JPH11261239A - Multi-layer printed circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent inter-layer peeling at an insulating layer under the heat in a reflow furnace at part mounting, related to a multi-layer printed circuit board wherein the insulating layer is obtained by molding under heat and pressure a layer of a nonwoven fabric of synthetic resin fiber impregnated with thermo-setting resin. SOLUTION: A water content diffusion factor of an insulating layer, related to a multi-layer printed circuit board, is 1.3×10<18> cm<2> /second or less. As a synthetic resin fiber nonwoven fabric which is impregnated with a thermo-setting resin to constitute the insulating layer, an aramid fiber nonwoven fabric, for example, is used. As the thermo-setting resin, for smaller water content diffusion factor, a material comprising a cycloalkane kind for the entire or a part of molecular structure is used. For example, it is cyclopentadiene epoxy resin, or cyclopentadiene cyanate ester resin. With a glass transition temperature of the insulating layer 150 deg.C or above, warping of the printed circuit board is less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer printed circuit board suitable for surface mounting of chip components such as resistors and ICs.

[0002]

2. Description of the Related Art In recent years, electronic components mounted on printed circuit boards have rapidly shifted to surface mount components (leadless chip components) in view of miniaturization, weight reduction, and higher density of electronic devices. Surface mounting has become the mainstream for mounting on circuit boards. In addition, demands for downsizing and multi-functionality of electronic devices have increased remarkably, and the wiring density of a printed circuit board used by being incorporated in electronic devices has been increasing. In order to increase the wiring density, the printed circuit board is a multilayer printed circuit board with circuits arranged on the inner layer via an insulating layer,
The number of circuit layers has been increased and the circuit width has been reduced.
Along with this, the number of through holes (holes penetrating a multilayer printed circuit board) for electrically connecting circuits arranged via insulating layers has also increased. When the number of through holes increases, the area available for circuit arrangement decreases, and high-density wiring cannot be performed.

[0003] Therefore, an aromatic polyamide fiber (aramid fiber) non-woven epoxy resin base material having a higher degree of freedom in circuit design is provided by connecting circuits arranged via an insulating layer through non-through holes formed by laser light or the like. Multilayer printed circuit boards have been proposed. Usually, an insulating layer is formed by impregnating a heat-resistant synthetic resin fiber base material such as an aramid fiber nonwoven fabric with a bisphenol-based epoxy resin. However, bisphenol-based epoxy resin has a large water diffusion coefficient, so a multilayer printed circuit board composed of such a combination of base material and resin is
Moisture adhering to the insulating layer expands due to heat in the reflow furnace at the time of component mounting, delamination of the insulating layer easily occurs, which is insufficient for practical use. Further, the printed circuit board is likely to warp due to the heat in the reflow furnace, and if a polyfunctional epoxy resin is used instead of a bisphenol-based epoxy resin to increase heat resistance, there is also a disadvantage that hygroscopicity is increased.

[0004]

The first problem to be solved by the present invention is that the insulating layer is formed by heating and pressing a layer of a synthetic resin fiber nonwoven fabric impregnated with a thermosetting resin. An object of the present invention is to prevent delamination of an insulating layer due to heat in a reflow furnace at the time of component mounting in a multilayer printed circuit board. In addition, a second problem is to prevent the printed circuit board from warping due to the heat in the reflow furnace.

[0005]

The multilayer printed circuit board according to the present invention has a low moisture diffusion coefficient of an insulating layer formed by heating and pressing a layer of a synthetic resin fiber nonwoven fabric impregnated with a thermosetting resin. By doing so, the first problem is solved. That is, in a multilayer printed circuit board in which a circuit is disposed on an inner layer and a surface, and an insulating layer between circuit layers is formed by heating and pressing a layer of a synthetic resin fiber nonwoven fabric impregnated with a thermosetting resin, The moisture diffusion coefficient of the insulating layer formed by heating and pressing a layer of a synthetic resin fiber nonwoven fabric impregnated with a curable resin is set to 1.3 × 10 ⁻⁸ cm ² / sec or less. The present invention is constructed by heating and pressing a layer of a synthetic resin fiber nonwoven fabric impregnated with a thermosetting resin on both or one side of a printed circuit board having a thermosetting resin-impregnated glass fiber substrate as an insulating layer. A multilayer printed circuit board having a configuration in which one or more circuits are arranged via an insulating layer is also intended. Again, in this case,
An insulating layer formed by heating and pressing a layer of a synthetic resin fiber nonwoven fabric impregnated with a thermosetting resin has a water diffusion coefficient of 1.3.
× 10 ⁻⁸ cm ² / sec or less.

