JPH11172025A - Printed-wiring board pre-preg and metal clad laminated board using this - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a printed-wiring board pre-preg which has an improved processibility and handleability and exerts an extremely low dusting characteristic when the pre-preg is cut or processed, and a metal clad laminated board with few dents using this. SOLUTION: A printed-wiring board pre-preg is obtained by impregnating a glass woven fabric or a glass bonded fabric with a varnish essentially comprising (a) a straight-chain, high-molecular-weight epoxy resin having an epoxy equivalent of 5,000 or larger and a weight average molecular weight of from 5,000 to 50,000, (b) a low-molecular-weight epoxy resin having a weight average molecular weight of 5,000 or smaller, (c) hardener and (d) a promoter, heating it and converting it to B-stage. A metal clad laminated board is obtained by laminating at least one piece of this printed-wiring board pre-preg and heat- pressure-molding it with metal foils applied on one side or both sides thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a prepreg used for an electrical insulating material such as a printed wiring board and a metal foil-clad laminate using the same.

[0002]

2. Description of the Related Art Epoxy laminates are manufactured by impregnating a woven glass or nonwoven glass fabric with a varnish solution of an epoxy resin composition, drying and drying a B-staged prepreg, and applying heat and pressure. The epoxy resin composition is obtained by blending a curing agent and a curing accelerator with a low molecular weight epoxy resin having an epoxy equivalent of about 150 to 1000, and blending a flame retardant and a filler as necessary.

[0003] Glass woven fabric or glass nonwoven fabric is often used in the form of a roll, and as a result, prepreg is also manufactured in the form of a roll, and then cut into predetermined dimensions.
It will be used in the next laminated board manufacturing process.

[0004]

However, the conventional epoxy resin prepreg generates a large amount of dust from the cut surface and the surface during cutting and before the lamination, and when the metal foil-clad laminate is formed, the resin powder is made of metal. By adhering to the foil surface,
Dent defects are likely to occur. As a countermeasure, there is a method of reheating the prepreg after cutting the prepreg and fusing the adhered powder, but by reheating, the curing reaction of the prepreg progresses, and the prepreg characteristics are changed, The reheated prepreg also has disadvantages such as rubbing during transportation and re-dusting, and cannot be said to be a definitive solution. In addition, the production efficiency decreases due to the increase in the number of steps.

An object of the present invention is to provide a prepreg for a printed wiring board, which has extremely reduced dusting properties and has improved workability and handleability, and a metal foil-clad laminate using the same.

[0006]

According to the present invention, there are provided (a) an epoxy equivalent of 5,000 or more and a weight average molecular weight of 5,000 to 5,
A varnish containing 0000 linear high molecular weight epoxy resin, (b) low molecular weight epoxy resin, (c) curing agent, and (d) curing accelerator as essential components is impregnated into glass woven fabric or glass nonwoven fabric, and heated. Then, a prepreg for a printed wiring board characterized in that the prepreg is formed into a B stage. Also,
The present invention is a prepreg for a printed wiring board, wherein the linear high molecular weight epoxy resin (a) is preferably 15 to 50% by weight of the resin solid content of the varnish. And it is a prepreg for a printed wiring board, wherein the linear high molecular weight epoxy resin of (a) is preferably a phenoxy resin or a polymer of biphenyldiol and diglycidyl ether of biphenyldiol. Further, the present invention is a metal-foil-clad laminate obtained by laminating at least one or more prepregs for a printed wiring board described above and heating and press-molding one or both surfaces thereof via a metal foil.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The linear high molecular weight epoxy resin (a) used herein is obtained by polymerizing a bifunctional epoxy resin and a bifunctional phenol to have a high molecular weight. The use of a high molecular weight epoxy resin having an epoxy equivalent of 5,000 or more and a weight average molecular weight of 5,000 to 50,000 is not limited. Since such a high molecular weight epoxy resin is a high molecular weight polymer which is linearly polymerized, it has the same properties as a thermoplastic resin. For example,
Phenoxy resin is also a kind of high molecular weight epoxy resin having a structure in which diglycidyl ether of bisphenol A and bisphenol A are polymerized, and this phenoxy resin is known as a thermoplastic resin, and includes paints, molding processes, adhesives, etc. Used in Therefore, by mixing such a high molecular weight epoxy resin into the varnish, it is possible to prevent the varnish from forming a film in the prepreg resin and generating dust.

