JP3287746B2 - 4-layer printed wiring board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a flame-retardant 4 using a copper foil having an undercoat layer and an interlayer insulating adhesive layer.
The present invention relates to a layer printed wiring board.

[0002]

2. Description of the Related Art In multilayer printed wiring boards, the miniaturization and multifunctionality of electronic devices have been progressing, and the direction of higher density has been shifted. That is, the circuit is becoming thinner, more multilayered, the diameter of the via hole smaller, thinner, and the like. Conventionally, when manufacturing a multilayer printed wiring board, one or more prepreg sheets obtained by impregnating a glass cloth base material with an epoxy resin and semi-curing are stacked on an inner circuit board on which a circuit is formed, and a copper foil is further placed thereon. It has undergone a process of integrally forming by heating with a lap hot plate press. However, in this step, since the impregnated resin is reflowed by heat and cured under a constant pressure, it takes 1 to 1.5 hours to uniformly cure and mold. As described above, the manufacturing process takes a long time, and the cost is high due to the costs of the multilayer laminating press and the glass cloth prepreg. In addition, the method of impregnating the glass cloth with a resin has made it difficult to make the interlayer thickness extremely thin.

In recent years, in order to solve these problems, a technique of a multilayer printed wiring board by a build-up system which does not perform hot press molding by a hot plate press and does not use a glass cloth as an interlayer insulating material has been renewed. I have. Generally, rubber-based compounds, polyvinyl butyral, phenoxy resin, polyester resin, etc. are compounded as a method of forming a film or a roll of the adhesive which is an interlayer insulating layer, but these components are used for thermal processing as a multilayer printed wiring board. Significantly degrade performance. In a multilayer printed wiring board by the build-up method, use a copper-clad insulating sheet in which an insulating resin layer is formed on the roughened surface of copper foil, or a prepreg sheet in which a glass cloth base material is impregnated with epoxy resin and semi-cured. When a film-like interlayer insulating resin layer is used instead, the working efficiency is significantly improved as compared with the method of forming the interlayer insulating resin layer using a prepreg. However, air at the step between the insulating substrate of the inner circuit board and the circuit cannot be completely removed, air remains, bubbles are generated, insulation failure and solder heat resistance deteriorate, and delamination occurs. This can be a problem. In order to prevent this, lamination must be performed under a reduced pressure environment, and special equipment is required. In addition, since the laminated insulating layer follows the step between the insulating substrate of the inner circuit board and the circuit, surface smoothness cannot be obtained, soldering failure or the like may occur at the time of component mounting, or the resist may not be formed in the etching resist forming step. There are problems such as peeling and a decrease in the pattern development degree, which makes it impossible to form a stable resist.

The same applies to the case where a prepreg is used. However, since the amount of resin to be embedded varies depending on the residual ratio of copper foil in the inner circuit pattern, the same copper-clad insulating sheet or film-like interlayer insulating resin layer is used. Also, the sheet thickness after molding does not become the same. In other words, when the copper foil residual ratio is large and the portion to be embedded is small, the plate thickness is large, and when the copper foil residual ratio is small and the portion to be embedded is large, the plate thickness is small. If you do not change, you cannot achieve the same thickness. In addition, when the residual ratio of copper foil is different depending on the location even in one inner layer circuit board, there is a problem that the obtained multilayer printed wiring board does not have a uniform plate thickness and the like. In such a process, the curing reaction of the interlayer insulating adhesive coated on the copper foil proceeds during its storage, and the integral curing is not performed well when laminated on the inner circuit board coated with the undercoat agent. There is a problem. Furthermore, since a glass fiber base material is not used for the interlayer insulating adhesive, there is a problem that flame retardation is difficult.

[0005]

SUMMARY OF THE INVENTION The present invention provides a thinner, less uneven thickness, and lower surface than the four-layer printed wiring board obtained by the hot plate press or the conventional built-up method. An object of the present invention is to provide a four-layer printed wiring board suitable for smooth high-density mounting.

