Carbon-coated thermal conductive material

Abstract

A carbon-coated thermal conductive material includes a coating layer comprising amorphous carbon on a surface of a thermal conductive material, wherein the thermal conductive material comprises a metal oxide, a metal nitride, a metal material, or a carbon-based material having a thermal conductivity of 10 W/mK or greater, the amorphous carbon is derived from carbon contained in an oxazine resin, a ratio of a peak intensity of a G band to a peak intensity of a D band is 1.0 or greater when the amorphous carbon is measured by Raman spectroscopy, an average film thickness of the coating layer is 500 nm or less, and a coefficient of variation (CV value) of a film thickness of the coating layer is 15% or less.

Claims

1. A carbon-coated thermal conductive material comprising: a thermal conductive material having a particle shape; and a coating layer comprising amorphous carbon on a surface of the thermal conductive material, wherein the thermal conductive material comprises at least one selected from the group consisting of a metal oxide, a metal nitride, a metal material, and a carbon-based material having a thermal conductivity of 10 W/mK or greater, the amorphous carbon is derived from carbon contained in an oxazine resin, a ratio of a peak intensity of a G band to a peak intensity of a D band is 1.0 or greater when the amorphous carbon is measured by Raman spectroscopy, an average film thickness of the coating layer is 500 nm or less, and a coefficient of variation (CV value) of a film thickness of the coating layer is 15% or less.

2. The carbon-coated thermal conductive material according to claim 1, wherein at least one of a mass spectrum resulting from a benzene ring and a mass spectrum resulting from a naphthalene ring is detected when the coating layer is measured by time-of-flight secondary ion mass spectrometry (TOF-SIMS).

3. The carbon-coated thermal conductive material according to claim 1, wherein no peak is detected at a position in which 20 equals 26.4 when the coating layer is measured by X-ray diffractometry.

4. The carbon-coated thermal conductive material according to claim 1, wherein the oxazine resin is a naphthoxazine resin.

5. The carbon-coated thermal conductive material according to claim 2, wherein the oxazine resin is a naphthoxazine resin.

6. The carbon-coated thermal conductive material according to claim 1, wherein the thermal conductive material comprises the metal oxide or the metal nitride, wherein the metal oxide is magnesium oxide (MgO), and wherein the metal nitride is aluminum nitride (AlN).

7. The carbon-coated thermal conductive material according to claim 2, wherein the thermal conductive material comprises the metal oxide or the metal nitride, wherein the metal oxide is magnesium oxide (MgO), and wherein the metal nitride is aluminum nitride (AlN).

8. The carbon-coated thermal conductive material according to claim 3, wherein the thermal conductive material comprises the metal oxide or the metal nitride, wherein the metal oxide is magnesium oxide (MgO), and wherein the metal nitride is aluminum nitride (AlN).

9. The carbon-coated thermal conductive material according to claim 4, wherein the thermal conductive material comprises the metal oxide or the metal nitride, wherein the metal oxide is magnesium oxide (MgO), and wherein the metal nitride is aluminum nitride (AlN).

10. The carbon-coated thermal conductive material according to claim 5, wherein the thermal conductive material comprises the metal oxide or the metal nitride, wherein the metal oxide is magnesium oxide (MgO), and wherein the metal nitride is aluminum nitride (AlN).

11. The carbon-coated thermal conductive material according to claim 1, wherein the thermal conductive material comprises the metal material, and wherein the metal material is at least one selected from the group consisting of copper (Cu), nickel (Ni), iron (Fe), and cobalt (Co).

12. The carbon-coated thermal conductive material according to claim 2, wherein the thermal conductive material comprises the metal material, and wherein the metal material is at least one selected from the group consisting of copper (Cu), nickel (Ni), iron (Fe), and cobalt (Co).

13. The carbon-coated thermal conductive material according to claim 3, wherein the thermal conductive material comprises the metal material, and wherein the metal material is at least one selected from the group consisting of copper (Cu), nickel (Ni), iron (Fe), and cobalt (Co).

