What is a ceramic heat sink? Introduction to the classification, advantages and application fields of ceramic heat sinks

What is a ceramic heat sink?

The components of modern technology products, such as computer chips or light-emitting diodes, generate more and more waste heat during operation. Generally, the existing heat sinks used to assist the heat dissipation of the heating components usually include at least a metal heat sink and a heat sink. The fan conducts the waste heat from the operation of the heating element through the heat sink and removes it by air convection, and uses the fan to forcefully accelerate the convection of the air around the heating element to achieve the effect of rapid heat removal.

However, the heat transfer coefficient of the existing metal heat sinks is not very good, so there are heat sinks made of ceramic materials with better heat transfer properties on the market, in order to achieve better heat dissipation effect, ceramic heat sinks This was born; the ceramic heat sink is mainly composed of a heat dissipation layer and a heat conduction layer. The heat dissipation layer is unevenly dispersed with a latex-like slurry using the principle of liquid phase chemical change to form a thin structure of ceramic powder, and is combined with sub-micron powder. The porosity of the heat dissipation layer is between 5% and 40%, and the particle size of the powder is between 90 nanometers and 300 nanometers. The heat source contact surface has a heat conduction layer, the heat conduction layer absorbs and conducts the heat source, and through the high surface area of the hole structure of the heat dissipation layer, air is used as the heat dissipation medium to improve the heat dissipation capacity for heat dissipation.

Introduction to the classification of ceramic heat sinks

A ceramic heat sink is a device that dissipates heat from heat-prone electronic components in electrical appliances. At present, thermally conductive alumina ceramic sheets, thermally conductive aluminum nitride ceramic sheets, and silicon carbide ceramic heat sinks are commonly used in the market.

Thermally conductive alumina ceramic sheet: thermally conductive alumina ceramic heat sink has high thermal conductivity, thermal conductivity: 24W/M.K; high temperature/high pressure resistance, uniform heating, fast heat dissipation; simple and compact structure, small size, smooth surface, high strength and not easy to break , acid and alkali corrosion resistance, durable.

Thermally conductive aluminum nitride ceramic sheet: High thermal conductivity aluminum nitride ceramic sheet is gray-white in color and smooth in surface. It can be customized into any shape or size, which is easy to use and install. This ceramic heat sink has a very high thermal conductivity, its thermal conductivity is 7-10 times that of alumina ceramic sheets, and can reach as high as 180W. Its electrical insulation performance is quite stable, its dielectric constant and dielectric loss are low, and it can withstand The ultra-high temperature of 1800 degrees Celsius does not affect the working performance of the product. With the rapid development of electronic equipment, the demand for electronic or auxiliary products is also increasing. This product is used as a matrix or packaging material. High thermal conductivity aluminum nitride ceramic heat sink The application rate in the market is also more and more extensive.

Silicon carbide ceramic heat sink: Silicon carbide ceramic heat sink is a green and environmentally friendly material. It belongs to a micro-porous structure and can have 30% more porosity under the same unit area, which greatly increases the heat dissipation area in contact with the air and enhances its performance. heat radiation. At the same time, its heat capacity is small, its own heat storage is small, and its heat can be transferred to the outside world more quickly. The main features of ceramic heat sinks are: environmental protection, insulation, high voltage resistance, efficient heat dissipation, and avoid breeding EMI problems. It can effectively solve the problems of heat conduction and heat dissipation in the electronics and home appliance industries. At the same time, it is especially suitable for small and medium wattage power consumption. The design space is light, thin, short and small. It can provide technical support for the innovation and development of electronic products. with application.

