JPH06224526A - Dielectric substrate - Google Patents

Abstract

PURPOSE:To provide a dielectric substrate which contains a polyolefin resin layer as a dielectric layer and improved in adhesion property and heat resistance while such excellent features as the ultra-low dielectric constant and ultra-low dielectric loss the polyolefin resin has are maintained. CONSTITUTION:The title substrate is constituted by laminating a porous fluoroplastic film on at least one surface of a polyolefin resin sheet or by coating the surface of the porous fluoroplastic film with a conductive layer after laminating the porous fluoroplastic film on at least one surface of the polyolefin resin sheet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dielectric substrate used as a printed wiring board, a planar antenna insertion substrate, a substrate having a high-frequency line, and a dielectric substrate used as an intermediate material.

[0002]

2. Description of the Related Art Polyolefin resin materials typified by polyethylene and polypropylene have extremely low dielectric constant and low dielectric loss, which are almost the same as those of fluororesin materials such as polytetrafluoroethylene. It is a body material. Further, the polyolefin resin material can be easily processed as a woven cloth, a nonwoven cloth, or a foam material,
It is also very cheap. Therefore, taking advantage of these features, the polyolefin-based resin material is widely used as a dielectric material such as a planar antenna and a high frequency coaxial wire for electronic materials.

However, since polyolefin resin materials have no polarity, they have very poor chemical adhesion, and generally have the drawback of being inferior in heat resistance as compared with other engineering plastics. Since the polyolefin resin material has such drawbacks, it is very difficult to form a composite with another material such as metal, and it has been used alone until now. Therefore, in reality, products such as polyolefin copper-clad substrates and polyolefin copper-clad films have not been put on the market.

By the way, recently, a special adhesive film or the like for a polyolefin resin material has begun to be developed. However, when compounding is performed using these adhesive films, electrical characteristics such as dielectric loss are deteriorated. However, use in high frequency applications is not preferable.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above problems of the prior art and includes a polyolefin resin as a dielectric layer, and is excellent in the ultra low dielectric constant and ultra low dielectric loss of the polyolefin resin. It is an object of the present invention to provide a dielectric substrate having excellent adhesiveness and heat resistance while maintaining the above features.

[0006]

The present inventors have completed the present invention as a result of intensive studies to solve the above problems. That is, according to the present invention, there is provided a dielectric substrate obtained by laminating a porous fluororesin film on at least one surface of a polyolefin resin sheet. Also,
According to the present invention, a porous fluororesin film is laminated on at least one surface of a polyolefin resin sheet,
Further, there is provided a dielectric substrate having a conductor layer provided on the surface of the porous fluororesin film.

The dielectric substrate of the present invention will be described in detail below. The dielectric substrate of the present invention is constituted by laminating a porous fluororesin film on at least one surface of a polyolefin resin sheet.

As the polyolefin resin sheet used in the present invention, a solid body of polyethylene or polypropylene and a known porous body such as woven cloth, non-woven cloth and foam material can be used. The thickness of the polyolefin resin sheet is 20μ
m to 4 mm, preferably 50 μm to 2 mm. When using a polyolefin-based resin sheet having a porous structure, in the case of a woven fabric or a non-woven fabric, a basis weight: 1 to 100 g / m ² ,
Preferably 10-30 g / m ² , thickness of woven or non-woven fabric:
It is 10 μm to 2 mm, preferably 50 μm to 0.2 mm. In the case of a foam material, the expansion ratio is 2 to 100 times, preferably 5 to 40 times, and the thickness of the foam material is 0.5 to 6 mm, preferably 2 to 3 mm.

The porous fluororesin used in the present invention is a conventionally known one, and its preferred resin is polytetrafluoroethylene (PTFE), but other than that, tetrafluoroethylene / hexafluoropropylene copolymer (FEP) is used. , Polyvinyl fluoride, polyvinylidene fluoride and the like can also be used.

The porous fluororesin preferably used in the present invention comprises a stretched product of tetrafluoroethylene and has an average pore diameter of 100 μm or less, preferably 10 μm or less and a porosity of 98 to 20%, preferably 90 to 50. %. About such things, Japanese Patent Publication Sho 56-
No. 45773, Japanese Patent Publication No. 56-17216, and U.S. Pat. No. 4,187,390. The thickness of the porous fluororesin sheet is preferably 10 to 100 μm from the viewpoint of cost.

