JP2012039064A - Heat-conductive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat conductive sheet that exhibits excellent thermoconductivity in the plane direction and also excels in an initial adhesion force.SOLUTION: The heat-conductive sheet 1 comprising plate-like boron nitride particles 2 has a coefficient of thermoconductivity of ≥4 W/m K in the plane direction SD of the heat-conductive sheet 1, and does not come off from an adherend in an initial adhesion force test (1). This heat-conductive sheet 1 can be surely fixed (temporarily fixed) to the adherend. As a result, the heat of the adherend can be surely released by the heat-conductive sheet 1.

Description

  The present invention relates to a heat conductive sheet, and more particularly to a heat conductive sheet used in power electronics technology.

  In recent years, power electronics technology that converts and controls electric power using a semiconductor element has been adopted in hybrid devices, high-brightness LED devices, electromagnetic induction heating devices, and the like. In the power electronics technology, in order to convert a large current into heat or the like, a material disposed in the vicinity of the semiconductor element is required to have high heat dissipation (high thermal conductivity).

  For example, it has been proposed to provide a heat sink so that the CPU is coated with a silicone-based resin and then covered (see, for example, Patent Document 1).

JP 2010-10469 A

  However, the silicone adhesive of Patent Document 1 has a problem that heat generated from the CPU cannot be efficiently conducted to the heat sink.

  In addition, when the silicone resin disclosed in Patent Document 1 is applied to the CPU, there is a problem that it is easily displaced with respect to the CPU and cannot be reliably fixed to the CPU.

  The objective of this invention is providing the heat conductive sheet which is excellent also in the initial stage adhesive force, while being excellent in the heat conductivity of a surface direction.

  In order to achieve the above object, the thermally conductive sheet of the present invention is a thermally conductive sheet containing plate-like boron nitride particles, and has a thermal conductivity in a direction perpendicular to the thickness direction of the thermally conductive sheet. 4 W / m · K or more, and the thermal conductive sheet is characterized in that it does not fall off from the adherend in the following initial adhesion test (1).

Initial adhesive strength test (1): A thermally conductive sheet is temporarily fixed on an adherend along the horizontal direction, and then the adherend is turned upside down.
It is a feature.

  The heat conductive sheet of the present invention has excellent heat conductivity in the surface direction orthogonal to the thickness direction, and also has excellent adhesive force (initial adhesive force) after heat-pressing at a predetermined temperature on the adherend.

  Therefore, if the heat conductive sheet of the present invention is thermocompression bonded to the adherend at a predetermined temperature, the heat conductive sheet can be reliably fixed (temporarily fixed) to the adherend.

  Therefore, the heat of the adherend can be reliably radiated by the heat conductive sheet by the heat conductive sheet.

FIG. 1 shows a perspective view of one embodiment of the thermally conductive sheet of the present invention. 2A and 2B are process diagrams for explaining a method of manufacturing the heat conductive sheet shown in FIG. 1, wherein FIG. 2A is a process of hot pressing a mixture or a laminated sheet, and FIG. The process of dividing into pieces, (c) shows the process of laminating the divided sheets.

  The thermally conductive sheet of the present invention contains boron nitride particles.

  Specifically, the heat conductive sheet contains boron nitride (BN) particles as an essential component, and further contains, for example, a resin component.

  The boron nitride particles are formed in a plate shape (or scale shape), and are dispersed in a form oriented in a predetermined direction (described later) in the heat conductive sheet.

  The boron nitride particles have an average length in the longitudinal direction (maximum length in a direction perpendicular to the thickness direction of the plate), for example, 1 to 100 μm, preferably 3 to 90 μm. The average length of the boron nitride particles in the longitudinal direction is 5 μm or more, preferably 10 μm or more, more preferably 20 μm or more, particularly preferably 30 μm or more, and most preferably 40 μm or more. 100 μm or less, preferably 90 μm or less.

  Moreover, the average of the thickness (length in the thickness direction of the plate, that is, the length in the short direction of the particles) of the boron nitride particles is, for example, 0.01 to 20 μm, preferably 0.1 to 15 μm.

  The aspect ratio (length / thickness in the longitudinal direction) of the boron nitride particles is, for example, 2 to 10000, preferably 10 to 5000.

  The average particle diameter of the boron nitride particles measured by the light scattering method is, for example, 5 μm or more, preferably 10 μm or more, more preferably 20 μm or more, particularly preferably 30 μm or more, and most preferably 40 μm or more. In general, it is 100 μm or less.

  In addition, the average particle diameter measured by the light scattering method is a volume average particle diameter measured by a dynamic light scattering particle size distribution measuring apparatus.

  If the average particle diameter measured by the light scattering method of the boron nitride particles is less than the above range, the thermally conductive sheet may become brittle and the handleability may deteriorate.

Further, the bulk density (JIS K 5101, apparent density) of the boron nitride particles is, for example, 0.3 to 1.5 g / cm ³ , preferably 0.5 to 1.0 g / cm ³ .

  As the boron nitride particles, a commercially available product or a processed product obtained by processing it can be used. Examples of commercially available boron nitride particles include the “PT” series (for example, “PT-110”, etc.) manufactured by Momentive Performance Materials Japan, and the “Shobi N UHP” series (manufactured by Showa Denko) ( For example, “Shoubi N UHP-1” and the like are included.

  The resin component can disperse boron nitride particles, that is, a dispersion medium (matrix) in which boron nitride particles are dispersed, and examples thereof include resin components such as a thermosetting resin component and a thermoplastic resin component.

  Examples of the thermosetting resin component include epoxy resins, thermosetting polyimides, phenol resins, urea resins, melamine resins, unsaturated polyester resins, diallyl phthalate resins, silicone resins, and thermosetting urethane resins.

