CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of and priority to European Patent Application No. 19184359.8, filed on July 4, 2019 and Indian Patent Application No. 201911008310, filed March 4, 2019, the entire contents of which are both incorporated by reference herein.

BACKGROUND

[0001] Thermoset polymers are used in a wide variety of consumer and industrial products including protective coatings, adhesives, electronic laminates (such as those used in the fabrication of printed circuit boards), flooring and paving, glass fiber-reinforced pipes, and automotive parts (such as leaf springs, pumps, and electrical components). Thermoset epoxies are derived from thermosetting epoxy resins that are polymerized in the presence of a co-reactive curing agent (also referred to in the art as a hardener), a catalytic curing agent (also referred to in the art as a cure accelerator or catalyst), or both, to afford a cured thermoset epoxy.

[0002] Epoxy laminates used for printed circuit boards demand high temperature stability, good dielectric attributes, and strong adhesion properties. However, conventional epoxy laminates cured with amine or anhydride curing agents often lack dimensional stability at temperatures higher than 220°C.

[0003] Accordingly, there remains a need for cured epoxy laminates that provide high temperature stability, good dielectric attributes, and strong adhesion properties.

BRIEF DESCRIPTION

[0004] In an aspect, a metal-clad laminate comprises a prepreg comprising a reinforcing structure and a curable epoxy composition, the curable epoxy composition comprising: 100 parts by weight of an epoxy resin composition comprising a non-fluorinated epoxy resin; 30 to 200 parts by weight of an aromatic dianhydride curing agent; optionally an additional anhydride curing agent; and optionally a curing catalyst, wherein the amounts are based on the total parts by weight of the epoxy resin composition and the aromatic dianhydride curing agent, and wherein the curable epoxy composition is impregnated into the reinforcing structure; and a conductive metal layer at least partially disposed on at least one surface of the prepreg, wherein the aromatic dianhydride curing agent has the formula (1)

wherein T is -0-, -S-, -SO2-, -SO-, -C _y H2 _y - wherein y is an integer from 1 to 5 or a halogenated derivative thereof, or -O-Z-O- wherein Z is an aromatic C6-24 monocyclic or polycyclic moiety optionally substituted with 1 to 6 Ci- ₈ alkyl groups, 1 to 8 halogen atoms, or a combination thereof.

[0005] In another aspect, a method of forming the metal-clad laminate comprises impregnating the reinforcing structure with the curable epoxy composition under conditions effective to form an impregnated structure, preferably at a temperature of 10 to 40°C; optionally drying the impregnated structure, preferably wherein the drying is at a temperature of 70 to 150°C for 30 to 60 minutes; partially curing the impregnated structure under conditions effective to form the prepreg, preferably wherein the partial curing is by heating at 120 to 200°C, preferably 130 to 180°C, more preferably 130 to 160°C for 1 to 10 minutes, preferably 1 to 5 minutes; and disposing the conductive metal layer on the at least one surface of the prepreg.

[0006] Also provided is a printed circuit board manufactured using the metal-clad laminate.

[0007] The above described and other features are exemplified by the following detailed description.

DETAILED DESCRIPTION

[0008] This disclosure relates to a metal-clad laminate comprising a prepreg that includes a curable epoxy composition impregnated into a reinforcing structure, and a conductive metal layer at least partially disposed on the prepreg. The inventors have discovered that an aromatic dianhydride, for example bisphenol-A dianhydride (BPA-DA), can be a useful curing agent for making high heat cured epoxy resins. The curable epoxy composition including the aromatic dianhydride as an epoxy curing agent can provide a cured thermoset product having good high heat resistance properties, such as a glass transition temperature that can be 230°C or greater. Moreover, the curable epoxy composition can be used in prepregs to provide metal clad laminates having dimensional stability, strong peel strength, low dissipation factor, and good dielectric strength. These properties are demonstrated, for example, by a peel strength of greater than 750 Newtons per millimeter (N/mm), a dissipation factor of less than 0.01, and a dielectric constant of 5 or less. [0009] Provided herein is a metal-clad laminate including a prepreg comprising a reinforcing structure and a curable epoxy composition, and a conductive metal foil that is at least partially disposed on one or more surface of the prepreg. For example, the conductive metal foil can be disposed on one or more sides of the prepreg, such as opposite sides, adjacent sides, or a combination thereof. The curable epoxy composition, which is impregnated into the reinforcing structure, includes an epoxy resin composition and an aromatic dianhydride curing agent. In some aspects, the aromatic dianhydride curing agent is soluble in the epoxy resin composition.

In particular aspects, the curable epoxy composition is substantially free of the additional anhydride curing agent.

[0010] The stoichiometric ratio between the aromatic dianhydride curing agent and the epoxy resin composition can be 0.1 : 1 to 2.0: 1, preferably 0.4: 1 to 1.2: 1, more preferably 0.6: 1 to 1 : 1. The stoichiometric ratio is the molar ratio of total anhydride functionalities from the dianhydride curing agent and the optional additional anhydride curing agent to the total epoxy functionalities in the epoxy resin composition. The stoichiometric ratio is also referred to herein as the anhydride to epoxy (A/E) ratio.

[0011] The prepreg can include 40 to 90 volume percent (vol%), preferably 50 to 90 vol%, more preferably 60 to 90 vol% of the curable epoxy composition, based on the total volume of the prepreg. The prepreg can include 60 to 10 vol%, preferably 50 to 10 vol%, more preferably 40 to 10 vol% of the reinforcing structure, based on the total volume of the prepreg. For example, the prepreg can include 40 to 90 vol% of the curable epoxy composition and 60 to 10 vol% of the reinforcing structure, based on the total volume of the prepreg.

[0012] The curable epoxy composition includes 100 parts by weight of the epoxy resin composition comprising a non-fluorinated epoxy resin, based on the total parts by weight of the epoxy resin composition and the aromatic dianhydride curing agent. The epoxy resin composition can include one or more epoxy resins, such as bisphenol A epoxy resin, a triglycidyl-substituted epoxy resin, a tetraglycidyl-substituted epoxy resin, a bisphenol F epoxy resin, a phenol novolak epoxy resin, a cresol novolak epoxy resin, a cycloaliphatic diglycidyl ester epoxy resin, a cycloaliphatic epoxy resin comprising a ring epoxy group, an epoxy resin containing a spiro-ring, a hydantoin epoxy resin, or a combination thereof. In a particular aspect, the epoxy resin is bisphenol-A diglycidyl ether (BPA-DGE). In some aspects, the epoxy resin composition does not include a fluorinated epoxy resin (i.e., is free from fluorinated epoxy resins). It is to be understood that when the curable epoxy composition further includes the optional additional anhydride curing agent, the amount of the epoxy resin composition is based on the total parts by weight of the epoxy resin composition, the aromatic dianhydride curing agent, and the additional anhydride curing agent.

[0013] In some aspects, the epoxy resin composition may include one or more“high heat” epoxy compounds of formulas (I) to (IX):

wherein, in Formulas (I) to (IX), R ¹ and R ² at each occurrence are each independently an epoxide-containing functional group; R ^a and R ^b at each occurrence are each independently halogen, C i-12 alkyl, C2-12 alkenyl, C3-8 cycloalkyl, or Ci-12 alkoxy; p and q at each occurrence are each independently 0 to 4; R ¹³ at each occurrence is independently a halogen or a Ci-6 alkyl group; c at each occurrence is independently 0 to 4; R ¹⁴ at each occurrence is independently a Ci - ₆ alkyl, phenyl, or phenyl substituted with up to five halogens or Ci- ₆ alkyl groups; R ^g at each occurrence is independently Ci-12 alkyl or halogen, or two R ^g groups together with the carbon atoms to which they are attached form a four-, five, or six-membered cycloalkyl group; and t is 0 to 10.

