CN107365155A - A kind of low-temperature sintering adjuvant system of aluminium nitride ceramics - Google Patents

Abstract

The invention relates to a low-temperature sintering aid system for aluminum nitride ceramics. The low-temperature sintering aid system includes component A and component B; the component A is at least one of TiO ₂ , ZrO ₂ , and HfO ₂ species; the component B is at least one of V ₂ O ₅ , Nb ₂ O ₅ , and Ta ₂ O ₅ . The sintering aid scheme proposed by the present invention, compared with the scheme reported in the literature at present, can realize the densification process of the material in a shorter time, the process is simple and reliable, and can obtain higher thermal conductivity.

Description

A low-temperature sintering aid system for aluminum nitride ceramics

technical field

Aiming at the problems of high sintering temperature, long sintering time, and high cost of aluminum nitride ceramics, the present invention proposes a sintering aid system with low sintering temperature, short holding time, and effective densification, which belongs to the preparation process and application field of ceramics .

Background technique

With the development of modern technology, especially the development of electronic packaging technology, the increase in the integration of power electronic devices, and the application of LED lighting, heat dissipation has become a key issue that needs to be solved urgently. If the heat generated cannot be dissipated in time, it will cause the temperature of the semiconductor chip to rise, resulting in unstable performance of electronic devices, or the rise of the junction temperature of the LED, resulting in a decrease in luminous efficiency and shortened life. At present, the problem of heat dissipation has become the key to restricting the application of power electronic components and high-power LEDs. The commonly used substrate materials are Al ₂ O ₃ , BeO, SiC and AlN. A1 ₂ O ₃ ceramics are currently the most mature ceramic substrate materials, because of their low price, good thermal shock resistance and electrical insulation performance, and mature production and processing technology, so they are the most widely used, accounting for 90% of ceramic substrate materials. . However, the thermal conductivity of Al ₂ O ₃ is only about 22-28W/m·K, which is far from meeting the heat dissipation requirements of high-power LEDs. Silicon carbide (SiC) ceramics have high thermal conductivity, and the thermal expansion coefficient is the closest to Si, but their insulation is poor, and sintering is difficult, making it difficult to produce dense products. Although a SiC substrate with high thermal conductivity (270W/m K) can be obtained by adding a small amount of beryllium oxide sintering aid and hot-pressing sintering method, the loss and high cost of hot pressing limit its development and scale. Apply in batches. BeO ceramic is currently the ceramic substrate material with the best thermal conductivity. Its comprehensive dielectric properties are good, but its thermal conductivity will drop sharply as the temperature rises. In addition, BeO is highly toxic, which limits its use. Currently, BeO is not allowed in Japan. Production, in Europe has also begun to limit the electronic products containing BeO.

AlN ceramics is a new type of packaging material favored by experts at home and abroad, and it has excellent electrothermal properties. Compared with alumina, aluminum nitride has high thermal conductivity, which is 5 to 10 times that of alumina, and is suitable for high power, high leads and large-size chips; its thermal expansion coefficient matches silicon, and its dielectric constant is low ;Material with high mechanical strength. As a high thermal conductivity and high sealing material, AlN ceramics have great potential for development, and are an important development direction for the research of ceramic packaging materials. It is expected that in the two fields of substrate and packaging, AlN ceramics will eventually replace the current Al ₂ O ₃ and BeO ceramics.

However, due to the high cost of aluminum nitride powder and the difficulty of sintering, the cost of aluminum nitride substrates remains high, which cannot meet the low-cost and batch application requirements of the LED industry. At present, the price of domestic aluminum nitride powder is relatively low. Although the oxygen content is high, it can already meet the application requirements of LEDs. The key issue is to reduce the sintering cost.

Aluminum nitride ceramics are non-oxide ceramics. Pure aluminum nitride is difficult to sinter densely at high temperatures, and usually requires the addition of sintering aids. The main function of the sintering aid is to react with the alumina on the surface of aluminum nitride to form a low-melting composite oxide during the sintering process, and produce a liquid phase to surround the aluminum nitride powder to achieve wetting, sticking, tensioning, and surface activation. The purpose is to promote the densification of the green body; secondly, the liquid phase is evenly distributed near the aluminum nitride grain boundary and the triple point, forming an oxygen trap, which can capture the oxygen in the aluminum nitride, and segregate at the triple point after cooling, so that the nitrogen The aluminum nitride grains can be in close contact to achieve the purpose of improving the thermal conductivity of the aluminum nitride ceramics. At present, the sintering aids commonly used in AlN ceramics mainly include Y ₂ O ₃ , CaO, Er ₂ O ₃ , Yb ₂ O ₃ , Sm ₂ O ₃ , Dy ₂ O ₃ , Li ₂ O, B ₂ O ₃ , CaF ₂ , YF _3. CaC ₂ etc. or mixed use can not only effectively promote the sintering of AlN powder, but also help to improve the thermal conductivity of sintered products. However, usually the sintering temperature is 1700-1850°C, the holding time is long, and the sintering cost is very high. The development of LEDs, especially in the field of civilian lighting, needs to continuously reduce costs to reach a cost level comparable to that of current fluorescent lamps or incandescent lamps before they can be introduced to the market. The cost problem has become a key factor limiting the application of aluminum nitride substrates in the LED field.

