JP2003127137A - Prepreg for electric insulating layer and method for manufacturing printed wiring board using prepreg - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the perforation properties of a prepreg by the irradiation with laser beam in the prepreg for an electric insulating layer obtained by holding a thermosetting resin to a flat glass fiber nonwoven fabric constituted using glass fibers having a flat cross-sectional shape. SOLUTION: The flat glass fiber nonwoven fabric substrate is impregnated with thermosetting resin varnish having a thixotropy imarting function and compounded with fine particles with a particle size of 1 μm or less and the impregnated substrate is dried to obtain the prepreg. The content of the fine particles is preferably set to 0.05-5 pts.mass with respect to 100 pts.mass of the resin solid. The bulk density of the flat glass fiber nonwoven fabric is set to 0.4 g/cm<3> or more.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a prepreg for electrical insulation using a glass nonwoven fabric composed of glass fibers having a flat cross section. The present invention also relates to a method of manufacturing a printed wiring board (including a multilayer printed wiring board in its concept) using the prepreg. This printed wiring board is suitable for surface-mounting leadless chip components such as resistors and ICs.

[0002]

2. Description of the Related Art As a method of mounting electronic parts (resistors, ICs, etc.) on a printed wiring board incorporated in an electronic device, a method of surface-mounting these parts as chips has become mainstream. The surface mounting method is a preferable mode in terms of downsizing and weight saving and high density of electronic devices. In addition, with the increase in the density of the printed wiring, the connection of the printed wiring through the insulating layer has come to be performed in an IVH (Interstitial Via Hole) opened in the insulating layer, and the insulating layer is irradiated with a laser beam so as not to be connected. IVH processing for making through holes has become the mainstream. It is desirable that the printed wiring board be provided with an insulating layer that can be easily drilled by laser light irradiation.

In recent years, with the development of the IVH processing technique, laser light is irradiated to a predetermined portion of a prepreg to form a through hole, and the through hole is filled with copper particles and a conductor paste mainly composed of a liquid resin. It has been proposed to manufacture a printed wiring board in which an electric insulating layer is formed by heat-press molding. For example, metal foils are integrated on both sides of the prepreg by heat and pressure molding, and the metal foils on both sides of the electric insulating layer constituted by the prepreg are electrically connected by a cured product of the conductor paste, and further, both sides of the electric insulating layer. Is a technique for forming a printed wiring by etching the metal foil. Alternatively, a separately prepared base printed wiring board is integrated with a metal foil by heat and pressure molding through the prepreg, and the metal foil on the surface of the electric insulating layer constituted by the prepreg and the base printed wiring board are connected to the conductor. This is a technique for forming a printed wiring by electrically connecting with a cured product of a paste and etching the metal foil on the surface of the electrical insulating layer (Japanese Patent Laid-Open No. 5-175650 and Japanese Patent Laid-Open No. 7-176).
No. 846, etc.).

According to the above technique, the printed wirings on both sides of the insulating layer are connected to each other through a complete IVH (Intersti).
It is possible to manufacture a multilayer printed wiring board to be connected at a tial via hole), and IVH can be further formed directly on the conductor formed by curing the conductor paste, which is advantageous for increasing the density of the printed wiring.

The surface smoothness of the prepreg used for manufacturing such a printed wiring board is important. This is because if the surface of the prepreg is not smooth, uniform filling cannot be performed when the conductive paste is filled into the through holes formed by irradiating the laser beam. A prepreg obtained by impregnating a non-woven fabric as a base material with a thermosetting resin and heating and drying it can ensure sufficient surface smoothness, and is therefore most suitable as a prepreg for filling the conductor paste. On the other hand, a prepreg using a woven fabric as a base material cannot secure surface smoothness because the texture of the woven fabric appears on the surface and is not suitable for filling with a conductor paste.

The non-woven fabric used in the above technique is mainly composed of aramid fibers, in which the fibers are entwined with a thermosetting resin (epoxy resin) binder, aramid fibrid or aramid fiber pulp, and heat-resistant thermoplastic resin fibers are melted. It is known that the clothes are bound together. For printed wiring boards, there are glass nonwoven fabrics in which glass fibers are bound to each other with a binder. However, glass nonwoven fabrics that are normally used are not suitable for thinning printed wiring boards because of their low bulk density. As a glass nonwoven fabric having a high bulk density, there is known a flat glass nonwoven fabric having a configuration in which glass fibers having a flat cross section are used to reduce voids between the fibers (JP-A-11-172559).

