JP3056676B2 - Method for manufacturing four-layer printed wiring board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-layer printed wiring board in which a copper foil having a light / thermosetting undercoat layer and a thermosetting insulating adhesive layer is laminated on an epoxy resin impregnated glass cloth cloth substrate. It is.

[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. 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, poor insulation and poor solder heat resistance, 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.

[0005]

SUMMARY OF THE INVENTION The present invention is thinner, has less variation in thickness, and has a smoother surface than a multilayer printed wiring board obtained by the above-mentioned hot plate press forming method or a conventional built-up method. It is intended to provide a four-layer printed wiring board suitable for high-density mounting.

[0006]

According to the present invention, an epoxy resin impregnated glass cloth substrate having a circuit pattern is coated with a light / thermosetting undercoat on both sides, and an active energy ray is applied.
And then laminating a copper foil coated with a thermosetting insulating adhesive layer to produce a four-layer printed wiring board.
A photo-thermosetting undercoat layer, wherein (a) an epoxy resin in a solid state at room temperature, (b) an epoxy resin curing agent, (c) glycidyl acrylate or glycidyl methacrylate.
Rate, (d) hydroxyethyl acrylate or hydroxy et
A method for producing a four-layer printed wiring board, comprising chill methacrylate and (e) a photopolymerization initiator.
Is the law. Preferably, the thermosetting insulating adhesive comprises an epoxy resin and a curing agent thereof, and the main component of the epoxy resin is a bisphenol type epoxy resin having a weight average molecular weight of 10,000 or more, and a bisphenol type epoxy resin having an epoxy equivalent of 500 or less. It becomes four-layer printed wiring board
It is a manufacturing method .

That is, according to the present invention, a liquid undercoat agent is applied to an inner layer circuit board made of an epoxy resin impregnated glass cloth substrate by screen printing, a roller coater, a curtain coater, or the like, so that a copper foil circuit gap of the inner layer circuit board is formed. After filling, the undercoat agent is made tack-free by irradiation with active energy rays using an exposure machine such as a UV irradiation conveyor. Thereafter, the uncured or semi-cured copper foil with a thermosetting 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 both sides simultaneously and adhered. Then, after lamination, heat and light
A multilayer printed wiring board can be produced by simultaneously and integrally curing reaction of a thermosetting undercoat agent and a copper foil with a thermosetting insulating adhesive. When laminating,
The undercoat agent is also re-melted 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 thermosetting insulating adhesive coated on the copper foil is bonded with the epoxy resin component having a weight-average molecular weight of 10,000 or more while maintaining its shape, that is, while maintaining the interlayer thickness, and thus depends on the residual ratio of the inner layer copper foil. Thus, the thickness of the multilayer printed wiring board is averaged without variation, and a four-layer printed wiring board having excellent board thickness accuracy can be manufactured.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The undercoat agent used in the undercoat layer in the present invention fills the gap between the copper foil circuits of the inner layer circuit board and smoothes the inner layer circuit surface. (B), (c) and (d). (A) epoxy resin in a solid state at normal temperature, (b) epoxy resin curing agent, (c) glycidyl acrylate or glycidyl methacrylate, (d) hydroxyethyl acrylate or hydroxyethyl methacrylate, (e)
Photopolymerization initiator.

The epoxy resin in the solid state at room temperature of the component (a) used in the present invention is a bisphenol-type epoxy resin, a novolak-type epoxy resin, or a mixture thereof, and is a solid at room temperature. The melting point is usually
What is necessary is just to be in the range of 50-100 degreeC. As the bisphenol type epoxy resin, A type or F type is used,
Particularly, the A type is preferable. As the novolak type epoxy resin, phenol novolak type, cresol novolak type, bisphenol A novolak type and the like are used.

