AU614106B2 - Photoimageable compositions containing acrylic polymers and epoxy resins - Google Patents

Description

;1.1 ii ~-ri i-l~ .'CYLlil- ii X

PCT

OPI DATE 05/07/89 AOJP DATE 27/07/89 APPLN. ID 29128 89 PCT NUMBER PCT/US88/04338 INTERNATIONAL APPLICATIO UBSH UN, ER E I NT COOPERATION TREATY (PCT) (51) International Patent Classification 4 I "T 11 Int tionWublication Number: WO 89/ 05476 G03C 1/68 Al (43) International Publication Date: 15 June 1989 (15.06.89) (21) International Application Number: PCT/US88/04338 (81) Designated States: AT (European patent), AU, BE (European patent), CH (European patent), DE (Euro- (22) International Filing Date: 5 December 1988 (05.12.88) pean patent), DK, FR (European patent), GB (European patent), IT (European patent), JP, KR, NL (European patent), NO, SE (European patent).

(31) Priority Application Number: 130,039 (32) Priority Date: 7 December 1987 (07.12.87) Published With international search report.

(33) Priority Country: US Before the expiration of the time limit for amending the claims and to be republished in the event of the receipt of amendments.

(71) Applicant: MORTON THIOKOL, INC. [US/US]; 110 North Wacker Drive, Chicago, IL 60606-1560 (US).

(72) Inventors: ERAMO, Lincoln, Junior 122 East LaPlacentia, San Clemente, CA 92672 WINKLER, William, J. 2332 Medlar Road, Tustin, CA 92680

(US).

(74) Agents: WHITE, Gerald, K. et al.; Morton Thiokol, Inc., 110 North Wacker Drive, Chicago, IL 60606-1560 (US).

(54)Title: PHOTOIMAGEABLE COMPOSITIONS CotOTAtAlG- A C./.-LljC ?OLyME(-S A F03 EPOy f (57) Abstract A photoimageable composition includes a polymeric binder which is soluble in aqueous solution; a cross-linking agent for the polymeric binder; a polymerizable acrylic substance; a chemical, photosensitive, free radical-generating initiating system; and a liquid epoxy resin composition and an epoxy cure catalyst. In one method of using the photoimageable composition of the present invention, the composition is applied as a film to a substrate, heated to make the film nontacky but still aqueous-soluble, exposed to actinic radiation, developed in aqueous solutions to wash away non-exposed portions of the film and heat-cured to harden the film.

U

SI'

LI~ -I WO 89/05476 PCT/US88/04338 PHOTOIMAGEABLE COMPOSITIONS C~oOTp AncL4c. PoLYMe-rs Aab £Po<y (..SIs The present invention is directed to compositions which may be applied as a layer on a substrate, photoimaged, developed and cured to form a patterned, permanent layer, suitable as a solder mask for a printed circuit board or the like.

Background of the Invention Solder masks are patterned films or layers which are designed to permanently overlie the printed circuitry on a printed circuit board. Patterned openings in solder masks selectively permit solder to adhere to metal of the printed board. The solder mask also protects the circuitry against short-circuiting.

Because solder masks are designed to provide a permanent layer, hardness and durability of the layer are considered important features of a solder mask composition. Among the hardest and most durable of photomask compositions are those which are epoxy-based.

Such compositions generally comprise an epoxy resin i dissolved in a solvent. A major disadvantage of epoxy >i v 1 WO 89/05476 PCT/US88/04338 2 compositions is that they are imagewise screen printed, a primitive technology compared to much more desirable photoimaging.

Photoimageable compositions which may be used to form solder masks or the like typically contain a film-forming material, a photo-polymerizable monomer, an acrylate monomer, and a photoinitiator. Examples of such compositions are described in U.S. Patent No. 4,528,261.

Although such compositions have the advantage of being photoimageable, they are not as strong or as durable as those based upon epoxy resins.

U.S. Patent No. 4,268,614, the teachings of which are incorporated herein by reference, describes photoimageable compositions which include acrylic resins, acrylic monomers and epoxy resins. The photoimageable compositions described in this '614 patent may be applied as a solution in an organic solvent directly to a circuit board or applied as a solution to a base sheet so as to form a dry film. Compositions such as described in the '614 patent which form a film upon evaporation of an organic solvent are disadvantageous with respect to the use of high levels of organic solvents. In forming films from solutions, the organic solvent typically comprises about one-half of the solution volume. The cost of the solvent, including the shipping and storage of the same, is quite significant. Furthermore, organic solvents, which must be evaporated from the layered compositions, pose substantial health and environmental problems. A further disadvantage of the photoimageable compositions described in the '614 patent is that once photoimaged, the film is developed by washing away the unexposed areas with an organic solvent.

i; I 'WO 89/05476 PCT/US88/04338 3 It is an object of the present invention to provide a photoimageable substance which at or near 100% solids may be formed into a film, exposed, developed with aqueous solution and thereafter cured to form a layer with hardness and permanency characteristics similar to films based entirely upon epoxy resins.

Summary of the Invention In accordance with the invention, there is provided a photoimageable composition comprising a flowable, aqueous-soluble, film-forming, polymeric binder; a cross-linking agent for the binder; a polymerizable acrylic substance; a photosensitive, free-radical generating material; an epoxy resin; and an epoxy cure catalyst. The aforesaid components are selected to be mutually miscible and are mixed together to form a homogeneous solution. The composition is preferably substantially free of organic solvent, i.e, at or near 100% solids. The substrate may be a surface of a printed circuit board. Alternatively, the substrate may be a backing sheet or other layer of a dry-film laminate from which the photosensitive film is transferred to a printed circuit board or the like. The polymerizable acrylic substance and photosensitive, free-radical generating material provide the means of imaging the film by forming a polymer which insolubilizes those portions of the film which are exposed to actinic radiation. The epoxy resin, as promoted by its cure catalyst, hardens the film so as to be suitable as a solder mask or as a layer in totally i additive plating. The binder is selected for its film-forming properties, whereby.the photoimageable i composition may be used, substantially in the absence of .1

-J

WO 89/05476 PCT/US88/04338 4 solvents, to form a layer on the substrate. Also, the binder is selected to have sufficient solubility in aqueous or alkaline aqueous solution that the photoimageable composition may be developed in either aqueous or alkaline aqueous solution. Upon sufficient reaction with the cross-linking agent, the binder will harden and become insoluble in aqueous or alkaline aqueous solution and thereby contribute to the permanency of the fully cured layer, a solder mask, which is eventually formed. However, as described in greater detail hereinafter, it is preferred that the binder and cross-linking agent be selected so that a partial cure may be effected under conditions which do not substantially cure the epoxy resin. For example, compositions according to this invention may be "heat-bumped" under mild conditions of time and temperature to effect a partial cure of the binder that renders the photoimageable composition non-tacky, yet leaves a film of the photoimageable composition soluble in aqueous or alkaline aqueous solution.

Detailed Description of Certain Preferred Embodiments The photoimageable compositions according to the present invention each contains at least the following components: a film-forming polymeric binder which is soluble in aqueous or alkaline aqueous solution, a cross-linking agent for the polymeric binder, a polymerizable acrylic substance, a photosensitive, free radical-generating initiator chemical system, an Scure C-p\ys -FtcShe compos it;oO epoxy resin composition and zazi epoxy resin_ These components are selected to be mutually miscible _and when mixed together form a homogeneous solution.