[0006]

According to the present invention, a light / thermosetting undercoat layer, an interlayer insulating adhesive layer and a copper foil are sequentially laminated on both sides of an inner circuit board made of a flame-retardant epoxy resin impregnated glass cloth substrate. A four-layer printed wiring board, wherein the photo-thermosetting undercoat layer comprises: (a) a novolak-type epoxy resin having a bromination ratio of 20% or more and a molecular weight of 500 to 4000; and (b) a molecular weight of 500 to 2000. Bisphenol epoxy resin having a molecular weight of 500 or less, (d) glycidyl acrylate or glycidyl methacrylate, (e) hydroxyethyl acrylate or hydroxyethyl methacrylate, (f) photopolymerization initiator, (g) melting point Is 130
C. or more of an imidazole compound, and (h) a low-temperature curing type imidazole compound,
(I) a bisphenol-type epoxy resin having a weight average molecular weight of 10,000 or more, (nu) a bisphenol-type epoxy resin having an epoxy equivalent of 500 or less, and (l) a melting point of 130 ° C.
A four-layer printed wiring board comprising the above imidazole compound.

That is, the present invention provides screen printing on an inner circuit board made of a glass cloth substrate impregnated with a flame-retardant epoxy resin,
A liquid undercoat agent is applied using a roller coater, a curtain coater, or the like to fill the copper circuit gap of the inner circuit board, and the undercoat agent is tack-free by irradiating active energy rays with a UV conveyor or the like. Thereafter, the uncured or semi-cured copper foil with an interlayer insulating adhesive is laminated on an inner circuit board coated with an undercoat agent by a heated roll or the like one by one or simultaneously on both sides and adhered. Then, after lamination, heating is performed to simultaneously and integrally cure the light / thermosetting undercoat agent and the copper foil with an interlayer insulating adhesive, whereby a four-layer printed wiring board can be produced. When laminating, the undercoat agent is also softened by being heated by the roll, and the thickness is averaged by the roll pressure, so that the surface smoothness of the copper foil surface can be obtained. At that time, the interlayer insulating adhesive coated on the copper foil is bonded while maintaining its shape by the epoxy resin component having a weight average molecular weight of 10,000 or more, that is, while maintaining the interlayer thickness. A flame-retardant four-layer printed wiring board having excellent thickness accuracy that can be manufactured without being dependent on the four-layer printed wiring board and without variance in thickness.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, an undercoating agent used for an undercoat layer fills a gap between copper foil circuits of an inner layer circuit board and smoothes the surface of the inner layer circuit. (H). (A) a bromination ratio of 20% or more and a molecular weight of 500 to 4000;
Novolak type epoxy resin, (b) molecular weight 500-2
000 bisphenol type epoxy resin, (c) bisphenol type epoxy resin having a molecular weight of 500 or less, (d) glycidyl acrylate or glycidyl methacrylate,
(E) hydroxyethyl acrylate or hydroxyethyl methacrylate, (f) a photopolymerization initiator, (g) an imidazole compound having a melting point of 130 ° C. or more, and (h) a low-temperature-curable imidazole compound

The epoxy resin having a bromination ratio of component (a) of 20% or more and a molecular weight of 500 to 4000 used in the present invention is used for improving heat resistance and flame retardancy. A novolak type epoxy resin of novolak type or cresol novolak type, which is solid at normal temperature. The melting point may be usually 50 ° C. or higher.
When the bromination ratio is less than 20%, the obtained four-layer printed wiring board cannot achieve the flame retardancy V-0 according to UL standard. Further, the upper limit of the bromination ratio is a case where all the brominated portions of the benzene nucleus of the epoxy resin are brominated, and the upper limit of the bromination is determined by this.

The bisphenol type epoxy resin having a molecular weight of 500 to 2,000 of component (b) is bisphenol A type,
There are bisphenol F type, bisphenol S type, etc., which are solid at normal temperature and are mainly used for improving the adhesion and flexibility with the inner circuit board and the interlayer insulating adhesive layer. (C) Interaction with the component affects heat resistance, moldability (voidless), and surface smoothness. When the molecular weight exceeds 2,000, the viscosity of the undercoat agent increases, and the fluidity and the embedding property decrease,
The surface smoothness deteriorates, which is not preferable. The bisphenol type epoxy resin having a molecular weight of 500 or less as the component (c) enhances embedding property and wettability, and improves moldability and surface smoothness. If the molecular weight exceeds 500, these effects are undesirably weakened.