14. The carbon-coated thermal conductive material according to claim 4, wherein the thermal conductive material comprises the metal material, and wherein the metal material is at least one selected from the group consisting of copper (Cu), nickel (Ni), iron (Fe), and cobalt (Co).

15. The carbon-coated thermal conductive material according to claim 5, wherein the thermal conductive material comprises the metal material, and wherein the metal material is at least one selected from the group consisting of copper (Cu), nickel (Ni), iron (Fe), and cobalt (Co).

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The FIGURE is a transmission electron micrograph of a particle having undergone a surface coating treatment.

DESCRIPTION OF EMBODIMENTS

(2) Hereinafter, one or more embodiments of the present invention will be more specifically described based on examples, but the present invention is not limited to the examples.

Example 1

(3) (Formation of Coating Layer)

(4) 0.1 g of 1,5-dihydroxynaphthalene (manufactured by TOKYO CHEMICAL INDUSTRY CO., LTD.), 0.05 g of 40% methylamine (manufactured by Wako Pure Chemical Industries, Ltd.), and 0.1 g of a 37% aqueous formaldehyde solution (manufactured by Wako Pure Chemical Industries, Ltd.) were sequentially dissolved in ethanol, thereby preparing 20 g of a mixed ethanol solution.

(5) Then, 0.2 g of thermal conductive particles (material: MgO, average particle size: 10 m) were added to the obtained mixed solution, and the solution was treated for 4 hours in an ultrasonic tank. The solution was filtered, washed 3 times with ethanol, and then dried for 3 hours at 50 C. in a vacuum. The particles dried as above were heated for 2 hours at 150 C., thereby obtaining carbon-coated thermal conductive particles.

(6) The surfaces of the thermal conductive particles having not yet been heated for 2 hours at 150 C. were measured by nuclear magnetic resonance spectroscopy (NMR spectroscopy). As a result, a peak (3.95 ppm) corresponding to a methylene group of benzene ring-CH.sub.2N of a naphthoxazine ring and a peak (4.92 ppm) corresponding to a methylene group of OCH.sub.2N were detected at almost the same intensity. Therefore, it was confirmed that a resin component containing a naphthoxazine ring was precipitated on the surfaces of the particles.

(7) The measurement by nuclear magnetic resonance spectroscopy was performed using .sup.1H-NMR (600 MHz) manufactured by Varian Inova. At the time of the measurement, deuterated dimethyl sulfoxide was used, spectra were integrated 256 times, and a mitigation time was set to be 10 seconds.

(8) The obtained carbon-coated thermal conductive particles were analyzed by Raman spectroscopy by using Almega XR (manufactured by Thermo Fisher Scientific Inc.). As a result, a peak was observed in both of a G band and a D band, and this leaded to a conclusion that the naphthoxazine resin turned into amorphous carbon.

(9) A ratio of a peak intensity of the G band to a peak intensity of the D band was 1.7, and a 530 nm-laser beam was used.

Example 2

(10) A carbon-coated thermal conductive particles were obtained in the same manner as in Example 1, except that in (Formation of coating layer) of Example 1, the step of heating dried particles for 2 hours at 150 C. was changed to a step of heating dried particles for 2 hours at 250 C.

Example 3

(11) (Formation of Coating Layer)

(12) 0.5 g of 1,5-dihydroxynaphthalene (manufactured by TOKYO CHEMICAL INDUSTRY CO., LTD.), 0.25 g of 40% methylamine (Wako Pure Chemical Industries, Ltd.), and 0.6 g of a 37% aqueous formaldehyde solution (manufactured by Wako Pure Chemical Industries, Ltd.) were sequentially dissolved in ethanol, thereby preparing 20 g of a mixed ethanol solution.

