Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
  • B05D7/14—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials to metal, e.g. car bodies
  • B05D7/142—Auto-deposited coatings, i.e. autophoretic coatings
• • 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
  • G03F7/16—Coating processes; Apparatus therefor
• • 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
  • H05K3/064—Photoresists
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
  • B05D3/06—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by exposure to radiation
  • B05D3/061—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by exposure to radiation using U.V.
  • B05D3/065—After-treatment
  • B05D3/067—Curing or cross-linking the coating
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
  • B05D7/14—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials to metal, e.g. car bodies
  • B05D7/142—Auto-deposited coatings, i.e. autophoretic coatings
  • B05D7/144—After-treatment of auto-deposited coatings
• • 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
  • H05K2203/0756—Uses of liquids, e.g. rinsing, coating, dissolving
  • H05K2203/0759—Forming a polymer layer by liquid coating, e.g. a non-metallic protective coating or an organic bonding 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
  • 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
  • H05K2203/0786—Using an aqueous solution, e.g. for cleaning or during drilling of holes
  • H05K2203/0796—Oxidant in aqueous solution, e.g. permanganate

Definitions

• the invention relates to the technical field of autodeposition emulsions and methods of selectively coating metallic surfaces therewith, especially those surfaces which are subjected to etchant baths as the surfaces are being processed as circuit traces for electronic circuit boards.
• metallic surfaces so as to protect the surfaces from corrosive environments.
• automobile underbodies are coated to protect them from road salt compounds.
• Marine vessel parts are coated to protect them from the marine air.
• a polymer coating is applied to the entire surface of the substrate, or, in the alternative, a prepolymer coating is applied to the substrate and then polymerized in toto.
• circuit traces can be made by using either of two photoresist systems in a coating, imaging, developing and etching process.
• the substrates or metallic surfaces are coated with a negative working photoresist which polymerizes upon exposure to actinic radiation.
• the substrate or metallic surface is coated with a positive acting photoresist which becomes soluble in developer solution upon exposure to actinic radiation.
• the surface is then exposed to actinic radiation.
• the negative resist the surface is exposed to radiation through a photographic negative bearing an image of the desired circuit. As a result, the sections of the resist exposed by the radiation become photopolymerized and thus less soluble in a developer solution.
• Photoresists have become important tools when preparing circuit boards having plated through holes. Such holes are being increasingly used as circuit boards are increasingly being made with two conductive sides. The additional conductive surface increases the boards 1 capabilities.
• the above-described two sided boards are conventionally made from a laminate consisting of copper/epoxy/copper sheets. Each copper side of the laminate has a circuit etched onto it. The two sides are connected electrically, as required for the particular circuits involved, by small apertures or "through holes”. Other terms used in the art are "component holes” or "vias.” Through holes, as initially drilled or otherwise formed, are not electrically conductive because of the intervening insulating epoxy layer. Accordingly, the holes 1 interiors must be coated with copper to electrically connect the two copper sheets.
• This copper coating can be applied by electroless copper deposition, thus forming one type of plated through hole (PTH) .
• PTH plated through hole
• Another type of PTH includes those holes which have copper electrolytically deposited thereon after the initial electroless deposition of copper. See Norman S. Einarson, Printed Circuit Technology (published by Printed Circuit Technology, 1977); Fisher, G.L. ; Sonnenberg, W. , & Bernards, R. ; "Electroplating of
• Two methods of protection include (1) paraffin plugs for the holes and (2) tenting with dry and liquid photoresist films.
• paraffin plugs are difficult to handle because of problems in removing the plugs when they are no longer needed.
• tenting has been used with greater success, the problems attendant upon tenting also make its use somewhat awkward.
• Tenting works by protecting the plated holes with a dry film comprising a photopolymerizable sheet. The areas of the sheet which cover and protect the holes are exposed to UV radiation and polymerized. The circuit board is then later processed with the plated holes remaining covered by the "tent". The tents are then later removed by proper solvents.
• tenting results in the formation of "annular rings" or shoulders on the board's surface. These rings result from the requirement that a tent's diameter must be larger than the hole diameter in order to provide an attachment point for the tent and to afford hole protection. Their formation occurs during the etching process, because, after etching, the tent has not only protected the inner lining of the aperture, but has also protected an annular portion of the metal surface surrounding the aperture.
• annular rings have become a problem as the trend towards smaller circuit boards and higher density circuits continues. For example, as circuit boards get smaller there will be less space available for the rings on the boards* surfaces. Thus, there will be less surface area onto which the tents can be anchored.
• the current resin/photoactive functionality combinations found in common photoresists are capable of resolving smaller features.