[0014] In other aspects, the epoxy resin composition does not include a compound of formulas (I) to (IX). That is, the epoxy resin composition is free of the high heat epoxy compounds of formulas (I) to (IX). Preferably, the epoxy resin composition does not include a compound of formulas (I) to (IX).

[0015] The curable epoxy composition includes 30 to 200 parts by weight of the aromatic dianhydride curing agent, based on the total parts by weight of the epoxy resin composition and the aromatic dianhydride curing agent. It is to be understood that when the curable epoxy composition further includes the optional additional anhydride curing agent, the amount of aromatic dianhydride curing agent is based on the total parts by weight of the epoxy resin composition, the aromatic dianhydride curing agent, and the additional anhydride curing agent. For example, the curable epoxy composition can include 50 to 150 parts by weight, preferably 60 to 140 parts by weight, more preferably 80 to 120 parts by weight of the aromatic dianhydride curing agent, based on the total parts by weight of the epoxy resin composition and the aromatic dianhydride curing agent.

[0016] The aromatic dianhydride curing agent has the formula (1)

wherein T is -0-, -S-, -SO2-, -SO-, -C _y FE _y - wherein y is an integer from 1 to 5 or a halogenated derivative thereof, or -O-Z-O- wherein Z is an aromatic C6-24 monocyclic or polycyclic moiety optionally substituted with 1 to 6 Ci- ₈ alkyl groups, 1 to 8 halogen atoms, or a combination thereof. In some aspects, the R ¹ is a monovalent Ci-13 organic group. In some aspects, T is -O- or a group of the formula -O-Z-O- wherein the divalent bonds of the -O- or the -O-Z-O- group are in the 3,3', 3,4', 4,3', or the 4,4' positions. In particular aspects, T is not -O-, -SO2-, or -SO-.

[0017] Exemplary groups Z include groups of formula (2)

wherein R ^a and R ^b are each independently the same or different, and are a halogen atom or a monovalent Ci- ₆ alkyl group, for example; p and q are each independently integers of 0 to 4; c is 0 to 4; and X ^a is a bridging group connecting the hydroxy-substituted aromatic groups, where the bridging group and the hydroxy substituent of each Ce arylene group are disposed ortho, meta, or para (specifically para) to each other on the Ce arylene group. The bridging group X ^a can be a single bond, -0-, -S-, -S(O)-, -S(0)2-, -C(O)-, or a Ci-is organic bridging group. The Ci-is organic bridging group can be cyclic or acyclic, aromatic or non-aromatic, and can further comprise heteroatoms such as halogens, oxygen, nitrogen, sulfur, silicon, or phosphorous. The Ci organic group can be disposed such that the Ce arylene groups connected thereto are each connected to a common alkylidene carbon or to different carbons of the Ci-is organic bridging group. A specific example of a group Z is a divalent group of the formula (3a) or (3b)

wherein Q is -0-, -S-, -C(0)-, -SO2-, -SO-, -P(R ^a )(=0)- wherein R ^a is a Ci- ₈ alkyl or C6-12 aryl, or -C _y Tk _y - wherein y is an integer from 1 to 5 or a halogenated derivative thereof (including a perfluoroalkylene group). In some aspects, Q is 2,2-isopropylidene. In some aspects, T is -0-Z-0-, preferably wherein Z is derived from bisphenol A (i.e., Z is

2,2-(4-phenylene)isopropylidene).

[0018] Illustrative examples of aromatic dianhydrides include 3,3-bis[4-(3,4- dicarboxyphenoxy)phenyl]propane dianhydride; 4,4'-bis(3,4-dicarboxyphenoxy)diphenyl ether dianhydride; 4,4'-bis(3,4-dicarboxyphenoxy)diphenyl sulfide dianhydride; 4,4'-bis(3,4- dicarboxyphenoxy)benzophenone dianhydride; 4,4'-bis(3,4-dicarboxyphenoxy)diphenyl sulfone dianhydride; 2,2-bis[4-(2,3-dicarboxyphenoxy)phenyl]propane dianhydride; 4,4'-bis(2,3- dicarboxyphenoxy)diphenyl ether dianhydride; 4,4'-bis(2,3-dicarboxyphenoxy)diphenyl sulfide dianhydride; 4,4'-bis(2,3-dicarboxyphenoxy)benzophenone dianhydride; 4,4'-bis(2,3- dicarboxyphenoxy)di phenyl sulfone dianhydride; 4-(2,3-dicarboxyphenoxy)-4'-(3,4- dicarboxyphenoxy)di phenyl -2, 2-propane dianhydride; 4-(2,3-dicarboxyphenoxy)-4'-(3,4- dicarboxyphenoxy)diphenyl ether dianhydride; 4-(2,3-dicarboxyphenoxy)-4'-(3,4- dicarboxyphenoxy)diphenyl sulfide dianhydride; 4-(2,3-dicarboxyphenoxy)-4'-(3,4- dicarboxyphenoxy)benzophenone dianhydride; and 4-(2,3-dicarboxyphenoxy)-4'-(3,4- dicarboxyphenoxy)diphenyl sulfone dianhydride. In particular aspects, the aromatic dianhydride curing agent is bisphenol-A dianhydride.

[0019] In a particular aspect, the aromatic dianhydride curing agent does not include substituted or unsubstituted benzophenonetetracarboxylic acid dianhydride, substituted or unsubstituted oxydiphthalic acid dianhydride, substituted or unsubstituted 4,4'- (hexafluoroisopropylidene) diphthalic acid dianhydride, or a combination thereof.

[0020] The curable epoxy composition can include a curing catalyst. For example, the curable epoxy composition can include 0.1 to 5 weight percent (wt%) of a curing catalyst, based on the total weight of the curable epoxy composition. The term“curing catalyst” as used herein encompasses compounds whose roles in curing epoxy resins are variously described as those of a hardener, a hardening accelerator, a curing catalyst, and a curing co-catalyst, among others. Exemplary additional curing promoters can include, for example, amines, dicyandiamide, polyamides, amidoamines, Mannich bases, anhydrides, phenol-formaldehyde resins, carboxylic acid functional polyesters, polysulfides, polymercaptans, isocyanates, cyanate esters, and combinations thereof.