The straight-chain, high-molecular-weight epoxy resin (a) used in the present invention is prepared by combining a bifunctional epoxy resin and a bifunctional phenol disclosed in JP-A-4-120124, for example, with an alkali metal compound catalyst. It can be produced by heating and polymerizing in a solvent in the presence and synthesizing. The bifunctional epoxy resin which is a raw material for synthesizing a high molecular weight epoxy resin is not limited as long as it is a compound having two epoxy groups in a molecule. For example, bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, alicyclic epoxy resin, aliphatic chain epoxy resin, other diglycidyl etherified products of bifunctional phenols, and bifunctional alcohols Diglycidyl ethers, and their halides, hydrogenated products, and the like. The molecular weight of these compounds is not limited, and several kinds can be used in combination. Further, components other than the bifunctional epoxy resin may be included.

The bifunctional phenol which is a raw material for synthesizing a high molecular weight epoxy resin is not particularly limited as long as it is a compound having two phenolic hydroxyl groups. For example, monocyclic bifunctional phenol hydroquinone, resorcinol, catechol, polycyclic bifunctional phenol bisphenol A, bisphenol F, dihydroxydiphenyl ether, naphthalene diol and halides thereof,
There are alkyl group substituents and isomers. The molecular weight of these compounds is not limited, and some of these compounds can be used in combination. In addition, components other than the bifunctional phenols may be contained in a small amount.

As a catalyst for synthesizing a high molecular weight epoxy resin,
It is preferred to use an alkali metal compound. Examples of alkali metal compounds include sodium, lithium and potassium hydroxides, halides, organic acid salts, alcoholates, phenolates, hydrides, borohydrides, amides and the like.

As a solvent for synthesizing the high molecular weight epoxy polymer, it is preferable to use an amide solvent or a ketone solvent having a boiling point of 130 ° C. or higher. An amide-based solvent that is preferable as a synthesis solvent can be used without limitation as long as it dissolves a bifunctional epoxy resin and a bifunctional phenol as raw materials. For example, formamide, N-methylformamide,
N, N-dimethylformamide, acetamide, N-methylacetamide, N, N-dimethylacetamide,
N, N, N ', N'-tetramethylurea, 2-pyrrolidone, N-methylpyrrolidone, carbamic acid esters and the like. Further, a ketone solvent preferable as a synthesis solvent has a boiling point of 130 ° C. or higher and is not limited as long as it dissolves a bifunctional epoxy resin as a raw material and a bifunctional phenol, and for example, cyclohexanone, acetylacetone, diisobutylketone, holone, isophorone, Methylcyclohexanone, acetophenone and the like can be mentioned. These solvents can be used in combination. Further, it may be used in combination with other solvents such as amides, ketones, ethers, alcohols and esters.

The conditions for synthesizing the high molecular weight epoxy resin are as follows: the blending equivalent ratio of the bifunctional epoxy resin and the bifunctional phenol is as follows: epoxy group / phenolic hydroxyl group = 1 / 0.9
It is desirable that the value be ~ 1.1. When the amount is less than 0.9 equivalent, a side reaction occurs without causing a high molecular weight in a linear form, whereby the polymer is crosslinked and insoluble in a solvent. If it exceeds 1.1 equivalents, the increase in the molecular weight will not proceed. The synthesis reaction temperature of the high molecular weight epoxy polymer is desirably 60 to 150 ° C. When the temperature is lower than 60 ° C., the reaction for increasing the molecular weight is remarkably slow, and when the temperature is higher than 150 ° C., side reactions increase and the molecular weight is not increased linearly. The solid content concentration during the synthesis reaction of the high molecular weight epoxy polymer is more preferably 50% by weight or less, more preferably 4% by weight.
It is desirable that the content be 0% by weight or less. As the concentration increases, side reactions increase and it becomes difficult to increase the molecular weight in a linear manner. Therefore, when performing a polymerization reaction at a relatively high concentration and obtaining a linear high molecular weight epoxy polymer, it is necessary to lower the reaction temperature and reduce the amount of catalyst.

This linear high molecular weight epoxy resin (a)
Must have an epoxy equivalent of 5000 or more. If the epoxy equivalent is smaller than this, it is difficult to prevent dust generation from the prepreg. The weight average molecular weight of the high molecular weight epoxy resin (a) is 5,000 to 50,000.
Must. If the weight average molecular weight is smaller than this range, dust generation from the prepreg cannot be prevented,
On the other hand, if it is too large, the viscosity of the high-molecular-weight epoxy resin increases, and the workability deteriorates. Further, the glass transition temperature (T
g) is reduced or heat resistance is deteriorated.

