PCB board classification and parameter explanation

PCB board classification and parameter explanation

PCB circuit board sheet introduction: According to the brand quality level from low to high, PCB substrates are divided as follows: 94HB-94VO-CEM-1-CEM-3-FR-4. ONESEINE TECHNOLOGY CO.LTD supplies all these substrate materials for different PCB projects, helping customers select proper sheets according to product working conditions and budget.

The detailed parameters and uses are as follows:

94HB: Ordinary cardboard, non-flame retardant. It is the lowest grade material. It is produced by die punching and cannot be used for power boards.

94V0: Flame retardant cardboard, also processed by die punching.

22F: Single-sided semi-fiberglass board, suitable for simple single layer circuits with die punching processing.

CEM-1: Single-sided fiberglass board. It must be drilled by CNC machine instead of die punching.

CEM-3: Double-sided semi-fiberglass board, the entry-level material for double-sided boards. Simple double-sided PCB can adopt this material. Its cost is 5~10 yuan per square meter cheaper than FR-4.

FR-4: Double-sided full fiberglass board, the most widely used substrate in PCB manufacturing.

The classification of flame retardant properties can be divided into 94V0－V-1 －V-2 －94HB. Different flame retardant grades meet different safety requirements for electronic products.

Semi-cured sheets (prepreg): 1080=0.0712mm, 2116=0.1143mm, 7628=0.1778mm. Prepreg acts as bonding dielectric for multilayer PCB lamination.

FR4 and CEM-3 are two common sheet types. FR4 is full fiberglass board, while CEM3 belongs to composite substrate.

Halogen-free refers to substrates that do not contain halogen elements such as bromine, fluorine and iodine. Bromine-containing materials will release toxic gas when burning, so halogen-free PCB is required for many environmentally friendly export products.

Tg is the glass transition temperature, which can be simply understood as the material’s softening temperature point.

The circuit board must have flame resistance. It will not burn under specific temperature and only turn soft. This critical temperature point is called the glass transition temperature (Tg point). This value directly affects the dimensional stability of PCB board during high temperature processing and operation.

What is high Tg? Let’s learn about high Tg printed circuit board and its advantages.

High Tg printed circuit board means when the temperature rises to a certain threshold, the substrate will change from glass state to rubber state. This critical temperature is defined as the glass transition temperature (Tg) of the board. In other words, Tg represents the maximum temperature at which the substrate can keep rigid. Ordinary PCB substrate will soften, deform and melt under continuous high temperature. Its mechanical and electrical performance will drop sharply, shortening the service life of electronic products. In general, regular Tg sheet is above 130℃, medium Tg is about more than 150℃, and high Tg PCB is defined as substrate with Tg ≥170℃. When the Tg value of the substrate increases, the PCB’s heat resistance, moisture resistance, chemical resistance and dimensional stability will be greatly improved. The higher the TG value, the better temperature resistance of the sheet. High Tg material is widely used especially in lead-free soldering process for its outstanding high heat resistance.

With the rapid development of the electronics industry, electronic products including computers are developing toward high functionality and multilayer design, which puts forward higher heat resistance requirements for PCB substrate materials. The popularization of high-density mounting technology like SMT makes PCBs rely heavily on substrate heat resistance when producing boards with small apertures, fine traces and thin thickness.

Therefore, there are obvious differences between general FR-4 and high Tg FR-4. At the same temperature, especially after moisture absorption and heating, the two materials show different performance in mechanical strength, dimensional stability, adhesion, water absorption, thermal decomposition and thermal expansion. High Tg PCB material performs much better than ordinary substrate. ONESEINE TECHNOLOGY CO.LTD can produce ordinary FR4 and high Tg FR4 circuit boards according to customers’ technical requirements.

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