Thermally conductive substrate

Abstract

A heat conduction substrate comprises an upper metal layer, a lower metal layer and an electric insulation heat conduction layer stacked between the upper metal layer and the lower metal layer. The electrically insulating heat-conducting layer includes a polymer substrate and a heat-conducting filler dispersed in the polymer substrate. The polymer substrate includes an epoxy resin composition composed of an epoxy resin and a chlorine-containing impurity. In addition, the chlorine content of chlorine-containing impurities in the electrically insulating heat-conducting layer is lower than 300 ppm.

Description

Technical Field

[0001] The invention relates to a heat-conducting substrate, in particular to a heat-conducting substrate with high weather resistance. Background Art

[0002] In order to produce electronic devices with specific functions, several electronic components in the electronic devices are assembled onto a carrier board. This carrier board serves as a carrier for holding these electronic components and electrically connecting them to an external power source. However, these electronic components will generate heat energy during operation, and excessive heat accumulation will affect the normal operation of the electronic device. In order to solve the heat dissipation problem, there are generally two traditional ways: first, additional heat dissipation elements are added outside the carrier board, such as heat sinks, fans, thermal paste or other heat dissipation elements outside the carrier board; second, the heat dissipation characteristics of the carrier board are directly improved, that is, a thermally conductive substrate with good thermal conductivity is made.

[0003] In the second method mentioned above, before forming the circuit layer, the most basic structure of the thermally conductive substrate is composed of two metal layers and a thermally conductive layer stacked therebetween. The upper metal layer can be used to form the circuit layer, the lower metal layer can be used as the base material of the thermally conductive substrate and play the role of dissipating heat energy to the external environment below, and the thermally conductive layer is an electrical insulating layer with good thermal conductivity and low thermal expansion coefficient. Traditionally, the thermally conductive layer is composed of resin and thermally conductive powder. The direction of improving the thermally conductive layer is generally committed to the selection of the types of resin and thermally conductive powder, trying to obtain the best combination of (one or more) resins and (one or more) thermally conductive powders. However, this method has the problem of high complexity in formula design. For example, every time the type of a component (resin or thermally conductive powder) is changed, the compatibility of the component with other components and its interface problem with the metal layer must be considered. Even if the compatibility and interface problems are solved, the optimal ratio of the formulation must be considered. If there are more than one type of resin (or thermally conductive powder), the aforementioned complexity will increase significantly. Not to mention that other additives are often mixed in addition to resin and thermally conductive powder. In addition, the types of electronic products are becoming more and more diverse, and the complexity of the environment in which they are used is also increasing. For this reason, the performance of thermally conductive substrates in harsh environments must also be improved. For example, traditionally, thermally conductive substrates often have copper ion migration in high temperature and high humidity bias tests (High Temperature High Humidity Bias Test, HHBT). This phenomenon will reduce the electrical insulation of the thermal conductive layer, and in turn affect the voltage resistance and other physical and chemical properties of the thermally conductive substrate.

[0004] Obviously, the problems of traditional thermal conductive substrates in formulation design and weather resistance need to be improved urgently. Summary of the invention

[0005] The present invention provides a thermally conductive substrate. The thermally conductive substrate is a laminated structure, comprising an upper metal layer, a lower metal layer, and an electrically insulating thermally conductive layer laminated between the upper metal layer and the lower metal layer. The electrically insulating thermally conductive layer comprises a polymer matrix and a thermally conductive filler, and thus has good insulation capability and excellent thermal conductivity. In the present invention, the main component of the polymer matrix is ​​an epoxy resin composition. By precisely controlling the chlorine content in the epoxy resin composition, the thermally conductive substrate has excellent weather resistance.

[0006] According to one embodiment of the present invention, a thermally conductive substrate comprises an upper metal layer, a lower metal layer and an electrically insulating thermally conductive layer stacked between the upper metal layer and the lower metal layer. The electrically insulating thermally conductive layer comprises a polymer matrix and a thermally conductive filler dispersed in the polymer matrix. The polymer matrix comprises an epoxy resin composition, and the epoxy resin composition consists of an epoxy resin and chlorine-containing impurities, wherein the epoxy resin is a main product synthesized using epichlorohydrin and dihydric phenol as raw materials, and the chlorine-containing impurities are byproducts and residual epichlorohydrin produced in the process of synthesizing epichlorohydrin and dihydric phenol. In addition, the chlorine content of the chlorine-containing impurities in the electrically insulating thermally conductive layer is less than 300 ppm.

