Aluminum nitride sintered body, method for producing aluminum nitride sintered body, and ceramic substrate

Abstract

The present invention relates to an aluminum nitride sintered body, a method for producing same, and a ceramic substrate comprising same, the aluminum nitride sintered body being obtained by continuously sintering a mixture comprising aluminum nitride powder, an oxide containing zirconium, and a sintering aid at different temperatures in two stages, wherein the oxide containing zirconium is included in an amount of 0.4-8.0 parts by weight with respect to 100 parts by weight of the aluminum nitride powder, the aluminum nitride sintered body does not contain an alkaline earth metal, the aluminum nitride sintered body contains aluminum nitride crystal grains, and the average grain size of the aluminum nitride crystal grains is 2.6-4.3 μm.

Description

Aluminum nitride sintered body, method for manufacturing aluminum nitride sintered body, and ceramic substrate

[0001] The present invention relates to an aluminum nitride sintered body having a certain level of thermal conductivity and improved bending strength and fracture toughness, a method for producing the aluminum nitride sintered body, and a ceramic substrate having high thermal conductivity and excellent thermal fatigue durability, including the aluminum nitride sintered body.

[0002] With the recent advancement of electronic devices, demand is increasing for power modules that perform high-efficiency power conversion and control. Ceramic substrates, which combine electrical insulation and high thermal conductivity, function as heat transfer media by rapidly transferring, dissipating, and cooling the heat generated by high-power power modules. Ceramic heat sink substrates exhibit minimal deformation at high temperatures and excellent insulation against high voltages, making them widely used as circuit boards for high-power inverter and converter power modules.

[0003] Ceramic substrates are categorized as DCB (Direct Copper Bond) and AMB (Active Metal Brazing) substrates, depending on the method of bonding copper to the ceramic. Commonly used ceramic substrate materials include alumina (Al2O3), aluminum nitride (AlN), silicon carbide (SiC), and silicon nitride (Si3N4). While inexpensive alumina (Al2O3) was widely used, its relatively low mechanical strength and thermal conductivity have led to the trend toward the use of aluminum nitride (AlN) and silicon nitride (Si3N4), which have relatively superior physical properties. The ceramic material and bonding method are determined by the output and application of the inverter or converter power module.

[0004] With the recent increase in demand for vehicles equipped with electric motors, such as electric and hybrid vehicles, demand for inverter and converter power module packages is also increasing. The development of new power modules tailored to automotive performance requirements is actively underway. One of the key requirements for automotive power modules is long-term reliability.

[0005] Power modules generate high heat from semiconductor elements during operation. This heat generation problem causes switching losses, and since silicon semiconductor elements can lose their semiconductor properties at temperatures above 150°C, a technology that can quickly dissipate the heat generated in the power module is required.

[0006] AlN substrates have the highest thermal conductivity of 170 W / mk compared to other substrate materials, enabling them to rapidly dissipate heat generated in power modules. However, their low mechanical strength limits their application. This low mechanical strength can lead to delamination, where the ceramic and copper separate during thermal fatigue tests involving repeated high- and low-temperature cycling of ceramic heat-dissipating substrates.

[0007] To overcome these limitations, various studies are being conducted to simultaneously improve the durability, including strength and toughness, of aluminum nitride sintered bodies.

[0008] The problem to be solved by the present invention is to provide a ceramic heat dissipation substrate that has excellent strength and can maintain a target level of thermal conductivity without deterioration of insulating properties by resolving the problem of reduced bonding strength between ceramic and copper after copper bonding using the DCB method.

[0009] Another problem to be solved by the present invention is to provide a method for manufacturing an aluminum nitride sintered body capable of providing the above aluminum nitride sintered body.

[0010] Another problem to be solved by the present invention is to provide a ceramic substrate including the above aluminum nitride sintered body.

[0011] The present invention provides an aluminum nitride (AlN) sintered body to solve the above problem.

[0012] [1] The present invention provides an aluminum nitride sintered body obtained by continuously sintering a mixture including aluminum nitride powder, an oxide including zirconium, and a sintering aid at two different temperatures, wherein the oxide including zirconium is included in an amount of 0.4 to 8.0 parts by weight based on 100 parts by weight of the aluminum nitride powder, the aluminum nitride sintered body does not include an alkaline earth metal, the aluminum nitride sintered body includes aluminum nitride crystal grains, and the average particle size of the aluminum nitride crystal grains is 2.6 to 4.3 ㎛.

[0013] [2] In the present invention, in the above [1], the aluminum nitride sintered body has a flexural strength of 600 MPa or more and a fracture toughness of 3.60 MPa·m 1 / 2 The present invention provides an aluminum nitride sintered body having a thermal conductivity of 100 W / mK or more and an insulating strength of 20 kV / mm or more.

[0014] In addition, the present invention provides a method for manufacturing an aluminum nitride (AlN) sintered body to solve the other problems mentioned above.

[0015] [3] The present invention provides a method for manufacturing an aluminum nitride sintered body, comprising the steps of (s1) mixing aluminum nitride powder, an oxide containing zirconium, and a sintering aid; (s2) forming a slurry by adding a solvent to the mixture; (s3) removing air bubbles from the slurry; (s4) forming a molding from the slurry and placing it into a sintering reactor; (s5) first sintering the molding by raising the temperature of the sintering reactor to 1,750°C to 1,850°C; and (s6) second sintering the molding continuously by lowering the temperature of the sintering reactor to 1,600°C to 1,700°C; wherein the zirconium-containing oxide is contained in an amount of 0.4 to 8.0 parts by weight based on 100 parts by weight of the aluminum nitride raw material powder.

