Ceramic substrate refers to a special process plate in which at a very high temperature copper foil is directly bonded to the surface(single sided or double sided) of Al2O3 or AlN ceramic substrate. The ultra-thin composite substrate made has excellent electrical insulation properties, high thermal conductivity, excellent solderability and high adhesion strength, and can be etched into various patterns like a PCB board, and has a large current carrying ability. Therefore, ceramic substrates have become the basic material for high-power power electronic circuit structure technology and interconnection technology.
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Ceramic substrate brings the new development of heat dissipation application industry. Due to the characteristic of its heat dissipation and advantage of high heat dissipation, low heat resistance, long using time and withstand voltage, with technique improvement and equipment improvement and accelerated rationalization of product price, application area in LED industry is enlarged, such as indicator light of household product, automobile lamp, street lamp and outdoor large billboard etc.. The successful development of ceramic substrates provides better services for indoor lighting and outdoor lighting products, and expands the future market areas of the LED industry.
- Strong mechanical stress, stable shape; high strength, high thermal conductivity, high insulation; strong bonding force, anti-corrosion.
- Good thermal cycle performance, with up to 50,000 cycles, high reliability
- Can do graphic etching on it, that is same as PCB plate or (IMS substrate), no pollution and no harmful
- Usage temperature:-55℃-850℃; the thermal expansion coefficient is close to silicon, simplifies the production process of power module
Ⅰ.Divide by material
- Aluminium oxide (Al2O3)
Al2O3 substrate is the most common basic material in electric industry. In the matter of mechanical, thermal and electric performance, comparing with the most other oxide ceramics, Al2O3 substrate has high strength and chemical stability, and because its raw material source is abundant, can be used for various technical manufacture and can be made as different shapes. Some productions of Al2O3 substrates can accept three-dimensional customized.
2. Beryllium oxide (BeO)
It has higher thermal conductivity than aluminium, and is used in applications requiring high thermal conductivity. But when the temperature is more than 300℃, thermal conductivity decreases rapidly. The most important is that its toxicity limits its development.
The main component of beryllium oxide ceramics is BeO. Mainly it is used for large scale integrated electrical substrate, big power gas laser tube, radiator housing of the transistor, microwave output window and neutron moderator etc..
Pure BeO belongs to cubic crystal system. Its density is 3.03g/cm3, and melting point is 2570℃. It has high thermal conductivity, almost equal to copper and pure aluminium. Thermal conductivity coefficient λ is 200-250W/(m.K). Besides, it has good thermal shock resistance, its dielectric constant is 6～7（0.1MHz). The tangent value of medium loss angle is about 4×10-4(0.1GHz). High toxic of powder is the biggest disadvantage, that makes contact wounds difficult to heal. It is made of beryllium oxide powder with alumina and other ingredients by high temperature sintering. Good protection measures are needed for producing the ceramics. The volatility of beryllium oxide is increased in high temperature media containing water vapor. Volatilization begins at 1000℃, and the amount of volatilization increases with the increase of temperature, which brings difficulties to production. Some countries no longer produce it. But the production performance is excellent, although the price is higher, there is still a big required quantity.
3. Aluminium nitride(AlN)
For AIN we need to pay attention to the two important performances: one is high thermal conductivity coefficient, other one is the coefficient of expansion matching Si. Its disadvantage is that even a very thin oxide layer on the surface will have an effect on thermal conductivity coefficient. Only by strictly controlling materials and process can produce good AIN substrates.
Considering the above reasons, we can know that aluminium oxide ceramics are widely used because of their superior comprehensive performance in the fields of microelectronics, power electronics, mixed microelectronics, power modules and etc..
4. Silicon nitride (Si3N4)
The flexural strength of the new ceramic substrate made of silicon nitride is higher than that of the substrate made of Al2O3 and AlN. The fracture toughness of Si3N4 even exceeds that of zirconia-doped ceramics. The extension of service life is critical for all power module applications where large semiconductor wafers are directly bonded to a substrate, and it is especially important for SiC and GaN wafers with higher junction temperatures (up to 250°C). The thermal conductivity of curamik® silicon nitride substrate is 90 W/mK, which exceeds the average value of other substrates on the market. The mechanical strength of the new substrate allows us to use a thinner ceramic layer, which reduces thermal resistance, increases power density, and reduces system costs. Compared with Al2O3 and AlN substrates, its flexural strength is much improved, and designers will benefit from this. The fracture toughness of silicon nitride even exceeds that of zirconia-doped ceramics, reaching 6.5-7 MPa/√m at a thermal conductivity of 90 W/mK.
