Technology Used in Ceramic PCBs Production
Ceramic substrate refers to a special process board where copper foil is directly bonded to the surface (single side or double side) of alumina (Al2O3) or aluminum nitride (AlN) ceramic substrate at high temperature. The produced ultra-thin composite substrate has excellent electrical insulation properties, high thermal conductivity, excellent solderability and high adhesion strength, and can etch various patterns like a PCB board, with a large current carrying capacity ability. Therefore, the ceramic substrate has become the basic material of high-power power electronic circuit structure technology and interconnection technology. It is widely used in many fields. So, in what fields are ceramic PCBs specifically used?
- High-power power semiconductor module, semiconductor refrigerator, electronic heater, power control circuit, power mixing circuit.
- Intelligent power components, high frequency switching power supply, solid state relay.
- Automotive electronics, and military electronic components.
- Solar panel components, special telecommunications exchanges, receiving systems, lasers and other industrial electronics.
Advantages and disadvantages of ceramic PCBs
- The first is the material, the traditional PCB substrate is mostly epoxy plastic. Due to its relatively good economy, it still occupies a dominant position in the entire electronic market so far. However, many special fields such as high temperature, corrosive environment, and high vibration frequency are not suitable.
- Ceramic materials are very suitable for use in electronic fields due to their advantages of high thermal conductivity, good chemical stability, high thermal stability and high melting point.
- Good thermal cycling performance, with 50,000 cycles and high reliability.
- Like PCB board (or IMS substrate), various patterns can be etched; no pollution and no pollution.
- The use temperature is wide -55℃～850℃. The coefficient of thermal expansion is close to silicon, simplifying the production process of the power module.
- The advantages of ceramic circuit boards also retain the characteristics of their materials, and unlike traditional PCBs need to use an insulating medium as an insulating layer. The ceramic itself is an insulating layer. At the same time, it also has a high frequency and a low dielectric constant, because its manufacturing process is easier in light, thin, and miniaturized.
- Raw materials are more expensive than traditional PCBs, and the cost is higher.
- The manufacturing area is small, and it is difficult to produce on a large area. High-end products are often used, and low-end products are not used.
- The processing difficulty is also relatively large because of the high hardness and density.
- It is easier to break during processing. In addition, because of the low toughness and brittleness of ceramic materials, the scrap rate in each process is relatively high.
- The final surface metallization is also a high cost of early equipment.
However, as an emerging product, ceramic PCBs are very suitable for the development of this intelligent era, and its shortcomings are constantly improving. A batch of new ceramic materials such as alumina ceramics were manufactured. This increases its toughness and reduces brittleness. At the same time, production technology is constantly improving, reducing costs.
- Drilling: Mechanical drilling holes are used to form connecting pipes between metal layers.
- Plated-through hole: After drilling the copper wire between the connecting layers, the circuit between the layers is not opened. Therefore, a conductive layer must be formed on the hole wall to connect the wires. This process is commonly referred to as “PTH” in industry. The technological process mainly includes 3 procedures: Desmear, chemical copper and electroplated copper.
- Dry film pressing: making photosensitive etched photosensitive layer.
- Layer image transfer: Use exposure to transfer the film image to the surface of the circuit board.
- Outer layer exposure: After the photosensitive film is attached, the circuit board is similar to the inner layer of the production process, exposed again and developed. The main function of this photographic film is to determine the area that needs to be electroplated. Electroplating is not required. The area we cover is the area that does not require electroplating.
- Magnetron sputtering: The energy and momentum between the positive ions generated and the atoms on the surface of the target during the gas glow discharge process. They will be exchanged and used to move the material from the source material to the substrate for thin film deposition.
- Etching-The formation of external lines: A technique that uses chemical reactions or physical impact to remove material. The function of etching is reflected in the selective removal of specific patterns.
- Solder-proof coating: The purpose of the ceramic circuit board is to carry electronic components and achieve the purpose of connection. Therefore, after completing the circuit of the circuit board, the area where the electronic components are assembled must be defined. And polymer materials should be used to properly protect non-assembled areas. Due to the assembly and soldering of electronic components, the polymer material that partially protects the circuit board is called “solder paint”. Most current photosensitive solder resists are wet ink coatings.
After the circuit is completed, the circuit board will be fed into the stripping and etching. The main job is to completely strip the plating resist and expose the copper to be etched to the etching solution. Since the top of the wiring area is already protected by tin, an alkaline etching solution is used to etch copper. However, since the wiring has been protected by tin, the wiring of the wiring area can be maintained, so that the wiring of the wiring area provides the entire wiring board.