A method for preparing and applying a vertically oriented boron nitride / epoxy resin thermally conductive composite material under a magnetic field.

Abstract

A method for preparing and applying a vertically oriented boron nitride / epoxy resin thermally conductive composite material under a magnetic field is disclosed, belonging to the field of composite materials. The purpose of this invention is to solve the problems of high cost, complex processes, and narrow application range of existing filler orientation methods. The method includes: 1. Preparing a mixed solution of boron nitride and iron(III) oxide; 2. Preparing a solution of boron nitride nanosheets with iron(III) oxide adhering to the surface; 3. Preparing BNNS@Fe3O4; 4. Preparing a vertically oriented boron nitride / epoxy resin thermally conductive composite material under a magnetic field. The application of this vertically oriented boron nitride / epoxy resin thermally conductive composite material under a magnetic field in electronic packaging is also discussed. This invention effectively improves the thermal conductivity of epoxy resin, and the process is simple, reliable, efficient, and low-cost, exhibiting a high thermal conductivity, making it suitable for electronic packaging.

Description

Technical Field

[0001] This invention belongs to the field of composite materials, specifically relating to a method for preparing and applying a vertically oriented boron nitride / epoxy resin thermally conductive composite material under a magnetic field. Background Technology

[0002] With the rapid development of electronic components towards high-density integration and miniaturization, the power density of electronic devices continues to rise. The accumulated heat generated during operation has become a major challenge affecting the reliability and efficiency of these components. In high-power applications, such as fast charging of electric vehicles and mobile phones, thermal runaway of batteries or chips has become a major cause of safety accidents. Statistics show that for every 2°C increase in operating temperature, the long-term stability of electronic devices decreases by 10%, and their lifespan decreases by half. Therefore, in order to quickly dissipate the heat accumulated in components, there is an urgent need for packaging materials with highly efficient heat dissipation capabilities.

[0003] Epoxy resins, with their advantages of low cost, good processability, and high insulation, are widely used in the field of electronic packaging. However, most epoxy resins have low intrinsic thermal conductivity (≤0.5 W / (m·K)), which cannot meet the heat dissipation requirements of advanced thermal management systems. Numerous studies have shown that boron nitride nanosheets (BNNS) have unique advantages in enhancing the thermal conductivity of epoxy resins. BNNS, with its two-dimensional sheet-like structure and high aspect ratio, possesses extremely high in-plane thermal conductivity (theoretically 1700–2000 W / (m·K)); however, its transplanar thermal conductivity is only 30 W / (m·K). To leverage the high in-plane thermal conductivity of BNNS, precise control of the microstructure arrangement of inorganic fillers is crucial. Several methods have been employed to achieve the directional alignment of BNNS, including blade coating, ice template method, and hot pressing, but these methods are either costly and have complex processing requirements, or their application areas are too narrow and lack universality. For example, Chinese patent 202310234646.5 describes a method of obtaining a multi-layer solid film through multiple coating processes, and then cutting a cross-section to obtain vertically arranged boron nitride pads. However, each coating requires a curing time, making this method complex, inefficient, and only applicable to thermoplastic materials. Therefore, there is an urgent need to develop a simple, efficient, and widely applicable method for directional packing to meet the heat dissipation requirements of advanced electronic components. Summary of the Invention

[0004] The purpose of this invention is to solve the problems of high cost, complex process and narrow application range of existing filler orientation methods, and to provide a method for preparing and applying a vertically oriented boron nitride / epoxy resin thermally conductive composite material under a magnetic field.

[0005] This invention utilizes the cyclic scouring of a high-pressure homogenizer to induce the exfoliation of boron nitride through various fluid dynamics mechanisms such as shearing, cavitation, and impact, and to achieve physical bonding with iron oxide, thus efficiently preparing magnetically functionalized boron nitride nanosheet fillers. Then, through the action of a magnetic field, the vertical orientation of the boron nitride nanosheets is achieved. The resulting composite material has a thermal conductivity of 1.81 W / (m·K), achieving the goal of enhancing the thermal conductivity of epoxy resin, and can be used for electronic packaging applications.

