JP2022068136A - Heat conductive sheet and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat conductive sheet capable of reducing a decrease in thermal conductivity when a load is increased.

SOLUTION: A heat conductive sheet 1 includes a binder resin, a scaly first heat conductive filler, and a non-scaly second heat conductive filler, and the first heat conductive filler and the second heat conductive filler are dispersed in the binder resin, the first heat conductive filler is boron nitride, and the average particle size of the second heat conductive filler is 5 μm or less, the long axis of the first heat conductive filler is oriented in the thickness direction of the heat conductive sheet, and the short axis of the first heat conductive filler is randomly oriented in the in-plane direction of the heat conductive sheet.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2022,JPO&INPIT

Description

This technique relates to a heat conductive sheet and a method for manufacturing a heat conductive sheet.

As the performance of electronic devices increases, the density and mounting of semiconductor devices are increasing. Along with this, it is important to more efficiently dissipate heat generated from the electronic components constituting the electronic device. For example, in a semiconductor device, in order to efficiently dissipate heat, electronic components are attached to heat sinks such as a heat dissipation fan and a heat sink via a heat conductive sheet. As the heat conductive sheet, for example, a silicone resin containing (dispersed) a filler such as an inorganic filler is widely used. A heat radiating member such as this heat conductive sheet is required to further improve the heat conductivity. For example, for the purpose of high thermal conductivity of a thermally conductive sheet, it has been studied to increase the filling rate of an inorganic filler blended in a matrix such as a binder resin. However, if the filling rate of the inorganic filler is increased, the flexibility of the heat conductive sheet is impaired and powder falling occurs, so that there is a limit to increasing the filling rate of the inorganic filler.

Examples of the inorganic filler include alumina, aluminum nitride, aluminum hydroxide and the like. Further, for the purpose of high thermal conductivity, the matrix may be filled with scaly particles such as boron nitride and graphite, carbon fibers and the like. This is due to the anisotropy of the thermal conductivity of the scaly particles and the like. For example, carbon fiber is known to have a thermal conductivity of about 600 to 1200 W / m · K in the fiber direction. Further, in the case of boron nitride, it may have a thermal conductivity of about 110 W / m · K in the plane direction and a thermal conductivity of about 2 W / m · K in the direction perpendicular to the plane direction. Are known. In this way, the fiber direction of the carbon fibers and the plane direction of the scaly particles are made the same as the thickness direction of the sheet, which is the heat transfer direction, that is, the carbon fibers and the scaly particles are oriented in the thickness direction of the sheet. It can be expected that the thermal conductivity will be dramatically improved.

Here, as the heat conductive sheet, a resin molded body obtained by curing a heat conductive resin composition in which a filler such as an inorganic filler is mixed with a binder resin into a block shape is prepared, and the molded body is sliced into a sheet shape. Manufactured by However, when slicing the resin molded product, if it cannot be sliced to a uniform thickness, the uneven portion on the sheet surface becomes large, and air is entrained in the uneven portion at the time of mounting, so that there is a problem that excellent heat conduction cannot be utilized.

Japanese Unexamined Patent Publication No. 2012-201106

In order to solve this problem, for example, Patent Document 1 proposes a heat conductive sheet containing boron nitride as a heat conductive filler in a predetermined ratio and in which the heat conductive filler is oriented in the thickness direction. In Patent Document 1, a silicone resin composition containing a predetermined ratio of boron nitride is extruded into a sheet to form a green sheet, and the green sheets are laminated to form a silicone laminate, and the silicone laminate is laminated in the lamination direction. By cutting, a thermally conductive sheet in which boron nitride is oriented in the thickness direction is obtained. However, in this manufacturing method, boron nitride is oriented by extruding the silicone resin composition with a coater or the like and is oriented in the thickness direction of the heat conductive sheet, but the orientation angle of boron nitride is parallel to the extrusion direction of the coater. Conceivable. Therefore, when the load on the heat conductive sheet is increased, there is a problem that the boron nitride collapses at a certain point and the thermal conductivity drops sharply. In addition, this manufacturing method requires a plurality of green sheet laminating processes, and there is a concern that the cost will increase.

This technology has been proposed in view of such conventional circumstances, and provides a method for manufacturing a heat conductive sheet and a heat conductive sheet that can reduce the decrease in thermal conductivity even when a load is increased. do.

The heat conductive sheet according to the present technology contains a binder resin, a scaly first heat conductive filler, and a non-scaly second heat conductive filler, and the above first heat conductive filler. In the heat conductive sheet in which the second heat conductive filler and the second heat conductive filler are dispersed in the binder resin, the first heat conductive filler is boron nitride, and the average particle size of the second heat conductive filler is The length is 5 μm or less, the long axis of the first heat conductive filler is oriented in the thickness direction of the heat conductive sheet, and the short axis of the first heat conductive filler is oriented in the in-plane direction of the heat conductive sheet. Is randomly oriented.

The method for producing a heat conductive sheet according to the present technology is to disperse a scaly first heat conductive filler and a non-scaly second heat conductive filler in a curable resin composition to conduct heat conduction. Step A for preparing a resin composition for forming a sex sheet, step B for forming a molded body block from the resin composition for forming a heat conductive sheet, and heat conduction by slicing the molded body block into a sheet. The heat conductive sheet has a step C of obtaining a property sheet, the first heat conductive filler is boron nitride, the average particle size of the second heat conductive filler is 5 μm or less, and the heat conductive sheet is: The major axis of the first heat conductive filler is oriented in the thickness direction, and the minor axis of the first heat conductive filler is randomly oriented in the in-plane direction.

According to the present technique, it is possible to provide a heat conductive sheet capable of reducing the decrease in thermal conductivity even when a load is increased.

