WO2023063406A1

WO2023063406A1 - Thermally conductive resin sheet

Info

Publication number: WO2023063406A1
Application number: PCT/JP2022/038304
Authority: WO
Inventors: 賢人土屋; 裕希星山; 奈未中島; 和幸矢原
Original assignee: 積水化学工業株式会社
Priority date: 2021-10-15
Filing date: 2022-10-14
Publication date: 2023-04-20
Also published as: JPWO2023063406A1

Abstract

The present invention provides a thermally conductive resin sheet which gives such a free induction decay curve of 1H spin-spin relaxation, as determined by means of pulsed NMR, that if the free induction decay curve is separated, through curve fitting, into three curves respectively derived from three components, namely, A component, B component and C component, and lying in ascending order of relaxation time, the proportion of C component is 5% to 35%, the relaxation time of C component is 600 milliseconds or less, and the product of the proportion of C component and the relaxation time of C component is less than 5,000.　The present invention is capable of providing a thermally conductive resin sheet which has high thermal conductivity, flexibility and low tack properties, while being suppressed in oil bleeding.

Description

Thermally conductive resin sheet

The present invention relates to a thermally conductive resin sheet.

A thermally conductive resin sheet is mainly placed between a heating element such as a semiconductor package and a radiator such as aluminum or copper, and has the function of quickly transferring the heat generated by the heating element to the radiator. have. In recent years, due to the high integration of semiconductor elements and the high density wiring in semiconductor packages, the amount of heat generated per unit area of semiconductor packages has increased. There is an increasing demand for thermally conductive resin sheets that can promote more rapid heat dissipation with improved efficiency.
As such a thermally conductive resin sheet, a thermally conductive resin sheet containing a thermally conductive filler is known. For example, Patent Document 1 describes an invention relating to a thermally conductive resin sheet containing liquid polybutene and a thermally conductive filler. Patent Document 2 describes an epoxy resin and hexagonal boron nitride or the like as a thermally conductive filler. An invention relating to a thermally conductive resin sheet containing
Further, Patent Document 3 describes a resin composition using both specific plate-shaped heat conductive particles and spherical heat conductive particles, and describes that the resin composition is excellent in heat conductivity.

JP 2012-38763 A JP 2013-254880 A JP 2015-174906 A

In general, thermally conductive resin sheets tend to harden when a large amount of thermally conductive filler is added to improve thermal conductivity. etc., and there is concern that electronic components may be damaged. There is a need for a thermally conductive resin sheet that prevents such problems and has good flexibility.
On the other hand, if the design emphasizes flexibility, the tackiness of the thermally conductive resin sheet becomes stronger, making it difficult to peel off the separate film attached to the surface of the thermally conductive resin sheet. Deformation of the sheet occurs, and the yield deteriorates. In addition, if the thermally conductive resin sheet has strong tackiness, a residue remains on the adherend when it is peeled off, which necessitates cleaning and replacement of parts for rework, increasing the process load. In addition, designing for flexibility increases oil bleeding, which may contaminate electronic components and cause contact failure.
SUMMARY OF THE INVENTION It is an object of the present invention to provide a thermally conductive resin sheet having excellent flexibility, low tackiness, and suppressed oil bleeding.

As a result of intensive studies to achieve the above object, the present inventors have found that the component ratio of the C component, which is a component with high molecular mobility measured by pulse NMR, the relaxation time of the C component, and the The inventors have found that the above problem can be solved by adjusting the product of the component ratio and the relaxation time of the C component within a specific range, and have completed the present invention.

That is, the present invention relates to the following [1] to [7].
[1] Waveform separation of the 1H spin-spin relaxation free induction decay curve measured in pulse NMR into three curves derived from the three components of the A component, the B component, and the C component in ascending order of relaxation time. The obtained component ratio of the C component is 5% or more and 35% or less, the relaxation time of the C component is 600 milliseconds or less, and the product of the component ratio of the C component and the relaxation time of the C component is less than 5000, thermal conductivity resin sheet.
[2] Using a tap tester, a SUS probe is pressed against the surface of the thermally conductive resin sheet with a load of 3000 gf / cm ² for 10 seconds, and then lifted vertically at a speed of 0.5 mm / s. The thermally conductive resin sheet according to [1] above, wherein the adhesion time from the start of pulling up until the probe is removed from the thermally conductive resin sheet is 1.5 seconds or less.
[3] The thermally conductive resin sheet according to [1] or [2] above, which has a thermal conductivity of 6 W/m·K or more.
[4] The thermally conductive resin sheet according to any one of [1] to [3] above, which has a 30% compressive strength of 3000 kPa or less.
[5] The thermally conductive resin sheet according to any one of [1] to [4] above, containing at least one resin selected from the group consisting of elastomer resins and acrylic resins.
[6] The thermally conductive resin sheet according to any one of [1] to [5] above, which contains a thermally conductive filler.
[7] The thermally conductive resin sheet according to any one of [1] to [6] above, wherein the thermally conductive filler contains boron nitride.