The photopolymerizable and thermoreactive monomers used in the photo-thermosetting undercoat agent are excellent in the thermosetting properties of the component (e) hydroxyethyl acrylate and hydroxyethyl methacrylate and the component (d). Glycidyl acrylate or glycidyl methacrylate. These components also function as a solvent such as an epoxy resin, and are used as a so-called solventless undercoat agent. The components (d) and (e) react by the irradiation of active energy rays, and the undercoat layer is tack-free depending on the degree of curing. The ratio of each compound is 20 ~
It is appropriately determined between 80% by weight. Further, the component (d) is epoxy-cured by imidazole, so that it is melted and mixed with other epoxy resins and reacts, so that heat resistance is enhanced and generation of voids is suppressed. Usually, the total amount of the monomers (d) and (e) is 20 to 100 parts by weight, preferably 30 to 70 parts by weight, based on 100 parts by weight of the total amount of the epoxy resin used.

Examples of the photopolymerization initiator (f) include benzophenones such as benzophenone, benzoylbenzoic acid, 4-phenylbenzophenone, and hydroxybenzophenone; benzoin, benzoin ethyl ether, benzoin isopropyl ether, benzoin butyl ether, and benzoin isobutyl ether. Benzoin alkyl ethers, 4-phenoxydichloroacetophenone, 4-t-butyl-dichloroacetophenone, 4-
acetophenones such as t-butyl-trichloroacetophenone and diethoxyacetophenone; thioxanthones such as thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone and 2,4-dimethylthioxanthone; ethylanthraquinone and butylanthraquinone; Alkyl anthraquinones and the like can be mentioned. These may be used alone or as a mixture of two or more. The addition amount of this photopolymerization initiator is usually 0.1 to 100 parts by weight of the photopolymerization and heat-reactive monomer.
Used in the range of 10 parts by weight.

The epoxy resin curing agent (g) has a melting point of 130 ° C. or higher, is solid at room temperature, has low solubility in the epoxy resin, and rapidly reacts with the epoxy resin at a high temperature of 150 ° C. or higher. Then, it is added to finally cure the epoxy resin. Specifically, 2
-Methylimidazole, 2-phenylimidazole, 2
-Phenyl-4-methylimidazole, bis (2-ethyl-4-methyl-imidazole), 2-phenyl-4-
Examples thereof include methyl-5-hydroxymethylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, and triazine-added imidazole. Epoxy adducts or microcapsules of these can also be used. These may be used alone or in combination of two or more.

As the epoxy resin curing agent (H), the epoxy resin starts a reaction from a low temperature range of 60 to 120 ° C. This curing agent is used to cause an initial reaction of the epoxy resin. . When integrally curing the undercoat agent and the interlayer insulating adhesive, it is important for moldability to start a curing reaction from the undercoat agent side. Specifically used are imidazole,
2-ethyl-4-methylimidazole, 2-undecylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-phenylimidazole,
1-cyanoethyl-2-ethyl-4-methylimidazole, 1-aminoethyl-2-methylimidazole, 1-
(Cyanoethylaminoethyl) -2-methylimidazole, 1-cyanoethyl-2-phenyl-4,5-bis (cyanoethoxymethylimidazole) and the like,
Epoxy adducts or microcapsules of these can also be used. These may be used alone or in combination of two or more. The amount of the epoxy resin curing agent varies depending on the type of the curing agent.
The total amount of the component (g) and the component (h) is 1 to 10 parts by weight with respect to 00 parts by weight, and the ratio of the component (h) is appropriately determined depending on the tack-free degree of the undercoat agent.

By using an epoxy resin or a phenoxy resin having a weight-average molecular weight of 10,000 or more for the interlayer insulating adhesive coated on the copper foil, the shape can be maintained.
In other words, since the bonding is performed while maintaining the interlayer thickness, there is no variation in the thickness of the multilayer printed wiring board without depending on the residual ratio of the inner layer copper foil, and it is possible to manufacture a multilayer printed wiring board having excellent thickness accuracy. Becomes However, this means that when laminating a copper foil with an interlayer insulating adhesive, the undercoat agent coated on the inner layer circuit board is softened by heating the hot roll, and the thickness is not averaged by the roll pressure. Cannot be realized. In addition, the softening of the undercoat agent has a great effect on the improvement of the adhesiveness with the interlayer insulating adhesive, and a fusion integration reaction can be performed at the polar interface.
This also affects the reliability between layers. However, when the curing reaction of the undercoat agent is delayed from the curing reaction of the interlayer insulating adhesive at the time of thermal curing, and the melt viscosity of the undercoat agent is reduced more than necessary, the shrinkage of the interlayer insulating adhesive is affected by wrinkles, Molding defects such as voids may occur. On the other hand, the undercoat agent used in the present invention promotes the reaction in the low-temperature region by the component (h) and suppresses an unnecessarily low melt viscosity. , Good smoothness, interlayer adhesion and the like can be achieved.