Introduction to the advantages of ceramic heat sinks

  1. The ceramic heat sink itself does not store heat, and directly dissipates heat, which is fast and reduces the influence of the insulating layer on the thermal efficiency;
  2. The polycrystalline structure of the ceramic heat sink enhances heat dissipation. Compared with the same conditions, it surpasses most thermally conductive insulating materials on the market;
  3. The multi-directional heat dissipation of ceramic heat sinks accelerates heat dissipation;
  4. Ceramic heat sink insulation, high thermal conductivity, high voltage resistance, high temperature resistance, wear resistance, high strength, oxidation resistance, acid and alkali resistance, long service life, low thermal expansion coefficient, ensuring high and low temperature environments or other harsh environments The stability of the ceramic heat sink;
  5. Ceramic heat sinks are effective against interference (EMI) and antistatic;
  6. Ceramic heat sinks are made of natural organic materials, which meet environmental protection requirements;
  7. The ceramic heat sink is small in size, light in weight, high in strength, saves space, saves materials, saves freight, and is more conducive to the rational layout of product design;
  8. The ceramic heat sink can withstand high current, high voltage, anti-leakage breakdown, no noise, and no coupling parasitic capacitance with MOS and other power tubes, thus simplifying the filtering process; the required creepage distance is higher than that of metal bodies The requirement is short, which further saves board space and is more conducive to engineers’ design and electrical certification.

Introduction to the application fields of ceramic heat sinks

  1. Ceramic heat sinks are mainly used in high-power equipment, IC MOS tubes, IGBT chip thermal insulation, high-frequency power supplies, communications, mechanical equipment, high current, high voltage, high temperature and other product components that require thermal conduction and thermal insulation.
  2. LED lighting, high-frequency welding machine, power amplifier/audio, power transistor, power module, chip IC, inverter, network/broadband, UPS power supply, high-power equipment, etc.

Thermal solution for power adapter

Power adapter is a power supply conversion device for small portable electronic equipment and electronic appliances. The power adapter is generally composed of a shell, a power transformer and a rectifier circuit. According to its output type, it can be divided into AC output type and DC output type; according to the connection method, it can be divided into wall type and desktop type. Power adapters are widely used in industrial automation control, military equipment, scientific research equipment, LED lighting, industrial control equipment, communication equipment, power equipment, instrumentation and other fields.

Since a large number of high-power semiconductor devices are used in the power adapter, such as rectifier bridge stacks, high-current rectifier tubes, high-power triodes or field effect transistors and other devices, they will generate a lot of heat when they work. Once the power supply temperature exceeds 75 ℃ or more, If the heat cannot be discharged in time and kept at a reasonable level, the normal operation of the power adapter will be affected, and the power adapter will be damaged in severe cases. Usually, power adapter manufacturers will use some thermally conductive insulating materials to help the power supply to dissipate heat during design and production. What are the thermally conductive insulating materials commonly used in power adapter cooling solutions?

Thermally conductive potting compound

Thermal adhesive potting is divided into partial potting and overall potting. The interior of the power adapter is uneven and irregular. What is needed is a thermal conductive material that can completely wrap the transformer and cannot be moved at will. Partial potting is generally concentrated in the case where the heat generation is large and cannot be replaced by other thermally conductive materials. The overall potting is because some power supplies have to work outdoors for a long time. In addition to solving the problem of heat dissipation, the waterproof and sealing of the power supply should also be considered, so the outdoor power supply basically adopts the overall potting for heat dissipation.

 potting compound

Thermally conductive silicone sheet

For the power supply industry, the proportion of thermally conductive silicone sheets is usually small, but sometimes it is indispensable. Usually, the application of thermally conductive silicone sheets for power adapters is mainly concentrated on the PCB board. A special application and demand must be There will be a special supply to meet it. The thermal conductive silicone sheet is applied on the PCB board, which has many functions such as high thermal conductivity, electrical insulation, shock resistance and puncture resistance, and can effectively solve the safety problem for the client.

thermal pad
thermal pad

One-component thermally conductive gel

One-component gel is usually used for local heat conduction of power components, and at the same time can play the role of fixing components, and has good adhesion and sealing for both metal and non-metal.

thermal conductive gel
thermal conductive gel

Thermally conductive silicone film

Generally used in power MOS tube packaging, conventional standard parts TO-220, TO-3P, etc., usually apply a layer of silicone grease on the silicon film and MOS tube to increase the fit and reduce the thermal resistance.

Thermally conductive silicone film

Alumina ceramics

Whether it is thermal conductivity, temperature resistance range or insulation performance, it is far superior to thermal conductive silicone cloth. It can be used to replace the position of silicone rubber in MOS tubes. There are standard parts for TO-220 and TO-3P series, which need to be increased by applying silicone grease. Contact area with MOS tube.

Alumina ceramics

What Does Thermal Ceramics Make?