According to the present invention, it is possible to provide a thermally conductive resin sheet with excellent flexibility, low tackiness, and suppressed oil bleeding.

1 is a schematic cross-sectional view of a thermally conductive resin sheet made of a laminate; FIG. FIG. 2 is a schematic cross-sectional view of a thermally conductive resin sheet composed of a laminate in use.

[Thermal conductive resin sheet]
In the thermally conductive resin sheet of the present invention, the 1H spin-spin relaxation free induction decay curve measured by pulse NMR is divided into three curves derived from three components, A component, B component, and C component, in order of shortest relaxation time. The component ratio of the C component obtained by waveform separation is 5% or more and 35% or less, the relaxation time of the C component is 600 milliseconds or less, and the product of the component ratio of the C component and the relaxation time of the C component is less than 5000. .

Generally, when a thermally conductive resin sheet is measured by pulse NMR, a 1H spin-spin relaxation free induction decay curve is obtained. The obtained free induction decay curve can be waveform-separated into three curves derived from the three components of the A component, the B component and the C component in ascending order of relaxation time. That is, the actually measured free induction attenuation curve is obtained by superimposing the free induction attenuation curve derived from the three components of the A component, the B component and the C component. Such a method of separating and analyzing three components using pulse NMR is known, and examples of literature include Japanese Patent Laid-Open No. 2018-2983.

The A component is a component with a short relaxation time in pulse NMR measurement, meaning a hard component with low molecular mobility. On the other hand, the C component is a component with a long relaxation time in pulse NMR measurement, and means a soft component with high molecular mobility. The B component has a relaxation time in pulsed NMR measurements between the A and C components, so the molecular mobility is also between the A and C components. Here, the component ratio is the ratio to the total amount of the A component, the B component and the C component.

In the thermally conductive resin sheet of the present invention, the component ratio of the C component, the relaxation time of the C component, and the product of the component ratio of the C component and the relaxation time of the C component are adjusted to specific ranges. The component ratio of the C component means the component ratio of the component with high molecular mobility in the thermally conductive sheet, and the relaxation time of the C component indicates the degree of molecular mobility of the component with high molecular mobility. show.
Note that the pulse NMR measurement is performed at 25° C. by the CPMG method.

The component ratio of the C component in the thermally conductive resin sheet of the present invention is 5% or more and 35% or less. If the component ratio of the C component is less than 5%, the flexibility of the thermally conductive resin sheet is reduced, and the sheet becomes hard, which may damage electronic components. If the component ratio of the C component exceeds 35%, the tackiness of the thermally conductive resin sheet increases, and problems such as difficulty in peeling the separate film from the thermally conductive resin sheet tend to occur. Increased oil bleeding.
The component ratio of component C is preferably 5.5% or more and 30% or less, more preferably 6% or more and 20% or less, and still more preferably, from the viewpoint of improving flexibility and lowering tackiness. It is 8% or more and 15% or less.

The relaxation time of the C component of the thermally conductive resin sheet of the present invention is 600 milliseconds or less. When the relaxation time of the C component exceeds 600 milliseconds, the tackiness of the thermally conductive resin sheet becomes high, and problems such as difficulty in peeling the separate film from the thermally conductive resin sheet tend to occur. more oil bleed to
The relaxation time of the C component of the thermally conductive resin sheet is preferably 300 milliseconds or less, more preferably 100 milliseconds or less, and still more preferably from the viewpoint of reducing tackiness and suppressing oil bleeding. is less than 50 milliseconds. In addition, the relaxation time of the C component is preferably 5 milliseconds or more, more preferably 9 milliseconds or more, from the viewpoint of ensuring the flexibility of the thermally conductive resin sheet.

The product (%·milliseconds) of the component ratio (%) of the C component and the relaxation time (milliseconds) of the C component in the thermally conductive resin sheet of the present invention is less than 5,000. When the product of the component ratio (%) of the C component and the relaxation time (milliseconds) of the C component is 5000 or more, there are many components with high molecular mobility in the thermally conductive resin sheet. The tackiness of the resin sheet becomes high, and problems such as difficulty in peeling of the separate film are likely to occur, and more oil bleeds onto the sheet surface.
The product of the component ratio (%) of the C component and the relaxation time (milliseconds) of the C component is preferably 3000 or less, more preferably 1000 or less, from the viewpoint of reducing tackiness and suppressing oil bleeding. Yes, more preferably 500 or less. Then, from the viewpoint of improving flexibility, the product of the component ratio (%) of the C component and the relaxation time (milliseconds) of the C component is preferably 30 or more, more preferably 50 or more, and further Preferably it is 100 or more.
In the present invention, by setting the component ratio of the C component, the relaxation time of the C component, and the component ratio of the C component and the relaxation time of the C component to the above-described predetermined ranges, flexibility and low tackiness can be obtained. A thermally conductive resin sheet in which oil bleeding is suppressed can be provided.
The component ratio of the C component, the relaxation time of the C component, and the product of the component ratio of the C component and the relaxation time of the C component are determined by the content of the resin and the thermally conductive filler contained in the thermally conductive resin sheet, the type of resin and A desired value can be obtained by adjusting the viscosity (or weight average molecular weight), the type of the thermally conductive filler, and the like.

