Polymers and use in photoimageable compositions

The present invention relates to light imaging compositions, such as photoresists, which are useful in the manufacture of printed circuit boards, and more particularly to such compositions which, after exposure to actinic radiation and development in alkaline aqueous solution, are further processed with strongly alkaline aqueous solutions. The invention is also directed to light imaging compositions for secondary imaging applications such as solder mask fabrication. The invention also relates to tack-free light imaging compositions for both primary and secondary imaging, which are tack-free and which can therefore be used for contact imaging.

Background of the Invention

Light imaging compositions useful, for example, as photoresists for making printed circuit boards, are described in Gilano et al., U.S. Patent No. 3,953,309. described. The main components of the composition are a photopolymerizable material, e.g. B. an α, β-ethylenically unsaturated monomer or short-chain oligomer, a photoinitiator chemical system and an acid functional binder, such as a copolymer of styrene and monobutyl maleate. The light imaging composition described in U.S. Patent 3,953,309 also has a free radical inhibitor to prevent premature heat-induced polymerization.

The light imaging compositions described in U.S. Patent 3,953,309 are developable in alkaline aqueous solution, such as in dilute sodium carbonate solution, as a result of significant carboxylic acid functionality of the binder polymer. For example, in a styrene / monobutyl maleate polymer, each monobutyl maleate unit contained provides an unesterified carboxyl group. A layer of the photoimageable composition, after imagewise exposure to actinic radiation and development in alkaline aqueous solution to remove unexposed areas of the layer, is exposed to an acid etching solution, such as ferric chloride, to etch underlying copper from a circuit board blank.

Light imaging compositions using styrene and monoesters of maleic anhydride as binder polymers are also described in U.S. Patents 4,273,857 and 4,293,635. Binders that are copolymers of styrene and monoesters of maleic anhydride are commercially available, e.g. B. Scripset® resins sold by Monsanto Chemical Co.

Although post processing development is done with an acidic solution in U.S. Patent 3,953,309, other post processing developments are carried out in strongly alkaline solutions such as ammoniacal etchants or metal plating solutions. The acid functionality of the polymers in the above-mentioned patents makes them developable in alkaline aqueous solutions, but also photopolymerizable areas of the resist layer are subject to degradation in strongly alkaline aqueous solutions. In highly alkaline environments, such resists would be delaminated and stripped.

U.S. Patent 4,987,054 describes the use of an amine modified methyl methacrylate / styrene / maleic anhydride "copolymer" which can be thermally cured after exposure and development. This thermal curing produces a film that has excellent resistance to alkaline processing media. However, the additional post-development thermal curing step can be impractical in the production of large volume printed circuit boards.

U.S. Patent No. 4,008,087 describes styrene / maleic anhydride copolymers esterified with phenethanol. The polymers are used in silver halide photoemulsions.

U.S. Patent 4,722,947 describes radiation curable polymers which are styrene / maleic anhydride copolymers esterified with a hydroxyalkylacrylyl compound and optionally with another alcohol, such as a monohydric arylalkyl alcohol. The compositions containing the esterified polymers are useful in radiation cured compositions such as coatings, adhesives and films.

U.S. Patent 4,273,857 describes light imaging compositions containing styrene / maleic anhydride copolymers which are partially esterified with methanol and isopropanol.

Summary of the invention

According to the invention, a new polymer is obtained which is a styrene / maleic anhydride copolymer in which the incorporated maleic anhydride units are about 50 - about 65 mol% with an alkyl, aryl, cycloalkyl, alkylaryl or arylalkyl alcohol with a molecular weight greater than 100, about 15 to about 50 mole percent with a C1 -C3 alkyl alcohol and at least about 80 mole percent total are monoesterified. The polymer has from about 45 to about 65 mole percent styrene units and from about 35 to about 55 mole percent maleic anhydride units, a weight average molecular weight between about 80,000 and about 200,000, and an acid number between about 170 and about 220.

