JPS61277208A - Dielectric substrate and its production - Google Patents

Abstract

PURPOSE:To reduce the dielectric constant and the dielectric loss tangent by joining electrolytic copper foils to both faces of a dielectric base material through crosslinked super molecular weight polyethylene layers so that surfaces opposite to specular surfaces of copper foils are brought into contact with super molecular weight polyethylene layers. CONSTITUTION:With respect to a dielectric substrate, two dielectric base materials each of which consists of a glass cloth 1 and a crosslinked polyethylene layer which is impregnated in the cloth 1 and covers surfaces of the cloth 1, and crosslinked UHPE layers 3 are arranged on both faces of these laminated base materials, and electrolytic copper foils 4 are arranged on UHPE layers 3 so that rough surfaces 5 of foils 4 face crosslinked UHPE layers 3, and they are joined into one body. A crosslinked polyethylene layer 6 is provided as desired for the purpose of adhering base materials to each other more firmly. UHPE films are crosslinked by irradiation of an electron beam or the like, and it is preferably from the aspect of adhesion that UHPE films are crosslinked in such degree that the gel rate is 30-100%, and it is obtained if the exposure of the electron beam is 0.1-10M rad normally. Thus, the dielectric constant and the dielectric loss tangent are reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a dielectric substrate suitable for manufacturing a microwave receiving planar antenna and a method for manufacturing the same.

(Prior Art) As a microwave receiving planar antenna, a patterned strip conductor made of electrolytic copper foil is laminated on one side of a sheet-like dielectric base material, and a ground conductor made of electrolytic copper foil is laminated on the other side.
Further, there are known structures in which a reinforcing body made of a fiber-reinforced plastic plate, an aluminum plate, or the like is provided on the ground conductor, if desired. In this planar antenna, the electrolytic copper foils are stacked so that the surface opposite to the mirror surface faces the dielectric base material.

(Problems to be Solved by the Invention) Important characteristics required of a microwave receiving planar antenna include a small dielectric constant and a small dielectric loss tangent.

It is known that the dielectric constant and dielectric loss tangent of the antenna are influenced by the dielectric base material that constitutes the antenna.

In addition, in this antenna, consideration must be given to the adhesive strength between the dielectric base material and the copper foil forming the strip conductor and the ground conductor.

By the way, conventionally, the base material for the dielectric substrate used to make this antenna is plastic! - There is a method in which glass cloth is embedded within the interior, and these methods include (a) spraying and coating the glass cloth with epoxy resin powder, and then laminating the glass cloths coated with this spray coating;
Alternatively, (b) it is obtained by dip coating a glass cloth with a fluororesin dispersion spray, drying it, and then laminating the dip coated glass cloths together.

However, test samples based on JIS C6481 were prepared, and their permittivity and dielectric loss tangent were determined to be 1 MHz.
When measured, the dielectric base material obtained by method (a) has a relative permittivity of about 4 to 5 and a dielectric loss tangent of about 0.01 to 5.
0.03, the dielectric base plate obtained by the L(b) method has a relative dielectric constant of about 2.2 to 2.8, and a dielectric loss tangent of about 0.00.
1 to 0.003, and there is still room for improvement in both of these characteristics.

In the dielectric base material in the above method (a), since an epoxy resin having a large dielectric constant and a large dielectric loss tangent is used as a plastic component, both of these characteristics are not reduced. On the other hand, although the dielectric base material produced by method (b) uses a fluororesin as a plastic component, which has a very low dielectric constant and dielectric voltage contact, it is expensive and has a tendency to dissipate into glass cloth. The drying and firing temperature after dip coating of Pagecon is extremely high at 350 to 400°C. Similarly, press molding of the dielectric base material also requires high temperatures and is extremely expensive in terms of equipment. Therefore, its uses are limited.

Another reason why the dielectric constant and dielectric loss tangent of the dielectric base material obtained by these conventional methods are not sufficient is that the penetration of the resin into the fiber bundles that make up the glass cloth in the dielectric base material is insufficient; This may also be due to the non-penetrated areas being scattered unevenly.

Therefore, an object of the present invention is to provide a dielectric substrate with a small dielectric constant and a small dielectric voltage contact.

(Means for Solving the Problems) First, in order to improve the dielectric constant and dielectric voltage contact of the dielectric base material, the inventors of the present invention found that polyethylene (hereinafter referred to as PE) was added to the inside of the glass cloth as a result of various studies. ), the surface of the cloth is covered with PE, and this PE is further impregnated with PE.
It was discovered that this purpose could be achieved by cross-linking.

