JP7467252B2 - Circuit wiring board and its manufacturing method - Google Patents

Description

The present invention relates to a circuit wiring board in which electrodes are formed on a base film, and by forming an optical waveguide or the like on the top of the circuit wiring board of the present invention, it can be applied to photoelectric conversion elements (optical modulators) in next-generation communication networks. Photoelectric conversion elements (optical modulators, etc.) are devices that convert electrical signals into optical signals by modulating the intensity of a light source using a certain conversion circuit in optical communications using optical fibers, and vice versa, converting optical signals into electrical signals.

The cyclic olefin resin used in the base film of the present invention is a resin with extremely low water absorption and moisture permeability, as well as excellent dielectric properties, and is one of the candidates for circuit board materials compatible with millimeter wave bands, which are expected to be used in next-generation communication networks.

・・・式（１） Conventionally, there is an invention of a circuit wiring board (touch sensor) in which electrodes are formed on a substrate film made of a cyclic olefin resin, as disclosed in Patent Document 1. In the invention of Patent Document 1, the substrate film is mainly composed of a hydrogenated ring-opening metathesis polymer having a ring structure in which the substituents _R1 and _R2 of formula (1) are linked, and the electrodes are copper electrodes, and the invention is characterized by its transparency, heat resistance, and the like.

...Equation (1)

Patent No. 6267056

However, the hydrogenated ring-opening metathesis polymer having a ring structure in which the substituents R ₁ and R ₂ of the formula (1) are connected becomes amorphous as the ring structure becomes larger. Although the transparency is excellent, there is a problem that the dielectric properties tend to decrease slightly. Since high transparency is an essential characteristic for touch sensor applications, a slight decrease in high dielectric properties is acceptable, but such properties are inappropriate for circuit wiring boards for photoelectric conversion elements compatible with millimeter wave band communication, which require high dielectric properties.

Furthermore, the more amorphous the film becomes, the lower the chemical adhesion to electrodes such as metal materials, and the smoother the surface becomes, which also leads to a problem of a physical decrease in adhesion to the electrode. Therefore, in order to maintain a certain level of adhesion strength, it is necessary to provide an anchor layer made of another material between the base film and the electrode such as a metal material, but the relatively poor dielectric property performance of this anchor layer causes a significant decrease in the dielectric properties of the entire circuit wiring board. In order to solve these problems, the inventors have invented the following circuit wiring board.

That is, the first characteristic feature of the present invention is a circuit wiring board in which an electrode is formed in direct contact with the surface of a base film, the base film being composed primarily of a cyclic olefin resin with a crystallinity of 1% to 30%, the arithmetic mean roughness Ra of the base film surface being 0.01 to 0.3 μm, and the electrode being a metal film with a thickness 3 to 20 times the arithmetic mean roughness Ra of the base film surface.

・・・式（１） A second characteristic feature of the present invention is a circuit wiring board in which the electrodes are formed of an antenna receiving or transmitting electrode pattern formed on one surface of the base film and a ground electrode formed on the other surface of the base film. A third characteristic feature of the present invention is a circuit wiring board in which the cyclic olefin resin has a structure of C _n H _2n+1 (n = 0 to 8) in which the substituents R ₁ and R ₂ in formula (1) are not connected to each other.

...Equation (1)

The fourth characteristic feature of the present invention is a circuit wiring board in which an optical waveguide is formed on top of an electrode. The fifth characteristic feature of the present invention is a method for manufacturing a circuit wiring board in which the surface of a base film is irradiated with ultraviolet light or treated with plasma so that the arithmetic mean roughness Ra of the surface is 0.01 to 0.3 μm, and an electrode that is a metal film and has a thickness 3 to 20 times that of the arithmetic mean roughness Ra is formed on the surface.

According to the first characteristic configuration of the present invention, the circuit wiring board of the present invention is a circuit wiring board in which an electrode is formed directly on and in contact with the surface of a base film, and is characterized in that the base film is mainly composed of a cyclic olefin resin with a crystallinity of 1% to 30%, the arithmetic mean roughness Ra of the base film surface is 0.01 to 0.3 μm, and the electrode is a metal film with a thickness 3 to 20 times the arithmetic mean roughness Ra of the base film surface. Therefore, since the C-H bonds in the crystalline part of the base film are almost regularly and densely oriented, the base film surface also has appropriate unevenness suitable for millimeter wave band communication, and the metal film electrode is also in a thickness range suitable for the unevenness of the base film surface, by performing a process to cut some of the C-H bonds and modify them into functional groups that have affinity with the electrode material, it is possible to obtain a circuit wiring board suitable for millimeter wave band communication in which an electrode with high adhesive strength to the base film is formed.