[0016] [4] The present invention provides a method for manufacturing an aluminum nitride sintered body, which further includes, after the secondary sintering step in the above [3], a step (s7) of lowering the temperature of the reactor from the temperature of step (s6) to the ambient temperature at a rate of 50°C to 70°C per hour.

[0017] [5] The present invention provides a method for manufacturing an aluminum nitride sintered body, wherein, in the above [3] or [4], the first sintering is performed for 1.5 to 2 hours, and the second sintering is performed for 4 to 6 hours.

[0018] In addition, the present invention provides a ceramic heat dissipation substrate to solve the above-mentioned further problem.

[0019] [6] The present invention provides a ceramic substrate comprising (i) a substrate including the aluminum nitride sintered body of [1] or [2]; and a copper layer formed on one surface and the other surface of the substrate including the aluminum nitride sintered body.

[0020] [7] The present invention provides a ceramic substrate according to the above [6], wherein an Al2O3 oxide film is formed on the aluminum nitride sintered body and the copper layer, and the thickness of the Al2O3 oxide film is 5 µm to 10 µm.

[0021] The aluminum nitride sintered body according to the present invention exhibits excellent thermal conductivity, while also exhibiting improved bending strength and fracture toughness, and has high durability against thermal fatigue after copper bonding by the DCB method, thereby maintaining the bonding strength between the ceramic and copper. Therefore, the aluminum nitride sintered body according to the present invention can be usefully used in the manufacture of a ceramic substrate having excellent thermal conductivity and mechanical strength as well as excellent durability against thermal fatigue.

[0022] In addition, the method for manufacturing an aluminum nitride sintered body according to the present invention suppresses grain growth by adding partially stabilized zirconia, and performs sintering in two stages to stop grain growth and densify the microstructure, thereby simultaneously improving excellent bending strength and fracture toughness while maintaining excellent thermal conductivity.

[0023] Figure 1 is a drawing showing a scanning electron microscope (SEM) photograph of the particle surface microstructure of the aluminum nitride sintered body manufactured in Example 1.

[0024] Figure 2 is a scanning electron microscope (SEM) photograph showing the microstructure of the particle surface of the aluminum nitride sintered body manufactured in Comparative Example 1.

[0025] Figure 3 is a diagram showing the shape of a specimen for thermal fatigue evaluation.

[0026] Figure 4 is a scanning electron microscope (SEM) photograph showing an Al2O3 oxide film formed on the surface of the aluminum nitride sintered body manufactured in Example 1.

[0027] Hereinafter, the present invention will be described in detail.

[0028]

[0029] The present invention provides an aluminum nitride sintered body.

[0030]

[0031] The aluminum nitride sintered body of the present invention is an aluminum nitride sintered body obtained by continuously sintering a mixture including aluminum nitride powder, an oxide including zirconium, and a sintering aid at two different temperatures, wherein the oxide including zirconium is included in an amount of 0.4 to 8.0 parts by weight based on 100 parts by weight of the aluminum nitride powder, the aluminum nitride sintered body does not include an alkaline earth metal, the aluminum nitride sintered body includes aluminum nitride crystal grains, and the average particle size of the aluminum nitride crystal grains is 2.6 to 4.3 µm.

[0032]

[0033] The above aluminum nitride powder can be manufactured by a conventional aluminum nitride manufacturing method. For example, it can be manufactured by carbothermal reduction, self-propagating high temperature synthesis (SHS), chemical vapor synthesis, etc.

[0034] Specifically, it can be manufactured by a carbothermal reduction method as in the following reaction scheme 1 under a synthesis temperature condition of 1,200°C or higher, or by a SHS method as in the following reaction scheme 2 in which aluminum nitride is synthesized at a high temperature (about 2,500°C or higher) through an exothermic reaction by direct nitridation of metallic aluminum by heating to 800°C or higher, or by a chemical vapor synthesis method as in the following reaction scheme 3 at 800°C or higher, but is not limited thereto.

[0035] [Reaction Formula 1]

[0036] Al2O3+3C(CH4)+N2→ 2AlN+3CO

[0037] [Reaction Formula 2]

[0038] 2Al+N2→ 2AlN

[0039] [Reaction Formula 3]

[0040] AlCl3+4NH3→ AlN+3NH4Cl

[0041] The median particle size (D) of the above aluminum nitride powder 50 ) can be measured using PSA (Particle Size Analyzer) after sufficiently dispersing the powder, for example, the median particle size (D) of the aluminum nitride powder 50 ) may be 1.0 to 1.2 μm.

[0042] The median particle size (D) of the above aluminum nitride powder 50 ) is less than 1.0 ㎛, the average grain size of the aluminum nitride sintered body becomes small and the grain boundary diffusion increases, which causes a decrease in thermal conductivity. In addition, if it exceeds 1.2 ㎛, the average grain size of the aluminum nitride sintered body becomes excessively large, which may cause the sintered body particles themselves to be destroyed by external force, which may cause a problem of reduced strength.

[0043] The oxide containing the above zirconium may be zirconia (ZrO2).

[0044] The above zirconia (ZrO2) is a material used in ceramics, and has high refractory properties (melting point of 2,700℃), low thermal conductivity, and is chemically very stable. When applied to ceramics, it can play a role in imparting high strength and toughness.