By the way, a dielectric substrate has a structure in which copper foil is bonded to both sides of a dielectric base material, but the inside of a glass cloth is impregnated with PK, the surface of the cloth is covered with PE, and the surface of the cloth is further coated with PE. A new problem arose in that the dielectric base material cross-linked with PK had low adhesive strength with the surface opposite to the mirror surface of the electrolytic copper foil.

The inventors of the present invention have further investigated this problem and have found that sufficient adhesion can be achieved by bonding the dielectric base material and electrolytic copper foil via cross-linked ultra-high molecular weight polyethylene (hereinafter referred to as UHPE). It was also found that strength can be obtained.

The present invention was completed based on these findings and provides a dielectric substrate having a novel structure.

That is, the present invention has an electrolytic copper foil bonded to both sides of a dielectric base material consisting of a glass cloth and a crosslinked PE layer impregnated into the glass cloth and covering the surface through a crosslinked UHPE layer. C. The copper foil has a cross-linked UH surface opposite to its mirror surface.
This dielectric substrate is characterized by being in contact with PEHJ.

In the dielectric base material used in the present invention, PE is impregnated inside the glass floss, a PK thin layer is formed on the surface of the cloth, and PE existing inside and on the surface of the cloth is cross-linked. This is what is happening.

The degree of cross-linking of PE with is due to the effect of improving the adhesion between PE and glass cloth, and the effect of UH interposed between the base material and electrolytic copper foil.
Adhesive strength with PE layer or overlapping two or more base materials,
Considering the adhesive force between the base materials when these are bonded together, the gel fraction (the measurement method will be described later) is set to 10% or more, preferably 20 to 90%.

PI as a constituent material of the dielectric base material can be any of low density, medium density, and high density PE.

One piece of this dielectric base material is used, and both sides of the dielectric base material are cross-linked with UH.
Electrolytic copper foil may be bonded via a PE layer, or two or more of the base materials may be stacked, and copper foil may be bonded to both sides of the stacked base materials via a crosslinked UHPE layer. .

Cross-linked UHPE for bonding dielectric base material and electrolytic copper foil
The layer can be formed using UHPE, which is commercially available under trade names such as Hi-Zex Million (manufactured by Mitsui Petrochemicals) and Hostalen GUR (manufactured by Hoechst).

The degree of crosslinking of UHPBH is such that its del fraction is 30 to 30 to increase the adhesive strength with the dielectric base material and electrolytic copper foil.
It is preferable to set it to 100%.

UHPE has a molecular weight of about 500,000 or more (measured by a viscosity method), which is larger than that of general polyethylene, which is about 100,000 or less.

On the other hand, as the copper foil bonded to the dielectric base material via the crosslinked UHPE layer, electrolytic copper foil can be used without particular limitation.

When producing the electrolytic foil, the surface (mirror surface) that comes into contact with the drum (roll) K is glossy and has a small degree of surface unevenness, and the surface opposite to the mirror surface (hereinafter referred to as the rough surface) is glossy. Moreover, the surface roughness is larger than that of a mirror surface, and in the present invention, the electrodeposited copper foil is bonded with the rough surface facing the crosslinked UHPE layer.

The present inventors investigated how to improve the operating gain of a microwave receiving planar antenna obtained from a dielectric substrate with a structure in which copper foil is bonded to both sides of the dielectric substrate. Not only did we discover that this objective can be achieved by reducing the roughness of the surface, but we also clarified this theoretically, which will be explained below.

The steel loss α'C when considering the surface roughness of the copper foil is as follows (1
) is expressed by the formula.

α'c = aa (1+"tan-' (1,4(
-e-)2J) ----=-(1)π By the way, the unevenness on the surface of the copper foil is schematically shown as shown in FIG. In the copper foil K shown in FIG. 2, minute irregularities exist continuously on the surface corresponding to the dielectric layer.

In the figure, q indicates the average value of the vertical distance between the peaks and valleys of fine irregularities on the surface of the copper foil, and p similarly indicates the average value of the horizontal distance between adjacent peaks or valleys.

Here, σ is electrical conductivity, Rs is surface resistance (1), and Rs is expressed by the following equation (4).

In the above formula (4), μ0 is magnetic permeability and f is frequency.