  Examples of the thermoplastic resin component include polyolefin (for example, polyethylene, polypropylene, ethylene-propylene copolymer, etc.), acrylic resin (for example, polymethyl methacrylate, etc.), polyvinyl acetate, ethylene-vinyl acetate copolymer, Polyvinyl chloride, polystyrene, polyacrylonitrile, polyamide, polycarbonate, polyacetal, polyethylene terephthalate, polyphenylene oxide, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polyallylsulfone, thermoplastic polyimide, thermoplastic urethane resin, polyaminobis Maleimide, polyamideimide, polyetherimide, bismaleimide triazine resin, polymethylpentene, fluororesin, liquid crystal polymer, Fin - vinyl alcohol copolymer, ionomer, polyarylate, acrylonitrile - ethylene - styrene copolymers, acrylonitrile - butadiene - styrene copolymer, acrylonitrile - styrene copolymer.

  These resin components can be used alone or in combination of two or more.

  Of the resin components, an epoxy resin is preferable.

  The epoxy resin is in a liquid, semi-solid, or solid form at normal temperature.

  Specifically, as the epoxy resin, for example, bisphenol type epoxy resin (for example, bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, hydrogenated bisphenol A type epoxy resin, dimer acid modified bisphenol type) Epoxy resin), novolak epoxy resin (eg, phenol novolac epoxy resin, cresol novolac epoxy resin, biphenyl epoxy resin), naphthalene epoxy resin, fluorene epoxy resin (eg, bisarylfluorene epoxy resin, etc.) ), Aromatic epoxy resins such as triphenylmethane type epoxy resin (for example, trishydroxyphenylmethane type epoxy resin), for example, triepoxypropyl isocyanur Nitrogen-containing ring epoxy resins such as sulfonate (triglycidyl isocyanurate) and hydantoin epoxy resins, for example, aliphatic epoxy resins, such as alicyclic epoxy resins (such as dicyclocyclic epoxy resins), such as glycidyl An ether type epoxy resin, for example, a glycidylamine type epoxy resin can be used.

  These epoxy resins can be used alone or in combination of two or more.

  A combination of a liquid epoxy resin and a solid epoxy resin is preferable, and a combination of a liquid aromatic epoxy resin and a solid aromatic epoxy resin is more preferable. Is mentioned. Specific examples of such combinations include a combination of a liquid bisphenol type epoxy resin and a solid triphenylmethane type epoxy resin, a combination of a liquid bisphenol type epoxy resin and a solid bisphenol type epoxy resin. .

  Moreover, as an epoxy resin, Preferably, the single use of a semi-solid epoxy resin is mentioned, More preferably, the single use of a semi-solid aromatic epoxy resin is mentioned. More specifically, such an epoxy resin includes a semi-solid fluorene type epoxy resin.

  If it is a combination of a liquid epoxy resin and a solid epoxy resin, or a semi-solid epoxy resin, the step followability (described later) of the heat conductive sheet can be improved.

  The epoxy resin has an epoxy equivalent of, for example, 100 to 1000 g / eqiv. , Preferably 180 to 700 g / eqiv. The softening temperature (ring and ball method) is, for example, 80 ° C. or lower (specifically 20 to 80 ° C.), preferably 70 ° C. or lower (specifically 25 to 70 ° C.).

  Moreover, the melt viscosity at 80 ° C. of the epoxy resin is, for example, 10 to 20,000 mPa · s, preferably 50 to 15,000 mPa · s. When using 2 or more types of epoxy resins together, the melt viscosity as a mixture thereof is set within the above-described range.

  Further, in the case where an epoxy resin that is solid at room temperature and an epoxy resin that is liquid at room temperature are used in combination, the softening temperature is, for example, less than 45 ° C, preferably 35 ° C or less, and the softening temperature. However, it has together with the 2nd epoxy resin of 45 degreeC or more, for example, Preferably 55 degreeC or more. Thereby, the kinematic viscosity (conforming to JIS K 7233, which will be described later) of the resin component (mixture) can be set in a desired range, and the step followability of the thermally conductive sheet can be improved.

  Moreover, an epoxy resin can be prepared as an epoxy resin composition by containing a hardening | curing agent and a hardening accelerator, for example.

  The curing agent is a latent curing agent (epoxy resin curing agent) that can cure the epoxy resin by heating. For example, an imidazole compound, an amine compound, an acid anhydride compound, an amide compound, a hydrazide compound, an imidazoline compound, and the like. Is mentioned. In addition to the above, phenol compounds, urea compounds, polysulfide compounds and the like can also be mentioned.

  Examples of the imidazole compound include 2-phenylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, and the like.

  Examples of the amine compound include aliphatic polyamines such as ethylenediamine, propylenediamine, diethylenetriamine, and triethylenetetramine, and aromatic polyamines such as metaphenylenediamine, diaminodiphenylmethane, and diaminodiphenylsulfone.

  Examples of the acid anhydride compound include phthalic anhydride, maleic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, 4-methyl-hexahydrophthalic anhydride, methyl nadic acid anhydride, and pyromellitic acid. Anhydride, dodecenyl succinic anhydride, dichlorosuccinic anhydride, benzophenone tetracarboxylic acid anhydride, chlorendic acid anhydride and the like can be mentioned.

  Examples of the amide compound include dicyandiamide and polyamide.

  Examples of the hydrazide compound include adipic acid dihydrazide.

