JPH0563321A - Wiring board - Google Patents

Abstract

PURPOSE:To provide a wiring board, which is suitable for transmission of a high-frequency signal and is low-cost. CONSTITUTION:1 A wiring board is formed by laminating by fusing conductor circuits on a porous polypropylene film and 2 moreover, the wiring board is formed into a structure, wherein polymer films are laminated on one surface of the porous polypropylene film, 3 a structure, wherein porous polypropylene films are laminated by fusing on the conductor circuit, 4 a structure, wherein polymer films are laminated on the porous polypropylene films laminated by fusing on the conductor circuits and 5 a structure, wherein the porous polypropylene films are crosslinked by irradiation with an ionizing radiation or water crosslinking.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION It is an object of the present invention to provide a wiring board having excellent high frequency characteristics, which is suitable for use in electronic equipment such as computers and communication equipment.

[0002]

2. Description of the Related Art In recent years, as electronic devices such as televisions, video recorders, and personal computers have become lighter, smaller, and have higher functions, flat cables and conductor cables formed on an insulating base material have been used in place of conventional insulated coated electric wires. Flexible printed wiring boards are being used.

In particular, in a wiring board used for a computer, a communication device, etc., since a signal to be handled is a high frequency radio wave of 1 MHz or more, a dielectric constant of an insulating base material or an adhesive layer of an insulating base material and a conductor circuit is high. If it is large, the capacitance between adjacent conductor circuits becomes large, which causes problems such as a large transmission loss and the fact that the waveform is not faithfully transmitted.

Further, in the wiring board in the above electronic device,
Electromagnetic noise generated from the conductor circuit adversely affects electronic components in the surroundings, and conversely electromagnetic noise generated in the surroundings adversely affects transmission signals flowing in the conductor circuit. An electromagnetic shield type wiring board having a structure in which a conductor layer is provided on or around an insulating base material is also used.

However, even in the wiring board having the above structure, if the dielectric constant of the insulating base material or the adhesive layer is large, the capacitance between the conductive layer and the conductor circuit becomes large, so that the transmission loss becomes large. This causes problems such as waveforms not being transmitted faithfully.

In order to increase the transmission loss of a high frequency signal and to faithfully transmit a signal waveform, a material having a small dielectric constant may be used for the insulating base material or the adhesive layer between the insulating base material and the conductor circuit. There is known a wiring board having a structure in which a tetrafluoroethylene film is impregnated with an adhesive and is bonded to a conductor foil.

[0007]

However, a wiring board using a porous polytetrafluoroethylene film is extremely expensive and cannot be used as a wiring board for general-purpose high-frequency signal transmission or a wiring board having a shield structure. At present, it can only be used for special limited purposes.

Further, there is no known adhesive capable of directly bonding the porous polytetrafluoroethylene film and the conductor circuit, and the porous polytetrafluoroethylene film itself has mechanical strength such as tensile strength and tear strength. Weak,
Unless it is in the state of prepreg impregnated with an adhesive, it cannot be handled or adhered to a conductor circuit. Therefore, the dielectric constant of the porous polytetrafluoroethylene film is 1.2.
There is also a drawback that a low dielectric constant of up to 1.5 cannot be effectively used.

For these reasons, there has been a demand for an inexpensive wiring board suitable for high frequency transmission and an inexpensive wiring board suitable for high frequency transmission and having a shielding effect.

[0010]

DISCLOSURE OF THE INVENTION As a result of intensive studies on the above problems, the present inventors have found a wiring board in which a conductor circuit is directly fused and laminated on a porous polypropylene film;
As an insulating layer on a conductor circuit, a wiring board in which a porous polypropylene film is laminated via an adhesive layer is found to be a wiring board suitable for high-frequency signal transmission and inexpensive, and based on such findings. The present invention has been completed.

That is, the present invention is the structure shown in Table 7 or Table 8 below:

[Table 7]

[0012]

[Table 8] Which is a wiring board in which a conductor circuit is fusion-laminated on a porous polypropylene film,

Structures shown in Table 9 below:

[Table 9] Having a feature that the polymer film is laminated on one side of the porous polypropylene film,

Structures shown in Table 10 below:

[Table 10] Is also characterized in that the porous polypropylene film is fusion-laminated on the conductor circuit,

Structures shown in Table 11 below:

[Table 11] Also characterized in that the polymer film is laminated on the porous polypropylene film fused and laminated on the conductor circuit,

Structures shown in Table 12 below:

[Table 12] Is also cross-linked by irradiation with ionizing radiation or water crosslinking.