• the current liquid and dry film photoresists do not maximize those capabilities in that to form finer features with a good manufacturing yield it is generally recognized that thinner films with fewer defects than those provided by current liquid and dry film photoresist application methods are needed.
• other known application methods such as lamination, roll coating, flood screen printing, spraying, dip coating, curtain coating, etc. , fail as an appropriate application method as the film thickness decreases below 1 mil.
• the film thickness of the protective covering used be 25% or less of the feature size being.resolved.
• the film thickness of the protective covering used be 25% or less of the feature size being.resolved.
• a photoresist coating is applied to the substrate by applying an electric charge to the substrate, which in turn attracts a charged photoresist. See U. S.
• Patents 4,632,900 to Demmer et al. and 3,954,587 to Kokawa Thus, in electrodeposition a thin film of resist forms directly onto the surfaces of the plated through holes and thus avoids the awkward tenting process of laying the film down, the attendant annular ring formation and the film flaw problem.
• electrodeposition involves additional equipment and time to construct the electrodeposition apparatus. Electrodeposition also consumes electrical power and requires charged resins. Even further, photoresist compositions usually have optimal component ratios at which the components should be applied to the surface. However, by using electrodeposition, preferential deposition of certain charged particles may alter the ratio of components actually deposited. Thus, a method which has the advantages of electrodeposition baths in that the substrate can be effectively coated and protected, but which also avoids the problems encountered when using electrodeposition methods would be desirable.
• the general object of the invention is to provide a method and emulsion which effectively coats and selectively protects metallic surfaces by inducing the deposition of a protective coating on the surface by simply immersing the surface in an emulsion and then selectively processing the coating so that only certain portions of the surface remain coated.
• a method comprises
• autodeposition baths are water based emulsions comprising resin, a surfactant and a combination of an acid and an oxidizing agent. All of those components are present in amounts sufficient to induce the resin to coat a metal surface when immersed in the bath. Further, such baths deposit coatings in such a manner that the coating grows in thickness with time.
• the art has described using such baths to coat steel, aluminum, zinc and some copper surfaces.
• the emulsion described herein contains photoactive functionality and is used to deposit a coating which can selectively protect metal surfaces, especially those surfaces which are being processed for electrical circuit traces.
• the emulsion comprises
• Resins which are suitable for the emulsion include, but are not limited to, acid containing polymers or copolymers of one of the following monomers: styrene, butadiene, isoprene, vinylidene chloride, methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, acrylonitrile, acrylic acid, itanoic acid, methacrylic acid, vinyl alcohol, maleic anhydride and vinyl acetate.
• copolymers include butadiene/acrylonitrile/methacrylic acid styrene/acrylic acid styrene/butadiene/acrylic acid styrene/butadiene/methacrylic acid styrene/butadiene/itaconic acid styrene/butadiene/maleic acid styrene/butadiene/butylacrylate/acrylic acid styrene/butadiene/butylacrylate/methacrylic acid styrene/butadiene/butylacrylate/itaconic acid styrene/butadiene/butylacrylate/maleic acid styrene/ethyl acrylate/methacrylic acid styrene/maleic anhydride styrene ethacrylic acid, and vinylidene chloride/ ethacrylic acid.
• Resins comprising acid copolymers which have been partially modified by compounds such as simple alkyl alcohols, e.g. acid resins esterfied with butanol, may also be used.
• acid resins include Joncryl® 67 styrene/acrylic acid copolymer from Joncryl® 67 styrene/acrylic acid copolymer from Joncryl® 67 styrene/acrylic acid copolymer from
• Suitable resins include novolak resins derived from an aldehyde, such as formaldehyde, and a phenolic compound, such as phenol or cresol.
• suitable examples include HT 9690, from Ciba-Geigy and HRJ 10805 from Schenectady, both cresol novolaks.
• the photoactive functionalities suitable for the emulsion are those functionalities or compounds which are positive or negative acting.
• a positive acting functionality is a functionality or compound which becomes soluble in a developer solution when exposed to actinic radiation.
• a negative acting functionality is a functionality or compound which polymerizes, and becomes less soluble, when exposed to radiation.
• the photoactive functionality can be a functionality or compound separate from the resin, or the functionality can be attached to the resin, e.g. a copolymer product from an additional monomer.
• Suitable positive acting photoactive functionalities include, but are not limited to, oxymethylene based monomers, o-nitrocarbinol esters, o-nitrophenyl acetals and polyesters and end-capped derivatives thereof, and benzo- and naphthoquinone diazide sulphonic esters. See U.S. Patent 4,632,900 to Demmer et al.