The invention is also directed to a light imaging composition which is both developable with an alkaline aqueous solution but which can also be processed after exposure and development in strongly alkaline media such as additional metal plating baths and ammoniacal caustic agents. The light imaging composition comprises A) between about 25 and about 75% by weight of a binder polymer, B) between about 20 and about 60% by weight of a photopolymerizable material which is a multifunctional photopolymerizable monomer or short-chain oligomer, and C) between about 2 and about 20% by weight of a chemical photoinitiator system, the weight percentages being based on the total weight of components A) - C). The improvement is the use of a binder polymer A) in the light imaging composition which is a styrene / maleic anhydride copolymer in which the maleic anhydride units contained are from about 50 to about 65 mol% with an alkyl, aryl, cycloalkyl, alkaryl or arylalkyl alcohol having a molecular weight greater than 100, about 15 to about 50 mole% with a C1 -C3 alkyl alcohol and at least about 80 mole% total mono-esterified. The polymer has about 45 to about 65 mole percent, preferably about 50 to about 55 mole percent, incorporated styrene units and about 35 to about 55 mole percent, preferably about 45 to about 50 mole percent incorporated maleic anhydride units, a weight average molecular weight between about 80,000 and about 200,000 and an acid number between about 170 and about 220.

The invention is also directed to a light imaging composition for secondary imaging such as for making a solder mask. A solder mask is a hard, permanent layer that meets at least the minimum requirements of the abrasion resistance test according to IPC-SM-840B, Table 12, Summary of Criteria for Qualification / Conformance (Institute for Interconnecting and Packaging Electronic Circuits). A solder mask composition according to the invention comprises A) about 20 to about 70% by weight of a binder polymer which is the new polymer described above, B) about 20 to about 55% by weight of a light imaging material which is a multifunctional photopolymerizable monomer or short chain oligomer C) about 2 to 15% by weight of a chemical photoinitiator system, D) about 5 to about 10% by weight of an epoxy acrylate oligomer in addition to and excluding B) and E) about 1 to about 5% by weight of an aminoplast with reactive hydroxyl groups. The weight percentages are based on the entirety of components A) to E).

The invention also relates to a secondary imaging light imaging composition comprising A) about 20 to about 50% by weight of a binder polymer which is the new polymer described above, B) about 20 to about 40% by weight of a light imaging material which is a multifunctional is photopolymerizable monomer or short-chain oligomer, C) about 2 to about 15% by weight of a chemical photoinitiator system, D) about 15 to about 35% by weight of an epoxy resin and E) about 0.01 to about 5% by weight hardener and / or curing catalyst for the epoxy resin. The weight percentages are based on the entirety of components A) to E).

The invention also relates to a method of exposing either a primary imaging or a secondary imaging light imaging composition containing the new binder polymer as indicated above by directly contacting the substantially non-tacky surface of the light imaging composition with a master, the light imaging composition having actinic Exposed to radiation and then removed the artwork, in order to be able to further process the light imaging composition.

Detailed description of certain preferred embodiments

The currently preferred method of forming the polymer of the present invention is to initially copolymerize styrene and maleic anhydride with a free radical polymerization process. As is known, styrene and maleic anhydride polymerize in a regular alternating pattern, which provides a polymer with an ordered basic structure. Accordingly, the molar ratio of styrene and maleic anhydride is about 1: 1, ie between about 45 and about 65 mole percent styrene and between about 35 and about 55 mole percent maleic anhydride. Styrene units -CH (phenyl) - CH 2 are incorporated into the polymer. Maleic anhydride units are incorporated into the polymer

Although styrene is the preferred comonomer used to form the binder polymer, styrene substituted with C1 -C6 alkyl, either α-substituted such as α-methylstyrene, or substituted on an aromatic ring such as vinyl toluene, can also be used , as well as mixtures of such styrene and / or substituted styrene can be used.

Although maleic anhydride is the preferred copolymer, C1 -C3 mono- or di-alkyl substituted and aryl substituted maleic anhydrides such as 2-methyl maleic anhydride, 2-ethyl maleic anhydride, 2-phenyl maleic anhydride and 2,3-dimethyl maleic anhydride can also be used.

The styrene / maleic anhydride backbone polymer is then esterified with what is referred to herein as "a first alcohol" or a "major alcohol" which is an alkyl, aryl, cycloalkyl, arylalkyl or alkylaryl monoalcohol with a molecular weight greater than 100 , A mixture of such alcohols is also suitable. The main alcohol used preferably has an aromatic radical or a cycloaliphatic radical. Some examples of suitable main alcohols are 3-cyclohexyl-1-propanol, cyclohexylmethanol, phenylethyl alcohol, methylcyclohexanol and 2-ethyl-1-hexanol. From the standpoint of performance, 3-cyclohexyl-1-propanol and cyclohexylmethanol are currently preferred. However, phenylethyl alcohol also performs well and is currently preferred from a cost standpoint. The main alcohol is provided to esterify about 50 to about 65 mole percent of the maleic anhydride units contained in the polymer. Typically, the esterification reaction is not complete. Thus a slight excess of the main alcohol is used, ie between about 1 and about 5 mol% in excess over the desired degree of esterification. The relatively large hydrophobic groups of the main alcohol are believed to be primarily responsible for imparting resistance to strongly alkaline solutions to the photoimageable composition containing the polymer. The molecular weight of the major alcohol is typically not above about 250 and usually not above about 200.