In addition, the light / thermosetting undercoat agent for a four-layer printed wiring board of the present invention may optionally contain an ultraviolet ray inhibitor, a thermal polymerization inhibitor, a plasticizer, etc. for storage stability. . Further, an acrylate monomer, a methacrylate monomer, a vinyl monomer, or the like may be added for adjusting the viscosity. Furthermore, fused silica, crystalline silica, calcium carbonate, aluminum hydroxide, alumina,
An epoxy silane coupling agent that can contain inorganic fillers such as barium sulfate, mica, talc, clay, white carbon, and E glass powder to improve adhesion and moisture resistance to copper foil and inner circuit boards. An antifoaming agent for preventing voids or a liquid or powdered flame retardant may be added.

The photo-thermosetting type undercoat agent for a four-layer printed wiring board of the present invention comprising these components, while being substantially solvent-free, fills the copper foil circuit gap of the inner layer circuit board, Smoothing the circuit surface. Further, it becomes easily solid by irradiation with active energy rays and can be made tack-free. Component (d) in prepared undercoat agent of the present invention
And (e) first act as a solvent, and the components (a) to
(C) and other components are dissolved to fill the gap between the copper foil circuits of the inner layer circuit board, thereby forming a varnish capable of smoothing the inner layer circuit surface. When the components (d) and (e) acting as a solvent are cured by irradiation with an active energy ray, the components (d) and (e) lose their effect as a solvent due to solidification of the cured product. Components (a) and (b) precipitate.
At this time, the cured components (d), (e) and other components are dispersed in the solid components (a) and (c). Therefore, if the components (a) and (b) which are in an appropriate tack-free solid state at room temperature are selected, the undercoat agent of the present invention is tack-free without a thermosetting reaction. Such a tack-free mechanism is the greatest feature of the present invention. In addition, the component (d) of the present invention which has been cured by irradiation with an active energy ray also has a heat-reactive functional group, and thus undergoes a curing reaction with the epoxy resin or the curing agent as a main component during a subsequent heating reaction. The material is also excellent in heat resistance, chemical resistance and the like.

Next, the interlayer insulating adhesive to be coated on the copper foil used in the present invention includes (i) a bisphenol type epoxy resin having a weight average molecular weight of 10,000 or more, (nu) a bisphenol type epoxy resin having an epoxy equivalent of 500 or less, and (1) It is an adhesive having a heat resistance consisting of an imidazole compound having a melting point of 130 ° C. or higher. Examples of the above-mentioned bisphenol type epoxy resin include bisphenol A type, bisphenol F type, bisphenol S type and the like.

In order not to lower the thermal performance as a printed wiring board, the adhesive used in the present invention suppresses the fluidity when hardening integrally with the undercoat agent, maintains the interlayer thickness, and maintains the composition. In order to impart flexibility to the film and give the film formability, a bisphenol type epoxy resin having a weight average molecular weight of 10,000 or more is blended as a component (i). In addition, the bisphenol type alone has a low crosslinking density after curing, has too high flexibility, and has a high viscosity when dissolved in a solvent and used as a varnish of a predetermined concentration for coating a copper foil. Workability deteriorates. In order to improve these drawbacks, a bisphenol-type epoxy resin having an epoxy equivalent of 500 or less is blended as a (nu) component. The mixing ratio of the epoxy resin is as follows: (i) component: (nu) component = 50 to 70% by weight: 50 to 30% by weight. (I) 50% by weight of component
If the amount is less than this, the viscosity does not increase and the thickness as an interlayer insulating adhesive cannot be maintained, and the smoothness of the outer layer circuit after lamination deteriorates. On the other hand, if it exceeds 70% by weight, the viscosity increases, Coating the foil becomes difficult and it is difficult to maintain a predetermined thickness, which is not preferable.