FIG. 1 is a cross-sectional view showing an example of a heat conductive sheet according to the present technique. FIG. 2 is a perspective view schematically showing scaly boron nitride having a hexagonal crystal shape. FIG. 3 is a diagram for explaining XRD measurement for investigating the orientation state of the first heat conductive filler. FIG. 4 is a diagram for explaining an XRD measurement surface. FIG. 5 is a front view showing an opening having a structure in which a plurality of cells having sides that are not orthogonal to each other are continuous. 6A and 6B are front views showing an opening according to a comparative example, where FIG. 6A shows an opening having a parallel slit structure and FIG. 6B shows an opening having a mesh structure. FIG. 7 is a cross-sectional view showing an example of a semiconductor device to which the heat conductive sheet according to the present technology is applied.

In the present specification, the average particle size (D50) of the heat conductive filler is an area length (μm) of 50% cumulative from the small particle size side of the particle size distribution of the heat conductive filler, and is the heat conductive filler. The area length when the cumulative value is 50% when the cumulative curve is obtained from the small particle size side of the particle size distribution of the heat conductive filler, assuming that the total area of the group is 100%. The particle size distribution (particle size distribution) in the present specification is obtained by the volume standard. As a method for measuring the particle size distribution, for example, a method using a laser diffraction type particle size distribution measuring machine can be mentioned.

<Thermal conductive sheet>
FIG. 1 is a cross-sectional view showing an example of a heat conductive sheet 1 according to the present technique. The heat conductive sheet 1 contains a binder resin 2, a scaly first heat conductive filler 3, and a non-scaly second heat conductive filler 4, and the first heat conductive filler 3 is contained. And the second heat conductive filler 4 are dispersed in the binder resin 2. Further, in the heat conductive sheet 1, the major axis of the first heat conductive filler 3 is oriented in the thickness direction of the sheet, and the minor axis of the first heat conductive filler 3 is oriented in the in-plane direction of the heat conductive sheet. Is randomly oriented. In such a heat conductive sheet 1, the decrease in thermal conductivity with an increase in load is small. For example, in the heat conductive sheet 1, when a load of 0.5 to 3 kgf / cm ² is applied to the thickness direction B, the difference between the maximum value and the minimum value of the effective thermal conductivity is 1.5 W / m. It can be K or less.

Hereinafter, the components of the heat conductive sheet 1 will be described.

<Binder resin>
The binder resin 2 is for holding the first heat conductive filler 3 and the second heat conductive filler 4 in the heat conductive sheet 1. The binder resin 2 is selected according to the characteristics such as mechanical strength, heat resistance, and electrical properties required for the heat conductive sheet 1. The binder resin 2 can be selected from a thermoplastic resin, a thermoplastic elastomer, and a thermosetting resin.

Examples of the thermoplastic resin include ethylene-α-olefin copolymers such as polyethylene, polypropylene, and ethylene-propylene copolymers, polymethylpentene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, and ethylene-vinyl acetate copolymers. Fluoropolymers such as polyvinyl alcohol, polyvinyl acetal, polyvinylidene fluoride and polytetrafluoroethylene, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polystyrene, polyacrylonitrile, styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene Polymethacryl such as polymer (ABS) resin, polyphenylene-ether copolymer (PPE) resin, modified PPE resin, aliphatic polyamides, aromatic polyamides, polyimide, polyamideimide, polymethacrylic acid, polymethacrylic acid methyl ester, etc. Examples thereof include acid esters, polyacrylic acids, polycarbonates, polyphenylene sulfides, polysulfones, polyether sulfones, polyether nitriles, polyether ketones, polyketones, liquid crystal polymers, silicone resins, ionomers and the like.

Examples of the thermoplastic elastomer include a styrene-butadiene block copolymer or a hydrogenated product thereof, a styrene-isoprene block copolymer or a hydrogenated product thereof, a styrene-based thermoplastic elastomer, an olefin-based thermoplastic elastomer, and a vinyl chloride-based thermoplastic elastomer. , Polyester-based thermoplastic elastomer, polyurethane-based thermoplastic elastomer, polyamide-based thermoplastic elastomer and the like.

Examples of the thermosetting resin include crosslinked rubber, epoxy resin, phenol resin, polyimide resin, unsaturated polyester resin, diallyl phthalate resin and the like. Specific examples of the crosslinked rubber include natural rubber, acrylic rubber, butadiene rubber, isoprene rubber, styrene-butadiene copolymer rubber, nitrile rubber, hydrogenated nitrile rubber, chloroprene rubber, ethylene-propylene copolymer rubber, and chlorinated polyethylene rubber. Examples thereof include chlorosulfonated polyethylene rubber, butyl rubber, halogenated butyl rubber, fluororubber, urethane rubber, and silicone rubber.

As the binder resin 2, for example, a silicone resin is preferable in consideration of the adhesion between the heat generating surface and the heat sink surface of the electronic component. The silicone resin is, for example, a two-component addition reaction type silicone resin containing a silicone having an alkenyl group as a main component, a main agent containing a curing catalyst, and a curing agent having a hydrosilyl group (Si—H group). Can be used. As the silicone having an alkenyl group, for example, a polyorganosiloxane having a vinyl group can be used. The curing catalyst is a catalyst for accelerating the addition reaction between the alkenyl group in the silicone having an alkenyl group and the hydrosilyl group in the curing agent having a hydrosilyl group. Examples of the curing catalyst include well-known catalysts as catalysts used in the hydrosilylation reaction, and for example, platinum group curing catalysts such as platinum group metal alone such as platinum, rhodium and palladium, platinum chloride and the like can be used. As the curing agent having a hydrosilyl group, for example, a polyorganosiloxane having a hydrosilyl group can be used. The binder resin 2 may be used alone or in combination of two or more.