[0021] The curing catalyst can be a heterocyclic curing catalyst. Heterocyclic curing catalysts include benzotriazoles; triazines; piperazines such as aminoethylpiperazine, N-(3- aminopropyl)piperazine, or the like; imidazoles such as 1-methylimidazole, 2-methylimidazole, 3-methyl imidazole, 4-methylimidazole, 5-methylimidazole, 1-ethylimidazole, 2-ethylimidazole, 3-ethylimidazole, 4-ethylimidazole, 5-ethylimidazole, 1-n-propylimidazole, 2-n- propylimidazole, 1-isopropylimidazole, 2-isopropylimidazole, 1-n-butylimidazole, 2-n- butylimidazole, 1-isobutylimidazole, 2-isobutylimidazole, 2-undecyl-lH-imidazole, 2- heptadecyl-lH-imidazole, 1,2-dimethylimidazole, 1,3-dimethylimidazole, 2,4- dimethylimidazole, 2-ethyl-4-methylimidazole, 1-phenylimidazole, 2-phenyl-lH-imidazole, 4- methyl-2-phenyl-lH-imidazole, 2-phenyl-4-methylimidazole, 1 -benzyl-2 -methylimidazole, 1- benzyl-2-phenylimidazole, 1 -cyanoethyl-2 -methylimidazole, 1 -cyanoethyl-2-ethyl-4- methylimidazole, 1 -cyanoethyl-2 -undecylimidazole, l-cyanoethyl-2-phenylimidazole, 2-phenyl- 4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 1 -cyanoethyl-2 - phenyl-4, 5-di(2-cyanoethoxy)methylimidazole; cyclic amidine such as 4- diazabicyclo(2,2,2)octane (DABCO), diazabicycloundecene (DBU), 2-phenyl imidazoline, or the like; N,N-dimethylaminopyridine (DMAP); sulfamidate; or a combination thereof. In a particular embodiment, the curable epoxy composition does not include a heterocyclic curing catalyst.

[0022] The curing catalyst can be an amine curing catalyst. Amine curing catalysts include isophoronediamine, triethylenetetraamine, diethylenetriamine, 1,2- and

1,3-diaminopropane, 2,2-dimethylpropylenediamine, 1,4-diaminobutane, 1,6-diaminohexane, 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane, 1,12-diaminododecane, 4- azaheptamethylenediamine, N,N’-bis(3-aminopropyl)butane-l, 4-diamine, dicyanamide, diamide diphenylmethane, diamide diphenylsulfonic acid (amine adduct), 4,4’-methylenedi aniline, di ethy It oluenedi amine, m-phenylenediamine, p-phenylenediamine, melamine formaldehyde resins, urea formaldehyde resins, tetraethylenepentamine, 3-diethylaminopropylamine,

3,3’-iminobispropylamine, 2,4-bis(p-aminobenzyl)aniline, tetraethylenepentamine,

3-diethylaminopropylamine, 2,2,4- and 2,4,4- trimethylhexamethylenediamine, 1,2- and 1,3- diaminocyclohexane, l,4-diamino-3,6-diethylcyclohexane, l,2-diamino-4-ethylcyclohexane, l,4-diamino-3,6-diethylcyclohexane, l-cyclohexyl-3,4-diminocyclohexane,

4,4’-diaminondicyclohexylmethane, 4,4’-diaminodicyclohexylpropane, 2,2-bis(4- aminocyclohexyl)propane, 3,3’ -dimethyl-4, 4’-diaminodicyclohexylmethane,

3-amino-l-cyclohexaneaminopropane, 1,3- and l,4-bis(aminomethyl)cyclohexane, m- and p- xylylenediamine, diethyl toluene diamines, or a combination thereof. The amine compound can be a tertiary amine hardening accelerator. The tertiary amine curing catalyst can be

triethylamine, tributylamine, dimethylaniline, diethylaniline, benzyldimethylamine (BDMA), a-methylbenzyldimethylamine, A', A -di methyl a i noethanol , A', A-di m ethyl am i nocresol , tri(A( A- dimethylaminomethyl)phenol, or a combination thereof. Amine curing catalysts also include acid-base complexes such as a boron trifluoride-trialkylamine complex.

[0023] The curing catalyst can be a phenol. Exemplary phenols include novolac type phenol resins, resole type phenol resins, aralkyl type phenol resins, dicyclopentadiene type phenol resins, terpene modified phenol resins, biphenyl type phenol resins, bisphenols, triphenylmethane type phenol resins, or a combination thereof.

[0024] The curing catalyst can be a latent cationic cure catalyst such as diaryliodonium salts, phosphonic acid esters, sulfonic acid esters, carboxylic acid esters, phosphonic ylides, triarylsulfonium salts, benzylsulfonium salts, aryldiazonium salts, benzylpyridinium salts, benzylammonium salts, isoxazolium salts, or a combination thereof. The diaryliodonium salt can have the structure [(R ¹⁰ )(R ^U )I] ⁺ X , wherein R ¹⁰ and R ¹¹ are each independently a C6-C14 monovalent aromatic hydrocarbon radical, optionally substituted with from 1 to 4 monovalent radicals selected from C1-C20 alkyl, C1-C20 alkoxy, nitro, and chloro; and wherein X is an anion. The curing catalyst can have the structure [(R ¹⁰ )(R ^U )I] ⁺ SbF ₆ , wherein R ¹⁰ and R ¹¹ are each independently a C6-C14 monovalent aromatic hydrocarbon radical, optionally substituted with from 1 to 4 monovalent radicals selected from C1-C20 alkyl, C1-C20 alkoxy, nitro, and chloro.

For example, curing catalyst can be a latent cationic cure catalyst comprising 4-octyloxyphenyl phenyl iodonium hexafluoroantimonate. The latent cationic cure catalysts also include metal salts including copper (II), tin (II), and aluminum (III) salts of an aliphatic or aromatic carboxylic acid, such as acetate, stearate, gluconate, citrate, benzoate, or combinations thereof; copper (II), tin (II), or aluminum (III) b-diketonates such as acetyl acetonate. In a particular embodiment, the curable epoxy composition does not include a latent cationic curing catalyst.

[0025] In as aspect, the curable epoxy composition can further include an additional anhydride curing agent. It is to be understood that the additional anhydride curing agent is an anhydride that is different from the aromatic dianhydride curing agent. Exemplary additional anhydride curing agent include, but are not limited to, norbornene dicarboxylic anhydrides (e.g., methyl-5-norbornene-2,3-dicarboxylic anhydride, or the like), hexahydrophthalic anhydrides (e.g., 1,2-cyclohexanedicarboxylic anhydride, 4-methylhexahydrophthalic anhydride, 5- methylhexahydrophthalic anhydride, or the like), tetrahydrophthalic anhydrides (e.g., 1, 2,3,6- tetrahydrophthalic anhydride, l,2,3,6-tetrahydro-4-methylphthalic anhydride, or the like), phthalic anhydrides (e.g., 3-fluorophthalic anhydride), maleic anhydrides (e.g., 2-methylmaleic anhydride, dimethylmaleic anhydride, or the like), succinic anhydrides (e.g., dodecenylsuccinic anhydride, hexadecenylsuccinic anhydride, or the like), trimellitic anhydride,

perfluoroglutaric anhydride, styrene maleic anhydrides (SMA), or the like, or a combination thereof. Preferably, the additional anhydride curing agent is maleic anhydride (MA), phthalic anhydride (PA), hexahydro-o-phthalic anhydride (HEP A), tetrahydrophthalic anhydride (THPA), methyltetrahydrophthalic anhydride (MTHPA), methylhexahydrophthalic anhydride (MHHPA), nadic methyl anhydride (methyl himic anhydride; MHA), tetrachlorophthalic anhydride (TCP A), trimellitic anhydride (TMA), or a combination thereof.