IL I- WO 89/05476 PCT/US88/04338 Herein, unless otherwise stated, all percentages are by weight and are calculated relative to the homogeneous solution of components Thus components 100 wt. percent. The amounts of any additional ingredients, such as fillers, solvents, etc. are calculated relative to the sum of At the outset, a photoimageable composition, in accordance with the invention, contains a substance or substances capable of forming a film on a substrate.

Because it is preferred that the photoimageable composition be substantially free of organic solvent, that is, approaching 100% solids, the film-forming binder material should be liquid at room temperature and preferably free-flowing at room temperature. In order that the photoimageable composition be developab-le in aqueous or alkaline aqueous solution, the film-forming material itself must be soluble in an aqueous solution, either water or a base-containing aqueous solution.

Furthermore, the film-forming material must be compatible with the other components of the photoimageable composition.

One important class of film-forming materials useful as binders in forming photoimageable compositions in accordance with the present invention comprises polymers and copolymers of acrylic acids. These polymers and copolymers contain free carboxyl groups and are therefore soluble in alkaline aqueous solutions. These binders are selected for sufficient solubility in alkaline aqueous solution and are employed at a sufficient weight percent of the photoimageable composition that the photoimageable composition is likewise soluble in alkaline aqueous ^r solutions (until exposure to actinic radiation) and hence developable in alkaline aqueous solution. Generally, the i j WO 89/05476 PCT/US88/04338 6 higher the acid number of the acrylic polymeric binder, the more soluble the photoimageable composition is in alkaline aqueous solution and the acrylic polymers and copolymers used in accordance with this invention generally have acid numbers greater than about 100, preferably greater than about 150 and most preferably greater than about 200. To provide a high acid number, the polymeric binder material must be formed from one or more acrylic monomers having a free carboxylic acid group, acrylic acid and methacrylic acid.

The selection of binders which are sufficiently soluble in aqueous solution or alkaline aqueous solution and to an extent sufficient to render the entire photoimageable composition soluble and developable in aqueous or alkali aqueous solution contrasts sharply with the photoimageable compositions provided by above-referenced U. S. Patent No. 4,268,614 which must be developed in organic solvents. Although U. S. Patent No. 4,268,614 teaches the use of acrylic polymers in photoimageable compositions, the polymers described therein are of low acid number and, therefore, do not render the compositions soluble in alkaline aqueous solutions.

The polymeric binder may, and generally is, formed from additional comonomers, including esters of acrylic acids, such as methyl acrylate, methyl methacrylate, hydroxy ethyl acrylate, butyl methacrylate, octyl acrylate, 2-ethoxy ethyl methacrylate, t-butyl acrylate, diacrylate, N,N-diethylaminoethyl acrylate, ethylene glycol diacrylate, 1,4-butanediol diacrylate, diethylene glycol diacrylate, hexamethylene glycol diacrylate, 1,3-propanediol diacrylate, decamethylene glycol diacrylate, decamethylene glycol dimethacrylate, 1,4-cyclohexanediol diacrylate, i WO 89/05476 PCT/US88/04338 7 2,2-dimethylol propane diacrylate, glycerol diacrylate, tripropylene glycol diacrylate, glycerol triacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, 2,2-di(p-hydroxy-phenyl)-propane diacrylate, pentaerythritol tetracrylate, 2,2-di(p-hydroxyphenyl)-propane dimethacrylate, triethylene glycol diacrylate, polyoxyethyl-2-2-di(p-hydroxyphenyl)-propane dimethacrylate, triethylene glycol dimethacrylate, polyoxypropyltrimethylol propane triacrylate, ethylene glycol dimethacrylate, butylene glycol dimethacrylate, 1,3-propanediol dimethacrylate, butylene glycol dimethacrylate, 1,3-propanediol dimethacrylate, 1,2,4-butanetriol trimethacrylate, 2,2,4-trimethyl-1,3pentanediol dimethacrylate, pentaerythritol trimethacrylate, 1-phenyl ethylene-1,2-dimethacrylate, pentaerythritol tetramethacrylate, trimethylol propane trimethacrylate, 1,5-pentanediol dimethacrylate, and l,4-benzenediol dimethacrylace.

Suitable non-acrylate co-monomers which may be incorporated in the binders include, but are not limited to, styrene, vinyl toluene, maleate esters such as dibutyl maleate, maleic anhydride, vinyl ethers, vinyl ketones, vinyl pyridines and allyl acetoacetates.

It will be appreciated by those skill in the art that certain functional groups on the various components of the photoimageable composition will, to a greater or lesser degree, interact with epoxy groups of the epoxy resin, and thereby cause premature cross-linking of 'he epoxy resin.

This is primarily a shelf-life problem, and the level of certain chemical functional groups may have to be limited to provide a desired shelf-life.. However, shelf-life is not the only concern in formulating photoimageable L II WO 89/05476 PCT/US88/04338 8 compositions, and compositions according to the invention may be finally formulated near to the time of use.

Generally, free amine groups cannot be used in the presence of epoxy resins if any degree of shelf-life is to be achieved. Carboxyl groups, hydroxyl groups and amide groups will also initiate epoxy polymerization, though the levels of these groups may be controlled to be consistent with reasonable shelf-life. Where shelf-life is important, in formulating dry films, it is especially desirable to control the level of epoxy-reactive groups, to the extent that is consistent with other desirable aspects of the photoimageable composition, providing requisite solubility in alkaline aqueous solution. Thus, for example, where shelf-life is to be extended, it is desirable that the acrylate binder contain few hydroxyl moieties, such as those found in N,N-diethylaminoethyl acrylate, glycerol diacrylate and pentaerythritol triacrylate.

The acrylate-containing polymers having high acid numbers are the preferred film formers or binders for compositions in accordance with this invention, particularly for use as a film on a printed circuit board which must pass IPC/ANSI SM-840A Class III tests. However, because of the large number of acidic groups in these polymers, there are limitations to long-term stability of compositions containing both acrylic film formers and the epoxy resins, which are another component of the photoimageable compositions. The acrylate-containing polymers are, however, compatible with epoxy resins for relatively short periods, and there is generally no urgency to apply these resins immediately after final formulation. Thus, compositions containing both acrylate polymers having free carboxylic acid groups and epoxide WO 89/05476 PCT/US88/04338 9 resins may be provided as one-part liquid compositions for application to printed circuit boards or even as partially cured (heat-bumped) layers of dry films. The shelf-life of such compositions depends upon the particular components of the system, the acid number of the particular acrylic binder which is used, and the temperature at which the composition is stored prior to use. The compatibility problems of epoxy resins in the presence of free carboxyl groups may, however, require liquid compositions or dry films formed therefrom to be used within a shorter period of time than is customary in the art. Because of the long-term compatibility problem of the acrylate-containing binder polymers and epoxy resins, a composition may be provided commercially as a two-part system, one part containing the acrylate-containing binder and the other part containing the epoxy resin. The remaining components are appropriately distributed among the two parts of the system, it being generally desirable in such two-part systems to keep curing agents separate from the corresponding polymerizable or cross-linkable materials.