When a two-component addition reaction type liquid silicone resin containing a silicone main agent and a curing agent is used as the binder resin 2, the mass ratio of the silicone main agent to the curing agent (silicone main agent: curing agent) is 5: 5 to 7: 3. Therefore, the compression rate of the heat conductive sheet 1 can be further increased.

The content of the binder resin 2 in the heat conductive sheet 1 is not particularly limited and can be appropriately selected depending on the intended purpose. For example, the lower limit of the content of the binder resin 2 in the heat conductive sheet 1 can be 20% by volume or more, 25% by volume or more, or 30% by volume or more. Further, the upper limit of the content of the binder resin 2 in the heat conductive sheet 1 can be 70% by volume or less, 60% by volume or less, or 50% by volume or less. From the viewpoint of improving the compression rate of the heat conductive sheet 1 and reducing the load dependence of the effective heat conductivity, the content of the binder resin 2 in the heat conductive sheet 1 may be 30 to 40% by volume. Preferably, it can be 30 to 37% by volume.

<First thermally conductive filler>
The first heat conductive filler 3 is a scaly heat conductive filler. The scaly heat conductive filler has a high aspect ratio and isotropic heat conductivity in the plane direction. The scaly heat conductive filler is not particularly limited as long as it is scaly, but a material capable of ensuring the insulating property of the heat conductive sheet 1 is preferable. For example, as the scaly heat conductive filler, boron nitride (BN), mica, alumina, aluminum nitride, silicon carbide, silica, zinc oxide, molybdenum disulfide and the like can be used.

Here, the scaly heat conductive filler is a heat conductive filler having a major axis, a minor axis, and a thickness, has a high aspect ratio (major axis / thickness), and is in the plane direction including the major axis. It has an isotropic thermal conductivity. The short axis is the direction orthogonal to the long axis of the scaly heat conductive filler on the surface including the long axis of the scaly heat conductive filler, and is the longest portion of the scaly heat conductive filler. It shall refer to the length. The thickness means a value obtained by measuring and averaging the thicknesses of the surfaces including the major axis of the scaly heat conductive filler at 10 points.

FIG. 2 is a perspective view schematically showing a scaly boron nitride 3A having a hexagonal crystal shape, which is an example of a scaly heat conductive filler. In FIG. 2, a represents the major axis of the scaly boron nitride 3A, b represents the thickness of the scaly boron nitride 3A, and c represents the minor axis of the scaly boron nitride 3A. As the scaly heat conductive filler, it is preferable to use scaly boron nitride 3A having a hexagonal crystal shape as shown in FIG. 2 from the viewpoint of the thermal conductivity of the heat conductive sheet 1. The scaly heat conductive filler may be used alone or in combination of two or more. The heat conductive sheet 1 according to the present technology, as the first heat conductive filler 3, is a scaly heat conductive filler (for example, scaly) which is cheaper than a spherical heat conductive filler (for example, spherical boron nitride). The boron nitride 3A) can be used to achieve both excellent thermal properties and cost reduction.

The average particle size (D50) of the scaly heat conductive filler is not particularly limited and can be appropriately selected depending on the intended purpose. For example, the lower limit of the average particle size of the scaly heat conductive filler can be 10 μm or more, may be 20 μm or more, may be 30 μm or more, or may be 35 μm or more. Further, the upper limit of the average particle size of the scaly heat conductive filler can be 150 μm or less, may be 100 μm or less, 90 μm or less, or 80 μm or less. It may be 70 μm or less, 50 μm or less, or 45 μm or less. From the viewpoint of improving the compressibility of the heat conductive sheet 1 and reducing the load dependence of the effective heat conductivity, the average particle size of the scaly heat conductive filler is preferably 20 to 100 μm, and is preferably 20 to 100 μm. It can also be 50 μm.

The aspect ratio (major axis / minor axis) of the scaly heat conductive filler is not particularly limited and can be appropriately selected depending on the intended purpose. For example, the aspect ratio of the scaly heat conductive filler can be in the range of 10 to 100. The major axis and the minor axis of the scaly heat conductive filler can be measured by, for example, a microscope, a scanning electron microscope (SEM), a particle size distribution meter, or the like. As an example, when scaly boron nitride 3A having a hexagonal crystal shape as shown in FIG. 2 is used as the scaly heat conductive filler, 200 or more boron nitrides are taken from the image taken by SEM. 3A may be arbitrarily selected, the ratio (a / c) of each major axis a and minor axis c may be obtained, and the average value may be calculated.

The content of the first heat conductive filler 3 in the heat conductive sheet 1 is not particularly limited and can be appropriately selected depending on the intended purpose. For example, the lower limit of the content of the first heat conductive filler 3 in the heat conductive sheet 1 can be 15% by volume or more, 20% by volume or more, or 25% by volume or more. There may be. Further, the upper limit of the content of the first heat conductive filler 3 in the heat conductive sheet 1 can be 45% by volume or less, 40% by volume or less, and 35% by volume or less. It may be present, and may be 30% by volume or less. From the viewpoint of improving the compressibility of the heat conductive sheet 1 and reducing the load dependence of the effective heat conductivity, the content of the first heat conductive filler 3 in the heat conductive sheet 1 is 20 to 28 volumes. It is preferably%, and it can be 23 to 27% by volume.

<Second thermally conductive filler>
The second heat conductive filler 4 is a heat conductive filler other than the above-mentioned first heat conductive filler 3. The second heat conductive filler 4 is non-scaly, and examples thereof include spherical, powder, granule, and flat heat conductive fillers. The material of the second heat conductive filler 4 is preferably a material capable of ensuring the insulating property of the heat conductive sheet 1 in consideration of the effect of the present technology, for example, aluminum oxide (alumina, sapphire), aluminum nitride, and nitride. Examples include boron, zirconia, and silicon carbide. The second heat conductive filler 4 may be used alone or in combination of two or more.