As described above, a multilayer printed circuit board in which the moisture diffusion coefficient of an insulating layer formed by heating and pressing a layer of a synthetic resin fiber nonwoven fabric impregnated with a thermosetting resin is reduced. Can be obtained by selecting, as a main component, a thermosetting resin containing cycloalkanes in part or all of the molecular skeleton. When an epoxy resin is selected as the main component as the thermosetting resin, it is obtained by including a cycloalkane in at least a part or all of the molecular skeleton of the epoxy resin and its curing agent.

Here, the water diffusion coefficient is obtained as follows. First, an insulating layer having a thickness of d (cm) is placed in an atmosphere of 60 ° C. and 90% RH for a time t (second) to absorb moisture. Then, the moisture absorption rate during the moisture absorption processing time t (second) is obtained by (Equation 1).

[0008]

(Equation 1)

Next, a moisture absorption curve is prepared by plotting (t ^1/2 / d) the horizontal axis and the moisture absorption rate on the vertical axis and the moisture absorption rate during the moisture absorption processing time t (second). From the created moisture absorption curve, the slope m of the first straight line portion of the curve is obtained. Further, a saturated moisture absorption rate M at which the moisture absorption rate does not increase any more is determined.
After making these preparations, the water diffusion coefficient D is determined by D = π (m / 4M) ² .

A nonwoven fabric made of synthetic resin fiber such as aramid fiber has a high moisture absorption rate, and thus moisture that has entered from the surface of a multilayer printed circuit board having a large water diffusion coefficient of an insulating layer is reduced by the synthetic resin fiber and thermosetting resin. There is a concern that moisture may expand due to rapid heating and cause delamination of the insulating layer. The moisture diffusion coefficient of the insulating layer is 1.3 × 10 ^-8
Above cm ² / sec, moisture in the air will more easily penetrate the surface of the printed circuit board.

In order to solve the second problem in addition to the first problem, the moisture diffusion coefficient of an insulating layer formed by heating and pressing a layer of a synthetic resin fiber nonwoven fabric impregnated with a thermosetting resin is determined. 1.3 × 10 ⁻⁸ cm ² / sec or less, and the glass transition temperature (measured by TMA method) of the insulating layer is set to 150 ° C. or more.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Nonwoven fabrics composed of synthetic resin fibers such as aramid fibers have a high moisture absorption. Therefore, the moisture diffusion coefficient of an insulating layer obtained by impregnating these nonwoven fabrics with a thermosetting resin and molding under heat and pressure is determined. It must be small so that moisture in the air does not enter the printed circuit board surface as much as possible.

In order to solve the first problem, the thermosetting resin used in the practice of the present invention is not particularly limited, such as polyimide, phenol resin, cyanate ester resin, epoxy resin, and unsaturated polyester. From the viewpoint, the thermosetting resin impregnated into the non-woven fabric composed of synthetic resin fibers eliminates atoms having dipoles such as oxygen, nitrogen, and phosphorus from the molecular skeleton as much as possible, and is composed of an aliphatic hydrocarbon. . Specifically, the main component is a resin containing cycloalkanes in a part or all of the molecular skeleton of the thermosetting resin. A plurality of thermosetting resins containing cycloalkanes in part or all of the molecular skeleton may be used in combination. When the thermosetting resin is mainly composed of an epoxy resin, one or both of the epoxy resin and its curing agent may contain cycloalkanes. In this case, the cycloalkane may be contained in a part or all of the molecular skeleton. Epoxy resins containing cycloalkanes in the molecular skeleton include, for example, cyclopentadiene epoxy resins having the molecular structural formula shown in Chemical Formula 1 (“HP-7200” manufactured by Dainippon Ink, epoxy equivalent: 26)
4). The curing agent for the epoxy resin containing a cycloalkane in the molecular skeleton is, for example, a phenol-added polybutadiene (“PP-700-300” manufactured by Nippon Petrochemical Co., hydroxyl equivalent: 317) having the molecular structural formula shown in Chemical Formula 2. Another thermosetting resin containing a cycloalkane in the molecular skeleton is, for example, a cyclopentadiene cyanate ester resin (cyanate ester equivalent: 233) having a molecular structural formula shown in (Chemical Formula 3).

