JP7025204B2 - Heat sink and electronic device using it - Google Patents

Description

The present disclosure relates to a heat sink and an electronic device using the heat sink.

An electronic device in which various electronic components such as a semiconductor element, a heat generating element, and a Pelche element are mounted on a heat sink is known.

In recent years, as the output of electronic components has been increasing, the amount of heat generated at the time of output of electronic components has been increasing. Further, since the miniaturization of electronic devices is progressing, there is a demand for miniaturization of heat sinks constituting electronic devices. Therefore, a heat sink in which a heat diffusion layer is directly mounted on a substrate has been proposed so as to have excellent heat dissipation characteristics even if the size is small (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 10-56114

Here, in the case of a heat sink in which the heat diffusion layer is directly mounted on a substrate made of metal, ceramics, etc., the heat diffusion layer may be peeled off from the substrate when the heat sink is repeatedly heated and cooled due to the operation of electronic components. rice field. When the heat diffusion layer is peeled off from the substrate, a gap that hinders heat conduction is generated between the heat diffusion layer and the substrate, and the heat dissipation characteristics are deteriorated.

The present disclosure has been devised to meet the above requirements, and provides a heat sink capable of maintaining excellent heat dissipation characteristics for a long period of time even after repeated heating and cooling, and an electronic device using the heat sink. With the goal.

The heat sink of the present disclosure includes a substrate having a first surface, a resin layer located in contact with the first surface, and a heat diffusion layer located in contact with the resin layer. The thermal conductivity in the first direction along the first surface of the heat diffusion layer is 8 times or more the thermal conductivity in the second direction orthogonal to the first surface of the heat diffusion layer. It is larger than the thermal conductivity of the substrate. Further, the average thickness of the resin layer is equal to or larger than the average thickness of the heat diffusion layer.

The heat sink of the present disclosure can maintain excellent heat dissipation characteristics for a long period of time even after repeated heating and cooling.

It is a top view which shows an example of the heat sink of this disclosure. It is sectional drawing of the heat sink shown in FIG.

The heat sink of the present disclosure and an electronic device using the same will be described in detail below with reference to the drawings.

As shown in FIGS. 1 and 2, the heat sink 10 of the present disclosure is located in contact with a substrate 1 having a first surface 1a, a resin layer 2 located in contact with the first surface 1a, and a resin layer 2. The heat diffusion layer 3 is provided. Here, the heat diffusion layer 3 is a layer in which the thermal conductivity in the first direction along the first surface 1a and the thermal conductivity in the second direction orthogonal to the first surface 1a are different. Such a layer is, for example, a layer composed of graphene, graphite, carbon nanotubes, or the like. The first direction is the left-right direction in FIG. 2, and the second direction is the up-down direction in FIG. 2, in other words, the thickness direction of the heat diffusion layer 3.

Further, in the heat sink 10 of the present disclosure, the thermal conductivity of the heat diffusion layer 3 in the first direction is 8 times or more the thermal conductivity of the heat diffusion layer 3 in the second direction, and is based on the thermal conductivity of the substrate 1. big. Here, even in the layer composed of graphene, graphite, or carbon nanotubes, the thermal conductivity in the first direction is not always eight times or more the thermal conductivity in the second direction.

By satisfying such a configuration, the heat generated at the time of output of the electronic component is efficiently diffused in the first direction in the heat diffusion layer 3, and the heat diffusion layer 3 is passed through the resin layer 2 to the substrate 1. Since heat is easily distributed throughout, heat can be dissipated by the entire substrate 1.

Further, in the heat sink 10 of the present disclosure, the average thickness of the resin layer 2 is equal to or larger than the average thickness of the heat diffusion layer 3. Here, the resin layer 2 and the heat diffusion layer 3 have a high chemical affinity. Then, by satisfying the relationship of the average thickness, the heat diffusion layer 3 is firmly bonded to the substrate 1 via the resin layer 2. As a result, even if the heat sink 10 is repeatedly heated and cooled due to the operation of the electronic components, the heat diffusion layer 3 is less likely to peel off from the resin layer 2, and heat conduction between the heat diffusion layer 3 and the resin layer 2 is hindered. It is difficult for voids to occur. Therefore, by satisfying the above-mentioned configuration, the heat sink 10 of the present disclosure can maintain excellent heat dissipation characteristics for a long period of time even if heating and cooling are repeated.