As the compounding amount of the high molecular weight epoxy resin (a), 15 to 50% by weight, more preferably 20 to 40% by weight of the resin solid content of the varnish can obtain good prepreg characteristics. If the amount is less than this range, dust generation from the prepreg cannot be suppressed. If too large, the heat resistance of the laminate deteriorates and the glass transition temperature (T
The characteristics of the laminate such as g) decrease.

The type of the low molecular weight epoxy resin (b) used in the present invention is not limited as long as it has two or more epoxy groups in the molecule. For example, bisphenol A type epoxy resin, Bisphenol F epoxy resin, bisphenol S epoxy resin, alicyclic epoxy resin, phenol novolak epoxy resin, cresol novolak epoxy resin, bisphenol A
There are novolak type epoxy resins, diglycidyl etherified products of polyfunctional phenols, diglycidyl etherified products of polyfunctional alcohols, halides thereof, hydrogenated products thereof, and the like, and some of them can be used in combination.

Examples of the curing agent (c) for the epoxy resin include amines, phenols, and acid anhydrides, but are not particularly limited as long as they are generally used for an electrically insulating varnish. Examples of the amines include diethylamine, diethylenetriamine, triethylenetetramine, diethylaminopropylamine, aminoethylpiperazine, mensendiamine, metaxylylenediamine, dicyandiamide, diaminodiphenylmethane, diaminodiphenylsulfone, methylenedianiline, and metaphenylenediamine. . Examples of phenols include biphenol, bisphenol A, bisphenol F, phenol novolak, cresol novolak, bisphenol A novolak, and halides and alkyl group-substituted products thereof. Examples of the acid anhydride include hexahydrophthalic anhydride (HPA) and tetrahydrophthalic anhydride (THA).
PA), pyromellitic anhydride (PMDA), chlorendic anhydride (HET), nadic anhydride (NA), methylnadic anhydride (MNA), dodecynylsuccinic anhydride (DDSA), phthalic anhydride (PA), methylhexa Examples include hydrophthalic anhydride (MeHPA) and maleic anhydride. Some of these curing agents may be used in combination.

As the curing accelerator (d), an imidazole compound, an organic phosphorus compound, a tertiary amine, a quaternary ammonium salt or the like is used, and the secondary amino group is changed to acrylonitrile, isocyanate, melamine, acrylate or the like. When a masked imidazole compound is used, the conventional 2
A prepreg having twice or more storage stability can be obtained. As the imidazole compound used here,
Imidazole, 2-methylimidazole, 2-ethyl-
4-methylimidazole, 2-phenylimidazole,
2-undecylimidazole, 1-benzyl-2-methylimidazole, 2-heptadecylimidazole, 4,
5-diphenylimidazole, 2-methylimidazoline, 2-ethyl-4-methylimidazoline, 2-phenylimidazoline, 2-undecylimidazoline, 2-heptadecylimidazoline, 2-isopropylimidazole, 2,4-dimethylimidazole, 2- Phenyl-4
-Methylimidazole, 2-methylimidazoline, 2-
There are isopropylimidazoline, 2,4-dimethylimidazoline, 2-phenyl-4-methylimidazoline and the like. Examples of the masking agent include acrylonitrile, phenylene diisocyanate, toluene diisocyanate, naphthalene diisocyanate, hexamethylene diisocyanate, methylene bisphenyl isocyanate, and melamine acrylate. Some of these curing accelerators may be used in combination.

The above (a), (b), (c) and (d)
Is an essential component, and if necessary, a filler, a coloring agent, an antioxidant, a reducing agent, an ultraviolet ray opaque agent and the like may be added.

The above (a), (b), (c) and (d)
A prepreg can be obtained by impregnating a glass woven fabric or a glass nonwoven fabric with an epoxy resin varnish obtained by blending in a solvent and drying the mixture. There is no particular designation for the type of glass woven or nonwoven glass used here,
Those having a thickness of 0.02 to 0.4 mm can be used according to the thickness of the target prepreg or laminate. The drying conditions for producing prepreg are drying temperature 60
The temperature can be freely selected in accordance with the desired prepreg characteristics at a temperature of 200 ° C. and a drying time of 1 to 30 minutes.