[0014]

Embedded image

[0015]

Embedded image

[0016]

Embedded image

In order to impart flame retardancy to the thermosetting resin, a flame retardant such as a halogen-containing organic compound, a flame retardant auxiliary such as antimony oxide, other organic or inorganic fillers, a coloring agent and the like are used. It may be added.

It is desirable that the synthetic resin fibers constituting the nonwoven fabric also have a moisture absorption rate as small as possible. For example, synthetic resins such as polyester fiber, nylon 66, m-phenylene isophthalamide fiber (meta-aramid fiber), p-phenylene terephthalamide fiber and p-phenylene phenyl ether terephthalamide fiber (para-aramid fiber) The fibers can be used alone or in combination to form a nonwoven fabric. Aramid fibers having heat resistance that does not soften or melt at the reflow temperature during component mounting are preferred.

The multilayer printed circuit board according to the present invention is manufactured using a layer of the synthetic resin fiber nonwoven fabric impregnated with the thermosetting resin as an insulating layer. For example, first, a metal foil is placed on both surfaces of a prepreg layer obtained by impregnating and drying a thermosetting resin in the synthetic resin fiber nonwoven fabric, and integrated by heating and pressing. A predetermined circuit is formed by etching the metal foil to obtain a double-sided printed circuit board. Next, metal foil is placed on both sides of the double-sided printed circuit board via the prepreg, and integrated by heating and pressing. A predetermined circuit is formed by etching this metal foil to obtain a four-layer printed circuit board. Further, when increasing the number of circuit layers, a metal foil is placed on both sides of the four-layer printed circuit board via the prepreg, integrated by heating and pressing, and the metal foil is etched to form a predetermined circuit. To form Hereinafter, the same steps are repeated as necessary to increase the number of circuit layers. Instead of the double-sided printed circuit board, a printed circuit board or a multilayer printed circuit board having a thermosetting resin-impregnated glass fiber substrate as an insulating layer may be used. By arranging the insulating layer of the glass fiber base material in the inner layer, the rigidity of the multilayer printed circuit board can be increased. In another manufacturing method, first,
A metal foil is placed on both surfaces of a prepreg layer obtained by impregnating and drying a thermosetting resin in the synthetic resin fiber nonwoven fabric, and integrated by heating and pressing. A predetermined circuit is formed by etching the metal foil to obtain a double-sided printed circuit board. Such a plurality of double-sided printed circuit boards are overlapped with each other via the prepreg, and a metal foil is placed on both sides of the prepreg via the prepreg. A predetermined circuit is formed by etching the metal foil on the surface.

As the above-mentioned metal foil, copper foil, aluminum foil, nickel foil and the like can be used. The type and thickness are not particularly limited as long as the metal foil has good conductivity. Further, a metal foil with an adhesive can be used if necessary. In this case, as the adhesive, a general-purpose metal foil adhesive such as a phenol resin, an epoxy resin, a butyral resin, a polyester, a polyurethane, or a mixture thereof can be used.

[0021] In order to solve the second problem in addition to the first problem, in the construction of the multilayer printed circuit board for solving the first problem, there is provided a synthetic resin fiber nonwoven fabric impregnated with a thermosetting resin. It is preferable to use a polyfunctional (trifunctional or higher) epoxy resin as the thermosetting resin in order to set the glass transition temperature of the insulating layer formed by heating and pressing the layer to 150 ° C. or higher. As a curing agent for the polyfunctional epoxy resin, a curing agent containing a cycloalkane in part or all of the molecular skeleton, for example, a phenol-added polybutadiene having the molecular structural formula shown in the above chemical formula (Nippon Petrochemical) "PP-700-300", hydroxyl equivalent 317)
Is used. The blending amount of the polyfunctional epoxy resin is 80 to 11 with respect to 100 parts by weight of the curing agent containing cycloalkanes.
0 parts by weight is preferred. 80 parts by weight is a compounding amount considered for maintaining the glass transition temperature of the laminate at 150 ° C. or higher, and 110 parts by weight is a compounding amount considered for suppressing the hygroscopicity of the laminate. In such a resin composition, more preferably, the ratio of hydroxyl group equivalent / epoxy equivalent is 1 to 1.
5 is assumed. This is because the appearance of the synthetic resin fiber nonwoven fabric (prepreg) impregnated with the epoxy resin composition and dried is improved.