Low temperature sintering can effectively reduce the cost of sintering, and it is one of the focuses at home and abroad. There have been a large number of literature reports. Commonly used sintering aid systems are Y ₂ O ₃ and CaO or Y ₂ O ₃ , CaO, Li ₂ O, and other rare earth oxides such as Dy ₂ O ₃ can be used instead of Y ₂ O ₃ , CaF ₂ can be used instead of CaO, and Li ₂ CO ₃ replaces Li ₂ O, etc. These sintering aid systems often require a long holding time, and after Ca is introduced, it can form a liquid phase with alumina, which has good wettability to AlN particles, often resulting in a serious drop in thermal conductivity, and cannot effectively reduce costs.

Contents of the invention

In view of the above problems, the present invention proposes a low-temperature sintering aid system for aluminum nitride ceramics, the low-temperature sintering aid system includes component A and component B;

The component A is at least one of TiO ₂ , ZrO ₂ , HfO ₂ , preferably one of TiO ₂ , ZrO ₂ , HfO ₂ ;

The component B is at least one of V ₂ O ₅ , Nb ₂ O ₅ , and Ta ₂ O ₅ , preferably one of V ₂ O ₅ , Nb ₂ O ₅ , and Ta ₂ O ₅ .

The invention proposes a new sintering aid system based on the long-term sintering research of aluminum nitride ceramics. Using binary components, component A contains at least one of TiO ₂ , ZrO ₂ , and HfO ₂ ; component B contains at least one of V ₂ O ₅ , Nb ₂ O ₅ , and Ta ₂ O ₅ . Their combination is used as a sintering aid, wherein the sintering aid system can form a liquid phase at a relatively low temperature, and use the liquid phase to promote sintering. At the same time, the sintering aid system reacts with oxygen impurities to form aluminate, which precipitates when cooling Two-phase, using the second phase to consolidate oxygen on the grain boundary, reducing the oxygen content of the sintered body, which is beneficial to improving the thermal conductivity of aluminum nitride ceramics.

Preferably, the mass ratio of component A to component B is 1:(1-5). When the value is in this range, it is beneficial to reduce the viscosity of the grain boundary phase, promote low-temperature sintering, and ensure the thermal conductivity of aluminum nitride ceramics.

Preferably, the particle size distribution of the low-temperature sintering aid system is 50 nm to 50 microns.

On the other hand, the present invention also provides a method for preparing aluminum nitride ceramics, comprising:

Dissolve the aluminum nitride powder and the above-mentioned warm sintering aid system in an organic solvent, and then add a dispersant, a binder, and a plasticizer and mix them uniformly to form a green body. The aluminum nitride powder and the low-temperature sintering aid system The mass ratio of the agent system is (90-95): (5-10);

Calcining the obtained green body at 1600-1700° C. for 1-12 hours to obtain aluminum nitride ceramics.

Specifically, the low-temperature sintering aid proposed by the present invention has the following characteristics. First of all, the sintering aid will not enter the aluminum nitride lattice into a solid solution, avoiding a serious drop in the thermal conductivity of aluminum nitride caused by solid solution; secondly, the sintering aid system can generate a low-temperature liquid phase during the sintering process, Effectively wet the surface of aluminum nitride ceramic particles, promote particle rearrangement and sintering process, reduce the sintering temperature (1600-1700 °C); it can also realize the densification process in a short time (1-2 hours). In addition, after sintering, the wettability of the sintering aid and aluminum nitride particles is poor, and it is easy to retreat to the position of the three-fork grain boundary, which ensures that the aluminum nitride grains can contact each other, which contributes to the thermal conductivity of aluminum nitride ceramics. Rate control creates the conditions. Therefore, by adopting the sintering aid system proposed by the present invention, the densification process of aluminum nitride ceramics can be realized in a relatively short period of time, which lays a foundation for the preparation of aluminum nitride ceramic systems with high thermal conductivity.

