JP2001026646A - Porous film for printed board, prepreg and printed circuit laminate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a prepreg for a printed board which allows piercing of needle-like articles having small diameters via the piercing method, a porous film for a printed board which is a base material for the prepreg and a printed circuit laminate which allows high integration via the piercing method. SOLUTION: A porous film for a printed board prepared via the piercing method comprises at least one heat-resistant resin chosen from resins having a deflection temperature under load of 200 deg.C or higher. The porous film has a coefficient of linear thermal expansion at a temperature ranging from 200 to 300 deg.C of from -50×10-6/ deg.C to +50×10-6/ deg.C, a void volume of from 30 to 95 vol.% and a displacement in a piercing test of 1.5 mm or smaller. A prepreg for a printed board is impregnated with this resin. A printed circuit laminate is prepared using this via the piercing method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a porous film for a printed circuit board, a prepreg, and a printed circuit laminate using the same.

[0002]

2. Description of the Related Art In recent years, demands for high-speed signal processing and digitalization for higher functions have been further increased in electronic devices. In particular, the method of drilling (via formation) in the manufacturing method called build-up is roughly classified into a photo via method in which a via is formed using light and a laser via method in which a laser is used. This is an important technology for integration. On the other hand, a manufacturing method of piercing a conductive needle-like object into an insulating layer made of synthetic resin or the like to form a hole and electrically connecting electric circuits on both sides of the insulating layer with the needle-like object (hereinafter referred to as a piercing method). Is sometimes known (Japanese Patent Application Laid-Open No. 7-86749). The needle-like object is formed on a position called a bump in an electric circuit. The piercing method can be implemented at a lower cost than the other two methods, and is industrially superior. However, it is preferable that the via diameter is small for high integration, but in order to make the via diameter as small as the other two types in the piercing method, it is necessary to reduce the diameter of the needle-like material. However, in this case, there is a possibility that the needle-shaped object is deformed before breaking through the insulating layer, and for example, high integration has been realized by using together with the other two types. Therefore, an insulating layer that can be pierced with smaller needles has been desired.

[0003] Further, US Patent No. 5,851,646 proposes a prepreg in which a porous para-oriented aromatic polyamide film is impregnated with a thermoplastic resin and / or a thermosetting resin.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a prepreg for a printed circuit board, which can be pierced by a needle-shaped object having a small diameter by a piercing method, a porous film for a printed circuit board serving as a base material of the prepreg, and the prepreg. It is an object of the present invention to provide a printed circuit laminate that can be highly integrated by a piercing method, using a prepreg.

[0005]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and have reached the present invention. That is, the present invention provides (1) at least one kind of heat-resistant resin selected from resins having a deflection temperature under load of 200 ° C. or more;
At any temperature in the range of -300 ° C, the coefficient of linear thermal expansion is −50 × 10 ⁻⁶ / ° C to + 50 × 10 ^−6.
/ C range, the porosity is 30 to 95% by volume,
The present invention relates to a porous film for a printed circuit board manufactured by a piercing method in which a displacement in a piercing test is 1.5 mm or less. Here, the displacement of the piercing test means that when a stainless steel needle having a curvature radius of the tip portion of 0.5 mm is pierced perpendicularly into a 25 μm-thick porous film at a speed of 200 mm / min, the needle pierces the stainless steel needle. It refers to the distance that the tip of the needle has moved from contact with the porous film to the opening of the hole. Also,
The present invention relates to (2) a prepreg for a printed circuit board obtained by impregnating the porous film of (1) with a thermoplastic resin and / or a thermosetting resin. Further, (3) the present invention relates to a printed circuit laminate manufactured by piercing using the prepreg of (2).

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The porous film for a printed board of the present invention is made of at least one heat-resistant resin selected from resins having a deflection temperature under load of 200 ° C. or higher. The deflection temperature under load is determined by JI
It refers to the deflection temperature under load in the measurement under a load of 18.6 kg / cm ² according to SK 7207. Examples of the resin having a deflection temperature under load of 200 ° C. or higher include polyimide, polyamideimide, aromatic polyamide (hereinafter, sometimes referred to as aramid), polyether sulfone, polyetherimide, and the like. Polyimide, polyamideimide, and aramid It is preferable to select from the group consisting of

Further, the porous film for a printed board of the present invention
Is at any temperature in the range of 200-300 ° C.
Even if it has a coefficient of linear thermal expansion (plane direction) of -50 × 10
^-6/ ℃ ～ + 50 × 10^-6/ ° C, preferably
Is -10 × 10^-6/ ℃ ～ + 50 × 10^-6/ ° C,
-10 x 10^-6/ ° C to + 25 × 10^-6/ ° C is more preferred
New The small coefficient of linear thermal expansion means that the dimension in the plane direction is small.
This indicates that the legal stability is good.

