JP2018181945A - High frequency board - Google Patents

Abstract

【Task】
An object of the present invention is to provide a high frequency substrate excellent in heat dissipation, which can enhance the heat dissipation of a high density mounted high frequency substrate, protect electronic devices from heat generation over a long period of time, and maintain stable reliability. .
[Solution means]
The high frequency substrate according to the present invention is a high frequency substrate for high speed transmission of high frequency signals, wherein one surface of a resin film as a base material is provided with a copper layer as a wiring layer and the other surface is a diamond like layer as a heat dissipation layer. And a carbon layer.
【Selection chart】 None

Description

  BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a high frequency substrate for high speed transmission of a high frequency signal, which improves the heat dissipation of the high frequency substrate and improves the long-term reliability.

  In recent years, with the demand for higher performance and miniaturization of electronic devices, higher density and higher functionality of electronic components such as semiconductors have been required. In particular, in addition to the miniaturization of the communication equipment using the high frequency band, the heat generation amount per unit volume is increased due to the speeding up of the communication speed.

  Various problems have been pointed out for practical use of such a high-speed signal transmission device for high frequency signals, but one of the biggest problems is the heat generation problem. The high power and high density operation results in high temperature, which greatly reduces the reliability. Therefore, it is important to prevent the deterioration of the reliability and improve the long-term reliability by radiating the heat quickly and efficiently.

  In order to realize high-speed transmission of high frequency signals, improvements in various wiring boards are being studied. Usually, the printed circuit board adopted for the high frequency circuit selects the most suitable printed circuit board material by comprehensively judging the frequency to be used, allowable size, cost, etc. Substrates to which copper foil is attached have been used.

  For example, in Patent Document 1, metal salts such as molybdenum, iron, cobalt, nickel, tungsten and the like are added to an electrolytic solution in order to enhance adhesion with a copper foil to be attached to a print substrate, and these metals A method for producing a printed circuit board, comprising forming a copper plating layer containing the metal layer, coarsening a part of the crystal grain size of copper in the plating layer, forming irregularities on the surface of the copper plating layer, and improving adhesion with a substrate Is disclosed. However, high-speed transmission of high-frequency signals has the problem that signals are reflected and transmission loss of high-frequency signals increases due to the presence of rough grained interfaces formed by the coarsened copper crystals and surface irregularities. .

  Further, Patent Document 2 discloses a technique for forming a roughened layer made of a large number of copper electrodeposits containing Ge in order to enhance the adhesion strength between a circuit copper foil and a resin substrate. The inclusion of Ge ions in the electrolyte suppresses dendrite formation of copper precipitates and makes them spherical, prevents powder loss due to the generation of copper fines during the subsequent etching treatment, and improves adhesion with the substrate. Although it can be seen, there is a problem that transmission loss of high frequency signal is inevitable.

Japanese Patent Application Laid-Open No. 11-256389 Patent 3201850

  An object of the present invention is to improve the heat dissipation of a high-density mounted high frequency substrate, protect electronic devices from heat generation over a long period of time, and provide a high frequency substrate for high speed transmission of high frequency signals excellent in heat dissipation.

  As a result of intensive investigations to solve the above problems, the inventor of the present invention has excellent smoothness of a predetermined film thickness on one surface of a resin film of a substrate as a configuration of a high frequency substrate for high speed transmission of high frequency signals. And, a dense film, a copper layer of a wiring layer having high adhesion to a substrate, and a diamond-like carbon layer having high thermal conductivity and high hardness on the other surface are provided as a heat dissipation layer. As a result, it has been found that the heat dissipation properties are excellent, and the present invention has been completed.

  That is, the high frequency substrate of the present invention is a high frequency substrate for high-speed transmission of high frequency signals, which comprises a copper layer on one surface of a resin film as a base material and diamond like carbon on the other surface. It is characterized by

  The high frequency substrate of the present invention comprises a copper film excellent in smoothness and dense film quality having a predetermined film thickness on one surface of the resin film of the base material, and having high thermal conductivity on the other surface and A diamond-like carbon layer having high hardness is provided as a heat dissipation layer. With such a configuration, transmission loss of high frequency signals is small, and excellent heat dissipation is provided, and even when used for a long time, the substrate is prevented from being exposed to high temperatures, and reliability is improved. Can. From the above, the high frequency substrate of the present invention can contribute to the practical use of a high speed transmission device.