Further, in the heat sink 10 of the present disclosure, the average thickness of the resin layer 2 may be 2 times or more and 5 times or less the average thickness of the heat diffusion layer 3. If such a configuration is satisfied, heat conduction from the heat diffusion layer 3 to the substrate 1 is effectively performed, and the heat diffusion layer 3 is more firmly bonded to the substrate 1 via the resin layer 2. ..

Further, in the heat sink 10 of the present disclosure, the average thickness of the heat diffusion layer 3 may be 15 μm or more and 40 μm or less. If such a configuration is satisfied, the heat generated at the time of output of the electronic component can be efficiently diffused in the first direction in the heat diffusion layer 3, and the heat to the resin layer 2 can be effectively transferred. The average thickness of the resin layer 2 is, for example, 15 μm or more and 200 μm or less.

Here, the average thickness of the resin layer 2 and the heat diffusion layer 3 is obtained by cutting the heat sink 10 so as to have the cross section shown in FIG. 2, and polishing the cross section with a cross section polisher (CP) with a scanning electron microscope (SEM). ), And in the photograph taken, the thickness of each of the resin layer 2 and the heat diffusion layer 3 may be measured at five or more points, and the average value may be calculated.

Further, in the heat sink 10 of the present disclosure, the thermal conductivity of the heat diffusion layer 3 in the first direction may be 40 times or more the thermal conductivity of the heat diffusion layer 3 in the second direction. If such a configuration is satisfied, the heat generated at the time of output of the electronic component is more efficiently diffused in the first direction in the heat diffusion layer 3, so that the heat can be efficiently dissipated in the entire substrate 1.

Further, the heat sink 10 of the present disclosure has A <B <C when the area of the heat diffusion layer 3 is A, the area of the resin layer 2 is B, and the area of the first surface 1a is C in plan perspective. May be good. If such a configuration is satisfied, the heat diffusion layer 3 is more firmly bonded to the substrate 1 via the resin layer 2, and the heat diffusion layer 3 becomes the resin layer 2 and the resin layer 2 becomes the substrate 1. The smooth transfer of heat improves heat dissipation characteristics. In addition, A: B: C may be 1: 1.02: 1.1 to 1: 1.2: 1.5.

Further, the main component of the resin layer 2 in the heat sink 10 of the present disclosure may be an epoxy resin, an acrylic resin or a silicone resin. Here, the fact that the main component is an epoxy resin, an acrylic resin or a silicone resin means that the epoxy resin, the acrylic resin or the silicone resin accounts for 50% by mass or more of 100% by mass of all the components constituting the resin layer 2. If such a configuration is satisfied, the epoxy resin, acrylic resin, and silicone resin are superior in heat resistance to other resins. Therefore, the resin layer 2 is a heat diffusion layer 3 or a substrate for a long period of time. The bonding strength with 1 can be maintained.

Here, as a method for confirming the principal component constituting the resin layer 2, the measurement may be performed by the following method. First, the resin layer 2 is scraped off, and the resin contained in the resin layer 2 is specified by using a Fourier transform infrared spectrophotometer (FTIR). After that, the heat sink 10 is cut so as to have the cross section shown in FIG. 2, and the resin layer 2 is measured by the energy dispersive X-ray analyzer (EDS) attached to the SEM with the cross section polished by CP as an observation surface. In this measurement, if the total amount of the components constituting the resin is larger than the total amount of the other components, it may be considered that the resin is the main component.

Further, the resin layer 2 in the heat sink 10 of the present disclosure may contain a filler made of aluminum oxide, aluminum nitride, boron nitride or diamond (hereinafter, also simply referred to as a filler). If such a configuration is satisfied, since the filler has a higher thermal conductivity than the resin, the inclusion of the filler increases the thermal conductivity of the resin layer 2 and improves the heat dissipation characteristics. The resin layer 2 may contain 10% by mass or more and 45% by mass or less of the filler in 100% by mass of all the components constituting the resin layer 2.

