JP6834462B2 - Heat dissipation board - Google Patents

Description

The present invention relates to a heat dissipation substrate.

In recent years, with the demand for higher performance and smaller size of electronic devices, higher density and higher functionality of electronic components such as semiconductors are required. In order to meet this demand, circuit boards on which various electronic components are mounted are also required to be smaller and have higher densities. As a result, a power semiconductor or the like having a relatively large calorific value (for example, controlling a large current of several tens of A or more) and a signal current having a relatively small calorific value (for example, controlling a signal current of several tens of mA or more) are controlled. ) It is required to mount general electronic components such as control semiconductors on circuit boards suitable for each application and connect them to each other.

Various problems have been specified for the practical use of such power semiconductor devices, but the biggest problem is the heat dissipation problem. Since it operates at high output and high density, it becomes hot and its reliability is lowered.

In addition, in order to simultaneously meet the demand for miniaturization and high density by mounting general-purpose electronic components such as control semiconductors on the same substrate, it is important how quickly and efficiently these heats are dissipated. It has become a challenge.

In order to deal with such a problem, it is considered to use various heat radiating sheet materials as a substrate.

For example, a heat radiating sheet using a resin having high thermal conductivity has an advantage of being excellent in workability and flexibility and capable of being laminated, but has a problem of low thermal conductivity as compared with a ceramic substrate. Therefore, a high thermal conductivity sheet is produced by containing a thermosetting resin and an inorganic filler having high thermal conductivity.

Patent Document 1 discloses that an epoxy resin is filled with spherical alumina powder and silica powder having finer particles and a larger average spherical shape. This requires more ceramic powder to increase thermal conductivity. As a result, the thermoelectric substrate becomes expensive because more expensive ceramic powder is used, and the mechanical strength of the epoxy composition and the substrate decreases.

Patent Document 2 discloses a sheet that improves thermal conductivity without increasing the amount of thermally conductive particles used in the thermally conductive sheet. This can be achieved by absorbing the heat conductive particles in the resin layer and curing them, and segregating the thermoelectric particles in the thickness direction. However, since the heat conductive particles are not uniformly dispersed, the heat dissipation effect is concentrated on the place where the particles are gathered, which is efficient. It is difficult to dissipate heat.

JP-A-2003-306594 Japanese Unexamined Patent Publication No. 2013-58700

An object of the present invention is to provide a substrate having both high frequency control and power supply functions, which enhances heat dissipation of high-density mounted electronic devices and circuits and has excellent heat dissipation to protect electronic devices from heat.

As a result of diligent studies to solve the above problems, the present inventor has a planar thermal conductivity of 1300 W / mk or more and 1600 W / mk or less and a longitudinal thermal conductivity of 3 W / mk or more and 6 W / mk or less. A graphite sheet is used as a base material, a copper layer of a conductive layer for high frequency control having a thickness of 2 μm or more and 4 μm or less is arranged on one surface of the base material, and power is supplied on the other surface with a thickness of 5 μm or more and 16 μm or less. It was found that by arranging the copper layer of the conductive layer for electric power, it is possible to obtain a heat radiating substrate having extremely excellent heat dissipation and having both high frequency control and power supply functions.

The heat dissipation substrate having the above configuration is extremely excellent in heat dissipation, and can provide a substrate effective for realizing miniaturization and high density.

The heat radiating substrate according to the embodiment of the present invention will be described in more detail below.

[1. Heat dissipation board]
The heat radiating substrate of the present invention uses a graphite sheet as a base material having a planar thermal conductivity of 1300 W / mk or more and 1600 W / mk or less and a longitudinal thermal conductivity of 3 W / mk or more and 6 W / mk or less on one surface thereof. A copper layer of a conductive layer for high frequency control having a thickness of 2 μm or more and 4 μm or less is arranged, and a copper layer of a conductive layer for power supply having a thickness of 5 μm or more and 16 μm or less is arranged on the other surface.

[1-1. Base material]
In order to produce a base material having excellent heat dissipation, it is necessary to use a material having excellent thermal conductivity. In the present invention, a graphite sheet having a planar thermal conductivity of 1300 W / mk or more and 1600 W / mk or less and a longitudinal thermal conductivity of 3 W / mk or more and 6 W / mk or less was selected, but this is obtained by heat-treating the polyimide. It is a material with extremely high thermal conductivity obtained by graphitization.

Generally, metal is mentioned as a material having high thermal conductivity. For example, copper (thermal conductivity 398 W / mk) and aluminum (thermal conductivity 237 W / mk), but graphite sheet has several times the thermal conductivity. It is a material having. Furthermore, since the density is as ^{light as 2 g / cm 3} , it can be said that it is an advantageous material for miniaturization and high density.