In particular, as the second heat conductive filler 4, aluminum nitride particles and alumina particles are used in combination from the viewpoint of improving the compressibility of the heat conductive sheet 1 and reducing the load dependence of the effective heat conductivity. Is preferable. The average particle size of the aluminum nitride particles is preferably 1 to 5 μm, preferably 1 to 3 μm, or 1 to 2 μm, from the viewpoint of reducing the viscosity of the heat conductive sheet 1 before heat curing. good. Further, the average particle size of the alumina particles is preferably 1 to 3 μm, and may be 1.5 to 2.5 μm, from the viewpoint of reducing the viscosity of the heat conductive sheet 1 before heat curing.

The content of the second heat conductive filler 4 in the heat conductive sheet 1 is not particularly limited and can be appropriately selected depending on the intended purpose. The lower limit of the content of the second heat conductive filler 4 in the heat conductive sheet 1 can be 10% by volume or more, may be 15% by volume or more, and may be 20% by volume or more. May be good. Further, the upper limit of the content of the second heat conductive filler 4 in the heat conductive sheet 1 can be 50% by volume or less, 40% by volume or less, and 30% by volume or less. It may be present, and may be 25% by volume or less. The total content of the second heat conductive filler 4 in the heat conductive sheet 1 can be, for example, 30 to 60% by volume.

When alumina particles are used alone as the second heat conductive filler 4, the content of the alumina particles in the heat conductive sheet 1 is 10 to 45 from the viewpoint of reducing the viscosity of the heat conductive sheet 1 before heat curing. The volume is preferably%. Further, as described above, when the aluminum nitride particles and the alumina particles are used in combination as the second heat conductive filler 4, the heat conductive sheet is obtained from the viewpoint of reducing the viscosity of the heat conductive sheet 1 before the heat curing. In 1, the content of alumina particles is preferably 10 to 25% by volume, and the content of aluminum nitride particles is preferably 10 to 25% by volume.

Further, the total content of the first heat conductive filler 3 and the second heat conductive filler 4 in the heat conductive sheet 1 is from the viewpoint of improving the compression rate and reducing the load dependence of the effective heat conductivity. In, it is preferably less than 70% by volume, and may be 67% by volume or less. Further, the lower limit of the total content of the first heat conductive filler 3 and the second heat conductive filler 4 in the heat conductive sheet 1 improves the compressibility of the heat conductive sheet 1 and is effective heat conduction. From the viewpoint of reducing the load dependence of the rate, it is preferably 60% by volume or more, and may be 63% by volume or more.

The heat conductive sheet 1 may further contain components other than the above-mentioned components as long as the effects of the present technique are not impaired. Examples of other components include dispersants, curing accelerators, retarders, tackifiers, plasticizers, flame retardants, antioxidants, stabilizers, colorants and the like.

[Orientation]
As described above, the heat conductive sheet 1 in which the first heat conductive filler 3 and the second heat conductive filler 4 are dispersed in the binder resin 2 is the thickness of the heat conductive sheet 1 shown in FIG. The long axis of the first heat conductive filler 3 is oriented in the direction B, and the short axis of the first heat conductive filler 3 is randomly oriented in the in-plane direction A of the heat conductive sheet 1. As a result, the thermal conductivity sheet 1 can reduce the decrease in thermal conductivity even when the load is increased.

The major axis of the first heat conductive filler 3 is oriented in the thickness direction B of the heat conductive sheet 1, for example, among all the first heat conductive fillers in the heat conductive sheet 1. It means that the ratio of the first heat conductive filler whose major axis is oriented in the thickness direction B of the heat conductive sheet 1 is 50% or more. Further, the fact that the minor axis of the first thermally conductive filler 3 is randomly oriented in the in-plane direction A of the thermally conductive sheet 1 means that the direction of the minor axis of the first thermally conductive filler 3 is thermally conductive. A state in which the sheet 1 is irregular in the in-plane direction A.

That is, in the heat conductive sheet 1, each first heat conductive filler 3 is dispersed in the vertical cross-sectional view with the major axis directed in the sheet thickness direction B, and each first in the cross-sectional view. The heat conductive filler 3 has a state in which the direction of the minor axis is irregular in the inward direction A of the sheet surface.

The orientation state of the first heat conductive filler 3 can be observed by measuring the signal intensity by XRD (X-ray diffraction method). For example, the signal intensities measured from the thickness direction of the sheet are the signal intensity A (corresponding to the 002 surface in FIG. 3) when the surface of the sheet is irradiated with X-rays when viewed from the thickness direction of the sheet, and the sheet. It is the signal intensity B (corresponding to the 110th plane in FIG. 3) when the X-ray is irradiated in the direction corresponding to the diagonal line, and the intensity ratio A / B is used as an index of the orientation state. Similarly, the intensity ratio A / B of the XRD signal measured from the front direction and the side surface direction of the sheet is obtained, and when the signal intensity ratios are compared, the direction in which the A / B is relatively small has higher orientation, that is, the first. It can be said that the major axis of the heat conductive filler is oriented.

For the heat conductive sheet 1 to which this technique was applied, the signal intensity ratios were obtained for each of the sheet thickness direction, the front direction, and the side surface direction. Specifically, as shown in FIG. 4, one side of the sheet in the thickness direction b is the upper surface 1a, one side surface of the sheet is the front surface 1b, and the other side surface adjacent to the front surface 1b is the side surface 1c. Then, when the signal intensity A (corresponding to the 002 surface in FIG. 3) when the upper surface 1a of the heat conductive sheet 1 is directed upward and X-rays are irradiated, and when the X-rays are irradiated in the direction corresponding to the diagonal line of the sheet. The signal strength B (corresponding to the 110th plane in FIG. 3) was measured, and the strength ratio A / B was obtained. Next, the strength ratio A / B was obtained in the same manner with the front surface 1b facing upward. Next, the strength ratio A / B was obtained in the same manner with the side surface 1c facing upward.