[0022]

EXAMPLES Example 1 100 parts by weight of a cyclopentadiene epoxy resin having the molecular structural formula shown in Chemical formula 1, 45 parts by weight of a cresol novolak resin as a curing agent, and 0.2 parts by weight of 2-ethyl 4-methylimidazole as a catalyst And a varnish (A) was prepared. For 100μm thick meta-aramid fiber non-woven fabric,
The varnish (A) was impregnated and dried to obtain a prepreg (A) having a resin content of 48% by weight. Eight prepregs (A) are superimposed, and copper foil (thickness: 18 μm) is placed above and below them.
It was heated and pressed at a temperature of 170 ° C. under a pressure of 40 kgf / cm ² for 60 minutes to obtain a copper-clad laminate (A) having a thickness of 0.8 mm. The copper foil was etched to form a predetermined circuit to obtain a double-sided printed circuit board (A). Next, copper foil (thickness: 18 μm) is placed on both sides of the double-sided printed circuit board (A) via one prepreg (A), and integrated by heating and pressing. The copper foil was etched to form a predetermined circuit to obtain a four-layer printed circuit board. The continuity between the circuit on the surface and the circuit on the inner layer is realized by forming a hole reaching the circuit on the inner layer in the insulating layer on the surface by laser processing technology, plating the hole, or filling the hole with a conductive resin. Alternatively,
A through hole is formed at a predetermined position of the prepreg (A) to be placed on both sides of the double-sided printed circuit board (A) (a position for conducting the circuit on the surface and the circuit in the inner layer) by a laser processing technique. Fill with conductive resin. Such prepreg (A) on both sides of double-sided printed circuit board (A)
A copper foil (thickness: 18 μm) is placed via one sheet, integrated by heating and pressing, and the copper foil on the surface is etched to form a predetermined circuit. Further, if necessary, a hole penetrating the four-layer printed circuit board is formed, and a through-hole plating is performed.

Example 2 Cyclopentadiene epoxy resin 1 used in Example 1
A varnish (B) was prepared by mixing 00 parts by weight, 120 parts by weight of a phenol-added polybutadiene having the molecular structural formula shown in Chemical Formula 2 as a curing agent, and 0.2 parts by weight of 2-ethyl 4-methylimidazole as a catalyst. The varnish (B) was impregnated into the meta-aramid fiber nonwoven fabric used in Example 1 and dried to obtain a prepreg (B) having a resin content of 48% by weight.
Using the prepreg (B), a four-layer printed circuit board (B) was obtained in the same manner as in Example 1 below.

Example 3 Bisphenol A type epoxy resin ("Ep" manufactured by Yuka Shell Co., Ltd.)
-1001 ", epoxy equivalent: 500) 100 parts by weight,
A varnish (C) was prepared by mixing 63 parts by weight of the phenol-added polybutadiene used in Example 2 as a curing agent and 0.2 parts by weight of 2-ethyl 4-methylimidazole as a catalyst. The varnish (C) was impregnated and dried in the meta-aramid fiber nonwoven fabric used in Example 1, and the resin content was 48% by weight.
Of prepreg (C) was obtained. Using prepreg (C)
Thereafter, a four-layer printed circuit board (C) was obtained in the same manner as in Example 1.

Example 4 Cyclopentadiene epoxy resin 1 used in Example 1
00 parts by weight, 130 parts by weight of cyclopentadiene cyanate ester resin having the molecular structural formula shown in Chemical Formula 3, 0.2 parts by weight of 2-ethyl 4-methylimidazole as a catalyst, and 0.2 parts by weight of zinc naphthenate A varnish (D) was prepared. The varnish (D) was impregnated and dried in the meta-aramid fiber nonwoven fabric used in Example 1 to obtain a prepreg (D) having a resin content of 48% by weight. Using the prepreg (D), a four-layer printed circuit board (D) was obtained in the same manner as in Example 1 below.

Example 5 The varnish (A) used in Example 1 was impregnated into a polyester fiber nonwoven fabric and dried to obtain a prepreg (E) having a resin content of 48% by weight. Example 1 using prepreg (E)
In the same manner as in the above, a four-layer printed circuit board (E) was obtained.

Example 6 The varnish (A) used in Example 1 was impregnated and dried in a 100 μm-thick nonwoven fabric made of a mixture of meta-aramid fibers and polyester fibers (70% by weight of meta-aramid fibers and 30% by weight of polyester fibers). A prepreg (F) having a resin content of 48% by weight was obtained. Example 1 using prepreg (F)
In the same manner as in the above, a four-layer printed circuit board (F) was obtained.