(Adhesion time)
The thermally conductive resin sheet of the present invention preferably has a contact time of 1.5 seconds or less as measured by a tap tester. When the adhesion time is 1.5 seconds or less, the thermally conductive resin sheet has low tackiness. From the viewpoint of lowering the tackiness of the thermally conductive resin sheet, the adhesion time is preferably 1.3 seconds or less, more preferably 1.0 seconds or less.
The adhesion time was measured by pressing a SUS (stainless steel) probe with a load of 3000 gf/cm ² onto the surface of the thermally conductive resin sheet for 10 seconds using a tap tester, and then vertically at a speed of 0.5 mm/s. It means the time from the start of pulling up until the probe comes off the thermally conductive resin sheet. The SUS probe diameter (diameter) is 5.6 mm.

(30% compressive strength)
The 30% compressive strength of the thermally conductive resin sheet of the present invention is preferably 3000 kPa or less. When the 30% compressive strength is 3000 kPa or less, the flexibility of the thermally conductive resin sheet is increased, and it becomes difficult to damage the electronic components inside the electronic device using the sheet. From the viewpoint of increasing the flexibility of the thermally conductive resin sheet, the 30% compressive strength of the thermally conductive resin sheet is preferably 1500 kPa or less, more preferably 1000 kPa or less, and even more preferably 800 kPa or less. Moreover, the 30% compressive strength of the thermally conductive resin sheet is usually 10 kPa or more, preferably 50 kPa or more.
The 30% compressive strength of the thermally conductive resin sheet can be adjusted by the type of resin constituting the thermally conductive resin sheet described later, the presence or absence of cross-linking, the type and amount of thermally conductive filler, and the like.
The 30% compressive strength means the load when compressed by a thickness corresponding to 30% of the initial thickness, and can be obtained by the method described in Examples.

(Thermal conductivity)
The thermal conductivity of the thermally conductive resin sheet of the present invention is preferably 6 W/m·K or more. When the thermal conductivity is 6 W/m·K or more, it becomes easy to effectively dissipate the heat generated from the heating element. From the viewpoint of improving the heat dissipation property of the thermally conductive resin sheet, the thermal conductivity of the thermally conductive resin sheet is preferably 8 W/mK or more, more preferably 10 W/m·K or more. Moreover, the higher the thermal conductivity of the thermally conductive resin sheet, the better, but it is usually 100 W/m·K or less. The thermal conductivity can be easily adjusted to a desired value by, for example, adjusting the content, orientation, etc. of the thermally conductive filler, which will be described later.

(resin)
The thermally conductive resin sheet of the present invention contains a resin, and the type of the resin is not particularly limited, but from the viewpoint of improving flexibility, one or more selected from the group consisting of elastomer resins and acrylic resins. is preferably
The resin contained in the thermally conductive resin sheet may be solid or liquid, but from the viewpoint of better flexibility, it is preferably a liquid resin such as a liquid elastomer resin.
In this specification, the term "liquid" means a liquid state at normal temperature (23°C) and normal pressure (1 atmosphere), and the term "solid state" means a solid state at normal temperature (23°C) and normal pressure (1 atmosphere). Say something.

Examples of elastomer resins include acrylonitrile butadiene rubber, ethylene-propylene-diene rubber, ethylene-propylene rubber, natural rubber, polyisoprene rubber, polybutadiene rubber, hydrogenated polybutadiene rubber, styrene-butadiene block copolymer, and hydrogenated styrene. -butadiene block copolymer, hydrogenated styrene-butadiene-styrene block copolymer, hydrogenated styrene-isoprene block copolymer, hydrogenated styrene-isoprene-styrene block copolymer and the like.
These elastomer resins may be solid or liquid, but liquid elastomer resins are preferred. The liquid elastomer resin is not particularly limited, and for example, among the elastomer resins described above, liquid ones can be used. Among them, liquid polyisoprene rubber and liquid polybutadiene rubber are preferable.
It is also preferable to use UV-curable liquid polyisoprene rubber as the liquid polyisoprene rubber. Examples of UV-curable liquid polyisoprene rubbers include liquid polyisoprene rubbers having (meth)acryloyl groups at their terminals. In addition, a (meth)acryloyl group means at least one of an acryloyl group and a methacryloyl group.
Only one type of elastomer resin may be used, or a plurality of types may be used in combination.

The viscosity of the elastomer resin at 38° C. is preferably 15 to 350 Pa·s, more preferably 20 to 200 Pa·s, still more preferably 30 to 100 Pa·s. The viscosity of the resin is within the above range, and by adjusting the type and content of the thermally conductive filler as described later, the component ratio of the C component measured by pulse NMR of the thermally conductive resin sheet, the C component and the product of the component ratio of the C component and the relaxation time of the C component can be easily adjusted within the predetermined ranges described above.
The viscosity can be measured with a Brookfield viscometer at 38°C.

