A method according to claim 4, in which the electrodeposited film comprises a copolymer of at least two ethylenically unsaturated monomers, at least one of the unsaturated monomers being an acrylic ester and at least one of the unsaturated monomers being a monomer containing a salt-forming group.
6. A method according to claim 4, in which the electrodeposited film comprises a copolymer of at least two vinyl monomers, at least one of the vinyl monomers being a monoacrylic ester and at least one of the vinyl monomers being a monoacrylic monomer containing a carboxyl or tertiary amino group.
7. A method according to claim 4, in which the electrodeposited film comprises an adduct of a diglycidyl ether of a bisphenol, or an advanced diglycidyl ether of a bisphenol, with a monoamine.
8. A method according to claim 1, in which the electrodeposited film is deposited from an aqueous electrodeposition medium containing from 2 to 60% by weight of electrodepositable resin.
9. A method according to claim 1, in which the electrode position is carried out at a voltage of from 2 to 200 volts.
10. A method according to claim 1, in which the electrodeposition is carried out in two stages, first at a low voltage and then at a higher voltage.
11. A method according to claim 1, in which the electrodeposited film is dried before removing the resist in step (ii).
12. A method according to claim 1, in which step (iv) is effected by applying a curable composition over the electrodeposited film directly in a predetermined pattern by screen printing and curing the curable composition.
13. A method according to claim 1, in which step (iv) is effected by (a) applying a layer of a photoresist over the electrodeposited film, (b) irradiating the photoresist layer in a predetermined pattern, thereby effecting a difference in solubility between exposed and unexposed parts of the layer, and (c) removing more soluble parts of the irradiated layer by treatment with a solvent.
14. A method according to claim 13, in which the photoresist is a negative photoresist.
15. A method according to claim 14, in which the photoresist is a solder mask.
16. A method according to claim 13, in which irradiation in step (iv) (b) is effected using electromagnetic radiation of wavelength 200-600 nm.
17. A method according to claim 13, in which the removal (v) of the electrodeposited film is effected by the solvent treatment (iv) (c).
18. A method according to claim 1, in which the first resist is removed by an aqueous solvent, the second resist is removed by means of an organic solvent and the electrodeposited film is removed by means of the organic solvent used to remove the second resist.
19. A method according to claim 1, in which the metallic pattern is a printed circuit and the metal is copper.
20. A metallic pattern on the surface of a substrate made by a method according to claim 1.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8712731 | 1987-05-30 | ||
| GB878712731A GB8712731D0 (en) | 1987-05-30 | 1987-05-30 | Metallic patterns |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1333578C true CA1333578C (en) | 1994-12-20 |
Family
ID=10618164
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 568036 Expired - Fee Related CA1333578C (en) | 1987-05-30 | 1988-05-27 | Production of metallic patterns |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0294325A3 (en) |
| JP (1) | JPS63310196A (en) |
| BR (1) | BR8802609A (en) |
| CA (1) | CA1333578C (en) |
| GB (1) | GB8712731D0 (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB8913090D0 (en) * | 1989-06-07 | 1989-07-26 | Ciba Geigy Ag | Method |
| GB8924142D0 (en) * | 1989-10-26 | 1989-12-13 | Ciba Geigy | Methods for making metallic patterns |
| EP0433720A3 (en) * | 1989-12-22 | 1992-08-26 | Siemens Aktiengesellschaft | Method of applying a solder stop coating on printed circuit boards |
| AU2001273598A1 (en) * | 2000-06-29 | 2002-01-14 | Huntsman Petrochemical Corporation | Carbonate-based photoresist stripping compositions |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1194826A (en) * | 1966-08-09 | 1970-06-10 | Ronson Products Ltd | Improvements relating to Electro-Plating and Etching Processes |
| DE1665151B1 (en) * | 1967-08-08 | 1970-12-17 | Montan Forschung Dr Hans Zille | Process for the production of electrical components of the printed circuit type |
| JPS5222742A (en) * | 1975-08-14 | 1977-02-21 | Mitsubishi Electric Corp | Tansmission line reconneting device |
| NL168769C (en) * | 1978-09-04 | 1982-05-17 | Schat Davit Bv | SHIP WITH AN INSTALLATION FOR LIFTING A LIFE BOAT. |
| JPS5623793A (en) * | 1979-08-02 | 1981-03-06 | Matsushita Electric Ind Co Ltd | Method of manufacturing printed circuit board |
| DE3214807C1 (en) * | 1982-04-21 | 1983-10-06 | Siemens Ag | Process for producing etched printed circuit boards |
| JPS61247090A (en) * | 1985-04-24 | 1986-11-04 | 日本ペイント株式会社 | Manufacture of circuit board having solder through hole |
-
1987
- 1987-05-30 GB GB878712731A patent/GB8712731D0/en active Pending
-
1988
- 1988-05-20 EP EP88810322A patent/EP0294325A3/en not_active Ceased
- 1988-05-27 CA CA 568036 patent/CA1333578C/en not_active Expired - Fee Related
- 1988-05-27 BR BR8802609A patent/BR8802609A/en not_active Application Discontinuation
- 1988-05-30 JP JP13252288A patent/JPS63310196A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| GB8712731D0 (en) | 1987-07-01 |
| JPS63310196A (en) | 1988-12-19 |
| EP0294325A2 (en) | 1988-12-07 |
| EP0294325A3 (en) | 1990-02-07 |
| BR8802609A (en) | 1988-12-27 |
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| Date | Code | Title | Description |
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| MKLA | Lapsed |