[0045] Zirconia generally exists in a monoclinic phase at room temperature, but transforms into a tetragonal structure around 1,150°C, and then transforms into a hexagonal structure around 2,300°C. This transformation from the monoclinic to the tetragonal phase involves a volume change of approximately 5%, which causes grain breakage and increases the defect rate in ceramic manufacturing.

[0046] Therefore, in one embodiment of the present invention, as the zirconia, partially stabilized zirconia (PSZ) in which a stabilizer is introduced into the zirconia in an optimal amount can be used.

[0047] When the above partially stabilized zirconia (PSZ) is used, compared to when stabilized zirconia (e.g., yttria-stabilized zirconia (YSZ) or ceria-stabilized zirconia (CSZ) is used), there is an effect of suppressing grain growth of the sintered body during sintering, and thus there is an effect of improving the bending strength according to a decrease in the average grain size of the sintered body.

[0048]

[0049] The above-mentioned partially stabilized zirconia may include zirconia partially stabilized with a yttrium oxide (Y2O3) stabilizer. Specifically, the above-mentioned partially stabilized zirconia may be a zirconia powder in which the stabilizer is uniformly dispersed. When manufacturing a substrate using magnesium oxide (MgO) or calcium oxide (CaO) as the stabilizer, thermal conductivity and insulation performance may be reduced.

[0050] The above stabilizer may be included in an amount of 1 to 5 wt% based on the total weight of the partially stabilized zirconia, and specifically, may be included in an amount of 2 to 4 wt%, or 2 to 3 wt%. When the content of the stabilizer is less than 1 wt% based on the total weight of the partially stabilized zirconia, the effect of inhibiting grain growth of the sintered body is minimal, and when it exceeds 5 wt%, a problem of reduced thermal conductivity may occur.

[0051] The zirconium-containing oxide is included in an amount of 0.4 to 8.0 parts by weight based on 100 parts by weight of the aluminum nitride powder, specifically, may be included in an amount of 0.5 to 6.0 parts by weight, and more specifically, may be included in an amount of 1 to 5.5 parts by weight. If the amount of the zirconium-containing oxide based on the aluminum nitride powder is too small, fracture toughness and bending strength may be reduced, and if the amount of the zirconium-containing oxide based on the aluminum nitride powder is too large, a problem of reduced thermal conductivity may occur.

[0052] The above sintering agent may include a rare earth metal oxide to improve the sinterability of the aluminum nitride sintered body.

[0053] The above rare earth metal oxide is Z x O y , wherein Z is any one selected from the group consisting of Sc, Y, La, Ce, Sm, Pr, Nd, Pm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and x and y may be real numbers satisfying 0 < x < 4 and 0 < y < 6, respectively.

[0054] The surface of aluminum nitride powder is partially oxidized and exists as Al2O3. However, when sintered in a nitrogen atmosphere, Y2O3, a rare earth metal oxide, reacts with Al2O3 to form YAG (Y5Al5O12 ), YAP (YAlO3), YAM (Y4Al2O9), etc., form secondary phase compounds. When secondary phase compounds are formed at the grain boundaries, they trap oxygen, which is a factor that interferes with thermal conductivity, thereby reducing the amount of residual oxygen and maintaining high thermal conductivity. For the above reasons, it is preferable to use Y2O3 as the sintering aid.

[0055] The above sintering aid may be included in an amount of 1 to 10 parts by weight based on 100 parts by weight of the aluminum nitride powder, and specifically, may be included in an amount of 4 to 7 parts by weight. If the amount of the sintering aid based on the aluminum nitride powder is too small, sinterability may be reduced, which may cause problems with bending strength and thermal conductivity, and if the amount of the sintering aid based on the aluminum nitride powder is excessive, the proportion of the aluminum nitride powder may be reduced, which may cause problems with the strength and thermal conductivity of the sintered body.

[0056] The above aluminum nitride sintered body does not contain alkaline earth metal. Conventional aluminum nitride sintered bodies are manufactured by firing a mixture containing a compound including alkaline earth metal in addition to zirconia to improve mechanical strength, and thus alkaline earth metal components remain. The alkaline earth metal components remaining in the aluminum nitride sintered body lower the thermal conductivity, which is a major characteristic of the aluminum nitride sintered body, thereby reducing heat dissipation performance and lowering insulation properties, making it difficult to apply it as a substrate for high-power power modules. On the other hand, the aluminum nitride sintered body of the present invention does not contain alkaline earth metal, and therefore does not cause problems of reduced thermal conductivity and reduced insulation properties.

[0057] In addition, the aluminum nitride sintered body does not additionally contain components such as Si, TiN, etc. When the aluminum nitride sintered body contains components such as Si, TiN, etc., foreign substances such as Si, TiN, etc. are exposed on the surface of the aluminum nitride sintered body, making it difficult for an Al2O3 film to be formed, thereby preventing the problem of reduced bonding strength after copper bonding.

[0058] The above aluminum nitride sintered body includes aluminum nitride crystal grains, and the average grain size of the aluminum nitride crystal grains may be 2.6 to 4.3 ㎛. The average grain size of the aluminum nitride sintered body can be measured by magnifying the scanning electron microscope (SEM) image to about ×3,000. When the average grain size of the aluminum nitride sintered body is less than 2.6 ㎛, thermal conductivity may be reduced, and when it is more than 4.3 ㎛, bending strength or fracture toughness may be reduced.