Then, when the XRD signal intensity ratios of the upper surface 1a, the front surface 1b, and the side surface 1c were compared, the heat conductive sheet 1 to which the present technology was applied had the XRD signal intensity ratio measured from the upper surface 1a, that is, the thickness direction of the sheet. The value was much smaller than the XRD signal intensity ratio measured from the front surface 1b and the side surface 1c. From this, it was found that the long axis of the first thermally conductive filler 3 was oriented in the thickness direction of the sheet.

Further, when the XRD signal intensity ratio measured from the front surface 1b and the XRD signal intensity ratio measured from the side surface 1c were compared, the difference became large. From this, it is presumed that the minor axis of the first thermally conductive filler 3 is randomly oriented in the direction of the sheet surface.

The heat conductive sheet 1 is a second heat conductive filler 4 and a first heat conductive filler 3 by using the first heat conductive filler 3 and the second heat conductive filler 4 in combination. Can support the above-mentioned orientation state.

In such a heat conductive sheet 1, since the long axis of the first heat conductive filler 3 is oriented in the thickness direction B (see FIG. 1) of the heat conductive sheet 1, the first heat conductivity is obtained. The thermal conductivity in the orientation direction of the long axis of the filler 3 (thickness direction B of the heat conductive sheet 1) is the non-orientation direction of the long axis of the first heat conductive filler 3 (for example, the surface of the heat conductive sheet 1). It can be at least twice the thermal conductivity in the direction A).

Here, the heat conductive sheet 1 in which the minor axis of the first heat conductive filler 3 is randomly oriented in the in-plane direction A of the sheet has a visible pattern on the sheet surface. The shape of the pattern is considered to reflect the random orientation of the minor axis of the first heat conductive filler 3, and is a pattern having sides that are not orthogonal to each other. The pattern on the surface of the sheet is, for example, a geometric pattern such as a polygonal shape having sides that are not orthogonal to each other, a pattern in which a plurality of circles or ellipses are continuous, or a pattern in which these geometric patterns and a circle or ellipse pattern are mixed. Is.

The heat conductive sheet 1 has a pattern having sides that are not orthogonal to each other on the sheet surface due to the random orientation of the minor axis of the first heat conductive filler 3, and the load is increased by the random orientation. Even in this case, the decrease in thermal conductivity can be reduced. That is, since the heat conductive sheet 1 has a pattern on the sheet surface showing the random orientation of the minor axis of the first heat conductive filler 3, the first heat conduction that is randomly oriented in the plane direction on the sheet surface. The property filler 3 has high thermal conductivity in the plane direction due to the short axis. This high thermal conductivity is short on the sheet surface even when a load is applied by being placed between the heating element and the radiator and the long axis of the first thermally conductive filler is tilted. Random orientation of the axis is maintained. As a result, the heat conductive sheet 1 has a short axis randomly oriented in the in-plane direction even if the long axis of the scaly first heat conductive filler whose major axis is oriented in the thickness direction is tilted due to an increase in load. The thermal conductivity in the sheet thickness direction is maintained, and the fluctuation range of the thermal conductivity with an increase in load can be reduced.

On the other hand, when the pattern appearing on the surface of the heat conductive sheet is composed of only the sides orthogonal to each other, the short axis of the scaly filler contained in this heat conductive sheet is oriented in a predetermined direction. Conceivable. In such a heat conductive sheet, since the minor axis of the scaly filler is oriented in a predetermined direction with respect to the surface direction of the sheet, the heat conductivity with respect to the surface direction is also low. Then, even when the long axis of the scaly first heat conductive filler whose major axis is oriented in the thickness direction is tilted due to an increase in load, it is uniformly tilted while the orientation of the minor axis is maintained. Therefore, the thermal conductivity decreases as the load increases.

The average thickness of the heat conductive sheet 1 is not particularly limited and can be appropriately selected depending on the intended purpose. For example, the lower limit of the average thickness of the heat conductive sheet can be 0.05 mm or more, or 0.1 mm or more. Further, the upper limit of the average thickness of the heat conductive sheet can be 5 mm or less, may be 4 mm or less, or may be 3 mm or less. From the viewpoint of handleability of the heat conductive sheet 1, the average thickness of the heat conductive sheet 1 is preferably 0.1 to 4 mm, preferably 0.5 to 3 mm, and 1 to 2 mm. You can also. The average thickness of the heat conductive sheet 1 can be obtained from, for example, the thickness of the heat conductive sheet measured at any five points and the arithmetic mean value thereof.

In the heat conductive sheet 1, the major axis of the scaly first heat conductive filler 3 is oriented in the thickness direction, and the minor axis of the scaly first heat conductive filler 3 is randomly oriented in the in-plane direction. Therefore, even if the load increases and the scaly thermal conductivity filler collapses, the thermal conductivity is maintained by the short axis randomly oriented in the in-plane direction, and the decrease in thermal conductivity due to the increase in load is small. can do.

<Manufacturing method of heat conductive sheet>
The method for manufacturing a heat conductive sheet according to the present technique includes, for example, the following steps A, B, and C.

<Process A>
In step A, a composition for forming a heat conductive sheet is prepared by dispersing the scaly first heat conductive filler 3 and the non-scaly second heat conductive filler 4 in the binder resin 2. The composition for forming a heat conductive sheet includes a first heat conductive filler 3, a second heat conductive filler 4, a binder resin 2, and various additives and volatile solvents as needed. Can be prepared by uniformly mixing with a known method.