Conventional Example 1 Bisphenol A type epoxy resin ("Ep"
-1001 ", epoxy equivalent: 500) 100 parts by weight,
A varnish (G) was prepared by mixing 21 parts by weight of a phenol novolak resin as a curing agent and 0.2 parts by weight of 2-ethyl 4-methylimidazole as a catalyst. The varnish (G) was impregnated and dried in the meta-aramid fiber nonwoven fabric used in Example 1 to obtain a prepreg (G) having a resin content of 48% by weight. Using prepreg (G), 4
A layer printed circuit board (G) was obtained.

Example 7 Orthocresol novolak type epoxy resin (mainly tetrafunctional or higher polyfunctional) 50 parts by weight, glycidylated triphenylol type trifunctional epoxy resin 50 parts by weight, tetrabromobisphenol A as a flame retardant 83 parts by weight A varnish (H) was prepared by blending 100 parts by weight of the phenol-added polybutadiene used in Example 2 as a curing agent and 0.2 parts by weight of 2-ethyl 4-methylimidazole as a catalyst. The hydroxyl equivalent / epoxy equivalent is 1.3. The varnish (H) was impregnated and dried in the meta-aramid fiber nonwoven fabric used in Example 1 to obtain a prepreg (H) having a resin content of 48% by weight. Using the prepreg (H), a four-layer printed circuit board (H) was obtained in the same manner as in Example 1 below.

Example 8 Glycidylated triphenylol type trifunctional epoxy resin 9
5 parts by weight, tetrabromobisphenol A as flame retardant
A varnish (I) was prepared by mixing 74 parts by weight, 100 parts by weight of the phenol-added polybutadiene used in Example 2 as a curing agent, and 0.2 parts by weight of 2-ethyl 4-methylimidazole as a catalyst. The hydroxyl equivalent / epoxy equivalent is 1.3. The varnish (I) was impregnated into the meta-aramid fiber nonwoven fabric used in Example 1 and dried to obtain a resin content of 48.
% By weight of prepreg (I) was obtained. Using a prepreg (I), a four-layer printed circuit board (I) in the same manner as in Example 1
I got

Example 9 The varnish (H) used in Example 7 was impregnated and dried in a 100 μm-thick nonwoven fabric made of a mixture of meta-aramid fibers and polyester fibers (70% by weight of meta-aramid fibers and 30% by weight of polyester fibers). A prepreg (J) having a resin content of 48% by weight was obtained. Example 1 using prepreg (J)
In the same manner as in the above, a four-layer printed circuit board (J) was obtained.

Example 10 Glycidylated triphenylol type trifunctional epoxy resin 1
0 parts by weight, brominated bisphenol A novolak type epoxy resin (main component is polyfunctional or more than tetrafunctional, epoxy equivalent:
398) 73 parts by weight, 100 parts by weight of the phenol-added polybutadiene used in Example 2 as a curing agent, and 0.2 part by weight of 2-ethyl 4-methylimidazole as a catalyst were prepared as varnish (K). The hydroxyl equivalent / epoxy equivalent is 1.3. The meta-aramid fiber nonwoven fabric used in Example 1 was impregnated with varnish (K) and dried to obtain a prepreg (K) having a resin content of 48% by weight. Using the prepreg (K), a four-layer printed circuit board (K) was obtained in the same manner as in Example 1 below.

Example 11 Bisphenol A type epoxy resin ("Ep" manufactured by Yuka Shell Co., Ltd.)
-8281 ", epoxy equivalent: 189) 12 parts by weight, brominated bisphenol A novolak type epoxy resin (polyfunctional having four or more functional groups as the main component, epoxy equivalent: 398) 70
A varnish (L) was prepared by mixing 100 parts by weight of the phenol-added polybutadiene used in Example 2 as a curing agent and 0.2 part by weight of 2-ethyl 4-methylimidazole as a catalyst. Hydroxyl equivalent / epoxy equivalent is 1.3
It is. The varnish (L) was impregnated and dried in the meta-aramid fiber nonwoven fabric used in Example 1, and the resin content was 48% by weight.
Of prepreg (L) was obtained. Using prepreg (L)
Thereafter, a four-layer printed circuit board (L) was obtained in the same manner as in Example 1.