Preferably, the organic solvent is at least one of ethanol, butanone, toluene, n-hexane, methanol, xylene, n-propanol and n-butanol, preferably ethanol/butanone, ethanol/toluene, ethanol/n-hexane Alkanes, butanone/methanol, xylene/n-propanol, or xylene/n-butanol, the addition amount is 15-30wt% of the total mass of the aluminum nitride powder and the low-temperature sintering aid system.

Preferably, the dispersant is at least one of triolein, phosphoric acid ester, castor herring oil, ascorbic acid and terpineol, and the amount added is the total of the aluminum nitride powder and the low-temperature sintering aid system. 0.5 to 4 wt% of the mass.

Preferably, the binder is polyvinyl butyral or/and polymethyl methacrylate, and the added amount is 6-9 wt% of the total mass of the aluminum nitride powder and the low-temperature sintering aid system.

Preferably, the plasticizer is dibutyl phthalate DBP or/and dibutyl benzyl phthalate BBP, and the amount added is 7-7% of the total mass of the aluminum nitride powder and the low-temperature sintering aid system. 12 wt%.

Preferably, the heating rate of the calcination is 1-15° C./min. Preferably, the particle size of the aluminum nitride powder is 100 nm-10 μm.

In another aspect, the present invention also provides an aluminum nitride ceramic prepared according to the above method.

The sintering aid scheme proposed by the present invention, compared with the scheme reported in the literature at present, can realize the densification process of the material in a shorter time, the process is simple and reliable, and can obtain higher thermal conductivity. Thus, the sintering cost can be greatly reduced. The invention is suitable for low-temperature sintering of aluminum nitride ceramics, and can meet the needs of various aspects such as industry, aviation, spaceflight and national defense. The system described in the present invention can realize the sintering of aluminum nitride ceramics in a relatively low temperature and in a short period of time, and the density can reach more than 99%.

detailed description

The present invention will be further described below through the following embodiments. It should be understood that the following embodiments are only used to illustrate the present invention, not to limit the present invention.

Aiming at the problem of high sintering cost of aluminum nitride ceramic substrates, the invention provides a new low-temperature sintering aid system for aluminum nitride ceramics in order to further shorten the sintering time and lower the sintering cost. The sintering aid contains two components: component A and component B. The sintering aid component A is a transition element oxide, including TiO ₂ , ZrO ₂ , HfO ₂ and the like. The sintering aid component B is a high-valence state transition element oxide, including V ₂ O ₅ , Nb ₂ O ₅ , Ta ₂ O ₅ and the like. Wherein, the weight ratio of component A and component B may be 1:1 to 1:5. The particle sizes of the two sintering aids (component A and component B) range from 50 nm to 50 microns. In general, the sintering aid system for low-temperature sintering of aluminum nitride ceramics according to the present invention uses a low-cost two-component transition metal oxide as a composite sintering aid system to generate a liquid phase at low temperature to promote the mass transfer process , to achieve densification. The liquid phase will form a crystal phase after sintering, which has little influence on the thermal conductivity of ceramics. The low-temperature sintering aid system proposed by the invention not only has low cost, but also can effectively realize low-temperature sintering of aluminum nitride ceramics, and has little influence on the thermal properties of the final aluminum nitride ceramics. The method is suitable for the preparation of low-cost aluminum nitride ceramic substrates and the application in the LED field.

The low-temperature sintering scheme proposed by the invention has simple and reliable technology, low cost and easy operation. Suitable for low temperature sintering of aluminum nitride ceramics. The preparation method of the aluminum nitride ceramic provided by the present invention is exemplarily described below.

Mix ceramic powder and sintering aid and disperse in organic solvent. Specifically, the aluminum nitride powder and the above-mentioned low-temperature sintering aid system are dissolved in an organic solvent, and after adding a dispersant, a binder, and a plasticizer, they are uniformly mixed to form a green body. The aluminum nitride powder The mass ratio to the low-temperature sintering aid system can be (5-10): (90-95). The low-temperature sintering aid system proposed by the present invention includes component A (TiO ₂ , ZrO ₂ , HfO ₂ , etc.) and component B (V ₂ O ₅ , Nb ₂ O ₅ , Ta ₂ O ₅ , etc.). The weight ratio of component A and component B may be from 1:1 to 1:5. The particle size of the aluminum nitride powder may be 100 nm˜10 μm. In addition, the method of making the green body includes but not limited to tape casting, dry pressing, cold isostatic pressing, gel injection molding and other methods.