(13) Then, 0.2 g of thermal conductive particles (material: AlN, average particle size: 16 m) were added to the obtained mixed solution, and the solution was treated for 4 hours in an ultrasonic rank. The solution was filtered, washed 3 times with ethanol, and dried for 3 hours at 50 C. in a vacuum. Furthermore, the particles dried as above were heated for 6 hours at 200 C., thereby obtaining carbon-coated thermal conductive particles.

Example 4

(14) Carbon-coated thermal conductive particles were obtained in the same manner as in Example 3, except that in (Formation of coating layer) of Example 3, the step of heating dried particles for 6 hours at 200 C. was changed to a step of heating dried particles for 6 hours at 350 C.

Example 5

(15) 0.1 g of 1,5-dihydroxynaphthalene (manufactured by TOKYO CHEMICAL INDUSTRY CO., LTD.), 0.05 g of 40% methylamine (manufactured by Wako Pure Chemical Industries, Ltd.), and 0.1 g of a 37% aqueous formaldehyde solution (manufactured by Wako Pure Chemical Industries, Ltd.) were sequentially dissolved in ethanol, thereby preparing 20 g of a mixed ethanol solution.

(16) Then, copper flakes (30 mm15 mm0.2 mm) were immersed into the obtained mixed solution, and the solution was treated for 4 hours in an ultrasonic tank. The solution was filtered, washed 3 times with ethanol, and dried for 2 hours at 80C in a vacuum. The flakes dried as above were heated for 2 hours at 150 C., thereby obtaining carbon-coated metal flakes.

Comparative Example 1

(17) The thermal conductive particles (material: MgO, average particle size: 10 m) used in Example 1 were used as they were without being treated in (Formation of coating layer).

Comparative Example 2

(18) The thermal conductive particles (material: AlN, average particle size: 16 m) used in Example 3 were used as they were without being treated in (Formation of coating layer).

Comparative Example 3

(19) The copper flakes (30 mm15 mm0.2 mm) used in Example 5 were used as they were without being treated in (Formation of coating layer).

Comparative Example 4

(20) As a solvent, 4.8 g of dimethyl sulfoxide-d.sub.6 (manufactured by Wako Pure Chemical Industries, Ltd.) was put into a 50 ml beaker. Then, as raw materials, 0.16 g of 1,5-dihydroxynaphthalene, 0.08 g of a 40% aqueous methylamine solution, and 0.16 g of a 37% aqueous formaldehyde solution were added thereto in this order. The raw materials were dissolved by being gently stirred with a glass bar, thereby preparing a mixed solution.

(21) The mixed solution was left to stand for 5 hours at room temperature, and 0.2 g of AlN (average particle size: 16 m) as thermal conductive particles was added to the solution. The particles separated through filtration were heated for 3 hours at 120 C. and then subjected to a thermal treatment for 3 hours at 250 C., thereby obtaining carbon-coated AlN particles.

Comparative Example 5

(22) In 50 ml of water, 0.5 g of AlN particles (average particle size: 16 m) and 3.0 g of glucose were dispersed by stirring. Then, the mixed solution was moved to a pressure-resistant container made of stainless steel including a Teflon (registered trademark) inner cylinder and subjected to a thermal treatment for 12 hours at 180 C. After the reaction, the mixed solution was cooled to room temperature and went through a step of centrifugation and washing, thereby obtaining carbon-coated AlN particles.

(23) (Evaluation Method)

(24) (1) Measurement of Film Thickness of Coating Layer (Average Film Thickness and CV Value)

(25) An average film thickness and a CV value of the coating layer were evaluated using a transmission microscope (FE-TEM).

(26) Specifically, for 20 random particles, sectional images of coating layers were captured using FE-TEM. Then, from the obtained sectional images, a film thickness was randomly measured at 10 different sites of each particle, and an average film thickness and a standard deviation were calculated. From the obtained numerical values, a coefficient of variation of the film thickness was calculated.

(27) There is a big difference in an atomic weight between carbon, with which the particle surface is coated, and the thermal conductive particles of the core. Therefore, from a contrast difference of the TEM image, a film thickness of the coating layer (carbon layer) can be estimated.