Next, equation (4) is substituted into equation (3) to obtain equation (5).

The physical property value of copper σ = 5.81X10” (Ω-1・
1-1), and μ is vacuum permeability po = 4 w
X 10-' (Henry/(X), and Kf is 11.95 GHz as a typical value used for broadcast satellite
Using 3 = o, 6o5 (μm).

By the way, the values of p and q of the rough surface of electrolytic copper foil are 1 to 1Oμ-p according to the measurement results of surface roughness meter, electron microscope, etc.
is about 10 to 30μ.

Therefore, as an example for electrolytic copper foil, if q = sμ false, △ = 1.443μ, and therefore α6 = 1.92
αc, similarly (1”3 μfi, l, 5 μm and 0.
Using 7μ shock, α′C is 1.78αc and 1.4, respectively.
0αC and 1.10αC. These results clearly demonstrate theoretically that the smaller the unevenness of the copper foil surface, the smaller the copper loss.

As described above, reducing the surface roughness of the copper foil improves the operational gain of the antenna, but reducing the surface roughness reduces the adhesive strength between the copper foil and the dielectric base material.

The inventors of the present invention have repeatedly studied this point, and found that when the surface roughness of the electrolytic copper foil is set to 1 to 4.5μ, the dielectric constant and dielectric loss tangent are small, and when used as an antenna. 11@Ij-11■■1m5s■11■■-
- I learned that the best results can be obtained with a dielectric substrate.

FIG. 1 shows a dielectric substrate according to the present invention, which has a thickness of approximately 30 to 30 mm.
Two dielectric substrates consisting of a glass cloth 1 with a 200μ groove and a cross-linked polyethylene layer 2 impregnated inside the cloth 1 and covering its surface are stacked on top of each other, and on both sides of this stacked substrate, A cross-linked UHPE 713 with a thickness of about 20 to 200 μm is placed, and an electrolytic copper foil 4 with a thickness of about 10 to 100 μm above the UHPE layer 3 is placed and bonded with its rough surface 5 facing the cross-linked UHPE layer 3. It is integrated. Reference numeral 6 denotes a crosslinked polyethylene layer provided as desired to strengthen the adhesion between the base materials.

In the present invention, when manufacturing such a dielectric substrate, PE films are placed on both sides of a glass cloth and heated and pressed. At least obtain a dielectric base material, then crosslink the PE in the base material, and then apply the crosslinked UHPE film and electrolytic copper foil to both sides of the base material so that the rough surface of the copper foil is in contact with the UHPE film. The feature is that the base material and the electrolytic copper foil are bonded by sequentially stacking them on top of each other and then applying heat and pressure.

In the manufacturing method of the present invention, PE films are first placed on both sides of a glass cloth and then heated and pressed. This heating and pressing can be done by overlapping PE films on both sides of the glass cloth and heating and pressing them using a lamination press machine, or by melting and extruding PE into a film on both sides of the glass cloth and then rolling it between rolling rolls. This can be done by a method of heating and pressurizing the mixture through the process.

The PE film used here can be any film formed from low density, medium density, or high density PE. The practical thickness of these PE films is about 20 to 250 μm.

The working conditions for heating and pressurizing PE film and glass cloth are that the temperature must be above the melting temperature of PE, and the pressure must be approximately 3~
The heating and pressurizing time is set to about 50 kg/J and about 5 to 60 minutes.

By placing the PE film on both sides of the glass cloth and applying heat and pressure in this way, the glass cloth is impregnated with PE, and the PE film and the glass cloth are bonded under heat and pressure to obtain a dielectric base material.

This dielectric substrate is then crosslinked with its constituent PE. Cross-linking of PE is about 0.5~
This can be carried out by heating and pressurizing a film irradiated with 20 Mrad, a silane compound mixed in advance into a PE film, a radical generator, and a siloxane condensation catalyst.

This crosslinking is mainly caused by f! between PE and glass cloth. This is done to improve the adhesion strength, and even if the dielectric substrate cross-linked with PK is deformed due to stress, it is difficult for the interface between the PK and the glass cloth to peel off. Has characteristics. As mentioned above, crosslinking of PE is carried out so that the del fraction is usually 10% or more,
Preferably it is 20-90%.

The gel fraction can be measured, for example, by the following method.