The second characteristic feature of the present invention is that the electrode is a circuit wiring board consisting of an antenna receiving or transmitting electrode pattern formed on one side of the base film and a ground electrode formed on the other side of the base film. Therefore, the ground electrode and base film shield radio wave noise coming from the back, which has the effect of improving the performance of the antenna receiving or transmitting. In addition, since each electrode pattern is formed in direct contact with the base film with high dielectric properties, there is little attenuation of the received or transmitted electrical signal, and it is possible to obtain a circuit wiring board suitable for high-performance millimeter wave band communication.

According to a third characteristic configuration of the present invention, the cyclic olefin resin is characterized in that the substituents _R1 and _R2 in formula (1) are not linked and have a structure of _{CnH2n +1} (n = 0 to 8). Therefore, since the substituents are not bulky, the polymer main chain is likely to be regularly oriented, and there is an effect that it is easy to produce a cyclic olefin resin with a large amount of crystalline portion.

Furthermore, according to a fourth characteristic configuration of the present invention, the circuit wiring board of the present invention is characterized in that it is a circuit wiring board in which an optical waveguide is formed on the upper part of the electrode. Therefore, it is possible to obtain a photoelectric conversion element having a substrate made of a cyclic olefin resin. As a result, it is possible to obtain a very high-performance photoelectric conversion element suitable for millimeter wave band communication.

Furthermore, according to a fifth characteristic configuration of the present invention, the method for manufacturing a circuit wiring board of the present invention is characterized in that the surface of a base film is irradiated with ultraviolet light or treated with plasma so that the arithmetic mean roughness Ra of the surface is 0.01 to 0.3 μm, and an electrode that is a metal film with a thickness 3 to 20 times the arithmetic mean roughness Ra is formed on the surface. Therefore, irradiation with ultraviolet light or plasma gas has the effect of forming a finely uneven surface on the surface of the base film that is suitable for millimeter wave band communication and contributes to improving adhesion strength.

1 is a schematic cross-sectional view showing an example of a circuit wiring board according to a first characteristic configuration of the present invention. FIG. 4 is a schematic perspective view showing an example of a circuit wiring board according to a second characteristic configuration of the present invention. FIG. 11 is a schematic cross-sectional view showing an example of a circuit wiring board and a photoelectric conversion element according to a fourth characteristic configuration of the present invention. FIG. 11 is a schematic perspective view showing an example of a circuit wiring board and a photoelectric conversion element according to a fourth characteristic configuration of the present invention.

The following describes an embodiment of the circuit wiring board according to the present invention with reference to the drawings. The circuit wiring board 1 of the present invention is a circuit wiring board in which an electrode 20 is formed directly on and in contact with a base film 10, the base film 10 being mainly composed of a cyclic olefin resin with a crystallinity of 1% to 30%, the arithmetic mean roughness Ra of the surface of the base film 10 being 0.01 to 0.3 μm, and the electrode 20 being a metal film with a thickness 3 to 20 times the arithmetic mean roughness Ra of the surface of the base film 10 (see FIG. 1).

The crystallinity of the cyclic olefin resin of the substrate film 10 is measured by X-ray diffraction, and the crystalline portion that forms the peak shape portion and the amorphous portion that forms the baseline portion are fitted, and the crystallinity is calculated by substituting each integrated intensity into the following formula: In the formula, X represents the crystalline scattering integrated intensity (i.e., the scattering integrated intensity derived from the crystalline portion), and Y represents the amorphous scattering integrated intensity (i.e., the scattering integrated intensity derived from the amorphous portion).
Crystallinity (%) = [X / (X + Y)] x 100

・・・式（１） Examples of the cyclic olefin resin having a crystallinity of 1% to 30% include cyclic olefin resins in which the substituents R ₁ and R ₂ in formula (1) are not connected and have a structure of C _n H _2n+1 (n = 0 to 8). In the case of a cyclic polyolefin polymer having a ring structure in which the substituents R ₁ and R ₂ in formula (1) are connected, the bulky substituents increase the distance between the main chains of the polymer, inhibiting the orientation of the main chains of the polymer, and as a result, the polymer tends to become an amorphous polymer with a crystalline portion of less than 1%.