[0007]

The prepreg obtained by holding the thermosetting resin on the flat glass nonwoven fabric described above is satisfactory in terms of surface smoothness. However, when a through hole was formed by irradiating it with a laser beam, the hole wall surface was It was found that the glass fibers did not become smooth and became fluffy. If a conductor paste is filled into a through hole having such a fluffed hole wall, not only the filling cannot be made uniform, but also a gap remains between the hole wall and the conductor paste, and a prepreg is heated and pressed to form an insulating layer. Even after this, the conductor paste is not sufficiently cured and the resistance value of the conductor becomes large. When a long-term reliability test such as a thermal cycle test was conducted with the conductor having a large resistance value as described above, it was found that a crack was generated in the conductor and the conduction reliability was lowered.

The problem to be solved by the present invention is to be carried out on a prepreg in an electric insulating layer prepreg in which a thermosetting resin is held in a flat glass nonwoven fabric formed by using glass fibers having a flat cross section. It is to improve the drilling property by laser light irradiation.

[0009]

In order to solve the above-mentioned problems, the prepreg for an electric insulating layer according to the present invention is a thermosetting material which is held in a flat glass nonwoven fabric composed of glass fibers having a flat cross section. The resin is characterized by containing fine particles having a thixotropy imparting function and having a particle diameter of 1 μm or less.

The hole formed by irradiating the prepreg with laser light is the result of the glass fiber and resin at the irradiation site being burned off. At this time, the thermosetting resin of the hole wall that is melted by the energy of laser light is used. In addition, the leveling effect is exerted by the presence of the fine particles having a thixotropy imparting function, and the hole wall is finished smoothly. The content of the fine particles having a thixotropy imparting function is preferably 0.0 with respect to 100 parts by mass of the resin solid content.
5 to 5 parts by mass.

The flat glass nonwoven fabric is formed into a sheet by paper-making with glass fibers having a flat cross section as a main component.
The fibers are bound together with a binder. In order to secure the strength of the nonwoven fabric, it is desirable that the bulk density is 0.4 g / cm ³ or more.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION An example of the prepreg for electrical insulation according to the present invention will be described below.

The type of glass fiber constituting the flat glass nonwoven fabric is not particularly limited, and includes E glass, T glass, C glass,
D glass and the like. The flatness of the glass fiber (major axis / minor axis of glass fiber cross section) is preferably 2 or more in order to increase the bulk density of the nonwoven fabric, but is not particularly limited. Such glass fibers having a flat cross section are dispersed in water to form a sheet, and the fibers are bound with a binder such as an epoxy resin to obtain a flat glass nonwoven fabric having a predetermined bulk density. A silane coupling agent or the like may be added in order to improve the adhesiveness between the glass fiber and the resin. The bulk density of the flat glass nonwoven fabric is preferably 0.4 g / cm ³ or more in order to secure the strength of the nonwoven fabric.

The type of thermosetting resin held in the flat glass nonwoven fabric is not particularly limited, but an epoxy resin or the like having a good compatibility with the thermosetting resin component of the conductor paste filled in the through holes formed in the prepreg. Is appropriately selected. As the curing agent and curing accelerator for the epoxy resin, those generally known can be appropriately selected. Preparation of the thermosetting resin varnish for holding the flat glass nonwoven fabric, first,
The whole amount of the fine particles having a thixotropy imparting function and a part of the resin used are kneaded, and then the remaining resin is added and mixed with a homomixer or the like. In this way, the fine particles are uniformly dispersed. The smaller the particle size of the fine particles, the more the thixotropy imparting effect increases, so the particle size is set to 1 μm or less. Specifically, it may be talc, asbestos, fine powder silica, colloidal hydrous aluminum silicate / organic composite, or the like, as long as it has the property of imparting thixotropy. Since the thixotropy imparting effect is increased as the amount of the fine particles is increased, the content thereof is preferably 1% of the solid content of the thermosetting resin.
It is 0.05 parts by mass or more with respect to 00 parts by mass.