The lamination of the polyolefin resin sheet material and the porous fluororesin film is carried out by a method of heat-sealing the both with a heat roll, and the surface of the polyolefin resin sheet is heated and melted to adhere to the porous fluororesin film. It can be performed by a frame bonding method or the like. In any of the laminating methods, the melted polyolefin resin material enters into some of the fine pores of the porous fluororesin material, and mechanically strong adhesion becomes possible.

Next, another dielectric substrate according to the present invention will be described. This dielectric substrate is formed by providing a conductor layer on the surface of the porous fluororesin film of the above-mentioned dielectric substrate. In this case, the same material as the above case can be used for the polyolefin resin sheet and the porous fluororesin film, and the film thickness, necessary characteristics, laminating method and the like can be the same as above.

As a material for the conductor layer provided on the surface of the porous fluororesin film, a metal such as gold, silver, copper, aluminum, nickel or an alloy thereof can be used. From the viewpoint of electrical characteristics, it is preferable to attach the conductive material to the porous fluororesin film by vapor deposition or by a plating method (wet or dry method) that does not use an adhesive.

When the conductive layer is formed by vapor deposition, a conventionally known vapor deposition method can be used. However, in order to form a uniform vapor deposition layer on the film surface, vapor deposition is performed using two vapor deposition sources. Alternatively, it is preferable to perform the vapor deposition by moving the film and the vapor deposition source relatively. Further, as the vapor deposition method, in addition to ion plating, sputtering, a method of performing vapor deposition while applying plasma, a method of performing vapor deposition after performing plasma treatment, and the like, conventionally known dry methods, physical methods, vapor phase methods, etc. Various particle attachment methods according to.

Further, when the conductor layer is formed by a plating method, a conventionally known plating method can be used, but it is particularly preferable to use a plating method comprising a hydrophilization step and a chemical plating step described below. This method will be described in detail below. (1) Hydrophilization step This step is a step of hydrophilizing the surface of the porous fluororesin film over the entire surface or in a required pattern. As a method for hydrophilizing, any method can be adopted as long as it can hydrophilize the surface of the porous fluororesin film, but preferably various hydrophilic polymers having a hydrophilic group are attached and bonded. In this case, the hydrophilic group is a hydroxyl group,
Carboxyl group, sulfone group, cyano group, pyrrolidone group, isocyanate group, imidazole group, phosphoric acid group, N
There may be mentioned an amide group which may be substituted, an amino group which may be N-substituted, a sulfonamide group and the like. In addition, alkylene oxide such as ethylene oxide or propylene oxide may be added to the active hydrogen of the hydrophilic group.

As the hydrophilic polymer, it is preferable to use a hydrophilic polymer which is soluble in an organic solvent and somewhat soluble in water or an aqueous solution, preferably substantially water-insoluble. Further, with respect to heat resistance, alkali resistance and acid resistance, those which can withstand the temperature and pH of the plating solution are preferable. Such hydrophilic polymers include polyvinyl alcohol, polyacrylic acid, polyacrylonitrile, polyvinyl sulfone, polyurethane, polyethylene oxide, starch, carboxymethyl cellulose, ethyl cellulose, sodium alginate, gluten, collagen,
Although various synthetic and natural polymers having hydrophilicity such as casein can be used, the use of fluorine-containing hydrophilic polymer is particularly advantageous from the viewpoint of adhesive bond to porous fluororesin. Such a fluorine-containing hydrophilic polymer can be obtained by copolymerizing a fluorine-containing ethylenically unsaturated monomer and a fluorine-free hydrophilic group-containing vinyl monomer. As the fluorine-containing monomer, for example,
Tetrafluoroethylene, vinyl fluoride, vinylidene fluoride, monochlorotrifluoroethylene, dichlorodifluoroethylene, hexafluoropropylene and the like can be mentioned. On the other hand, as the hydrophilic group-containing monomer, vinyl monomers having various hydrophilic groups described above and monomers obtained by addition-reacting alkylene oxide, such as ethylene oxide or propylene oxide, with active hydrogen of the hydrophilic groups are also preferable. After copolymerization, like vinyl acetate,
Those which give a hydrophilic group-containing copolymer by hydrolysis are also used.

Specific examples of the hydrophilic monomer include unsaturated alcohols such as vinyl alcohol, acrylic acid, methacrylic acid, fumaric acid, maleic acid and itaconic acid,
Examples thereof include alkylene oxide adducts of acrylic acid and methacrylic acid.