Further, the porous film for a printed board of the present invention has a porosity of 30 to 95% by volume, preferably 35 to 90% by volume. Porosity is 30% by volume
If it is less than 1, the amount of the varnish obtained by dissolving the thermoplastic resin and / or the thermosetting resin in the solvent when producing the prepreg becomes insufficient. On the other hand, when the content exceeds 95% by volume, the strength of the porous film becomes insufficient and handling becomes difficult.

[0009] The porous film for a printed board of the present invention is characterized in that the displacement in the piercing test is within 1.5 mm. Here, the displacement in the piercing test means that a stainless steel needle having a radius of curvature of 0.5 mm at the tip is 200 mm /
When the needle is vertically pierced into a 25-μm-thick porous film at a speed of minute, the distance traveled by the needle from the contact of the needle with the porous film to the opening of the hole. During the test, the porous film is sandwiched and fixed between two cylinders having an inner diameter of 12 mm. When this displacement is larger than 1.5 mm, holes are hardly formed, and when the piercing method is performed, an unnecessary force is applied to the needle-like object, which is not preferable.

[0010] The heat-resistant resin used in the present invention is a para-oriented aromatic polyamide (hereinafter sometimes referred to as para-aramid).
Is particularly preferred. Para-aramid is obtained by condensation polymerization of a para-oriented aromatic diamine and a para-oriented aromatic dicarboxylic acid halide, and the amide bond has a para-position of an aromatic ring or an alignment position corresponding thereto (for example, 4,4′-).
It consists essentially of repeating units that are linked in opposite directions, coaxial or parallel, such as biphenylene, 1,5-naphthalene, 2,6-naphthalene, and the like. Specifically, poly (paraphenylene terephthalamide), poly (parabenzamide), poly (4,4'-
Benzanilide terephthalamide), poly (paraphenylene-4,4′-biphenylenedicarboxylic acid amide),
Para orientation such as poly (paraphenylene-2,6-naphthalenedicarboxylic acid amide), poly (2-chloro-paraphenyleneterephthalamide), paraphenylenediamine / 2,6-dichloroparaphenylenediamine / terephthalic acid dichloride copolymer Examples thereof include para-aramid having a structure according to the type or para-oriented type.

[0011] The porous film for a printed board of the present invention is preferably a porous film obtained from the above-mentioned para-aramid, and the film is made of para-aramid fibrils. Among the porous films, those made of fibrils having a diameter of 1 μm or less are preferable. Further, as the porous film, a film in which the fibrils are arranged in a network or a nonwoven fabric on a substantially flat surface and overlapped in layers is preferable. Here, being arranged in a plane means that the fibrils are arranged in parallel to the film surface.

[0012] The thermoplastic resin used in the present invention is not particularly limited as long as it is a resin having thermoplasticity, but a thermoplastic resin having a melting point of 150 ° C or more is preferable. For the production of a printed circuit laminate, which is the main use of the prepreg according to the present invention, a prepreg that has sufficient adhesiveness between a material for forming an electronic circuit and the prepreg is preferable. Examples of such a thermoplastic resin include at least one thermoplastic resin selected from polyethersulfone, polysulfone, polyetherimide, polysulfidesulfone, polycarbonate, polyimide, polyamideimide, and polyetherketone. They are,
They can be used alone or in appropriate combination.

On the other hand, the thermosetting resin used in the present invention is not particularly limited, but may be an epoxy resin, a bismaleimide-triazine resin, a polyimide resin, a diallyl phthalate resin, an unsaturated polyester resin, a cyanate resin, and an aryl-modified polyphenylene ether. At least one kind of thermosetting resin selected from resins can be exemplified. These can be used alone or in appropriate combination.