[0026] When included in the curable epoxy composition, the curable epoxy composition can include 30 to 200 parts by weight of an additional anhydride curing agent, wherein the amounts are based on the total parts by weight of the epoxy resin composition, the aromatic dianhydride curing agent, and the additional anhydride curing agent. In a particular aspect, the curable epoxy composition can include 100 parts by weight of an epoxy resin composition comprising a non-fluorinated epoxy resin; 30 to 200 parts by weight of an aromatic dianhydride curing agent; and 30 to 200 parts by weight of an additional anhydride curing agent, wherein the amounts are based on the total parts by weight of the epoxy resin composition, the aromatic dianhydride curing agent, and the additional anhydride curing agent.

[0027] In a particular aspect, the additional anhydride curing agent is a monoanhydride curing agent. In an aspect, the additional anhydride curing agent is a liquid monoanhydride curing agent.

[0028] In particular aspects, the curable epoxy composition can be substantially free of additional anhydride curing agent. The term“substantially free of additional anhydride curing agent” means that the curable epoxy composition contains less than 500 parts per million (ppm) by weight of the additional anhydride curing agent. For example, the curable epoxy composition can have less than 450 ppm by weight, preferably less than 300 ppm by weight, more preferably less than 200 ppm by weight, even more preferably less than 100 ppm by weight of the additional anhydride curing agent, based on the total weight of the curable epoxy composition.

[0029] Reinforcing structures suitable for prepreg formation are known in the art. The reinforcing structure can comprise a reinforcing fabric comprising fibers such as glass fibers, carbon fibers, aromatic polyamide fibers, or combination thereof. Reinforcing fabrics include those having complex architectures, including two or three-dimensional braided, knitted, woven, and filament wound. The curable epoxy composition is capable of permeating such complex reinforcing structures. Suitable reinforcing structures are described, for example, in Anonymous (Hexcel Corporation),“Prepreg Technology”, March 2005, Publication No. FGU 017b;

Anonymous (Hexcel Corporation),“Advanced Fibre Reinforced Matrix Products for Direct Processes”, June 2005, Publication No. ITA 272; and Bob Griffiths,“Farnborough Airshow Report 2006”, CompositesWorld.com, September 2006. The weight and thickness of the reinforcing structure are chosen according to the intended use of the composite using criteria well known to those skilled in the production of fiber reinforced resin composites. The reinforced structure can contain various finishes suitable for the epoxy matrix.

[0030] Glass fibers include quartz glass fibers and glass fibers other than quartz glass fibers, such as E glass fibers, D glass fibers, S glass fibers, R glass fibers, NE glass fibers, or T glass fibers. Suitable glass styles include, but are not limited to, 106, 1080, 2112, 2113, 2116, and 7628, wherein the term glass style is known to those skilled in the art and refers to the size of glass fibers and number of fibers in a bundle. The reinforcing structure can further include inorganic fibers other than glass fibers, polypropylenes, polyimides, polyamides, polyesters, carbon fibrils, acrylic fibers, or cellulose fibers. In some aspects, the reinforcing structure is a fibrous preform that includes a woven or non-woven glass or carbon fabric, or comprises glass cloth. Additional reinforcing structures include co-woven structures comprising at least two types of fibers, including glass fiber-carbon fiber, carbon fiber-aromatic polyimide (aramid) fiber, and aromatic polyimide fiber-glass fiber. Reinforcing structures further include non- woven fibrous reinforcements such as continuous strand mat, chopped strand mat, tissues, papers, felts, three-dimensional woven reinforcements, preforms, and braids.

[0031] The conductive metal layer includes one or more metals, for example copper, zinc, tin, chromium, molybdenum, nickel, cobalt, aluminum, iron, gold, silver, platinum, titanium, an alloy thereof, or a combination thereof. Exemplary alloys include, but are not limited to, brass, chrome, stainless steel, a copper molybdenum alloy, a nickel-cobalt iron alloy such as KOVAR (available from Carpenter Technology Corporation), a nickel -iron alloy such as INVAR (available from National Electronic Alloys, Inc.), a bimetal, a trimetal, a trimetal derived from two-layers of copper and one layer of INVAR, and a trimetal derived from two layers of copper and one layer of molybdenum. In particular aspects, the conductive metal layer comprises copper or a copper-based alloy. For example, copper foils can be used.

[0032] Conductive metal layers can have a thickness of 2 to 200 micrometers (pm), specifically 5 to 50 pm, and more preferably 5 to 40 pm.

[0033] In some aspects, the curable epoxy composition includes an additive composition. The additive composition can include a particulate filler, a fibrous filler, a reinforcing material, an antioxidant, a heat stabilizer, a light stabilizer, a ultraviolet light stabilizer, a ultraviolet light absorbing compound, a near infrared light-absorbing compound, an infrared light-absorbing compound, a plasticizer, a lubricant, a release agent, a antistatic agent, an anti-fog agent, an antimicrobial agent, a colorant, a surface effect additive, a radiation stabilizer, a flame retardant, flame retardant synergists such as antimony pentoxide, an anti-drip agent, a fragrance, an adhesion promoter, a flow enhancer, a coating additive, a polymer different from the thermoset (epoxy resin) polymer, or a combination thereof. In a preferred aspect, the curable epoxy composition is substantially free of any polymer other than the thermoset (epoxy resin) polymer.

[0034] The curable epoxy composition can be prepared by combining the epoxy resin composition, the aromatic dianhydride curing agent, and optionally the curing catalyst. For example, the curable epoxy composition is prepared by combining the epoxy resin composition, the aromatic dianhydride curing agent, and optionally the curing catalyst, in a solvent at a temperature of 20 to 80°C, preferably 20 to 30°C. Accordingly, the curable epoxy composition can further include a solvent.

[0035] Exemplary solvents include C _3-8 ketones, C _4-8 A^/V-dialkylamides, C _4-16 dialkyl ethers, Ce-u aromatic hydrocarbons, C _3-6 alkyl alkanoates, C _2-6 alkyl nitriles, C _2-6 dialkyl sulfoxides, or a combination thereof. Examples of C _3-8 ketones include acetone, methyl ethyl ketone, methyl isobutyl ketone, and combinations thereof. Examples of C _4-8 W-dialkylamides include dimethylformamide, dimethylacetamide, V-m ethyl -2-pyrrol i done, and combinations thereof. Examples of C _4-16 dialkyl ethers include tetrahydrofuran, dioxane, and combinations thereof. The C _4-16 dialkyl ether can optionally further include one or more ether oxygen atoms within the alkyl groups and one or more hydroxy substituents on the alkyl groups, for example the C _4-16 dialkyl ether can be ethylene glycol monomethyl ether. The aromatic hydrocarbon solvent can be an ethylenically unsaturated solvent. Examples of C _6-12 aromatic hydrocarbons include benzene, toluene, xylenes, styrene, divinylbenzenes, and combinations thereof. Examples of C3-6 alkyl alkanoates include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, and combinations thereof. Examples of C2-6 alkyl cyanides include acetonitrile, propionitrile, butyronitrile, and combinations thereof. Examples of C2-6 dialkyl sulfoxides include dimethyl sulfoxide, methyl ethyl sulfoxide, diethyl sulfoxide, and combinations thereof. In some aspects, the solvent comprises acetone, methyl ethyl ketone, A -m ethyl -2-pyrrol i done, toluene, or a combination thereof. In still other aspects, the solvent can be a halogenated solvent such as methylene chloride, chloroform, 1,1,1-trichloroethane, chlorobenzene, or the like. In a particular aspect, the solvent comprises THF.