Another type of material used as binders in photoimageable compositions in accordance with the present invention are styrene-maleic anhydride copolymers in which the mer units derived from maleic anhydride remain in the anhydride state. The polymers, while having no free hydroxyl or carboxylic acid groups, may be saponified in alkaline solution to the acid form. Styrene-maleic anhydride copolymers, which are saponifiable to acid numbers of about 100 or more, are preferred, as they i provide good solubility in aqueous solution. A type of film-forming binder which is long-term compatible with epoxy resins is polyvinyl alcohols.

1 WO 89/05476 PCT/US88/04338 Polyvinyl alcohols are substantially saponified poly-vinyl acetates, preferably being at least about 80% hydrolyzed.

Polyvinyl alcohols are available in a wide variety of viscosities, and viscosities are selected for the particular application.

Carboxylated polyvinyl alcohols are similar to polyvinyl alcohols, but between about 1 and about 5% of the per units contain free carboxyl groups. Carboxylated polyvinyl alcohols are formed by copolymerizing vinyl acetate and an alkyl ester of acrylic acid and then hydrolyzing the ester bonds of the polymer. Carboxylated polyvinyl alcohols are hydrolyzed to at least about Because of the free carboxyl groups, this polymer is somewhat less compatible with epoxy resins.

Polyvinyl alcohols suitable for use in accordance with the invention are available from Air Products, Allentown, PA, under the tradenames Vinol 125, 165, 107, 325, 350, 425, WS-42, 205, 523, 540, 205S, 523S and 540S.

Carboxylated polyvinyl alcohols suitable for use in the invention are sold by Air Products, under the trade name Vinol 118M. Polyvinyl alcohol and carboxylated polyvinyl alcohol, unlike the acrylate-containing polymers having high acid numbers, are soluble in water, generally regardless of the pH, and therefore do not require basic developers, that is, photoimageable compositions based upon these binder materials may be developed in water.

Polyvinyl alcohol and carboxylated polyvinyl alcohols are considered less desirable binders as compared with acrylate binders with respect to hardness and water-susceptability of the finally cured film.

Novolac resins, such as those described in Polymer j Chemistry, Malcolm P. Stevens, Addison-Wesley Publishing Company, Inc., Reading, Massachusetts, (1975) pp 324-327, i 1 _I I

I-

I i I WO 89/05476 PCT/US88/04338 11 the teachings of which are incorporated herein by reference, are also suitable as binders. Novolac resins have relatively good stability with epoxy resins (an advantage in one part formulations) and can be used to form binders which pass Class III standards.

Other suitable film-forming resins for use in the invention include, but are not limited to, cellulose, and hydroxyethyl cellulose. Furthermore, mixtures of the several polymeric binders discussed above may be included in a photoimageable composition formulation.

The polymeric binder or mixture of polymeric binder materials compriseF between about 10 and about 40% by weight of the homogeneous solution of components preferably between about 15 and about 25% by weight.

The photoimageable composition is applied as a viscous, tacky, flowable liquid to a substrate, such as a printed circuit board or to a backing sheet to form a dry film. As explained in greater detail hereinafter, it is often desired that the photoimageable composition be partially curable to either partially harden or to insolubilize the film, and to this end, the photoimageable composition contains a cross-linking agent which cross-links the binder and may also cross-link certain other components of the photoimageable composition.

Desirably, the cross-linking agent acts primarily at temperatures somewhat above room temperature, above 0 C, whereby the photoimageable composition may be applied to a substrate at or near room temperature and subsequently heat-bumped to effect a controlled level of cross-linking. It is important for several applications that the controlled level of cross-linking be effected using relatively mild temperatures and in a relatively short period of time. By relatively mild temperatures and t_ WO 89/05476 PCT/US88/04338 12 relatively short periods of time, is herein meant, in comparison to the substantially higher temperatures and/or longer periods of time required to finally cure the epoxy resins, as described hereinafter.

Preferred cross-linking agents are melamineformaldehyde condensation products, such as those sold under the trademark Resimene by Monsanto, St. Louis, MO.

.r Cymel by American Cyanimide. The functional groups on the amino moieties react with complementary reactive groups, hydroxyl groups, on the resin, forming a three-dimensional thermoset polymer network. Other suitable cross-linking agents include urea-formaldehyde resins and phenolic resols. Novolac resins may be crosslinked by formaldehyde, paraformaldehyde or hexamethylene tetramine. The cross-linking agent comprises between about and about 25% by weight of the homogeneous solution of components Generally for photoimageable compositions which are to be applied as a liquid film, the amount of the cross-linking agent is toward the lower end of this range; in forming dry films, the amount of the cross-linking agent is toward the upper end of this range.

The photoimaging system is based upon the polymerizable acrylic subtances The polymerizable acrylic substances are generally monomers containing one or more acrylic moieties. They can, however, contain acrylic dimers or trimers. Any of the acrylic monomers listed above as components of an acrylic polymeric binder is suitable as a polymerizable acrylic substance for purpose of this invention. Mixtures of acrylates are also suitable. As in polyacrylate binder, the polymerizable acrylate substance(s) must be selected with the intended shelf-life of the photoimageable.composition in mind, and levels of free carboxyl, hydroxyl, amide and other i I y

K

r-r WO 89/05476 PCT/US88/04338 13 epoxy-reactive functional groups appropriately controlled.

The polymerizable acrylic materials comprise between about and about 35 wt. percent of homogeneous solutions according to the invention and preferably from about 18 to about 25 wt. percent.

In some cases, it has been found to be advantageous to use an acrylic monomer that includes at least one free hydroxyl group, for example, hydroxy alkyl acrylates and methacrylates, such as pentaerythritol tetraacrylate, 2-hydroxy ethyl acrylate, 2-hydroxy ethyl methacrylate and 2-ethoxy ethyl methacrylate. The free hydroxy groups are acted upon by the cross-linking agent during the heat-bump, chemically linking at least some of the polymerizable acrylates to the polymeric binder and thereby providing a more integrated cross-linked film structure.

Also required in conjunction with the polymerizable acrylate substance is a chemical initiator system which generates free radicals in the presence of actinic radiation and polymerizes the acrylic substance.

Polymerization of acrylic monomer units into a threedimensional structure insolubilizes the photoimageable composition by immobilizing the polymeric binder. The choice of the photosensitive, free radical-generating initiator system is not considered to be critical to the practice of the present invention, and a wide variety of such compounds may be successfully utilized in the practice of this invention. Examples of chemical photoinitiator systems include benzophenone, benzoin ether, benzil ketals and acetophenone and its derivatives.

Other suitable initiator systems are described, for example, in U.S. Patent Nos. 3,469,982, 4,451,523 and 4,358,477, the teachings of which are incorporated herein i~ 1 WO 89/05476 PCT/US88/04338 14 by reference. The amount of photoinitiator employed may vary over a wide range, depending upon the polymerizable acrylic substance(s), the particular photoinitiator system and the desired time of development. Generally, the photoinitiator chemical system comprises between about 0.01 and about 15 wt. of the homogeneous solution The material which imparts the excellent hardness and durability to the film or layer after development and final curing is the epoxy resin or mixture of epoxy resins. The epoxy resin or resins comprise between about and about 50 percent by weight of the homogeneous solution At high temperatures and/or in the presence of a catalyst, the epoxy groups of the resin molecules open and react with other materials present.

