JP2001007609A - High frequency circuit substrate and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a high frequency circuit metal substrate that meets all the requirements by forming a fluoropolymer layer containing heat resistant binder on at least the outermost surface of the metallic substrate as a dielectric layer. SOLUTION: The fluoropolymer layer containing heat resistant binder is formed to be at least on the outermost surface of the substrate, and the composition ratio of the heat resistant binder in the fluoropolymer in terms of the weight ratio of the fluoropolymer layer to he heat resistant binder is selected as 49/1 to 1/1, preferably 19/1 to 1/1. In the case of adopting a plurality of layers, the thickness of the outermost surface layer is preferably 2 to 10 μm. Employing the fluoropolymer layer, containing heat resistant binder for the outermost surface of the substrate, can improve the adhesive property between the fluoropolymer layer and circuit metallic parts and the bonding performance because of the enhanced hardness, and can prevent cissing in the case of forming a circuit in this way. The dielectric constant and the dielectric loss of the heat resistant binder are limited within a prescribed level for reducing this effect.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency circuit board used for a high-frequency communication device and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, the amount of information communication has been increasing.
Communication in a higher frequency region is becoming popular. Therefore, there is a demand for a circuit board that can be used in a high frequency range and has stable quality. The required performance that the circuit board must meet in order to be usable in the high frequency range is described below.

(1) It is necessary to increase the signal speed on the substrate as much as possible so as not to cause transmission delay. By the way, assuming that the signal transmission speed on the substrate is V and the relative permittivity of the substrate material is εr, it is expressed as V∝1 / √εr ----------. Therefore, it is understood that εr needs to be small in order to increase V.

(2) In microwaves and millimeter waves, since signals are transmitted as electromagnetic waves in a dielectric substrate, there is a transmission loss αd due to the dielectric, but it is necessary to minimize this loss. Operating frequency F, relative permittivity ε of substrate material
Assuming that r is the dielectric loss tanδ of the substrate material, in a generally used microstrip type signal line, it is expressed as αd∝F × √εr × tanδ -----. Therefore, it can be seen that the higher the frequency, the more it is necessary to reduce the εr and tanδ of the substrate in order to reduce the transmission loss.

(3) In order to keep the characteristic impedance constant, the size and shape of the substrate are limited. Given a characteristic impedance Z _{0 , a} dielectric thickness H, and a line width W, a commonly used microstrip signal line is expressed as Z ₀ √ (1 / √εr) × (H / W) ---- . Even when the wiring density is increased and W is made small, Z ₀ must be maintained at a predetermined value, and for this purpose, H needs to be made small.

(4) When the signal processing speed is increased by using microwaves or millimeter waves, the operating speed of the semiconductor to be mounted is increased, the amount of heat generated is increased, and it is necessary to dissipate this heat. Therefore, the substrate is required to have high thermal conductivity. The above is summarized as follows.・ Material with low relative dielectric constant for high signal transmission speed. -A material having a small relative dielectric constant and a small dielectric loss to reduce transmission loss. -The thickness of the dielectric layer of the substrate is small to achieve high-density wiring while maintaining the impedance at a predetermined value.・ A material that dissipates more heat as the amount of heat generated increases.

[0007]