Further, if the material of the filler contained in the resin layer 2 is the same as the material of the substrate 1, the coefficient of thermal expansion of the resin layer 2 becomes close to the coefficient of thermal expansion of the substrate 1, and even if heating and cooling are repeated. , The resin layer 2 is more difficult to peel off from the substrate 1.

Here, the content of the filler in the resin layer 2 may be calculated by the following method. First, the resin layer 2 is measured using an X-ray diffractometer (XRD), and the filler contained in the resin layer 2 is used from the obtained 2θ (2θ is a diffraction angle) value using a JCPDS card. Is identified. Next, the resin layer 2 is scraped off, the weight of the scraped resin layer 2 is measured, the resin of the resin layer 2 is dissolved with a chemical solution, and the weight of the remaining filler is measured. Then, the content of the filler can be calculated by dividing the weight of the filler by the weight of the scraped resin layer 2.

Further, in the contact portion (hereinafter, also simply referred to as a contact portion) in contact with the resin layer 2 of the first surface 1a of the substrate 1 in the heat sink 10 of the present disclosure, the arithmetic mean roughness Ra obtained from the roughness curve is 0. It may be less than 3 μm and the skewness Rsk obtained from the roughness curve may be less than −0.5.

Here, the arithmetic mean roughness Ra means a value specified in JIS B 0601 (2013). Further, the skewness Rsk is defined in JIS B 0601 (2013), and is an index showing the ratio of the mountain part and the valley part to the average height of the roughness as the center line. If the skewness Rsk is negative, it indicates that the mountainous region is larger than the valley region.

If such a configuration is satisfied, the contact portion has less unevenness and particularly has a surface texture with few peaks, so that the thermal resistance of the contact portion is reduced and heat is smoothly transferred from the resin layer 2 to the substrate 2. By transmitting, heat dissipation characteristics are improved.

Further, the contact portion in the heat sink 10 of the present disclosure may have the above-mentioned arithmetic mean roughness Ra and skewness Rsk, and the maximum cross-sectional height Rt obtained from the roughness curve may be 0.5 μm or more and 5 μm or less. Here, the maximum cross-sectional height Rt is defined in JIS B 0601 (2013), and is an index indicating the sum of the height of the maximum peak portion and the depth of the maximum valley portion in the evaluation length.

If such a configuration is satisfied, the contact portion has a surface texture with few protruding peaks and valleys while maintaining a large contact area with the resin layer 2, so that the thermal resistance of the contact portion is increased. The amount is further reduced, and heat is more smoothly transferred from the resin layer 2 to the substrate 1, so that the heat dissipation characteristics are further improved.

Here, the arithmetic mean roughness Ra, the skewness Rsk, and the maximum cross-sectional height Rt at the contact portion of the first surface 1a may be measured by the following method in accordance with JIS B 0601 (2013). First, the resin layer 2 is melted using a chemical solution that dissolves the resin, and the contact portion of the first surface 1a is exposed. After that, the measurement conditions are set, for example, the measurement length is 2.0 mm, the cutoff value is 0.1 mm, the scanning speed of the stylus having a stylus radius of 2 μm is set to 0.1 mm / sec, and the first surface 1a is set. At least three points may be measured at the contact portion of the above, and the average value may be obtained.

When the heat sink 10 was cut so as to have the cross section shown in FIG. 2 and the cross section polished by CP was observed using SEM, the contact portion of the first surface 1a and the resin of the first surface 1a were observed. If it can be determined that the surface texture is the same as that of the exposed portion that is not in contact with the surface, the exposed portion of the first surface 1a is measured, and the measurement result is regarded as the measurement result of the contact portion of the first surface 1a. May be good.

Further, the thermal conductivity of the heat diffusion layer 3 in the heat sink 10 of the present disclosure in the first direction may be 7 times or more the thermal conductivity of the substrate 1. If such a configuration is satisfied, the heat dissipation characteristics of the heat sink 10 of the present disclosure will be improved.

Further, the substrate 1 in the heat sink 10 of the present disclosure has a second surface 1b facing the first surface 1a, and the second surface 1b may have a plurality of protrusions. Here, the protrusion refers to a portion of the second surface 1b that protrudes from the line connecting the portions having no protrusion. Further, with respect to the second surface 1b, facing the first surface 1a means, in other words, being located opposite to the first surface 1a. If such a configuration is satisfied, the heat sink 10 of the present disclosure has improved heat dissipation characteristics due to a plurality of protrusions on the second surface 1b of the substrate 1.