In the present invention, the thermoplastic resin and the thermosetting resin can be used alone, but they can also be used simultaneously as a composition or separately in the prepreg production process. Compared to the case where the thermosetting resin is used alone, it is preferable to blend both of them because the toughness of the cured product is excellent and the flexibility in the B-stage can be controlled.

The addition amount of the thermoplastic resin and the thermosetting resin alone or as a composition is 1/9 to 7 / compared to para-aramid alone or as a composition / para-aramid ratio (weight ratio).
3, more preferably 2/8 to 6 /
4. If the composition is less than 1/9 weight ratio, the voids of the porous film composed of para-aramid may not be able to be sufficiently filled with the composition, and if it exceeds 7/3 weight ratio, the coefficient of linear thermal expansion of the prepreg may be reduced. In some cases, it becomes large and becomes unsuitable as a laminate. In addition, it is preferable that the mixing ratio of the thermoplastic resin and the thermosetting resin is in a range of 7/3 to 3/7 as a weight ratio of the thermoplastic resin / the thermosetting resin. When the weight ratio exceeds 7/3, there is not much difference from a system using only a thermoplastic resin as a matrix, and there is a case where the use of a thermosetting resin becomes meaningless. For example, as an advantage of using a thermosetting resin, there is an improvement in adhesive strength between a prepreg and a copper foil which is a conductive layer of a printed circuit board.
This effect may be reduced. If the weight ratio is less than 3/7, the toughness of the cured product and the flexibility at the B-stage may not be obtained.

[0016] The prepreg of the present invention is characterized in that the porous film of the present invention is impregnated with a thermoplastic resin and / or a thermosetting resin. At any temperature in the range of 200 to 300 ° C., the sheet obtained by curing the prepreg of the present invention has a coefficient of linear thermal expansion (in the plane direction) of −7.
It is preferably in the range of 0 × 10 ⁻⁶ / ° C. to + 70 × 10 ⁻⁶ / ° C., and more preferably −10 × 10 ⁻⁶ / ° C. to +
70 × 10 ⁻⁶ / ° C., more preferably −5 × 1
0 ⁻⁶ / ° C. to + 35 × 10 ⁻⁶ / ° C. Such a small coefficient of linear thermal expansion indicates that the dimensional stability in the planar direction is good, which is a property suitable for a printed circuit board.

The prepreg of the present invention can be made thinner by reducing its thickness. However, the film thickness is 10 μm
If it is less than 10%, wrinkles are easily formed and handling may be difficult.
Specifically, the thickness of the porous film is 10 to 1
50 μm is preferred, and more preferably 30 to 100 μm
It is. There is no particular upper limit, but if it exceeds 150 μm, the important feature of the laminate, namely, light and thin, may be lost.

In the method for producing a prepreg of the present invention, examples of using para-aramid as a heat-resistant resin include:
The method described in US Pat. No. 5,851,646 is exemplified. Hereinafter, the main points will be described. These are merely examples and do not limit the present invention in any way. Representative examples of the method for producing a prepreg of the present invention include the following (a)
To (d). (A) In a polar amide solvent or a polar urea solvent, 1 to 10% by weight of paraaramid having an intrinsic viscosity of 1.0 to 2.8 dl / g, and 1 to 10% by weight of an alkali metal or alkaline earth metal chloride. A step of forming a film from a solution containing 10% by weight. (B) a step of maintaining the film in an atmosphere at a temperature of 20 ° C. or higher and a relative humidity of 60% or higher to precipitate para-aramid from the film; (C) immersing the film obtained in the step (b) in an aqueous solution or an alcoholic solution to elute the solvent and the chloride of the alkali metal or alkaline earth metal, and then drying;
A step of obtaining a para-aramid porous film. (D) A step of producing a prepreg by using the porous film obtained in the step (c) as a substrate and impregnating the substrate with a thermoplastic resin and / or a thermosetting resin.

The para-aramid solution used in step (a) is
For example, it can be suitably manufactured by the operation described below. That is, a polar amide-based solvent or a polar urea-based solvent contains one alkali metal or alkaline earth metal chloride.
To 10% by weight of para-oriented aromatic diamine and 1.0 mol of para-oriented aromatic dicarboxylic acid halide.
94 to 0.99 mol, and the temperature is -20 ° C to 50 ° C.
To produce a para-aramid solution having a para-aramid concentration of 1 to 10% by weight.

