ceramic pcb



Common ceramic PCB : Advantages, Uses and Trends, etc
Ceramic PCB substrate refers to a special process board with copper foil directly bonded to the surface (single or double sides) of alumina (Al2O3) or aluminum nitride (AlN) ceramic PCB substrate at high temperature. The manufactured ultra-thin composite substrate has excellent electrical insulation, high thermal conductivity, excellent solderability and high adhesion strength, and can etch various patterns, so it has great current carrying capacity. Therefore, ceramic PCB substrate has become the basic material of high-power power electronic circuit structure technology and interconnection technology.

The advent of ceramic PCB substrate products has started the new development of heat dissipation application industry. Because of the heat dissipation characteristics of ceramic PCB substrate, and the advantages of ceramic PCB substrate such as high heat dissipation, low thermal resistance, long life and voltage resistance, with the improvement of production technology and equipment, the product price has been accelerated and rationalized, thus expanding the application fields of LED industry, such as indicator lights of household appliances, car lights, street lamps and outdoor large billboards. The successful development of ceramic PCB substrate provides better service for indoor lighting and outdoor lighting products, and makes the LED industry have a broader market in the future.

Characteristic of ceramic PCB
◆ Strong mechanical stress and stable shape; High strength, high thermal conductivity and high insulation; Strong binding force and corrosion resistance.
◆ Good thermal cycle performance with 50,000 cycles and high reliability.
◆ The same structure as PCB board (or IMS substrate) can etch various patterns; Pollution-free and pollution-free.
◆ The operating temperature is-55℃ ~ 850℃; The thermal expansion coefficient is close to silicon, which simplifies the production process of power module.
Advantage of ceramic PCB
◆ The thermal expansion coefficient of ceramic PCB substrate is close to that of silicon chip, which can save Mo slice of transition layer, save labor, material and reduce cost;
◆ Reduce welding layer, thermal resistance, voids and yield;
◆ Under the same current carrying capacity, the line width of 0.3mm thick copper foil in ceramic PCB is only 10% of that of ordinary printed circuit boards;
◆ Excellent thermal conductivity makes the package of the chip very compact, thus greatly increasing the power density and improving the reliability of the system and device;
◆ Ultra-thin (0.25mm) ceramic PCB substrate can replace BeO without environmental toxicity;
◆ The current carrying capacity is large, and the current of 100A continuously passes through a copper body with a width of 1mm and a thickness of 0.3mm, and the temperature rises by about 17℃; A current of 100A continuously passes through a copper body 2mm wide and 0.3mm thick, and the temperature rise is only about 5℃.
◆ Low thermal resistance. The thermal resistance of 10×10mm ceramic PCB substrate is 0.31K/W for 0.63mm ceramic PCB substrate, 0.19K/W for 0.38mm ceramic PCB substrate and 0.14K/W for 0.25mm ceramic PCB substrate.
◆ High insulation and withstand voltage, ensuring personal safety and protection ability of equipment.
◆ New packaging and assembly methods can be realized, which can make the products highly integrated and reduce the volume.
Performance requirement of ceramic PCB
(1) Mechanical properties
With high enough mechanical strength, ceramic PCB can also be used as a supporting member in addition to carrying components; Good processability and high dimensional accuracy; Easy to realize multilayer; Smooth surface, no warping, bending, microcracks, etc.

(2) Electrical properties
High insulation resistance and insulation breakdown voltage; Low dielectric constant; Low dielectric loss; Stable performance under the condition of high temperature and high humidity, ceramic PCB ensures reliability.

(3) Thermal properties
High thermal conductivity; The thermal expansion coefficient is matched with the related materials (especially with the thermal expansion coefficient of Si); Excellent heat resistance.

(4) Other properties.
Good chemical stability; Easy metallization, strong adhesion between circuit patterns and them; No hygroscopicity; Oil and chemical resistance; ɑ the amount of radiation emitted is small; The adopted substances are pollution-free and non-toxic; The crystal structure does not change within the use temperature range; Rich raw materials; Mature technology; Easy to manufacture; Low price.

Use way of ceramic PCB
◆ High-power power semiconductor module; Semiconductor refrigerator, electronic heater; RF power control circuit, power hybrid circuit.
◆ Intelligent power components; High frequency switching power supply, solid state relay.
◆ Automotive electronics, aerospace and military electronic components.
◆ Solar panel assembly; Telecommunications private exchange, receiving system; Laser and other industrial electronics.

Species of ceramic PCB divided by material
1. Alumina ceramic PCB
Alumina ceramic PCB substrate is the most commonly used substrate material in electronic industry, because of its high strength and chemical stability compared with most other oxide ceramics in mechanical, thermal and electrical properties, and abundant raw materials, it is suitable for various technical manufacturing and different shapes. The alumina substrate can be customized in three dimensions.