  Examples of the imidazoline compound include methyl imidazoline, 2-ethyl-4-methyl imidazoline, ethyl imidazoline, isopropyl imidazoline, 2,4-dimethyl imidazoline, phenyl imidazoline, undecyl imidazoline, heptadecyl imidazoline, 2-phenyl-4-methyl. Examples include imidazoline.

  These curing agents can be used alone or in combination of two or more.

  As the curing agent, an imidazole compound is preferable.

  Examples of the curing accelerator include tertiary amine compounds such as triethylenediamine and tri-2,4,6-dimethylaminomethylphenol, such as triphenylphosphine, tetraphenylphosphonium tetraphenylborate, tetra-n-butylphosphonium- Phosphorus compounds such as o, o-diethyl phosphorodithioate, for example, quaternary ammonium salt compounds, for example, organometallic salt compounds, for example, derivatives thereof and the like can be mentioned. These curing accelerators can be used alone or in combination of two or more.

  The compounding ratio of the curing agent in the epoxy resin composition is, for example, 0.5 to 50 parts by mass, preferably 1 to 10 parts by mass with respect to 100 parts by mass of the epoxy resin. For example, 0.1 to 10 parts by mass, preferably 0.2 to 5 parts by mass.

  The above-mentioned curing agent and / or curing accelerator can be prepared and used as a solvent solution and / or a solvent dispersion dissolved and / or dispersed with a solvent, if necessary.

  Examples of the solvent include organic solvents such as ketones such as acetone and methyl ethyl ketone, esters such as ethyl acetate, amides such as N, N-dimethylformamide, and the like. Examples of the solvent include water-based solvents such as water, for example, alcohols such as methanol, ethanol, propanol, and isopropanol. The solvent is preferably an organic solvent, more preferably ketones and amides.

  Of the thermoplastic resin components, preferably, polyolefin is used.

  Preferred examples of the polyolefin include polyethylene and ethylene-propylene copolymer.

  Examples of polyethylene include low density polyethylene and high density polyethylene.

  Examples of the ethylene-propylene copolymer include a random copolymer, a block copolymer, or a graft copolymer of ethylene and propylene.

  These polyolefins can be used alone or in combination of two or more.

  Moreover, the weight average molecular weight and / or number average molecular weight of polyolefin are 1000-10000, for example.

  Polyolefins can be used alone or in combination.

In addition, according to a kinematic viscosity test (temperature: 25 ° C. ± 0.5 ° C., solvent: butyl carbitol, resin component (solid content) concentration: 40% by mass) based on JIS K 7233 (foam viscometer method) of the resin component The measured kinematic viscosity is, for example, 0.22 × 10 ^{−4 to} 2.00 × 10 ⁻⁴ m ² / s, preferably 0.3 × 10 ^{−4 to} 1.9 × 10 ⁻⁴ m ² / s. s, more preferably 0.4 × 10 ^{−4 to} 1.8 × 10 ⁻⁴ m ² / s. Further, the kinematic viscosity of the, for ^{example, 0.22 × 10 -4 ~1.00 × 10} -4 m 2 / s, ^{preferably, 0.3 × 10 -4 ~0.9 × 10} -4 m 2 / S, more preferably 0.4 × 10 ^{−4 to} 0.8 × 10 ⁻⁴ m ² / s.

  When the kinematic viscosity of the resin component exceeds the above range, it may be impossible to impart excellent flexibility and step following ability (described later) to the heat conductive sheet. On the other hand, when the kinematic viscosity of the resin component is less than the above range, the boron nitride particles may not be oriented in a predetermined direction.

  In the kinematic viscosity test based on JIS K 7233 (foam viscometer method), the rising speed of the foam in the resin component sample is compared with the rising speed of the foam in the standard sample (kinematic viscosity is known). The kinematic viscosity of the resin component is measured by determining that the matching kinematic viscosity of the standard sample is the kinematic viscosity of the resin component.

  In the thermally conductive sheet, the volume-based content ratio of the boron nitride particles (solid content, that is, the volume percentage of the boron nitride particles with respect to the total volume of the resin component and the boron nitride particles) is, for example, 35% by volume or more, preferably Is 60% by volume or more, preferably 75% by volume or more, and usually 95% by volume or less, preferably 90% by volume or less.

  When the volume-based content ratio of the boron nitride particles is less than the above range, the boron nitride particles may not be oriented in a predetermined direction in the thermally conductive sheet. On the other hand, when the volume-based content ratio of the boron nitride particles exceeds the above-described range, the thermally conductive sheet becomes brittle, and the handleability and the step following ability may be deteriorated.

  Further, the mixing ratio of the boron nitride particles based on the total amount (solid content) of each component (boron nitride particles and resin component) forming 100 parts by mass of the heat conductive sheet is, for example, 40 to 95 parts by mass, preferably Is 65 to 90 parts by mass, and the blending ratio of the resin component based on 100 parts by mass of the total amount of each component forming the heat conductive sheet is, for example, 5 to 60 parts by mass, preferably 10 to 35 parts by mass. Part. In addition, the mixture ratio of the mass reference | standard of boron nitride particle with respect to 100 mass parts of resin components is 60-1900 mass parts, for example, Preferably, it is also 185-900 mass parts.

  Further, when two types of epoxy resins (first epoxy resin and second epoxy resin) are used in combination, the mass ratio of the first epoxy resin to the second epoxy resin (the mass of the first epoxy resin / the mass of the second epoxy resin) ) Can be appropriately set according to the softening temperature of each epoxy resin (first epoxy resin and second epoxy resin), for example, 1/99 to 99/1, preferably 10/90 to 90 / 10.

  The resin component includes, for example, a polymer precursor (for example, a low molecular weight polymer including an oligomer) and / or a monomer in addition to the above-described components (polymerized products).