(28) (2) Average Particle Size

(29) By using X-ray diffractometry (device: LA-950, manufactured by HORIBA, Ltd.), an average particle size of the obtained particles was measured.

(30) (3) TOF-SIMS Measurement

(31) For the coating layer of the obtained particles, by using a TOF-SIMS 5-type device (manufactured by ION-TOF GmbH), a mass spectrum (at around 77.12) resulting from a benzene ring and a mass spectrum (at around 127.27) resulting from a naphthalene ring were confirmed by Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS). The TOF-SIMS measurement was performed under the following conditions. Furthermore, in order to avoid contamination resulting from contaminants in the air or from the storage case as much as possible, the prepared sample was stored in a clean case for storing a silicon wafer.

(32) Primary ion: 209Bi+1

(33) Ion voltage: 25 kV

(34) Ion current: 1 pA

(35) Mass range: 1 to 300 mass

(36) Analysis area: 500500 m

(37) Prevention of charging: neutralization by electron irradiation

(38) Random raster scan

(39) (4) X-Ray Diffraction

(40) By using an X-ray diffractometer (SmartLab Multipurpose, manufactured by Rigaku Corporation), diffraction data was obtained under the following measurement conditions. X-ray wavelength: CuK 1.54 A, measurement range: 2=10 to 70, scan rate: 4/min, step: 0.02

(41) Regarding the obtained diffraction data, whether or not a peak is detected at a position of 2=26.4 was confirmed.

(42) Furthermore, from the obtained diffraction data, a half-width was calculated and plugged into the Scherrer equation, thereby determining a crystallite size. Specifically, an average crystallite diameter calculated from a half-width at the time when 2=27.86 was adopted. Furthermore, an average crystallite diameter obtained after the particles were fired for 2 hours at 800 C. was also measured.

(43) A series of analyses described above was performed using analysis software (PDXL 2).

(44) (5) Evaluation of Water Resistance

(45) (5-1) MgO-Containing Particles

(46) 1 g of the particles obtained in Examples 1 and 2 and Comparative Example 1 were spread onto the bottom of a glass container and tested by being left to stand for 1 week (168 hours) in a thermohygrostat with a temperature of 85 C. and a relative humidity of 85%. A rate of weight change before and after the test was calculated using the following equation, and then water absorbing properties of the particles were evaluated based on the following criteria.
Rate of weight change (% by weight)=(weight after being left to standinitial weight)100

(47) O (Excellent): a rate of weight change is less than 1.0% by weight

(48) X (Poor): a rate of weight change is 1.0% by weight or greater

(49) (5-2) AlN-Containing Particles

(50) 1.0 g of the particles obtained in Examples 3 and 4 and Comparative Examples 2, 4, and 5 were left to stand for 72 hours in an airtight container at 121 C. and 2 atm, which are conditions for a pressure cooker test (PCT), and an oxygen content in the particles before and after being left to stand was measured. From the measured result, an increase of oxygen was calculated using the following equation and evaluated based on the following criteria. The pressure cooker test (PCT) is a testing method authorized as a method for evaluating moisture resistance of electronic parts.
Increase of oxygen=oxygen amount in particles after PCT treatment/oxygen amount in particles before PCT treatment

(51) O (Excellent): an increase of oxygen is less than 1.2%

(52) X (Poor): an increase of oxygen is 1.2% or greater

(53) (5) Oxidation Resistance

(54) The flakes obtained in Example 5 and Comparative Example 3 were heated for 3 hours at 200 C. in the air.

(55) Through XPS, an increase of oxygen before and after heating was measured, and then oxidation resistance was evaluated based on the following criteria.