[0059] The sintering of the above aluminum nitride sintered body is liquid-phase sintering. When the sintering agent is liquefied, the material movement of the aluminum nitride powder through the liquid phase becomes active, and as a result, the particle size increases, resulting in sintering. At this time, to prevent the particle size from becoming too large, the oxide containing the aforementioned zirconium is added in an optimal amount, thereby suppressing the particle growth of the sintered body, thereby reducing the intragranular fracture behavior and improving durability such as bending strength and fracture toughness.

[0060]

[0061] The fracture toughness of the above aluminum nitride sintered body is 3.60 MPa·m 1 / 2 It can be ideal, for example, 3.70 MPa·m 1 / 2 Above, 3.80 MPa·m 1 / 2 or 3.85 MPa·m 1 / 2 It could be strange.

[0062] The flexural strength of the above aluminum nitride sintered body may be 600 MPa or more, for example, 603 MPa or more.

[0063] The thermal conductivity of the above aluminum nitride sintered body may be 100 W / mk or more, for example, 105 W / mk or more, 120 W / mk or more, 130 W / mk or more, 140 W / mk or more, or 150 W / mk or more.

[0064] The insulating strength of the above aluminum nitride sintered body may be 20 kV / mm or more.

[0065] For example, in one embodiment of the present invention, the aluminum nitride sintered body has a flexural strength of 600 MPa or more and a fracture toughness of 3.60 MPa·m 1 / 2 It may have a thermal conductivity of 100 W / mK or more and an insulation strength of 20 kV / mm or more.

[0066]

[0067] In addition, the present invention provides a method for manufacturing a sintered aluminum nitride body.

[0068] The method for manufacturing the above aluminum nitride sintered body comprises: (s1) a step of mixing aluminum nitride powder, an oxide containing zirconium, and a sintering aid; (s2) a step of forming a slurry by adding a solvent to the mixture; (s3) a step of removing bubbles from the slurry; (s4) a step of forming a molding from the slurry and placing the molding into a sintering reactor; (s5) a step of first sintering the molding by raising the temperature of the sintering reactor to 1,750°C to 1,850°C; and (s6) a step of secondarily sintering the molding by lowering the temperature of the sintering reactor to 1,600°C to 1,700°C; wherein the oxide containing zirconium is included in an amount of 0.4 to 8.0 parts by weight based on 100 parts by weight of the aluminum nitride raw material powder.

[0069] The average grain size of the aluminum nitride sintered body manufactured according to the above manufacturing method may be 2.6 ㎛ to 4.3 ㎛.

[0070]

[0071] (s1) A step of mixing aluminum nitride powder, an oxide containing zirconium, and a sintering agent.

[0072] Specifically, the method for manufacturing the aluminum nitride sintered body may include a step of mixing 100 parts by weight of the aluminum nitride powder, 1 to 5 parts by weight of the oxide containing zirconium based on 100 parts by weight of the aluminum nitride powder, and 1 to 10 parts by weight of the sintering aid based on 100 parts by weight of the aluminum nitride powder.

[0073] The above mixture may further include a binder, etc. The binder may mainly include, but is not limited to, polyvinyl butyral resin, cellulose resin, acrylic resin, vinyl acetate resin, polyvinyl alcohol resin, etc.

[0074]

[0075] (s2) Step of forming a slurry by adding a solvent to the mixture

[0076] The step of forming a slurry by adding a solvent to the above mixture may include a step of ball milling the mixture to undergo a dispersion and grinding process.

[0077] The above solvent may include distilled water; alcohols such as ethanol, methanol, or isopropanol; or ketones such as acetone or methyl ethyl ketone; and it is preferable to use isopropanol for the sinterability of the sintered body.

[0078] The content of the above solvent is not limited as long as it can prevent the aluminum nitride powder from being hydrated or oxidized, but may be included in an amount of, for example, 30 to 300 parts by weight based on 100 parts by weight of the aluminum nitride powder.

[0079] The balls used in the above ball milling may be made of ceramics such as alumina or zirconia, and the balls may all be of the same size, or balls of different sizes may be used in combination.

[0080] By adjusting the ball size, milling time, and rotational speed of the ball mill, etc., the mixture is pulverized into the target particle size. The ball milling process can be performed at room temperature for 1 to 24 hours at 10 to 100 rpm, taking into account the particle size of the target sintered body. By ball milling, the mixture is pulverized into fine particles, and has a uniform particle size distribution, resulting in an intermediate particle size (D 50 ) is 0.6 to 2.0 ㎛, preferably 0.9 to 1.2 ㎛, a slurry having the intermediate particle size (D 50 ) can be measured using a Particle Size Analyzer (PSA).

[0081]

[0082] (s3) Step of removing bubbles from the slurry

[0083] After the above steps are performed to form a slurry, a defoaming step is performed to remove air bubbles from the slurry.

[0084] By removing air bubbles from the above slurry, the sintered body manufactured can prevent the formation of defects due to air bubbles, thereby further improving mechanical properties such as flexural strength and fracture toughness.

[0085]

[0086] (s4) A step of forming a molded body from the above slurry and putting it into a sintering reactor.

[0087] The above slurry can be formed into a thin plate using a tape casting molding method. The tape casting molding method involves moving the slurry to a storage dam, adjusting the blade slit height to adjust the thickness of the molded body, and then moving the lower tape to extract the slurry through friction between the slurry and the tape.

[0088] Afterwards, a step of removing the solvent from the molded body using hot air at 60°C to 120°C can be performed.