In the present invention, the organic solvent can be at least one of ethanol, butanone, toluene, n-hexane, methanol, xylene, n-propanol and n-butanol, preferably ethanol/butanone, ethanol/toluene, ethanol/ n-Hexane, MEK/Methanol, Xylene/n-Propanol, or Xylene/n-Butanol. Its addition amount can be 15-30wt% of the total mass of the aluminum nitride powder and the low-temperature sintering aid system.

In the present invention, commonly used dispersants are glyceryl trioleate, phosphoric acid ester, castor oil herring oil, ascorbic acid, terpineol, etc., and the addition amount can be 0.5% of the total mass of aluminum nitride powder and low-temperature sintering aid system. ~4wt%.

In the present invention, commonly used binders include polyvinyl butyral, polymethyl methacrylate, etc., and their addition amount can be 6-9 wt% of the total mass of aluminum nitride powder and low-temperature sintering aid system.

In the present invention, commonly used plasticizers have dibutyl phthalate (DBP) and dibutyl benzoate (BBP), and their addition amount can be the total amount of aluminum nitride powder and low-temperature sintering aid system. 7 to 12 wt% of the mass.

Calcining the obtained body at 1600-1700° C. for 1-12 hours to obtain aluminum nitride ceramics. The heating rate of the calcination is 1-15° C./minute.

The invention adopts the Archimedes drainage method to measure the density of the aluminum nitride ceramics to be 99-99.5%. The invention uses a laser thermal conductivity meter to measure the thermal conductivity of the alumina ceramics to be 130-160 W·m ^-1 ·K ^-1 .

The invention proposes the method of using a low-temperature sintering aid to reduce the sintering cost, and can obtain dense aluminum nitride ceramics by sintering in the temperature range of 1600-1700°C. Compared with the commonly used low-temperature sintering aids reported at home and abroad, this sintering aid can adopt the method of rapid sintering to achieve densification of materials in a relatively short period of time, thereby greatly reducing the sintering cost, and is an excellent choice for the application of AlN ceramic substrates. Create conditions.

Examples are further listed below to describe the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention, and should not be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art according to the above contents of the present invention all belong to the present invention scope of protection. The specific process parameters and the like in the following examples are only examples of suitable ranges, that is, those skilled in the art can make a selection within a suitable range through the description herein, and are not limited to the specific values exemplified below. Unless otherwise specified, the particle size of the aluminum nitride powder in the following examples is generally 100 nm to 10 μm. The particle size distribution of the low-temperature sintering aid system is 50 nm to 50 microns.

Example 1

Add 95g of aluminum nitride powder and 5g of sintering aids titanium oxide and vanadium oxide to 21g of ethanol/butanone solvent system (the mass ratio of ethanol and acetone is 40:60), the ratio of titanium oxide and vanadium oxide is 1:1 . Using 2g triolein as a dispersant, adding 8g PVB as a binder and 8g DBP as a plasticizer after ball milling, defoaming and casting after ball milling again, and preparing a cast film with a thickness of 0.15-0.2mm. After the cast film is debonded, it is sintered in a carbon tube furnace, and the temperature is raised to 1650 °C at a rate of 5 °C/min, and the sintering is achieved by keeping the temperature for 2 hours. A dense and complete aluminum nitride substrate can be obtained.

Example 2

Add 94g of aluminum nitride powder and 6g of sintering aids titanium oxide and niobium oxide to 21g of ethanol/toluene solvent system (the mass ratio of ethanol and toluene is 40:60), and the ratio of titanium oxide and niobium oxide is 1:2. Using 2.5g phosphate ester as dispersant, after ball milling, add 8.5g PVB as binder, 9g DBP as plasticizer, after ball milling again, defoaming, casting, and prepare casting film with thickness of 0.15-0.2mm. After the cast film is debonded, it is sintered in a carbon tube furnace, and the temperature is raised to 1650 °C at a rate of 5 °C/min, and the sintering is achieved by keeping the temperature for 2 hours. A dense and complete aluminum nitride substrate can be obtained.

Example 3

Add 93g of aluminum nitride powder and 7g of sintering aids titanium oxide and tantalum oxide to 21g of ethanol/n-hexane solvent system (the mass ratio of ethanol and n-hexane is 50:50), the ratio of titanium oxide and tantalum oxide is 1: 3. Using 2.0g castor oil as dispersant, after ball milling, add 9g PVB as binder, 10g DBP as plasticizer, after ball milling again, defoaming, casting, and prepare cast film with thickness of 0.15-0.2mm. After the cast film is debonded, it is sintered in a carbon tube furnace, and the temperature is raised to 1650°C at a rate of 5°C/min, and the sintering is achieved by holding the heat for 2 hours. A dense and complete aluminum nitride substrate can be obtained.