Hereinafter, embodiments of the present invention will be described in detail.
The high-frequency substrate of the present invention is a high-frequency substrate for high-speed transmission of high-frequency signals, characterized in that a copper layer is provided on one surface of a resin film as a substrate and diamond-like carbon is provided on the other surface. .

  The high frequency substrate of the present invention enhances the heat dissipation of the high density mounted substrate, and efficiently dissipates the heat generated by long-term use, thereby preventing the decrease in the reliability of the mounted electronic device. Excellent heat dissipation as a substrate. The shape of the high frequency substrate of the present invention is not particularly limited as long as it has excellent heat dissipation properties. For example, the thickness of the resin film of the base material or the thickness of the copper layer as the wiring layer Can be adjusted.

  Hereinafter, the present invention will be described in the order of (1) base material, (2) copper layer, (3) diamond like carbon layer, and (4) method of manufacturing high frequency substrate.

(1) Substrate The substrate of the high frequency substrate of the present invention can be selected from materials suitable for the application of the high frequency substrate. For example, inexpensive and widely used polyethylene terephthalate (PET), liquid crystal polymer (LCP) excellent in heat resistance, chemical resistance and dimensional stability, cyclo also having transparency, low dielectric constant and excellent heat resistance Resins, such as an olefin polymer (COP) and polyimide resin (PI) which has mechanical strength and a low dielectric constant and is excellent also in heat resistance, can be mentioned.

  As the form of the base material, a resin film with high surface smoothness is selected as the base material of the high frequency substrate because it is mounted at high density and used as a wiring substrate for high speed transmission.

  In addition to the shape, the copper layer as a wiring layer and the diamond like carbon layer as a heat dissipation layer are supported depending on the application and purpose of use of the high frequency substrate of the present invention, and the thickness of the resin film is arbitrary Can be selected.

  The thickness of the resin film is preferably in the range of 10 μm to 400 μm, and more preferably in the range of 20 μm to 200 μm. If the thickness of the resin film is less than 10 μm, it is not preferable because the strength as a substrate for supporting the copper layer and the diamond-like carbon layer is insufficient. When the thickness of the resin film exceeds 400 μm, it is not preferable because the heat generated on the copper layer side as the wiring layer becomes difficult to be efficiently transmitted to the diamond like carbon layer as the heat dissipation layer. Moreover, it is not preferable because the processability and the handling property deteriorate.

(2) Copper Layer In the wiring layer of the high frequency substrate of the present invention, copper which is used for general purpose in electric wiring circuits with small electric resistance is used. Copper is preferable because it is relatively inexpensive and easy to process wiring. The thickness of the copper layer as the wiring layer can be set arbitrarily, but the thickness of the copper layer when used as a high-frequency substrate mounted at high density is preferably in the range of 1 μm to 20 μm. In order to further increase the density, it is more preferable to use a copper layer with a thickness of 1 μm to 4 μm. If the thickness is less than 1 μm, the wiring layer is too thin and there is a fear of disconnection, and if the thickness exceeds 20 μm, the cross section of the wiring becomes trapezoidal, and a difference occurs in the wiring width between the upper and lower parts. When wiring is performed at the density, there is a possibility that a short circuit may occur between the wirings, which is not preferable.

  In the copper layer of the present invention, it is desirable to form a copper layer formed by sputtering on a base layer. The adhesion between the copper layer formed by sputtering and the resin film of the substrate is extremely high due to chemical bonding. By selecting a substrate having a smooth surface, the copper layer obtained by the sputtering method becomes a smooth film because the film is directly deposited on the surface of the smooth substrate without roughening the surface. Furthermore, a smooth film can be obtained from the copper layer formed by the plating method. Therefore, when a high frequency signal is transmitted at high speed using the high frequency substrate of the present invention, the reflection and disturbance of the signal are less likely to occur, and the transmission loss of the signal can be reduced.