Graphite sheets with a planar thermal conductivity of 1300 W / mk or more and 1600 W / mk or less and a longitudinal thermal conductivity of 3 W / mk or more and 6 W / mk or less are commercially available from Panasonic Corporation and Kaneka Co., Ltd. Can be obtained and used.

Further, in order to produce a graphite sheet, it is usually obtained by heating a polymer film typified by polyimide to a temperature of 1000 ° C. or higher in an inert gas and carbonizing it. Further, heating to a high temperature of 2600 ° C. or higher is preferable for graphitization.

[1-2. Copper layer]
By forming copper wiring based on this base material, a substrate having excellent heat dissipation can be obtained. That is, the heat radiating substrate according to the present invention uses a graphite sheet as a base material, and copper layers are arranged on both sides thereof.

In the present invention, a copper layer of a high frequency control conductive layer having a thickness of 2 μm or more and 4 μm or less is arranged on one surface of the base material, and a power supply conductive layer having a thickness of 5 μm or more and 16 μm or less is arranged on the other surface. The copper layer is arranged.

As described later, the copper layer of the conductive layer for high frequency control is formed by a sputtering method, and then a film is formed to a predetermined thickness by a plating method. Therefore, since it is an amorphous base layer, the plating method is used. The formed copper layer is also a copper layer having excellent etching properties.

Further, since the electrolytic copper foil is not attached by the laminating method, a thin film can be formed, and since it has good etching properties, there is an advantage that the wire can be thinned.

[2. Manufacturing method of heat dissipation board]
Next, a method for manufacturing a heat radiating substrate according to the present invention will be described.

In the heat dissipation substrate according to the present invention, first, a graphite sheet as a base material is prepared, and a copper layer of a conductive layer for high frequency control having a thickness of 2 μm or more and 4 μm or less is formed on one surface of the graphite sheet of the base material. It is obtained by forming a copper layer of a conductive layer for power supply having a thickness of 5 μm or more and 16 μm or less on one surface.

[2-1. Preparation of graphite sheet]
As the graphite sheet of the base material used for the heat dissipation substrate of the present invention, a high thermal conductivity graphite sheet is commercially available from Kaneka Corporation, Panasonic Corporation and the like. Therefore, it can be used as a base material by using these commercially available products.

Further, in order to produce a graphite sheet, for example, it is obtained by heating a polyimide film, which is a typical polymer film, to a temperature of 1000 ° C. or higher in an inert gas and carbonizing it. Further, in order to prevent the film from being damaged, the temperature is gradually raised from 500 ° C. to 1000 ° C. in argon gas, preheating is performed, and then the film is heated to a high temperature of 2600 ° C. or higher, more preferably 3000 ° C. or higher. High temperature is preferable for graphitization. The higher the heat treatment temperature, the higher the thermal conductivity of the graphite sheet can be obtained.

[2-2. Formation of copper layer of base layer by sputtering method]
Next, a copper layer of a conductive layer for high frequency control having a thickness of 2 μm or more and 4 μm or less is formed on one surface of a graphite sheet as a base material, and power is supplied to the other surface with a thickness of 5 μm or more and 16 μm or less. The heat-dissipating substrate of the present invention is produced by forming a copper layer of a conductive layer for use. First, copper layers of a base layer are formed on both sides of a graphite sheet by a sputtering method.

Examples of the method for forming a copper layer of the base layer include a vapor deposition method in which the copper layer is heated by an electron gun to evaporate, and a sputtering method in which argon ions are accelerated using a copper target to knock out copper atoms of the copper target to form a film on the film. However, it is desirable to use a sputtering method in which the film is dense and the adhesion to the substrate is excellent. The copper layer formed by the sputtering method is smooth and has a strong chemical bond with the base material, so that high adhesion can be obtained.

In order to further improve the adhesion between the base material and the copper layer of the base layer, for example, a method of cleaning the base material surface with argon ions or a method of generating oxygen plasma to attach an active group to the base material surface can be performed. ..

Next, a copper layer as a base layer is formed on the graphite sheet of the base material. In order to further improve the adhesion between the base material and the copper layer, a thin film of 20 nm to 100 nm of a chromium, nickel, or nichrome alloy is formed, and then the copper layer is laminated to a thickness of 50 nm to 300 nm to further enhance the adhesion. Can be raised.

[2-3. Formation of copper layer of conductive layer]
Finally, one surface of the base material has a copper layer of a conductive layer for high frequency control having a thickness of 2 μm or more and 4 μm or less, and the other surface has a copper layer of a conductive layer for power supply having a thickness of 5 μm or more and 16 μm or less. Form. In order to form a copper layer having the above thickness as the conductive layer, it is desirable to make copper a predetermined film thickness by a plating method.