A flat glass nonwoven fabric is impregnated with the thermosetting resin varnish prepared as described above and dried by heating to produce a prepreg. At this time, if the content of the fine particles having a thixotropy imparting function is too large, the viscosity of the thermosetting resin varnish increases and the impregnating workability decreases, so that the content is preferably a solid of the thermosetting resin. 5 for 100 parts by weight
It should be less than or equal to parts by mass.

A printed wiring board having an insulating layer formed by hot pressing the above prepreg is manufactured by the following steps. First, laser light is irradiated to a predetermined portion of the prepreg to open a through hole, and the through hole is filled with a conductor paste. The conductor paste is mainly composed of conductive particles such as copper particles and a liquid epoxy resin. A metal foil (copper foil, aluminum foil, nickel foil) is integrated on both sides of the prepreg obtained by the process by heat and pressure molding, and the metal foil on both sides of the electric insulation layer constituted by the prepreg is cured by the conductor paste. Make an electrical connection with something. The conductor paste is compressed as the thickness of the prepreg is reduced by heating and pressing, and becomes a conductor in which copper particles are dispersed in an epoxy resin cured product. This conductor penetrates the insulating layer formed by curing the prepreg and is in contact with the metal foils on both sides. Further, printed wiring is formed by etching the metal foils on both sides of the electric insulating layer. A printed wiring board arranged via an insulating layer becomes a double-sided printed wiring board connected by the conductor.

When manufacturing a multilayer printed wiring board,
A separately prepared printed wiring board (may be a multilayer printed wiring board) is used as the base printed wiring board. The base printed wiring board may be the double-sided printed wiring board described above. A metal foil is integrated with the base printed wiring board by heat and pressure molding through a prepreg filled with a conductive paste in the same manner as described above, and the metal foil on the surface of the electric insulating layer formed by the prepreg and the base printed wiring board. Are electrically connected with the cured product of the conductor paste. Then, the metal foil on the surface is etched to form a printed wiring. If necessary, this process is repeated to sequentially increase the number of layers of printed wiring.

[0018]

Examples Examples 1 to 6 [Preparation of flat glass nonwoven fabric] Flat glass fiber (E glass, fiber diameter major axis 18 μm, minor axis 9 μm, fiber length 10 m)
m) as a main fiber is dispersed in water to form a sheet, and an epoxy resin binder in an emulsion form using water as a dispersion medium is sprayed to prepare a flat glass nonwoven fabric by a wet nonwoven fabric forming method. This non-woven fabric has a unit mass of 5
It was adjusted to 0 g / m ² and a bulk density of 0.4 g / cm ³ . [Preparation of Epoxy Resin Varnish] 16 parts by mass of bisphenol A type epoxy resin (“Ep-828” manufactured by Yuka Shell, epoxy equivalent 189), cresol novolac type epoxy resin ( Toto Kasei “YDCN704”, epoxy equivalent 212) 25 parts by mass, brominated epoxy resin 29 parts by mass, novolac type phenol resin 30 parts by mass, and 2-ethyl-4-methylimidazole 0.2 parts by mass as a catalyst are blended, An epoxy resin varnish having a resin solid content of 65 mass% was prepared. A predetermined amount of fine powder silica (“Aerosil RY-200” manufactured by Nippon Aerosil Co., Ltd.) as fine particles having a thixotropy imparting function was mixed with the above epoxy resin varnish and kneaded to prepare an epoxy resin varnish (A). The content of the finely divided silica and the particle size of the finely divided silica with respect to the resin solid mass of 100 are shown in Table 1. [Preparation of prepreg] A flat glass nonwoven fabric was impregnated with the above-mentioned epoxy resin varnish (A) and dried by heating to give a resin content of 5
0% by mass of prepreg (A) was obtained. The resin content includes
Contains the content of finely divided silica. [Manufacture of Printed Wiring Board] A through hole is formed in a predetermined portion of the prepreg (A) by irradiating laser light. Hole diameter is φ
It was set to 200 μm. A conductor paste mainly composed of copper particles and a liquid epoxy resin is prepared, and the conductor paste is filled in the through holes and dried. A copper foil (18 μm thick) was placed on both sides of one prepreg (A) thus prepared, and heat-pressed at a temperature of 175 ° C. and a pressure of 5 MPa to form a copper-clad laminate. The prepreg serves as an electric insulating layer, and the conductor paste is compressed and hardened to become a conductor, which electrically connects the copper foils on both surfaces of the insulating layer. A copper foil on both sides of the insulating layer was etched to form a predetermined printed wiring, and a double-sided printed wiring board in which the printed wiring arranged via the insulating layer was connected by the conductor was manufactured.