As the epoxy resin curing agent of the component (b), various commonly used curing agents can be used. For example, 4,4'-diaminodiphenylmethane, 4,4'-
Aromatic diamines such as diaminodiphenyl sulfone, m-phenylenediamine and p-phenylenediamine; aliphatic polyamines such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, hexamethylenetriamine, mensendiamine and isophoronediamine; phthalic anhydride; Tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylendomethylenetetrahydrophthalic anhydride, methylbutenyltetrahydrophthalic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, hexahydrophthalic anhydride, trimellitic anhydride , Pyromellitic anhydride, acid anhydrides such as benzophenonetetracarboxylic acid anhydride, and the like. The amount of epoxy resin curing agent varies depending on the type of curing agent, but is usually glycidyl. 0.1 to 1.0 equivalents relative.

Other epoxy resin curing agents include imidazole, 2-methylimidazole, 2-ethyl-4-
Methylimidazole, 2-phenylimidazole, 1-
Benzyl-2-methylimidazole, 2-undecylimidazole, 2-phenyl-4-methylimidazole,
Bis (2-ethyl-4-methyl-imidazole), 2-
Imidazoles such as phenyl-4-methyl-5-hydroxymethylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole or triazine-added imidazole; amine complexes of boron trifluoride, dicyandiamide or derivatives thereof; The amount of the epoxy resin curing agent varies depending on the type of the curing agent, but the amount is 0.1 to 100 parts by weight of the epoxy resin resin.
It is 1 to 10 parts by weight. Epoxy adducts or microcapsules of these can also be used.

In the present invention, a curing accelerator for the epoxy resin may be added as required. As the curing accelerator, various commonly used curing accelerators can be used, for example, tertiary amines such as tributylamine, benzylmethylamine, 2,4,6-tris (dimethylaminomethyl) phenol, 2-ethyl Imidazoles such as -4-methylimidazole and N-benzylimidazole, ureas, phosphines, metal salts and the like;
These may be used alone or in combination of two or more.

The photopolymerizable and thermoreactive monomers used in the photo-thermosetting type undercoat agent include (c) glycidyl acrylate or glycidyl methacrylate which is excellent in thermosetting after tack-free by irradiation with active energy rays. And (d) hydroxyethyl acrylate or hydroxyethyl methacrylate having high hydroxyl group activity. Usually, the total amount of the monomers (c) and (d) is the amount of the epoxy resin 1 (a).
20 to 100 parts by weight, preferably 3 to 100 parts by weight
0 to 70 parts by weight. Thus, as a photopolymerizable and thermally reactive monomer, a compound having one or more acryloyl groups or methacryloyl groups and one or more glycidyl groups in one molecule, and one or more acryloyl groups or By using a compound having a methacryloyl group and one or more hydroxyl groups in combination,
Tack-free of the undercoat agent by light irradiation, and integral curing after lamination with a copper foil with a thermosetting insulating adhesive are performed well, and a good four-layer printed wiring board can be obtained.

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

In addition, if necessary, the photo-thermosetting undercoat agent for a four-layer printed wiring board of the present invention may contain an ultraviolet 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 undercoat material 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. In particular, the fact that the step of drying and tack-free by heat is possible only by irradiation with active energy rays is based on the photopolymerization and thermal reaction of the epoxy resin in the solid state at room temperature with the component (a) and the component (c). It is characterized by using a diluent composed of a reactive monomer. The components (c) and (d) in the prepared undercoat agent of the present invention first act as a solvent, dissolve the component (a) and other components, and fill the copper foil circuit gap of the inner circuit board, The surface of the inner layer circuit is in a varnish state capable of being smoothed. When the components (c) and (d) acting as a solvent are cured by irradiating an active energy ray thereto, the components (c) and (d) lose their effect as a solvent due to the solidification of the curing. Component (a) precipitates. At this time, the cured components (c) and (d) and other components are dispersed in the solid component (a). Therefore, if the component (a) which is in an appropriate tack-free solid state at room temperature is selected, the undercoat agent of the present invention
Tack-free without thermosetting reaction. Such a tack-free mechanism is the greatest feature of the present invention.
In addition, since the components (c) and (d) of the present invention which are cured by irradiating with active energy rays also have a heat-reactive functional group, they undergo a curing reaction with the epoxy resin or the curing agent as a main component during a subsequent heating reaction. Therefore, the cured product is excellent in heat resistance, chemical resistance and the like.