The protrusion may be made of any material, but if it is made of the same material as the substrate 1, there is a low possibility that the protrusion will fall off due to the difference in thermal expansion between the substrate 1 and the protrusion. Excellent heat dissipation characteristics are maintained.

Further, the protrusions in the heat sink 10 of the present disclosure may have an average diameter of 10 μm or more and 40 μm or less in front view of the second surface 1b. In other words, the front view here is a plan view of the second surface 1b. If such a configuration is satisfied, the possibility that the protrusions can be removed from the substrate 1 is low, and the surface area of the protrusions can be increased, so that the heat dissipation characteristics of the heat sink 10 of the present disclosure are improved.

Here, the average diameter of the protrusions in the front view of the second surface 1b can be calculated by the following method. First, a photograph of the second surface 1b viewed from the front is taken using an SEM. Next, in this photograph, the outline of the protrusion is outlined in black. After that, using the bordered photograph, image analysis is performed by applying a technique called particle analysis of image analysis software "A image-kun" (registered trademark, manufactured by Asahi Kasei Engineering Co., Ltd.). Then, the average value of the circle-equivalent diameters of the protrusions calculated by this image analysis may be the average diameter of the protrusions in the front view of the second surface 1b. As the analysis conditions for "A image-kun", for example, the brightness of the crystal particles may be "bright", the binarization method may be "automatic", and the shading may be "presence".

The material of the substrate 1 in the heat sink 10 of the present disclosure is metal, ceramics, or the like. Examples of the metal include aluminum, copper, silver and alloys thereof. On the other hand, examples of the ceramics include aluminum oxide ceramics, silicon nitride ceramics, aluminum nitride ceramics, silicon carbide ceramics, and the like. If the substrate 1 is made of aluminum oxide ceramics, it is easy to process and has excellent mechanical strength. Further, if the substrate 1 is made of aluminum nitride ceramics, the heat dissipation characteristics are particularly excellent. For example, aluminum oxide ceramics contain 70% by mass or more of aluminum oxide in 100% by mass of all the components constituting the ceramics.

Here, the material of the substrate 1 in the circuit board 10 of the present disclosure can be confirmed by the following method. First, the substrate 1 is measured using XRD, and identification is performed using a JCPDS card from the obtained 2θ values. Next, a fluorescent X-ray analyzer (XRF) is used to perform a quantitative analysis of the contained components. Then, for example, if the presence of aluminum oxide is confirmed by the above identification and the content converted from the Al content measured by XRF into aluminum oxide (Al ₂ O ₃ ) is 70% by mass or more, the aluminum oxide ceramics Is.

Further, the electronic device of the present disclosure includes a heat sink 10 having the above-described configuration and electronic components located on the heat diffusion layer 3 of the heat sink 10.

Here, the electronic component includes a semiconductor element, a Pelche element, a light emitting element, a resistor, a capacitor, an inductance, and a switching power supply, and may further include a transformer, a relay, an electric motor, and the like.

Next, an example of the heat sink of the present disclosure and a method of manufacturing an electronic device using the heat sink will be described. In the following description, a case where the substrate is made of ceramics will be described as an example.

A substrate having a first surface and a second surface facing the first surface is produced by the following method. First, a sintering aid, a binder, a solvent, a dispersant and the like are added to the powder of the raw material (silicon carbide, aluminum oxide, etc.) as the main component and appropriately mixed to prepare a slurry. Next, using this slurry, a molded product is obtained by the doctor blade method.

As another method for obtaining a molded product, the slurry is spray-dried by a spray granulation method (spray drying method) to granulate granules, and the granules are used by a mold pressing method, a roll compaction method, or a method. Injection molding may be used.

By cutting by machining, punching by a die, laser processing, etc., a molded body having an arbitrary shape can be obtained.

Then, a portion to be a protrusion may be formed in advance on the surface of the molded body to be the second surface of the substrate. For example, a mold having a recess may be pressed against the surface, or the surface may be scraped by laser processing or blasting to form a portion to be a protrusion. Alternatively, the powder to be a protrusion may be sprinkled on the surface by using a sieve or the like.