In step (a), the condensation polymerization of para-aramid is carried out in a polar amide solvent or a polar urea solvent. Examples of these solvents include N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, or N, N, N ', N'-tetramethylurea, preferably N-methyl-
2-pyrrolidone.

In the step (b), after a film-like substance is formed from the para-aramid solution in the step (a), para-aramid is precipitated before coagulation.

In the step (c), the film obtained in the step (b) is immersed in an aqueous solution or an alcoholic solution, and a solvent and an alkali metal or alkaline earth metal chloride are removed from the film. Remove. An aqueous solution or an alcoholic solution can be suitably used because it can dissolve both the solvent and the chloride. Water may be used as the aqueous solvent. The film from which the solvent and chloride have been removed is then dried to obtain a porous film. The drying method is not particularly limited, and a known method can be used.

The method for impregnating the porous film with the thermoplastic resin and / or the thermosetting resin in the step (d) is not particularly limited, and a conventionally known method for impregnating a paper or glass cloth with a thermosetting resin is known. Etc. can be applied. For example, it is possible to prepare a varnish obtained by dissolving a composition comprising a thermoplastic resin and a thermosetting resin in a solvent, coat and impregnate the porous film of the present invention, and evaporate the solvent to produce a prepreg. it can. In the prepreg using only a thermoplastic resin as a resin or in a prepreg using a thermoplastic resin and a thermosetting resin,
From the viewpoint of uniformly dispersing the thermoplastic resin in the porous film, all or part of the thermoplastic resin is subjected to the above step (a).
Is preferably added to the solution used for forming the film.

The prepreg of the present invention has a low coefficient of linear thermal expansion, is excellent in mechanical strength, and can be pierced even with a needle-like object having a small diameter. Therefore, the prepreg is suitably used for a printed circuit laminate manufactured by a piercing method. it can. Further, a printed circuit laminate manufactured by a piercing method using the prepreg of the present invention can be highly integrated.

[0025]

The present invention will be described below in detail with reference to examples. Tests, evaluation methods and criteria in Examples and Comparative Examples are as follows.

(1) Intrinsic Viscosity For a solution in which 0.5 g of para-aramid was dissolved in 100 ml of 96-98% sulfuric acid and 96-98% sulfuric acid, the flow time was measured at 30 ° C. using a capillary viscometer, and the calculated flow rate was determined. The intrinsic viscosity was determined from the ratio of time by the following equation. Intrinsic viscosity = ln (T / T ₀ ) / C [unit: dl / g] Here, T and T ₀ are the flow times of the para-aramid sulfate solution and sulfuric acid, respectively, and C is the concentration of para-aramid in the para-aramid sulfate solution (g / g). dl).

(2) Porosity Porous film is cut into a square shape (length of one side L: c
m), weight (W: g), and thickness (D: cm).
Assuming that the true density of para-aramid was 1.45 g / cm ³ , the porosity (% by volume) was determined by the following equation. Porosity (% by volume) = 100−100 × (W / 1.45)
/ (L ² × D)

(3) Piercing test The displacement in the piercing test means that the inner diameter of the porous film is 12
mm is fixed between two cylinders, and a stainless steel needle having a tip R of 0.5 mm at a speed of 200 mm / min.
pierce vertically into a porous film having a thickness of m. The distance traveled by the tip of the needle from the contact of the needle with the porous film to the opening of the hole is defined as the displacement.

(4) Coefficient of linear thermal expansion According to ASTM D696, it was measured using a thermal analyzer TMA120 manufactured by Seiko Denshi Co., Ltd., and calculated by the following equation. _{α1 = ΔL / (L 0 ·} ΔT) where, [alpha] 1: linear thermal expansion coefficient (/ ℃) ΔL: change in specimen length L _0: specimen length before test [Delta] T: Temperature difference (℃)

