Generally, an important variety of rigid substrate materials is copper clad laminate. It is made of reinforced material (Reinforeing Material), impregnated with resin adhesive, dried, cut and laminated into blanks, then covered with copper foil, used steel plate as a mold, and processed by high temperature and high pressure forming in a hot press. The semi-cured sheet used in the general multilayer board is the semi-finished product of the copper clad laminate in the production process (mostly glass cloth impregnated with resin, dried and processed). In a rigid PCB, the substrate material is typically FR-4. However, in the Flex PCB, the commonly used substrate materials are polyimide (PI) film and PET (polyester) film, and besides these, polymer films such as PEN (polyethylene phthalate),PTFE, and aramid can be used.
 

Generally, according to the different reinforcing materials of the board, it can be divided into five categories: paper base, glass fiber cloth base, composite base (CEM series), laminated multilayer board base and special material base (ceramic, metal core base, etc.). If the board is classified according to the different resin adhesives used, the common paper-based CCI. There are: phenolic resin (XPc, XxxPC, FR 1, FR 2, etc.), epoxy resin (FE 3), polyester resin and other types. Common glass fiber cloth based CCL epoxy resin (FR 4, FR 5), it is currently the most widely used glass fiber cloth type. In addition, there are other special resins (glass fiber cloth, polyamide fiber, non-woven fabric, etc.): bismaleimide modified triazine resin (BT), polyimide resin (PI), diphenylene ether resin (PPO), maleic anhydride imide-styrene resin (MS), polycyanate ester resin, polyolefin resin, etc.
 

According to the flame retardant performance of CCL, it can be divided into flame retardant type (UL94 VO, UL94 V1 level) and non flame retardant type (UL94 HB level). In the past year or two, with more attention to environmental protection issues, a new type of CCL without bromine has been separated from 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 above 150 ℃), low thermal expansion coefficient CCL (generally used on package substrate) and other types.