[0036] The curable epoxy composition can include 2 to 100 parts by weight (pbw), preferably 50 to 80 pbw, more preferably 10 to 60 pbw of the solvent, based on 100 parts by weight total of the epoxy resin composition and the aromatic dianhydride curing agent. The solvent may be chosen, in part, to adjust the viscosity of the curable epoxy composition. Thus, the solvent amount may depend on variables including the type and amount of epoxy resin, the type and amount of aromatic dianhydride curing agent, and the processing temperature used for impregnation of the reinforcing structure with the curable epoxy composition.

[0037] In some aspects, the aromatic dianhydride curing agent can be soluble in the epoxy resin composition. The term“soluble in the epoxy resin composition” means that there can be a temperature range where a combination of the aromatic dianhydride and the epoxy resin composition can be combined to form a homogeneous phase. As used herein,“forming a homogeneous phase” means creating a state where there is no visible separation between the components. The homogeneous phase can be formed in a certain temperature range without regard to any separation that may occur outside of that temperature range, for example, at room temperature. For example, a combination of the aromatic dianhydride and the epoxy resin composition can be stirred, heated, or heated under stirring to form a homogeneous phase.

[0038] The aromatic dianhydride can be soluble in the epoxy resin composition at a temperature from 50 to 200°C. For example, the aromatic dianhydride can be soluble in the epoxy resin composition from 80 to 200°C, more preferably from 100 to 190°C, even more preferably from 120 to 180°C.

[0039] When no solvent is used, the curable epoxy composition can be manufactured by combining the epoxy resin composition and the aromatic dianhydride curing agent at a temperature of 100 to 200°C, preferably 120 to 190°C, more preferably 130 to 180°C to provide the curable epoxy composition. The optional curing catalyst can be added to the curable epoxy composition or when first combining the epoxy and dianhydride components. [0040] The metal-clad laminate can be prepared by contacting the curable epoxy composition and the reinforcing structure. In an aspect, the reinforcing structure is coated or impregnated with the curable epoxy composition at a temperature of 10 to 40°C, preferably 20 to 40°C, more preferably 20 to 30°C to form an impregnated structure. The impregnated structure can optionally be shaped, for example shaped before, or after removing any solvent used to prepare the curable epoxy composition. The impregnated structure can optional be dried at a temperature of 70 to 150°C for 30 to 60 minutes.

[0041] The impregnated structure is subsequently partially cured to the“B-staged” form. Partial curing is curing sufficient to reduce or eliminate the wetness and tackiness of the curable epoxy composition but not so great as to fully cure the composition. The resin in a prepreg is customarily in the partially cured state, and those skilled in the thermoset arts, and particularly the reinforced composite arts, understand the concept of partial curing and how to determine conditions to partially cure a resin without undue experimentation. There is no particular limitation on the method by which the composition may be cured or partially cured. The composition may, for example, be cured or partially cured thermally or by using irradiation techniques, including UV irradiation and electron beam irradiation. These curing methods apply to both curing and partial curing. When a heat curing method is used, the temperature selected may be 80 °C to 300 °C, preferably 120 °C to 240 °C, more preferably 120 to 200°C, even more preferably 130 to 180°C, still more preferably 130 to 160°C. The heating period may be 1 minute to 10 hours, though such heating period may advantageously be 1 minute to 6 hours, more preferably 1 to 10 minutes, even more preferably 1 to 5 minutes. The partially cured structure can optionally be shaped.

[0042] References herein to properties of the“cured composition” refer to a composition that is substantially fully cured. For example, the resin in a laminate formed from prepregs is typically substantially fully cured, whereas a prepreg is partially cured. One skilled in the thermoset arts can determine whether a sample is partially cured or substantially fully cured without undue experimentation. For example, one can analyze a sample by differential scanning calorimetry to look for an exotherm indicative of additional curing occurring during the analysis. A sample that is partially cured will exhibit an exotherm. A sample that is substantially fully cured will exhibit little or no exotherm.

[0043] Commercial-scale methods for forming composites such as prepregs are known in the art, and the curable epoxy compositions described herein are readily adaptable to existing processes and equipment. For example, prepregs are often produced on treaters. The main components of a treater include feeder rollers, a resin impregnation tank, a treater oven, and receiver rollers. The reinforcing structure (E-glass, for example) is usually rolled into a large spool. The spool is then put on the feeder rollers that turn and slowly roll out the reinforcing structure. The reinforcing structure then moves through the resin impregnation tank, which contains the curable epoxy composition, and the curable epoxy composition impregnates the reinforcing structure. After emerging from the tank, the coated reinforcing structure moves upward through the vertical treater oven, which is typically at a temperature of 175 to 200°C, and the solvent can be boiled away. The resin begins to polymerize at this time. When the prepreg comes out of the tower it is sufficiently cured so that the web is not wet or tacky. The cure process, however, is stopped short of completion so that additional curing can occur when laminate is made. The web then rolls the prepreg onto a receiver roll.

[0044] The conductive metal layer is then disposed on at least one surface of the prepreg to form the metal-clad laminate. The metal-clad laminate can then be cured. For example, the curing can be by thermal lamination of the conductive metal layer under pressure without using thermosetting adhesives. The laminating can be by hot press or roll calendaring methods, i.e., a roll-to-roll method. It will also be understood that the process of laminating includes further curing the partially cured epoxy composition of the prepreg. For example, laminating can be conducted for 30 minutes to 5 hours, at a temperature of 100 to 300° C, at a pressure of 10 to 100 megapascals (MPa). In some aspects, the curing comprises laminate molding at a temperature of 120 to 300°C, a pressure of 2 to 100 kilogram-force per square centimeter, and a heating time of 30 minutes to 5 hours. The conductive metal layer can optionally be etched to form an electrical circuit following lamination.

[0045] The cured epoxy composition can exhibit good ductility, good fracture toughness, unnotched Izod impact strength, good tensile elongation, decreased dielectric properties, and exhibit low moisture absorption.

[0046] The cured product of the curable epoxy composition can have a glass transition temperature (T _g ) of 120 to 320°C, preferably 160 to 320°C, more preferablyl80 to 320°C, even more preferably 200 to 320°C, still more preferably 250 to 320°C, as determined by dynamic mechanical analysis (DMA).

[0047] The prepreg after curing can have a T _g of 230 to 320°C, preferably 240 to 320°C, more preferably 250 to 320°C, as determined by DMA.

[0048] In an aspect, the metal-clad laminate can further include a supporting metal matrix layer, for example on a surface (e.g., a side) opposite the conductive metal layer. The supporting metal matrix layer can be a thermally conductive metal such as aluminum, boron nitride, aluminum nitride, copper, iron, steel, or the like. A thermally conductive, electrically conductive metal can be used provided that the metal is electrically isolated from the conductive metal layer. The supporting metal matrix layer can have a thickness of 0.1 to 20 mm, preferably 0.5 to 10 mm, more preferably 0.8 to 2 mm. The conductive metal layer of the metal -clad laminates can further be patterned to provide a printed circuit board. Furthermore, the copper clad laminates can be shaped to provide a circuit board having the shape of a sheet, a tube, or a rod.