  FIG. 1 is a perspective view of one embodiment of the thermally conductive sheet of the present invention, and FIG. 2 is a process diagram for explaining a method for producing the thermally conductive sheet shown in FIG.

  Next, a method for producing an embodiment of the thermally conductive sheet of the present invention will be described with reference to FIGS. 1 and 2.

  In this method, first, the above-described components are blended at the blending ratio described above, and the mixture is prepared by stirring and mixing.

  In the stirring and mixing, in order to mix each component efficiently, for example, a solvent can be blended with the above-described components, or the resin component (preferably, a thermoplastic resin component) can be melted by heating, for example.

  Examples of the solvent include the same organic solvents as described above. In addition, when the above-described curing agent and / or curing accelerator is prepared as a solvent solution and / or a solvent dispersion, the solvent of the solvent solution and / or the solvent dispersion without adding a solvent in the stirring and mixing. Can be used as a mixed solvent for stirring and mixing as it is. Alternatively, a solvent can be further added as a mixed solvent in the stirring and mixing.

  When stirring and mixing using a solvent, the solvent is removed after stirring and mixing.

  To remove the solvent, for example, it is allowed to stand at room temperature for 1 to 48 hours, for example, heated at 40 to 100 ° C. for 0.5 to 3 hours, or reduced pressure of 0.001 to 50 kPa, for example. Heat at 20-60 ° C. for 0.5-3 hours under atmosphere.

  When the resin component is melted by heating, the heating temperature is, for example, a temperature near or exceeding the softening temperature of the resin component, specifically, 40 to 150 ° C., preferably 70 to 140 ° C. It is.

  In this method, the resulting mixture is then hot pressed.

  Specifically, as shown in FIG. 2A, the mixture is hot-pressed through, for example, two release films 4 as necessary to obtain a press sheet 1A. The conditions of the hot press are that the temperature is, for example, 50 to 150 ° C., preferably 60 to 140 ° C., the pressure is, for example, 1 to 100 MPa, preferably 5 to 50 MPa, and the time is, for example, 0 .1 to 100 minutes, preferably 1 to 30 minutes.

  More preferably, the mixture is vacuum hot pressed. The degree of vacuum in the vacuum hot press is, for example, 1 to 100 Pa, preferably 5 to 50 Pa, and the temperature, pressure, and time are the same as those in the above-described hot press.

  When the temperature, pressure and / or time in the hot press are out of the above range, the porosity P (described later) of the heat conductive sheet 1 may not be adjusted to a desired value.

  The thickness of 1 A of press sheets obtained by hot press is 50-1000 micrometers, for example, Preferably, it is 100-800 micrometers.

  Next, in this method, as shown in FIG. 2B, the press sheet 1A is divided into a plurality (for example, four) to obtain a divided sheet 1B (a dividing step). In the division of the press sheet 1A, the press sheet 1A is cut along the thickness direction so as to be divided into a plurality when projected in the thickness direction. The press sheet 1A is cut so as to have the same shape when the divided sheets 1B are projected in the thickness direction.

  Next, in this method, as shown in FIG. 2C, the divided sheets 1B are laminated in the thickness direction to obtain a laminated sheet 1C (laminating step).

  Thereafter, in this method, as shown in FIG. 2A, the laminated sheet 1C is hot-pressed (preferably vacuum hot-pressed) (hot-pressing step). The conditions for the hot press are the same as the conditions for the hot press of the mixture described above.

  The thickness of the laminated sheet 1C after hot pressing is, for example, 1 mm or less, preferably 0.8 mm or less, usually, for example, 0.05 mm or more, preferably 0.1 mm or more.

  Thereafter, in order to efficiently orient boron nitride particles 2 in the resin component 3 in a predetermined direction in the heat conductive sheet 1, the above-described dividing step (FIG. 2B), laminating step (FIG. 2C), and A series of steps of the hot press step (FIG. 2A) is repeatedly performed. The number of repetitions is not particularly limited, and can be appropriately set according to the filling state of the boron nitride particles, and is, for example, 1 to 10 times, preferably 2 to 7 times.

  In the above-described hot pressing step (FIG. 2A), for example, the mixture and the laminated sheet 1C can be rolled with a plurality of calendar rolls.

  Thereby, the heat conductive sheet 1 can be obtained.

  The thickness of the obtained heat conductive sheet 1 is, for example, 1 mm or less, preferably 0.8 mm or less, usually, for example, 0.05 mm or more, preferably 0.1 mm or more.

  Further, as described above, the volume-based content ratio of the boron nitride particles in the heat conductive sheet 1 (solid content, that is, the volume percentage of the boron nitride particles with respect to the total volume of the resin component and the boron nitride particles) is, for example, 35 Volume% or more (preferably 60 volume% or more, more preferably 75 volume% or more), usually 95 volume% or less (preferably 90 volume% or less).

  When the content ratio of the boron nitride particles is less than the above range, the boron nitride particles 2 may not be oriented in a predetermined direction in the heat conductive sheet 1.

  Further, when the resin component 3 is a thermosetting resin component, for example, the above-described dividing step (FIG. 2B), laminating step (FIG. 2C), and hot pressing step (FIG. 2A). ) Is repeatedly performed in an uncured state to obtain the uncured thermally conductive sheet 1 as it is.

  In addition, the heat conductive sheet 1 will be in a semi-hardened (B stage) state at the time of the thermocompression bonding with respect to the to-be-adhered body mentioned later, and the heat conductive sheet 1 is thermoset after the thermocompression bonding with respect to the to-be-adhered body.