The prepregs obtained according to the desired thickness of the laminated board are laminated, and a metal foil is laminated on one or both sides thereof, and heated and pressed to produce a laminated board. A copper foil or an aluminum foil is mainly used as the metal foil, but another metal foil may be used. The thickness of the metal foil is usually 5 to 200 μm.

The heating temperature during the production of the laminate is 130 to 200
° C, more preferably 160-180 ° C, pressure 0.5
The pressure is from 10 to 10 MPa, more preferably from 1 to 4 MPa, and is determined according to the prepreg characteristics, the capacity of the press machine, the thickness of the target laminate, and the like.

[0022]

EXAMPLES (Example 1) (a) As a linear high molecular weight epoxy resin having an epoxy equivalent of 5,000 or more and a weight average molecular weight of 5,000 to 50,000, an epoxy equivalent of a bisphenol A type epoxy resin and a polymer of bisphenol A is used. As a low molecular weight epoxy resin having a weight average molecular weight Mw of 27000 and a low molecular weight epoxy resin having a weight average molecular weight of 5000 or less, bisphenol A type epoxy resin (Epicoat, a trade name of Yuka Shell Epoxy Co., Ltd.) E5
048) 100 parts by weight, (c) 15 parts by weight of phenol novolak resin as a curing agent (trade name: Phenolite TD-2131 of Dainippon Ink and Chemicals, Inc.), and (d) 2-phenyl as a curing accelerator 0.10 parts by weight of imidazole was mixed with a mixed solvent of methyl ethyl ketone and ethylene glycol monomethyl ether (weight ratio: 10:
By dissolving in 1), a varnish having a resin solid content of 65% by weight was obtained (the compounding ratio of the high molecular weight epoxy resin was 49% by weight of the resin solid content). This varnish was applied to a 100 μm glass woven fabric (MIL).
No. 2116 type) and dried in a dryer at 150 ° C. for 4 minutes to obtain a prepreg in a B-stage state having a resin content of 58% by weight. This prepreg did not scatter resin powder from the cut end and the surface during cutting and handling. The obtained four prepregs were stacked, copper foil having a thickness of 18 μm was arranged on both sides thereof, and heated and pressed at a pressure of 2 MPa and a temperature of 170 ° C. for 90 minutes to obtain a double-sided copper-clad laminate. The copper foil peel strength of this double-sided copper-clad laminate was 1.39 kN / m.

(Example 2) The linear high molecular weight epoxy resin in Example 1 was replaced with a linear high molecular weight epoxy resin having a polymer structure of bisphenol A type epoxy resin and tetrabromobisphenol A (epoxy resin). Equivalent: 7
400, Mw: 34000) and a resin solid content of 6 in the same manner as in Example 1 except that the blending amount was 75 parts by weight.
A varnish of 0% by weight was obtained (the compounding ratio of the high molecular weight epoxy resin was 39% by weight of the resin solids). 100μ of this varnish
m woven glass (MIL crystal No. 2116 type) and dried in a dryer at 150 ° C. for 4 minutes to obtain a B-stage prepreg having a resin content of 56% by weight. This prepreg did not scatter resin powder from the cut end and the surface during cutting and handling. The obtained four prepregs were stacked, copper foil having a thickness of 18 μm was arranged on both sides thereof, and heated and pressed at a pressure of 2 MPa and a temperature of 170 ° C. for 90 minutes to obtain a double-sided copper-clad laminate. It was 1.51 kN / m as a result of measuring the copper foil peeling strength of this double-sided copper-clad laminate.

Example 3 100 parts by weight of a bisphenol A novolak type epoxy resin (using Epicron N-865 of Dainippon Ink and Chemicals, Inc.) and a modified phenol novolak resin (trademark of Dainippon Ink and Chemicals, Inc.) Name phenolite VH-4170) 45 parts by weight, 30 parts by weight of tetrabromobisphenol A, 0.2 parts by weight of undecylimidazole, and a high molecular weight epoxy resin (epoxy equivalent: 14000, Mw: 3000)
0, phenoxy resin) was dissolved in a mixed solvent (weight ratio 10: 1: 4) of methyl ethyl ketone, ethylene glycol monomethyl ether and cyclohexanone to obtain a varnish having a resin solid content of 50% by weight (high molecular weight) The mixing ratio of the epoxy resin is 30% by weight of the resin solids). This varnish was applied to a 100 μm glass woven fabric (MIL part number 2116).
) And dried in a dryer at 170 ° C. for 2 minutes to obtain a prepreg in a B-stage state having a resin content of 60% by weight. This prepreg did not scatter resin powder from the cut end or the surface during cutting and handling. The obtained four prepregs were stacked, copper foil having a thickness of 18 μm was arranged on both sides thereof, and heated and pressed at a pressure of 2 MPa and a temperature of 170 ° C. for 90 minutes to obtain a double-sided copper-clad laminate. The copper foil peel strength of the double-sided copper-clad laminate was 1.65 kN / m.