• a preferred positive acting functionality is a 4- or 5- sulfonic acid derivative of an orthodiazonaphthoquinone, e.g. a 2-diazo-l- naphthoquinone sulfonate ester.
• An especially preferred functionality is the 2-diazo-l- naphthoquinone-5-sulfonate triester of 2,3,4- trihydroxybenzophenone.
• a commercially available adduct is that known as THBP 215 Diazoester from International Photochemicals.
• Another preferred positive acting functionality is o-nitrocarbinol ester.
• This monomer may be polymerized as a homopolymer to form the functionality or, as in one embodiment of the invention, preferably polymerized as part of a copolymer with an unsaturated acid and the same or a different ester. Such copolymers are formed using standard emulsion polymerization techniques described later below.
• suitable copolymers therefrom should have a molecular weight of at least 500 and contain in the molecule at least 5% by weight, by reference to the molecular weight, of aromatic carbocyclic or heterocyclic o-nitrocarbinol ester groups of formula r
• A denot s an aromatic carbocyclic or heterocyclic ring that may be substituted and has 5 to 14 members
• R 4 denotes a hydrogen atom, an alkyl group of from 1 to 8 carbon atoms, or an optionally substituted aryl or aralkyl group, the optional substituents on the groups A and R being alkyl or alkoxy groups of from 1 to 8 carbon atoms, halogen atoms, nitro, amino, or carboxylic acid groups.
• Suitable ring systems A may be mononuclear or polynuclear, such as benzene, naphthalene, anthracene, anthraquinone, phenanthrene, or pyridine rings.
• Suitable aromatic o-nitrocarbinols upon which these o-nitrocarbinol ester groups are based include o-nitrobenzyl alcohol, 2-nitroveratryl alcohol, 6-nitroveratryl alcohol, 2-nitro-4- aminobenzyl alcohol, 2-nitro-4-dimethylaminobenzyl alcohol, 2-nitro-5-dimethylaminobenzyl alcohol, 2- nitro-5-aminobenzyl alcohol, 2-nitro-4,6- dimethoxybenzyl alcohol, 2,4-dinitrobenzyl alcohol, 3- methy1-2,4-dinitrobenzyl alcohol, 2-nitro-4- methylbenzyl alcohol, 2,4,6-trinitrobenzyl alcohol, 2- nitrobenzhydrol, 2,2'-dinitrobenzhydrol, 2,4-dinitro- benzhydrol, 2,2' ,4,4'-tetranitrobenzhydrol, 2-nitro- 4-methylaminobenzyl alcohol, 2-nitro-3-hydroxymethyl naphthalene, l-nitro-2-hydroxy
• photosensitizers such as aromatic ketones and thioxanthones may be included with the positive acting functionalities.
• Suitable negative acting photoactive functionalities include, but are not limited to, a variety of photoprepolymers.
• Generically those prepolymers include, but are not limited to acrylates. More specifically, they include acrylic and methacrylic acid esters of mono-, di-, and polyhydric alcohols; and mono-, di-, and polyalkoxy acrylate and methacrylate.
• mono-, di-, and poly- acrylates or methacrylates which are derivatized from the reaction of hydroxyl terminated acrylate or methacrylate esters with mono-, di-, and polyisocyanates, epoxides, and other hydroxy reactive compounds.
• ethylene glycol diacrylate ethylene glycol dimethacrylate propylene glycol diacrylate propylene glycol dimethacrylate trimethylolpropane triacrylate trimethylolpropane ethoxylate triacrylate trimethylolpropane propoxylate triacrylate trimethylolpropane ethoxylate trimethacrylate trimethylolpropane propoxylate trimethacrylate bisphenol A diacrylate phenoxyethyl methacrylate hexanediol diacrylate neopentyl glycol diacrylate neopentyl propoxylate diacrylate pentaerythritol triacrylate dipentaerythritol hydroxypentaacrylate polyethylene glycol diacrylate
• Trimethylolpropane ethoxylate triacrylate is available as Photomer® 4149 and 4155 from Henkel Corporation.
• Other preferred negative acting prepolymers include those known as Sartomer® 454, 205, and 399 from Sartomer Co.
• photoinitiator When using the negative acting functionalities described above, it. is necessary to use a photoinitiator. Thus hereinafter, unless described otherwise, when the term “photoactive functionality" is specifically used in regards to a negative acting functionality, the term “photoactive functionality” also includes a photoinitiator. Suitable photoinitiators for initiating polymerization of the negative acting photoprepolymers with UV radiation include, but are not limited to, benzoin ethers, benzil ketones, and phenones and phenone derivatives. Examples are:
• a commercially available photoinitiator used in the Examples below is Irgacure® 651 from Ciba-Geigy.