  In order to thermally cure the heat conductive sheet 1, the above-described hot press or dryer is used. Preferably, a dryer is used. As for the conditions of such thermosetting, the temperature is, for example, 60 to 250 ° C, preferably 80 to 200 ° C.

  In the heat conductive sheet 1 thus obtained, the longitudinal direction LD of the boron nitride particles 2 intersects the thickness direction TD of the heat conductive sheet 1 as shown in FIG. 1 and a partially enlarged schematic view thereof. They are oriented along the (orthogonal) plane direction SD.

  Further, the arithmetic average of the angles formed by the longitudinal direction LD of the boron nitride particles 2 in the surface direction SD of the thermal conductive sheet 1 (orientation angle α of the boron nitride particles 2 with respect to the thermal conductive sheet 1) is, for example, 25 degrees or less, Preferably, it is 20 degrees or less, and is usually 0 degrees or more.

  The orientation angle α of the boron nitride particles 2 with respect to the heat conductive sheet 1 is determined by cutting the heat conductive sheet 1 along the thickness direction with a cross-section polisher (CP), and the resulting cross section is scanned with an electron microscope. With (SEM), a photograph was taken at a magnification of the field of view where 200 or more boron nitride particles 2 can be observed. From the obtained SEM photograph, the surface direction SD of the thermal conductive sheet 1 in the longitudinal direction LD of the boron nitride particles 2 The inclination angle α with respect to (the direction orthogonal to the thickness direction TD) is acquired and calculated as an average value thereof.

  Thereby, the thermal conductivity in the surface direction SD of the heat conductive sheet 1 is 4 W / m · K or more, preferably 5 W / m · K or more, more preferably 10 W / m · K or more, and still more preferably, It is 15 W / m · K or more, particularly preferably 25 W / m · K or more, and usually 200 W / m · K or less.

  Moreover, the thermal conductivity of the surface direction SD of the heat conductive sheet 1 is substantially the same before and after thermosetting when the resin component 3 is a thermosetting resin component.

  If the thermal conductivity in the surface direction SD of the thermal conductive sheet 1 is less than the above range, the thermal conductivity in the surface direction SD is not sufficient, and therefore for heat dissipation applications that require such thermal conductivity in the surface direction SD. It may not be used.

  In addition, the heat conductivity of the surface direction SD of the heat conductive sheet 1 is measured by the pulse heating method. In the pulse heating method, a xenon flash analyzer “LFA-447 type” (manufactured by NETZSCH) is used.

  Moreover, the heat conductivity of the thickness direction TD of the heat conductive sheet 1 is 0.5-15 W / m * K, for example, Preferably, it is 1-10 W / m * K.

  The thermal conductivity in the thickness direction TD of the thermal conductive sheet 1 is measured by a pulse heating method, a laser flash method, or a TWA method. In the pulse heating method, the same one as described above is used, in the laser flash method, “TC-9000” (manufactured by ULVAC-RIKO) is used, and in the TWA method, “ai-Phase mobile” (manufactured by Eye Phase). Is used.

  Thereby, the ratio of the thermal conductivity in the plane direction SD of the thermal conductive sheet 1 to the thermal conductivity in the thickness direction TD of the thermal conductive sheet 1 (thermal conductivity in the plane direction SD / thermal conductivity in the thickness direction TD). Is, for example, 1.5 or more, preferably 3 or more, more preferably 4 or more, and usually 20 or less.

  Further, although not shown in FIG. 1, for example, a gap (gap) is formed in the heat conductive sheet 1.

  The void ratio in the thermal conductive sheet 1, that is, the void ratio P is the content ratio (volume basis) of the boron nitride particles 2, and further, hot pressing of a mixture of the boron nitride particles 2 and the resin component 3 (FIG. )) Can be adjusted by the temperature, pressure and / or time. Specifically, the temperature, pressure and / or time of the above-described hot press (FIG. 2 (a)) is set within the above range. Can be adjusted.

  The porosity P in the heat conductive sheet 1 is, for example, 30% by volume or less, and preferably 10% by volume or less.

  For example, the porosity P described above is obtained by first cutting the thermally conductive sheet 1 with a cross section polisher (CP) along the thickness direction, and using a scanning electron microscope (SEM) to show the cross section that appears. The image is obtained by observing at a magnification, and from the obtained image, the void portion and the other portion are binarized, and then the area ratio of the void portion to the cross-sectional area of the entire thermal conductive sheet 1 is determined. It is measured by calculating.

  In addition, in the heat conductive sheet 1, the porosity P2 after hardening is 100% or less with respect to the porosity P1 before hardening, for example, Preferably, it is 50% or less.

  In the measurement of the porosity P (P1), when the resin component 3 is a thermosetting resin component, the thermally conductive sheet 1 before thermosetting is used.

  If the porosity P of the heat conductive sheet 1 is in the above-described range, the step following property (described later) of the heat conductive sheet 1 can be improved.

  On the other hand, the heat conductive sheet 1 does not fall off from the adherend in the following initial adhesion test (1). That is, the temporarily fixed state of the heat conductive sheet 1 and the adherend is maintained.

    Initial adhesive strength test (1): The thermal conductive sheet 1 is heat-pressed and temporarily fixed on the adherend along the horizontal direction, left for 10 minutes, and then the adherend is turned upside down.

  As the adherend, for example, a substrate made of stainless steel (for example, SUS304) or a mounting substrate for a notebook computer on which a plurality of electronic components such as an IC (integrated circuit) chip, a capacitor, a coil, and a resistor are mounted. Can be mentioned. In the mounting board for notebook personal computers, the electronic components are usually arranged on the upper surface (one surface) at a distance from each other in the surface direction (the surface direction of the mounting board for notebook personal computer).