Then, a substrate is produced by firing this molded product. In addition, in order to make the first surface of the substrate an arbitrary surface texture, it may be polished.

Next, the thermal conductivity in the first direction along the first surface is 8 times or more the thermal conductivity in the second direction orthogonal to the first surface, and is larger than the thermal conductivity of the substrate, for example, graphene. Prepare a thermal diffusion layer composed of graphite or carbon nanotubes.

Next, a resin layer, which is a double-sided adhesive tape, is attached to the heat diffusion layer. Alternatively, a paste to be a resin layer is applied to the heat diffusion layer and then heat-treated to form a resin layer on the heat diffusion layer. Here, the average thickness of the resin layer is set to be equal to or larger than the average thickness of the heat diffusion layer.

The resin layer may be mainly composed of an epoxy resin, an acrylic resin or a silicone resin. Further, the resin layer may contain a filler made of aluminum oxide, aluminum nitride, boron nitride or diamond in order to improve heat dissipation.

Next, the heat diffusion layer on which the resin layer is formed is cut to a predetermined size by a method such as a cutter, a cutting machine, punching with a press, laser cutting, or the like. After that, using a press machine, a rolling roll, a roller for bonding, etc., the heat diffusion layer having the resin layer is bonded to the first surface of the substrate so that large bubbles do not remain between the substrate and the resin layer. Thereby, the heat sink of the present disclosure is obtained.

Further, by mounting an electronic component on the heat diffusion layer of the heat sink of the present disclosure, the electronic device of the present disclosure can be obtained. If necessary, the heat diffusion layer and the electronic component may be joined by using a joining material made of a metal brazing material, solder, a thermosetting resin adhesive, grease, a double-sided adhesive tape, or the like.

1: Substrate 2: Resin layer 3: Heat diffusion layer 10: Heat sink

Claims (12)

A substrate having a first surface and
A resin layer located in contact with the first surface and
A heat diffusion layer located in contact with the resin layer is provided.
The thermal conductivity in the first direction along the first surface of the heat diffusion layer is 8 times or more the thermal conductivity in the second direction orthogonal to the first surface of the heat diffusion layer, and the substrate. Greater than the thermal conductivity of
The average thickness of the resin layer is equal to or greater than the average thickness of the heat diffusion layer .
In the contact portion of the first surface in contact with the resin layer, the arithmetic mean roughness Ra obtained from the roughness curve is less than 0.3 μm, and the skewness Rsk obtained from the roughness curve is less than −0.5. be
heatsink. The heat sink according to claim 1, wherein the average thickness of the resin layer is 2 times or more and 5 times or less the average thickness of the heat diffusion layer. The heat sink according to claim 1 or 2, wherein the average thickness of the heat diffusion layer is 15 μm or more and 40 μm or less. The heat sink according to any one of claims 1 to 3, wherein the thermal conductivity of the heat diffusion layer in the first direction is 40 times or more the thermal conductivity of the heat diffusion layer in the second direction. Any one of claims 1 to 4 in which A <B <C, where A is the area of the heat diffusion layer, B is the area of the resin layer, and C is the area of the first surface in planar fluoroscopy. Heat sink described in. The heat sink according to any one of claims 1 to 5, wherein the main component of the resin layer is an epoxy resin, an acrylic resin, or a silicone resin. The heat sink according to any one of claims 1 to 6, wherein the resin layer contains a filler made of aluminum oxide, aluminum nitride, boron nitride or diamond. The heat sink according to any one of claims 1 to 7, wherein the contact portion has a maximum cross-sectional height Rt obtained from a roughness curve of 0.5 μm or more and 5 μm or less. The heat sink according to any one of claims 1 to 8 , wherein the thermal conductivity of the heat diffusion layer in the first direction is 7 times or more the thermal conductivity of the substrate. The heat sink according to any one of claims 1 to 9 , wherein the substrate has a second surface facing the first surface, and the second surface has a plurality of protrusions. The heat sink according to claim 10 , wherein the protrusion has an average diameter of 10 μm or more and 40 μm or less in front view of the second surface. An electronic device comprising the heat sink according to any one of claims 1 to 11 and an electronic component located on the heat diffusion layer.

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