As the curing agent of the component (L), it is preferable to use the same type as the component (G) used in the undercoat agent described above. That is, it has a melting point of 130 ° C. or more, is solid at room temperature, has low solubility in epoxy resin, and has a melting point of 150 ° C.
It is added because the above-mentioned high temperature causes rapid reaction with the epoxy resin and finally the epoxy resin is cured. Specifically, 2-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, bis (2-ethyl-4-methyl-imidazole),
Examples include 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, and triazine-added imidazole. Epoxy adducts or microcapsules of these can also be used. These may be used alone or in combination of two or more. These imidazoles are finely divided and are uniformly dispersed in the epoxy resin varnish. 100 ° C due to low compatibility with epoxy resin
In the following, the reaction does not proceed, so that the varnish can maintain good storage stability. 1 for copper foil as interlayer insulating adhesive
If the coating is performed at a temperature of 00 ° C. or less, the epoxy resin remains uncured, so that the storability as the adhesive can be kept good. When laminated with an inner layer circuit board provided with an undercoat layer, and then heated to 150 ° C. or higher during curing, the epoxy resin reacts with the undercoat agent and partially melts and mixes on the contact surface. Is obtained.

The interlayer insulating adhesive may contain, in addition to the epoxy resin and the curing agent, a component that reacts with the epoxy resin or the curing agent. For example, epoxy-reactive diluents (phenylglycidyl ether nad as monofunctional type, resolving ricidyl ether, ethylene glycol glycidyl ether as bifunctional type, glycerol triglycidyl ether as trifunctional type, etc.), resole type or novolac type phenolic resin And isocyanate compounds. In addition to the above components, in order to improve the coefficient of linear expansion, heat resistance, flame resistance, etc., fused silica, crystalline silica, calcium carbonate, aluminum hydroxide, alumina, barium sulfate, mica, talc, clay, white carbon, E
Add inorganic filler such as glass powder to epoxy resin.
You may mix | blend 0 weight% or less. If the content is more than 40% by weight, the viscosity of the adhesive increases, and the adhesiveness decreases.
Further, an epoxy silane coupling agent for improving the adhesion to the copper foil and moisture resistance, an antifoaming agent for preventing voids, or a liquid or powdered flame retardant may be added.

As a solvent, an adhesive is applied to a copper foil and
After drying at ~ 130 [deg.] C, one must choose what does not remain in the adhesive. For example, there are acetone, methyl ethyl ketone, toluene, xylene, n-hexane, methanol, ethanol, methyl cellosolve, cyclohexanone and the like. Copper foil with an interlayer insulating adhesive is coated with an adhesive varnish obtained by dissolving an adhesive component in a predetermined solvent at a predetermined concentration on the anchor surface of the copper foil, and then 80 to 130
It is prepared by drying at a temperature of ° C. so that no solvent remains in the adhesive. The thickness of the adhesive layer is preferably from 15 to 120 μm. If the thickness is less than 15 μm, the interlayer insulating property may be insufficient. If the thickness is more than 120 μm, there is no problem with the interlayer insulating property. .

In this manner, as the photopolymerizable and thermally reactive monomer, a compound having one or more acryloyl or methacryloyl groups and one or more glycidyl groups in one molecule, and one or more compounds in one molecule By using a compound having an acryloyl group or a methacryloyl group and one or more hydroxyl groups in combination, the undercoat agent can be tack-free by irradiation with active energy rays, and can be integrally cured after lamination with a copper foil with an interlayer insulating adhesive. And a good four-layer printed wiring board can be manufactured.

An outline of a method of applying an undercoat agent and laminating and curing a copper foil with an interlayer insulating adhesive to achieve the object of the present invention will be described with reference to FIGS. (A) A liquid undercoat layer (3) is screen-printed on the inner circuit board (1), and one side of the inner circuit (2) is completely coated using a conventional coating equipment such as a roller coater or a curtain coater. Apply to the thickness to cover. If the embedding amount is insufficient, air will be entrained in the subsequent laminate. Then, it is made tack-free by irradiating active energy rays with a UV irradiation conveyor or the like. Next, the other surface of the inner circuit board (2) is coated with an undercoat layer (3) in the same manner. (B) A copper foil (5) with an interlayer insulating adhesive (4) is laminated on the surface. The laminator uses a roll (6) coated with a pair of silicon rubber or the like to achieve surface smoothness, and is laminated on both sides of the inner circuit board (2). Lamination conditions vary depending on the pattern of the inner layer circuit,
The pressure is about 0.5 to ⁶ kgf / cm ² , the surface temperature is from normal temperature to about 100 ° C., and the laminating speed is about 0.1 to 6 m / min. Under such conditions, the photocured undercoat agent can achieve surface smoothness by using a hard roll. At this time, the interlayer thickness between the inner layer circuit (2) and the copper foil (5) can be achieved by the thickness of the interlayer insulating adhesive. (C) Next, a four-layer printed wiring board in which an undercoat layer (3) and a thermosetting insulating adhesive layer (4) coated on a copper foil are integrally formed by performing a simultaneous integral curing reaction by heating. Can be formed.