  In the pressure bonding, for example, the surface of the heat conductive sheet 1 is rolled while pressing a sponge roll made of a resin such as a silicone resin against the heat conductive sheet 1.

  Moreover, the temperature of thermocompression bonding is 80 degreeC, for example, when the resin component 3 is a thermosetting resin component (for example, epoxy resin).

  On the other hand, when the resin component 3 is a thermoplastic resin component (for example, polyethylene), the thermocompression bonding temperature is, for example, a temperature obtained by adding 10 to 30 ° C. to the softening point or melting point of the thermoplastic resin component, Preferably, it is a temperature obtained by adding 15 to 25 ° C. to the softening point or melting point of the thermoplastic resin component, more preferably a temperature obtained by adding 20 ° C. to the softening point or melting point of the thermoplastic resin component. Is 120 ° C. (that is, the temperature at which the softening point or melting point of the thermoplastic resin component is 100 ° C., and 20 ° C. is added to 100 ° C.).

  When the thermal conductive sheet 1 falls off from the adherend in the initial adhesive strength test (1) described above, that is, when the temporarily fixed state between the thermal conductive sheet 1 and the adherend is not maintained, The conductive sheet 1 cannot be temporarily fixed securely to the adherend.

  In addition, when the resin component 3 is a thermosetting resin component, the heat conductive sheet 1 used for the initial adhesive strength test (1) and the initial adhesive strength test (2) (described later) is uncured heat. It is the conductive sheet 1, and the heat conductive sheet 1 is brought into a B-stage state by thermocompression bonding in the initial adhesive strength test (1) and the initial adhesive strength test (2).

  Moreover, when the resin component 3 is a thermoplastic resin component, the heat conductive sheet 1 used for the initial adhesive strength test (1) and the initial adhesive strength test (2) (described later) is a solid heat conductive material. The heat conductive sheet 1 is in a softened state by thermocompression bonding in the initial adhesive strength test (1) and the initial adhesive strength test (2).

  Preferably, the heat conductive sheet 1 does not fall off from the adherend in both the initial adhesive strength test (1) and the initial adhesive strength test (2) described below. That is, the temporarily fixed state of the heat conductive sheet 1 and the adherend is maintained.

    Initial adhesion test (2): The thermal conductive sheet 1 is heat-pressed and temporarily fixed on the adherend along the horizontal direction, and left for 10 minutes, and then the adherend is placed in the vertical direction (vertical direction). Arrange along.

  The temperature in the thermocompression bonding in the initial adhesive strength test (2) is the same as the temperature in the thermocompression bonding in the initial adhesive strength test (1).

  Moreover, when the heat conductive sheet 1 is evaluated under the following test conditions in a bending resistance test based on the cylindrical mandrel method of JIS K 5600-5-1, preferably no breakage is observed.

Test conditions Test equipment: Type I
Mandrel: 10mm in diameter
Bending angle: 90 degrees or more Thickness of the thermal conductive sheet 1: 0.3 mm
More preferably, the thermal conductive sheet 1 is not observed to break even when the bending angle is set to 180 degrees under the test conditions described above.

  When the resin component 3 is a thermosetting resin component, the heat conductive sheet 1 subjected to the flexibility test is a semi-cured (B stage state) heat conductive sheet 1 (that is, before thermosetting). The heat conductive sheet 1).

  When breakage is observed in the heat conductive sheet 1 in the above-described bending resistance test at the bending angle, excellent flexibility and step following ability (described later) cannot be imparted to the heat conductive sheet 1 There is.

  Moreover, when this heat conductive sheet 1 is evaluated on the following test conditions in the 3 point | piece bending test based on JISK7171 (2008), a fracture | rupture is not observed, for example.

Test conditions Test piece: Size 20mm x 15mm
Distance between fulcrums: 5mm
Test speed: 20 mm / min (pressing speed of indenter)
Bending angle: 120 degrees Evaluation method: When tested under the above test conditions, the presence or absence of breakage such as cracks at the center of the test piece is visually observed.

  In the three-point bending test, when the resin component 3 is a thermosetting resin component, the thermally conductive sheet 1 before thermosetting is used.

  Therefore, since this heat conductive sheet 1 is not observed in the above-described three-point bending test, the step followability is excellent. Note that the step following property is formed by the step (for example, the electronic component described above) when the thermal conductive sheet 1 is provided on a stepped installation target (for example, the above-described mounting board for a notebook personal computer). This is a characteristic of following along a step).

  Moreover, marks, such as a character and a symbol, can be made to adhere to the heat conductive sheet 1, for example. That is, the heat conductive sheet 1 is excellent in mark adhesion. The mark adhesion is a characteristic that allows the above-described marks to be reliably adhered to the heat conductive sheet 1.

  Specifically, the mark is attached (applied, fixed, or fixed) to the heat conductive sheet 1 by printing or engraving.

  Examples of printing include ink jet printing, letterpress printing, intaglio printing, and laser printing.

  In addition, when a mark is printed by inkjet printing, letterpress printing, or intaglio printing, for example, an ink fixing layer for improving the fixability of the mark is provided on the surface (printing side surface) of the heat conductive sheet 1. be able to.

  Further, when the mark is printed by laser printing, for example, a toner fixing layer for improving the fixability of the mark can be provided on the surface (printing side surface) of the heat conductive sheet 1.

  Examples of the marking include laser marking and stamping.

  And the above-mentioned heat conductive sheet 1 is excellent also in the adhesive force (initial adhesive force) after thermocompression-bonding of the predetermined temperature with respect to a to-be-adhered body, being excellent in the surface direction SD.