2. Beryllium oxide ceramic PCB
Its thermal conductivity is higher than that of aluminum, so it can be used in occasions where high thermal conductivity is needed, but it decreases rapidly when the temperature exceeds 300℃. The most important thing is that its toxicity limits its own development.
Beryllium oxide ceramics are ceramics with beryllium oxide as the main component. It is mainly used as large-scale integrated circuit substrate, high-power gas laser tube, heat sink shell of transistor, microwave output window and neutron moderator.

3. Aluminum nitride ceramic PCB
AlN has two very important properties worth noting: one is high thermal conductivity, and the other is the expansion coefficient matching with Si. The disadvantage is that even if there is a very thin oxide layer on the surface, it will affect the thermal conductivity. Only by strictly controlling the materials and processes can AlN substrates with good consistency be manufactured. There are few AlN production technologies in China that can be produced on a large scale like Sliton, and the price of AlN is relatively high compared with Al2O3, which is also a small bottleneck restricting its development. However, with the improvement of economy and technology, this bottleneck will eventually disappear.
From the above reasons, it can be known that alumina ceramics are widely used because of their superior comprehensive performance, and they are still in a dominant position in microelectronics, power electronics, hybrid microelectronics, power modules and other fields.
AlN can be stabilized up to 2200℃. The strength is high at room temperature, and the strength decreases slowly with the increase of temperature. Good thermal conductivity, small thermal expansion coefficient, and is a good thermal shock-resistant material. With strong resistance to molten metal erosion, it is an ideal crucible material for melting and casting pure iron, aluminum or aluminum alloy. Aluminum nitride is also an electrical insulator with good dielectric properties, and it is also promising to be used as an electrical component. The aluminum nitride coating on the surface of gallium arsenide can protect it from ion implantation during annealing. It is also a catalyst for converting aluminum nitride from hexagonal boron nitride to cubic boron nitride. It reacts slowly with water at room temperature. It can be synthesized from aluminum powder at 800~1000℃ in ammonia or nitrogen atmosphere. The product is white to gray powder blue. Or synthesized by reaction of Al2O3-C-N2 system at 1600~1750℃, and the product is off-white powder. Or aluminum chloride and ammonia are prepared by gas phase reaction. The coating can be synthesized from AlCl3-NH3 system by gas phase deposition.

4. Silicon nitride ceramic PCB
Rogers Company introduced the new curamik® series silicon nitride (Si3N4) ceramic PCB substrate in 2012. As the mechanical strength of silicon nitride is higher than that of other ceramics, the new curamik® substrate can help designers achieve a long life in harsh working environment and HEV/EV and other renewable energy applications.
The flexural strength of the new ceramic PCB 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.
Up to now, the reliability of copper-clad ceramic PCB substrate used in power modules has been limited by the low flexural strength of ceramics, which will reduce the thermal cycle capability. For those applications that combine extreme thermal and mechanical stress, such as hybrid vehicles and electric vehicles (HEV/EV), the commonly used ceramic PCB substrate is not the best choice. The thermal expansion coefficients of the substrate (ceramic PCB) and the conductor (copper) are very different, which will exert pressure on the bonding area during the thermal cycle, thus reducing the reliability. This curamik® series silicon nitride (Si3N4) ceramic PCB substrate introduced by Rogers Company at this year's PCIM exhibition will prolong the life of power electronic modules by 10 times.

With the growth of HEV/EV and renewable energy applications, designers have found new ways to ensure the reliability of these electronic components needed to promote the development of challenging new technologies. Since the service life is 10 times or more longer than that of other ceramics used in power electronics, the silicon nitride substrate can provide mechanical strength which is essential to meet the necessary reliability requirements. The life of the ceramic PCB substrate is measured by the number of thermal cycles that the substrate can bear without peeling and other faults that affect the circuit function and safety. This test is usually done by circulating the sample from-55 C to 125°C or 150 C.
Manfred Goetz, Curamik product marketing manager, said, "Our current test results (-55 C to 150°C) show that the service life of Curamik silicon nitride substrate is more than ten times longer than that of the substrate commonly used in automobile market, especially HEV/EV. Similarly, the life of the whole module is greatly improved by using the silicon nitride substrate. "
The extension of service life is very important for all power module applications where large semiconductor wafers are directly bonded to the substrate, especially for SiC and GaN wafers with high junction temperature (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 enables us to use thinner ceramic PCB layer, thus reducing thermal resistance, increasing power density and cutting system cost.
Compared with Al2O3 and AlN substrates, its flexural strength is much improved, which will benefit designers. The fracture toughness of silicon nitride is even higher than that of zirconia doped ceramics, reaching 6.5~7 MPa/√m at the thermal conductivity of 90 W/MK.
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