The weight average molecular weight of the elastomer resin is preferably 10,000 to 40,000, more preferably 15,000 to 35,000, still more preferably 20,000 to 30,000. When the weight average molecular weight of the resin is in such a range, the component ratio of the C component measured by pulse NMR of the thermally conductive resin sheet, the relaxation time of the C component, and the component ratio of the C component and the relaxation time of the C component. It becomes easy to adjust the product of to within the predetermined range described above.
A weight average molecular weight is a weight average molecular weight in terms of polystyrene measured by gel permeation chromatography (GPC).

Examples of acrylic resins include polymers of monomer components containing one or more acrylic monomers selected from acrylic acid, acrylic acid esters, methacrylic acid, and methacrylic acid esters. It may be a combination or a copolymer of acrylic monomers and other monomers.
The acrylic resin may be a solid acrylic resin or a liquid acrylic resin.
The acrylic resin is preferably a polymer of a monomer component containing one or more selected from acrylic acid ester and methacrylic acid ester, more preferably a polymer of a monomer component containing acrylic acid ester. The acrylic acid ester is not particularly limited, and examples thereof include methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate and the like. The methacrylic acid ester is not particularly limited, and examples thereof include methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate and the like.

The acrylic resin is preferably an acrylic resin having at least one functional group selected from the group consisting of a carboxyl group, a hydroxyl group, an epoxy group and an amide group, and more preferably selected from the group consisting of a carboxyl group and a hydroxyl group. Acrylic resins having at least one functional group are preferred.
Only one type of acrylic resin may be used, or a plurality of types may be used in combination.

The acrylic resin preferably has a weight average molecular weight of 50,000 to 1,000,000, more preferably 100,000 to 1,000,000, and still more preferably 300,000 to 900,000. When the weight average molecular weight of the acrylic resin is in such a range, the component ratio of the C component measured by pulse NMR of the thermally conductive resin sheet, the relaxation time of the C component, the component ratio of the C component and the relaxation of the C component It becomes easier to adjust the product of time to the predetermined range described above.
A weight average molecular weight is a weight average molecular weight in terms of polystyrene measured by gel permeation chromatography (GPC).

The content of at least one resin selected from the group consisting of elastomer resins and acrylic resins in the thermally conductive resin sheet of the present invention is preferably 30% by mass or more, based on the total amount of the thermally conductive resin sheet. More preferably 35% by mass or more, still more preferably 40% by mass or more, and preferably 60% by mass or less, more preferably 55% by mass or less.

The content of the liquid resin is preferably 60% by mass or more, more preferably 90% by mass or more, and still more preferably 100% by mass, based on the total amount of resin in the thermally conductive resin sheet of the present invention. is.

(Thermal conductive filler)
The thermally conductive resin sheet of the present invention preferably contains a thermally conductive filler. The thermally conductive filler is dispersed in the resin component of the thermally conductive resin sheet to increase thermal conductivity.
The average particle size of the thermally conductive filler is preferably 0.1-300 μm, more preferably 0.5-100 μm, still more preferably 5-50 μm. The average particle size can be obtained by measuring the particle size distribution with a laser diffraction particle size distribution analyzer.

The thermally conductive filler may be a spherical filler or a non-spherical filler, but from the viewpoint of increasing the thermal conductivity of the thermally conductive resin sheet, it is preferable to contain at least a non-spherical filler. In addition, only 1 type may be used for a thermally conductive filler, and 2 or more types may be used together.

Examples of non-spherical fillers include plate-like fillers such as scaly and flaky fillers, needle-like fillers, fibrous fillers, dendritic fillers, amorphous fillers, aggregated fillers, and the like. Among them, a plate-like filler is preferable from the viewpoint of improving the thermal conductivity of the thermally conductive resin sheet.
Here, "spherical" means a shape with an aspect ratio of 1.0 to 2.0, preferably 1.0 to 1.5, and does not necessarily mean a true sphere. In addition, the aspect ratio in the case of a spherical filler means length / breadth ratio. In addition, "non-spherical" means a shape other than the above spherical shape, that is, a shape with an aspect ratio of more than 2.

From the viewpoint of increasing thermal conductivity, the aspect ratio of the thermally conductive filler is preferably 5 or more, more preferably 10 or more, and usually 200 or less.
When two or more types of thermally conductive fillers are used, the aspect ratio is an average aspect ratio calculated by weighted averaging the aspect ratios of the respective thermally conductive fillers.

In the thermally conductive resin sheet, the thermal conductivity in the thickness direction can be improved by orienting the thermally conductive filler having a high aspect ratio at a high orientation angle as described later.
In the non-spherical filler, the aspect ratio is the ratio of the maximum length to the minimum length of the filler (maximum length/minimum length). is the ratio of length to thickness (maximum length/thickness). The aspect ratio may be determined as an average value by observing a sufficient number (for example, 250) of thermally conductive fillers with a scanning electron microscope.