[0006] A method for preparing a vertically oriented boron nitride / epoxy resin thermally conductive composite material under a magnetic field is specifically carried out according to the following steps:

[0007] I. Preparation of a mixed solution of boron nitride and iron(III) oxide:

[0008] Boron nitride and iron oxide were added to isopropanol and dispersed evenly under ultrasonic conditions to obtain a mixed solution of boron nitride and iron oxide.

[0009] 2. A solution of boron nitride and iron oxide was treated with a high-pressure homogenizer for a period of time to obtain a boron nitride nanosheet solution with iron oxide adhering to its surface.

[0010] 3. Vacuum filtration was performed on the solution of boron nitride nanosheets with iron oxide on the surface. The obtained solid material was washed, and then isopropanol was added. After centrifugation for a period of time, the supernatant was collected and the collected supernatant was vacuum dried to obtain BNNS@Fe3O4.

[0011] 4. BNNS@Fe3O4, epoxy resin, curing agent and accelerator are vacuum stirred for a period of time and mixed evenly to obtain a mixed colloid; the mixed colloid is transferred to a polytetrafluoroethylene disc mold, and the mold containing the mixed colloid is placed between two electromagnets and heated and cured under a magnetic field to obtain a vertically oriented boron nitride / epoxy resin thermally conductive composite material under a magnetic field.

[0012] Application of a vertically oriented boron nitride / epoxy resin thermally conductive composite material under a magnetic field in electronic packaging.

[0013] The significant advantages of this invention compared to existing technologies are:

[0014] (1) This invention provides a method for preparing a vertically oriented boron nitride / epoxy resin thermally conductive composite material under a magnetic field. This method can achieve vertical orientation of fillers in epoxy resin, which can make full use of the high in-plane thermal conductivity of boron nitride. This method can construct vertical chain thermal conductive pathways, which improves the out-of-plane thermal conductivity of the polymer matrix. The thermal conductivity of the vertically oriented boron nitride / epoxy resin thermally conductive composite material (BNNS@Fe3O4 / EP composite material) prepared by this invention reaches 1.81 W / (m·K), which is 9.05 times that of pure epoxy resin (0.2 W / (m·K)). At the same time, the magnetically assisted high orientation method can be adapted to the current industrial epoxy resin preparation process, can be molded simultaneously with the substrate, and can meet various shape and size requirements, which has the universality of industrial preparation.

[0015] (2) The present invention uses a high-pressure homogenizer to perform functional treatment on boron nitride. The liquid phase scouring of the high-pressure homogenizer can simultaneously achieve the stripping and magnetic functionalization of boron nitride. Compared with liquid phase ultrasonic stripping and hydrothermal magnetization, this method has high stripping efficiency, simple and stable process and can be prepared on a large scale in industrial applications.

[0016] (3) This invention avoids the use of harsh chemicals and high energy consumption procedures. The auxiliary solvent isopropanol in the magnetization stripping process is green and safe, does not involve dangerous goods, and has the characteristics of sustainable development. The isopropanol used as the auxiliary solvent for stripping magnetization can be reused multiple times and is recyclable.

[0017] (4) The present invention uses a boron nitride / epoxy resin thermally conductive composite material with a high thermal conductivity that is vertically oriented under a magnetic field, which can be applied to electronic packaging. Attached Figure Description

[0018] Figure 1 Image of BNNS@Fe3O4 powder prepared in Example 1 dispersed in isopropanol and attracted by a permanent magnet;

[0019] Figure 2 SEM image of BNNS@Fe3O4 prepared in Example 1;

[0020] Figure 3 SEM image of the cross section of the vertically oriented boron nitride / epoxy thermally conductive composite material prepared in Example 1 under a magnetic field;

[0021] Figure 4 Comparison of XRD patterns of the vertically oriented boron nitride / epoxy thermally conductive composite material prepared under a magnetic field in Example 1 and the boron nitride / epoxy thermally conductive composite material prepared without a magnetic field;

[0022] Figure 5The graph shows a comparison of the thermal conductivity of the vertically oriented boron nitride / epoxy resin thermally conductive composite materials prepared under a magnetic field in Examples 1-4 and the boron nitride / epoxy resin thermally conductive composite materials prepared without using a magnetic field. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0024] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0025] Specific Implementation Method 1: This implementation method describes a method for preparing a vertically oriented boron nitride / epoxy resin thermally conductive composite material under a magnetic field, specifically completed according to the following steps:

[0026] I. Preparation of a mixed solution of boron nitride and iron(III) oxide:

[0027] Boron nitride and iron oxide were added to isopropanol and dispersed evenly under ultrasonic conditions to obtain a mixed solution of boron nitride and iron oxide.