The graphite sheet on which the copper layer of the base layer is formed is put into a double-sided copper plating apparatus, and copper is plated on both sides. For copper plating, an oxidation bath using copper sulfate, which is not toxic and has excellent operability, is desirable.

Since the required thickness is different between the high frequency control conductive layer and the power supply conductive layer, the high frequency control conductive layer has a thickness of 2 μm or more and 4 μm or less, and the power supply conductive layer has a thickness of 5 μm or more and 16 μm or less. Set the current value to be passed through the electrolytic tank. As specific plating conditions, for example, the bath temperature is 45 ° C., the voltage is 5 V, and the current density is 3 A / dm ² to 10 A / dm ² , so that copper plating can be preferably performed.

The heat-dissipating substrate of the present invention is produced by the above treatment, but a copper layer can be formed thinner than usual by forming a copper layer as a base layer by a sputtering method and then using copper as a conductive layer by a plating method. Therefore, it can be said that it is an effective substrate for high-frequency control because it has excellent etching properties and can be thinned, and because it is a flat film.

The present invention will be described in more detail with reference to Examples below, but the present invention is not limited to these Examples.

(Example 1)
A commercially available graphite sheet manufactured by Kaneka Co., Ltd. (planar thermal conductivity: 1500 W / mk, vertical thermal conductivity: 5 W / mk, thickness: 40 μm, size: 20 cm square) was used as the base material. A graphite sheet was set in a sputtering apparatus (manufactured by Shibaura Seisakusho, model: CFS-4ES), and a nichrome alloy layer and a copper layer underlayer were formed on both surfaces thereof. The target used was a nichrome alloy and a copper 3 inch diameter 99.9% pure target. As the sputtering conditions, the ultimate vacuum degree was 6.5 × 10 ^-3 Pa, and the DC output was 200 W. As a reaction gas, argon gas was introduced in an amount of 15 sccm. Under the above conditions, a nichrome alloy was first formed on both sides of the graphite sheet so as to have a thickness of 20 nm. Subsequently, the copper was formed with a DC output of 300 W, and the copper layer was formed to have a thickness of 100 nm under the same conditions under other conditions.

The graphite sheet thus obtained was set in a plating apparatus using copper sulfate. The bath temperature was 45 ° C., the voltage was 5 V, the current density on one side was 3 A / dm ² , and the current density on the other side was 15 A / dm ² , and the copper plating treatment was performed for 15 minutes. As a result, the thickness of the copper layer of the conductive layer for high frequency control was 4 μm, and the thickness of the copper layer of the conductive layer for power supply was 16 μm.

When the obtained heat-dissipating substrate was attached to the device and operated for 1 hour, it was found that the temperature of the device increased from room temperature to 40 ° C.

(Example 2)
At a current density conditions of copper plating, one side of the current density is 3A / dm ^2, that the other side of the current density was set to 15A / dm ^2, one side of the current density is 3A / dm ^2, the other surface current density A heat dissipation substrate was obtained in the same manner as in Example 1 except that the current value was changed to 10 A / dm ^2. The thickness of the copper layer of the high-frequency control conductive layer of the obtained heat-dissipating substrate was 4 μm, and the thickness of the copper layer of the power supply conductive layer was 10 μm.

When the obtained heat radiating substrate was attached to the device and operated for 1 hour, it was found that the temperature of the device rose from room temperature to 45 ° C.

(Comparative Example 1)
A heat-dissipating substrate was obtained in the same manner as in Example 1 except that a polyimide film having a thickness of 100 μm and a size of 20 cm was used as the base material instead of the graphite sheet. The obtained copper layer of the conductive layer for high frequency control of the heat radiation substrate was 4 μm, and the copper layer of the conductive layer for power supply was 16 μm.

When the obtained heat-dissipating substrate was attached to the device and operated for 1 hour, it was found that the temperature of the device rose from room temperature to 70 ° C.

From the above results, it was found that the heat radiating substrate of the present invention efficiently dissipates the heat generated and suppresses the temperature rise of the device.

Claims (2)

A graphite sheet having a planar thermal conductivity of 1300 W / mk or more and 1600 W / mk or less and a longitudinal thermal conductivity of 3 W / mk or more and 6 W / mk or less is used as a base material, and one surface of the base material has a thickness. A heat dissipation substrate characterized in that a copper layer of a conductive layer for high frequency control of 2 μm or more and 4 μm or less is arranged, and a copper layer of a conductive layer for power supply having a thickness of 5 μm or more and 16 μm or less is arranged on the other surface. A thickness selected from the group of chromium, nickel, and nichrome alloys is 20 nm between the copper layer of the base material and the conductive layer for high frequency control and between the copper layer of the base material and the conductive layer for power supply. The heat-dissipating substrate according to claim 1, wherein a thin film having a thickness of 100 nm is arranged.