<Process B>
In step B, a molded body block is formed from the prepared composition for forming a heat conductive sheet. Examples of the method for forming the molded body block include an extrusion molding method and a mold molding method. The extrusion molding method and the mold molding method are not particularly limited, and are required for the viscosity of the composition for forming a heat conductive sheet and the heat conductive sheet from among various known extrusion molding methods and mold molding methods. It can be appropriately adopted depending on the characteristics and the like.

For example, in the extrusion molding method, when the composition for forming a heat conductive sheet is extruded from a die, or in the mold molding method, when the composition for forming a heat conductive sheet is pressed into a mold, the binder resin flows. The long axis of the scaly heat conductive filler 3 is oriented along the flow direction.

The size and shape of the molded body block can be determined according to the required size of the heat conductive sheet 1. For example, a rectangular parallelepiped having a vertical size of 0.5 to 15 cm and a horizontal size of 0.5 to 15 cm can be mentioned. The length of the rectangular parallelepiped may be determined as needed. In the extrusion molding method, a columnar molded body block made of a cured product of a resin composition for forming a thermally conductive sheet can be formed.

[Aperture]
Here, in the step of forming the molded body block, the heat conductive sheet forming composition passes through the opening 5 having one or a plurality of cells having sides that are not orthogonal to each other when viewed from the flow direction thereof. Let me. As shown in FIG. 5A, for example, such an opening 5 can exemplify a structure in which a plurality of regular pentagonal cells are continuous. In addition, a structure in which a plurality of hexagonal honeycomb cells are continuous (FIG. 5 (b)), a structure in which a plurality of substantially circular cells are continuous (FIG. 5 (c)), and the like may be used. That is, the opening 5 according to the present technique is composed of only sides orthogonal to each other such as a square or a rectangle, for example, a parallel slit structure as shown in FIG. 6 (a) or as shown in FIG. 6 (b). A rectangular mesh structure in which a plurality of rectangular cells orthogonal to each other are continuous is excluded.

The opening 5 may have a cell that is partially composed of only sides that are orthogonal to each other. Further, the opening shapes of the plurality of cells may all be the same, or cells having different opening shapes may be combined and configured. Further, each opening shape of the plurality of cells may be a regular polygon or may not be a regular polygon. Further, the opening 5 may be composed of one opening and may have sides whose opening shapes are not orthogonal to each other, in addition to the one in which a plurality of cells having sides not orthogonal to each other are continuously formed.

By passing through such an opening 5, the long axis of the first heat conductive filler 3 contained in the composition for forming a heat conductive sheet is oriented in the flow direction, and the first heat conductive filler 3 is oriented in the flow direction. The minor axis of is randomly oriented (that is, non-oriented) in a direction orthogonal to the flow direction. This is because, in the step of forming the molded body block, when the composition for forming a heat conductive sheet is flowed through a substantially rectangular parallelepiped mold, it is passed through an opening composed of only sides orthogonal to each other. The minor axis of the heat conductive filler 3 of 1 is oriented in a direction orthogonal to each other, whereas when the minor axis of the heat conductive filler 3 is passed through an opening 5 having sides not orthogonal to each other, the first heat conductive filler 3 is used. This is probably because the orientation of the minor axis is disturbed.

The opening 5 can take any shape as long as it has sides that are not orthogonal to each other, but it is preferably a polygonal shape having five or more sides. This makes it possible to improve the random orientation of the minor axis.

In the molded body block formed from the composition for forming a heat conductive sheet that has passed through such an opening 5, the long axis of the first heat conductive filler 3 is oriented in the flow direction and the major axis of the first heat conductive filler 3 is oriented with respect to the flow direction. In the cross section orthogonal to each other, the minor axis of the first thermally conductive filler 3 is randomly oriented.

<Process C>
In step C, the molded block is sliced into a sheet to obtain a heat conductive sheet 1. The scale-like first heat conductive filler 3 is exposed on the surface (sliced surface) of the sheet obtained by slicing. The slicing method is not particularly limited, and can be appropriately selected from known slicing devices depending on the size and mechanical strength of the molded block. The slice direction of the molded block is preferably 60 to 120 degrees with respect to the flow direction, preferably 70 to 100 degrees, because the long axis of the first heat conductive filler 3 is oriented in the flow direction. The orientation is more preferred, and the 90 degree (vertical) orientation is even more preferred. When a columnar molded body block is formed in step B and the long axis of the first heat conductive filler 3 is oriented in the length direction of the molded body block, in step C, in the length direction of the molded body block. On the other hand, it is preferable to slice in a substantially vertical direction.

As described above, according to the method for manufacturing a heat conductive sheet having step A, step B, and step C, the above-mentioned heat conductive sheet 1 can be obtained.

The method for producing a heat conductive sheet according to the present technique is not limited to the above-mentioned example, and may further include, for example, a step D for pressing the sliced surface after the step C. By having the step D in which the method for manufacturing the heat conductive sheet is pressed, the surface of the sheet obtained in the step C is further smoothed, and the adhesion with other members can be further improved. As a pressing method, a pair of pressing devices including a flat plate and a pressing head having a flat surface can be used. Alternatively, it may be pressed with a pinch roll. The pressure at the time of pressing can be, for example, 0.1 to 100 MPa. In order to further enhance the effect of pressing and shorten the pressing time, it is preferable that the pressing is performed at the glass transition temperature (Tg) or higher of the binder resin 2. For example, the press temperature can be 0 to 180 ° C., may be in the temperature range of room temperature (for example, 25 ° C.) to 100 ° C., or may be 30 to 100 ° C.

<Electronic equipment>
The heat conductive sheet 1 according to the present technology is, for example, arranged between a heating element and a heat radiating element, so that heat generated by the heating element is dissipated to the radiating element, and electrons having a structure arranged between them are arranged. It can be a device. The electronic device has at least a heating element, a heat radiator, and a heat conductive sheet 1, and may further have other members, if necessary.