(56) O: A color change was not visually recognized before and after heating, or an increase of oxygen before and after heating is less than 10%

(57) X: A color change was visually recognized before and after heating, or an increase of oxygen before and after heating is 10% or greater

(58) (6) Dispersibility

(59) 650 parts by weight of the particles obtained in examples and comparative examples were added to 350 parts by weight of an epoxy resin, and the particles were dispersed in the resin by using Rentaro (1,500 rpm, for 2 minutes). The viscosity of the obtained dispersed material was measured immediately after dispersion. Furthermore, the viscosity of a liquid of an upper layer formed after the dispersed material was left to stand for 3 hours was measured. Then, by using the following equation, a rate of decrease of viscosity was calculated. By using the obtained rate of decrease of viscosity, dispersibility was evaluated based on the following criteria.
Rate of decrease of viscosity (%)=((viscosity immediately after dispersionviscosity after being left to stand for 3 hours)/viscosity immediately after dispersion)100

(60) O: a rate of decrease of viscosity is less than 5%

(61) : a rate of decrease of viscosity is 5% to 10%

(62) X: a rate of decrease of viscosity is greater than 10%

(63) (7) Measurement of Rate of Change of Thermal Conductivity

(64) The particles obtained in examples and comparative examples and imide-modified epoxy resin powder were thoroughly mixed together by a ball mill, thereby preparing a resin composition (a content of the thermal conductive particles with respect to a total content of the resin and the thermal conductive particles: 80% by weight)

(65) Then, by using a heated pressing machine, the obtained resin composition was heated for 25 minutes at 180 C., thereby obtaining a molded material having a diameter of 10 mm and a height of 2 mm. The molded material was then cured by being subjected to a heating treatment for 2 hours at 200 C.

(66) The obtained cured molded material was subjected to a PCT test for 72 hours. Thermal conductivities of the cured molded articles before and after the test were measured by a laser flash method and compared with each other.
Rate of change of thermal conductivity (%)=((thermal conductivity before PCT testthermal conductivity after PCT test)/thermal conductivity before PCT test)100

(67) TABLE-US-00001 TABLE 1 Evaluation Thermal Coating Layer Water Water Oxidation Rate of conductive Aver- CV resistance resistace resistance change material age value Ratio TOF-SIMS (MgO) (AlN) (copper) of Thermal film of film of measurment X-ray Rate of Increase Increase thermal conduc- thick- thick- peak Ben- Naph- dif- weight Deter- of Deter- of Deter- conduc- Ma- tivity ness ness inten- zene thal frac- change min- oxygen min- oxygen min- Disper- tivity terial (W/mk) (nm) (%) sity ring ring tion (%) ation (%) ation (%) ation sibility (%) Example 1 MgO 50 30 4 1.7 Present Present No peak 0.8 5.2 Example 2 MgO 50 30 4 2.5 Present Present No peak 0.5 4.8 Example 3 AlN 170 450 13 3.3 Present Present No peak 10 3.1 Example 4 AlN 170 450 13 4.1 Present Present No peak 6 2.8 Example 5 Cop- 390 110 8 1.5 Present Present No peak 5 8.5 per Compar- MgO 50 Absent Absent No peak 25 X X 90 ative Example 1 Compar- AlN 170 Absent Absent No peak 40 X X 96 ative Example 2 Compar- Cop- 390 Absent Absent No peak X 30 X 80 ative per Example 3 Compar- AlN 170 550 30 1.5 Present Present No peak 20 X 40 ative Example 4 Compar- AlN 170 300 18 0.8 Absent Absent No peak 25 X 30 ative Example 5

(68) According to one or more embodiments of the present invention, it is possible to provide a carbon-coated thermal conductive material which can improve water resistance while maintaining excellent thermal conductive performance.

(69) Furthermore, according to one or more embodiments of the present invention, it is possible to provide a method for manufacturing the carbon-coated thermal conductive material.

(70) Although embodiments of the disclosure have been described using specific terms, devices, and methods, such description is for illustrative purposes only. The words used are words of description rather than limitation. It is to be understood that changes and variations may be made by those of ordinary skill in the art without departing from the spirit or the scope of the present disclosure, which is set forth in the following claims. In addition, it should be understood that aspects of the various embodiments may be interchanged in whole or in part. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained therein.