  Since the copper layer of the present invention is used as a wiring for high-speed transmission of high frequency signals, it is required to have high adhesion to the base material and good etching properties when wiring is processed later. In order to satisfy these required characteristics, the copper layer of the wiring layer can be realized by forming a film by a dry method such as a chemical vapor deposition method, a physical vapor deposition method, or a sputtering method. In particular, the sputtering method is suitable for obtaining a dense and smooth film or a film having higher adhesion. However, the film formation time is long, which is disadvantageous in cost.

  Therefore, in order to make the most of the characteristics of the sputtering method and compensate for the decrease in productivity, the copper layer for wiring is first formed by sputtering a copper layer as a base layer on the substrate surface, and then the copper layer is electroplated. The method of forming a film to a predetermined film thickness can be selected, and the copper layer of the obtained wiring layer can satisfy various qualities required for the wiring of the substrate for high-speed transmission of high frequency signals.

(3) Diamond-like carbon layer The diamond-like carbon layer of the present invention is a heat dissipation layer for efficiently releasing the heat generated from the device installed on the wiring. Diamond-like carbon (hereinafter sometimes referred to as DLC) is a carbon material similar to diamond, and has a crystal structure intermediate between diamond and graphite. More specifically, it has an amorphous structure which contains carbon and a slight amount of hydrogen, and in which both a diamond structure (SP3 bond) and a graphite structure (SP2 bond) are mixed. DLC is a material having predetermined heat dissipation, and also a material having electrical insulation and gas barrier properties.

  In order to ensure sufficient heat dissipation, the thermal conductivity of the diamond-like carbon layer is preferably 30 W / mK or more. The upper limit of the thermal conductivity of the DLC layer is usually 2000 W / mK or less of the thermal conductivity of diamond.

  The thermal conductivity of the diamond-like carbon layer can be measured using a light AC method. Thermal conductivity is measured using a heat sink on a high frequency substrate as a heat source with a diode laser as the heat source and atmospheric pressure (20 ° C) as the heat source using the light AC method thermal diffusion measurement device (Advance Riko Co., model: LaserPIT-1) can do.

  The thermal conductivity of the diamond-like carbon layer can be controlled by the composition of DLC. Specifically, DLC usually contains a predetermined amount of hydrogen, which may cause the thermal conductivity to be less than 30 W / mK. For this reason, it is preferable to adjust the content of hydrogen in order to control the thermal conductivity with high precision.

  In the high frequency substrate of the present invention, the copper layer of the wiring layer is disposed on one side of the resin film of the base material, and the diamond like carbon layer of the heat dissipation layer is disposed on the other side. The heat dissipation improves as the thickness of the diamond-like carbon layer increases, but the thickness can be set according to the amount of heat required.

  When used as a high-frequency substrate for high-speed transmission of high-frequency signals, the thickness of the diamond-like carbon layer is preferably 0.1 μm to 5 μm, and more preferably 0.5 μm to 1 μm. If the thickness is less than 0.1 μm, the heat radiation effect is small and it is difficult to obtain an efficient heat radiation effect. If the thickness exceeds 5 μm, the bending resistance of the substrate is unfavorably lowered. Moreover, even if it is thicker than this, the improvement of the heat radiation effect is not seen, it is only expensive and not preferable.

  Also, the diamond like carbon layer has high thermal conductivity and high hardness. Therefore, it is not necessary to provide a protective layer on the surface of the heat dissipation layer, and improvement in long-term reliability can be expected as a film having scratch resistance. Furthermore, since it also has a gas barrier property, when using a polyimide film for the resin film of a base material, the prevention effect of a deformation | transformation and peeling by the water vapor | steam which permeate | transmits can also be anticipated. The DLC film also has insulating properties, and is a useful functional thin film capable of simultaneously meeting various requirements of the high frequency substrate.

(4) Method of Manufacturing High Frequency Substrate The method of manufacturing the high frequency substrate of the present invention will be described below. The high frequency substrate of the present invention is obtained by the following steps (A) to (C).
(A) Step of preparing a resin film of a substrate (B) A DLC layer of a heat dissipation layer is formed on the substrate obtained in the step of forming a copper layer of a wiring layer on one surface of the resin film (C) (B) Process of film formation

Each of the steps will be described below.
(A) Step of Preparing a Resin Film of the Substrate As described above, as the substrate of the high frequency substrate of the present invention, polyethylene terephthalate (PET), which is used widely and inexpensively, heat resistance, chemical resistance, dimensions Liquid crystal polymer (LCP) having excellent stability, cycloolefin polymer (COP) having transparency and low dielectric constant and excellent in heat resistance, polyimide resin having mechanical strength and low dielectric constant and excellent in heat resistance (PI Choose a material suitable for the application from among resinous substrates such as). In the present invention, since it is used for high-speed transmission of high frequency signals, a resin film having high surface smoothness is selected as a substrate in order to suppress transmission loss.