[0089] After the above-mentioned molded body is formed, it is placed in a sintering reactor for sintering.

[0090]

[0091] (s5) A step of first sintering the molded product by raising the temperature of the sintering reactor to 1,750°C to 1,850°C, and (s6) A step of secondarily sintering the molded product by lowering the temperature of the sintering reactor to 1,600°C to 1,700°C.

[0092]

[0093] In the method for manufacturing an aluminum nitride sintered body of the present invention, sintering is performed in two stages: primary sintering and secondary sintering.

[0094] The first sintering may be performed by raising the temperature of the sintering reactor to 1,750°C to 1,850°C for 1.5 to 2 hours. The temperature of the sintering reactor for the first sintering may be specifically 1,750°C to 1,800°C, more specifically 1,750°C to 1,780°C. If the first sintering temperature is lower than the above range, the energy required for sintering the aluminum nitride crystal grains is low, so that atomic diffusion is small, and thus sintering with strong bonding may be difficult. If the first sintering temperature is higher than the above range, the particles undergo active atomic diffusion, coarsening of the crystal grains may occur, and thus the flexural strength may be reduced. If the first sintering time is short, the growth of the crystal grains may be insufficient, and if the first sintering time is long, the crystal grains of the aluminum nitride may continuously grow due to the heat of the sintering furnace, making it difficult to control the size of the crystal grains.

[0095] The secondary sintering may be performed by continuously sintering the molded product by lowering the temperature of the sintering reactor to a temperature of 1,600°C to 1,700°C, and the secondary sintering may be performed for 4 to 6 hours. The temperature of the sintering reactor for the secondary sintering may be specifically 1,650°C to 1,700°C. The secondary sintering temperature is a temperature at which grain growth does not occur and the microstructure can be densified, and when the secondary sintering is performed for 4 to 6 hours in the temperature range, a microstructure of a target size can be obtained. If the secondary sintering temperature is lower than the range, it is difficult to smoothly densify the microstructure, and if the secondary sintering temperature is higher than the range, continuous grain growth may occur and the microstructure cannot be densified, making it difficult to obtain a microstructure of a desired size.

[0096] The above first sintering and second sintering are performed continuously. For example, the temperature of the sintering reactor is raised to a temperature for first sintering, and first sintering is performed for 1.5 to 2 hours. Then, the temperature of the sintering reactor is lowered from the temperature for first sintering to a temperature for second sintering, and second sintering is performed continuously for 4 to 6 hours.

[0097] The above sintering can be performed under a nitrogen atmosphere, and further, the above sintering can be performed under atmospheric pressure conditions or under pressurized conditions.

[0098]

[0099] A method for manufacturing an aluminum nitride sintered body according to one embodiment of the present invention may further include, after the secondary sintering step, a step (s7) of lowering the temperature of the reactor from the temperature of step (s6) to the ambient temperature at a rate of 50°C to 70°C per hour.

[0100]

[0101] The above-mentioned contents can be equally applied to the aluminum nitride powder, zirconium-containing oxide, sintering agent, solvent, molded body, and aluminum nitride sintered body.

[0102] The present invention provides an aluminum nitride sintered body manufactured according to the method for manufacturing an aluminum nitride sintered body described above.

[0103] The above aluminum nitride sintered body may have an oxygen content of 0.1 wt% or less and a carbon content of 0.1 wt% or less based on the total weight of the aluminum nitride sintered body. As described above, when the oxygen and carbon contents of the aluminum nitride sintered body are each 0.1 wt% or less, high thermal conductivity characteristics may be exhibited.

[0104] The aluminum nitride sintered body manufactured according to the manufacturing method of the aluminum nitride sintered body as described above has excellent mechanical strength, such as bending strength and fracture toughness, and thermal conductivity, and is therefore suitable as a ceramic substrate material applied to high-output power modules.

[0105]

[0106] In addition, the present invention provides a ceramic substrate including the above aluminum nitride sintered body.

[0107] The ceramic substrate of the present invention may include a substrate including the aforementioned aluminum nitride sintered body; and a copper layer formed on one side and the other side of the substrate including the aluminum nitride sintered body.

[0108] In addition, an Al2O3 oxide film is formed on the aluminum nitride sintered body, and the thickness of the Al2O3 oxide film may be 5 ㎛ to 10 ㎛.

[0109] In one embodiment of the present invention, the ceramic substrate can be manufactured by a manufacturing method including the steps of: (i) heat-treating an aluminum nitride sintered body at a temperature of 1000°C to 1300°C for 30 to 90 minutes to form an Al2O3 oxide film on the surface of the aluminum nitride sintered body; (ii) placing copper on the aluminum nitride sintered body and applying a temperature of 1050°C or higher in a nitrogen atmosphere to bond the copper to the aluminum nitride sintered body; and (iii) attaching a dry resist film (DRF) to the copper and performing exposure, development, and etching to form a circuit pattern.

[0110] In order to directly bond an aluminum nitride sintered body substrate to copper, it is necessary to form an Al2O3 oxide film on the surface of the aluminum nitride sintered body substrate. The Al2O3 oxide film can be formed by heat treating the aluminum nitride sintered body substrate at a temperature of 1,000°C to 1,300°C for 30 to 90 minutes. At a temperature below 1,000°C, the oxide film formation rate is slow and the oxide film thickness is uneven, which may significantly increase the unbonded area during copper bonding. At a temperature above 1,300°C, the oxide film may be formed too thick, which may cause the copper and ceramic to easily separate after copper bonding.