[0028] 2. A solution of boron nitride and iron oxide was treated with a high-pressure homogenizer for a period of time to obtain a boron nitride nanosheet solution with iron oxide adhering to its surface.

[0029] 3. Vacuum filtration was performed on the solution of boron nitride nanosheets with iron oxide on the surface. The obtained solid material was washed, and then isopropanol was added. After centrifugation for a period of time, the supernatant was collected and the collected supernatant was vacuum dried to obtain BNNS@Fe3O4.

[0030] 4. BNNS@Fe3O4, epoxy resin, curing agent and accelerator are vacuum stirred for a period of time and mixed evenly to obtain a mixed colloid; the mixed colloid is transferred to a polytetrafluoroethylene disc mold, and the mold containing the mixed colloid is placed between two electromagnets and heated and cured under a magnetic field to obtain a vertically oriented boron nitride / epoxy resin thermally conductive composite material under a magnetic field.

[0031] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the particle size of boron nitride mentioned in step one is 10μm to 30μm, and the particle size of iron(III) oxide is 20nm to 100nm. The other steps are the same as in Specific Implementation Method One.

[0032] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that: the mass ratio of boron nitride to iron(III) oxide in step one is 5:(0.25-1); the concentration of boron nitride in the mixed solution of boron nitride and iron(III) oxide in step one is 10 mg / mL. Other steps are the same as in Specific Implementation Method One or Two.

[0033] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the pressure of the high-pressure homogenizer mentioned in step two is 50MPa to 180MPa, the number of cycles is 10 to 30, and the working rate is 5L / h to 10L / h. The other steps are the same as in Specific Implementation Methods One to Three.

[0034] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that: in step three, the obtained solid substance is washed 3 to 5 times with deionized water; the mass ratio of the solid substance to the volume of isopropanol in step three is (10g to 25g):(1L to 2.5L). Other steps are the same as in Specific Implementation Methods One to Four.

[0035] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that: the centrifugation speed in step three is 1500 r / min, and the centrifugation time is 10 min; the vacuum drying temperature in step three is 60℃~80℃, and the vacuum drying time is 16h~24h. Other steps are the same as in Specific Implementation Methods One to Five.

[0036] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that: the epoxy resin mentioned in step four is E51; the curing agent mentioned in step four is methylhexahydrophthalic anhydride; and the accelerator mentioned in step four is DMP-30. The other steps are the same as in Specific Implementation Methods One to Six.

[0037] Specific Implementation Method Eight: The difference between this implementation method and Specific Implementation Methods One to Seven is that the mass ratio of epoxy resin, curing agent and accelerator in step four is 100:80:2; the mass ratio of BNNS@Fe3O4 to the total mass of epoxy resin, curing agent and accelerator in step four is (5g~30g):(70g~95g).

[0038] The other steps are the same as those in Specific Implementation Methods 1 to 7.

[0039] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in the following ways: the vacuum stirring time in step four is 1.5h to 2.5h; the temperature-raising magnetic curing procedure in step four is as follows: raise the temperature from room temperature to 80℃, hold at 80℃ for 2h, then raise the temperature to 120℃, hold at 120℃ for 2h, finally raise the temperature to 160℃, hold at 160℃ for 2h, and then cool down to room temperature; the heating rate is 5℃ / min to 10℃ / min; the cooling rate is 10℃ / min to 15℃ / min; the magnetic field strength in step four is 0.5T to 1T. Other steps are the same as in Specific Implementation Methods One to Eight.