Primarily the epoxy resin molecules react with each other; however, to a certain extent, the epoxy molecules react during final curing with the cross-linking agent, and perhaps also with the acrylic binder material and the remaining polymerized and unpolymerized acrylate substances. The major consideration of selection of the epoxy resin or mixture of resins is that the epoxy resin composition be a liquid at about room temperature, whereupon the photoimageable composition can be applied as a liquid film to the substrate. Generally, lower molecular weight epoxies, having molecular weights between about 240 and about 260, tend to be liquid, and preferably at least about 70% by weight of the epoxy re,ins comprises polyepoxy molecules having molecular weights below 260. It is permissible, however, to dissolve higher molecular weight, solid epoxies in the ij lower molecular weight, liquid epoxies, providing that the combination of epoxy resins is liquid. Higher molecular i i il :1 1 'WO 89/05476 PCT/US88/04338 weight epoxies may be advantageously incorporated into a photoimageable composition to control viscosity of the photoimageable composition. The inclusion of some higher molecular weight epoxy resin dissolved in lower molecular weight epoxy resin may result in formation of a harder, more durable film.

A wide variety of epoxy resins are suitable for use in accordance with the present invention. Suitable epoxy resins are described, for example, in U.S. Patent No.

4,092,443, the teachings of which are incorporated herein by reference. Preferred epoxy resins for purpose of the invention are cycloaliphatic epoxides, such as those sold under the trade names Cyanacure UVR-6100 and UVR-6110 by Union Carbide, Danbury, CT.

Epoxy resins are generally heat-curable; high temperatures open the epoxy groups, thereby causing them to react. Several applications of photoimageable compositions in accordance with the invention require that curing of the epoxy resin composition takes place at a higher temperature and/or is cured over a longer period of time than the temperature and time required for the heat-bump, during which the acrylic binder is cross-linked to a controlled extent. Although some degree of curing of the epoxy resins may take place continuously and even at a somewhat increased rate during the heat-bump, the epoxy resin composition in several applications must remain substantially uncured until after exposure to patterned actinic radiation and development. Once the epoxy resin composition cures to any appreciable extent, the photoimageable composition becomes insoluble in aqueous and alkaline aqueous solutions and therefore i non-developable. Accordingly, the epoxy resin composition is further selected so as to be curable under harsher L i I--;i WO 89/05476 PCT/US88/04338 16 Sconditions of time and temperature than are required for the initial heat-bump.

The photoimageable composition includes a cure catalyst for the epoxy resin composition which promotes more rapid curing at the final heat cure temperature.

Suitable heat-activated curing agents include polycarboxylic acid anhydrides, dicyandiamides, complexes of amines, such as solely tertiary amines, with boron trifluoride or boron trichloride, latent boron difluoride chelates, aromatic polyamines and imidazoles, such as 2-ethyl-4-methylimidazole. Other examples of epoxy cure catalysts are found in U.S. Patent No. 4,438,189, the teachings of which are incorporated herein by reference.

Preferred epoxy catalysts are blocked or latent catalysts, such as those sold under the trade name SA-102.by Air Products. Such catalysts have an epoxy-catalyzing group, an acid group or amine or amide group, appropriately blocked. At a threshold temperature, the catalyst releases its blocking group and catalyzes epoxy ring opening. The threshold activation temperature of such catalysts is particularly advantageous in a process which includes an initial, relatively low-temperature, relatively short-time heat-bump and a subsequent heat-cure under more vigorous temperature/time conditions. Epoxy cure catalysts are used at levels of from about 0.01 to about 5 wt. percent of the homogeneous solution The components of the photoimageable composition are selected to be mutually soluble to form a single-phase liquid composition. The liquid photoimageable composition may be applied to a substrate by a variety of application methods, including screen printing, curtain coating, roller coating and extrusion coating. Each application method has its own particularities, and photoimageable i C i WO 89/05476 PCT/US88/04338 17 compositions in accordance with this invention may be formulated in accordance with the particular requirements of the particular method of application, to provide a suitable photoimageable composition viscosity.

It may be appreciated at this time that all of the components described above remain present in the final cured film which is formed, that is, the formulation supplies substantially 100% solids. This is an important advantage of the photoimageable compositions of the present invention, in contrast to films which are formed by solvent evaporation. It is contemplated, however, that the photoimageable composition may contain minor amounts of organic solvent, up to about 20% by weight relative to the homogeneous solution and preferably less than about 2% by weight. Some solvent may be present only because certain of the components of the system may be commercially provided along with a volatile organic solvent.

In addition to the components described above which are essential to a photoimageable composition in accordance with the invention, the photoimageable composition may optionally contain additional components which are standard in the art. The photoimageable composition may contain organic or inorganic fillers at levels up to about 35 wt. percent relative to the homogeneous solution Some examples of fillers are micro talc, ground polyethylene, clay, fumed silica and polyvinyledene fluoride. Also, relatively small amounts of flow-control agents, antioxidants, dyes, etc.

may be added.

The compositions in accordance with the invention which provide a photoimaging reaction in combination with a two-stage cure are useful in several types of t i' i WO 89/05476 PCT/US88/04338 18 applications, and advantages of the compositions will become more fully appreciated as the use of these compositions is discussed with respect to several applications. It will be appreciated, that the exact formulation and treatment conditions for any formulation will depend upon the application to which it is to be put.

An important use of the compositions of the present invention is for direct application to a printed circuit board where contact printing is to be employed. The composition is applied as a layer on the surface of the board. Subsequent to application of the photoimageac-e composition to the surface, the photoimageable composition is heat-bumped for a controlled period of time so that the photoimageable composition forms a non-tacky layer, yet leaves the photoimageable composition soluble in an appropriate aqueous solution. The heat-bump takes place at a controlled temperature and for a controlled time period to achieve the non-tacky condition; however, care must be taken to avoid excess cross-linking of the several components which would render the photoimageable composition insoluble in aqueous or alkaline aqueous solutions. Heat-bump times and temperatures must be determined for each particular photoimageable composition.

For any particular photoimageable composition, different temperatures may be used with different times. Typically, heat-bump temperatures range from about 70-100 0 C at times of from 5 to 60 min.; however, it can easily be appreciated that lower temperatures with longer heat-bump times may be employed.

During the heat-bump, the primary reaction is between the cross-linking agent and the polymeric binder; however, minor reactions probably involve.interactions between a number of components. Heat-bump reactions contribute to

L

WO 89/05476 PCT/US88/04338 19 non-tackiness of the film. For applications where the film is to remain soluble and developable in an appropriate aqueous or alkaline aqueous solution, reactions which occur during the heat-bump must be consistent with continued solubility of the film.

For contact printing and dry film applications, the non-tacky, but developable film which forms after the heat-bump is ready for exposure to actinic radiation. For contact-printing, the artwork, diazo artwork, is laid directly on the film. The non-tacky nature of the film at this stage enables the artwork to be contacted with the film. As those with skill in the art readily appreciate, contact printing is generally preferred over remote exposure techniques for producing sharply defined images. Light intensities (which generally depends upon the unit used) and exposure times (which are generally determined by the operator) deter-mine the light energy applied during exposure. Required light energies for exposure depends primarily on the polymerizable acrylic substances and the photoinitiator systems used and amounts thereof. Exposure must be determined for each photoimageable composition.

For non-contact printing, the film may be exposed either after a heat-bump, which leaves the film soluble in aqueous or alkali aqueous solution, or with the film in unaltered, tacky form.