Although the thermal conductivity of the thermally conductive filler is not particularly limited, it is preferably 12 W/m·K or more, more preferably 15 to 70 W/m·K, still more preferably 25 to 70 W/m·K.

Materials for the thermally conductive filler include, for example, carbides, nitrides, oxides, hydroxides, metals, and carbonaceous materials.
Carbides include, for example, silicon carbide, boron carbide, aluminum carbide, titanium carbide, and tungsten carbide.
Examples of nitrides include silicon nitride, boron nitride, boron nitride nanotubes, aluminum nitride, gallium nitride, chromium nitride, tungsten nitride, magnesium nitride, molybdenum nitride, and lithium nitride.
Examples of oxides include iron oxide, silicon oxide (silica), aluminum oxide (alumina) (including hydrates of aluminum oxide (boehmite, etc.)), magnesium oxide, titanium oxide, cerium oxide, zirconium oxide, and the like. mentioned. Examples of oxides include transition metal oxides such as barium titanate, and metal ion-doped materials such as indium tin oxide and antimony tin oxide.

Hydroxides include, for example, aluminum hydroxide, calcium hydroxide, magnesium hydroxide and the like.
Metals include, for example, copper, gold, nickel, tin, iron, or alloys thereof.
Carbon-based materials include, for example, carbon black, graphite, diamond, graphene, fullerene, carbon nanotubes, carbon nanofibers, nanohorns, carbon microcoils, and nanocoils.
Talc, which is a silicate mineral, can be mentioned as a thermally conductive filler other than the above.
These thermally conductive fillers can be used alone or in combination of two or more.

Among these, the thermally conductive filler is preferably boron nitride, magnesium hydroxide, or magnesium oxide, and more preferably contains boron nitride.

The content of the non-spherical filler in the thermally conductive filler is preferably 60% by mass or more, more preferably 90% by mass or more, and preferably 100% by mass, based on the total amount of the thermally conductive filler. More preferred.

The content of the thermally conductive filler in the thermally conductive resin sheet is preferably 40 to 70% by mass, more preferably 45 to 65% by mass, and still more preferably 50 to 70% by mass, based on the total amount of the thermally conductive resin sheet. 60% by mass. By setting the content of the thermally conductive filler in such a range, the thermal conductivity of the thermally conductive resin sheet is increased, and the component ratio of the C component measured by pulse NMR of the thermally conductive resin sheet, the C component It becomes easy to adjust the relaxation time and the product of the component ratio of the C component and the relaxation time of the C component within the predetermined range described above.

(orientation)
In the thermally conductive resin sheet, the orientation angle of the thermally conductive filler is preferably greater than 45°, more preferably 50° or more, still more preferably 70° or more, and even more preferably 80° or more. Here, the orientation angle is the angle of the long axis of the thermally conductive filler with respect to the surface of the thermally conductive resin sheet. The major axis of the thermally conductive filler is aligned with the maximum length of the thermally conductive filler. When the orientation angle of the thermally conductive filler is within the above range, it becomes easier to increase the thermal conductivity.

The orientation angle can be measured by observing a cross section of the thermally conductive resin sheet in the thickness direction with a scanning electron microscope. For example, first, a thin film slice of the central portion in the thickness direction of the thermally conductive resin sheet is produced. Then, using a scanning electron microscope (SEM), the thermally conductive filler in the thin film section is observed at a magnification of 3000 times, and the angle formed between the observed long axis of the filler and the plane constituting the sheet surface is measured. can be obtained by In this specification, angles of 45°, 50°, 70°, 80° or more mean that the average value of the values measured as described above is the angle or more. For example, "an orientation angle of 50° or more" does not deny the existence of thermally conductive fillers with an orientation angle of less than 50°, because 50° is an average value. If the angle exceeds 90°, the supplementary angle is taken as the measured value.

(Other additives)
The thermally conductive resin sheet of the present invention may optionally contain antioxidants, thermal stabilizers, colorants, flame retardants, antistatic agents, fillers other than the thermally conductive fillers, decomposition temperature adjusters, and the like. Additives commonly used in thermally conductive resin sheets may be added.

(Laminate)
The thermally conductive resin sheet of the present invention may be a single layer or a laminate. From the viewpoint of improving thermal conductivity, a laminate obtained by laminating resin layers containing a resin and an aspherical filler is preferable. An example of an embodiment of a laminate in which resin layers containing resin and non-spherical filler are laminated will be described below with reference to FIG.
In each figure, each filler overlaps the vertically adjacent filler, but in the present invention, the fillers do not necessarily have to overlap each other.
As shown in FIG. 1, the thermally conductive resin sheet 1 has a structure in which a plurality of resin layers 2 are laminated. A surface perpendicular to the lamination surface of the plurality of resin layers 2 is a sheet surface 5 which is the surface of the resin sheet 1 .