[0111] The thickness of the Al2O3 oxide film formed on the surface of the above aluminum nitride sintered body may be 5 ㎛ to 10 ㎛, and when the thickness of the Al2O3 oxide film satisfies the above range, the copper-ceramic bonding strength is the best, and in the thermal reliability evaluation, the occurrence of peeling starts the latest, so that a DCB product without non-bonding during copper bonding can be manufactured.

[0112] In order to bond copper to the above aluminum nitride sintered body, the aluminum nitride sintered body and copper are brought into contact and laminated, and then a temperature of 1,050°C or higher is applied in a nitrogen atmosphere.

[0113] Afterwards, a dry resist film (DRF) that is cured by ultraviolet rays is attached to the above-mentioned bonded copper, and exposure, development, and etching are performed to form a circuit pattern.

[0114]

[0115] In addition, in one embodiment of the present invention, the ceramic substrate can be manufactured by a manufacturing method including (i) a step of printing a paste including silver, copper, and an active metal on the surface of an aluminum nitride sintered body to form a bonding layer; and (ii) a step of laminating copper by contacting it on the bonding layer, and then heat-treating it in a nitrogen atmosphere. Here, the active metal can include at least one selected from the group consisting of titanium (Ti), zirconium (Zr), hafnium (Hf), titanium hydride (TiH2), and zirconium hydride (ZrH2).

[0116]

[0117] Hereinafter, the present invention will be described in more detail through examples.

[0118] However, these examples are only intended to aid understanding of the present invention and the scope of the present invention is not limited to these examples in any way.

[0119]

[0120] Examples 1 to 4

[0121] A raw material having the composition shown in Table 1 below was prepared, and a mixture was prepared by mixing 5 wt% of PVB binder and 3 wt% of DOP plasticizer in 100 ml of isopropanol. The mixture was ball milled at 30 rpm at room temperature for 24 hours using zirconia balls to disperse the raw material, thereby preparing a slurry. The obtained slurry was used to remove the solvent with hot air at 80°C using a tape casting facility, and a plate-shaped molded body measuring 170 mm in width, 220 mm in length, and 0.730 mm in thickness was manufactured.

[0122] The above-mentioned molded body was placed into a sintering reactor, and the temperature was gradually increased at 2°C per minute in the sintering reactor to reach a first sintering temperature of 1750°C to 1780°C, and sintering was performed. At this time, a nitrogen atmosphere was maintained during the sintering reaction to prevent oxidation during sintering. The first sintering was performed at 1750°C to 1780°C for 2 hours under a nitrogen atmosphere.

[0123] Next, the temperature of the sintering reactor was lowered to a secondary sintering temperature of 1650°C to 1700°C, and maintained in the above temperature range for 4 hours under a nitrogen atmosphere.

[0124] After the above secondary sintering, the temperature of the sintering reactor was lowered to the ambient temperature at a rate of 60°C per hour to manufacture an aluminum nitride sintered body.

[0125] Comparative Examples 1 to 3

[0126] A raw material having the composition shown in Table 1 below was prepared, and a mixture was prepared by mixing 5 wt% of PVB binder and 3 wt% of DOP plasticizer in 100 ml of isopropanol. The mixture was ball milled at 30 rpm at room temperature for 24 hours using zirconia balls to disperse the raw material, thereby preparing a slurry. The obtained slurry was used to remove the solvent with hot air at 80°C using a tape casting facility, and a plate-shaped molded body having a width of 170 mm, a length of 220 mm, and a thickness of 0.730 mm was manufactured.

[0127] In Comparative Examples 1 and 2, the molded body was placed in a sintering reactor, and the temperature was gradually increased at 2°C per minute in the sintering reactor to reach a sintering temperature of 1750 to 1780°C, and sintering was performed. At this time, a nitrogen atmosphere was maintained during the sintering reaction to prevent oxidation during sintering. The sintering was performed at 1750 to 1780°C for 3 hours under a nitrogen atmosphere, thereby producing an aluminum nitride sintered body.

[0128] In Comparative Example 3, the molded body was placed in a sintering reactor, and the temperature was gradually increased at 2°C per minute in the sintering reactor to reach a first sintering temperature of 1650°C to 1700°C, and sintering was performed. At this time, a nitrogen atmosphere was maintained during the sintering reaction to prevent oxidation during sintering. The first sintering was performed at 1650 to 1700°C for 4 hours under a nitrogen atmosphere.

[0129] Next, the temperature of the sintering reactor was increased to a secondary sintering temperature of 1750°C to 1780°C, and maintained in the above temperature range for 2 hours under a nitrogen atmosphere.

[0130] After the above secondary sintering, the temperature of the sintering reactor was lowered to the ambient temperature at a rate of 60°C per hour to manufacture an aluminum nitride sintered body.

[0131] Classification (weight part) Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 AlN9595959595959595Y2O35555555PSZ1234101 Sintering condition 2 steps 2 steps 2 steps 2 steps 1 step 1 step 2 steps (reverse order)

[0132] The components used in the above examples and comparative examples are as follows: 1. AlN: H-Grade, Tokuyama Co.

[0133] 2. Y2O3: NIPPON YTTRIUM CO.,LTD

[0134] 3. PSZ: TZ-3Y-E, Tosoh Corporation

[0135]

[0136] Experimental Example 1

[0137] average grain size

[0138] The average grain size of the sintered body was measured visually by magnifying ×3,000 using a scanning electron microscope (SEM) and averaging the size values ​​of at least 50 particles.