Subsequent to exposure, the non-exposed portions are dissolved and washed away in aqueous or alkaline aqueous solution. Films based upon polyvinyl alcohol, carboxylated polyvinyl alcohol, cellulose or the like are soluble in water and may be developed in an aqueous solution, including water. Photoimageable compositions based upon acrylic binder-containing films having high _1 i. i i=i L~ WO 89/05476 PCT/US88/04338 acid numbers, on the other hand, must be developed in an alkaline aqueous solution. Typical alkaline developers contain from 0.5 to about 3% by weight of a weak base, such as potassium carbonate, sodium carbonate or ammonium hydroxide or from about 0.4% to about 3% by weight of a strong base, such as sodium hydroxide or potassium hydroxide. Novolac-containing films are also developed in alkaline aqueous developers.

The ability to be developed with aqueous or alka-line aqueous solutions is considered to be an important advantage of the photoimageable composition of the present invention. Eliminating the need for solvent-based developers eliminates the cost of the solvents as well as health, environmental and recycling problems. Although .the films formed in accordance with the inven-tion are developable in aqueous solutions without any organic solvents, developers may include some organic solvents, providing that the added organic solvent does not solubilize the exposed portions of the film.

Following development, it is preferred to again expose the film to actinic radiation to effect a UV-cure.

The UV-cure is optional, but is helpful in producing a stronger permanent film. Primarily, the UV-cure is believed to polymerize or cross-link any remaining polymerizable acrylic substance.

The primary cure of the exposed and developed film is the thermal cure which opens the epoxy groups of the epoxy resin molecules, resulting cross-linking of the epoxy resin molecules with each other and with the other materials in the film. The thermal cure is generally i carried out at temperatures ranging from about 100°C to about 200 0 C for a period of from.about 15 min. to about 2 hrs. A typical cure would be 150 0 C for an hour. The i _1 1 i I WO 89/05476 PCT/US88/04338 21 actual cure time and cure temperature depends upon the epoxy resin used, the epoxy cure catalyst and the amounts of each. If a blocked or latent epoxy cure catalyst is used, curing is done at a temperature above that which deblocks the catalyst.

It is very often the case that a solder mask must be applied to two sides of a printed circuit board.

Generally, for contact printing of a solder mask on both sides of a printed circuit board, the following modification of the above-described procedure is followed.

The composition is applied to "side 1" of the board; the composition is heat-bumped to non-tackiness and the board is cooled. The composition is applied to "side 2" of the board; the composition is heat-bumped to non-tackiness and the board is cooled. The two sides are then contact-printed, and both sides of the board are developed simultaneously by washing the board in water or alkaline solution, as appropriate. Final curing is then effected.

It may be appreciated that "side 1" is "heat-bumped" for a longer period of time than is "side Careful control of the two heat-bumps is required so that "side 2" can be heat-bumped to non-tackiness while leaving "side I" still soluble in the developer. The composition must therefore be formulated so as to provide a sufficiently wide "cure window" of heat-bump time which provides a non-tacky, yet developable film.

It is also contemiplated that the photoimageable composition of the present invention be used for off-contact printing using highly collimated light for good resolution. Other considerations may apply when off-contact printing is used. Particularly, it is not necessary that a non-tacky layer-be provided prior to exposure, and even a film of viscous liquid may be i 1 F ij- iI i WO 89/05476 PCT/US88/04338 22 exposed. Nevertheless, the two-stage cure provided by the compositions of the present invention is advantageous for off-contact printing.

A typical procedure for off-contact printing of two sides of a printed circuit board is as follows. The composition is qpplied as a film to "side 1" of the circuit board. The film is exposed to patterned actinic radiation. Resulting polymerization of the acrylic substance both hardens the exposed portions of the film and renders such portions insoluble to developer. The film is then developed in aqueuus (or aqueous alkaline) solution. At this time, a heat-bump is employed to sufficiently harden and render non-tacky the portions of the film which remain so that these portions are not lost during subsequent handling of the board. This heat-bump further insolubilizes the remaining portions of the film, protecting the film against treatment of "side A film of composition is then applied to "side the film is exposed and the film on "side 2" is developed. At this point, the board is baked, resulting in cross-linking of the binder on "side 2" and curing of the epoxy resin on both sides of the board. It can be appreciated that the "window" of curing provided by the heat-bump in this procedure, where the heat-bump of side 1 follows exposure and development, may differ from that required in the :ontact printing procedure, described above, in which the heat-bump precedes exposure and development. In either case, the intermediate ctre achieved during the "heat-bump", as provided by the acrylic binder, obviates the need to fully cure the epoxy resin of "side 1" before proceeding with treatment of "side 2".

In forming a dry film, the photoimageable composition is applied as a layer to the backing sheet and then i i

A

WO 89/05476 PCT/US88/04338 23 heat-bumped to non-tackiness. The film is subsequently transferred from the backing sheet to a solid substrate, a printed circuit board, and then exposed, developed and cured as discussed above.

In forming a dry film, general considerations and techniques of dry film application apply. The film must be selectively adherent to the substrate as compared to its adherence to the backing sheet material, e.g., polyethyleneterphthalate. The backing sheet may be appropriately coated to provide such selective adherence.

The dry film may also include other layers, such as an oxygen-impermeable membrane, polyethylene, which remains on the film until just prior to or following exposure to radiation and which is then removed to allow development of the layer.

The invention will now be described in greater detail by way of specific examples.

WO 89/05476 PCT/US88/04338 24 EXAMPLE 1 A photoimageable composition having the following composition was prepared: Component Wt.

acrylic resin (binder), acid no. 200 22.6 1,8 diaza-bicyclo-(5,4,0)-undecene-7-phenol salt 1.2 equal wt. mixture of hydroxyethyl methacrylate, bisphenol A diacrylate, and dipentaerithritol monohydroxy pentaacrylate 21.8 2,2 dimethyl 2 phenyl-acetophenone liquid cycloalphatic monoepoxy, epoxy equiv. 120-130 42.4 methylated melamine 100.0 plus leveling agent 1.2 pigment (phthalocyanine green CI#74260) 1.2 Fillers fumed silica 1.8 micro talc 14.4 ground polyethylene 0.9 The photoimageable composition was applied as a .0381 mm thick layer on a printed circuit board. The photoimageable composition was heat-bumped at 80 0 C for 30 minutes, providing a non-tacky film. A diazo artwork was placed directly on the film, and the film was exposed to actinic radiation having an intensity of 200 mJ/cm for 1 min. The film was then developed in a basic aqueous solution, i.e., 1% by weight sodium carbonate monohydrate. The film was L I I r WO 89/05476 PCT/US88/04338 UV-cured by exposure to actinic radiation having an intensity of 2 Joules for 2 min. Heat-curing was at 150°C for 1 hour.

The following additional compositions according to this invention are prepared and processed in accordance with Example 1.

EXAMPLE 2 Components Wt.

Acrylic resin with minimum acid number 37.3 of two hundred Hydroxyethyl acrylate 26.8 Hexamethylmelamine 10.9 Benzophenone 1.9 Liquid cycloalphatic diepoxy 22.6 1,8 diaza-bicyclo-(5,4,0) undecene 7 100.0 plus Leveling agent 1.2 Pigment (phthalocyanine green CI#74260) 1.2 Fillers polyvinylidene fluoride 9.3 micro talc 22.3 i 1. 1. i. i. i WO 89/05476 PCT/US88/04338 26 EXAMPLE 3 Component wt.