• resin (i) and the photoactive functionality (ii) may be chemically separate components in the bath or they may be chemically bound.
• an embodiment in which (i) and (ii) are bound can be prepared by emulsion polymerizing a monomer containing the photoactive functionality with another monomer to produce a resin having the photoactive functionality attached thereto, e.g. the nitrocarbinol ester co ⁇ polymer.
• a monomer containing the photoactive functionality e.g. the nitrocarbinol ester co ⁇ polymer.
• nitrocarbinol ester co ⁇ polymer e.g. the nitrocarbinol ester co ⁇ polymer.
• Emulsion polymerization techniques, conditions and polymerization initiators are those well known in the art.
• Known techniques for the addition of monomers in emulsion polymerization techniques include continuous addition or sequential addition of monomer in separate portions.
• Known surfactants suitable for emulsifying the monomers in aqueous solution include, but are not limited to, 2,4,7,9-tetramethyl-5-decyn- 4,7-diol, 3,5-dimethyl-l-hexyn-3-ol, glycerol monostearate, dipropylene glycol monostearate, dipropylene glycol monolaurate, dipropylene glycol monooleate, pentaerythritol monooleate, sodium dioctyl sulfosuccinate, sorbitan monolaurate, sodium lauryl ether sulfate, potassium xylene sulfonate, sodium cumene sulfonate, ethylene glycol monostearate, glycerol, nonyl phenol ethoxylate, polyoxyethylene cetyl
• Suitable polymerization initiators include free radical generators such as peroxy disulfates- and persulfate-iron-bisulfate or metabisulfate systems. Detailed techniques, methods and conditions for emulsion polymerization are described in F. W. Billmeyer, Textbook of Polymer Science (Wiley- Interscience, New York; 2ed 1971) ; K. Bovey, et al. , Emulsion Polymerization, (Interscience Publishers, Inc.; New York 1955); and G. M. Dekker, Kinetics and Mechanisms of Polymerization, Vol. 1 (Ed. by G.E. Ham 1969) .
• a preferred embodiment of the emulsion in which resin (i) is not already prepared in emulsion form can be prepared by direct emulsification of (i) and (ii) .
• standard emulsion techniques can be used. See U. S. 4,177,177 to Vanderhoff and Kirk-Othner Encyclopedia of Chemical Technology,, 3rd edition, Volume 8, "Emulsions - Preparation", pp. 919- 923.
• certain resins and photoactive functionalities may require other emulsion techniques.
• one preferable technique is a combination of phase inversion and comminution techniques.
• a water-in-oil (w/o) emulsion is formed by preparing resin (i) and photoactive functionality (ii) in solution by mixing (i) and (ii) into organic solvents such as ethyl acetate and then adding to that solution a lesser amount of water, e.g. about fifty percent by weight of the solution.
• the resulting w/o emulsion is then inverted into an oil-in-water (o/w) emulsion by addition of well known surfactants such as sodium alkyl benzene sulfonates, sodium alkyl sulfates or alky phenol ethoxylates in aqueous solution.
• the emulsion is comminuted by well known homogenizer or, preferably, ultrasound techniques. Any of the resins described above can be used in this technique.
• a resin latex can be prepared by the standard emulsion polymerization techniques described above for the above-mentioned resins.
• the resulting latex contains resin particles which would constitute resin (i) of the emulsion.
• latex particles are preferable to use with certain photoactive functionalities because they appear to emulsify the functionality component.
• they can provide acid functionalities to the coating so that when using an alkali developing solution, the uncured coatings can be removed more easily.
• the latices are generally made with high molecular weight material, the latices act as fillers to provide a more uniform coating.
• a wide variety of latices is available and are made from the monomers suitable for preparing resin (i) .
• latices include Darex® 528L from the Organic Chemicals Division of W. R. Grace & Co.-Conn. Acrysol® ASE-75 from Rohm & Haas is also suitable.
• a surfactant from the group described earlier may be used to emulsify components (i) and (ii) in order to assist the deposition process.
• a commercially available surfactant used in the Examples herein is Surfynol TG surfactant from Air Products, Inc.
• the amounts of (i) and (ii) should be sufficient, so that the total solids content of the emulsion is in the range of about 1 to 20% by weight.
• the acid and oxidizing agent include those known in the art of autodeposition. It is thought that the acid and oxidant cause metal from metallic surfaces to dissolve, thus creating metal ions. Those metal ions are believed to destabilize the emulsion near the metallic surface and cause the resin particles in the emulsion to deposit thereon. See U.S. Patent 4,177,180 to Hall.