Example 4 The high molecular weight epoxy resin in Example 3 was replaced with a linear high molecular weight epoxy resin having a polymer structure of biphenyldiol and a diglycidyl etherified product of biphenyldiol (epoxy equivalent: 750).
0, Mw: 27000) and a varnish having a resin solid content of 63% by weight was obtained in the same manner as in Example 3 except that the compounding amount was changed to 60 parts by weight (the compounding ratio of the high molecular weight epoxy resin was all solids). 26% by weight). This varnish is impregnated with 100 μm glass woven fabric (MIL part number 2116 type),
It is dried in a dryer at 0 ° C. for 2 minutes, and contains 55% by weight of resin B
-A prepreg in a stage state was obtained. This prepreg did not scatter resin powder from the cut end or the surface during cutting and handling. Stack the four prepregs obtained,
A copper foil with a thickness of 18 μm is arranged on both sides thereof, and a pressure of 2 MPa is applied.
It was heated and pressed at a temperature of 170 ° C. for 90 minutes to obtain a double-sided copper-clad laminate. The copper foil peel strength of this double-sided copper-clad laminate was 1.
It was 61 kN / m.

Comparative Example 1 The high molecular weight epoxy resin in Example 1 was a linear high molecular weight epoxy resin having a structure of a bisphenol A type epoxy resin and a polymer of bisphenol A (epoxy equivalent: 2700, Mw: 1700).
Example 1 except that the compounding amount was changed to 95 parts by weight instead of 0).
A varnish having a resin solid content of 70% by weight was obtained in the same manner as described above (the compounding ratio of the high molecular weight epoxy resin was 45% by weight of the resin solids). This varnish was applied to a 100 μm glass woven fabric (M1L
No. 2116 type) and dried in a dryer at 150 ° C. for 4 minutes to obtain a prepreg in a B-stage state having a resin content of 58% by weight. In the prepreg, resin powder scattered from the cut end and the surface during cutting and handling. The obtained four prepregs were stacked, copper foil having a thickness of 18 μm was arranged on both sides thereof, and heated and pressed at a pressure of 2 MPa and a temperature of 170 ° C. for 90 minutes to obtain a double-sided copper-clad laminate. As a result of measuring the copper foil peeling strength of this double-sided copper-clad laminate, 1.42 kN / m was obtained.
Met.

Comparative Example 2 The high molecular weight epoxy resin in Example 3 was replaced with a linear high molecular weight epoxy resin having a structure of a polymer of bisphenol A and a bisphenol A type epoxy resin (epoxy equivalent: 7800, Mw: 940
00), a varnish having a resin solid content of 55% by weight was obtained in the same manner as in Example 3 except that the mixing amount was changed to 60 parts by weight.
weight%). The varnish was applied to a 100 μm glass woven fabric (MI
L part number 2116 type) and dried in a dryer at 175 ° C. for 2 minutes to obtain a B-stage prepreg having a resin content of 62% by weight. This prepreg did not scatter resin powder from the cut end or the surface during cutting and handling. The obtained four prepregs were stacked, copper foil having a thickness of 18 μm was arranged on both sides thereof, and heated and pressed at a pressure of 2 MPa and a temperature of 170 ° C. for 90 minutes to obtain a double-sided copper-clad laminate. The copper foil peel strength of the double-sided copper-clad laminate was 1.50 kN / m.