The following are examples of circuit boards using a base material having a small dielectric constant. A substrate in which a glass fiber is impregnated with a fluorine resin or a polyimide resin as a base material, a copper foil is adhered to the base material via an adhesive, and a circuit pattern is formed by etching or the like. -A circuit pattern formed by thickening or thinning metallization on a substrate made of ceramics such as alumina or aluminum nitride. However, in the case of a substrate in which glass fiber is impregnated with a fluororesin, the fluororesin itself has a small relative dielectric constant and a low dielectric loss.
Since the copper foil is bonded via the adhesive, the ratio of the adhesive
Affected by dielectric constant and dielectric loss. Further, since the glass fiber is used as the reinforced base material, the thickness is as thin as 0.1 mm, and cannot be reduced to less than 0.1 mm. -As for ceramics, SiO ₂ has a small relative dielectric constant and a small dielectric loss, but is too fragile to be reduced to 0.1 mm or less. In addition, ceramics generally have poor thermal conductivity, and there is a problem that special ceramics must be used to improve thermal conductivity.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the conventional circuit board and to provide a board which satisfies all the required performances of a high-frequency circuit board. It is characterized in that a perfluorinated polymer layer is formed as a dielectric layer on the material, and at least the outermost surface is a perfluorinated polymer layer containing a heat-resistant binder. Further, the surface of the perfluorinated polymer layer may be subjected to a hydrophilic treatment.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The metal substrate used in the present invention is not particularly limited as long as it is conductive.
Among them, those having high thermal conductivity (that is, heat dissipation) are preferable. For example, Al, Cu, Fe, Ni, S
US steel, Al alloy (Mg-Mn system), Fe-Ni-Co,
Cu-W, alloys such as Cu-Mo, metal composites, and
These complexes can be used. Further, among these, aluminum and aluminum alloys are particularly preferable in that they have the characteristics of high thermal conductivity, high strength at a practical level, easy processing and low cost. Further, the metal substrate is made of aluminum or an aluminum alloy on the side of the metal substrate on which the perfluorinated polymer layer is provided, and the opposite surface is made of a metal composite plate having two or more layers combined with another metal. For example, by controlling the coefficient of thermal expansion, the heat cycle resistance of the circuit board can be improved. The thickness of the metal substrate may be 0.1 mm or more, preferably 0.5 mm to 2 mm, from the viewpoint of strength. When making high-density wiring while maintaining the impedance at a predetermined value, the thickness of the substrate dielectric must be small,
The thickness of the conductive metal substrate is not limited. In addition, the shape of the metal substrate can take any shape such as a circle, a square, and a rectangle.

The perfluorinated polymer used in the present invention includes PTFE, PFA, FEP, THE / PDD (perfluorocyclic polymer, Cytop, etc.), and homopolymers or mixtures of these copolymers. These polymers are used in the form of a dispersion system of emulsion polymerized particles, powders (molding powders such as fine powders obtained by filtering and washing the dispersion, granulated powders, fine powders, molding powders, or pulverized products thereof). I can do it. As for the thickness of the perfluorinated polymer layer formed on the metal substrate, in the case of a plurality of layers, the total thickness thereof is preferably 10 μm or more and 100 μm or less. If the thickness is less than 10 μm, it is difficult to form a plurality of layers. Conversely, if it exceeds 100 μm, the hardness of the substrate required for the wire bonding process for connecting the metallized wiring thereon and the outside becomes insufficient due to the softness of the perfluorinated polymer. By the way, the thickness of the perfluorinated polymer layer is 50
The circuit board of μm or less is a region that could not be achieved by the above-mentioned conventional circuit board, and even in high-density wiring such as four circuits in a width of 1 mm, the impedance can be kept at a predetermined value, It is expected to be widely used in communication circuits using microwaves and millimeter waves in the future.

The heat-resistant binder used in the present invention includes:
Any of a polyamideimide resin, a polyimide resin, a polyethersulfone resin, a polysulfone resin, an epoxy resin, a silicon resin, an organic titanium compound, an organic silicon compound, a phosphate, or a mixture thereof is used.
In the present invention, the perfluorinated polymer layer containing the heat-resistant binder selected from the above is formed so as to be at least the outermost surface, but the composition ratio of the heat-resistant binder in the perfluorinated polymer is Fluorinated polymer / heat resistant binder = 49/1 to 1/1, preferably 19/1 to 1/1. When a plurality of layers are provided, the thickness of the outermost layer is preferably 2 μm to 10 μm. In this way, by making the outermost surface a perfluorinated polymer layer containing a heat-resistant binder, the adhesion between the perfluorinated polymer layer and the circuit metal is improved, the repelling during circuit formation is prevented, and the bonding property is improved by the hardness up, Can be achieved. The dielectric constant and dielectric loss of the heat-resistant binder are the dielectric constant of the perfluorinated polymer,
Although larger than the dielectric loss, the effect can be reduced by limiting the blend ratio with the perfluorinated polymer, the thickness of the layer, and the like to predetermined ranges.

A method for forming a perfluorinated polymer layer on a metal substrate can be a conventional method for coating a perfluorinated polymer, and is not particularly limited. For example, film lamination, spin coating, spray coating, roll coating, screen printing, pad printing, inkjet,
Powder electrostatic coating, wet electrostatic coating, or the like can be used. This applies to the case of a perfluorinated polymer layer containing a heat-resistant binder and the case of a perfluorinated polymer layer containing no heat-resistant binder. Also, after forming a perfluorinated polymer layer on a metal substrate, surface smoothing treatment is effective for stabilizing the electrical characteristics of the circuit board. The method is not particularly limited as long as it is a method in which pressure is applied while heating at a temperature equal to or higher than 80 ° C. below the melting point. For example, a method such as hot pressing, a rolling roll, or pressing in a high-temperature oven can be used.