[0049] In another aspect, a printed circuit board is provided, and includes a composite formed by laminating a plurality of prepregs, wherein each prepreg comprises a reinforcing structure and an at least partially cured epoxy composition at least partially coating the reinforcing structure. For example, laminating the plurality of prepregs can be by exposing the plurality of prepregs to a temperature of 175 to 205° C and a pressure of 17 to 23 megapascals, and further exposing the plurality of prepregs to a temperature of 185 to 215°C and a pressure of 32 to 40 megapascals. Methods of forming circuit boards that include a prepreg lamination step are known in the art and are described in, for example, U.S. Pat. No. 5,582,872 to Prinz, U.S.

Pat. No. 5,622,588 to Weber, and U.S. Pat. No. 7,655,278 to Braidwood.

[0050] After curing, the prepreg can have a glass transition temperature of greater than or equal to 230°C, preferably greater than or equal to 240°C, more preferably greater than or equal to 250°C, as determined by differential scanning calorimetry (DSC).

[0051] After curing, the prepreg can have a dielectric constant of less than or equal to 5, more preferably less than or equal to 4.9, even more preferably less than or equal to 4.8, still more preferably less than or equal to 4.7, as measured at 23°C and 1.1 gigahertz, as determined according to ASTM D150.

[0052] The metal clad laminate comprising the prepreg, after curing, can have a peel strength of greater than 750 Newtons per millimeter, preferably greater than 900 Newtons per millimeter, more preferably greater than 1,000 Newtons per millimeter, as determined according to IPC 2.4.8.

[0053] The metal clad laminate comprising the prepreg, after curing, can have a dissipation factor of less than 0.01, preferably less than or equal to 0.009, more preferably less than or equal to 0.0008, as measured at 23°C and 1.1 gigahertz, as determined according to ASTM D150.

[0054] In some aspects, the metal-clad laminate includes a prepreg comprising a reinforcing structure and a curable epoxy composition, the curable epoxy composition comprising: 100 parts by weight of an epoxy resin composition comprising a bisphenol A epoxy resin; 30 to 200 parts by weight of bisphenol A dianhydride curing agent; optionally an additional anhydride curing agent; and optionally a curing catalyst, wherein the amounts are based on the total parts by weight of the epoxy resin composition and the aromatic dianhydride curing agent, and wherein the curable epoxy composition is impregnated into the reinforcing structure; and a conductive metal layer is at least partially disposed on at least one surface of the prepreg.

[0055] In some aspects, the copper clad laminate includes a prepreg comprising a reinforcing structure and a curable epoxy composition, the curable epoxy composition comprising: 100 parts by weight of an epoxy resin composition comprising a bisphenol A epoxy resin; 30 to 200 parts by weight of bisphenol A dianhydride curing agent; optionally an additional anhydride curing agent; and optionally a curing catalyst, wherein the amounts are based on the total parts by weight of the epoxy resin composition and the aromatic dianhydride curing agent, and wherein the curable epoxy composition is impregnated into the reinforcing structure; and a conductive copper layer is at least partially disposed on at least one surface of the prepreg.

[0056] In some aspects, the metal-clad laminate includes a prepreg comprising a reinforcing structure and a curable epoxy composition, the curable epoxy composition comprising: 100 parts by weight of an epoxy resin composition comprising a bisphenol A epoxy resin; 30 to 200 parts by weight of bisphenol A dianhydride curing agent; optionally an additional anhydride curing agent; and optionally a curing catalyst, wherein the amounts are based on the total parts by weight of the epoxy resin composition and the aromatic dianhydride curing agent, and wherein the curable epoxy composition is impregnated into the reinforcing structure; and a conductive metal layer is at least partially disposed on at least two surfaces of the prepreg.

[0057] Articles comprising the metal-clad laminates are also provided. Articles include those comprising printed circuits as used in medical or aerospace industries. Still other articles include antennae or like articles. Other articles can include, but are not limited to, those comprising printed circuit boards, which are used, for example, in lighting, solar energy, displays, cameras, audio and video equipment, personal computers, mobile telephones, electronic notepads, and like devices, or office automation equipment.

[0058] This disclosure is further illustrated by the following examples, which are non limiting.

EXAMPLES

[0059] Materials used in the examples are described in Table 1. Table 1.

Sample preparation

Example 1

[0060] BPA-DGE (100 parts by weight, pbw), BP AD A (122 pbw), and 2,4-EMI (2 parts per hundred resin, phr) were dissolved in THF to provide a 50 wt% solution at ambient temperature (ca. 23°C). Once dissolved, the resulting solution was transferred to a pan and the glass fabric was submerged in the solution. Once properly wetted, the resulting pre-preg was removed from the solution, air dried for 12 hours at 23 °C, and then further dried in an oven at 85°C to remove the residual solvent prior to B-staging. The non-tacky prepregs were obtained after B-staging at 170°C for 90 seconds. The pre-preg was layered with copper foil on the top and bottom, placed in a polytetrafluorethylene coated aluminum foil pouch, and placed on a PHI Laminate press at 120°C. The temperature was then increased to 200°C for 3 hours to provide the cured laminate.

Comparative Example 1

[0061] BPADGE (100 parts by weight, pbw), SMA (163 pbw), and 2,4-EMI (2 parts per hundred resin, phr) were dissolved in THF to provide a 50 wt% solution at ambient temperature (ca. 23 °C). Once dissolved, the resulting solution was transferred to a pan and the glass fabric was submerged in the solution. Once properly wetted, the resulting pre-preg was removed from the solution, air dried for 12 hours at 23°C, and then further dried in an oven at 85°C to remove the residual solvent prior to B-staging. The non-tacky prepregs were obtained after B-staging at 170°C for 2 minutes. The pre-preg was layered with copper foil on the top and bottom, placed in a polytetrafluorethylene coated aluminum foil pouch, and placed on a PHI Laminate press at 120 °C. The temperature was then increased to 200°C for 3 hours to provide the cured laminate.

Test methods [0062] Peel strength values were determined according to IPC 2.4.8,“Peel Strength of Metallic Clad Laminates”, Revision C, December 1994, except that the specimen size was 12 centimeters (cm) x 12 cm with a thickness of 1 millimeter (mm). At least four resist strips having a width of 5 mm were cut from the same copper clad laminate. The test strip was peeled back 5 cm at the tab end. The clamp was attached to the peeled back end of the test strip. The specimen was fastened with the hold down fixture so that an unencumbered vertical pull could be exerted. The end of the test strip was in a vertical position ready for testing. The tester was started and force was applied in the vertical direction at the rate of 50.8 mm per minute

(mm/min), until an 8 cm peel was completed. The minimum load was observed and recorded. The actual width of the test strip was measured and recorded. If the full width of the test strip did not peel, the results were discarded and another strip tested. The peel strength, expressed in units of Newtons per mm (N/mm) was calculated according to the formula: N = LM/WS, where LM is the minimum load (N) and WS is the width of peel strip (mm).

[0063] The dielectric constant (D _k ) and dissipation factor (D _f ) of the laminates were measured at 23°C using an Agilent Network Analyzer E8363B with QWED SPDR at a frequency of 1.1 Gigahertz (GHz) according to ASTM D150.

[0064] Glass transition temperature (T _g ) was measured on a RDA III dynamic mechanical analyzer from TA Instruments. Samples (40 mm x 5 mm x 3 mm) were heated in the range of -100°C to 300°C at a heating rate of 5 °C/min and a frequency of 1 Hertz (Hz). T _g was determined as the temperature of the tan d maximum.