The moisture resistance and heat resistance of the four-layer printed circuit boards in the above Examples and the conventional examples were examined as follows.
First, after removing the entire surface circuit by etching,
Place in a 90% RH atmosphere for 72 hours. Thereafter, the resultant was passed through a reflow apparatus (maximum temperature: 250 ° C., passing time: 30 seconds) to observe whether or not there was peeling between the insulating layers. As a result of the observation, the results are shown in Table 1 along with the water diffusion coefficient (× 10 ⁻⁸ cm ² / sec), with “○” indicating no peeling and “X” indicating peeling. Also,
Table 1 also shows the measured values of the glass transition temperature (Tg) of the insulating layer alone by the TMA method and the measured values of the warpage of the four-layer printed circuit board passed through the reflow apparatus.

[0035]

[Table 1]

It should be noted that para-aramid fibers are superior to meta-aramid fibers in all of strength, heat resistance and moisture absorption resistance. Therefore, in Examples 1 to 4 and 6 to 11, in the configuration using para-aramid fibers instead of meta-aramid fibers, the characteristics shown in the above table are more excellent. Also, in each of the above embodiments, when a glass fiber substrate (glass woven substrate, glass nonwoven substrate, or a combination of these substrates) is used as the double-sided printed circuit board, the rigidity of the multilayer printed circuit board increases, so that warpage occurs. Can be further reduced.

[0037]

As is apparent from Table 1, the multilayer print according to the present invention has a water diffusion coefficient of an insulating layer formed by heating and pressing a layer of a synthetic resin fiber nonwoven fabric impregnated with a thermosetting resin. Is set to 1.3 × 10 ⁻⁸ cm ² / sec or less, it is possible to suppress the penetration of moisture from the surface of the printed circuit board and to prevent delamination of the insulating layer due to heat. It has remarkable resistance to moisture and heat and is useful as a multilayer printed circuit board for surface mounting. Further, when the water diffusion coefficient of the insulating layer is set to 1.3 × 10 ⁻⁸ cm ² / sec or less and the glass transition temperature is set to 150 ° C. or more, the warpage of the multilayer printed circuit board can be suppressed to be small. .

Claims (8)

[Claims] 1. A multilayer printed circuit board having a circuit disposed on an inner layer and a surface, and an insulating layer between circuit layers formed by heating and pressing a layer of a synthetic resin fiber nonwoven fabric impregnated with a thermosetting resin. In the above, an insulating layer formed by heating and pressing a layer of a synthetic resin fiber nonwoven fabric impregnated with a thermosetting resin has a water diffusion coefficient of 1.3.
A multilayer printed circuit board characterized by being at most 10 ^-8 cm ² / sec. 2. A printed circuit board having a thermosetting resin-impregnated glass fiber substrate as an insulating layer is formed by heating and pressing a layer of a synthetic resin fiber nonwoven fabric impregnated with a thermosetting resin on both surfaces or one surface thereof. In a multi-layer printed circuit board in which one or more circuits are arranged via an insulating layer, the moisture diffusion coefficient of an insulating layer formed by heating and pressing a layer of a synthetic resin fiber nonwoven fabric impregnated with a thermosetting resin is reduced. 1.3
A multilayer printed circuit board characterized by being at most 10 ^-8 cm ² / sec. 3. A thermosetting resin impregnated in a layer of a synthetic resin fiber non-woven fabric is mainly composed of a thermosetting resin containing cycloalkanes in a part or all of a molecular skeleton. 3. The multilayer printed circuit board according to 1 or 2. 4. A thermosetting resin impregnated in a layer of a synthetic resin fiber non-woven fabric is mainly composed of an epoxy resin, and cycloalkanes are partially or entirely contained in at least one of the molecular skeletons of the epoxy resin and its curing agent. The multilayer printed circuit board according to claim 1, wherein the multilayer printed circuit board is contained. 5. An insulating layer formed by heating and pressing a layer of a synthetic resin fiber non-woven fabric impregnated with a thermosetting resin, has a water diffusion coefficient of 1.3 × 10 ⁻⁸ cm ² / sec or less, 3. The multilayer printed circuit board according to claim 1, wherein the insulating layer has a glass transition temperature of 150 ° C. or higher. 6. A thermosetting resin impregnated in a layer of a synthetic resin fiber nonwoven fabric is a polyfunctional epoxy resin, and a part or all of a molecular skeleton of a curing agent of the polyfunctional epoxy resin contains cycloalkanes. The multilayer printed circuit board according to claim 5, wherein: 7. The cycloalkane-containing curing agent is a cycloalkane phenol adduct.
The multilayer printed circuit board as described. 8. The multilayer printed circuit board according to claim 1, wherein a part or all of the fibers constituting the synthetic resin fiber nonwoven fabric are aromatic polyamide fibers.