Knowledge of PCB Material Types

 PCB materials are classified by brand and quality level from lowest to highest as follows: 94HB － 94V0 － 22F － CEM-1 － CEM-3 － FR-4.Detailed parameters and applications are as follows:

  • 94HB: Ordinary paper-based board, non-flame retardant (the lowest-grade material). It can be die-punched and cannot be used for power supply boards.
  • 94V0: Flame-retardant paper-based board (can be die-punched).
  • 22F: Single-sided semi-glass fiber board (can be die-punched).
  • CEM-1: Single-sided glass fiber board (must be computer-drilled, cannot be die-punched).
  • CEM-3: Double-sided semi-glass fiber board (the lowest-grade material for double-sided boards except double-sided paper-based boards). It can be used for simple double-sided boards and is 5~10 yuan per square meter cheaper than FR-4.
  • FR-4: Double-sided glass fiber board. Its flame-retardant grades are divided into four categories: 94V0 － V-1 － V-2 － 94HB.
  • Prepreg: 1080 = 0.0712mm, 2116 = 0.1143mm, 7628 = 0.1778mm.
  • Both FR4 and CEM-3 refer to board materials. FR4 is a glass fiber board, and CEM-3 is a composite substrate.
  • Halogen-free: Refers to substrates that do not contain halogens (such as fluorine, bromine, iodine). Bromine produces toxic gases when burned, so halogen-free materials meet environmental protection requirements.
  • Tg (Glass Transition Temperature): The temperature at which the circuit board softens instead of burning when heated. It is the temperature at which the substrate transitions from a “glass state” to a “rubber state” and is related to the dimensional durability of the PCB.

What is High Tg? PCB Circuit Boards and Advantages of Using High Tg PCBs


For high Tg printed circuit boards, when the temperature rises to a certain threshold, the substrate transitions from a “glass state” to a “rubber state” — this temperature is the glass transition temperature (Tg) of the board. In other words, Tg is the maximum temperature (℃) at which the substrate maintains rigidity. Ordinary PCB substrate materials will soften, deform, melt, etc., at high temperatures, and their mechanical and electrical properties will drop sharply, affecting product service life. Generally, substrates with a Tg above 130℃ are considered common Tg, those above 150℃ are medium Tg, and those above 170℃ are high Tg. Usually, PCBs with Tg ≥ 170℃ are called high Tg printed circuit boards.

Improving the Tg of the substrate enhances the PCB’s heat resistance, moisture resistance, chemical resistance, and stability. A higher Tg value means better temperature resistance of the board, which is widely used in lead-free processes. With the rapid development of the electronics industry, especially electronic products represented by computers moving towards high functionality and high multilayerization, PCB substrate materials require higher heat resistance. The emergence and development of high-density mounting technologies such as SMT and CMT make PCBs increasingly dependent on the high heat resistance of substrates in terms of small apertures, fine wiring, and thinness.
The difference between ordinary FR-4 and high Tg lies in their performance under high temperatures, especially when heated after moisture absorption. High Tg products are significantly superior to ordinary PCB substrates in terms of mechanical strength, dimensional stability, adhesion, water absorption, thermal decomposition, and thermal expansion.

PCB Board Material Knowledge and Standards


Currently, the commonly used copper-clad laminates in China have the following types and characteristics: Copper-clad laminates can be classified in multiple ways.

Classification by Reinforcement Material


They are divided into five categories: paper-based, glass fiber cloth-based, composite-based (CEM series), build-up multilayer board-based, and special material-based (ceramic, metal core-based, etc.).

Classification by Resin Adhesive

  • Common paper-based CCLs include phenolic resin (XPc, XxxPC, FR-1, FR-2, etc.), epoxy resin (FE-3), polyester resin, etc.
  • Common glass fiber cloth-based CCLs include epoxy resin (FR-4, FR-5), which is currently the most widely used glass fiber cloth-based type.
  • Other special resins (with glass fiber cloth, polyamide fiber, non-woven fabric, etc. as reinforcement materials) include bismaleimide-modified triazine resin (BT), polyimide resin (PI), polyphenylene ether resin (PPO), maleic anhydride imide-styrene resin (MS), cyanate ester resin, polyolefin resin, etc.

Classification by Flame Retardancy


They are divided into flame-retardant type (UL94-V0, UL94-V1 grades) and non-flame-retardant type (UL94-HB grade). In recent years, with increasing attention to environmental protection, a new type of halogen-free flame-retardant CCL has been developed, known as “green flame-retardant CCL”.

Classification by Performance


They are divided into general-performance CCL, low dielectric constant CCL, high heat resistance CCL (generally with Tg above 150℃), low thermal expansion coefficient CCL (generally used for packaging substrates), etc. With the development of electronic technology, new requirements are constantly put forward for printed circuit board substrate materials, promoting the continuous development of copper-clad laminate standards.

Current Main Standards for Substrate Materials


① National Standards: China’s national standards for substrate materials include GB/T4721–47221992 and GB4723–4725–1992. Taiwan China’s copper-clad laminate standard is the CNS standard, formulated based on Japan’s JIS standard and released in 1983.② International Standards: Japan’s JIS standard, the United States’ ASTM, NEMA, MIL, IPC, ANSI, UL standards, the United Kingdom’s BS standard, Germany’s DIN, VDE standards, France’s NFC, UTE standards, Canada’s CSA standard, Australia’s AS standard, the former Soviet Union’s GOST standard, and the international IEC standard, etc.

Common and Frequently Used Suppliers of PCB Design Materials


Common and frequently used suppliers include: Unimicron, Kingboard, Tenco, Shengyi, etc.

Acceptable Files


Protel99, PowerPCB/PADS, Allegro, P-CAD2004, AutoCAD, Gerber, or physical board cloning, etc.

Board Material Types


CEM-1, CEM-3, FR4, high Tg materials.

Maximum Board Size


600mm700mm (24000mil27500mil)

Processed Board Thickness


0.2mm-4.0mm (8mil-157.5mil)

Maximum Processing Layers


32 Layers

Copper Foil Thickness


1/3oz — 4oz

Finished Board Thickness Tolerance


±0.1mm (4mil) for boards thinner than 1.0mm; ±10% for boards thicker than 1.0mm.

Forming Dimension Tolerance


Computer milling: 0.15mm (6mil); Die punching: 0.10mm (4mil)

Minimum Line Width/Space


0.075mm (3mil); Line width control capability: ＜±20％

Minimum Finished Drilled Hole Diameter


0.1mm (4mil)

Minimum Finished Punched Hole Diameter


0.9mm (35mil)

Finished Hole Diameter Tolerance


PTH: ±0.075mm (3mil); NPTH: ±0.05mm (2mil)

Finished Hole Wall Copper Thickness


18–25um (0.71–0.99mil)

Minimum SMT Placement Pitch


0.15mm (6mil)

Surface Finish


Electroless Nickel Immersion Gold (ENIG), Hot Air Solder Leveling (HASL), Entire Board Nickel-Gold Plating (Water/Soft Gold), OSP (Organic Solderability Preservative), Silk Screen Solder Mask, Carbon Ink, etc.

Solder Mask Thickness on Board


10–30μm (0.4–1.2mil)

Peel Strength

  1. 5N/mm (59N/mil)

If you want to know more about PCB knowledge, please contact Sandy at sales9@hitechpcb.com

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