[0013] In order to improve the adhesion between the metal substrate and the perfluorinated polymer, the metal substrate may be roughened and / or anodized. The degree of surface roughening is R
When the thickness is 0.1 μm or more, improvement in adhesiveness due to the anchor effect is achieved. However, when Ra is 20 μm or more, the smoothness of the surface of the dielectric layer is lost, the thickness of the dielectric layer becomes unstable, and it becomes difficult to keep the impedance constant. Therefore, it is preferable to roughen the surface in the range of Ra 0.1 to 20 μm. Also, roughening in the range of 0.5 to 5.0 μm,
More preferably, surface roughening in the range of 1.0 to 3.0 μm is even more preferred. As a means for roughening, any one of blasting, mechanical polishing, chemical etching, and electrochemical etching, or a method in which these are arbitrarily combined can be used. Anodizing is a process in which a metal substrate is immersed in a strong acid, the metal substrate is used as an anode, and electricity is applied to oxidize the surface of the metal substrate. , Phosphate alumite, oxalate alumite and the like. In addition, by performing the anodic oxidation treatment after the surface roughening treatment, the adhesiveness between the metal substrate and the perfluorinated polymer can be further improved.

Further, in order to improve the adhesion between the metal substrate and the perfluorinated polymer layer, the perfluorinated polymer layer immediately above the metal substrate is replaced with the same as the outermost layer of the perfluorinated polymer layer.
It may be a perfluorinated polymer layer containing a heat resistant binder. Also in this case, in order to reduce the effects of the dielectric constant and the dielectric loss of the heat-resistant binder, it is necessary to limit the blend ratio with the perfluorinated polymer and the thickness of the layer to predetermined ranges. Same as in the case.

It is also effective to treat the surface of the perfluorinated polymer layer with a hydrophilic treatment. By the hydrophilic treatment, high-precision wiring formation by wet processing such as photolithography becomes easier, and the adhesion durability to the circuit is improved even after the circuit is formed and also in actual use, which is preferable.

The hydrophilic treatment can be carried out using any material selected from the following materials. Hydroxyl groups, carboxyl groups, sulfone groups,
Examples include a cyano group, a pyrrolidone group, an isocyanate group, an imidazole group, a sulfonamide group, and a phosphoric acid group. Examples of the monomer include the above-mentioned vinyl monomers having various hydrophilic groups and active hydrogens of the hydrophilic groups, such as ethylene oxide and propylene oxide. And the like. Examples of the monomer include an addition reaction with an alkylene oxide such as vinyl alcohol, acrylic acid, methacrylic acid, fumaric acid, maleic acid, and unsaturated carboxylic acid such as itaconic acid. An alkylene oxide adduct of acrylic acid or methacrylic acid can also be used. Surfactants include anionic,
Any of cationic, amphoteric, and nonionic types may be used. As the polymer, polyvinyl alcohol, polyacrylic acid,
Examples include polyacrylonitrile, polyvinyl sulfone, polyurethane, polyethylene oxide, starch and the like.

The hydrophilic treatment is performed by forming an active site on the surface of the dielectric, and bringing the active site into contact with any one or a mixture of the above-mentioned highly hydrophilic functional group, monomer, oligomer, and polymer. Can be. Any of or a mixture of highly hydrophilic functional groups, monomers, oligomers, and polymers is brought into contact with a gas, a liquid directly, or a mixed gas diluted with a carrier gas, an aqueous solution, or an organic solvent solution. As a method of forming an active point, a method of irradiating the dielectric surface with active light, for example, UV lamp, excimer laser light irradiation, corona discharge,
There are methods of plasma discharge and immersion in an alkali metal complex solution. In addition, highly hydrophilic functional groups, monomers,
It is also effective to irradiate the active ray with any one or a mixture of the oligomer and the polymer in a state of being brought into contact with a gas, a liquid directly, or a mixed gas diluted with a carrier gas, an aqueous solution or an organic solvent solution. Among the methods of irradiating actinic rays, a method using a UV lamp is preferable because it is inexpensive. In the case of irradiation with a UV lamp, the irradiated light is 200-
It has a wide wavelength distribution at 700 nm (near ultraviolet to visible range). Although the preferred wavelength range in the present invention is not necessarily clear, it is arbitrarily stated that "the entire ultraviolet range (100-400 nm), preferably near ultraviolet.
(200-400 nm) ". The irradiation dose depends on the wavelength of the UV light used, but is usually 0.1 to 20000 J / cm ² , preferably 5 to 10
00J / cm ² . The types of UV lamps include carbon arc lamps (370-380 nm) and xenon lamps (800-900n).
m), ultraviolet fluorescent lamp (290-320nm), metal halide lamp (360-380nm), low pressure mercury lamp (200-300nm), high pressure mercury lamp (300-400 & 500-600nm), ultra high pressure mercury lamp (300-4
50 & 500-600nm). The wavelength of the excimer laser is also in the ultraviolet range. However, unlike the above-mentioned UV lamp, it does not have a broad wavelength distribution, has a single wavelength, has high luminance, and emits short pulses. The wavelength is determined by the type of gas, for example, F2 (157 nm), ArF (193 nm), KrF (248 nm), XeCl (308n
m) and XeF (351 nm).