[0025]

The present invention will be described below with reference to examples.
"Parts" represents parts by weight. << Example 1 >> 100 parts of bisphenol A type epoxy resin (epoxy equivalent 6400, weight average molecular weight 30000) and bisphenol F type epoxy resin (epoxy equivalent 17
5. Epicron 830) manufactured by Dainippon Ink and Chemicals, Inc.
0 parts were dissolved in 150 parts of MEK while stirring, and 4 parts of 2-phenyl-4-methyl-5-hydroxymethylimidazole as a curing agent and 1 part of a silane coupling agent (A-187 manufactured by Nippon Unicar Co., Ltd.) were dissolved therein. Was added to prepare an interlayer insulating adhesive varnish. The varnish was applied to an anchor surface of a copper foil having a thickness of 18 μm by a roller coater so that the thickness after drying became 40 μm, and dried to prepare a copper foil with an interlayer insulating adhesive. Next, 100 parts of brominated cresol novolak epoxy resin (35% brominated, epoxy equivalent 280, weight average molecular weight 1400), bisphenol A type epoxy resin (epoxy equivalent 950, weight average molecular weight 16)
00) and 40 parts of a bisphenol F type epoxy resin (epoxy equivalent: 175, Epicron 830 manufactured by Dainippon Ink and Chemicals, Inc.) are dissolved in 80 parts of glycidyl methacrylate and 90 parts of hydroxyethyl methacrylate, and a curing agent is added thereto. , 2-phenyl-4-methyl-5-hydroxymethylimidazole, 8 parts of 1-cyanoethyl-2-ethyl-4-methylimidazole and 10 parts of a photopolymerization initiator (Irgacure 651 manufactured by Ciba Geigy) were added. Was sufficiently stirred to obtain an undercoat agent. Further, a flame-retardant glass epoxy double-sided copper-clad laminate having a base material thickness of 0.2 mm and a copper foil thickness of 35 μm was patterned to obtain an inner circuit board. After the surface of the copper foil was blackened, the undercoat agent was applied to one surface of the inner circuit board to a thickness of about 40 μm using a curtain coater. Then, about 2J / cm with two 80W / cm high pressure mercury lamps by UV conveyor machine.
^The undercoat layer was irradiated with ultraviolet light under the conditions of ² and made tack-free by irradiation with active energy rays, and then the undercoat layer was formed on the other surface of the inner circuit board in the same manner. Then, a temperature of 100 is applied on the undercoat layer.
The copper foil with the interlayer insulating adhesive was laminated using two rolls at a temperature of 2 ° C., a pressure of 2 kg / cm ² , and a laminating speed of 0.8 m / min. Was prepared.

Example 2 In the undercoat agent and the interlayer insulating adhesive, a curing agent for epoxy resin,
A four-layer printed wiring board was produced in the same manner as in Example 1 except that 2-phenyl-4-methylimidazole was used instead of phenyl-4-methyl-5-hydroxymethylimidazole.

<< Comparative Example 1 >> In the undercoat agent,
A four-layer printed wiring board was produced in exactly the same manner as in Example 1 except that 160 parts of glycidyl methacrylate was used instead of glycidyl methacrylate and hydroxyethyl methacrylate. << Comparative Example 2 >> A four-layer printed wiring board was produced in exactly the same manner as in Example 1 except that 160 parts of hydroxyethyl methacrylate was used instead of glycidyl methacrylate and hydroxyethyl methacrylate in the undercoat agent. << Comparative Example 3 >> 2-phenyl-4-methyl-5 was used without using 1-cyanoethyl-2-ethyl-4-methylimidazole as a curing agent for the epoxy resin of the undercoat agent.
A four-layer printed wiring board was prepared in exactly the same manner as in Example 1 except that only 12 parts of hydroxymethylimidazole was used.