[0040] Specific Implementation Method 10: This implementation method describes the application of a vertically oriented boron nitride / epoxy resin thermally conductive composite material under a magnetic field in electronic packaging.

[0041] The beneficial effects of the present invention are verified using the following embodiments:

[0042] Example 1: A method for preparing a vertically oriented boron nitride / epoxy resin thermally conductive composite material under a magnetic field, specifically completed according to the following steps:

[0043] I. Preparation of a mixed solution of boron nitride and iron(III) oxide:

[0044] Add 10g of boron nitride and 1g of iron oxide to 1L of isopropanol and sonicate for 20min to obtain a mixed solution of boron nitride and iron oxide.

[0045] The boron nitride particles mentioned in step one have a particle size of 25 μm, and the iron oxide particles have a particle size of 20 nm.

[0046] 2. The mixed solution of boron nitride and iron oxide was circulated and washed 20 times using a high-pressure homogenizer. Through various fluid dynamics such as shearing, turbulence and collision caused by liquid phase washing, boron nitride was induced to peel off and physically bond with iron oxide, resulting in a boron nitride nanosheet solution with iron oxide attached to the surface.

[0047] The high-pressure homogenizer mentioned in step two has a homogenization pressure of 100 MPa and a working rate of 10 L / h.

[0048] 3. The solution of boron nitride nanosheets with iron oxide on the surface was vacuum filtered, and the obtained solid material was washed 5 times with deionized water. Then isopropanol was added, and the supernatant was collected after centrifugation for a period of time. The collected supernatant was vacuum dried to obtain BNNS@Fe3O4.

[0049] The mass ratio of the solid substance to the volume of isopropanol in step three is 10 g: 1 L;

[0050] The centrifugation speed in step three is 1500 r / min, and the centrifugation time is 10 min;

[0051] The vacuum drying temperature in step three is 60°C, and the vacuum drying time is 24 hours.

[0052] 4. Mix BNNS@Fe3O4, epoxy resin, curing agent and accelerator in a vacuum mixing box for 2 hours until homogeneous to obtain a mixed colloid; transfer the mixed colloid into a polytetrafluoroethylene disc mold, place the mold containing the mixed colloid between two electromagnets, and heat and cure under a magnetic field to obtain a vertically oriented boron nitride / epoxy resin thermally conductive composite material under a magnetic field (filler addition amount is 5%).

[0053] The epoxy resin mentioned in step four is E51;

[0054] The curing agent mentioned in step four is methyl hexahydrophthalic anhydride (MHHPA);

[0055] The accelerator mentioned in step four is DMP-30;

[0056] The mass ratio of epoxy resin, curing agent, and accelerator mentioned in step four is 100:80:2;

[0057] The total mass ratio of BNNS@Fe3O4 to epoxy resin, curing agent and accelerator mentioned in step four is 5g:95g;

[0058] The heating and curing procedure described in step four is as follows: heat from room temperature to 80°C, hold at 80°C for 2 hours, then heat to 120°C, hold at 120°C for 2 hours, finally heat to 160°C, hold at 160°C for 2 hours, and then cool down to room temperature; the heating rate is 5°C / min; the cooling rate is 10°C / min.

[0059] The strength of the magnetic field mentioned in step four is 0.75T.

[0060] Example 2: The difference between this example and Example 1 is that the total mass ratio of BNNS@Fe3O4 to epoxy resin, curing agent, and accelerator in step four is 10g:90g (filler addition is 10%). All other steps and parameters are the same as in Example 1.

[0061] Example 3: The difference between this example and Example 1 is that the total mass ratio of BNNS@Fe3O4 to epoxy resin, curing agent, and accelerator in step four is 20g:80g (filler addition is 20%). All other steps and parameters are the same as in Example 1.

[0062] Example 4: The difference between this example and Example 1 is that the total mass ratio of BNNS@Fe3O4 to epoxy resin, curing agent, and accelerator in step four is 30g:70g (filler addition is 30%). All other steps and parameters are the same as in Example 1.