Example 4

Add 92g of aluminum nitride powder and 8g of sintering aids zirconia and niobium oxide to 21g of butanone/methanol solvent system (the mass ratio of butanone and methanol is 50:50), and the ratio of zirconia and niobium oxide is 1: 4. Using 2g of ascorbic acid as a dispersant, adding 7.5g of PVB as a binder and 8.5g of BBP as a plasticizer after ball milling, degassing and casting after ball milling again, and preparing a cast film with a thickness of 0.15-0.2mm. After debonding, the cast film was sintered in a carbon tube furnace, and the temperature was raised to 1650°C at a heating rate of 5°C/min for 2 hours to achieve sintering. A dense and complete aluminum nitride substrate can be obtained.

Example 5

Add 90g of aluminum nitride powder and 10g of sintering aids hafnium oxide and niobium oxide to 21g of xylene/n-propanol solvent system (the mass ratio of xylene and n-propanol is 50:50), the ratio of hafnium oxide to niobium oxide 1:5. Using 1.8g triolein as a dispersant, after ball milling, add 8.5g PVB as a binder, 10g BBP as a plasticizer, after ball milling again, defoaming, casting, and prepare a casting film with a thickness of 0.15-0.2mm . After the cast film is debonded, it is sintered in a carbon tube furnace, and the temperature is raised to 1650 °C at a rate of 5 °C/min, and the sintering is achieved by keeping the temperature for 2 hours. A dense and complete aluminum nitride substrate can be obtained.

Table 1 is the preparation method and performance parameters of the aluminum nitride substrate obtained in Examples 1-5 of the present invention:

.

Claims (10)

1. A low-temperature sintering aid system for aluminum nitride ceramics, characterized in that, the low-temperature sintering aid system comprises component A and component B; The component A is at least one of TiO ₂ , ZrO ₂ , HfO ₂ ; The component B is at least one of V ₂ O ₅ , Nb ₂ O ₅ , and Ta ₂ O ₅ . 2. The low-temperature sintering aid system according to claim 1, characterized in that, the mass ratio of the component A to the component B is 1: (1-5). 3. The low-temperature sintering aid system according to claim 1 or 2, characterized in that the particle size distribution of the low-temperature sintering aid system is 50 nm to 50 microns. 4. A method for preparing aluminum nitride ceramics, comprising: Dissolving the aluminum nitride powder and the low-temperature sintering aid system described in any one of claims 1-3 in an organic solvent, and then adding a dispersant, a binder, and a plasticizer, and then uniformly mixing to form a green body, the The mass ratio of the aluminum nitride powder and the low-temperature sintering aid system is (5-10): (90-95); Calcining the obtained body at 1600-1700° C. for 1-12 hours to obtain aluminum nitride ceramics. 5. The preparation method according to claim 4, characterized in that the particle size of the aluminum nitride powder can be 100 nm to 10 μm; The organic solvent is at least one of ethanol, butanone, toluene, n-hexane, methanol, xylene, n-propanol and n-butanol, preferably ethanol/butanone, ethanol/toluene, ethanol/n-hexane, butanone /methanol, xylene/n-propanol, or xylene/n-butanol, the addition amount is 15-30wt% of the total mass of the aluminum nitride powder and the low-temperature sintering aid system. 6. according to the preparation method described in claim 4 or 5, it is characterized in that, described dispersant is at least one in glyceryl trioleate, phosphoric acid ester, castor oil herring oil, ascorbic acid and terpineol, add The amount is 0.5-4wt% of the total mass of the aluminum nitride powder and the low-temperature sintering aid system. 7. according to the preparation method described in any one in the claim 4-6, it is characterized in that, described binding agent is polyvinyl butyral or/and polymethyl methacrylate, and add-on is nitriding 6-9wt% of the total mass of the aluminum powder and the low-temperature sintering aid system. 8. according to the preparation method described in any one in claim 4-7, it is characterized in that, described plasticizer is dibutyl phthalate DBP or/and dibutyl benzyl phthalate BBP, adds The amount is 7-12wt% of the total mass of the aluminum nitride powder and the low-temperature sintering aid system. 9. The preparation method according to any one of claims 4-8, characterized in that the heating rate of the calcination is 1-15° C./min. 10. An aluminum nitride ceramic prepared by the method according to any one of claims 4-9.