The present invention will be described more specifically. The porous polypropylene film of the present invention is disclosed in JP-B-52-15.
It can be obtained by the methods described in Japanese Patent Publication No. 627, Japanese Patent Publication No. 52-137026, Japanese Patent Publication No. 63-29906, Japanese Patent Publication No. 63-29907, and the like. For example, a basic manufacturing method is a method in which a melt-formed unstretched polypropylene film is heat-treated, and then stretched at room temperature or a low temperature to form pores, and then heat-treated again.

When the wiring board is required to have soldering heat resistance,
May be used in a high temperature atmosphere, in such a case, it is desirable that the porous polypropylene film is crosslinked, by irradiation with ionizing radiation such as electron beam or γ-rays or by a method such as water crosslinking, A porous polypropylene film having a crosslinked structure can be obtained.

In this case, in crosslinking by irradiation with ionizing radiation, not only a propylene homopolymer but also a random or block copolymer of propylene with a small amount of another unsaturated monomer or oligomer, particularly ethylene, It is preferable to use a raw material to which a crosslinking aid such as a polyfunctional monomer is added.

Examples of the crosslinking aid include (meth) acrylic acid esters such as trimethylolethane (meth) acrylate and trimethylolpropane (meth) acrylate, triallyl cyanurate and triallyl isocyanurates. In the case of water-crosslinking, a mixture of a silane-modified polypropylene and a water-crosslinking catalyst such as an organic tin compound may be used as a raw material.

Further, regarding the lamination of the porous polypropylene film and the conductor circuit, it is desirable to adjust the degree of crosslinking of the porous polypropylene film.
When laminating is performed using a hot press machine at 80 ° C., it is desirable to set the degree of crosslinking of the porous polypropylene film to about 30 to 40% in terms of gel fraction using xylene as an extraction solvent.

The gel fraction can be adjusted by the addition amount and irradiation dose of the polyfunctional monomer added to the raw material in the case of irradiation with ionizing radiation, and in the case of water crosslinking, the treatment time of pressurized steam or immersion in water. It can be set by adjusting the temperature and time, and further, the degree of crosslinking of the porous polypropylene film can be finally increased by a method such as re-irradiation with ionizing radiation after the fusion.

At this time, for the purpose of increasing the adhesive strength between the porous polypropylene film and the conductor circuit, it is effective to emboss the bonding surface of the conductor circuit.

The porosity of the porous polypropylene film used in the present invention is 50 to 80% mainly from the relation of the dielectric constant.
More preferably, it is desirable to use a film having a porosity of 60 to 70%. For example, in the case of a film having a porosity of 60%,
The dielectric constant is 1.5 to 1.6.

As the polymer film used in the present invention,
It is not particularly limited as long as it has a function as a dielectric film, but particularly crosslinked polyethylene film, crosslinked polypropylene film, biaxially stretched polyester film, polyimide film, polyetherimide film, polyethersulfone film, polyetheretherketone film, etc. It can be preferably used, and its type and thickness can be appropriately selected according to the purpose of use.

For laminating the porous polypropylene film and the polymer film, a method such as laminating with an adhesive may be employed. Examples of the adhesive that can be used in this case include a propylene-maleic anhydride copolymer and an ethylene-propylene-maleic anhydride copolymer from the viewpoint of the dielectric constant of the adhesive itself, the porous polypropylene film, and the adhesiveness with the conductor circuit. Polymer, ethylene-glycidyl methacrylate copolymer, ethylene-propylene-glycidyl methacrylate copolymer, ethylene-ethyl acrylate-maleic anhydride copolymer, ethylene-ethyl acrylate-
Examples thereof include carbon monoxide copolymers and silane-modified ethylene-ethyl acrylate copolymers, and they can be used as a single or a mixture of a plurality of types, or as a single layer or a multilayer.

Further, in order to prevent the adhesive from penetrating into the pores of the porous polypropylene film at the time of laminating, a method of partially cross-linking (B stage) the adhesive layer before laminating can be adopted. ..

[0028]

EXAMPLES The present invention will be described in more detail with reference to examples below, but these do not limit the scope of the present invention.

Example 1 Using a material obtained by adding 2 parts by weight of triallyl isocyanurate to 100 parts by weight of an ethylene-propylene copolymer (Vicat softening point 129 ° C., melt flow rate 1.2), a blank having a thickness of 25 μm was used. A porous polypropylene film having a porosity of 60% was produced.