• acids include hydrochloric, hydrofluoric, phosphoric, citric, sulfuric and acetic acids.
• An example of an oxidizing agent is hydrogen peroxide. The acid should be added in amounts so that the pH of the resulting emulsions is generally in the range of 1-5 and preferably in the range of 1.7-3.
• metal halides such as cupric chloride and ferric chloride can also be used as oxidizing agents.
• a metal salt such as a metal halide
• CuCl 2 can be used in conjunction with H 2 0 2 .
• the addition of CuCl 2 may help induce autodeposition. See Examples 5 and 7-12.
• the embodiment comprising preformed resin latices e.g.
• the surfactant (v) used in the autodeposition emulsion can be any of those well known in the art.
• additives can also be included in the emulsion.
• the additives can be included as one of the original emulsion forming components or they can be added after the emulsion has been formed, depending on the additive used.
• Such additives include, but are not limited to, coalescing agents, stabilizers, pigments, flow aids and adhesion promoters.
• Commercially available stabilizers for negative photoactive functionalities include hydroquinone, p- methoxyphenol, pyrogallol, 2,6-di-t-butyl-4- methylphenol and phenothiazine.
• Available flow aids include Modaflow® from Monsanto and Lithene PL® from Rivertex.
• Available- pigments and dyes include any of a wide variety, e.g.
• Neopen Blue 808® from BASF.
• Suitable coalescing agents are glycol ethers and esters such as PM Acetate® (propylene glycol monomethyl ether acetate) from Eastman Chemical Co. and Butyl Dipropasol® (dipropylene glycol monobutyl ether) , Hexyl Carbitol® (hexyloxyethoxy ethanol) and UCAR® ester EEP (ethyl 3-ethoxy propionate) from Union Carbide.
• PM Acetate® propylene glycol monomethyl ether acetate
• Butyl Dipropasol® dipropylene glycol monobutyl ether
• Hexyl Carbitol® hexyloxyethoxy ethanol
• UCAR® ester EEP ethyl 3-ethoxy propionate
• a coating of (i) and (ii) on a metallic surface standard autodeposition techniques are used. For instance, the surface is immersed in the emulsion for about 30 seconds to 15 minutes. After the surface has been immersed for a period of time so that the desired coating thickness has been obtained, the coated surface is removed from the emulsion and preferably rinsed and dried.
• the coated metallic surface is exposed to actinic radiation in an image-wise fashion.
• the coating is exposed to radiation through an image bearing transparency such that only the coating on the metal areas to be protected from the etchant bath remain unexposed. If negative acting functionalities are being used, the image-bearing transparency used is such that the coating on the metal areas to be protected from the etchant bath are exposed to the radiation.
• Radiation used in the present invention preferably has a wavelength of 200-600 nm.
• Suitable sources of actinic radiation include carbon arcs, mercury vapor arcs, fluorescent lamps with phosphors emitting ultraviolet light, argon and xenon glow lamps, tungsten lamps, and photographic flood lamps. Of these, mercury vapor arcs, fluorescent sun lamps, and metal halide lamps are most suitable.
• the time required for the exposure will depend upon a variety of factors which include for example, the individual photoactive groups used in the emulsion, the proportion of these groups in the emulsion, the type of light source, and its distance from the composition. Suitable times may be readily determined by those familiar with photoimaging techniques.
• the developer used in the present process is selected according to the nature of the resin and photoactive functionality and photolysis products and may be an aqueous or aqueous organic solution of a base; or an organic solvent or mixture of solvents.
• a base to form a salt, and hence solubilize the fractions of photoactive functionality or resin remaining in the areas of coating which are to be removed after irradiation, is preferred.
• Such basic solutions are, typically, 0.25-3.0% by weight sodium or potassium hydroxide or carbonate.
• the image resulting from development selectively coats and the imaged metal surface can be left "as is" or further processed.
• the selectively coated surface is copper and can be further processed to prepare electrical traces for circuit boards.
• the processing step taken would be to process the copper surface in an etching solution.
• Etching solutions that may be used to remove the uncovered copper metal after development are known in the art and may be varied according to the nature of the metal surface. For example, with a copper surface, an acidic solution of ammonium persulfate, cupric chloride or ferric chloride is usually used. Another cupric chloride etching solution is basic aqueous ammonium hydroxide/cupric chloride.
• Suitable surfaces are copper laminate wherein a copper layer has been laminated onto a reinforcing layer.
• Suitable reinforcing layers include paper, epoxy, glass reinforced epoxy, polyimide, polytetrafluorethylene and the like.