(B) Step of forming a copper layer of a wiring layer on one side of a resin film The copper layer of the present invention has high adhesion to a substrate because it is used as a wiring for high-speed transmission of high frequency signals. It is required that the film quality is good for etching when wiring processing. In order to satisfy these required characteristics, the copper layer of the wiring layer can be realized by forming a film by a dry method such as a chemical vapor deposition method, a physical vapor deposition method, or a sputtering method. In particular, the sputtering method is suitable for obtaining a dense and smooth film or a film having higher adhesion. However, the film formation time is long, which is disadvantageous in cost.

  Therefore, in order to make the most of the characteristics of the sputtering method and compensate for the decrease in productivity, the copper layer for wiring is first formed by sputtering a copper layer as a base layer on the substrate surface, and then the copper layer is electroplated. The method of forming a film to a predetermined film thickness can be selected.

  That is, in the present invention, as the copper layer, the copper layer of the base layer is formed by sputtering to a thickness of 50 nm to 300 nm and thereafter, the thickness is finally 1 μm to 20 μm by electroplating. It can be formed by film formation.

  The copper layer of the base layer can be obtained by setting the base material in a sputtering apparatus using a copper target, performing sputtering while introducing argon gas, and forming a copper layer having a predetermined film thickness. . In order to further improve the adhesion between the substrate and the copper layer, before forming the copper layer, an underlayer selected from the group of chromium, nickel, and nickel-chromium alloy with a thickness of 20 nm or more and 100 nm It is preferable to form a film. In addition, it is effective to wash the surface of the substrate with argon ions or to generate oxygen plasma to activate the surface of the substrate to enhance adhesion.

  Next, the base on which the copper layer of the base layer is formed is subjected to copper plating using a plating apparatus, and a wiring copper layer is finally formed to have a thickness of 1 μm to 20 μm. In copper plating, it is desirable to use a plating apparatus of an oxidation bath using copper sulfate which has low toxicity and is excellent in operability.

(C) Step of forming a DLC layer of the heat dissipation layer on the substrate obtained in (B) Finally, on the substrate on which the copper layer of the wiring layer obtained in the step of (B) was formed, The high frequency substrate of the present invention is produced by forming the DLC layer of the heat dissipation layer on the surface of the base material.

  For diamond like carbon, film formation using a plasma CVD method is suitable. In the plasma CVD method, an acetylene gas is introduced as a compound gas, and the acetylene gas is decomposed by plasma to form a DLC layer on the surface of the resin film of the substrate. In the plasma CVD method, since the compound gas is activated using plasma, the film can be formed at a low temperature, so that it is particularly suitable for film formation on a resin film.

  As described above, in the high frequency substrate of the present invention, neither the copper layer of the wiring layer nor the DLC layer of the heat dissipation layer is formed on the surface of the resin film of the substrate by the dry method, and no adhesive layer is provided. Dense film quality and excellent adhesion to the substrate, and it can be said that the method is useful as a method for producing a substrate for high-speed transmission of high frequency signals.

  Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples. In addition, the following evaluation methods evaluated the high frequency substrate of the Example shown below and a comparative example.

(A) Evaluation of heat dissipation A total of 10 W LED lights are attached to the obtained substrate, operated for 1 hour while blinking 100 times per second, a thermotape is attached to the back of the substrate, and the substrate temperature after operation is measured. The heat dissipation performance of the board was evaluated.

(B) Evaluation of Thermal Conductivity The thermal conductivity of the heat dissipation layer can be measured using a light AC method. Thermal conductivity is measured using a heat sink on a high frequency substrate as a heat source with a diode laser as the heat source and atmospheric pressure (20 ° C) as the heat source using the light AC method thermal diffusion measurement device (Advance Riko Co., model: LaserPIT-1) did.