The heating element is not particularly limited, and for example, an electronic component that generates heat in an electric circuit such as a CPU, a GPU (Graphics Processing Unit), a DRAM (Dynamic Random Access Memory), an integrated circuit element such as a flash memory, a transistor, and a resistor. And so on. Further, the heating element also includes a component that receives an optical signal such as an optical transceiver in a communication device.

The radiator is not particularly limited, and examples thereof include those used in combination with integrated circuit elements, transistors, optical transceiver housings, and the like such as heat sinks and heat spreaders. In addition to the heat spreader and heat sink, the radiator may be any one that conducts heat generated from a heat source and dissipates it to the outside. Examples include heat pipes, metal covers, and housings.

FIG. 7 is a cross-sectional view showing an example of a semiconductor device 50 to which the heat conductive sheet 1 according to the present technology is applied. For example, as shown in FIG. 7, the heat conductive sheet 1 is mounted on a semiconductor device 50 built in various electronic devices and is sandwiched between a heating element and a heat radiating element. The semiconductor device 50 shown in FIG. 7 includes an electronic component 51, a heat spreader 52, and a heat conductive sheet 1, and the heat conductive sheet 1 is sandwiched between the heat spreader 52 and the electronic component 51. The heat conductive sheet 1 is sandwiched between the heat spreader 52 and the heat sink 53 to form a heat radiating member that dissipates heat from the electronic component 51 together with the heat spreader 52. The mounting location of the heat conductive sheet 1 is not limited to between the heat spreader 52 and the electronic component 51 and between the heat spreader 52 and the heat sink 53, and can be appropriately selected depending on the configuration of the electronic device or the semiconductor device.

Hereinafter, examples of this technique will be described. In the example, a thermal conductivity sheet was prepared, and the effective thermal conductivity and the compression rate were measured. The present technique is not limited to these examples.

<Example 1>
34% by volume of silicone resin, 26% by volume of scaly boron nitride (D50: 40 μm) having a hexagonal crystal shape, 20% by volume of aluminum nitride (D50: 1.2 μm), and spherical alumina particles (D50: 40 μm). A resin composition for forming a thermally conductive sheet was prepared by uniformly mixing 2 μm) with 20% by volume. By the extrusion molding method, a resin composition for forming a thermally conductive sheet is passed through an opening (see FIG. 5) in which a plurality of cells having sides not orthogonal to each other are continuous, and a mold having a rectangular parallelepiped internal space (see FIG. 5). It was poured into an opening diameter (opening diameter: 50 mm × 50 mm) and heated in an oven at 60 ° C. for 4 hours to form a columnar molded block. A peeled polyethylene terephthalate film was attached to the inner surface of the mold so that the peeled surface was on the inside. The obtained molded block was sliced into a sheet with an ultrasonic cutter to obtain a 1.0 mm-thick thermally conductive sheet in which scaly boron nitride was oriented in the thickness direction of the sheet.

<Example 2>
37% by volume of silicone resin, 23% by volume of scaly boron nitride (D50: 40 μm) having a hexagonal crystal shape, 20% by volume of aluminum nitride (D50: 1.2 μm), and spherical alumina particles (D50: 40 μm). A 1.0 mm thick heat conductive sheet was obtained by the same method as in Example 1 except that a resin composition for forming a heat conductive sheet was prepared by uniformly mixing 2 μm) 20% by volume. rice field.

<Example 3>
A 2.0 mm thick heat conductive sheet was obtained by the same method as in Example 1.

<Example 4>
A 2.0 mm thick heat conductive sheet was obtained by the same method as in Example 2.

<Comparative Example 1>
34% by volume of silicone resin, 26% by volume of scaly boron nitride (D50: 40 μm) having a hexagonal crystal shape, 20% by volume of aluminum nitride (D50: 1.2 μm), and spherical alumina particles (D50: 40 μm). A resin composition for forming a thermally conductive sheet was prepared by uniformly mixing 2 μm) with 20% by volume. Except for the fact that this resin composition for forming a thermally conductive sheet was passed through a 6 mm wide parallel slit (see FIG. 6A) by an extrusion molding method and poured into a mold to form a molded block. , A heat conductive sheet having a thickness of 1.0 mm was obtained by the same method as in Example 1.

<Comparative Example 2>
34% by volume of silicone resin, 26% by volume of scaly boron nitride (D50: 40 μm) having a hexagonal crystal shape, 20% by volume of aluminum nitride (D50: 1.2 μm), and spherical alumina particles (D50: 40 μm). A resin composition for forming a thermally conductive sheet was prepared by uniformly mixing 2 μm) with 20% by volume. Except for the fact that this resin composition for forming a heat conductive sheet was passed through a rectangular mesh-shaped opening (see FIG. 6B) by an extrusion molding method and poured into a mold to form a molded body block. Obtained a heat conductive sheet having a thickness of 1.0 mm by the same method as in Example 1.

<Comparative Example 3>
A 2.0 mm thick heat conductive sheet was obtained in the same manner as in Comparative Example 1.

<Comparative Example 4>
A 2.0 mm thick heat conductive sheet was obtained in the same manner as in Comparative Example 2.

<Difference between maximum and minimum effective thermal conductivity / effective thermal conductivity>
The effective thermal conductivity (W / m · K) of the thermal conductivity sheet is determined by a predetermined load (0.5 kgf / cm ² , 1.0 kgf / cm ² , using a thermal resistance measuring device compliant with ASTM-D5470). The thickness direction of the heat conductive sheet when 2.0 kgf / cm ² or 3.0 kgf / cm ² ) was applied was measured.