[0007] According to some embodiments, the chlorine content of the chlorine-containing impurity of the electrically insulating and thermally conductive layer is between 80 ppm and 260 ppm.

[0008] According to some embodiments, the chlorine content of the chlorine-containing impurity of the electrically insulating and thermally conductive layer is between 80 ppm and 90 ppm.

[0009] According to some embodiments, based on 100% weight of the electrically insulating heat-conductive layer, the weight percentage of the epoxy resin composition is 10% to 40%, and the weight percentage of the heat-conductive filler is 60% to 90%.

[0010] According to some embodiments, based on 100% weight of the electrically insulating heat-conductive layer, the weight percentage of the epoxy resin composition is 30% to 40%, and the weight percentage of the heat-conductive filler is 60% to 70%.

[0011] According to some embodiments, the thermally conductive substrate has a service life of more than 200 hours in a harsh environment, wherein the harsh environment includes a high temperature of 85° C., a relative humidity of 85%, and a DC voltage of 1 kV.

[0012] According to some embodiments, the service life is 200 hours to 900 hours.

[0013] According to some embodiments, the service life is 800 hours to 900 hours.

[0014] According to some embodiments, the thermally conductive substrate has a metal adhesion between 1 kg / cm and 2.1 kg / cm.

[0015] According to some embodiments, the thermally conductive filler is selected from the group consisting of zirconium nitride, boron nitride, aluminum nitride, silicon nitride, aluminum oxide, magnesium oxide, zinc oxide, silicon dioxide, titanium dioxide, and any combination thereof.

[0016] According to some embodiments, the electrically insulating and thermally conductive layer does not contain glass fibers.

[0017] According to some embodiments, the epoxy resin composition has a glass transition temperature (Tg) of 130° C. or more.

[0018] According to some embodiments, the thickness of the upper metal layer is 0.01 mm to 3 mm, and the thickness of the lower metal layer is 0.1 mm to 3 mm.

[0019] According to some embodiments, the electrically insulating and heat-conductive layer has a thickness of 0.03 mm to 0.3 mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic cross-sectional structure diagram showing a thermally conductive substrate according to an embodiment of the present invention; and

[0021] Figure 2 A schematic cross-sectional structure diagram of a thermally conductive substrate according to another embodiment of the present invention is shown.

[0022] The reference numerals are described as follows:

[0023] 10 Upper metal layer

[0024] 11Metal plating

[0025] 20Electrically insulating thermal conductive layer

[0026] 30 Lower metal layer

[0027] 100 Thermally Conductive Substrate DETAILED DESCRIPTION

[0028] In order to make the above and other technical contents, features and advantages of the present invention more clearly understood, relevant embodiments are given below and described in detail with reference to the accompanying drawings.

[0029] Please refer to Figure 1, which is a schematic diagram of the cross-sectional structure of the thermally conductive substrate 100 of the present invention. The thermally conductive substrate 100 of the present invention comprises an upper metal layer 10, a lower metal layer 30 and an electrically insulating thermally conductive layer 20. The electrically insulating thermally conductive layer 20 is in contact with the upper metal layer 10 and the lower metal layer 30 and is stacked therebetween to form a three-layer structure. Preferably, the upper metal layer 10 is formed of copper foil or copper plate, and the lower metal layer 30 is formed of aluminum plate or copper plate. Moreover, by providing the electrically insulating thermally conductive layer 20, the upper metal layer 10 and the lower metal layer 30 are electrically isolated from each other. In one embodiment, the thickness of the upper metal layer is 0.01 mm to 3 mm; the thickness of the lower metal layer is 0.1 mm to 3 mm; and the thickness of the electrically insulating thermally conductive layer 20 is 0.03 mm to 0.3 mm. The upper metal layer 10 can be processed into a circuit layer later, and various electronic components can be assembled thereon, while the lower metal layer 30 serves as the base material of the heat-conducting substrate 10 and allows heat to dissipate from the bottom to the external environment. In one embodiment, the upper metal layer 10 and the lower metal layer 30 are both composed of copper foil or copper plate, so both can be processed into circuit layers and made into double-sided circuit boards. In another embodiment, the upper metal layer 10 is copper foil, and the lower metal layer 30 is a metal plate composed of metal other than copper, such as an aluminum plate. In addition, if it is a double-sided copper-clad heat-conducting substrate 100, it can be freely selected to be processed into a single-sided circuit board, a double-sided circuit board or other types of circuit boards later. In addition to the heat-conducting properties of the circuit layer or the metal base plate itself, the electrically insulating heat-conducting layer 20 also has excellent heat-conducting capacity, which can quickly transfer the heat energy generated by the electronic components to the metal layer body for heat dissipation. The electrically insulating heat-conducting layer 20 includes a polymer substrate and a heat-conducting filler. The polymer substrate can provide the electrically insulating heat-conducting layer 20 with good insulation capacity, and improve its heat-conducting capacity by the heat-conducting filler.