It has been found necessary for the binder polymer to be esterified to the greatest possible extent, ie preferably up to at least about 80 mol% of the maleic anhydride units present. Such a high degree of esterification cannot usually be easily achieved using the main alcohol alone. Accordingly, the partially esterified polymer is further esterified with the C1 -C3 alkyl alcohol, which is referred to herein as a "second alcohol" or "minor alcohol". Suitable minor alcohols are therefore methanol, ethanol and n-propanol. Isopropanol did not work very well. Methanol is the preferred minor alcohol. The minor alcohol probably achieves the total degree of esterification due to the small molecular size, which cannot be achieved using the main alcohol alone. The additional esterification obtained from the lower alcohol increases the acid number by generating the non-esterified carboxyl residue of the incorporated maleic anhydride half-ester units. Again, a slight excess of the lower alcohol, e.g. B. between about 1 and about 5 mol% excess used.

In both esterification processes, a half ester of each maleic anhydride residue is obtained, the second functional carboxylic acid group being more difficult to esterify. The esterification reaction thus also produces the acid functionality, which makes the polymer developable in an alkaline aqueous solution. Although 100% of the maleic anhydride residues can be esterified acceptably, a small percentage, e.g. B. 20 or less mol% of the maleic anhydride residues unesterified.

In order to produce the image, the negative-acting light imaging composition B) contains photopolymerizable multifunctional monomers or oligomers with a low molecular weight, especially α, β-ethylenically unsaturated monomers or oligomers. Some particularly suitable multifunctional acrylic monomers are tetraethylene glycol diacrylate (TEGDA), trimethylolpropane triacrylate (TMPTA), butanediol dimethacrylate (BDDMA) and pentaerythritol triacrylate (PETA). Other multifunctional monomers are, for example, 1,5-pentanediol diacrylate, ethylene glycol diacrylate, 1,3-propanediol diacrylate, decamethylene glycol diacrylate, decamethylene glycol dimethacrylate, 1,4-cyclohexanediol diacrylate, 2,2-dimethylolpropane diacrylate, glycerol diacrylate (2,2-diacrylate) hydroxyphenyl) propane dimethacrylate, triethylene glycol diacrylate, polyoxyethyl 2,2-di (p-hydroxyphenyl) propane dimethacrylate, triethylene glycol dimethacrylate, Polyoxypropyltrimethylolpropane triacrylate, ethylene glycol dimethacrylate, butylene glycol dimethacrylate, 1,3-propanediol dimethacrylate, 1,2,4-butanetriol trimethacrylate, 2,2,4-trimethyl-1,3-pentanediol dimethacrylate, pentaerythritol trimethacrylate, 1-phenylethylene-trimolethacrylate, 1-phenylethylene-1,2-methacrylate, p-dimethyl methacrylate, 1,5-pentanediol dimethacrylate and 1,4-benzenediol dimethacrylate. Acrylate multifunctional oligomers, polyester, urethane, epoxy and acrylic oligomers functionalized with acrylate or methacrylate residues are also useful in this invention. Such oligomers should have molecular weights below about 3,000, preferably below about 2,000.

To initiate the polymerization of the monomers and / or oligomers after exposure to actinic radiation, the light imaging composition C) contains one or more suitable photoinitiators or chemical photoinitiator systems. Suitable photoinitiators are, for example, benzoin ethers, benzil ketals, acetophenones, benzophenones and related compounds with amines.

The composition generally contains additional minor ingredients as known in the art. For example, the composition generally contains a free radical inhibitor to prevent premature thermal polymerization of the monomer or oligomer B). Other conventional additives include colorants, flow control modifiers, anti-foaming agents, pigments, antioxidants, etc.

The ingredients of the composition are dissolved in a suitable solvent such as acetone or methyl ethyl ketone (MEK). Typically, the solids content of the composition is between about 20 and about 60%, but this can vary depending on the application.