In addition, the difference between the maximum value and the minimum value of the effective thermal conductivity when a predetermined load was applied was obtained. It can be said that the smaller this difference is, the lower the load dependence of the effective thermal conductivity is, and the more stable the effective thermal conductivity is obtained even when the load is increased. For example, in Example 1, the maximum value of the effective thermal conductivity is 8.3 W / m · K (load 1.0 kgf / cm ² and load 2.0 kgf / cm ² ), and the minimum value is 7.6 W / m. -Since it is K (load 0.5 kgf / cm ² ), the difference is 0.7 W / m · K.

<Compression rate>
The compression rate (%) of the heat conductive sheet is such that a predetermined load (0.5 kgf / cm ² , 1.0 kgf / cm ² , 2.0 kgf / cm ² or 3.0 kgf / cm ² ) is applied to the heat conductive sheet. The thickness of the heat conductive sheet after being stabilized by applying the load was measured, and the thickness was calculated from the thickness of the heat conductive sheet before and after the load was applied.

<Evaluation judgment>
The evaluation and judgment of the heat conductive sheets of Examples and Comparative Examples were performed according to the following criteria. When the difference between the maximum value and the minimum value of the effective thermal conductivity of the thermal conductivity sheet was 1.5 W / m · K or less, it was evaluated as OK, and in other cases, it was evaluated as NG. The results are shown in Table 1.

As shown in Table 1, the thermal conductivity sheets of Examples 1 to 4 have the maximum and minimum effective thermal conductivity when a load of 0.5 to 3 kgf / cm ² is applied in the thickness direction. It was found that the difference between the two was 1.5 W / m · K or less, the load dependence of the effective thermal conductivity was low, and the effective thermal conductivity could be stably exhibited. This is because the heat conductive sheets of Examples 1 to 4 contain a curable resin composition, a scaly heat conductive filler, and a non-scaly heat conductive filler, and are scaly in the thickness direction. Since the long axis of the heat conductive filler is oriented and the short axis of the scaly heat conductive filler is randomly oriented in the in-plane direction, the load increases and the long axis is oriented in the thickness direction. It is considered that the thermal conductivity was maintained by the short axis randomly oriented in the in-plane direction even if the sex filler collapsed, and the fluctuation range of the thermal conductivity with the increase of the load became small.

In the thermal conductivity sheets of Comparative Examples 1 to 4, the difference between the maximum value and the minimum value of the effective thermal conductivity is 1.5 W / cm when a load of 0.5 to 3 kgf / cm ² is applied in the thickness direction. It was found that it was more than m · K, the effective thermal conductivity was highly load-dependent, and it was difficult to reduce the decrease in thermal conductivity with the increase in load. This is because the heat conductive sheets of Comparative Examples 1 and 2 have a short scale-like heat conductive filler because the resin composition for forming the heat conductive sheet passes through the openings of the parallel slit structure and the mesh structure. Since the shaft is also oriented in a predetermined direction in the in-plane direction, the short shaft maintains thermal conductivity when the load increases and the scaly heat conductive filler in which the long shaft is oriented in the thickness direction collapses. It is probable that it was not possible.

1 Thermal Conductive Sheet, 2 Binder Resin, 3 Scale-like First Thermal Conductive Filler, 3A Scale-like Boron Nitride, 4 Non-scaly Second Thermal Conductive Filler, 50 Semiconductor Equipment, 51 Electronic Parts, 52 heat spreader, 53 heat sink

Claims (9)

The binder resin, the scaly first heat conductive filler, and the non-scaly second heat conductive filler are contained, and the first heat conductive filler and the second heat conductive filler are described. In the heat conductive sheet dispersed in the binder resin
The first thermally conductive filler is boron nitride.
The average particle size of the second heat conductive filler is 5 μm or less, and the average particle size is 5 μm or less.
Heat in which the long axis of the first heat conductive filler is oriented in the thickness direction of the heat conductive sheet and the minor axis of the first heat conductive filler is randomly oriented in the in-plane direction of the heat conductive sheet. Conductive sheet. The heat conductive sheet according to claim 1, wherein the content of the second heat conductive filler is 30 to 60% by volume. The heat conductive sheet according to claim 1 or 2, wherein the second heat conductive filler is a mixture of two kinds of heat conductive fillers, and the content of each heat conductive filler is 10 to 25% by volume. .. The heat conductive sheet according to any one of claims 1 to 3, wherein the total content of the first heat conductive filler and the second heat conductive filler is less than 70% by volume. Claims 1 to 4 in which the difference between the maximum value and the minimum value of the effective thermal conductivity is 1.5 W / m · K or less when a load of 0.5 to 3 kgf / cm ² is applied in the thickness direction. The heat conductive sheet according to any one of the above items. Step A to prepare a resin composition for forming a heat conductive sheet by dispersing a scaly first heat conductive filler and a non-scaly second heat conductive filler in a curable resin composition. When,
Step B of forming a molded block from the resin composition for forming a heat conductive sheet, and
It has a step C of slicing the molded body block into a sheet to obtain a heat conductive sheet.
The first thermally conductive filler is boron nitride.
The average particle size of the second heat conductive filler is 5 μm or less, and the average particle size is 5 μm or less.
The heat conductive sheet is a heat conductive sheet in which the major axis of the first heat conductive filler is oriented in the thickness direction and the minor axis of the first heat conductive filler is randomly oriented in the in-plane direction. Production method. The method for producing a heat conductive sheet according to claim 6, wherein in the step B, the resin composition for forming the heat conductive sheet is passed through an opening formed in a die or a mold and having sides that are not orthogonal to each other. The sixth or seventh aspect of claim 6 or 7, wherein in the step C, the molded body block is sliced in a direction substantially perpendicular to the extrusion direction of the resin composition for forming the heat conductive sheet to obtain a heat conductive sheet. A method for manufacturing a thermally conductive sheet. With a heating element,
With the radiator
An electronic device comprising the heat conductive sheet according to any one of claims 1 to 5, which is arranged between a heating element and a heat radiating element.

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