• the coating covering the protected metal traces is then exposed to actinic radiation to render the coating soluble. Any exposed positive acting coating is then removed with a stripping solution, usually aqueous NaOH. Exposed negative acting coating is generally removed by a warm (57°F) spray of 3-5% by weight aqueous sodium hydroxide.
• the autodeposition emulsion method is useful in protecting conductive apertures or "through holes" in two sided circuit boards.
• an autodeposition method By using an autodeposition method, the surfaces of the conductive metallic linings of these apertures are covered and effectively protected from the etching bath.
• the above emulsion provides protection equal to that obtained by electro- deposition, but it is more advantageous in that emf inducing equipment is not needed nor is there a need for an additional process step of connecting the metallic surface to an electrical current.
• resin (i) and functionality (ii) do not need to be processed to contain a charge, nor is there the preferential deposition which results from electro- depositing such charged particles.
• the positive acting system is sometimes preferable to a negative acting system.
• a negative imaging system is employed to protect the lining of the holes, it is difficult to fully irradiate and polymerize, and thus render insoluble, the coating on the inside surfaces of the apertures.
• the composition will not be fully resistant to the normal development and etching processes, and the metal lining in the aperture may be etched away, even though this was not intended.
• the use of a positive acting functionality avoids the above described problem because the positive phototool is designed to shield the apertures from the actinic radiation.
• unirradiated areas of a positive resist coating are insoluble and remain intact during and after development, linings are protected from the etching bath.
• the dried coating was covered with a silver halide phototool and exposed for 12 minutes under a 1 kW high-pressure, mercury-xenon, UV light source rich in light of 365 nm. Following this exposure, the coated substrate was immersed in 5.0% (by weight) aqueous sodium hydroxide for 30 seconds, resulting in removal of coating that had been exposed to the UV light, and leaving a positive image of the phototool. The photoimaged board was then immersed in a hydrochloric acid/cupric etchant bath for five (5) minutes. After removal, the areas of the substrate that had been covered with the coating were protected while the exposed copper had been etched away.
• a mixture of 8.9g vinylidene chloride and 41.4g O-nitrobenzyl acrylate was added dropwise (30 to 60 drops per minute) into a resin kettle containing 120.0ml deionized water, 10.0ml of 10% by weight aqueous sodium dodecylbenzene sulfonate, l.Og sodium bisulfite, and O.Olg ammonium iron(II) sulfate.
• the kettle mixture was stirred mechanically. Concurrently, a mixture of 30.0ml deionized water and l.Og sodium persulfate was added dropwise (5 to 10 drops per minute) to the kettle. Before, during, and after the additions, the kettle temperature was maintained at 42°C. The stirring and heating continued for one hour after both additions were complete. The result was a latex emulsion containing 22.4% total solids by weight.
• Resin Latex 50g Darex 528L styrene butadiene methacrylic acid copolymer
• the components above were prepared in an emulsion by first blending the above amounts of latex and surfactant in 100ml of water. Second, the photoactive functionality components were added with subsequent addition of 100ml of water and high speed blending for
• Example 3 To 100ml of the emulsion prepared in Example 3, lg of hydrofluoric acid (HF) and lg of hydrogen peroxide (H 2 0 2 ) were added. A copper panel was immersed in the resulting emulsion for 10 minutes. Deposition of coating on the copper was observed. Coatings from the emulsion were found to be photoi agable and etch resistant.
• HF hydrofluoric acid
• H 2 0 2 hydrogen peroxide
• cupric chloride (CuCl 2 ) was added to the deposition bath prepared according to Example 4. A 0.2 mil coating was deposited after immersion of a copper panel for 10 minutes followed by a water rinse. The deposited coating was found to be photoimageable and etch resistant. .
• Example 6 0.5g CuCl 2 was added to the emulsion prepared according to Example 6. A 0.15 mil coating was deposited on a copper panel which had been immersed for 10 minutes. The coating was both photoimageable and etch resistant.
• Photoactive Functionality 38g Photomer 4149 ethoxylated TMPTA from Henkel Corporation and 1.75g Irgacure 651 photoinitiator Surfactant: 5g Surfynol TG
• Photoactive Functionality l.9g TMPTA, 38g Photomer 4155 and 1.75g Irgacure 651 photoinitiator
• An emulsion was prepared according to Example 9 except 38g of Photomer 4149 was used instead of Photomer 4155.
• the components for the bath were diluted to 500ml.
• Photoactive Functionality 38g dipentaerythritol hydroxy pentaacrylate and 1.75g Irgacure 651 photoinitiater
• Surfactant 5g Surfynol TG
• An emulsion was prepared according to Example 11, except 38g of pentaerythritol triacrylate was added instead of dipentaerythritol hydroxypentaacrylate. The above components were diluted to 500ml.