(Comparative Example 3) The same method as in Example 1 was used except that the compounding amount of the high molecular weight epoxy resin in Example 1 was changed to 15 parts by weight and the compounding amount of 2-phenylimidazole was changed to 0.17 parts by weight. A varnish having a resin solid content of 75% by weight was obtained.
2% by weight). This varnish was applied to a 100 μm glass woven fabric (M
(IL part number 2116 type) and dried in a dryer at 150 ° C. for 4 minutes to obtain a prepreg in a B-stage state having a resin content of 58% by weight. Although no resin powder was generated from the surface of this prepreg, when the resin was cut with a cutter knife, scattering of the resin from the cut end was observed. The obtained four prepregs were stacked, copper foil having a thickness of 18 μm was arranged on both sides thereof, and heated and pressed at a pressure of 2 MPa and a temperature of 170 ° C. for 90 minutes to obtain a double-sided copper-clad laminate. As a result of measuring the copper foil peeling strength of this double-sided copper-clad laminate, 1.37 kN /
m.

After etching the copper foil of the double-sided copper foil-clad laminate thus obtained, the heat resistance and Tg were measured. The results are shown in Table 1. The heat resistance is as follows: saturated vapor pressure, 1
In a pressure cooker at 20 ° C and 2027 hPa,
The result of having observed visually the change of the external appearance after the time process described in the table | surface is shown. Each symbol indicates ○: no change, Δ: occurrence of measling or bleeding, ×: whitening, and three symbols indicate the results of evaluation using three test pieces, respectively. In addition, the measurement of Tg showed a value measured by a dynamic thermomechanical analyzer 982 manufactured by DuPont (hereinafter abbreviated as DMA).

[0030]

[Table 1] Item Example 1 Example 2 Example 3 Example 4 Comparative example 1 Comparative example 2 Comparative example 3 Heat resistance A △△△ ○ △△ ○○ △ ○○○ △△△ △ ×× ○○○ Heat resistance B △ ×× △△△ ○ △△ ○ △△ △ ×× ××× ○ △△ Tg (℃) 137 144 219 228 125 120 146 Heat resistance A: 96 hours, Heat resistance B: 192 hours

In the examples using a phenoxy resin (Example 3) or a polymer of biphenyldiol and a diglycidyl etherified product of biphenyldiol (Example 4) as the linear high molecular weight epoxy resin, the Tg is high and the heat resistance is high. The properties are also good. In addition, the resin powder was not scattered from the cut end portion or the surface during cutting or handling of the prepreg, and no dents were observed. On the other hand, the conventional epoxy resin prepreg has scattering of resin powder from the cut end or the surface when cutting or handling the prepreg, and when the epoxy equivalent of the high molecular weight epoxy resin of Comparative Example 1 is 5000 or less, Tg decreases. In Comparative Example 2 in which the weight average molecular weight of the high molecular weight epoxy resin exceeds the range of 5,000 to 50,000, heat resistance and Tg are inferior. Furthermore, Comparative Example 3, in which the blending ratio of the high molecular weight epoxy resin is 15% by weight or less of the resin solid content, is excellent in heat resistance and Tg, but the resin powder is scattered from the cut end and the surface during cutting or handling of the prepreg. There is. The copper-clad laminates obtained from the prepregs of these comparative examples had dents on the copper foil surface.

[0032]

According to the present invention, it is possible to obtain a prepreg with less scattering of resin powder at the time of cutting or handling, without deteriorating the laminate properties such as heat resistance and Tg. Also, by using this prepreg, a laminate excellent in copper foil peeling strength can be obtained.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI // H05K 1/03 610 H05K 1/03 610L

Claims (4)

[Claims] 1. A linear high molecular weight epoxy resin having an epoxy equivalent of 5,000 or more and a weight average molecular weight of 5,000 to 50,000, (b) a low molecular weight epoxy resin having a weight average molecular weight of 5,000 or less, and (c) curing A prepreg for a printed wiring board, which is obtained by impregnating a glass woven fabric or a nonwoven glass fabric with a varnish containing an agent and (d) a hardening accelerator as an essential component, heating and drying to form a B-stage. 2. The prepreg for a printed wiring board according to claim 1, wherein the linear high molecular weight epoxy resin (a) is 15 to 50% by weight of the resin solid content of the varnish. 3. The prepreg for a printed wiring board according to claim 1, wherein the linear high molecular weight epoxy resin (a) is a phenoxy resin or a polymer of biphenyldiol and diglycidyl ether of biphenyldiol. . 4. A metal foil obtained by laminating at least one or more prepregs for printed wiring boards according to claim 1 and heating and press-molding the prepreg on one or both sides thereof via a metal foil. Upholstered laminate.