The thickness T1 of the thermally conductive resin sheet 1 (that is, the distance between the sheet surfaces 5) is not particularly limited, but can be in the range of 0.1 to 30 mm, for example.
The thickness W1 (resin layer width) of one layer of the resin layer 2 is not particularly limited, but is preferably 1000 μm or less, more preferably 500 μm or less, and preferably 0.1 μm or more, more preferably 0.5 μm or more, More preferably, it can be 1 μm or more. Thermal conductivity can be improved by adjusting the thickness in this way.
The resin layer 2 is a thermally conductive resin layer 7 containing thermally conductive fillers 6 . The thermally conductive resin layer 7 has a structure in which thermally conductive fillers 6 are dispersed in a resin 8 .
In each resin layer 2, the thermally conductive filler has an angle larger than 45°, more preferably 50° or more, still more preferably 60°C or more, still more preferably 70° or more, and further preferably 70° or more with respect to the sheet surface as described above. It is preferably oriented at an angle of 80° or more.

The thickness of the thermally conductive resin layer 7 is preferably 1 to 1000 times the thickness of the thermally conductive filler 6 contained in the thermally conductive resin layer 7, more preferably 1 to 500 times.
By setting the width (thickness) of the thermally conductive resin layer 7 within the above range, the long axis of the thermally conductive filler 6 is easily oriented at an angle close to 90° with respect to the sheet surface. The width of the thermally conductive resin layer 7 does not have to be uniform as long as it is within the above range.

[Method for producing thermally conductive resin sheet]
The method for producing the thermally conductive resin sheet of the present invention is not particularly limited. A thermally conductive resin sheet may be formed by extruding a mixture obtained by supplying the mixture to a machine and melt-kneading it into a sheet form from an extruder.

(Laminate manufacturing method)
The method for producing the thermally conductive resin sheet comprising the laminate of the present invention is not particularly limited. can.

<Kneading process>
A thermally conductive filler and a resin are kneaded to prepare a thermally conductive resin composition.
For the kneading, for example, the thermally conductive filler and the resin are preferably kneaded under heating using a twin-screw kneader such as Plastomill or a twin-screw extruder. is uniformly dispersed in the resin to obtain a thermally conductive resin composition.
Then, by pressing the thermally conductive resin composition, a sheet-like resin layer (thermally conductive resin layer) can be obtained.

<Lamination process>
In the lamination step, the resin layers obtained in the kneading step are laminated to form a laminate having an n-layer structure. As a lamination method, for example, the resin layer produced in the kneading step is divided into xi _and laminated, and after producing a laminate having an _xi layer structure, hot pressing is performed as necessary, and then, further, if necessary. Accordingly, it is possible to use a method of repeating the division, lamination, and the above-described hot press to fabricate a laminated body having a width of D μm and an n-layer structure.
When the thermally conductive filler is plate-shaped, the width W2 (D μm) of the laminate after the lamination step and the thickness t (d μm) of the thermally conductive filler are 0.0005≦d/(D/n)≦1. is preferably satisfied, more preferably 0.001≤d/(D/n)≤1, and even more preferably 0.02≤d/(D/n)≤1.
In this way, when molding is performed a plurality of times, the molding pressure in each time can be made smaller than in the case of performing molding once, so phenomena such as destruction of the laminated structure caused by molding can be prevented. can be avoided.
As another lamination method, for example, an extruder equipped with a multilayer forming block is used, the multilayer forming block is prepared, and co-extrusion is performed to obtain a laminate having the n-layer structure and the thickness of D μm. can also be used.
Specifically, the thermally conductive resin composition obtained in the kneading step is introduced into both the first extruder and the second extruder, and the thermally conductive resin composition is introduced from the first extruder and the second extruder. The resin composition is extruded at the same time. The thermally conductive resin composition extruded from the first extruder and the second extruder is sent to the feedblock. In the feed block, the thermally conductive resin composition extruded from the first extruder and the second extruder join together. Thereby, a two-layer body in which the thermally conductive resin composition is laminated can be obtained. Next, the two-layer body is transferred to a multi-layer forming block, and the two-layer body is divided into a plurality of pieces along a plurality of planes parallel to the direction of extrusion and perpendicular to the plane of lamination, and then laminated. , n-layer structure, and a laminate having a thickness of D μm can be produced. At this time, the thickness per layer (D/n) can be adjusted to a desired value by adjusting the multi-layer formation block.

(Slicing process)
A thermally conductive resin sheet can be produced by slicing the laminate obtained in the lamination step in a direction parallel to the lamination direction.

(Other processes)
In the method for producing a thermally conductive resin sheet, a step of cross-linking the resin may be provided. Crosslinking may be carried out by, for example, a method of irradiating ionizing radiation such as electron beams, α-rays, β-rays, and γ-rays, a method of using an organic peroxide, or the like. The acceleration voltage for electron beam irradiation is preferably 50 to 800 kV, more preferably 200 to 700 kV, even more preferably 400 to 600 kV. From the same point of view, the dose of electron beam irradiation is preferably 200 to 1200 kGy, more preferably 300 to 1000 kGy, even more preferably 400 to 800 KGy.