Next, the thermosetting insulating adhesive to be coated on the copper foil will be described. 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. For this reason, the adhesive used in the present invention is a bisphenol A having a weight average molecular weight of 10,000 or more in order to keep the fluidity small and maintain the interlayer thickness when integrally curing with the undercoat agent, and to impart film formability. Type epoxy resin or bisphenol F type epoxy resin.
The mixing ratio of the epoxy resin is 30% of the total epoxy resin.
９０90% by weight, preferably 50-90% by weight. As the curing agent, those used for the undercoat agent described above can be used.

An outline of a method of applying an undercoat agent and laminating and curing a copper foil with a thermosetting insulating adhesive to achieve the object of the present invention will be described with reference to FIGS. (A) A liquid undercoating agent is screen-printed on the inner layer circuit board (1), and the inner layer circuit (2) is formed by using a conventional coating equipment such as a roller coater or a curtain coater.
To a thickness that completely covers the undercoat layer (3)
And If the embedding amount is insufficient, air will be entrained in the subsequent laminate. After that, it is tack-free by irradiating active energy rays with an exposure machine such as a UV irradiation conveyor. (B) A copper foil (5) with a thermosetting insulating adhesive layer (4) is laminated on the surface. The laminator preferably uses a roll (6) to achieve surface smoothness, and the copper foil (5) is laminated on both sides by the two rolls (6). Lamination conditions vary depending on the pattern of the inner layer circuit, but the pressure is about 0.5 to ⁶ kgf / cm ² , the surface temperature is from normal temperature to about 100 ° C., the lamination speed is about 0.1 to 6 m / min, By using this, surface smoothness can be achieved. 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 thermosetting insulating adhesive. (C) Next, a simultaneous integrated curing reaction is performed by heating to form a multilayer printed wiring board integrally molded with the undercoat agent (3) and the thermosetting insulating adhesive (4) coated on the copper foil. In addition, a circuit is formed on both sides by a usual method to obtain a completed four-layer printed wiring board (7).

[0019]

The present invention will be described below with reference to examples.
"Parts" represents parts by weight. << Example 1 >> 150 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) 3, manufactured by Dainippon Ink and Chemicals, Inc.
0 parts were dissolved in MEK while stirring, and 5 parts of 2-phenyl-4-methyl-5-hydroxymethylimidazole as a curing agent and a silane coupling agent (Nihon Unicar
A-187) (10 parts) was added to prepare a thermosetting insulating adhesive varnish. The varnish was applied to an anchor surface of a copper foil having a thickness of 18 μm with a roller coater so that the thickness after drying became 40 μm, and dried to prepare a copper foil with a thermosetting insulating adhesive. Next, a bisphenol A type epoxy resin (epoxy equivalent of about 470, weight average molecular weight of about 9
100) was dissolved in 30 parts of glycidyl methacrylate and 30 parts of hydroxyethyl methacrylate, and as a curing agent, 4 parts of 2-phenylimidazole and 3 parts of a photopolymerization initiator (Irgacure 651 manufactured by Ciba Geigy) were added. The mixture was sufficiently stirred with a mixer to obtain an undercoat agent. Furthermore, a glass epoxy double-sided copper-clad laminate having a base material thickness of 0.1 mm and a copper foil thickness of 35 μm was patterned to obtain an inner layer circuit board. After the surface of the copper foil was blackened, the undercoat agent was applied to a thickness of about 40 μm using a curtain coater. Thereafter, UV irradiation was performed using a UV conveyer machine with two 80 W / cm high-pressure mercury lamps under the condition of about 2 J / cm ² , and a temperature of 100 ° C. and a pressure of 2 kg / cm ² were applied to the tack-free undercoat agent by irradiation with active energy rays. Laminating the above-mentioned copper foil with thermosetting insulating adhesive using a hard roll under the conditions of a laminating speed of 0.8 m / min,
The resultant was cured by heating at 150 ° C. for 30 minutes to produce a four-layer printed wiring board.