[0030] In the present invention, the main component of the polymer substrate is an epoxy resin composition, and when the chlorine content in the electrically insulating heat-conducting layer 20 is reduced to below 300 ppm, it is found that the thermally conductive substrate 100 has excellent improvements in electrical properties. It should be understood that chlorine-containing impurities will inevitably be produced during the synthesis process of existing epoxy resins, so there will be no epoxy resin with a purity of 100% in actual industrial use. Specifically, the synthetic raw materials of epoxy resins are epichlorohydrin and diphenol (such as bisphenol A, bisphenol S, bisphenol F or other bisphenol compounds), and these two raw materials can be used to obtain epoxy resins of a certain purity through ring-opening reactions, dechlorination reactions and other steps. However, the chlorine in epichlorohydrin will generate several chlorine-containing by-products in the aforementioned steps, and even if extraction, precipitation or other various existing means are used, it is impossible to completely remove them. Furthermore, epichlorohydrin may also have a certain amount of residue due to incomplete reaction. The aforementioned chlorine-containing impurities are generally composed of chlorine-containing byproducts and residual epichlorohydrin, and the epoxy resin composition defined herein refers to epoxy resins with a purity of not 100%.

[0031] The present invention has found that when the chlorine content of the chlorine-containing impurity is extremely low, the weather resistance of the thermally conductive substrate 100 is improved, especially in the high temperature and high humidity bias test (HHBT). The reason is that the chlorine content is closely related to the phenomenon of copper ion migration. In the high temperature and high humidity bias test (HHBT), a direct current is passed through the thermally conductive substrate 100, and an electric field is formed between the upper metal layer 10 and the lower metal layer 30. At this time, the upper metal layer 10 and the lower metal layer 30 can be regarded as two electrodes in the redox reaction, for example: the upper metal layer 10 is the anode, and the lower metal layer 30 is the cathode. At the anode end, copper will be oxidized to copper ions, as shown in the following formula: Cu→Cu 2+ +2e - At the cathode end, copper is reduced to copper as follows: Cu 2+ +2e - →Cu. Under the action of the electric field, the copper ions at the anode will gradually migrate through the electrically insulating thermally conductive layer 20 to the cathode, which may eventually cause the insulation failure of the electrically insulating thermally conductive layer 20 and short circuit. It should be noted that the amount of chlorine content in the electrically insulating thermally conductive layer 20 is positively correlated with the corrosion rate of copper, such as the oxidation reaction at the anode end mentioned above. The chlorine ions from the electrically insulating thermally conductive layer 20 can react with the copper at the anode end to produce copper chloride, as shown in the following formula: Then, copper chloride further dissociates and reacts with O2 to be oxidized to Cu 2+ . It can be seen that the higher the chlorine content, the faster the rate of copper ion generation. In the high temperature and high humidity bias test (HHBT), excessively high chlorine content will cause the copper ion migration phenomenon to be more significant, and eventually lead to insulation failure of the electrically insulating thermal conductive layer 20 and burnout of the thermal conductive substrate 100. In addition, in addition to the above-mentioned copper ion migration problem, chlorine-containing impurities may also be converted into hydrochloric acid or hypochlorous acid during the process, thereby corroding the circuit. In other words, chlorine-containing impurities will also affect the performance of the thermal conductive substrate 100 in the subsequent circuit design.

[0032] The aforementioned high temperature and high humidity bias test (HHBT) is mainly used to simulate the accelerated aging test of components in harsh environments (i.e., high temperature of 85°C, relative humidity of 85% and DC voltage of 1kV). The service life calculated in this accelerated aging test is conducive to calculating the actual service life value of the component under normal temperature and normal pressure. In one embodiment, in order to increase the service life to 200 hours to 900 hours, the chlorine content of the chlorine-containing impurity is between 80ppm and 260ppm. In a preferred embodiment, in order to increase the service life to 800 hours to 900 hours, the chlorine content of the chlorine-containing impurity is between 80ppm and 90ppm. In the present invention, based on the weight of the electrically insulating heat-conductive layer 20 as 100%, the weight percentage of the epoxy resin composition is 10% to 40%, and the weight percentage of the thermally conductive filler is 60% to 90%. In some cases, the weight percentage of the epoxy resin composition can be increased as needed while still maintaining an extremely low chlorine content of chlorine-containing impurities, so the service life is still longer than that of traditional thermally conductive substrates. For example, in one embodiment, based on the weight of the electrically insulating thermally conductive layer 20 being 100%, the weight percentage of the epoxy resin composition can be adjusted to 30% to 40%, and the weight percentage of the thermally conductive filler is 60% to 70%, wherein the chlorine content of the aforementioned epoxy resin composition is below 90ppm.