Many people believe that ceramic substrates are the future trend of the electronics industry, and this trend is irreversible – this is mainly due to the fact that ceramic substrates can solve the increasingly serious heat dissipation problems of electronic packaging compared to other substrate materials, Therefore it is valued.

At present, ceramic substrate materials mainly include alumina, beryllium oxide and aluminum nitride, of which alumina ceramics are the most mature type, and are widely used for their good thermal shock resistance and electrical insulation properties, as well as mature manufacturing and processing technology. widely used.

Alumina ceramics
Alumina Ceramics

However, it should be noted that “widely used” is not the same as “lower-end application”, and the two are often easily confused. In fact, although ceramic substrates have been maturely used in LED high-power lighting, high-power modules, refrigeration chips, automotive electronics and other fields, due to the difficulty of production and few production enterprises, product prices have been high, and the market is highly dependent on external high.

Take the alumina substrate as an example, it can be divided into different models such as 75 porcelain, 85 porcelain, 95 porcelain and 99 porcelain according to the purity. The biggest feature is low dielectric loss, little relationship between electrical properties and temperature, high mechanical strength, good chemical stability – and with the increase of alumina content, the above advantages will be further amplified, so 99.5%, or even The market for 99.9% alumina ceramic substrates is considerable. However, it is not easy to do high-purity alumina substrates well. Elastic modulus, elastic deformation cycle times, service life and reliability are all indispensable. Therefore, there are not many companies that have the ability to do well.

Performance comparison of alumina substrates with different purities

Mmaterial99.9% Al2O399.5% Al2O396% Al2O3
Density (g/cm3)3.93.93.8
Bending strength (MPa)660440300
Thermal conductivity (W/m・K)333223
Relative permittivity (25℃ 1MHz)9.6
Relative dielectric constant (25℃ 10GHz)109.9
Dielectric loss (25℃ 1MHz)2*10-4
Dielectric loss (25℃ 10GHz)1*10-41*10-4
Volume resistance (Ω・cm)101510151014

The Magical Use of High Purity Alumina Substrate

When it comes to the application of alumina substrates, we have to mention high-frequency circuit substrates. In recent years, the electronic communication market dominated by 5G communication is developing rapidly, product technology is constantly innovating, and the requirements for high-frequency and high-speed signals on materials are also increasing. In terms of material selection, high-purity alumina ceramics are the first choice because they can well meet the characteristics of high-frequency signals (high-frequency: above 300MHZ, that is, the short-wave frequency range with a wavelength of more than 1 meter).

Alumina ceramics

Why do you say that? This is because as high frequency signals (which are constantly shifting between positive and negative phases) pass through the dielectric layer, the molecules in the dielectric try to orientate according to these electromagnetic signals, although in reality, since these molecules are cross-linked, they cannot really be Orientation. However, the change of frequency makes the molecules move continuously, generating a lot of heat, resulting in the loss of energy, which is also called “dielectric loss”. The dielectric loss of high-purity alumina ceramics is in a wide frequency range (including ultra-high frequency), and the loss value is small, and it does not change much with the increase of temperature, and has good thermal conductivity, strength and insulation. It is very suitable for use in high frequency bands.

In addition, substrates for optical communication devices, relay substrates and circuit substrates for other communication devices are also the advantageous application areas of high-purity alumina ceramics.

Preparation of alumina substrate

At present, the preparation process of alumina substrate can be divided into the following steps: raw material selection, mixing and crushing, defoaming, substrate forming, punching, sintering, cutting processing, finishing, and inspection.

Needless to say, the importance of raw material selection, in addition, the molding and sintering process is also a key factor in determining success or failure. In terms of molding technology, injection molding, dry pressing molding and tape casting are commonly used. However, although the injection molding efficiency is high, it is difficult to make large-sized sheets; dry pressing products have high density, and the flatness of the substrate is easy to ensure, but the production efficiency is low , high cost, and it is difficult to prepare ultra-thin substrates; tape casting has the dual advantages of high production efficiency and ultra-thinness, but due to the low density of the green body, it is easy to deform during sintering. Therefore, in order to improve the quality rate of large-sized substrates, the industry is currently focusing on the optimization of sintering methods and the selection of sintering aids.

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