[0063] Comparative Example 1: The preparation method of boron nitride / epoxy resin thermally conductive composite material is carried out according to the following steps:

[0064] Boron nitride (BN), epoxy resin, curing agent and accelerator were stirred in a vacuum mixing box for 2 hours to obtain a mixed colloid. The mixed colloid was transferred into a polytetrafluoroethylene disc mold and the mold containing the mixed colloid was heated and cured to obtain a boron nitride / epoxy resin thermally conductive composite material (BN / EP).

[0065] The epoxy resin is E51;

[0066] The curing agent is methyl hexahydrophthalic anhydride (MHHPA);

[0067] The accelerator mentioned is DMP-30;

[0068] The mass ratio of the epoxy resin, curing agent, and accelerator is 100:80:2;

[0069] The total mass ratio of BN to epoxy resin, curing agent and accelerator is 0:100, 5:95, 10:90, 20:80 or 30:70;

[0070] The heating and curing procedure is as follows: heat from room temperature to 80°C, hold at 80°C for 2 hours, then heat to 120°C, hold at 120°C for 2 hours, finally heat to 160°C, hold at 160°C for 2 hours, and then cool down to room temperature; the heating rate is 5°C / min; the cooling rate is 10°C / min.

[0071] Figure 1 Image of BNNS@Fe3O4 powder prepared in Example 1 dispersed in isopropanol and attracted by a permanent magnet;

[0072] Figure 1 The BNNS@Fe3O4 powder dispersed in isopropanol was attracted by a permanent magnet, and no separation of the two fillers was observed, indicating that the magnetic response characteristics of boron nitride changed from non-magnetic to magnetic.

[0073] Figure 2 SEM image of BNNS@Fe3O4 prepared in Example 1;

[0074] from Figure 2It can be seen that Fe3O4 spherical particles are distributed on BNNS, indicating that the liquid phase scouring of the high-pressure homogenizer can successfully bond Fe3O4 nanoparticles to the BNNS surface.

[0075] Figure 3 SEM image of the cross section of the vertically oriented boron nitride / epoxy thermally conductive composite material prepared in Example 1 under a magnetic field;

[0076] from Figure 3 It can be seen that most of the BNNS@Fe3O4 particles inside the composite material are arranged vertically in the out-of-plane direction.

[0077] Figure 4 Comparison of XRD patterns of the vertically oriented boron nitride / epoxy thermally conductive composite material prepared under a magnetic field in Example 1 and the boron nitride / epoxy thermally conductive composite material prepared without a magnetic field;

[0078] from Figure 4 It can be seen that the (110) diffraction peak, which indicates the vertical orientation of boron nitride, is significantly higher after magnetization compared to the unmagnetized boron nitride composite material, indicating that the vertical orientation of the filler was successful.

[0079] Thermal conductivity testing: The thermal conductivity of the composite materials obtained in Examples 1-4 was tested using an LFA447 laser thermal conductivity meter manufactured by Netzsch GmbH, Germany. The thermal conductivity measured is in the out-of-plane direction perpendicular to the plane of the composite material. Before testing, the samples were prepared as cylinders with a diameter of 12.7 mm and a thickness of approximately 1 mm. The upper and lower surfaces of the composite material were ground until parallel and smooth, and a thin layer of graphite was sprayed onto both surfaces. The results are as follows: Figure 5 As shown, the out-of-plane thermal conductivity of the epoxy composite material increases significantly with the increase of BNNS@Fe3O4 filler content. The thermal conductivity of the BNNSs / EP composite material in Example 4 reached 1.81 W / (m·K), which is 9.05 times that of pure epoxy resin (0.2 W / (m·K)).

[0080] The above description is merely a preferred embodiment of the present invention. These specific embodiments are different implementations based on the overall concept of the present invention, and the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a vertically oriented boron nitride / epoxy resin thermally conductive composite material under a magnetic field, characterized in that... The preparation method is specifically carried out according to the following steps: I. Preparation of a mixed solution of boron nitride and iron(III) oxide: Boron nitride and iron oxide were added to isopropanol and dispersed evenly under ultrasonic conditions to obtain a mixed solution of boron nitride and iron oxide.