The fluorine content of the fluorine-containing hydrophilic copolymer preferably used in the present invention is usually 2% to 60%, preferably 10% to 60%, more preferably 20% to 60% on a weight basis. . When the fluorine content of the fluorine-containing hydrophilic copolymer is too high, the heat resistance and electric characteristics are improved, but the hydrophilicity of the polymer is lowered. On the other hand, if the fluorine content is too low, the adhesiveness of the fluorine-containing hydrophilic copolymer to the material will be low, and the heat resistance will also be low.

In the fluorine-containing hydrophilic copolymer preferably used in the present invention, the hydrophilic group equivalent is generally 45 to
700, preferably 60-500, more preferably 60
~ 450.

In order to attach the hydrophilic polymer to the surface of the porous fluororesin film by adhesive bonding, for example, a fluorine-containing hydrophilic copolymer is dissolved in an organic solvent such as alcohol, ketone, ester, amide or hydrocarbon. The solution is applied to the surface of the porous fluororesin film by a coating method using a spray or a roller, and then dried. In this way, the outer surface of the porous fluororesin film can be formed into a hydrophilic surface.

(2) Chemical plating step In this step, the hydrophilic portion formed on the entire surface of the porous fluororesin film as described above or in the required pattern is subjected to a pretreatment for chemical plating, followed by chemical treatment. This is a step of performing a plating process. Each step of these pretreatment and chemical plating treatment may be performed according to a conventionally known method. That is, in the pretreatment step, a noble metal serving as a catalyst for chemical plating is attached to the inner surface of the pores of the material. As the noble metal, palladium, platinum, gold or the like is used, but palladium is preferable. As a method of attaching the noble metal, for example, tin chloride (I
A method of contacting with the aqueous solution of I), followed by washing with water, contacting with an aqueous solution of palladium chloride, and then washing with water can be employed. Such pretreatment for chemical plating is a well known technique.

Next, the porous fluororesin film that has been pretreated for chemical plating as described above is immersed in a chemical plating solution for chemical plating. The chemical plating solution generally contains a metal, a reducing agent, a complexing agent, a buffer, a stabilizer and the like. In this case, as the reducing agent, sodium hypophosphite, sodium borohydride, amine borane, formalin, hydrazine and the like are adopted, and as the complexing agent and buffering agent, formic acid, acetic acid, succinic acid, citric acid, tartaric acid. , Malic acid, glycine, ethylenediamine, EDT
A, triethanolamine, sodium / potassium tartrate, etc. are adopted. As the plating metal, for example,
Various metals such as copper, gold, silver, platinum, rhodium, nickel, cobalt, tungsten, zinc, iron and alloys thereof such as solder can be used. When obtaining a metal film of an alloy, a metal salt having a component composition corresponding to a desired alloy film may be used as the metal salt added to the plating solution.

To obtain a metal film made of platinum, gold, or an alloy thereof, or any other metal film that is difficult to form by chemical plating on the surface of the porous fluororesin film, cobalt or cobalt is formed on the resin film. It is preferable to previously form a metal film which can be easily formed by chemical plating of nickel, copper or the like, and then subject this to chemical plating treatment or electroplating treatment. As a method of forming the conductor layer pattern, a method of growing a metal film on the entire surface and etching it into a desired pattern, a known additive method of selectively growing the metal film in a desired pattern, and the like can be adopted. In this way, a dielectric substrate having a circuit or a high frequency line on the surface of the porous fluororesin film can be obtained.

The formation of the conductor layer on the porous fluororesin film may be performed on the porous fluororesin film laminated on the polyolefin resin sheet, or on the polyolefin resin sheet. It may be performed on the former porous fluororesin film.

The dielectric substrate according to the present invention is advantageously used as a general printed wiring board or flexible board. When used as a printed wiring board, a metal layer is provided on the back surface of the polyolefin-based resin sheet (the surface opposite to the surface on which the porous fluororesin film is laminated) and then formed on the porous fluororesin film. It is necessary to electrically connect the conductive layer and the metal layer. For this purpose, a method of forming a through hole and forming a metal plating layer on the inner wall surface, a method of inserting a metal rod into the through hole, a method of embedding a conductive paste in the through hole, etc. Is adopted.