Styrene maleic anhydride, acid no. 200, M.W. 10,000 22.2 Trimethyloipropane triacrylate 33. 9 Butylated melamine 5.6 Isobutyl benzoin ether 0.9 Solid bisphenol-A epoxy, epoxy equiv. 525-1800 35.8 1,8. diaza-bicyclo-(5,4,0)--undecene-7-ethyl hexanoic acid salt 1.6 100 .0 plus Leveling agent A 1.2 Pigment (phthalocyanine green CI#74260) 1.2 Fillers clay 3. 6 micro talc 6.2 ground polyethylene 1.1 EXAMPLE 4 Component wt.

Styrene maleic anhydride, acid no. 200, 10,000 28.8 Ethoxylated trimethylolpropane triacrylate 16.7 Methyl-butyl melamine 22.3 Isopropyl thioxanthone Solid multifunctional novalac epoxy 27.7 1,8 diaza-bicyclo-(5, J)-undecerie-7-p-toluene sulfonic acid salt 100o. 0 plus Leveling agent 1.2 Pigment (phthalocyanine green CI#74260) 1.2 WO 89/05476 PCT/US88/04338 27 Fillers fumed silica 1.8 micro talc 14.4 ground polyethylene 0.9 EXAMPLE Component Wt.

Acrylic resin with minimum acid number of two hundred 35.9 Diethyleneglycol diacrylate 15.7 Hexa-alkoxy methylol melamine resin 23.8 2 chlorothioxanthone 4.1 Liquid cycloalphatic monoepoxy, epoxy equiv. 120-130 20.2 1,8 diaza-bicyclo-(5,4,0)-undecene-7-formic acid salt 0.3 100.0 plus Leveling agent 1.2 Pigment (phthalocyanine green CI#74260) 1.2 Fillers fumed silica 1.8 micro talc 14.4 ground polyethylene 0.9 EXAMPLE 6 Components Wt.

Styrene maleic anhydride, acid no. 200, 10,000 17.3 Polyethylenglycol diacrylate 20.1 Unsaturated acrylic melamine 20.4 Isobutyl benzoin ether 3.3 Solid multifunctional novalac epoxy 37.7

I

WO 89/05476 PCT/US88/04338 28 1,8 diaza-bicyclo-(5,4,0)-undecene-7-phenol salt 1.2 100. 0 plus Leveling agent 1.2 Pigment (phthalocyanine green CI#74260) 1.2 Filler clay 22.1 EXAMPLE 7 Components wt.

Acrylic resin with minimum acid number of two hundred 12.2 Tetraethyleneglycol diacrylate 31.8 Butyl-esterified-phenol formaldehyde 5 .7 Diethoxy-2-methyl-1-phenylpropane-l-one 3.7 Liquid cycloalphatic monoepoxy 45.6 1,8 Diaza-bicyclo-(5,4,0)-undecene-7-ethyl-hexanoic acid salt 100 .0 plus Leveling agent 1.2 Pigment (phthalocyanine green CI#74260) 1.2 Fillers fumed silica 1.8 micro talc 14 .4 ground polyethylene 0.9 WO 89/05476 PCT/US88/04338 29 EXAMPLE 8 Components Wt.

Acrylic resin with minimum acid number of two hundred 21.5 Cyclohexyl acrylate 18.3 Butylated urea 14.9 2,2 dimethyl-2-phenyl-acetophenone 2.2 Solid bisphenol-A-epoxy, epoxy equiv. 525-1800 42.1 1,8 Diaza-bicyclo-(5,4,0)-undecene-7-phenol salt 100.0 plus Leveling agent 1.2 Pigment (phthalocyanine green CI#74260) 1.2 Fillers fumed silica 32.3 EXAMPLE 9 Acrylic resin with minimum acid number of two hundred 30.3 Isodecylglycol triacrylate 16.2 Methylated urea 14.3 2,2-dimethyl-2-phenyl-acetophenone 2.1 Liquid cycloaliphatic diepoxy, epoxy equiv. 120-145 35.3 1,8 diaza-bicyclo-(5,4,0)-undecene-7 1.8 100.0 plus Leveling agent 1.2 Pigment (phthalocyanine green CI#74260) 1.2 _i ii 1 c WO 89/05476 PCT/US88/04338 Fillers fumed silica micro talc ground polyethylene 1.8 14.4 0.9 While the invention has been described in terms of certain preferred embodiments, modifications obvious to one with ordinary skill in the art may be made without departing from the scope of the present invention.

Various features of the invention are set forth in the following claims.

i

Claims (5)

1. A photoimageable composition comprising a homogeneous solution of between 10 and abett 40 wt. percent of a flowable, film-forming polymeric binder which is soluble in aqueous or alkaline aqueous solution, between about 5 and abeet-25 wt. percent of a cross-linking agent for said polymeric binder, between out- 15 and about 35 wt. percent of a polymerizable acrylic substance, between ab -eot 0.01 and -a-ebo 15 wt. percent of a photosensitive, free radical-generating initiator chemical system which in the presence of actinic radiation initiates polymerization of said acrylic substance to form a three-dimensional chemical structure that renders actinic radiation-exposed portions of said photoimageable composition insoluble to aqueous or alkaline aqueous solutions, between about' 20 and -ab4eu 50 wt. percent of an epoxy resin composition which is curable to harden said photoimageable composition subsequent to exposure to actinic radiation, and between ~bout 0.01 and aeebt- 5 wt. percent of a cure catalyst for said epoxy resin, said polymeric binder being sufficiently soluble in aqueous or alkaline aqueous solution and used at a sufficient level that said photoimageable composition as a whole is developable in aqueous or alkaline aqueous solution, said components being selected to be mutually miscible and mixed together to form .said homogene s solu n--

2. A photoimageable com ition in accordance with Claim 1 wherein said cross-linking agen acts with said polymeric i *-b'4:er -in a &fte-r-oli--e mRRT- L i said homogeneous solution, said cross-linking agent reacting with said polymeric binder in a controlled manner, whereby said photoimageable composition may be mildly heated to render said photoimageable composition non-tacky, yet developable in aqueous or alkaline aqueous solution, said epoxy resin being selected so that any curing of said epoxy resin during said mild heating conditions leaves said photoimageable composition soluble in aqueous or alkaline aqueous solution. 9 *9 0* *9 a **I EJD 3* *l- EJ