It is further within the spirit of the present invention to include a post-development chemical system that makes the light imaging composition hard and durable. Such hardening systems increase the crosslinking density and thereby make the composition suitable as a mask, such as a solder mask. The system can be cured, for example, by heat, ultraviolet radiation (UV) or electron beam radiation (EB). Typically, the thermal curing chemical system is an epoxy resin plus a curing agent and / or curing catalyst for the epoxy resin. Examples of light imaging compositions containing chemical systems for post-development curing can be found in U.S. Patents 5,229,252 and 5,364,736.

One type of secondary imaging composition according to the present invention contains an epoxy acrylate oligomer and an aminoplast resin with reactive hydroxyl groups, such as a melamine-formaldehyde resin or a urea-formaldehyde resin. Epoxy acrylate oligomer is understood here to mean an oligomer formed from an epoxy backbone which is reacted with acrylic acids in such a way that at least about 90% of the epoxy groups are esterified with the acrylic acids. Acrylic acids are understood to mean acrylic acid and substituted acrylic acids, such as methacrylic acid, ethacrylic acid and hydroxyethylacrylic acid. When the carboxyl group reacts with the epoxy groups of the epoxy oligomer, the carboxylic acid residue forms an ester bond with the epoxy oligomer backbone and a hydroxyl group is formed on the vicinal carbon atom. Since essentially all of the epoxy groups are reacted with acrylic acid residues, the epoxy acrylate oligomer acts primarily as an acrylate, with the acrylate residues of the oligomer polymerizing along with the acrylic monomers and / or other acrylic oligomers during the photoinitiated reaction, rendering exposed areas of the light imaging composition layer insoluble in aqueous alkaline solution. The essential hydroxyl functionality provides the basis for crosslinking with the aminoplast resin with hydroxyl group reactivity after development.

The aminoplast resin for crosslinking the epoxy acrylate oligomer is a urea-formaldehyde resin or melamine-formaldehyde resin, the latter being preferred. Preferred melamine-formaldehyde resins have methylated melamine residues.

Another type of secondary imaging composition according to the present invention uses an epoxy resin and an epoxy curing agent and / or an epoxy curing catalyst. A wide variety of epoxy resins are suitable for use in accordance with the present invention. Bisphenol A type and Novalac type epoxy compounds are typically used. Other suitable epoxy resins are described, for example, in US Pat. No. 4,092,443. Cycloaliphatic epoxies, such as those sold under the trade names Cynacure®-UVR-6100 and UVR-6110 by Union Carbide, Danbury Conn. are also usable. Epoxy resins useful in the invention preferably have epoxy equivalent weights between about 200 and about 700.

Epoxy curing agents can be selected from those known in the art, such as carboxylic anhydrides. Preferred epoxy curing agents are blocked isocyanate, such as -caprolactam-blocked isophorone, which is unblocked at a threshold curing temperature.

Examples of epoxy curing catalysts include dicyandiamide, complexes of amines such as tertiary amines alone with boron trifluoride or boron trichloride, latent bordifluoride chelates, aromatic polyamines and imidazoles such as 2-ethyl-4-methylimidazole.

The composition can be applied directly to a blank, e.g. A copper-plated epoxy board used to form a printed circuit board or, in the case of a solder mask forming composition, are applied to a printed circuit board and then dried to remove solvent composition. Alternatively, the composition can be used to form a dry film by applying the composition to a backing sheet such as a polyester sheet, drying the composition and then applying a protective sheet such as polyethylene. The composition, whether applied directly or transferred from a dry film, is processed in a conventional manner. The composition is exposed to imagewise actinic radiation through a artwork and then developed in an alkaline aqueous solution, such as a 1% sodium carbonate solution. After development, the remaining photopolymerizable areas can be processed further, such as in a strongly alkaline aqueous solution.

Although a major advantage of light imaging compositions using the polymer of the present invention is resistance to strongly alkaline solutions, other surprising advantages are also achieved. The compositions show improved resistance to "cold flow" and "edge fusion" even at very high levels, ie more than 2%, of residual solvent in the dried film. This is surprising since conventional styrene / maleate polymers such as Scripset® resins or acrylate ester polymers show edge fusion at this residual solvent content in a relatively short period of time.

The resistance of the exposed and developed composition to alkaline media includes localized alkaline environments as developed in gold plating processes. For example, U.S. Patent 4,987,054 aligns an alkaline etching process with a gold electroplating process. The acidity (pH) of the gold plating solution can be acidic or neutral. However, since the gold is electrodeposited on a copper surface, electrodeposited by-products such as hydroxide and cyanide ions accumulate near the copper resist interface, resulting in a localized alkaline concentration that is temporarily developed. This localized alkaline concentration can attack the photoresist and can cause delamination of the photoresist.