[0033] In addition, the polymer matrix further comprises a modified polymer, which can effectively improve the impact resistance of the epoxy resin composition. The modified polymer is selected from the group consisting of phenoxy resin, polysulfone, polyethersulfone, polystyrene, polyoxyxylene, polyphenylene sulfide, polyamide, polyimide, polyetherimide, block copolymer of polyetherimide and silicone, polyurethane, polyester resin, polycarbonate, polymethyl methacrylate, styrene / propylene, styrene block copolymer and any combination thereof.

[0034] As for the thermally conductive filler, the present invention does not use glass fiber as the thermally conductive filler of the electrically insulating thermally conductive layer 20 of the present invention because the thermal conductivity of glass fiber is too poor and does not require the support provided by glass fiber. That is, the electrically insulating thermally conductive layer 20 of the present invention does not contain glass fiber. The thermally conductive filler of the present invention is selected from the group consisting of zirconium nitride, boron nitride, aluminum nitride, silicon nitride, aluminum oxide, magnesium oxide, zinc oxide, silicon dioxide, titanium dioxide and any combination thereof. In a preferred embodiment, the thermally conductive filler of the present invention is aluminum oxide. In the case where the chlorine content of the chlorine-containing impurity is extremely low, the use of aluminum oxide as the thermally conductive filler can further improve the thermal conductivity of the thermally conductive substrate 100 and make the thermal conductivity coefficient of the thermally conductive substrate 100 between 2.4W / mK and 2.7W / mK.

[0035] In the present invention, the glass transition temperature (Tg) of the epoxy resin composition is above 130°C. The glass transition temperature (Tg) is the temperature point at which the epoxy resin composition switches between the glass state and the rubber state. In one embodiment, the glass transition temperature (Tg) of the epoxy resin composition is between 130°C and 350°C. If the glass transition temperature is too low (such as below 130°C), the epoxy resin composition will easily soften in a low temperature environment, causing the thermal conductive substrate 100 to be structurally unstable, thereby reducing the anti-HHBT capability and applicability. If the glass transition temperature is too high (such as above 350°C), the hardness of the epoxy resin composition after curing will be too high, which is not conducive to its mechanical processing or other molding processes after curing.

[0036] In order to further verify the performance of the thermally conductive substrate 100 of the present invention, various tests were conducted and the results are summarized in Table 1 below.

[0037] Table 1

[0038]

[0039] As shown in Table 1, Group E1 to Group E4 are Examples E1 to E4 of the present invention, and Group C1 is Comparative Example C1. The top view size of the thermally conductive substrate 100 of Examples E1 to E4 of the present invention is 10 mm×10 mm; the upper metal layer 10 is composed of a copper foil with a thickness of 0.035 mm, and the lower metal layer 30 is composed of an aluminum plate with a thickness of 1.5 mm; and the thickness of the electrically insulating thermally conductive layer 20 is 0.1 mm, and is composed of an epoxy resin with a purity of not 100% (i.e., the epoxy resin composition described above) and aluminum oxide (i.e., the thermally conductive filler described above). In addition, based on the weight of the electrically insulating thermally conductive layer 20 being 100%, the epoxy resin composition of Examples E1 to E3 accounts for 15%, and the aluminum oxide accounts for 85%. Based on the weight of the electrically insulating thermally conductive layer 20 being 100%, the epoxy resin composition of Example E4 accounts for 30%, and the aluminum oxide accounts for 70%. The top view dimensions of the thermally conductive substrate of Comparative Example C1, the composition of the upper / lower metal layers, the thickness of each layer, and the ratio of epoxy resin / aluminum oxide are the same as those of Examples E1 to E3 of the present invention, and the only difference is the chlorine content.