[0139]

[0140] The results of examining the microstructure of the particle surface of the aluminum nitride sintered body manufactured according to Example 1 and Comparative Example 1 using a scanning electron microscope (SEM) are shown in FIGS. 1 and 2, respectively.

[0141] Example 1, Comparative Examples 1 and 3 are aluminum nitride sintered bodies manufactured with slurries having the same composition, and the sintering was performed in the reverse order of steps 2, 1, and 2, respectively. The grain size of the aluminum nitride sintered body of Example 1 manufactured through the two-step sintering shown in Fig. 1 was measured to be 3.5 ㎛, and the grain size of the aluminum nitride sintered body of Comparative Example 1 manufactured through the one-step sintering shown in Fig. 2 was measured to be 4.3 ㎛. In the aluminum nitride sintered body of Comparative Example 3, as the heat treatment time increased and the heat supply increased, the grains grew larger, and the size of the aluminum nitride sintered body was measured to be 4.7 ㎛. Through this, it was confirmed that when the two-step sintering as in the examples was performed by controlling the sintering temperature, it was effective in controlling the grain size.

[0142]

[0143] Experimental Example 2

[0144] The results of evaluating the flexural strength, fracture toughness, thermal conductivity, and insulating strength of the aluminum nitride sintered bodies manufactured according to Examples 1 to 4 and Comparative Examples 1 to 3, respectively, according to the evaluation methods below are shown in Table 2 below.

[0145] Flexural strength

[0146] Flexural strength specimens were prepared by cutting the substrate into a rectangular shape of 4.0 mm × 0.63 mm × 50 mm using a laser. The bending strength was measured using a 3-point bending test using a UTM (universal test machine, Z020, Zwick / Roell AG, Germany). The measurement condition was a cross-head speed of 0.2 mm / min.

[0147] Destructive force

[0148] Fracture toughness was measured using a Vickers hardness tester using the indentation measurement method.

[0149] thermal conductivity

[0150] The laser flash method was used to evaluate the thermal conductivity of solid materials. The thermal diffusivity measured by the laser flash method was calculated as the product of the specific heat capacity and density, which were separately obtained. The laser flash method was used to obtain the thermal diffusivity (α) of a flat sample in the thickness (d) direction by measuring the time (τ) until the temperature of the sample surface increased and the temperature of the entire sample became uniform after pulse heating with laser light using a radiation thermometer.

[0151] Insulation strength

[0152] Measured according to ASTM D149.

[0153] Classification Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Flexural strength (MPa) 625 630 60 460 357 55 40 520 Fracture toughness (MPa m) 1 / 2 )3.853.943.903.893.402.983.20Thermal Conductivity (W / mK)153132122106150170142Insulation Strength (kV / mm)20202020202020

[0154] As can be confirmed through Table 2 above, the aluminum nitride sintered bodies manufactured in Examples 1 to 4 were significantly superior to those of Comparative Examples 1 to 3 in flexural strength and fracture toughness, and the insulating strengths of Examples 1 to 4 and Comparative Examples 1 to 3 were the same. It was confirmed that the aluminum nitride sintered bodies manufactured in Examples 1 to 4 had thermal conductivity of 106 W / mK or higher, which is sufficient to secure heat dissipation required for a high-output power module. Therefore, it was confirmed that the aluminum nitride sintered bodies manufactured in Examples 1 to 4 had thermal conductivity required as a material for a ceramic substrate, while also exhibiting superior mechanical strength, such as improved flexural strength and fracture toughness.

[0155]

[0156] Experimental Example 3

[0157] Examples 1-1 to 4-1, Comparative Examples 1-1 to 3-1

[0158] Each of the aluminum nitride sintered bodies manufactured according to Examples 1 to 4 and Comparative Examples 1 to 3 was used as a substrate, and a metal powder was obtained by mixing Ti powder with an alloy powder composed of silver (Ag) and copper (Cu) on one side and the other side of the aluminum nitride sintered body substrate, and then a paste manufactured by mixing α-terpineol and diethyl glycol monobutyl ether acetate with the metal powder was screen-printed to form a bonding layer, respectively.

[0159] After manufacturing a laminate by laminating a 0.3 mm thick copper foil on each of the above bonding layers, the laminate was placed in a vacuum furnace at a vacuum of 0.1 torr or less and a temperature of 850°C and bonded.

[0160]

[0161] Copper bonding strength

[0162] Copper bond strength was measured by pulling the copper and peeling it off after fixing the specimen.

[0163]

[0164] Thermal cycle test (TCT)

[0165] After completing the patterning process on the ceramic substrate, the point at which the ceramic substrate and the metal layer delaminate was determined by applying repeated thermal shocks. Specifically, the ceramic substrate was subjected to one cycle of thermal shocks, with each cycle consisting of -50°C for 15 minutes and 150°C for 15 minutes, and the point at which the metal layer delaminates from the ceramic substrate was measured.

[0166] The shape of the evaluation specimen used for thermal fatigue evaluation is shown in Fig. 3.

[0167]

[0168] Classification Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Copper joint strength (N / mm) 12 14 14 16 11 10 10 Thermal fatigue evaluation 2 7 0 5 0 0 6 5 0 6 5 0 26 0 25 0 20 0

[0169] Table 3 above shows the results of evaluating copper bonding strength and thermal fatigue for ceramic substrates manufactured by the active metal brazing (AMB) method using the aluminum nitride sintered bodies manufactured in Examples 1 to 4 and Comparative Examples 1 to 3 as substrates.