Ⅱ. According to the manufacturing process
- HTCC (High-Temperature Co-fired Ceramic)
HTCC is also called high-temperature co-fired multilayer ceramics. The manufacturing process is very similar to LTCC. The main difference is that the ceramic powder of HTCC is not added to the glass material. Therefore, HTCC must be dried and hardened at a high temperature of 1300~1600℃. The green embryo is then drilled into via holes, and the holes are filled and printed with screen printing technology. Due to the high co-firing temperature, the choice of metal conductor materials is limited. The main material is high melting point but conductive Metals such as tungsten, molybdenum, manganese, etc., which have poor properties, are finally laminated and sintered.
- LTCC (Low-Temperature Co-fired Ceramic)
LTCC is also known as low-temperature co-fired multilayer ceramic substrate. This technology must first mix inorganic alumina powder and about 30%~50% glass material with an organic binder to make it evenly mixed into a mud-like slurry, and then Use a scraper to scrape the slurry into a sheet, and then through a drying process to form a thin green embryo, and then drill the via hole according to the design of each layer, as the signal transmission of each layer, the internal circuit of LTCC Screen printing technology is used to fill holes and print circuits on the green embryo. The inner and outer electrodes can be made of silver, copper, gold and other metals. Finally, each layer is laminated and placed at 850~900℃. Sintering and forming in the sintering furnace can be completed.
- DBC (Direct Bonded Copper)
The direct copper coating technology uses copper’s oxygen-containing eutectic solution to directly apply copper to the ceramic. The basic principle is to introduce an appropriate amount of oxygen between the copper and the ceramic before or during the bonding process, at 1065℃~1083 In the range of ℃, copper and oxygen form a Cu-O eutectic solution. DBC technology uses the eutectic solution to chemically react with the ceramic substrate to form CuAlO2 or CuAl2O4 phase, and on the other hand to infiltrate the copper foil to achieve the combination of the ceramic substrate and the copper plate.
◆The thermal expansion coefficient of the ceramic substrate is close to that of the silicon chip, which can save transition layer Mo slices, save labor, save materials and reduce costs;
◆Reduce welding layer, reduce thermal resistance, reduce voids, and improve yield;
◆The line width of 0.3mm thick copper foil is only 10% of the ordinary printed circuit board under the same current carrying capacity;
◆ Excellent thermal conductivity, so that the chip package is very compact, so that the power density is greatly increased, and the reliability of the system and the device is improved;
◆ Ultra-thin (0.25mm) ceramic substrate can replace BeO without environmental toxicity issues;
◆Large current carrying capacity, 100A current continuously passes through 1mm wide and 0.3mm thick copper body, and the temperature rise is about 17℃; 100A current continuously passes through 2mm wide and 0.3mm thick copper body, and the temperature rise is only about 5℃;
◆Low thermal resistance, the thermal resistance of a 10×10mm ceramic substrate is 0.31K/W for a 0.63mm thick ceramic substrate, the thermal resistance of a 0.38mm thick ceramic substrate is 0.19K/W, and the thermal resistance of a 0.25mm thick ceramic substrate The thermal resistance is 0.14K/W.
◆ High insulation withstand voltage to ensure personal safety and equipment protection.
◆ New packaging and assembly methods can be realized, so that the product is highly integrated and the size is reduced.
(1) Mechanical properties
It has high enough mechanical strength, in addition to carrying components, it can also be used as a supporting member; it has good processability and high dimensional accuracy; it is easy to realize multi-layering;
The surface is smooth, without warpage, bending, microcracks, etc.
(2) Electrical properties
High insulation resistance and insulation breakdown voltage;
Low dielectric constant;
Low dielectric loss;
Stable performance under high temperature and high humidity conditions to ensure reliability.
(3) Thermal properties
High thermal conductivity;
The thermal expansion coefficient is matched with related materials (especially the thermal expansion coefficient of Si should be matched);
Excellent heat resistance.
(4) Other properties
Good chemical stability; easy to metallize, strong adhesion to the circuit pattern;
No hygroscopicity; oil and chemical resistance; a-ray emission is small;
The materials used are pollution-free and non-toxic; the crystal structure does not change within the operating temperature range;
The raw materials are abundant; the technology is mature; the manufacturing is easy; the price is low.
◆ High-power power semiconductor modules; semiconductor refrigerators, electronic heaters; radio frequency power control circuits, power mixing circuits.
◆Intelligent power components; high-frequency switching power supplies, solid state relays.
◆Automotive electronics, aerospace and military electronic components.
◆Solar panel components; telecommunications dedicated exchanges, receiving systems; industrial electronics such as lasers.
The advent of ceramic substrate products has opened up the development of the heat dissipation application industry. Due to the heat dissipation characteristics of ceramic substrates, and the advantages of ceramic substrates such as high heat dissipation, low thermal resistance, long life, and withstand voltage, with the improvement of production technology and equipment, product prices have accelerated and rationalized , And then expand the application areas of the LED industry, such as indicator lights for home appliances, car lights, street lights and outdoor large signs. The successful development of ceramic substrates will provide services for indoor lighting and outdoor lighting products, and broaden the future market areas of the LED industry.