The dielectric substrate according to the present invention is also preferably used in high frequency applications. That is, it is preferably used as a double-sided board using a microstrip line, a flat cable, or the like, but it is also possible to stack and use two boards to have a stripline structure, for example. The substrates can be easily laminated by using base materials having different melting points such as polypropylene and polyethylene, and heat-melting polyethylene having a low melting point to use as an adhesive.

[0027]

INDUSTRIAL APPLICABILITY In the present invention, the dielectric substrate in which a polyolefin resin film is laminated on at least one side of a polyolefin resin sheet has the following advantages. (1) Since the porous fluororesin film is laminated, an increase in the dielectric constant is suppressed, and a substrate that maintains the extremely low dielectric constant and dielectric loss of the polyolefin resin can be provided at low cost. (2) The conductor film can be firmly attached to the surface of the porous fluororesin film without using an adhesive. (3) Short-term heat resistance is improved because a porous fluororesin sheet having heat resistance and high heat insulation effect is laminated on the surface. (4) Since the substrates can be bonded to each other by using a polyolefin resin material as an adhesive, a laminate can be formed.

Such a dielectric substrate is used as an intermediate material for forming a conductor layer on its surface.

In the present invention, a porous fluororesin film having a conductor layer on its surface can be used as a general circuit board or a flexible board. Etc. or an intermediate material thereof can be preferably used. (1) Dielectric substrate or film of planar antenna for BS etc. (2) Flexible high frequency substrate (3) Micro strip line, strip line, substrate having high frequency line such as coplanar line with ground, flat cable (4) Coaxial wire dielectric

[0030]

EXAMPLES Next, examples of the present invention will be described, but the present invention is not limited to these examples.

Example 1 A porous polytetrafluoroethylene film (manufactured by Japan GORE-TEX Co., Ltd.) having a thickness of 40 μm, a porosity of 80% and an average pore diameter of 0.2 μm was formed on both sides of a polypropylene film having a thickness of 100 μm. Speed 2 using a heat roll at ℃
A substrate was prepared by laminating at m / min.

Example 2 Both sides of the substrate prepared in Example 1 were coated with a methanol solution containing 0.3 wt% of a tetrafluoroethylene / vinyl alcohol copolymer and then dried at 100 ° C. for 2 minutes to give a porous film. Only the surface of the polytetrafluoroethylene film was made hydrophilic. Then, a known method was used to prepare a copper-clad substrate having a thickness of 10 μm and subjected to electroless plating. The relative permittivity of this substrate is 2.1,
The dielectric loss was 0.0002 (measured at 1 MHz).
The copper foil peeling strength was 2 kgf / cm.

Example 3 A porous polytetrafluoroethylene film having a thickness of 40 mm, a porosity of 80% and an average pore diameter of 0.2 μm was formed on both sides of an electron beam cross-linked foamed polyethylene having a thickness of 2 mm and a foaming ratio of 10 times. (Japan GORE-TEX Co., Ltd.) was laminated by a frame bonding method to prepare a substrate. Both sides of this substrate were subjected to electroless plating with a thickness of 10 μm in the same manner as in Example 2 to prepare a copper-clad substrate. The relative permittivity of this substrate was 1.1 and the dielectric loss was 0.0002 (1 MH
z). Copper foil peeling strength is 1.5kgf / cm
Met.

Example 4 The copper-clad substrate prepared in Example 2 was pattern-etched to form a copper circuit. As shown in FIG. 1, a two-layered substrate having a thickness of 30 μm and a polyethylene film interposed between the two substrates was pressed by a hot press at a temperature of 130 ° C. and a pressure of 5 kg / cm ² for 5 minutes to form a stripline laminated plate. It was created.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a stripline laminated plate prepared in Example 4;

[Explanation of symbols]

 1, 1'substrate 2, 2 ', 3 copper 4 polyethylene film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Urakami 1-42-5-5 Akakutsumi, Setagaya-ku, Tokyo Inside Japan Gore-Tex Co., Ltd.

Claims (5)

[Claims] 1. A dielectric substrate formed by laminating a porous fluororesin film on at least one surface of a polyolefin resin sheet. 2. A dielectric substrate obtained by laminating a porous fluororesin film on at least one surface of a polyolefin resin sheet, and further providing a conductor layer on the surface of the porous fluororesin film. 3. The dielectric substrate of claim 2, wherein the conductor layer forms a circuit. 4. The dielectric substrate according to claim 1, wherein the polyolefin resin sheet has a porous structure. 5. The dielectric substrate according to claim 1, wherein the polyolefin resin is polyethylene or polypropylene.