2. A solution of boron nitride and iron oxide was treated with a high-pressure homogenizer for a period of time to obtain a boron nitride nanosheet solution with iron oxide adhering to its surface.

3. Vacuum filtration was performed on the solution of boron nitride nanosheets with iron oxide on the surface. The obtained solid material was washed, and then isopropanol was added. After centrifugation for a period of time, the supernatant was collected and the collected supernatant was vacuum dried to obtain BNNS@Fe3O4.

4. BNNS@Fe3O4, epoxy resin, curing agent and accelerator are vacuum stirred for a period of time and mixed evenly to obtain a mixed colloid; the mixed colloid is transferred to a polytetrafluoroethylene disc mold, and the mold containing the mixed colloid is placed between two electromagnets and heated and cured under a magnetic field to obtain a vertically oriented boron nitride / epoxy resin thermally conductive composite material under a magnetic field.

2. The method for preparing a vertically oriented boron nitride / epoxy resin thermally conductive composite material under a magnetic field according to claim 1, characterized in that... The boron nitride particles mentioned in step one have a particle size of 10 μm to 30 μm, and the iron oxide particles have a particle size of 20 nm to 100 nm.

3. The method for preparing a vertically oriented boron nitride / epoxy resin thermally conductive composite material under a magnetic field according to claim 1, characterized in that... The mass ratio of boron nitride to iron oxide in step one is 5:(0.25~1); the concentration of boron nitride in the mixed solution of boron nitride and iron oxide in step one is 10 mg / mL.

4. The method for preparing a vertically oriented boron nitride / epoxy resin thermally conductive composite material under a magnetic field according to claim 1, characterized in that... The pressure of the high-pressure homogenizer mentioned in step two is 50MPa to 180MPa, the number of cycles is 10 to 30, and the working rate is 5L / h to 10L / h.

5. The method for preparing a vertically oriented boron nitride / epoxy resin thermally conductive composite material under a magnetic field according to claim 1, characterized in that... In step three, the obtained solid substance is washed with deionized water 3 to 5 times; the mass ratio of the solid substance to the volume of isopropanol in step three is (10g to 25g): (1L to 2.5L).

6. The method for preparing a vertically oriented boron nitride / epoxy resin thermally conductive composite material under a magnetic field according to claim 1, characterized in that... The centrifugation speed in step three is 1500 r / min, and the centrifugation time is 10 min; the vacuum drying temperature in step three is 60℃~80℃, and the vacuum drying time is 16h~24h.

7. The method for preparing a vertically oriented boron nitride / epoxy resin thermally conductive composite material under a magnetic field according to claim 1, characterized in that... The epoxy resin mentioned in step four is E51; the curing agent mentioned in step four is methylhexahydrophthalic anhydride; and the accelerator mentioned in step four is DMP-30.

8. The method for preparing a vertically oriented boron nitride / epoxy resin thermally conductive composite material under a magnetic field according to claim 1, characterized in that... The mass ratio of epoxy resin, curing agent and accelerator mentioned in step four is 100:80:2; the total mass ratio of BNNS@Fe3O4 to epoxy resin, curing agent and accelerator mentioned in step four is (5g~30g):(70g~95g).

9. The method for preparing a vertically oriented boron nitride / epoxy resin thermally conductive composite material under a magnetic field according to claim 1, characterized in that... The vacuum stirring time in step four is 1.5h to 2.5h; the temperature-raising magnetic curing procedure in step four is as follows: raise the temperature from room temperature to 80℃, hold at 80℃ for 2h, raise the temperature to 120℃, hold at 120℃ for 2h, finally raise the temperature to 160℃, hold at 160℃ for 2h, and then cool down to room temperature; the heating rate is 5℃ / min to 10℃ / min; the cooling rate is 10℃ / min to 15℃ / min; the magnetic field strength in step four is 0.5T to 1T.

10. The application of a vertically oriented boron nitride / epoxy resin thermally conductive composite material prepared by the preparation method according to claim 1, characterized in that... Application of a vertically oriented boron nitride / epoxy resin thermally conductive composite material under a magnetic field in electronic packaging.

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