Example 2 In an undercoat agent,
As a curing agent for the epoxy resin, instead of 2-phenylimidazole, 2-methylimidazole, 2-phenyl-4-methylimidazole, bis (2-ethyl-4-methyl-imidazole), 2-phenyl-4-methyl- 5
-Hydroxymethylimidazole, 2-phenyl-4,
A four-layer printed wiring board was produced in the same manner as in Example 1 except that 5-dihydroxymethylimidazole was used. As a result, similar characteristics were obtained.

<< 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 glycidyl methacrylate and 60 parts of glycidyl methacrylate were 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 60 parts of hydroxyethyl methacrylate was used instead of glycidyl methacrylate and hydroxyethyl methacrylate in the undercoat agent. << Comparative Example 3 >> A multilayer 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 280 ° C., no swelling for 120 sec. 3. Embedding property: After peeling the outer layer copper foil, the embedding property in the inner layer circuit was visually judged using an optical microscope, and the completely embedded one was evaluated as O, and the one with incomplete embedding was evaluated as X. 4. Interlayer insulation layer thickness: The multilayer 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. 5. Remaining molded voids: The entire surface of the multilayer printed wiring board was etched, and the presence or absence of voids was visually measured. Those with no void remaining were marked with ○, those with slight void remaining were marked with Δ, and those with completely voids were marked with x.

Table 1 ───────────────────────────────── Surface Smoothness Moisture Absorbing Solder Embedding Interlayer Insulation Molding Void ( μm) Heat resistance Layer thickness (μm) Remaining ───────────────────────────────── Example 13 3 ○ ○ 35 ○ Example 2 3 ○ ○ 35 ○ Comparative Example 15 ○ ○ 40 △ Comparative Example 25 × × 30 ○ Comparative Example 3 30 × × 30 × ───────────────── ────────────────

[0024]

According to the present invention, the surface smoothness is good, and the thermosetting insulating adhesive coated on the copper foil maintains the thickness, so that the plate is not dependent on the residual ratio of the inner layer copper foil. A four-layer printed wiring board having a uniform thickness, good heat resistance to moisture absorption solder, and excellent embedding properties was obtained.

[Brief description of the drawings]

FIG. 1 is a cross-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 one example of a process for producing a four-layer printed wiring board of the present invention.

[Explanation of symbols]

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

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H05K 3/46 B32B 15/08

Claims (2)

(57) [Claims] 1. A photo- and thermosetting undercoat on both sides of an epoxy resin impregnated glass cloth substrate having a circuit pattern.
After applying and irradiating with active energy rays, a copper foil coated with a thermosetting insulating adhesive layer is laminated.
The method for producing a four-layer printed wiring board according to claim 1, wherein the light / thermosetting undercoat layer comprises the following components (a):
(B), (c), (d) and (e)
A method for manufacturing a four-layer printed wiring board . (A) epoxy resin in a solid state at room temperature, (b) epoxy resin curing agent, (c) glycidyl acrylate or glycidyl methacrylate
Rate, (d) hydroxyethyl acrylate or hydroxy et
Tyl methacrylate, (e) photopolymerization initiator 2. A thermosetting insulating adhesive comprising an epoxy resin and a curing agent thereof, wherein a main component of the epoxy resin is a bisphenol epoxy resin having a weight average molecular weight of 10,000 or more, and a bisphenol epoxy resin having an epoxy equivalent of 500 or less. The method for manufacturing a four-layer printed wiring board according to claim 1, comprising a resin.