Comparative Example 1 A double-sided printed wiring board was manufactured in the same manner as in the above-described Examples except that fine powder silica was not contained.

Comparative Example 2 A double-sided printed wiring board was manufactured in the same manner as in the above-described example except that the particle size of finely divided silica was 5 μm and the content was 1 part by mass relative to 100 parts by mass of resin solid content.

Table 1 shows the results of an examination of the conduction resistance between the printed wirings (that is, the conductors penetrating the insulating layer) through the insulating layer of the printed wiring board in each of the above examples, and the workability in preparing the prepreg. . The conduction resistance is measured from the printed wiring on one surface to the printed wiring on the other surface, and then to the original surface. The conduction resistance of the wiring pattern serially connected by 100 conductors penetrating the insulating layer is measured in milliohms. It was measured with a meter.

[0022]

[Table 1]

From Table 1, the printed wiring boards manufactured using the prepregs according to the examples of the present invention have a content of fine particles imparting thixotropy of 0.01% by mass or more and a particle diameter of 1 μm or less. As a result, it can be seen that the conduction resistance value of the conductor mainly made of the conductor paste can be halved as compared with Comparative Example 1 (a contrast between the example and the comparative example). Furthermore, by setting the particle size of the fine particles imparting thixotropy to 1 μm or less, the conduction resistance value can be reduced (the contrast between the example and the comparative example 2). When the content of the fine particles imparting thixotropy is 5% by mass or less, the impregnation property at the time of producing a prepreg is also good (control of Example 5 and other examples).

[0024]

As described above, the flat glass nonwoven fabric prepreg for the electric insulating layer according to the present invention is excellent in the perforation property (wall surface smoothness) by laser light irradiation, and as a result, the conductor paste is surely provided in the through hole. It can be filled, and such a prepreg can be heated and pressure-molded to greatly improve the conduction reliability of the printed wiring board that forms the electric insulating layer and the conductor.

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Claims (5)

[Claims] 1. A prepreg in which a thermosetting resin is held in a glass non-woven fabric composed of glass fibers having a flat cross section, wherein the thermosetting resin has a thixotropy imparting function and a particle size of 1 μm or less. A prepreg for an electric insulating layer, which contains the fine particles of 2. The prepreg for an electric insulating layer according to claim 1, wherein the content of fine particles in the thermosetting resin is 0.05 to 5 parts by mass with respect to 100 parts by mass of the resin solid content. 3. The bulk density of the glass non-woven fabric is 0.4 g / cm ^3.
It is above, The prepreg for electric insulation layers of Claim 1 or 2 characterized by the above-mentioned. 4. A step of irradiating a predetermined position of the prepreg according to claim 1 with a laser beam to open a through hole, and filling the through hole with a conductor paste. Integrating metal foils on both sides by heat and pressure molding, and electrically connecting the metal foils on both sides of the electrical insulating layer constituted by the prepreg with the cured product of the conductor paste, A method of manufacturing a printed wiring board, which comprises a step of forming a printed wiring by etching. 5. A step of irradiating a predetermined portion of the prepreg according to any one of claims 1 to 3 with a laser beam to open a through hole and filling the through hole with a conductor paste, a separately prepared base print wiring. On the board, the metal foil is integrated by heat and pressure molding through the prepreg obtained in the above step, and the metal foil on the surface of the electric insulating layer and the base printed wiring board configured by the prepreg is a cured product of the conductor paste. A method for manufacturing a printed wiring board, comprising the steps of electrically connecting and further forming a printed wiring by etching a metal foil on the surface of the electrical insulating layer.