The thermally conductive resin sheet of the present invention can promote heat dissipation from the heat generating body to the heat radiating body, for example, by placing it between the heat generating body and the heat radiating body inside the electronic device. This will be explained using the thermally conductive resin sheet 1 explained in FIG.
As shown in FIG. 2 , the thermally conductive resin sheet 1 is arranged so that the sheet surface 5 is in contact with the heating element 3 and the radiator 4 . Also, the thermally conductive resin sheet 1 is arranged in a compressed state between two members such as the heating element 3 and the radiator 4 . At this time, the thermally conductive resin sheet 1 of the present invention can exhibit stable heat radiation performance even at a relatively wide compression rate. The heating element 3 is, for example, a semiconductor package or the like, and the radiator 4 is, for example, metal such as aluminum or copper. By using the thermally conductive resin sheet 1 in such a state, the heat generated by the heating element 3 can be easily thermally diffused to the radiator 4, enabling efficient heat dissipation.

Although the present invention will be described in more detail by way of examples, the present invention is not limited by these examples.

Materials used in the following examples and comparative examples are as follows.
Resin/liquid elastomer 1: Liquid polybutadiene rubber, manufactured by Kuraray Co., Ltd., trade name “LBR-305” Viscosity: 40 Pa s (38° C.), weight average molecular weight: 26,000
・ Liquid elastomer 2: Liquid polyisoprene rubber, manufactured by Kuraray Co., Ltd., trade name “LIR-403” Viscosity: 200 Pa s (38 ° C.), weight average molecular weight: 34,000
・ Liquid elastomer 3: UV curable liquid polyisoprene rubber, manufactured by Kuraray Co., Ltd., trade name “UC-102M” Viscosity: 30 Pa s (38 ° C.), weight average molecular weight: 17,000
・Liquid elastomer 4: Liquid polyisoprene rubber, manufactured by Kuraray Co., Ltd., product “LIR-390” Viscosity: 400 Pa s (38 ° C.), weight average molecular weight: 48,000
・ Liquid elastomer 5: Liquid polybutadiene rubber, manufactured by Kuraray Co., Ltd., trade name “L-1203” Viscosity: 10 Pa s (38 ° C.), weight average molecular weight: 7,000
・ Acrylic resin 1: manufactured by Nagase ChemteX, trade name “SG-708-6”, weight average molecular weight: 700,000
・ Acrylic resin 2: manufactured by Nagase ChemteX, trade name “SG-600TEA”, weight average molecular weight: 1,200,000

(2) Thermally conductive filler Boron nitride Denka, trade name “SGP”, average particle size 15 μm, plate shape, aspect ratio 20

Various physical properties and evaluation methods are as follows.

<Component ratio of C component and measurement of relaxation time>
The thermally conductive resin sheet produced in each example and comparative example was placed in a glass sample tube with a diameter of 10 mm (manufactured by BRUKER, product number 1824511, 10 mm diameter length 180 mm, flat bottom) to a height of 1.5 cm (about 2 g). filled to The sample tube was placed in a pulse NMR device ("the minispec mq20" manufactured by BRUKER). The measurement was carried out by the CPMG method after incubating at 25 ° C. for 10 minutes, and the obtained 1H spin-spin relaxation free induction decay curve was divided into three curves derived from the three components of the A component, the B component, and the C component. separated. Waveform separation was performed by fitting using an exponential type. From the curves derived from the three components obtained in each measurement, the component ratio and relaxation time of each component were obtained.
All of the A, B and C components were subjected to exponential fitting according to the product manual using analysis software "TD-NMRA (Version 4.3 Rev 0.8)" manufactured by BRUKER.

Also, the following formula was used for fitting.
Y=A1*exp(-1/w1*(t/T2A)^w1)+B1*exp(-1/w2*(t/T2B)^w2)+C1*exp(-1/w3*(t/ T2C)^w3)
where Y is the relaxation strength. w1 to w3 are Weibull coefficients, all of which take a value of one. A1 is the A component, B1 is the B component, and C1 is the C component, respectively. t is time.
<CPMG method>
Scans: 256 times
Recycle Delay: 1sec
90-180 Pulse Separation (tau): 0.1ms
Number of Points: 8000
The above measurement conditions are an example, the number of scans is set so that the normalized relaxation curve strength is 0.02 msec or less, and the recycle delay is preferably five times the longitudinal relaxation time T1. 90-180 Pulse Separation (tau) and Number of Points set the values at which the transition curve completely decays.

<Thermal conductivity>
The thermal conductivity in the thickness direction of the obtained thermally conductive resin sheet was measured using a laser flash method thermal constant measuring device (“LFA447” manufactured by NETZSCH).
<30% Compressive Strength>
The 30% compressive strength of the resulting thermally conductive resin sheet was measured using "RTG-1250" manufactured by A&D. The measurement was performed with a sample size of 2 mm×15 mm×15 mm, a measurement temperature of 23° C., and a compression rate of 1 mm/min.