The compositions provide improved film flexibility, which is of particular importance in the internal plating of through holes in printed circuit boards. This is particularly surprising since polymers containing high levels of styrene, ie more than 30%, usually form films that are extremely brittle and easily destroyed.

There are two very surprising advantages of the binder polymer of the present invention. Photoimageable compositions using the novel polymer of the present invention are very tack-free, in fact sufficient so that an original can be placed directly on top of a dried photoimageable composition of the present invention, the photoimageable composition can be exposed through the original, and the original without entraining the photoimageable composition can be removed. This applies to both primary and secondary imaging light imaging compositions according to the present invention. Furthermore, light imaging compositions, both primary and secondary, using the new polymer of the present invention show almost complete elimination of an inhibition of polymerization by oxygen.

The benefits of non-tackiness and very low oxygen polymerization inhibition are both important to enable light imaging compositions of the present invention to image with a print template in direct contact with a dried light imaging composition layer. Almost all of today's compositions must be exposed through some type of protective sheet or protective polyester layer, otherwise the artwork would adhere to the soft, sticky, dry film composition. For example, dry films of a light imaging composition have a backing that is left on the film when the artwork is placed over it. The protective layer is only removed after the light imaging composition has been exposed and after the artwork has subsequently been removed. Another way has been to provide one or more protective layers or "cover layers" as taught in US Patents 4,318,957 and 5,270,146. Whether the light imaging composition layer is exposed through a protective layer such as a polyester sheet or through a "top coat", resolution is lost due to the additional distance that the light must travel to the underlying light imaging composition. The industry trend is to move towards smaller line and space requirements, which requires higher resolution.

The same applies to secondary imaging applications. U.S. Patents 5,164,284, 4,992,354 and 4,889,790 describe methods of applying secondary imaging (solder mask forming) light imaging compositions to printed circuit boards so that the light imaging compositions conform to the contours of the printed circuit boards. The dry films described in these patents as being useful in the practice of these methods have an intermediate layer or top coat overlying the light imaging composition and preventing the light imaging composition from adhering to the artwork and protecting the light imaging composition from oxygen. Light imaging compositions of the present invention which are non-tacky and which are not subject to substantial inhibition of polymerization by oxygen do not require such an intermediate layer or additional processing such as heat curing. Therefore, not only better resolution can be achieved, but also better match to encapsulate surface features.

Another very important advantage associated with the ability to omit a top coat is cost savings. The material that forms the top coat is not only expensive, but an additional coating step is also required in the formation of the dry film. The invention thus offers very substantial cost savings.

The invention will now be described in more detail with reference to the specific examples.

example 1

A monomer mixture was prepared by combining 178.3 g maleic anhydride, 215.6 g styrene, 117.5 g methyl ethyl ketone (MEK) and 3.3 g benzoyl peroxide. 470 g of MEK was heated to 75-80 ° C in a flask equipped with a mechanical stirrer and a condenser. The monomer mixture was added to the hot MEK over a 6 hour period while maintaining the flask contents at 75-80 ° C. The reaction mixture was heated at 75-80 ° C for an additional 12 hours with 0.66 g of benzoyl peroxide being added every 2 hours for the first 8 hours.

148.1 g of phenylethyl alcohol plus 11.1 g of 4- (N, N-dimethylamino) pyridine were added to the styrene / maleic anhydride copolymer solution and the combined mixture was kept at 75-80 ° C for 14 hours. At the end of that time, 265 g MEK and 22.5 g methanol were added. The mixture was then held at 75-80 ° C for 6 hours. The esterified polymer solution was then cooled and bottled.

The polymer was determined to have a weight average molecular weight of 167,000 and an acid number of 185. 52 mol% of the polymer backbone was incorporated styrene units, 48 ​​mol% incorporated maleic anhydride units. 56 mole percent of the maleic anhydride units contained were half esterified with phenylethyl alcohol, 36 mole percent were half esterified with methanol, and 8 mole percent were unesterified.

Example 2

A polymer was prepared as in Example 1, except that 138.4 g of cyclohexylmethanol was used in place of the phenylethyl alcohol.

The polymer was determined to have a weight average molecular weight of 124,000 and an acid number of 193. 51 mole% of the polymer backbone were contained styrene units, 49 mole% maleic anhydride units. 53 mole percent of the maleic anhydride units contained were semi-esterified with cyclohexylmethanol, 33 mole percent were half-esterified with methanol, and 14 mole percent were unesterified.