This film was irradiated with an electron beam having an accelerating voltage of 200 kV for 5 Mrad to obtain a porous polypropylene film having a gel fraction of 34% by hot xylene extraction. An electrolytic copper foil having a thickness of 35 μm was applied to both sides of this porous polypropylene film at a temperature of 180 ° C. using a hot press machine at 10 kg /
After thermocompression bonding at a surface pressure of cm ² for 3 minutes, the mixture was water-cooled and fixed under pressure to obtain a double-sided plate having a structure in which electrolytic copper foil was attached to both surfaces of a porous polypropylene film. An electron beam having an accelerating voltage of 2 MV was irradiated from both sides of this double-sided plate at 20 Mrad to further crosslink the porous polypropylene film layer.

A striped circuit having a circuit width of 1 mm and a circuit interval of 1 mm as shown in FIG. 1 was formed on the copper foil layers on both sides of the double-sided plate by an etching method using an aqueous ferric chloride solution. As a result of measuring the capacitance between A and B of this circuit board at 1 MHz, the circuit length was 16 pF / 10 cm and the circuit length between circuits A and C was 0.7 pF / 10 cm. Further, this board endured manual soldering at 220 ° C. for 10 seconds.

[0031]

[Example 2] Silane-modified polypropylene (manufactured by Mitsubishi Petrochemical Co., Ltd., melt flow rate 11, dry blend of 5 parts by weight of catalyst masterbatch) was used, and the thickness was 25.
A porous polypropylene film having a porosity of 70% and a porosity of 31% was prepared by a method of immersing it in water at 80 ° C. for 24 hours to obtain a porous polypropylene film having a gel fraction of 31% by heat extraction.

Propylene-maleic anhydride copolymer (maleic anhydride content 5%, melt flow rate 4) (a)
And ethylene-ethyl acrylate-carbon monoxide copolymer (ethyl acrylate content 11%, carbon monoxide content 5
%, Melt flow rate 10) (b) mixture [(a)
And (b) are mixed in a mixing ratio of 1: 1] to form a film having a thickness of 20 μm by a melt molding method.
An electron beam of 0 kV was irradiated at 3 Mrad to form a B stage.

A 25 μm thick B-staged adhesive having a thickness of 20 μm is provided on one side of the porous polypropylene film.
A biaxially stretched polyester film with a thickness of 35 μm and an electrolytic copper foil with a thickness of 35 μm on the other side were thermocompression bonded at a surface pressure of 10 kg / cm ² for 3 minutes using a hot press machine at 170 ° C., and then fixed by water cooling under pressure. Then, the single-sided plate shown in FIG. 2 was obtained. An electron beam having an accelerating voltage of 2 MV was irradiated with 10 Mrad from the polyester film side of the one-sided plate to cure the adhesive layer.

A polyester film having a thickness of 25 μm and a porous polypropylene film having a gel fraction of 34% used in Example 1 were heat-pressed at 170 ° C. using a B-staged adhesive having a thickness of 20 μm. The lamination was performed to obtain the insulating base material shown in FIG.

After forming a stripe-shaped circuit having a circuit width of 1 mm and a circuit interval of 1 mm from the copper foil layer shown in FIG. 2 by an etching method, this one-sided plate was immersed in hot water at 70 ° C. for 6 hours,
The porous polypropylene layer was further crosslinked.

After the porous polypropylene film side of the insulating base material shown in FIG. 3 was laminated on a strip-shaped circuit by using a heat pressing device at 180 ° C., an electron beam with an accelerating voltage of 200 kV was irradiated at 10 Mrad, and the figure The porous polypropylene film layer on the insulating substrate side shown in 2 was cross-linked and the adhesive layer was cured to obtain a double-sided circuit board having a laminated structure shown in FIG.

The capacitance between the circuits A and C of the circuit board shown in FIG. 4 was 0.8 pF / 10 as a result of measurement at 1 MHz.
The circuit length was cm. Further, this board endured manual soldering at 220 ° C. for 10 seconds.

[0038]

Example 3 The shield layer D shown in FIG. 5 is formed by cutting the double-sided circuit board shown in FIG. 4 of Example 2 into a width of 100 mm and applying a silver paste around the biaxially oriented polyester.
A formed circuit board was obtained. As a result of measuring the electrostatic capacitance between the shield layer D and the circuit A at 1 MHz, the average is 27 pF / 10 cm.
It was the circuit length.