• a liter of emulsion was prepared as follows: log of Irgacure 651 was dissolved in 50g of Photomer 4149. This was added to 375ml of Aerysol® ASE-75 aqueous acrylic emulsion (150g solids) made by Rohm & Haas Company, in a blender. Enough water was then added to make 1 liter of solution. The resulting solids content of this emulsion was 21%.
• Deposition baths were prepared from the above- described emulsion as follows: a. 3g of 30% H 2 0 2 was added to lOOmls of emulsion. A 10% phosphoric acid solution was used to titrate this solution to a pH of 1.8. b. 150g of 30% H 2 0 2 was added to 5 liters of emulsion. Concentrated phosphoric acid was used to titrate this bath to a pH of 1.8.
• Emulsions were prepared as in Example 13 except for substituting hydrofluoric, sulfuric, or citric acid for the phosphoric acid.
• the pH was maintained at 1.8 for all examples.
• the resulting emulsions were all acceptable but the emulsion containing phosphoric acid was preferred because it gave more polymer deposition per unit amount of copper removed by the microetchant. In other words, that emulsion was more efficient.
• a mixture of 0.5g Triton X-100 nonionic surfactant from Rohm and Haas and 20g water was then dripped in resulting in an oil-in-water (o/w) emulsion before sonicating the emulsion for 2 minutes at about 180W estimated intensity with a Sonics and Materials 500W cell disrupter with a 3/4" high gain Q horn.
• the low boiling ethyl acetate solvent was removed on a rotary evaporator.
• the resulting o/w emulsion contained 31.7% solid ⁇ following concentration.
• a deposition bath was then prepared by diluting the emulsion to 10% solids with water, acidifying to pH 1.8 with phosphoric acid, and adding an amount of hydrogen peroxide equal to 1% of the total bath weight.
• a copper foil/epoxy glass laminate strip was immersed into the bath for 1 minute, resulting in the deposition of about 0.2-0.3 mil coating which was dried and coalesced for 5 minutes at 80°C.
• the coating was imagewise exposed to UV light for 30 seconds (about 40 mJ/cm 2 on an EIT radiometer) and then developed by immersion in 1% NaOH until the exposed parts of the coating completely developed away, i.e. 1-2 minutes.
• the patterned coating was sufficiently resistant to etching in aqueous CuCl 2 /HCl so that the pattern was etched into the underlying metal after about 2 minutes in a spray etching system.
• An emulsion was prepared from a solution of 25g of Charkit PR-12 positive photoresist, a 2-diazo-l- naphthoquinone-5-sulfonate ester of a t-butyl phenol/formaldehyde resin and 25g of ethyl acetate from Charkit.
• To the above solution was added 0.16g Triton X-100, followed by dropwise addition of 25g deionized (DI) water.
• DI deionized
• a solution of 0.5g Polystep A 16-22 surfactant in 35g Dl water was added dropwise, followed hy 20g of DI water and a further solution of 0.6g Polystep A16-22 surfactant in 40g DI water.
• a water-in-oil emulsion resulted.
• a copper foil/epoxy glass laminate strip was immersed in the bath for 1 minute, and the resulting coating rinsed and dried.
• the coating was imagewise exposed through a positive pattern to UV light (90 mJ/cm 2 ) and developed by immersion in a 5:1 dilution of a positive photoresist developer from MacDermid to give a coated pattern corresponding to the positive pattern.
• the patterned coating was sufficiently resistant to etching in a 10% CuCl 2 /10% HCl bath at 60°C to etch the coating pattern into the underlying metal.
• a copper foil/epoxy glass laminate coupon was immersed in the bath for 1 minute, rinsed, and dried for 4 minutes at 100°C to give a coalesced coating of a thickness of 0.2 to 0.3 mil.
• the coating was imagewise exposed to UV light through a positive pattern (90mJ/cm 2 ) and immersed in a developer solution of 0.5% aqueous sodium hydroxide. The exposed area of the coating was developed to leave a coating corresponding to the positive pattern.
• the copper uncovered during developing was etched away with an acidic cupric chloride spray.
• the remaining coating was further exposed (without pattern) to UV light (200 mJ/cm 2 ) after which it was dissolved away by immersion in 0.5% aqueous sodium hydroxide to leave a copper pattern on the epoxy glass laminate corresponding to the imaging pattern.