<Evaluation of tackiness (adhesion time)>
Using a tap tester (UBM "TA500"), a SUS probe was pressed against the surface of the thermally conductive resin sheet with a load of 3000 gf/cm ² for 10 seconds, and then vertically at a speed of 0.5 mm / s. When the probe was pulled up, the adhesion time from the start of pulling up until the probe came off the thermally conductive resin sheet was measured. Measurements were made at 23°C.

<Oil bleed>
A sample (thermal conductive resin sheet) having a thickness of 2 mm and a size of 30 mm square was placed in the center of A4 size paper, and after 336 hours at 125.degree. The seepage distance was calculated as the average value of the maximum seepage distances from each side of the sample. When the oil seepage distance was 10 mm or less, it was judged that "there was little oil bleeding", and when the oil seepage distance was more than 10 mm, it was judged that "there was a lot of oil bleeding".

<Film peelability>
A 50 μm-thick PET separate film (manufactured by Toray Industries, Inc., product name Lumirror S) was attached to both surfaces of the thermally conductive resin sheet, and left at rest at 50° C. for 48 hours. After that, when the separate film on one side is peeled off, "A" indicates that no tearing or deformation of the thermally conductive resin sheet is confirmed, and "B" indicates that at least one of tearing or deformation is confirmed. evaluated.

(Example 1)
Liquid Elastomer 1 (manufactured by Kuraray Co., Ltd., trade name “LBR-305”) and boron nitride (manufactured by Denka Co., Ltd., trade name “SGP”) were mixed so that the content of boron nitride was 55 based on the total amount of the thermally conductive resin sheet. The mixture was mixed so as to make the mass %, melted and kneaded, and then pressed to obtain a sheet-like resin layer having a thickness of 0.5 mm, a width of 80 mm, and a depth of 80 mm. Next, as a lamination step, the obtained resin layer was divided into 16 equal parts and superimposed to obtain a laminate consisting of 16 layers with a total thickness of 8 mm, a width of 20 mm and a depth of 20 mm. Then, it was sliced parallel to the stacking direction to obtain a thermally conductive resin sheet having a thickness of 2 mm, a width of 8 mm and a depth of 20 mm. The thickness of one of the resin layers constituting the laminate of the thermally conductive resin sheets was 0.5 mm. Various evaluation results are shown in Table 1.

(Examples 2 to 6, Comparative Examples 1 to 5)
A thermally conductive resin sheet was obtained in the same manner as in Example 1, except that the composition was changed as shown in Table 1. Various evaluation results are shown in Table 1.

The thermally conductive resin sheet shown in each example is a thermally conductive resin sheet that satisfies the requirements of the present invention, has high thermal conductivity, is flexible, has low tackiness, and suppresses oil bleeding. .
On the other hand, the thermally conductive resin sheet of Comparative Example 1 had a large component ratio of C component and was poor in tackiness and oil bleeding. The thermally conductive resin sheets of Comparative Examples 2 and 3 had a small component ratio of the C component, a high 30% compressive strength value, and poor flexibility. In addition, the thermally conductive resin sheets of Comparative Examples 4 and 5 had a large value of the product of the component ratio of the C component and the relaxation time of the C component, resulting in poor tackiness and oil bleeding.

REFERENCE SIGNS LIST 1 thermally conductive resin sheet 2 resin layer 3 heating element 4 radiator 5 sheet surface 6 thermally conductive filler 7 thermally conductive resin layer 8 resin

Claims

The 1H spin-spin relaxation free induction decay curve measured in pulsed NMR was waveform-separated into three curves derived from three components, the A component, the B component, and the C component, in order of decreasing relaxation time. A thermally conductive resin sheet, wherein the component ratio is 5% or more and 35% or less, the relaxation time of the C component is 600 milliseconds or less, and the product of the component ratio of the C component and the relaxation time of the C component is less than 5000.
Using a tap tester, a SUS probe was pressed against the surface of the thermally conductive resin sheet with a load of 3000 gf / cm 2 for 10 seconds, and then lifted vertically at a speed of 0.5 mm / s. 2. The thermally conductive resin sheet according to claim 1, wherein the contact time until the probe is detached from the thermally conductive resin sheet is 1.5 seconds or less.
The thermally conductive resin sheet according to claim 1 or 2, which has a thermal conductivity of 6 W/m·K or more.
The thermally conductive resin sheet according to any one of claims 1 to 3, which has a 30% compressive strength of 3000 kPa or less.
The thermally conductive resin sheet according to any one of claims 1 to 4, containing at least one resin selected from the group consisting of elastomer resins and acrylic resins.
The thermally conductive resin sheet according to any one of claims 1 to 5, which contains a thermally conductive filler.
The thermally conductive resin sheet according to any one of claims 1 to 6, wherein the thermally conductive filler contains boron nitride.