When the surface of the perfluorinated polymer layer is subjected to hydrophilic treatment by the method described above, a precision circuit such as photolithography can be more easily formed as described above. Since the graft layer has a thickness of not less than 3 μm and a single molecular chain length of either oligomer or polymer, there is almost no adverse effect on transmission speed and transmission loss.

[0019]

The present invention will be described in more detail with reference to Examples and Comparative Examples. Aluminum alloy plate as metal substrate
(Kobe Steel ASB material) was used. This metal substrate is subjected to electrochemical etching and anodization, and then PTF
E The aqueous dispersion is coated by spin coating, dried at 100 ° C, and then baked at 380 ° C for 15 minutes.
A perfluorinated polymer layer was formed. Examples of the aqueous PTFE dispersion include Daikin EK-1909BKN containing a heat-resistant binder PAI (polyamide imide), and a PTFE aqueous dispersion containing no heat-resistant binder (Daikin D
-1F) was used alone or in combination.

In Example 1, coating, drying and sintering were repeated by the above-mentioned method. As shown in Table 1, as shown in Table 1, the first layer had a PAI content of 19%, the thickness was 7 μm, and the second layer had a PAI content. 0%, thickness 25 μm, third layer: a fluororesin layer having a PAI content of 30% and a thickness of 5 μm. In Comparative Example 1, the first layer and the second layer had the same configuration as in Example 1, and the third layer was not provided.

[0021]

[Table 1]

A thin film of Al-Ni-Au was deposited on the surface of the PTFE layer of each substrate of Example 1 and Comparative Example 1 by a vacuum deposition apparatus to form a ring resonance circuit for evaluating dielectric properties, and then a network analyzer was used. The transmission characteristics at 10 GHz were evaluated. In addition, P of each substrate of Example 1 and Comparative Example 1
On the surface of the TFE layer, a thin film of Al was deposited to a size of 10 mm square using a vacuum deposition apparatus. Then, the strength when the Al thin film was peeled off from the PTFE layer surface was measured.
The results of these measurements are as shown in the lower part of Table 1. In both Example 1 and Comparative Example 1, the permittivity and the dielectric loss were sufficiently small.
This is a level that can be used as a high-frequency circuit board. However, in Comparative Example 1, the peeling strength of the aluminum film was low, and this was not practical for a circuit having a narrow width. On the other hand, in the first embodiment, the peeling strength is high, and even a narrow circuit can be used practically, so that the density of the circuit can be increased.

Next, as Examples 2 to 5, perfluorinated polymer layers were formed in the same procedures as described above, with the configurations shown in Table 2, respectively. Further, as Example 6, while heating the sample of Example 2 at 280 ° C., 500 kgf / cm ²
The sample was subjected to hot pressing at a pressure of 5 ° C. to smooth the dielectric surface. Subsequently, Example 2 to Example 6
Each sample was subjected to a hydrophilic treatment on its dielectric surface. The hydrophilic treatment was performed by irradiating the surface of the PTFE layer with an ultraviolet ray for 10 minutes using a UV lamp in a state where the surface of the PTFE layer was in contact with an aqueous solution of methylcellulose (MARVOLOWS M-4000, manufactured by Matsumoto Yushi Seiyaku Co., Ltd., concentration: 0.15 wt%) .