3 W019f11474PCF/USaU/04336 32 -CMPOAJP4Hiinv. MAY, he. I4bl4.ne compohItton. non -tacky, yet developable in aqueous orli aqueous molution, said epoxy resin bei acted to be insufficiently cured Linda mild heating conditions to render said photoi a composition insoluble to aqueous or alkaline A.d A photoimaseable composition according to Claim I wherein said cure catalyst Is a iLntent: catalyst htivtng b lockLng moa tien, said catalyst becoming unb lockevd 4bove a thresholId temperature, whereupon cure of sAid epoxy resin to promoted aboye 4aLdt threshold temperas.urs, 3fVr A photoima~eabLe composition according to Claim I wherein sa~id binder Ii formed at las~t in part fromn acrylic monomers having free carboxylic Acid iroups, said binder having an acid number of At least about 100,. q ~YA photo imnage-b to composition according to C14im I wherein said binder materiA.l is selected from the group connistina of polyvinyl alcohol, carboxylatad polyvinyl Alcohol, collulose, hydroxy ethyl ce1Lulose, styrene maIeiC anhydride copolymer, Anti Novolac resins, g h~ A photaimageable composition according to Claim 1 further comprising a dispersible organic or inorganic filler At a level of up to about 35 wt, percent relative to said homogeneous solution of components A photoimaseable composition accordina to Claim I wharein said epoxy resin composition is liquid At about room temperature, .4 1' U WO 89/05476 PCT/US88/04338 33 7 In combination, a substrate and a layer of photoimageable composition in accordance with Claim 1 thereon. -7 9 A combination in accordance with Claim .8wherein said substrate is a printed circuit board, said layer of photoimageable composition being processable to provide a solder mask. -7 S)cB. A combination in accordance with Claim,2iwherein said substrate is a flexible backing sheet, said backing sheet and said photoimageable composition layer being partially curable by cross-linking of said binder to form a dry film which is developable in aqueous or alkaline aqueous solution. 10 ,yi. A composition in accordance with Claim 1 provided as a two-part solution, one part containing said binder and the other part containing said epoxy resin composition. A composition in accordance with Claim 1 having no more than about 20% by weight organic solvents, relative to said homogeneous solution of components A composition in accordance with Claim 1 having no more than about 2% by wt. organic solvents, relative to said homogeneous solution of components I A composition in accordance with Claim 1 free of organic solvents. S A method of forming a hard, permanent, patterned film on a solid substrate comprising providing a photoimageable composition comprising a homogeneous solution of between abet -10 and about 40 wt. i- I It. 34 percent of a flowable, film-forming, polymeric binder which is soluble in aqueous or alkaline aqueous solution; between abo-ut 5 and-a-be 25 wt. percent of a cross-linking agent for said polymeric binder which when under mild heating conditions cross-links said binder to render said photoimageable composition non-tacky, while leaving said photoimageable composition soluble in aqueous or alkaline aqueous solution; between a-bu--e 15 and wt. percent of a polymerizable acrylic substance; between -a bub- 0.01 and -aout 15 wt. percent of a photosensitive, free radical-generating initiator chemical system which in the presence of actinic rtdiation initiates polymerization of said acrylic substance to form a three-dimensional chemical structure which renders actinic radiation-exposed portions of said photoimageable composition insoluble in aqueous or alkaline aqueous solutions; between -abo4t -20 and 50 wt.'percent of an epoxy resin composition which is curable for sufficient time and/or high temperature to harden said photoimageable composition subsequent to exposure to actinic radiation, said epoxy resin being selected to be insufficiently cured under said mild heating conditions so as to render said photoimageable composition insoluble in aqueous or alkaline aqueous solution; and between ab-&e 0.01 and wt. percent of a cure catalyst for said epoxy resin, said components being selected to be mutually miscible and mixed together to form said homogeneous solution, coating a film of said photoimageable composition on a surface of said substrate, heating said film of photoimageable composition for such time and temperature as to sufficiently cross-link said binder to render said film non-tacky yet still soluble in aqueous or alkaline aqueous solution, i: P i'T -I- WO 89/05476 PCT/US88/04338 exposing said film to patterned actinic radiation so as to polymerize said acrylic substance and render exposed portions of said film insoluble to aqueous or alkaline aqueous solution, developing said film in aqueous or alkaline aqueous solution to remove non-exposed portions of said film, and curing said epoxy resin in said photoimageable composition at such time and temperature as to render said film hard and permanent.

1516. A method according to Claim f including UV-curing said exposed, developed film. I17. The product of the process of Claim A method according to Claim 1-5 of forming a hard, permanent, patterned film on each of a first side and a second side of a solid substrate comprising providing said photoimageable composition according to step preparing said first side according to steps and preparing said second side according to steps and exposing each of said sides according to step developing said sides according to step and then curing said epoxy resin in said films of photoimageable composition according to step The product of the process according to Claim Itj A method of forming a hard, permanent, patterned film on a solid substrate comprising providing a photoimageable composition comprising a homogeneous solution of between abeou 10 and eabou 40 wt. percent of a flowable, film-forming polymeric binder which is soluble in aqueous or alkaline aqueous solution; between at- 5 and-sbei-t 25 wt. percent of a cross-linking agent for said WO 89/05476 PCT/US88/0433 8 36 polymeric binder which under mild heating conditions cross-links said binder to render said photoimageable composition non-tacky, while leaving said photoimageable composition soluble in aqueous or alkaline aqueous solution; between about 15 and -abee4 wt. percent of a polymerizable acrylic substance; between 4 -b-e 0.01 and abut- 15 wt. percent of a photosensitive, free radical-generating initiator chemical system which in the presence of actinic radiation initiates polymerization of said acrylic substance to form a three-dimensional chemical structure which renders actinic radiation-exposed portions of said photoimageable composition insoluble to aqueous or alkaline aqueous solution; and between about-20 and abe~t-50 wt. percent of an epoxy resin composition which is curable for sufficient time and/or high temperature to harden said photoimageable composition subsequent to exposure to actinic radiation, said epoxy resin being insufficiently cured under said mild heating conditions to render said photoimageable composition non-tacky so as to render said photoimageable composition insoluble in aqueous or alkaline aqueous solution, and (f) between bou-t 0.01 and--eut 5 wt. percent of a cure catalyst for said epoxy resin, applying said photoimageable composition as a film on a backing sheet, heating said film of photoimageable composition for such time and temperature as to sufficiently cross-link said binder to render said film non-tacky yet still soluble in aqueous or alkaline aqueous solution, transferring said non-tacky film from said backing sheet to a solid substrate, exposing said transferred film to patterned actinic radiation so as to polymerize said acrylic substance and render exposed portions of said film insoluble to aqueous or alkaline aqueous solution, A A K ,*1 -WO 89/05476 PCT/US88/04338 37 developing said film in aqueous or alkaline aqueous solution to remove non-exposed portions of said layer, and curing said epoxy resin at such time and temperature as to render said film hard and permanent. 2o01. A method of preparing a dry film comprising providing a photoimageable composition comprising a homogeneous solution of between e44bt- 10 and ~abi-t-40 wt. percent of a flowable, film-forming polymeric binder which is soluble in aqueous or alkaline aqueous solution; between ab e4t-5 and 4ab-t 25 wt. percent of a cross-linking agent for said polymeric binder which under mild heating conditions cross-links said binder to render said photoimageable composition non-tacky, while leaving said photoimageable composition soluble in aqueous or alkaline aqueous solution; between -a4-t- 15 and *bot-t 35 wt. percent of a polymerizable acrylic substance; (d) between abet- 0.01 and -abeut 15 wt. percent of a photosensitive, free radical-generating initiator chemical system which in the presence of actinic radiation initiates polymerization of said acrylic substance to form a three-dimensional chemical structure which renders actinic radiation-exposed portions of said photoimageable composition insoluble to aqueous or alkaline aqueous solutions; between eabte- 20 and abe-te- 50 wt. percent of an epoxy resin composition which is curable for sufficient time and/or high temperature to harden said photoimageable composition subsequent to exposure to actinic radiation, said epoxy resin being selected to be insufficiently cured under said mild heating conditions to render said photoimageable composition insoluble in aqueous or alkaline aqueous solution, and (f) between buet -0.01 and 4ab4et 5 wt. percent of a cure catalyst for said epoxy resin, said components being selected to be mutually miscible and mixed together-to form said homogeneous solution. 1 WO 89/05476 PCT/US88/04338 38 applying said photoimageable composition as a film on a backing sheet, and heating said film of photoimageable composition for such time and temperature as to sufficiently cross-link said binder to render said film non-tacky yet still soluble in aqueous or alkaline aqueous solution. The product of the process of Claim/2l'. ZT1Z. A method of forming a hard, permanent, patterned film on each of a first side and a second side of a solid substrate, the method comprising providing photoimageable composition comprising a homogeneous solution of between about- 10 and eseut 40 wt. percent of a flowable, film-forming polymeric binder which is soluble in aqueous or alkaline aqueous solution; between -b-~et 5 and abeat 25 wt. percent of a cross-linking agent for said polymeric binder which cross-links said binder; between -ab-e t- 15 and ab-ut- 35 wt. percent of a polymerizable acrylic substance; between ahout 0.01 and abeit 15 wt. percent of a photosensitive, free radical-generating initiator chemical system which in the presence of actinic radiation initiates polymerization of said acrylic substance to form a three-dimensional chemical structure that renders actinic radiation-exposed portions of said photoimageable composition insoluble in aqueous or alkaline aqueous solutions; between and *a.bet 50 wt. percent of an epoxy resin composition which is curable to harden said photoimageable composition subsequent to exposure to actinic radiation; and between b.eEt-0.01 and .ebst-5 wt. percent of a cure catalyst for said epoxy resin; said polymeric binder being sufficiently soluble in aqueous or alkaline aqueous solution-and used at a sufficient level that said photoimageable composition as a whole is I WO 89/05476 PCT/US88/04338 developable in aqueous or alkaline aqueous solution, said components being selected to be mutually miscible and mixed together to form said homogeneous solution, coating a film of said photoimageable compositions on said first side, exposing said film to patterned actinic radiation so as to polymerize said acrylic substance and render exposed portions of said film insoluble to aqueous or alkaline aqueous solution, developing said film in aqueous or alkaline aqueous solution to remove non-exposed portions of said film, heating said film of photoimageable composition for such time and temperature as to cross-link said polymeric binder, repeating steps through on said second side, and heating said films on said first and said second side to cross-link said polymeric binder of said film on said second side and to cure said epoxy resin of said films on said first and second sides. 22- 2-M The product of the process of Claim 2S. a~- 24. A photoimageable composition substantially as herein- before described with reference to any one of Examples 1 to 9. DATED: 11 June 1991 PHILLIPS ORMONDE FITZPATRICK Attorneys for: 's MORTON THIOKOL, INC. *9 EJD 40 EJD 40 aUJ. i 'I 1- i-- INTERNATIONAL SEARCH REPORT International Application No PCT/US 88/04338 I. CLASSIFICATION OF SUBJECT MATTER (if several classification symbols apply, indicate all) According to International Patent Classification (IPC) or to both National Classification and IPC IPC4: G 03 C 1/68 II, FIELDS SEARCHED Minimum Documentation Searched 7 Classification System Classification Symbols