<< Comparative Example 4 >> As a curing agent for an epoxy resin as an interlayer insulating adhesive, 2-phenyl-4-methyl-5-
A four-layer printed wiring board was produced in exactly the same manner as in Example 1 except that 12 parts of 1-cyanoethyl-2-ethyl-4-methylimidazole was used without using hydroxymethylimidazole. Comparative Example 5 In the undercoat agent, bisphenol A type epoxy resin (epoxy equivalent 950, weight average molecular weight 1600) was used without using 100 parts of brominated cresol novolak epoxy resin (epoxy equivalent 280, weight average molecular weight 1400) as epoxy resin. A four-layer printed wiring board was prepared in the same manner as in Example 1 except that 200 parts) and 40 parts of a bisphenol F type epoxy resin (epoxy equivalent: 175, Epicron 830 manufactured by Dainippon Ink and Chemicals, Inc.) were used. << Comparative Example 6 >> A four-layer printed wiring board was produced in the same manner as in Example 1 except that the undercoat agent was not applied. The obtained four-layer printed wiring board has characteristics as shown in Table 1.

(Test Method) Inner layer circuit board test piece: 150 μm pitch between lines, clearance hole 2.54 mmφ 1. Surface smoothness: JIS B 0601 R (max) 1. Moisture absorption heat resistance test Moisture absorption conditions: pressure cooker treatment, 125 ° C,
Test conditions: 3 atm, 30 min. Test conditions: n = 5, all were not swelled at 280 ° C. for 120 seconds, and ○ were swelled. 3. Interlayer insulation layer thickness: A four-layer printed wiring board was cut, and its cross section was observed with an optical microscope to measure the thickness of the interlayer insulation layer between the inner layer circuit and the surface copper foil. 4. Flame retardancy: according to UL standard 94

Table 1-Example Comparative Example 1 2 1 2 3 4 5 6 表面 Surface smoothness (μm) 3 3 10 3 5 20 15 35 Heat resistance of moisture absorption solder ○ ○ ○ × × ○ ○ × Interlayer insulation layer thickness (μm) 50 50 55 50 50 55 60 40 Flame retardant V-1 V-1 V-1 V-1 V-1 V-1 V-2 V-2 ───────────────────────────────────

[0031]

According to the present invention, the surface is smooth and the thermosetting insulating adhesive coated on the copper foil maintains its thickness.
It is possible to obtain a flame-retardant four-layer printed wiring board excellent in controlling the thickness without depending on the residual ratio of the inner layer copper foil.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a layer configuration of a four-layer printed wiring board of the present invention.

FIG. 2 is a schematic cross-sectional view showing a step of manufacturing a four-layer printed wiring board (one example) of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 inner circuit board 2 inner circuit 3 undercoat layer 4 interlayer insulating adhesive layer 5 copper foil 6 hard roll 7 four-layer printed wiring board

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-7-202433 (JP, A) JP-A-7-245480 (JP, A) JP-A-7-245485 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H05K 3/46 H05K 1/03 H05K 3/38

Claims (1)

(57) [Claims] 1. A four-layer printed wiring board in which a light / thermosetting undercoat layer, an interlayer insulating adhesive layer and a copper foil are sequentially laminated on both sides of an inner circuit board made of a flame-retardant epoxy resin-impregnated glass cloth substrate. Wherein the photo-thermosetting undercoat layer comprises: (a) a novolak type epoxy resin having a bromination ratio of 20% or more and a molecular weight of 500 to 4000;
(B) bisphenol type epoxy resin having a molecular weight of 500 to 2,000, (c) bisphenol type epoxy resin having a molecular weight of 500 or less, (d) glycidyl acrylate or glycidyl methacrylate, (e) hydroxyethyl acrylate or hydroxyethyl methacrylate, (f) photopolymerization An initiator, (g) an imidazole compound having a melting point of 130 ° C. or higher, and (h) a low-temperature curing type imidazole compound, wherein the interlayer insulating adhesive layer has a weight average molecular weight of 1).
Bisphenol type epoxy resin of 0000 or more, (Nu)
A four-layer printed wiring board comprising a bisphenol-type epoxy resin having an epoxy equivalent of 500 or less and an imidazole compound having a melting point of 130 ° C. or more.