[0024]

[Table 2]

A thin film of Al—Ni—Au is deposited on the surface of the PTFE resin of each of the substrates obtained in Examples 2 to 6 by a vacuum deposition apparatus to obtain a ring resonance circuit for evaluating dielectric properties. Was formed, and the transmission characteristics at 10 GHz were evaluated using a network analyzer. In addition, the surface of the perfluorinated polymer layer of each substrate was
An Al thin film was deposited to a size of mm square, and the strength when the Al thin film was peeled off from the surface of the fluorine resin layer was measured.

The results of the above measurements are shown in Table 2 below. The combination of the metal substrate and the perfluorinated polymer composition according to the present invention shows that the perfluoropolymer has a low dielectric constant,
The low dielectric loss was fully utilized, and favorable results were obtained as a high-frequency circuit board. Also, sufficient peel strength was obtained. Such a large peeling strength is particularly effective in narrowing the width of the circuit. If at least the outermost surface contains a heat-resistant binder, photolithography can be used to reduce the width of the circuit to 0.1 mm or less. It was confirmed that even if a density circuit was formed, it was sufficiently practical.

As another comparative example, a conventionally used ceramic substrate (Comparative Example 2) and a glass fiber fluorine substrate were used.
(Comparative Example 3) also formed a ring resonant circuit in the same manner and evaluated the electrical characteristics.However, these had a problem that the dielectric loss was large, and the thickness of the dielectric could not be reduced to 0.1 mm or less. Therefore, while the impedance was maintained at 50Ω, the width of the circuit could not be reduced to 0.3 mm or less.

[0028]

As described above, by combining a perfluorinated polymer and a metal substrate, a dielectric layer having a small dielectric constant and a small dielectric loss can be made sufficiently thin to 0.1 mm or less. This is effective for making the circuit thinner in order to increase the wiring density of the circuit while maintaining the impedance at a predetermined value. Furthermore, at least the outermost surface is made of a perfluorinated polymer layer containing a heat-resistant binder, so that the adhesive strength between the dielectric and the circuit can be improved. As a result, even a thin circuit of 0.1 mm or less can be sufficiently used for practical use. This is very effective in increasing the density of circuit wiring. As described above, according to the present invention, a very preferable high-frequency circuit board can be obtained and can be used for high-frequency communication.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 83/04 C08L 83/04 101/16 H05K 1/03 610H H05K 1/03 610 C08L 101/00 (72 Inventor Toshihiko Takiguchi 1-3-1 Shimaya, Konohana-ku, Osaka-shi Sumitomo Electric Industries, Ltd. (72) Inventor: Kazuhiro Kizawa, 950 Noda, Kazatori-cho, Sennan-gun, Osaka Sumitomo Electric Industries, Ltd.Kumatori Works (72) F-term in Kumatori Works (reference) 4J002 BD12W BD15W BE04W CD00X CM04X CN03X CP03X DH046 EX006 EZ006 GQ00 5J014 CA05 CA42 CA53

Claims (7)

[Claims] Claims: 1. A combination of a metal substrate layer and a perfluorinated polymer layer, wherein at least the outermost surface has
A high-frequency circuit board comprising a perfluorinated polymer layer containing a heat-resistant binder. 2. The heat-resistant binder is any one of a polyamideimide resin, a polyimide resin, a polyether sulfone resin, a polysulfone resin, an epoxy resin, a silicone resin, an organic titanium compound, an organic silicon compound, and a phosphate, or any one selected from these. The high-frequency circuit board according to claim 1, further comprising a mixture. 3. The method according to claim 1, wherein the weight ratio of the heat-resistant binder to the perfluorinated polymer in the perfluorinated polymer layer containing the heat-resistant binder is from 1/1 to 1/49. High frequency circuit board. 4. The high-frequency circuit board according to claim 1, wherein the thickness of the perfluorinated polymer layer containing a heat-resistant binder is 2 μm to 10 μm. 5. The high-frequency circuit board according to claim 1, wherein the outermost perfluorinated polymer layer containing a heat-resistant binder is subjected to a hydrophilic treatment. 6. A high-frequency circuit board according to claim 1, wherein a perfluorinated polymer layer as a dielectric layer is formed on the surface of the metal substrate, at least the outermost surface is a perfluorinated polymer layer containing a heat-resistant binder. Production method. 7. A process for smoothing the surface of the dielectric by applying pressure while heating under reduced pressure at a temperature not higher than the melting point of the perfluorinated polymer and not lower than 80 ° C. below the melting point. The method for manufacturing a high-frequency circuit board according to claim 6.