Example 1 1) Polymerization of poly (paraphenylene terephthalamide) 5 having a stirring blade, a thermometer, a nitrogen inlet tube and a powder addition port
Using a liter (l) separable flask, poly (paraphenylene terephthalamide) (hereinafter referred to as PPTA)
Abbreviated. ) Was carried out. Dry the flask thoroughly,
-Methyl-2-pyrrolidone (hereinafter abbreviated as NMP) 4
200 g was charged, and 272.7 g of calcium chloride dried at 200 ° C. for 2 hours was added, and the temperature was raised to 100 ° C. After the calcium chloride is completely dissolved, the temperature is returned to room temperature, and paraphenylenediamine (hereinafter abbreviated as PPD) 132.9 is used.
g was added and completely dissolved. While maintaining this solution at 20 ± 2 ° C., terephthalic acid dichloride (hereinafter referred to as TPC)
Abbreviated. ) 243.3 g were added in 10 portions and added approximately every 5 minutes. Thereafter, the solution was aged for 1 hour while maintaining the solution at 20 ± 2 ° C., and stirred for 30 minutes under reduced pressure to remove bubbles. The obtained polymerization liquid (polymer dope) showed optical anisotropy. A portion was sampled, reprecipitated with water, taken out as a polymer, and the intrinsic viscosity of the obtained PPTA was measured.
It was 96 dl / g.

2) Porosity and coefficient of linear thermal expansion of the PPTA film A porous film made of PPTA was prepared from the polymerization solution of the above item 1). That is, 100 g of the polymerization solution of the item 1) was added to a 500 having a stirring blade, a thermometer, a nitrogen injection pipe, and a liquid addition port.
It was weighed into a ml separable flask and diluted with 150 g of NMP. The resulting solution has a PPTA concentration of 2.4% by weight.
And calcium chloride is 2 per mole of amide group of PPTA.
It was a mole ratio. Next, a film-like material of the solution was prepared on a glass plate using a bar coater (0.8 mm in thickness) manufactured by Tester Sangyo Co., Ltd., and immediately kept in a heating oven at 80 ° C. for about 20 minutes. During this time, PPTA was deposited, and a porous film was obtained. This porous film was immersed in ion-exchanged water. After 3 minutes, the porous film was peeled off from the glass plate. After sufficient washing with flowing deionized water, a porous film was taken out of the water and free water was wiped off. This porous film is sandwiched between filter papers,
In addition, it is sandwiched between glass cloths. An aluminum plate was placed with the porous film material sandwiched between filter paper and glass cloth, a nylon film was placed on the aluminum plate, the nylon film and the aluminum plate were sealed with gum, and a conduit for decompression was attached. . The whole was put into a hot oven and dried at 120 ° C. while drying the porous film. The obtained porous film had a thickness of 32 μm and a porosity of 60%. Also, 200
The linear thermal expansion coefficient at -300 ° C is -6.5 × 10 ^-6 /
° C. The displacement measurement in the piercing test was performed by changing the coating thickness and creating a porous film having a thickness of 25 μm. The displacement at this time was 0.8 mm.

3) Preparation of Prepreg, Printed Circuit Substrate, and Laminated Board (1) Preparation of Varnish A solvent (methyl ethyl ketone, hereinafter abbreviated as MEK) was added to a mixture of the following composition, and a reflux pipe was attached to the mixture.
In a 1 Erlenmeyer flask, the mixture was heated and refluxed for 90 minutes while stirring with a magnetic stirrer to obtain a varnish. Varnish composition: (parts by weight) Main agent: Sumiepoxy LDX-4120 (manufactured by Sumitomo Chemical Co., Ltd.) 100.0 Curing agent: dicyandiamide (DICY, manufactured by Tokyo Chemical Industry) 2.7 Catalyst: 2-methyl-4-ethylimidazole (Shikoku Chemicals) 0.2)

(2) Preparation of prepreg The porous film was cut into 100 mm squares, and the varnish prepared in (1) was applied to both sides. During the impregnation of the varnish, the film is sandwiched between fluorine films (trade name: TOYOFLON 50F, manufactured by Toray Industries, Inc.) so that the solvent does not evaporate, and further pressed.
The varnish was spread evenly. After leaving the porous film uniformly impregnated with the varnish for 10 minutes, it was transferred onto a glass cloth (product code: YES-2101, manufactured by Nippon Sheet Glass Fiber Co., Ltd.) and heated at 150 ° C. for 3 minutes to remove the solvent. It was removed and the epoxy resin was semi-cured to prepare a prepreg.