[0065] The compositions, T _g , D _f , D _k , and peel strength for Example 1 and Comparative Example 1 were determined and the results are provided in Table 2.

Table 2.

^† normalized to 50 vol% glass fabric content

[0066] As provided in Table 2, the BPADA cured laminate (Example 1) demonstrated a significantly higher T _g (257°C) relative to the SMA-cured laminate of Comparative Example 1 (213°C). In addition, the use of BPADA as curing agent resulted in a 30% reduction to D _f relative to Comparative Example that used SMA as curing agent. BPADA as curing agent did result in a marginal increase (5.7%) to D _k . It was unexpectedly found that despite the use of a lower resin content in Example 1, the copper peel strength when BPADA was used as the curing agent (1,082 N/mm) was greater than Comparative Example 1 that used SMA as the curing agent (750 N/mm). These results show that using BP ADA as curing agent instead of SMA results in copper clad laminates (CCL) having better heat properties, enhanced dielectric performance, and superior adhesion properties.

[0067] This disclosure further encompasses the following aspects.

[0068] Aspect 1. A metal-clad laminate comprising: a prepreg comprising a reinforcing structure and a curable epoxy composition, the curable epoxy composition comprising: 100 parts by weight of an epoxy resin composition comprising a non-fluorinated epoxy resin; 30 to 200 parts by weight of an aromatic dianhydride curing agent of formula (1) as defined herein;

optionally an additional anhydride curing agent; and optionally a curing catalyst, wherein the amounts are based on the total parts by weight of the epoxy resin composition and the aromatic dianhydride curing agent, and wherein the curable epoxy composition is impregnated into the reinforcing structure; and a conductive metal layer at least partially disposed on at least one surface of the prepreg.

[0069] Aspect la. A metal-clad laminate comprising: a prepreg comprising a reinforcing structure and a curable epoxy composition, the curable epoxy composition comprising: 100 parts by weight of an epoxy resin composition comprising a non-fluorinated epoxy resin; 30 to 200 parts by weight of an aromatic dianhydride curing agent of formula (1) as defined herein;

optionally an additional anhydride curing agent; and optionally a curing catalyst, wherein the amounts are based on the total parts by weight of the epoxy resin composition and the aromatic dianhydride curing agent, and wherein the curable epoxy composition is impregnated into the reinforcing structure; and a conductive metal layer at least partially disposed on at least one surface of the prepreg, wherein the epoxy resin composition does not include a high heat epoxy compound of formulas (I) to (IX) as provided herein.

[0070] Aspect 2. The metal-clad laminate of aspect 1, wherein the prepreg comprises: 40 to 90 volume percent, preferably 50 to 90 volume percent, more preferably 60 to 90 volume percent of the curable epoxy composition; and 60 to 10 volume percent, preferably 50 to 10 volume percent, more preferably 40 to 10 volume percent of the reinforcing structure, based on the total volume of the prepreg.

[0071] Aspect 3. The metal-clad laminate of any one or more of the preceding aspects, wherein an anhydride to epoxy stoichiometric ratio (A/E) is 0.1 : 1 to 2.0: 1, as determined by molar ratio of total anhydride functionalities from the dianhydride curing agent and optionally the additional anhydride curing agent to the total epoxy functionalities in the epoxy resin. [0072] Aspect 4. The metal-clad laminate of any one or more of the preceding aspects, wherein the non-fluorinated epoxy resin is a bisphenol A epoxy resin, a triglycidyl-substituted epoxy resin, a tetraglycidyl-substituted epoxy resin, a bisphenol F epoxy resin, a phenol novolak epoxy resin, a cresol novolak epoxy resin, a cycloaliphatic diglycidyl ester epoxy resin, a cycloaliphatic epoxy resin comprising a ring epoxy group, an epoxy resin containing a spiro- ring, a hydantoin epoxy resin, or a combination thereof; preferably wherein the epoxy resin composition comprises bisphenol-A diglycidyl ether.

[0073] Aspect 5. The metal-clad laminate of any one or more of the preceding aspects, wherein T is -O- or a group of the formula -O-Z-O- wherein Z is of the formula (2) as provided herein; more preferably wherein T is a group of the formula -O-Z-O- wherein Z is a divalent group of formulas (3 a) or (3b) as provided herein; even more preferably wherein the aromatic dianhydride curing agent comprises bisphenol-A dianhydride.

[0074] Aspect 6. The metal-clad laminate of any one or more of the preceding aspects, wherein the reinforcing structure comprises a glass fiber; preferably wherein the reinforcing structure comprises a glass fabric comprising a plurality of glass fibers; more preferably wherein the reinforcing structure comprises a woven glass fabric; even more preferably wherein the reinforcing structure comprises a woven E-glass fabric.

[0075] Aspect 7. The metal-clad laminate of any one or more of the preceding aspects, wherein the conductive metal layer comprises a metal that is copper, zinc, tin, chromium, molybdenum, nickel, cobalt, aluminum, iron, gold, silver, platinum, titanium, an alloy thereof, or a combination thereof; preferably wherein the conductive metal layer comprises copper.

[0076] Aspect 8. The metal-clad laminate of any one or more of the preceding aspects, wherein the curable epoxy composition is substantially free of any polymer other than the epoxy resin.

[0077] Aspect 9. The metal-clad laminate of any one or more of the preceding aspects, wherein the curable epoxy composition further comprises a solvent.

[0078] Aspect 10. The metal-clad laminate of any one or more of the preceding aspects, wherein the curable epoxy composition further comprises an additive composition; preferably wherein the additive composition comprises an additive that is a particulate filler, a fibrous filler, an antioxidant, a heat stabilizer, a light stabilizer, a ultraviolet light stabilizer, a ultraviolet light absorbing compound, a near infrared light-absorbing compound, an infrared light-absorbing compound, a plasticizer, a lubricant, a release agent, a antistatic agent, an anti-fog agent, an antimicrobial agent, a colorant, a surface effect additive, a radiation stabilizer, a flame retardant, an anti-drip agent, a fragrance, an adhesion promoter, a flow enhancer, a coating additive, or a combination thereof.

[0079] Aspect 11. The metal-clad laminate of any one or more of the preceding aspects, wherein the prepreg after curing has at least one of: a glass transition temperature of greater than or equal to 230°C, preferably greater than or equal to 240°C, more preferably greater than or equal to 250°C, as determined by dynamic mechanical analysis; or a dielectric constant of less than or equal to 5, more preferably less than or equal to 4.9, even more preferably less than or equal to 4.8, still more preferably less than or equal to 4.7, as measured at 23°C and 1.1 gigahertz; or the metal-clad laminate comprising the prepreg after curing has at least one of: a peel strength of greater than 750 Newtons per millimeter, preferably greater than 900 Newtons per millimeter, more preferably greater than 1,000 Newtons per millimeter, as determined according to IPC 2.4.8; or a dissipation factor of less than 0.01, preferably less than or equal to 0.009, more preferably less than or equal to 0.0008, as measured at 23°C and 1.1 gigahertz.