[0039]

[Comparative Example 1] Thermoplastic saturated copolyester adhesive on both sides of a biaxially oriented polyester film [TOYOBO CO., LTD.
Manufactured, melting point 125 ° C., glass transition point −28 ° C., melt viscosity 2,000 poise (200 ° C.)] to a thickness of 15 μm, and then a hot pressing machine at 180 ° C. is used to form 35 μm thick electrolytic copper on both sides. The foil was placed, thermocompression-bonded at a surface pressure of 20 kg / cm ² for 5 minutes, and then fixed by water cooling under pressure to obtain a double-sided circuit board shown in FIG.

The copper foil of this double-sided plate was made into a striped electrode having a circuit width of 1 mm and a circuit interval of 1 mm by an etching method. As a result of measuring the capacitance between the circuits A and B at 1 MHz, 41
It was found that the circuit length was pF / 10 cm and that between the circuits A and C was 1.9 pF / 10 cm, and the capacitance was much larger than the result of Example 1.

[0041]

[Comparative Example 2] A biaxially stretched polyester film having a thickness of 25 µm and an electrolytic copper foil having a thickness of 35 µm were used in Example 1 with a thickness of 15 µ
After being bonded by a hot press machine at 180 ° C. using an adhesive of m, a copper foil was formed into a striped circuit having a circuit width of 1 mm and a circuit interval of 1 mm by an etching method.

After the above adhesive was formed on one surface of a biaxially stretched polyester film having a thickness of 75 μm to a thickness of 35 μm, the adhesive surface was laminated on a copper foil circuit by a hot press machine at 180 ° C. The laminated circuit board shown in was obtained.

The capacitance between the circuits A and C on the circuit board of FIG. 7 was 2.1 pF / 10 cm as a result of measurement at 1 MHz, and the capacitance was much larger than that of the second embodiment. It turned out to be big.

[0044]

COMPARATIVE EXAMPLE 3 The circuit board shown in FIG. 7 was cut into a width of 100 mm, and the silver paste was used in the same manner as in Example 3 to obtain the circuit board with the shield layer shown in FIG. Shield layer D
As a result of measuring the capacitance between the circuit A and the circuit A at 1 MHz, 75
It was found that the circuit length was pF / 10 cm and the electrostatic capacity was much larger than the result of Example 3.

[0045]

As described above, according to the present invention, the electrostatic capacitance between the conductor circuits or between the conductor circuits and the shield layer can be reduced without using the expensive porous polytetrafluoroethylene film. A small circuit board suitable for transmitting high-frequency current can be obtained, and its utility value as a circuit board for wiring in equipment such as computers and communication equipment is very high.

[Brief description of drawings]

FIG. 1 is a schematic view showing a laminated structure of a circuit board having copper foil layers on both sides obtained in Example 1.

2 is a schematic diagram showing a laminated structure of a single-sided board having a copper foil layer on one side obtained in Example 2. FIG.

FIG. 3 is a schematic diagram showing a laminated structure of an insulating substrate obtained in Example 2.

FIG. 4 is a schematic view showing a laminated structure of a double-sided circuit board obtained by laminating the single-sided substrates of FIGS.

5 is a schematic view showing a laminated structure in which a shield layer is formed around the double-sided circuit board of FIG.

FIG. 6 is a schematic view showing a laminated structure of a double-sided circuit board obtained in Comparative Example 1.

7 is a schematic diagram showing a laminated structure of a circuit board obtained in Comparative Example 2. FIG.

8 is a schematic diagram showing a laminated structure of a circuit board obtained in Comparative Example 3. FIG.

Claims (5)

[Claims] 1. A structure shown in Table 1 or 2 below: [Table 2] A wiring board having a conductor circuit fused and laminated on a porous polypropylene film. 2. The structure shown in Table 3 below: The wiring board according to claim 1, wherein the polymer film is laminated on one surface of a porous polypropylene film having the following. 3. The structure shown in Table 4 below: The wiring board according to claim 1 or 2, wherein the porous polypropylene film is fusion-laminated on the conductor circuit having the above-mentioned. 4. Structures shown in Table 5 below: The wiring board according to claim 3, wherein the polymer film is laminated on the porous polypropylene film fusion-bonded and laminated on the conductor circuit, which has: 5. The structure shown in Table 6 below: The wiring board according to any one of claims 1 to 4, wherein the porous polypropylene film having: is crosslinked by irradiation of ionizing radiation or water crosslinking.