(3) Production of Printed Circuit Base Material The prepregs were cut into 40 mm squares, 12 sheets were superimposed and pressed at 170 ° C. under a pressure of 10 kg / cm ² for 2 hours to completely cure the epoxy resin. 0.34mm
A thick printed circuit board was produced. The dielectric constant of the obtained printed circuit board was 3.8 (1 MHz) and 1
The coefficient of linear thermal expansion in the plane direction in the temperature range from 00 ° C. to 200 ° C. was 1.2 × 10 ⁻⁵ / ° C. When measuring the coefficient of linear thermal expansion, an expansion-compression type probe was used, and the measurement was performed at a pressing load of 3 g, a temperature rising rate of 10 ° C./min, and a temperature range of 25 ° C. to 300 ° C.

(4) Production of Printed Circuit Laminate The prepreg was cut into a 40 mm square, 12 sheets were laminated, and further, copper foil (TTAI treatment, 35 μm thickness, made by Furukawa Circuit Foil Co., Ltd.) was laminated, and 10 kg was laminated. / Cm
Pressing was performed at 170 ° C. for 2 hours under a pressure of ² , and the epoxy resin was completely cured to produce a printed circuit laminate having a thickness of 0.37 mm. When the copper foil peeling strength of the produced printed circuit laminate was measured, it was 1.3 kg / cm.

[0036]

The prepreg using the porous film for a printed circuit board of the present invention can be pierced by a piercing method even with a needle-like object having a small diameter, and a printed circuit manufactured by the piercing method using the prepreg. The industrial laminate has high industrial value because of high integration.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4F071 AA42 AA50 AA56 AA60 AA64 AD03 AF62Y AG12 AH13 BC01 BC02 BC10 BC17 4F072 AA01 AA07 AA08 AD08 AD09 AD23 AD41 AD42 AD44 AD45 AD46 AG03 AG17 AH05 AJ02 AJ03 AJ01 DB05 DB04 DC16 DD04 EB37 EB46 EB55 EC36 EC46 EC65 FA03 FB03 FC03 FC06 FD01 GA13 GD07 HA10 JA07 JA12 JB14 JB21 JB50 JC03

Claims (7)

[Claims] 1. A heat-resistant resin selected from resins having a deflection temperature under load of 200 ° C. or more,
At any temperature in the range of 300 ° C., the coefficient of linear thermal expansion is −50 × 10 ⁻⁶ / ° C. to + 50 × 10 ⁻⁶ /
C., a porosity of 30 to 95% by volume, and a displacement in a piercing test of 1.5 mm or less. Here, the displacement of the piercing test means that a stainless steel needle having a radius of curvature of 0.5 mm at the tip is 200 m.
When the needle is vertically pierced into a 25-μm-thick porous film at a speed of m / min, it refers to the distance traveled by the tip of the needle from when the needle comes into contact with the porous film until a hole is formed. 2. The porous film for a printed circuit board according to claim 1, wherein the heat-resistant resin is a para-oriented aromatic polyamide. 3. The para-oriented aromatic polyamide is poly (paraphenylene terephthalamide), poly (parabenzamide), poly (4,4′-benzanilide terephthalamide), poly (paraphenylene-4,4′-biphenylenedicarbon). Acid amide), poly (paraphenylene-2,6)
3. Naphthalenedicarboxylic acid amide), poly (2-chloro-paraphenyleneterephthalamide), or paraphenylenediamine / 2,6-dichloroparaphenylenediamine / terephthalic acid dichloride copolymer. Porous film for printed circuit boards. 4. A prepreg for a printed circuit board, wherein the porous film according to claim 1 is impregnated with a thermoplastic resin and / or a thermosetting resin. 5. The thermoplastic resin is polyether sulfone,
The prepreg for a printed circuit board according to claim 4, wherein the prepreg is a polysulfone, a polyetherimide, a polysulfide sulfone, or a polycarbonate. 6. The thermosetting resin according to claim 4, wherein the thermosetting resin is an epoxy resin, a bismaleimide-triazine resin, a polyimide resin, a diallyl phthalate resin, an unsaturated polyester resin, a cyanate resin, or an aryl-modified polyphenylene ether resin. Prepreg for printed circuit boards. 7. A printed circuit laminate, wherein the prepreg according to claim 4 is manufactured by a piercing method.