After the copper foil on the dielectric substrate is completely removed by etching or the like, it is thoroughly washed with water and dried. This is a certain amount of small pieces (X,
! Cut out the sample and incubate the sample in xycin at 105°C (approximately 200 to 500 times the volume of the sample) for 2 hours.
After refluxing for 4 hours, the mixture was separated and thoroughly dried to determine the amount of insoluble gel (Y, !iF). This is then incinerated in a crucible to determine the weight of only the glass cloth (CZJ), which is calculated according to the following formula.

Further, in the case of a crosslinked PE film or crosslinked UI (PE film, the above-mentioned ashing treatment is not necessary and corresponds to z=0.

In this way, in the present invention, PE in the dielectric base material is crosslinked, and such crosslinking of the base material before lamination has the advantage of making the degree of crosslinking uniform in the thickness direction of the base material.

In the present invention, U crosslinked in advance is applied to both sides of the dielectric base material crosslinked with PK as described above.
HPE film and electrolytic copper foil coat the rough surface of the copper foil with UH
The dielectric base material and the electrolytic copper foil are bonded together using the UHPE film as an adhesive layer by superimposing them so as to be in contact with the PE film and applying heat and pressure.

At this time, a single dielectric base material may be used, but two or more dielectric base materials may be used in a stacked manner so as to have a predetermined thickness. In addition, when using two or more dielectric substrates stacked together, an adhesive material, such as a crosslinked PE film (
A gel fraction of 20 to 100%) may be present.

The UHPE film for joining the dielectric base material and the electrolytic copper foil usually has a thickness of 20 to 200 μm and is crosslinked by electron beam irradiation or the like. From the viewpoint of adhesion, the degree of crosslinking of this UHPI film is approximately 30 to 10.
It is preferable to perform this so that it becomes 0%-. Therefore, the crosslinked UHPE film having the above del fraction is
Although it depends on other conditions, the amount of electron beam irradiation is usually 0.1 to 1.
This can be obtained by setting it to 0 Mrad.

The working conditions when joining the dielectric base material and the electrolytic copper foil via the crosslinked UHPE film can be set as appropriate depending on the degree of crosslinking of the PE constituting the dielectric base material, the degree of crosslinking of the UHPE film, etc. Usually temperature 145-200℃, pressure 5-3
The temperature was 0 to 9/e4, and the heating and pressurizing time was 5 to 60 minutes.

In the dielectric substrate obtained in this way, PE has sufficiently penetrated into the fiber bundles constituting the glass cloth, and as is clear from the examples described later, this dielectric substrate has a dielectric constant and Both have small tangents, making them useful as insulating materials. The reason for this is not necessarily clear, but when PE films are placed on both sides of glass cloth and heated and pressurized, the
It is inferred that this is because K is melted and pressure is applied to the molten PE, thereby promoting the impregnation of PE into the fiber bundle of the glass cloth.

(Example) Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 Density 0.92 on both sides of 100μ thick duck glass cloth
A 50 μm PE film made of
The glass cloth was heated and pressurized for 10 minutes under the conditions of kg/-j to impregnate the inside of the glass cloth with PE, and the PE film and the glass cloth were bonded under heat and pressure to obtain a dielectric base material having a thickness of 145 μm.

Next, this dielectric base material is irradiated with an electron beam of 6.5 M rad to crosslink PE (gel fraction 55%).

On the other hand, in addition to this, a UHP E sheet with a thickness of 130μ made from UHPE with 477.31 million molecules was
Crosslink by irradiating with Mrad electron beam (gel fraction 98%)
).

Thereafter, two dielectric base materials cross-linked with PE are superimposed, and the cross-linked UHP is applied to both sides of the superimposed base materials.
An E film and an electrolytic copper foil having a thickness of 35 μm (surface roughness of the rough surface is 3 μm) are sequentially arranged so that the rough surface of the copper foil faces the UHPE film.

Note that the PK having a density of 0.92 is provided between the dielectric base materials.
A film having a thickness of 200 .mu.m and a gel fraction of 48% was interposed therebetween, and was cross-linked by 5 Mrad O electron beam irradiation.

Next, these were put into a lamination press machine at a temperature of 170°C and a pressure of 15 kl. The substrates were heated and pressurized for 30 minutes under the conditions of /I4 to bond the substrates together and the substrate and the copper foil to obtain a dielectric substrate (sample number 1).

Note that the surface roughness of the electrolytic copper foil was measured using a Super 1 Rasa inspection machine, model AB-2, manufactured by Mitoyo Seisakusho Co., Ltd.