  Example 1 A polyimide film (manufactured by Ube Industries, Ltd., product name: UPILEX-S (registered trademark), film thickness: 75 μm) cut into a 20 cm square was used as a substrate.

  First, a polyimide film was set in a sputtering apparatus (CFS-4ES, manufactured by Shibaura Mechatronics Co., Ltd.), and a Ni-25 mass% Cr film was formed to a thickness of 20 nm as a base layer on one surface of this polyimide film, and then 100 nm of copper was formed.

Specifically, a 3-inch diameter disk-shaped target of nichrome alloy (Ni-25% Cr, purity 99.9% by mass) and copper (purity 99.9% by mass) was used as a target. As film forming conditions, the ultimate vacuum degree is 6.5 × 10 ^-3 Pa, the DC output is 200 W, and argon gas (flow rate 15 sccm) is introduced as a reaction gas, so that the film thickness is formed first on one side of the film. A 20 nm Ni-20 mass% Cr underlayer was deposited. Subsequently, a DC underlayer of 300 W, an ultimate vacuum of 6.5 × 10 ⁻³ Pa, and an argon gas (flow rate of 15 sccm) as a reaction gas are introduced to form a copper underlayer of 100 nm in thickness. The film was laminated.

  In order to apply electrolytic copper plating to the obtained film, the film which formed the base layer into a film was set to the plating apparatus using copper sulfate.

The plating conditions were a bath temperature of 45 ° C., a voltage of 5 V, and a current density of 3 A / dm ² for plating for 15 minutes to produce a copper layer of a wiring layer. The thickness of the obtained copper layer was 4 μm.

  Next, in order to form a DLC film on a polyimide film on which the obtained copper layer was formed, the film was set in a plasma CVD apparatus (manufactured by Samco Inc., model PD-100D).

Specific film forming conditions are: an ultimate vacuum degree is 2 × 10 ⁻² Pa, and an acetylene gas (flow rate 10 L / min) is introduced as a reaction gas, and a high frequency of 13.56 MHz is applied and excited. A high-frequency substrate was obtained by forming a DLC layer having a thickness of 1 μm by ionizing it at a deposition rate of 630 nm / min.

    When the heat dissipation performance of the high frequency substrate obtained by the above evaluation method was evaluated, the temperature of the substrate after one hour of operation was 46 ° C. The thermal conductivity of the DLC layer was 20 W / mK. Further, the hardness of the DLC layer was as high as 2200 Hv in Vickers hardness.

(Example 2)
A high frequency substrate was obtained in the same manner as in Example 1 except that the thickness of the DLC layer was set to 0.5 μm.

  The heat dissipation performance of the high frequency substrate obtained by the same evaluation method as in Example 1 was evaluated. As a result, the temperature of the substrate after one hour of operation was 47.degree. The thermal conductivity of the DLC layer was 19 W / mK. Further, the hardness of the DLC layer was as high as 2200 Hv in Vickers hardness.

Comparative Example 1 A copper layer was formed on a polyimide film (made by Ube Industries, Ltd., product name: UPILEX-S (registered trademark), film thickness: 75 μm) as a substrate under the same conditions as in Example 1, and a DLC layer was formed. A high frequency substrate was produced without film formation.

  This high frequency substrate was evaluated in the same manner as in Example 1. The temperature of the substrate after one hour of operation was 58.degree.

  As described above, since the high frequency substrate of the present invention has good heat dissipation performance and high hardness of the DLC layer, it is understood that the substrate is excellent in heat dissipation and can be expected to improve long-term reliability. And a substrate that can be suitably used as a wiring substrate for high-speed transmission of high frequency signals.

Claims (4)

  What is claimed is: 1. A high frequency substrate for high speed transmission of high frequency signals, comprising a copper layer on one surface of a resin film as a base material and a diamond like carbon layer on the other surface.   The high frequency substrate according to claim 1, wherein the resin film is one selected from the group consisting of polyethylene terephthalate, polyimide resin, cycloolefin polymer, fluorine resin, and liquid crystal polymer.   The high frequency substrate according to claim 1, wherein the copper layer has a thickness of 1 μm to 20 μm. The high frequency substrate according to any one of claims 1 to 3, wherein the diamond like carbon layer has a thickness of 0.1 μm to 5.0 μm.