• a solution of a negative acting formulation was prepared with the following components:
• Triton X- 100 surfactant To lOOg of the above solution was added 0.3g Triton X- 100 surfactant followed by 50g water, dropwise with mechanical stirring to form a water-in-oil emulsion. A mixture of 0.9g Polystep A16-22 surfactant from Stepan in 70g water was then added dropwise to invert the emulsion to an oil-in-water (o/w) emulsion. The resulting o/w emulsion was sonicated for 2 minutes with a Sonics & Materials 500W disruptor using a 3/4" high gain Q horn at an estimated 180W intensity level. The ethyl acetate was then removed on a rotary evaporator.
• a deposition bath was then prepared by diluting the emulsion to 10% solids with water, acidifying to pH 1.8 with phosphoric acid, and adding an amount of hydrogen peroxide equal to 1% of the total bath weight.
• Immersion of a copper foil/epoxy glass laminate strip in the bath for 20 seconds resulted in about 0.8 mil of coating which was dried and coalesced for 5 minutes at 80°C.
• the coating was imagewise exposed to UV light for 90 seconds (about 110 mJ/cm 2 on an EIT radiometer) and then developed by immersion in 0.5% NaOH until the exposed parts of the coating completely developed away, i.e. in 1-2 minutes.
• the patterned coating was sufficiently resistant to aqueous CuCl 2 /HCl so that the pattern was etched into the underlying metal after about 2 minutes in a spray etching system.
• a solution of a negative acting formulation was prepared with the following components:
• a deposition bath was then prepared by diluting the emulsion to 10% solids with water, acidifying to pH 2.0 with phosphoric acid, and adding an amount of hydrogen peroxide equal to 0.3% of the total bath weight.
• Immersion of a copper foil/epoxy glass laminate strip in the bath for 30 seconds caused deposition of about 0.4 mil of coating which was dried and coalesced for 5 minutes at 80°C.
• the coating was imagewise exposed to UV light for 3 minutes (about 220 mJ/cm 2 on an EIT radiometer) and then developed by immersion in 0.5% NaOH until the exposed parts of the coating completely developed away, i.e. in 1-2 minutes.
• the patterned coating was sufficiently resistant to aqueous CuCl 2 /HCl such that the pattern was etched into the underlying metal after about 2 minutes in a spray etching system.
• a solution of a negative acting formulation was prepared with the following components:
• Stepan in 70g water was added dropwise to invert the emulsion to form an oil-in-water (o/w) emulsion.
• the o/w emulsion was sonicated for 2 minutes with a Sonics & Materials 500W disruptor using a 3/4" high gain Q horn at an estimated 180W intensity level.
• the ethyl acetate was then removed on a rotary evaporator.
• a deposition bath was then prepared by diluting the emulsion to 10% solids with water, acidifying to pH 2.0 with phosphoric acid, and adding an amount of hydrogen peroxide equal to 0.3% of the total bath weight.
• Immersion of a copper foil/epoxy glass laminate strip in the bath for 2 minutes caused deposition of about 1.0 mil of coating which was dried and coalesced for 5 minutes at 80°C.
• the coating was imagewise exposed to UV light for 1.5 minutes (about 110 mJ/cm 2 on an EIT radiometer) and then developed by immersion in 0.5% NaOH.
• the coating was developable but was not as cleanly developed as that for the coatings illustrated in Examples 18 and 19. As a result, the etching was retarded in some areas of the coated substrate in this example.
• a solution of a negative acting formulation was prepared with the following components:
• Triton X-100 surfactant followed by 50g water, dropwise with mechanical stirring to form a water-in-oil emulsion.
• a mixture of 0.9g Stepan Polystep A16-22 surfactant in 70g water was added dropwise to invert the emulsion to an oil-in-water (o/w) emulsion.
• the o/w emulsion was sonicated for 2 minutes with a Sonics & Materials 500W disruptor using a 3/4" high gain Q horn at an estimated 180W intensity level.
• the ethyl acetate was then removed on a rotary evaporator.
• a deposition bath was prepared by diluting the emulsion to 10% solids with water, acidifying to pH 2.0 with phosphoric acid, and adding an amount of hydrogen peroxide equal to 0.3% of the total bath weight.
• Immersion of a copper foil/epoxy glass laminate strip in the bath for 2 minutes caused deposition of about 0.8 mil of coating which was dried and coalesced for 5 minutes at 80°C.
• the coating was imagewise exposed to UV light for 3 minutes (about 220 mJ/cm 2 on an EIT radiometer) and then developed in a 1% Na 2 C0 3 spray.
• the coating was developable but was not as cleanly developed as that for the coatings illustrated in Examples 18 and 19. As a result, the etching was retarded in some areas of the coated substrate in this example.

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