The results obtained by measuring the dielectric constant, dielectric loss tangent, adhesive force between the copper foil and crosslinked UHP E layer of the dielectric substrate, and the operational gain of this dielectric substrate are shown in Table 1 below.

The measurement frequency of the dielectric constant and dielectric loss tangent is IMHz.

Further, the adhesive strength was measured by the 180 peeling method under the conditions of a temperature of 25° C. and a peeling rate of 50 H/min.

To measure the operating gain, one copper foil of the dielectric substrate was etched to form a pattern to obtain a microwave receiving planar antenna, and the operating gain (G) of this antenna was measured. This antenna is 446×436-1 number of elements = 1
There were 6 elements x 32 rows.

For this measurement, a method of comparison with a standard antenna was used.

As shown in Fig. 3, a transmitting antenna 6 is connected to the transmitter (CW oscillation), and a standard antenna 7 with a gain of Ga (dBi) is connected to the receiver. By appropriately rotating the
Transmit horizontally polarized waves and measure the amplitude ratio of a standard antenna. Next, a planar antenna is connected to the receiver instead of the standard antenna, and the amplitude ratio of the planar antenna is measured in the same manner.

The operating gain G (dBl) of the planar antenna is determined by the following equation.

G = Gs + (amplitude ratio of planar antenna (dB))
- [Amplitude ratio of standard antenna (dB)) + Correction for C circular polarization (dB)) The correction value for circular polarization in the above formula is 3 dB.

Dielectric substrates of sample numbers 2.3 and 4 were obtained in the same manner as in Example 1 except that electrolytic copper foils with rough surfaces of 1.5 μm, 4.5 μm, and 10 μm were used. Ta. The characteristics of these substrates are shown in Table 1.

Example 3 Sample No. 5 was prepared in the same manner as in Example 1 except that the electron beam irradiation amount to the dielectric base material was 2.5 Mrad and 12 Mrad, and the gel fraction of PE was 20% and 70%. and 6 dielectric substrates were obtained.

(Effects of the Invention) The present invention is constructed as described above, and as can be seen from the examples, a glass cloth is impregnated with PE and the surface of the cloth is covered in a thin layer to serve as a dielectric base material.
It is characterized by low dielectric constant and dielectric loss tangent.

In addition, in the manufacturing method of the present invention, PE films are placed on both sides of the glass cloth, and the dielectric base material is obtained by heating and pressing the films, so that the penetration of PE into the glass cloth is ensured and sufficient. Moreover, since the polyethylene, which is a component of the dielectric base material, is cross-linked and then the base materials are bonded together, the adhesive strength between the polyethylene film and the glass cloth is improved.

[Brief explanation of the drawing]

FIG. 1 is a front view showing an example of a dielectric substrate according to the present invention;
. FIG. 2 is a schematic diagram showing the surface roughness of copper foil, and FIG. 3 is a circuit diagram for measuring the operating gain.

Claims (5)

[Claims] (1) Electrolytic copper foil is bonded to both sides of a dielectric base material consisting of a glass cloth and a crosslinked polyethylene layer impregnated into the glass cloth and covering the surface through a crosslinked ultra-high molecular weight polyethylene layer. , a dielectric substrate characterized in that the opposite surface of the copper foil is in contact with an ultra-high molecular weight polyethylene layer. (2) The dielectric substrate according to claim 1, wherein two or more dielectric substrates are stacked on top of each other. (3) The dielectric substrate according to claim 1 or 2, wherein the surface of the electrolytic copper foil in contact with the ultra-high molecular weight polyethylene layer has a surface roughness of 1 to 4.5 μm. (4) By placing polyethylene films on both sides of the glass cloth and applying heat and pressure, the glass cloth is impregnated with polyethylene, and the polyethylene film and the glass cloth are bonded under heat and pressure to obtain a dielectric base material. Cross-linked polyethylene and then cross-linked ultra-high molecular weight polyethylene film and electrolytic copper foil on the screen of the base material are sequentially stacked so that the opposite mirror surface of the copper foil is in contact with the ultra-high molecular weight polyethylene film, and then A method for manufacturing a dielectric substrate, characterized by joining a base material and electrolytic copper foil by applying heat and pressure. (5) A dielectric base material is irradiated with radiation to cross-link polyethylene, and then two or more dielectric base materials cross-linked with polyethylene in this manner are stacked together as described in claim 4. A method for manufacturing a dielectric substrate.