  Therefore, if the heat conductive sheet 1 is heat-bonded to the adherend, the heat conductive sheet 1 can be reliably fixed (temporarily fixed) to the adherend.

  Therefore, the heat conductive sheet 1 is temporarily fixed to the adherend in a B-stage state, and then the heat conductive sheet 1 is thermally cured by heating, so that the heat conductive sheet 1 is securely attached to the adherend. The heat of the adherend can be efficiently conducted along the surface direction SD of the heat conductive sheet 1 by the heat conductive sheet 1 while being adhered to the surface.

  In addition, it does not specifically limit as a to-be-adhered body, For example, a light emitting diode etc. are mentioned besides the above-mentioned electronic component.

  On the other hand, after temporary fixing to the adherend of the heat conductive sheet 1, there may be a case where it is desired to peel once for position adjustment and reattach (rework) if necessary. It is in the B stage state and reworkability is good. Therefore, the heat conductive sheet 1 can be easily reworked while preventing the heat conductive sheet 1 from remaining on the surface of the adherend during peeling.

  Furthermore, even if the heat conductive sheet 1 remains on the surface of the adherend, since the heat conductive sheet 1 is uncured (before curing), the residue can be easily wiped off (removed). .

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the examples.

Example 1
PT-110 (trade name, plate-like boron nitride particles, average particle diameter (light scattering method) 45 μm, manufactured by Momentive Performance Materials Japan) 13.42 g and JER828 (trade name, bisphenol A type epoxy resin) , First epoxy resin, liquid, epoxy equivalent 184 to 194 g / eqiv, softening temperature (ring and ball method) less than 25 ° C., melt viscosity (80 ° C.) 70 mPa · s, manufactured by Japan Epoxy Resin Co., Ltd. 1.0 g, and EPPN -501HY (trade name, triphenylmethane type epoxy resin, second epoxy resin, solid, epoxy equivalent of 163 to 175 g / eqiv., Softening temperature (ring and ball method) 57 to 63 ° C., manufactured by Nippon Kayaku Co., Ltd.) 2.0 g And 5% by weight methyl ethyl ketone dispersion of curing agent (CURESOL 2P4MHZ-PW (trade name, manufactured by Shikoku Kasei Co., Ltd.) 3 g (solid content 0.15 g) (5% by mass based on the total amount of epoxy resin JER828 and EPPN-501HY) and stirred, left at room temperature (23 ° C.) overnight to stand for methyl ethyl ketone (cured) The dispersion medium of the agent was volatilized to prepare a semi-solid mixture.

  In the above formulation, the volume percentage (volume%) of the boron nitride particles with respect to the total volume of the solid content excluding the curing agent (that is, the solid content of the boron nitride particles and the epoxy resin) was 70% by volume. .

  Next, the obtained mixture was sandwiched between two release films treated with silicone, and they were placed in a vacuum heating press machine at 80 ° C. in an atmosphere of 10 Pa (vacuum atmosphere) under a load of 5 tons (20 MPa) for 2 minutes. A press sheet having a thickness of 0.3 mm was obtained by hot pressing (see FIG. 2A).

  After that, when the obtained press sheet is projected in the thickness direction of the press sheet, a divided sheet is obtained by cutting so as to be divided into a plurality of pieces (see FIG. 2B), and then the divided sheet. Were laminated in the thickness direction to obtain a laminated sheet (see FIG. 2C).

  Subsequently, the obtained laminated sheet was hot-pressed under the same conditions as described above using a vacuum heating press similar to the above (see FIG. 2A).

  Subsequently, the above-described series of operations of cutting, laminating and hot pressing (see FIG. 2) was repeated four times to obtain a thermally conductive sheet (uncured state) having a thickness of 0.3 mm.

Examples 2-16
Based on the formulation and production conditions in Tables 1 to 3, the same treatment as in Example 1 was performed to obtain a heat conductive sheet.

(Evaluation)
1. Thermal conductivity The thermal conductivity was measured about the heat conductive sheet obtained by Examples 1-16.

  That is, the thermal conductivity in the plane direction (SD) was measured by a pulse heating method using a xenon flash analyzer “LFA-447 type” (manufactured by NETZSCH).

The results are shown in Tables 1 to 3.
2. Initial adhesion test 2-1. Initial Adhesive Strength Test for Laptop PC Mounting Board Initial adhesive strength test for notebook PC mounting board on which a plurality of electronic components are mounted (1) and (2) for the thermally conductive sheets obtained in Examples 1-16 Carried out.

  That is, using a sponge roll made of silicone resin on the surface (the side on which the electronic component is mounted) of the mounting board for a notebook computer along the horizontal direction of the heat conductive sheet, 80 ° C. (Examples 1 to 9 and Examples) 11 to 16) or 120 ° C. (Example 10) by thermocompression bonding and temporarily fixed, and left to stand for 10 minutes, and then installed a mounting board for a notebook computer along the vertical direction (Initial Adhesion Test (2)) ).

  Subsequently, the mounting board for the notebook personal computer was installed so that the heat conductive sheet was directed downward (that is, upside down from the state immediately after temporary fixing) (initial adhesive force test (1)).

  And in the above-mentioned initial adhesive strength test (1) and initial adhesive strength test (2), the heat conductive sheet was evaluated according to the following criteria. The results are shown in Tables 1 to 3.

<Standard>
○: It was confirmed that the thermal conductive sheet did not fall off from the mounting board for notebook computers.

    X: It was confirmed that the heat conductive sheet was detached from the mounting board for the notebook computer.