[0040] Chlorine content refers to the chlorine content in the electrically insulating thermally conductive layer, which mainly comes from epoxy resins with a purity of not 100% (i.e., the epoxy resin composition mentioned above). As mentioned above, the epoxy resin composition is composed of epoxy resin and chlorine-containing impurities, or in other words, the epoxy resin composition must have a certain degree of chlorine-containing impurities in addition to the epoxy resin, which leads to excessive chlorine content in the electrically insulating thermally conductive layer. The chlorine content can be measured by existing standard methods. The chlorine content in the electrically insulating thermally conductive layer mentioned in this article is quantified by inductively coupled plasma optical emission spectroscopy (ICE-OES).

[0041] Metal adhesion, also known as peel strength, refers to the strength required for a single metal layer to be peeled off from an electrically insulating and thermally conductive layer.

[0042] Thermal conductivity, also known as thermal conductivity, is the ability of a material to conduct heat. The thermal conductivity formula is k = (Q / t)*L / (A*ΔT), where k is thermal conductivity (W / mk), Q is heat (W), t is time, L is the distance of heat conduction (m), A is the cross-sectional area of ​​the object through which heat is conducted (m2), and ΔT is the temperature difference between the hot and cold ends. This test measures the thermal conductivity of a thermally conductive substrate according to the standard method of ASTM D5470.

[0043] HHBT, which refers to the High Temperature High Humidity Bias Test, is mainly used to simulate the life of components under high temperature, high humidity and high pressure environments. The sample to be tested (i.e. the thermal conductive substrate) is placed in an environment with a high temperature of 85°C and a relative humidity of 85%, and a direct current (DC) of 1kV is applied to it. The sample to be tested will burn out after a certain number of hours of voltage application, so as to evaluate its service life under accelerated aging test.

[0044] As can be seen from Table 1, the chlorine content in the epoxy resin composition will significantly affect the number of hours of HHBT, and there are also differences in metal adhesion and thermal conductivity. As far as HHBT is concerned, as the chlorine content in the electrically insulating thermal conductive layer is reduced from 251ppm in Example E1 to 85.4ppm in Example E3, the number of hours of HHBT is correspondingly increased from 224 hours to 899 hours. As mentioned above, the presence of chlorine will promote the phenomenon of copper ion migration, resulting in insulation failure of the electrically insulating thermal conductive layer and burning of the thermal conductive substrate. In contrast, the chlorine content of the epoxy resin composition in Comparative Example C1 is as high as 400ppm, so the number of hours in the HHBT test is quite short, which is 89 hours. In addition, in terms of metal adhesion, excessive chlorine content will affect the curing of the epoxy resin, resulting in the interface between the electrically insulating thermal conductive layer and the metal not being tightly fitted, that is, a poor interface. Therefore, the metal adhesion in Comparative Example C1 (i.e., 1.5 kg / cm) is also lower than the metal adhesion in Examples E1 to E3 (i.e., 1.7 to 2.1 kg / cm). In addition, considering the allowable error range in practical application, the metal adhesion of Examples E1 to E5 of the present invention can generally fall between 1 kg / cm and 2.5 kg / cm. It is worth mentioning that this experiment further found that the thermal conductivity of the thermally conductive substrate can be further improved when the chlorine content is extremely low. In Examples E1 to E3, the thermal conductivity is 2.4 W / mk to 2.7 W / mk, which is higher than the thermal conductivity of Comparative Example C1 (i.e., 2.2 W / mk).

[0045] It should also be noted that in some cases, in order to effectively improve the insulation capability or to meet other requirements, the proportion of the epoxy resin composition in the electrically insulating thermally conductive layer 20 will be increased. Therefore, in Example E4, the proportion of the epoxy resin composition is deliberately increased while maintaining a low proportion of chlorine content to simulate the aforementioned situation. Similarly, in Example E4, the HHBT hours can still be as high as 800 hours, and the metal adhesion and thermal conductivity are also improved.