4 I PC G 03 C 1/00 Documentation Searched other than Minimum Documentation to the Extent that such Documents are Included in the Fields Searched III. DOCUMENTS CONSIDERED TO BE RELEVANT' Category Citation of Document, with Indication, where aopropriate. of the relevant oasagea 1 I Relevant to Claim No i X Patent Abstracts of Japan, vol. 12, no. 40, 1-24 S (C-474)(2887)

5 February 1988 JP, A, 62187722 (JAPAN SYNTHETIC RUBBER CO.) 17 August 1987 see abstract X EP, A, 0063304 (HOECHST) 27 October 1982, 1 see the whole document X DE, A, 2520775 (HITACHI) 1 April *1976, 1 see the whole document X Patent Abstracts of Japan, vol. 9, no. 276, i (P-402)(1999) 2nd November 1985 JP, A, 60121444 (NIPPON SODA) S 28 June 1985 see abstract X DE, A, 2207853 (IBM) 31 August 1972, 1 see the whole document Special categories of cited documents: 10 later document published after the international filing date dinin t g s o t a wi or priority date and not in conflict with the application but document defining the general state of the art which not cited to understand the principle or theory underlying the considered to be of particular relevance invention earlier document but published on or after the international document of particular relevance: the claimed invention filing date cannot be considered novel or cannot be considered to document which may throw doubts on priority claim(s) or involve an inventive step which is cited to establish the publication date of another document of particular relevance; the claimed invention citation or other special reason (as specified) cannot be considered to involve an inventive step when the document referring to an oral disclosure, use, exhibition or document is combined with one or more other such oocu- other means ments, such combination being obvious to a person skilled document published prior to the international filing date but in the art. later than the priority date claimed document member of the same patent family IV. CERTIFICATION Date of the Actual Completion of the International Search Date of Mailing of this International Search Report 9th March 1989 I 4. 04, 89 International Searching Authority SIgn atu aol*il orit Officer EUROPEAN PATENT OFFICE AN DER PUTTEM Form PCT/ISA/210 rsecond sheet) (January 1985) i r i. International Application No, PCT /US 88 0433 8 -2 Ill. DOCUMENTS CONSIDERED TO SE RELEVANT (CONTINUED FROM THE SECOND SHEET) Category Citation of Doctment, with in dkAtiori, whore appropriate, of the retvantl passage$ Relevant to Clarnm No X ;DE, A, 2406400 (HITACHI) September 1974 P,X IEP, A, 0280295 (TOKYO OHKA KOGYO CO.LTD) 31 August 1988 Form PCT ISA'210 (extra sheot) (January 1985) A ANN ON]I This annex lists the patent fami The mecmbers are as contained The European Patent Office is EX TO THE INTERNATIONAL SEARCH REPORT INTERNATIONAL PATENT APPLICATION NO. US 8804338 SA 26136 Iy members relating to the patent document,; cited in the aho'.o-mentioned international scarch report. in the European Patent Office EDP ile on 30/03/89 in no )say liable for these particulars s~hich are merel% gi~en for the purpoqe of information. Patent document Publication Patent family Publicatio n cited in search report date member(s) date EP-A- 0063304 27-10-82 OE-A- 3114931 28-10-82 JP-A- 57178237 02-11-82 AU-A- 8250582 21-04-83 US-A- 4485166 27-11-84 CA-A- 1185387 09-04-85 AU-B- 548860 02-01-86 DE-A- 2520775 01-04-76 US-A- 4025348 24-05-77 GB-A- 1517920 19-07-78 JP-A- 50144429 20-11-75 JP-A- 50144430 20-11-75 JP-A- 50144431 20-11-75 OE-A- 2207853 31-08-72 FR-A,B 2150657 13-04-73 US-A- 3776729 04-12-73 CA-A- 960077 31-12-74 GB-A- 1386122 05-03-75 OE-A- 2406400 05-09-74 GB-A- 1449326 15-09-76 US-A- 3989610 02-11-76 JP-A- 49107333 11-10-74 JP-A- 50030515 26-03-75 JP-A- 50055404 15-05-75 EP-A- 0280295 31-08-88 JP-A- 1006943 11-01-89 ZFor more details about this annex :see Official Journal of the European Patent Office, No. 12/82