2-2. Initial adhesive strength test for stainless steel substrate For the thermally conductive sheets obtained in Examples 1 to 16, initial adhesive strength tests (1) and (2) for a stainless steel substrate (made of SUS304) were performed in the same manner as described above.

  As a result, in both the initial adhesive strength tests (1) and (2), the heat conductive sheet did not fall off from the stainless steel substrate.

  And in the above-mentioned initial adhesive strength test (1) and initial adhesive strength test (2), the heat conductive sheet was evaluated according to the following criteria. The results are shown in Tables 1 to 3.

<Standard>
○: It was confirmed that the heat conductive sheet did not fall off from the stainless steel substrate.

X: It confirmed that the heat conductive sheet fell from the stainless steel substrate.
3. Porosity (P)
The porosity (P1) of the heat conductive sheet obtained by Examples 1-16 was measured with the following measuring method.

Method for measuring porosity: First, a thermally conductive sheet is cut along a thickness direction by a cross section polisher (CP), and a cross section that appears is observed at 200 times with a scanning electron microscope (SEM). And got a statue. Thereafter, the void portion and other portions were binarized from the obtained image, and then the area ratio of the void portion to the cross-sectional area of the entire heat conductive sheet was calculated. The results are shown in Tables 1 to 3.
4). Step following ability (3-point bending test)
About the heat conductive sheet obtained by Examples 1-16, the three-point bending test in the following test conditions is implemented based on JISK7171 (2008), and level | step difference followability is according to the following evaluation criteria. evaluated. The results are shown in Tables 1 to 3.

Test conditions Test piece: Size 20mm x 15mm
Distance between fulcrums: 5mm
Test speed: 20 mm / min (pressing speed of indenter)
Bending angle: 120 degrees (evaluation criteria)
A: No fracture was observed at all.

  ○: Fracture was hardly observed.

X: Breakage was clearly observed.
5. Print mark visibility (print mark adhesion: mark adhesion by inkjet printing or laser printing)
The mark was printed on the heat conductive sheet obtained by Examples 1-16 by inkjet printing and laser printing, and this mark was observed.

  As a result, for any of the thermally conductive sheets of Examples 1 to 16, it was confirmed that marks by both ink jet printing and laser printing could be seen well, and the print mark adhesion was good.

  The numerical value in each component in Tables 1 to 3 indicates the number of grams unless otherwise specified.

  In the column of boron nitride particles in Tables 1 to 3, the upper numerical value is the compounding mass (g) of boron nitride particles, and the intermediate numerical value is the solid content excluding the curing agent in the thermally conductive sheet (that is, , The volume percentage (volume%) of the boron nitride particles to the total volume of the boron nitride particles and the solid content of the epoxy resin or polyethylene), and the lower number is the solid content of the thermally conductive sheet (that is, boron nitride particles) And the volume percentage (volume%) of the boron nitride particles with respect to the total volume of the solid content of the epoxy resin and the curing agent.

Details of the components marked with * among the components in Tables 1 to 3 are described below.
PT-110 ^{* 1} : Product name, plate-like boron nitride particles, average particle size (light scattering method) 45 μm, UHP-1 manufactured by Momentive Performance Materials Japan Ltd. ^{* 2} : Product name: Shovie N UHP- 1, plate-like boron nitride particles, average particle diameter (light scattering method) 9 μm, Showa Denko Epoxy Resin A ^{* 3} : Ogsol EG (trade name), bisarylfluorene type epoxy resin, semi-solid, epoxy equivalent 294 g / Eqiv. , Softening temperature (ring and ball method) 47 ° C., melt viscosity (80 ° C.) 1360 mPa · s, epoxy resin B manufactured by Osaka Gas Chemical Co., Ltd. ^{* 4} : JER828 (trade name), bisphenol A type epoxy resin, liquid, epoxy equivalent 184 to 194 g / Eqiv. , Softening temperature (ring ball method) less than 25 ° C., melt viscosity (80 ° C.) 70 mPa · s, epoxy resin C ^{* 5} manufactured by Japan Epoxy Resin Co., Ltd .: JER1002 (trade name), bisphenol A type epoxy resin, solid, epoxy equivalent 600 -700 g / eqiv. , Softening temperature (ring and ball method) 78 ° C., melt viscosity (80 ° C.) 10000 mPa · s or more (measurement limit or more), epoxy resin D ^{* 6} manufactured by Japan Epoxy Resin Co., Ltd .: EPPN-501HY (trade name), triphenylmethane type epoxy Resin, solid, epoxy equivalent 163-175 g / eqiv. , Softening temperature (ring and ball method) 57-63 ° C., Nippon Kayaku Co., Ltd. curing agent ^{* 7} : Curazole 2PZ (trade name, manufactured by Shikoku Kasei Co., Ltd.) 5 mass% methyl ethyl ketone solution curing agent ^{* 8} : Cureazole 2P4MHZ-PW (Product) 5% by weight methyl ethyl ketone dispersion polyethylene ^{* 9} : low density polyethylene, weight average molecular weight (Mw) 4000, number average molecular weight (Mn) 1700, melting point 100 ° C. to 105 ° C., made by Aldrich

1 Thermal Conductive Sheet 2 Boron Nitride Particles TD Thickness Direction SD Plane Direction (Orthogonal Direction)

Claims (1)

A thermally conductive sheet containing plate-like boron nitride particles,
The thermal conductivity in the direction orthogonal to the thickness direction of the thermal conductive sheet is 4 W / m · K or more,
The heat conductive sheet is characterized in that the heat conductive sheet does not fall off from the adherend in the following initial adhesion test (1).
Initial adhesive strength test (1): A thermally conductive sheet is temporarily fixed on an adherend along the horizontal direction, and then the adherend is turned upside down.