[0080] Aspect 12. A method of forming the metal-clad laminate of any one or more of the preceding aspects, the method comprising: impregnating the reinforcing structure with the curable epoxy composition under conditions effective to form an impregnated structure, preferably at a temperature of 10 to 40°C; optionally drying the impregnated structure, preferably wherein the drying is at a temperature of 70 to 150°C for 30 to 60 minutes; partially curing the impregnated structure under conditions effective to form the prepreg, preferably wherein the partial curing is by heating at 120 to 200°C, preferably 130 to 180°C, more preferably 130 to 160°C for 1 to 10 minutes, preferably 1 to 5 minutes; and disposing the conductive metal layer on the at least one surface of the prepreg.

[0081] Aspect 13. The method of aspect 12, further comprising curing the metal-clad laminate after the step of disposing the conductive metal layer.

[0082] Aspect 14. The method of any one or more of the preceding aspects, wherein the curing comprises laminate molding, preferably wherein the curing comprises a temperature of 120 to 300°C, a pressure of 2 to 100 kilogram -force per square centimeter, and a heating time of 30 minutes to 5 hours.

[0083] Aspect 15. A printed circuit board manufactured using the metal-clad laminate of any one or more of the preceding aspects.

[0084] The compositions, methods, and articles can alternatively comprise, consist of, or consist essentially of, any appropriate materials, steps, or components herein disclosed. The compositions, methods, and articles can additionally, or alternatively, be formulated so as to be devoid, or substantially free, of any materials (or species), steps, or components, that are otherwise not necessary to the achievement of the function or objectives of the compositions, methods, and articles.

[0085] All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other (e.g., ranges of“up to 25 wt%, or, more specifically,

5 wt% to 20 wt%”, is inclusive of the endpoints and all intermediate values of the ranges of“5 wt% to 25 wt%,” etc.). Disclosure of a narrower range or more specific group in addition to a broader range is not a disclaimer of the broader range or larger group.

[0086] The singular forms“a”“an,” and“the” include plural referents unless the context clearly dictates otherwise. “Combination” is inclusive of blends, mixtures, alloys, reaction products, and the like. The terms“first,”“second,” and the like, do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. “Or” means“and/or” unless clearly stated otherwise. Reference throughout the specification to“an aspect” means that a particular element described in connection with the aspect is included in at least one aspect described herein and may or may not be present in other aspects. In addition, it is to be understood that the described elements may be combined in any suitable manner in the various aspects. A“combination thereof’ is open and includes any combination comprising at least one of the listed components or properties optionally together with a like or equivalent component or property not listed.

[0087] Unless specified to the contrary herein, all test standards are the most recent standard in effect as of the filing date of this application, or, if priority is claimed, the filing date of the earliest priority application in which the test standard appears. Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art to which this application belongs. All cited patents, patent applications, and other references are incorporated herein by reference in their entirety. However, if a term in the present application contradicts or conflicts with a term in the incorporated reference, the term from the present application takes precedence over the conflicting term from the incorporated reference.

[0088] Compounds are described using standard nomenclature. For example, any position not substituted by any indicated group is understood to have its valency filled by a bond as indicated, or a hydrogen atom. A dash that is not between two letters or symbols is used to indicate a point of attachment for a substituent. For example, -CHO is attached through carbon of the carbonyl group.

[0089] The term“hydrocarbyl” refers to a monovalent group containing carbon and hydrogen. Hydrocarbyl can be alkyl, cycloalkyl, alkenyl, cycloalkenyl, aryl, alkylaryl, or arylalkyl as defined below. The term“hydrocarbylene” refers to a divalent group containing carbon and hydrogen. Hydrocarbylene can be alkylene, cycloalkylene, arylene, alkylarylene, or arylalkylene as defined below. The term "alkyl" means a branched or straight chain, unsaturated aliphatic hydrocarbon group, e.g., methyl, ethyl, n-propyl, i-propyl, n-butyl, s-butyl, t-butyl, n- pentyl, s-pentyl, and n- and s-hexyl. “Alkenyl” means a straight or branched chain, monovalent hydrocarbon group having at least one carbon-carbon double bond (e.g., ethenyl (-HC=CH2)). “Alkoxy” means an alkyl group that is linked via an oxygen (i.e., alkyl-O-), for example methoxy, ethoxy, and sec-butyloxy groups. "Alkylene" means a straight or branched chain, saturated, divalent aliphatic hydrocarbon group (e.g., methylene (-CH2-) or, propylene (-(CH2)3- )). “Cycloalkylene” means a divalent cyclic alkylene group, -CiTUn-x, wherein x is the number of hydrogens replaced by cyclization(s). “Cycloalkenyl” means a monovalent group having one or more rings and one or more carbon-carbon double bonds in the ring, wherein all ring members are carbon (e.g., cyclopentyl and cyclohexyl). "Aryl" means an aromatic hydrocarbon group containing the specified number of carbon atoms, such as phenyl, tropone, indanyl, or naphthyl. “Arylene” means a divalent aryl group.“Alkylaryl” means an aryl group substituted with an alkyl group. “Arylalkyl” means an alkyl group substituted with an aryl group (e.g., benzyl). “Aryloxy” means an aryl group with the indicated number of carbon atoms attached through an oxygen bridge (-0-). “Amino” means a monovalent radical of the formula— NRR' wherein R and R' are independently hydrogen or a Ci-30 hydrocarbyl, for example a Ci-20 alkyl group or a C6-30 aryl group.“Halogen” or“halogen atom” means a fluorine, chlorine, bromine, or iodine atom. The prefix "halo" means a group or compound including one more of a fluoro, chloro, bromo, or iodo substituent. A combination of different halo groups (e.g., bromo and fluoro), or only chloro groups can be present. The prefix“hetero” means that the compound or group includes at least one ring member that is a heteroatom (e.g., 1, 2, or 3 heteroatom(s)), wherein the heteroatom(s) is each independently N, O, S, Si, or P.

[0090] Unless substituents are otherwise specifically indicated, each of the foregoing groups can be unsubstituted or substituted, provided that the substitution does not significantly adversely affect synthesis, stability, or use of the compound. “Substituted” means that the compound, group, or atom is substituted with at least one (e.g., 1, 2, 3, or 4) substituents instead of hydrogen, where each substituent is independently nitro (-NO ₂ ), cyano (-CN), hydroxy (-OH), halogen, thiol (-SH), thiocyano (-SCN), Ci- ₆ alkyl, C _2-6 alkenyl, C _2-6 alkynyl, Ci- ₆ haloalkyl, C _1-9 alkoxy, Ci- ₆ haloalkoxy, C3-12 cycloalkyl, C5-18 cycloalkenyl, C6-12 aryl, C7-13 arylalkyl (e.g., benzyl), C _7-12 alkylaryl (e.g., toluyl), C _4-12 heterocycloalkyl, C _3-12 heteroaryl, Ci- ₆ alkyl sulfonyl (-S(=0) ₂ -alkyl), C _6-12 arylsulfonyl (-S(=0) ₂ -aryl), or tosyl (CH ₃ C ₆ H ₄ SO ₂ -), provided that the substituted atom’s normal valence is not exceeded, and that the substitution does not significantly adversely affect the manufacture, stability, or desired property of the compound. When a compound is substituted, the indicated number of carbon atoms is the total number of carbon atoms in the compound or group, including those of any substituents.

[0091] While particular aspects have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are or may be presently unforeseen may arise to applicants or others skilled in the art. Accordingly, the appended claims as filed and as they may be amended are intended to embrace all such alternatives, modifications variations, improvements, and substantial equivalents.