Examples 3-5

Compositions were prepared as follows:

Components weight%

Example 3

Polymer (Example 1) 64.4

Trimethylolpropane triacrylate 20.6

Tetraethylene glycol diacrylate 10.3

Benzophenone 3.62

Michler's ketone 0.50

Adhesion promoter 0.17

Dye materials 0.134

Antioxidants 0.11

River conveyor 0.17

Example 4

Polymer (Example 1) 60.8

Trimethylolpropane triacrylate 19.8

Polyethylene glycol diacrylate 10.7

Ethyl Michler's ketone 0.3

2-ethylhexyl p- (N, N-dimethylamino) benzoate 3.0

Benzophenone 4.6

Thiodiethylene bis (3,5-di-tert-butyl 4-hydroxyhydrocinnamate) (antioxidant) 0.4

Adhesion promoter 0.15

Dye materials 0.05

River conveyor 0.20

Example 5

Polymer (Example 2) 52.9

acid functional oligomer (MW, 2000, acid number 174) * 8.33

Ethoxylated neopentyl glycol diacrylate 10.6

Ethoxylated trimethylolpropane triacrylate 15.9

Isopropylthioxanthone 1.7

2-methyl-1- [4- (methylthio) phenyl] -2-morpholinopropan-1-one 6.0

1-hydroxycyclohexylphenyl ketone 2.0

Thiodiethylene bis-3,5-di-tert-butyl-4-hydroxyhydrocinnamate 0.33

Liability promoter 0.43

Dye material 1.32

Antioxidant 0.70

River conveyor 0.26

* RSX-89395 available from UCB-Radcure

Example 6

Each of the light imaging compositions of Examples 3-5 was applied to a polyester support sheet and dried. Then a protective polyethylene sheet was applied. A 1.4 mil (3.556 x 10-2 mm) thick film was obtained. The polyethylene sheet was removed and the dried film with the carrier sheet was laminated to a copper-plated board using a hot roll laminator. The roller temperature was 122 ° C. The roller speed was 1 m per minute and the roller pressure was 2.8 bar (2.8 x 105 Pa). The polyester carrier sheet was removed and a artwork was placed directly on the light imaging composition layer. The light imaging composition was exposed to 81 mJ / cm² of actinic radiation through the artwork. After removal of the artwork, the light imaging composition was developed in 1% sodium carbonate monohydrate solution for 35 seconds at 29.4 ° C and the board was etched in AC-CU-Guard (Olin-Hunt), ammoniacal etchant, at pH greater than 9 for 2 minutes at 49 ° C ,

Example 7

A solder mask forming light imaging composition is assembled as follows:

Components weight%

Polymer (Example 1) 60.0

Novacure® 3701 (diacrylate ester of a bisphenol A epoxy resin) 10.2

Trimethylolpropane triacrylate 8.2

Tetraethylene glycol diacrylate 6.0

methylated melamine (crosslinker) 9.2

Benzophenone 4.6

Michler's ketone 0.5

Liability promoter 0.2

Pigment 1.0

Antioxidant 0.1

River conveyor 0.2

The light imaging composition is dissolved in acetone at 55% solids. The composition was applied to a polyester backing sheet and dried. A polyethylene protective sheet was then applied. A 2.0 mil (5.08 x 10-2 mm) thick film was obtained. The polyethylene sheet was removed and the dry film with the carrier sheet was laminated to a printed circuit board using a vacuum laminator. The polyester support sheet was removed and the artwork was placed directly on the light imaging composition layer and the light imaging composition was exposed to 165 mJ / cm² of actinic radiation through a artwork. After removal of the artwork, the light imaging composition was developed in 1% sodium carbonate monohydrate solution for 45 seconds at 29.4 ° C. The remaining light imaging composition was then cured by baking at 150 ° C for 60 minutes.

Example 8

A solder mask forming light imaging composition is assembled as follows:

Components weight%

Polymer (Example 2) 46.0

liquid cycloaliphatic monoepoxy resin, epoxy equivalent weight 120-130 31.0

Trimethylolpropane triacrylate 8.2

Tetraethylene glycol diacrylate 6.0

methylated melamine 3.2

Benzophenone 3.6

Michler's ketone 0.5

Liability promoter 0.2

Pigment 1.0

Antioxidant 0.1

River conveyor 0.2

Filler (silica) 5.0

This light imaging composition was used to form a dry film and then a solder mask as in Example 7.