...Equation (1)

By carrying out some kind of surface modification treatment on the cyclic olefin resin surface of the base film 10, some of the C-H bonds are cut and converted into functional groups such as -OH groups, -COOH groups, and -CO groups that have affinity with metal materials, etc., thereby improving the adhesive strength between the base film 10 and the electrode 20.

In particular, since the C-H bonds in the crystalline portion are oriented almost regularly and densely, modifying these portions with the above-mentioned functional groups can effectively improve the adhesive strength. Therefore, the higher the crystallinity, the more effectively the adhesive strength can be improved, so it is preferable that the substituents _R1 and _R2 have a low value of n in C _n H _2n+1 . If the value of n is large, such as exceeding 8, there is a tendency for there to be no significant difference from the case of a substituent in which _R1 and _R2 are connected.

Furthermore, by forming fine irregularities 11 on the surface of the base film 10 (see Figure 1) and forming an electrode 20 directly on that surface, metal particles and the like are deposited so as to penetrate into the deep recesses of the fine irregularities 11, and this anchor effect can further improve the adhesive strength between the base film 10 and the electrode 20.

However, if the surface of the base film 10 is made uneven with large projections and recesses on the order of tens to hundreds of microns, as is done in general plating methods, the path of the electrical signals that move within the electrode 20 near the interface with the base film 10 is reduced, which creates problems when applied to millimeter wave-compatible circuit boards, where a high proportion of electrical signals move near the interface. Therefore, it was necessary to newly invent and devise a shape of fine projections and recesses 11 that maintains the anchor effect while ensuring sufficient paths for electrical signals that move near the interface, and a method for producing the same.

After much ingenuity in determining what the appropriate shape of the fine irregularities 11 should be, the inventors discovered that if the fine irregularities 11 have an arithmetic mean roughness Ra of 0.01 to 0.3 μm, the anchor effect can be maintained while a sufficient path for electrical signals moving near the interface can be secured. In other words, if Ra is less than 0.01 μm, sufficient adhesion strength cannot be obtained, and if Ra is more than 0.3 μm, it is insufficient for application to circuit boards compatible with millimeter wave band waves (see Table 1).

Furthermore, after much ingenuity in figuring out how to produce the fine irregularities 11, they invented a method of surface modification using ultraviolet irradiation or plasma treatment under specific conditions. Thermal imprinting is one method, but it is not very suitable for endless mass production over a large area. Corona discharge treatment, which is also widely used, is also one method, but the set conditions for stably forming the fine irregularities 11 within the above range are narrow.

The conditions for surface modification by ultraviolet irradiation are, for example, to use an ultraviolet lamp and irradiate the substrate film 10 from a distance of 1 to 3 cm for about 3 to 10 minutes (see Tables 2 and 3). If the distance is greater than the above or the irradiation time is shorter, the desired fine irregularities 11 cannot be obtained. Conversely, if the distance is closer than the above or the irradiation time is longer, there is a problem that the irregularities become too large or the variation in the irregularities becomes too large.

Conditions for surface modification by plasma treatment include, for example, using a xenon excimer lamp emitting vacuum ultraviolet light in an oxygen or carbon tetrafluoride atmosphere, irradiating the light for about 2 to 5 minutes from a distance of 0.5 to 2 cm from the substrate film 10. If the distance is increased or the irradiation time is shortened, the desired fine irregularities 11 cannot be obtained, while if the distance is reduced or the irradiation time is longer than the above, the irregularities become too large or the variation in the irregularities becomes too large.

The thickness of the electrode 20 must be 3 to 20 times the arithmetic mean roughness Ra of the surface of the base film 10. If the thickness of the electrode 20 is less than 30 nm (i.e., 3 times the arithmetic mean minimum roughness Ra of the surface of the base film 10 = 0.01 μm), the cross-sectional area of the electrode 20 becomes small, and a path for transmitting a sufficient electrical signal cannot be secured. On the other hand, if the thickness of the electrode 20 exceeds 20 times the arithmetic mean roughness of the surface of the base film 10, the anchor effect decreases and the electrode 20 becomes easily peeled off from the surface of the base film 10, even if fine irregularities 11 of the desired range are formed on the surface of the base film 10.