[0170] *Referring to Table 3, it was confirmed that the ceramic substrate manufactured using the substrate of the aluminum nitride sintered body manufactured in Examples 1 to 4 was superior to Comparative Examples 1 to 3 in copper bonding strength and was also significantly superior in thermal fatigue evaluation, thereby exhibiting superior durability in thermal shock.

[0171]

[0172] Experimental Example 4

[0173] Examples 1-2 to 4-2, Comparative Examples 1-2 to 3-2

[0174] Each of the aluminum nitride sintered bodies manufactured according to Examples 1 to 4 and Comparative Examples 1 to 3 was heat-treated at a temperature of 1,200°C for 50 minutes to form an oxide film.

[0175] A copper thin plate with a thickness of 0.3 mm was laminated on one side and the other side of an aluminum nitride sintered substrate on which an oxide film was formed, and the copper was bonded by heat treatment at a temperature of 1,050°C in a nitrogen atmosphere.

[0176]

[0177] SEM image

[0178] The oxide film formed by heat-treating the aluminum nitride sintered body manufactured according to Example 1 above was enlarged at ×3,000 magnification using a scanning electron microscope (SEM) and is shown in Fig. 4.

[0179] Referring to Fig. 4, it can be confirmed that an Al2O3 oxide film is formed on the microstructure of the aluminum nitride sintered body.

[0180]

[0181] Copper bonding strength

[0182] Copper bond strength was measured by pulling the copper and peeling it off after fixing the specimen.

[0183]

[0184] Thermal cycle test (TCT)

[0185] After completing the patterning process on the ceramic substrate, the point at which the ceramic substrate and the metal layer delaminate was determined by applying repeated thermal shocks. Specifically, the ceramic substrate was subjected to one cycle of thermal shocks, with each cycle consisting of -50°C for 15 minutes and 150°C for 15 minutes, and the point at which the metal layer delaminates from the ceramic substrate was measured.

[0186]

[0187] Classification Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Copper bonding strength (N / mm) 6.5 6.8 7.0 6.7 6.9 6.9 6.5 Thermal fatigue evaluation 6 5 1 1 0 1 0 5 1 1 0 5 5 4 5 4 7

[0188] Table 4 above shows the results of evaluating copper bonding strength and thermal fatigue for ceramic substrates manufactured by direct copper bonding (DCB) using the aluminum nitride sintered bodies manufactured in Examples 1 to 4 and Comparative Examples 1 to 3 as substrates. Referring to Table 3, the ceramic substrates manufactured using the aluminum nitride sintered bodies manufactured in Examples 1 to 4 as substrates showed a similar level of copper bonding strength to Comparative Examples 1 to 3, but showed better results in the thermal fatigue evaluation, confirming that they exhibited significantly superior durability in thermal shock.

Claims

1. An aluminum nitride sintered body obtained by continuously sintering a mixture containing aluminum nitride powder, an oxide containing zirconium, and a sintering agent at two different temperatures. The oxide containing the zirconium is included in an amount of 0.4 to 8.0 parts by weight based on 100 parts by weight of the aluminum nitride powder, The above aluminum nitride sintered body includes aluminum nitride crystal grains, An aluminum nitride sintered body having an average particle size of the above aluminum nitride crystal grains of 2.6 ㎛ to 4.3 ㎛.

2. In paragraph 1, The above aluminum nitride sintered body has a flexural strength of 600 MPa or more and a fracture toughness of 3.60 MPa·m 1 / 2 An aluminum nitride sintered body having a thermal conductivity of 100 W / mK or more and an insulating strength of 20 kV / mm or more. 3.(s1) A step of mixing aluminum nitride powder, an oxide containing zirconium, and a sintering agent; (s2) a step of forming a slurry by adding a solvent to the above mixture; (s3) a step of removing bubbles from the slurry; (s4) A step of forming a molded product from the above slurry and putting it into a sintering reactor; (s5) a step of first sintering the molded product by raising the temperature of the sintering reactor to 1,750°C to 1,850°C; and (s6) a step of continuously sintering the molded product by lowering the temperature of the sintering reactor to a temperature of 1,600°C to 1,700°C; A method for producing an aluminum nitride sintered body, wherein the oxide containing the zirconium is included in an amount of 0.4 to 8.0 parts by weight based on 100 parts by weight of the aluminum nitride raw material powder.

4. In paragraph 3, A method for manufacturing an aluminum nitride sintered body, comprising, after the above-mentioned secondary sintering step, an additional step (s7) of lowering the temperature of the reactor from the temperature of step (s6) to the ambient temperature at a rate of 50°C to 70°C per hour.

5. In paragraph 3, A method for manufacturing an aluminum nitride sintered body, wherein the first sintering is performed for 1.5 to 2 hours, and the second sintering is performed for 4 to 6 hours.

6. A substrate comprising an aluminum nitride sintered body according to paragraph 1; and a ceramic substrate comprising a copper layer formed on one surface and the other surface of the substrate comprising the aluminum nitride sintered body.

7. In paragraph 6, A ceramic substrate in which an Al2O3 oxide film is formed on the aluminum nitride sintered body and the copper layer, and the thickness of the Al2O3 oxide film is 5 ㎛ to 10 ㎛.

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