PCB circuit board sheet classification and detailed explanation
PCB board knowledge and standards
At present, there are several types of copper-clad plates that are widely used in China, and their characteristics are as follows: types of copper-clad plates, knowledge of copper-clad plates, and classification methods of copper-clad plates. Generally, according to the different reinforcement materials of the board, it can be divided into five categories: paper base, glass fiber cloth base, composite base (CEM series), laminated multilayer base and special material base (ceramic, metal core base, etc.). If it is classified according to the different resin adhesives used in the board, the common paper-based CCI. There are various types of phenolic resin (XPc, XxxPC, FR-1, FR-2, etc.), epoxy resin (FE-3), polyester resin and so on. Common glass fiber cloth base CCL has epoxy resin (FR-4, FR-5), it is currently the most widely used type of glass fiber cloth base. In addition, there are other special resins (using glass fiber cloth, polyamide fiber, non-woven fabric, etc. as additional materials): bismaleimide modified triazine resin (BT), polyimide resin (PI) , Diphenylene ether resin (PPO), maleic anhydride imide-styrene resin (MS), polycyanate resin, polyolefin resin, etc. According to the classification of CCL's flame retardant performance, it can be divided into two types of flame retardant type (UL94-VO, UL94-V1 level) and non-flame retardant type (UL94-HB level). In the past year or two, with more emphasis on environmental protection issues, a new type of CCL without bromine is classified in the flame retardant CCL, which can be called "green flame retardant cCL". With the rapid development of electronic product technology, there are higher performance requirements for cCL. Therefore, from the performance classification of CCL, it is divided into general performance CCL, low dielectric constant CCL, high heat resistance CCL (general board L is above 150 ℃), low thermal expansion coefficient CCL (generally used on packaging substrates ) And other types. With the development and continuous progress of electronic technology, new requirements are continuously put forward for printed board substrate materials, thereby promoting the continuous development of copper clad laminate standards.
At present, the main standards of substrate materials are as follows
① National standards: China ’s national standards on substrate materials are GB / T4721-47221992 and GB4723-4725-1992. The copper-clad laminate standard in Taiwan, China is the CNS standard, which was based on the Japanese JIs standard and was formulated in 1983. release.
② International standards: Japanese JIS standards, American ASTM, NEMA, MIL, IPc, ANSI, UL standards, British Bs standards, German DIN, VDE standards, French NFC, UTE standards, Canadian CSA standards, Australian AS standards, FOCT standards of the former Soviet Union, international IEC standards, etc .; PCB design materials suppliers, common and commonly used are: Shengyi \ Kingboard \ International and so on.
Introduction of PCB circuit board materials: according to the brand quality level from bottom to high is divided as follows: 94HB-94VO-CEM-1-CEM-3-FR-4
The detailed parameters and uses are as follows:
94HB: ordinary cardboard, not fireproof (the lowest grade material, die punching, can not be used as power board)
94V0: Flame retardant cardboard (die punching)
22F: Single-sided half-glass fiber board (die punching)
CEM-1: Single-sided fiberglass board (computer drilling is necessary, not die punching)
CEM-3: Double-sided semi-glass fiber board (except for double-sided cardboard, which belongs to the lowest end of the double-sided board. Simple double-sided board can use this material, which is 5 ~ 10 yuan / square meter cheaper than FR-4)
FR-4: Double-sided glass fiber board
1. The classification of flame retardant properties can be divided into four types: 94VO－V-1 －V-2 －94HB
2. Semi-cured tablets: 1080 = 0.0712mm, 2116 = 0.1143mm, 7628 = 0.1778mm
3. FR4 CEM-3 means sheet, fr4 is fiberglass board, cem3 is composite substrate
4. Halogen-free refers to substrates that do not contain halogens (e.g., fluorine, bromine, iodine, etc.), because bromine generates toxic gases when burned, which requires environmental protection.
5. Tg is the glass transition temperature, ie the melting point.
6. The circuit board must be flame resistant. It cannot be burnt at a certain temperature but can only be softened. The temperature point at this time is called the glass transition temperature (Tg point), and this value is related to the dimensional durability of the PCB board.
What is high Tg? The advantages of PCB circuit boards and the use of high Tg PCB:
When the temperature of a high Tg printed circuit board rises to a certain threshold, the substrate will change from "glass state" to "rubber state". The temperature at this time is called the glass transition temperature (Tg) of the board. That is, Tg is the maximum temperature (° C) at which the base material remains rigid. That is to say, ordinary PCB substrate materials continuously produce softening, deformation, melting and other phenomena at high temperatures, but also show a sharp decline in mechanical and electrical characteristics, which affects the service life of the product. The general Tg sheet is 130 Above ℃, high Tg is generally greater than 170 ℃, medium Tg is approximately greater than 150 ℃; usually PCB printed board with Tg ≥ 170 ℃ is called high Tg printed board; the Tg of the substrate is improved, the heat resistance of the printed board, Moisture resistance, chemical resistance, stability and other characteristics will be improved and improved. The higher the TG value, the better the temperature resistance of the sheet. Especially in the lead-free process, high Tg is more used; high Tg refers to high heat resistance. With the rapid development of the electronics industry, especially the electronic products represented by computers, the development of high functionality and high multilayer requires the higher heat resistance of PCB substrate materials as a premise. The emergence and development of high-density mounting technologies represented by SMT and CMT have made PCBs more and more inseparable from the support of high heat resistance of substrates in terms of small apertures, fine wiring, and thinness.
Therefore, the difference between general FR-4 and high Tg: at the same temperature, especially under the heat after moisture absorption, the mechanical strength, dimensional stability, adhesion, water absorption, thermal decomposition, thermal expansion, etc. of the material There are differences in this situation. High Tg products are obviously better than ordinary PCB substrate materials.