The electrode 20 is a layer made of a metal film, and examples of materials include pure conductive metals such as copper, gold, silver, aluminum, nickel, palladium, and indium, as well as conductive paste films containing the above metals, conductive fibers containing the above metals, and oxide films containing the above metals. Methods for forming the electrode 20 include electrolytic or electroless plating, as well as methods such as sputtering, vacuum deposition, and diffusion transfer.

The electrode 20 may also be an antenna receiving or transmitting electrode pattern 201 that receives radio signals transmitted from the outside and transmits radio signals to the outside. It may also be a ground electrode 202 that blocks radio signal noise. The electrode 201 consisting of the antenna receiving or transmitting electrode pattern and the electrode 202 consisting of a ground electrode that blocks radio signal noise may be formed on both sides of the base film 10 (see FIG. 2).

By forming electrodes 201, 202 of the desired thickness on both sides of the base film 10 consisting of the desired fine irregularities 11, a circuit wiring board 1 is obtained in which the attenuation of received or transmitted electrical signals is reduced and the performance of antenna reception or transmission is improved. And because the electrodes 201, 202 are formed in direct contact with the base film 10 with high dielectric properties, the circuit wiring board 1 is suitable for high-performance millimeter wave band communications. As a result, it can be deployed in products for various applications such as millimeter wave optical modulators, millimeter wave photocells, collision prevention millimeter wave radar using optical fibers, antenna converters, marine radar, wireless LAN, FWA, ETC, etc.

Among them, by forming an optical waveguide 3 on the upper part of this circuit wiring board 1, a next-generation photoelectric conversion element 5 suitable for millimeter wave band communication, for example, a next-generation millimeter wave optical modulator, can be obtained (see Figures 3 and 4). The optical waveguide 3 may be formed, for example, by changing the refractive index of a part of a plate-shaped substrate such as lithium niobate having a thickness of about 0.3 mm by annealing and proton exchange. Since light is confined within the optical waveguide 3 due to the difference in refractive index, when light is input from one direction, the light travels along the optical waveguide 3 and a wireless electric signal converted according to the input optical signal is transmitted as a radio wave from the antenna transmission electrode pattern 201 during the time until it is output. In addition, the radio electric signal of the radio wave received by the antenna reception electrode pattern 201 can also be converted into an optical signal. For lamination of the plate-shaped substrate and the circuit wiring board, for example, a method of applying and placing a low-dielectric polyimide adhesive can be used.

Example 1
As a substrate film, a 200 μm thick cyclic olefin resin polymer film having a structure in which the substituents R ₁ and R ₂ of formula (1) are hydrogen atoms, ethyl groups, n-octane groups, or n-nonane groups was used. Both sides of the substrate film were irradiated with a 254 nm ultraviolet lamp at a distance of 2 cm from the substrate film for 10 minutes, and then immersed in an electroless copper plating bath at 25° C. (copper sulfate pentahydrate 0.03 mol/L, formalin 0.3 mol/L, Rochelle salt complexing agent 0.3 mol/L, pH 12.5), and then immersed in an electrolytic copper plating bath at 25° C. (copper sulfate pentahydrate 10%, sulfuric acid 18%, hydrochloric acid 0.5%, organic additives 1%, ion-exchanged water 70.5%) to form a copper film having a thickness of 0.3 to 5 μm on both sides.

The peel strength results of the copper film from the substrate film of the obtained circuit wiring board are shown in Table 1. The peel strength tended to be higher as the copper film was relatively thinner, and higher as the substituents R ₁ and R ₂ were smaller. The crystallinity of each substrate film was measured in advance, and it was found that the smaller the substituents R ₁ and R ₂ were, the higher the crystallinity of the functional group. The dielectric properties of the obtained circuit wiring board at a frequency of 60 GHz were evaluated, and the dielectric loss tangent was low at 0.0008 to 0.0015 and the relative dielectric constant was low at 2.3 to 2.7 in all the circuit wiring boards, and the smaller the substituents R ₁ and R ₂ were, the better the properties were.

Subsequently, photosensitive films were attached to both sides of the copper film, and exposed and developed using a photomask to obtain a circuit wiring board in which an antenna transmission pattern electrode and an electromagnetic wave shielding pattern electrode were formed. An optical waveguide made of lithium niobate with a thickness of 0.25 mm was then laminated on top of the antenna transmission pattern electrode of the obtained circuit wiring board to produce a photoelectric conversion element. When the obtained photoelectric conversion element was connected to an optical fiber and an optical signal was input from the optical fiber, it was confirmed that a wireless electrical signal corresponding to the optical signal was emitted from the antenna transmission pattern electrode as a radio wave with a frequency of 60 GHz via the optical waveguide.