[0046] Continue to refer to Figure 2 , which is another embodiment of the thermally conductive substrate 100 of the present invention. Figure 2 In the embodiment, the upper metal layer 10, the lower metal layer 30 and the electrically insulating and thermally conductive layer 20 have been discussed above and will not be described again here. Figure 2 and Figure 1 The difference is, Figure 2A metal plating layer 11 is added to the thermally conductive substrate 100 in the embodiment. In order to further improve the problem of copper ion migration, the bottom surface of the upper metal layer 10 may be plated with a metal plating layer 11 with a thickness between 1 μm and 10 μm. That is, the thermally conductive substrate 100 may further include a metal plating layer 11, which is disposed between the upper metal layer 10 and the electrically insulating thermally conductive layer 20 and contacts the upper metal layer 10. The material of the metal plating layer 11 is selected from the group consisting of nickel, tin, zinc, chromium, bismuth, cobalt and any combination thereof. In a preferred embodiment, the metal plating layer 11 is composed of nickel. The metal plating layer 11 not only provides a physical barrier function, but also has better chemical inertness. In this way, it is difficult for copper ions to penetrate the metal plating layer 11 from the upper metal layer 10 to the electrically insulating thermally conductive layer 20, which can further improve the service life of the thermally conductive substrate 100. It should be noted that, generally speaking, although adding a metal plating layer 11 can improve the problem of copper ion migration, it will increase the overall thermal resistance of the thermally conductive substrate 100, that is, the thermal conductivity coefficient decreases. However, the present invention has noticed that by reducing the chlorine content in the epoxy resin composition, the defect of the metal plating layer 11 in thermal resistance can be compensated, and the withstand time of the HHBT can be significantly improved.

[0047] The technical content and technical features of the present invention have been disclosed as above, but a person skilled in the art with ordinary knowledge may still make various substitutions and modifications based on the teachings and disclosures of the present invention without departing from the spirit of the present invention. Therefore, the protection scope of the present invention should not be limited to those disclosed in the embodiments, but should include various substitutions and modifications without departing from the present invention, and be covered by the following claims.

Claims

1. A thermally conductive substrate, comprising: One metal layer; a lower metal layer; and An electrically insulating heat-conductive layer is stacked between the upper metal layer and the lower metal layer and comprises a polymer substrate and a heat-conductive filler dispersed in the polymer substrate, wherein: The polymer matrix comprises an epoxy resin composition, and the epoxy resin composition is composed of an epoxy resin and a chlorine-containing impurity, wherein the epoxy resin is a main product synthesized using epichlorohydrin and dihydric phenol as raw materials, and the chlorine-containing impurity is a byproduct and residual epichlorohydrin generated in the process of synthesizing the epoxy resin from the epichlorohydrin and the dihydric phenol; and The chlorine content of the chlorine-containing impurity in the electrically insulating thermally conductive layer is lower than 300 ppm. 2 . The thermally conductive substrate according to claim 1 , wherein the chlorine content of the chlorine-containing impurity is between 80 ppm and 260 ppm. 3 . The thermally conductive substrate according to claim 2 , wherein the chlorine content of the chlorine-containing impurity is between 80 ppm and 90 ppm.

4. The thermally conductive substrate according to claim 1, wherein based on the weight of the electrically insulating thermally conductive layer being 100%, the weight percentage of the epoxy resin composition is 10% to 40%, and the weight percentage of the thermally conductive filler is 60% to 90%.

5. The thermally conductive substrate according to claim 4, wherein based on the weight of the electrically insulating thermally conductive layer being 100%, the weight percentage of the epoxy resin composition is 30% to 40%, and the weight percentage of the thermally conductive filler is 60% to 70%. 6 . The thermally conductive substrate according to claim 1 , wherein the thermally conductive substrate has a service life of more than 200 hours in a harsh environment, wherein the harsh environment comprises a high temperature of 85° C., a relative humidity of 85%, and a DC voltage of 1 kV. The thermally conductive substrate according to claim 6 , wherein the service life is 200 hours to 900 hours. The thermally conductive substrate according to claim 7 , wherein the service life is 800 hours to 900 hours. 9 . The thermally conductive substrate according to claim 1 , wherein the thermally conductive substrate has a metal adhesion between 1 kg / cm and 2.1 kg / cm. 10 . The thermally conductive substrate according to claim 1 , wherein the thermally conductive filler is selected from the group consisting of zirconium nitride, boron nitride, aluminum nitride, silicon nitride, aluminum oxide, magnesium oxide, zinc oxide, silicon dioxide, titanium dioxide, and any combination thereof. The thermally conductive substrate according to claim 1 , wherein the electrically insulating thermally conductive layer does not contain glass fiber. 12 . The thermally conductive substrate according to claim 1 , wherein the epoxy resin composition has a glass transition temperature of 130° C. or higher. 13 . The thermally conductive substrate according to claim 1 , wherein the thickness of the upper metal layer is 0.01 mm to 3 mm, and the thickness of the lower metal layer is 0.1 mm to 3 mm. The thermally conductive substrate according to claim 1 , wherein the electrically insulating thermally conductive layer has a thickness of 0.03 mm to 0.3 mm.

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