When the emitted radio waves of 60 GHz frequency were received and evaluated by a receiver 100 m away, the communication speed was 1.2 Gb/s on average, the transmission density was 5-8 Gb/s per ^m2 , the line density that could be connected per ^m2 was equivalent to 4-7 channels, and the transmission loss was suppressed to less than 20%. Therefore, it was confirmed that by using the circuit wiring board for photoelectric conversion elements of the present invention, high-speed, large-capacity optical signal data can be efficiently converted into radio waves in the 60 GHz band and transmitted.

Example 2
As the base film, a 200 μm thick cyclic olefin resin polymer film in which the substituents R ₁ and R ₂ in formula (1) are n-octane groups was used, and a circuit wiring board and a photoelectric conversion element were produced and evaluated under the same conditions as in Example 1, except for changing the irradiation time and distance of the ultraviolet lamp. For the evaluation, the arithmetic mean roughness Ra of the surface of the cyclic olefin resin polymer film irradiated with the ultraviolet lamp was measured using a surface roughness meter. The results are shown in Tables 2 and 3. As a result of the evaluation, it was confirmed that if the arithmetic mean roughness Ra of the surface of the cyclic olefin resin polymer film was in the range of 0.01 to 0.3 μm and the thickness of the copper film was in the range of 3 to 20 times Ra, the copper film was bonded to the film, and a wireless electric signal corresponding to the optical signal was emitted from the electrode of the antenna transmission pattern as a radio wave with a frequency of 60 GHz. In particular, if Ra was 0.04 to 0.3 μm and the thickness of the copper film was in the range of 3 to 5 times Ra, a circuit wiring board with a peel strength of 10 N/cm or more was obtained. On the other hand, when the arithmetic mean roughness Ra exceeded 0.3 μm, although the adhesion to the copper film was strong, radio waves with a frequency of 60 GHz were not detected.

(Examples 3 and 4)
As a result of carrying out the same test using a vacuum ultraviolet xenon excimer lamp in an oxygen atmosphere instead of the ultraviolet lamp, although there are differences in conditions such as distance from the substrate film and irradiation time, the evaluation results of the arithmetic mean roughness Ra of the surface of the cyclic olefin resin polymer film and adhesion with the copper film, radio wave performance at a frequency of 60 GHz, etc. were similar. From this, it was confirmed that if the arithmetic mean roughness Ra of the surface of the cyclic olefin resin polymer film and the relationship between the thickness of the copper film and Ra are within the above-mentioned specified range, a circuit wiring board for a desired photoelectric conversion element can be manufactured regardless of the method of surface modification of the substrate file.

REFERENCE SIGNS LIST 1 Circuit wiring board 3 Optical waveguide 5 Photoelectric conversion element 10 Base film 11 Fine irregularities on the surface of the base film 20 Electrode 201 Electrode consisting of an antenna receiving or transmitting electrode pattern 202 Ground electrode

Claims (4)

A step of preparing a substrate film mainly composed of a cyclic olefin resin having a crystallinity of 1% to 30% and having C-H bonds regularly and densely oriented;
a step of subjecting a surface of the base film to ultraviolet irradiation or plasma treatment so that the arithmetic mean roughness Ra of the surface is 0.01 to 0.3 μm;
forming an electrode made of a metal film having a thickness 3 to 20 times the arithmetic mean roughness Ra on the surface of the substrate film that has been subjected to the ultraviolet irradiation or plasma treatment;
The method for manufacturing a circuit wiring board comprising the steps of: The step of forming the electrode includes:
forming an antenna receiving or transmitting electrode pattern on one surface of the base film;
forming a ground electrode on the other surface of the base film;
The method for producing a circuit wiring board according to claim 1 , comprising: The cyclic olefin resin is a compound represented by the following formula (1): ₁ and R ₂ And it doesn't connect, and C _n H _2n+1 The method for producing a circuit wiring board according to claim 1, wherein the circuit wiring board has a structure of (n=0 to 8).

...Equation (1) The method for manufacturing a circuit wiring board according to claim 1 , further comprising the step of forming an optical waveguide on said electrode.

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