FR4 Fiberglass Sheets Selection & Engineering Guide
Selecting an FR4 sheet means matching laminate grade, thickness, and dielectric performance to the electrical and mechanical duty of the part. As a thermoset glass-epoxy, FR4 is valued for stable insulation, good machinability, and a UL 94 V-0 flammability rating.
💡 Pro Tip: Seal Machined Edges Against Moisture Tracking
Machining exposes glass fibers at cut edges, which can wick moisture and lower surface resistivity over time. Dry machining with sharp tooling, followed by edge sealing, preserves dielectric integrity in high-voltage and humid service.
1. Choosing the Right Grade: FR4, G10, and High-Tg Variants
Standard FR4 (IEC 60893 EPGC202) adds brominated flame retardants to a G10 (EPGC201) glass-epoxy base to reach UL 94 V-0. For higher continuous service temperatures, high-Tg FR4 (Tg 170-180°C) or FR5 grades extend thermal headroom, while halogen-free formulations suit applications that restrict brominated additives.
2. How Well Does FR4 Insulate Electrically?
The glass-epoxy matrix is the workhorse dielectric for PCBs and electrical equipment. Key electrical metrics:
| Property |
Typical Value |
Why It Matters |
| Dielectric Strength |
~20 kV/mm |
Withstands high voltage without breakdown |
| Dielectric Constant (1 MHz) |
4.4 – 5.0 |
Stable impedance control for PCBs |
| Volume Resistivity |
up to 10¹⁶ Ω·cm |
High insulation resistance in humid conditions |
| Water Absorption |
< 0.25% (24 h) |
Low moisture uptake preserves properties |
3. What Mechanical Strength Can You Expect?
FR4 carries substantial load for an insulation material: flexural strength above 55,000 psi lengthwise, compressive strength near 60,000 psi flatwise, and Rockwell hardness around M110, so it doubles as a structural insulator in switchgear and test fixtures.
4. How Is FR4 Machined and Fabricated?
Sheets machine cleanly on CNC routers, drilling, milling, and waterjet equipment. For PCB fabrication, FR4 supports high-speed drilling, V-scoring, and routing. Use carbide tooling, adequate feed rates, and dust extraction; the material does not melt, so it cuts rather than burns, but glass dust requires controlled removal.
5. Where Are FR4 Sheets Most Commonly Used?
🔌 Electronics & PCB
PCB substrates, drilling backers, FPC reinforcement, and test fixtures.
⚙️ Electrical Equipment
Busbar supports, insulating spacers, transformer and motor insulation parts, and switchgear components.
6. What Sizes, Thicknesses, and Finishes Are Available?
Standard sheets come in 1020×1220 mm and 1220×2440 mm, with thicknesses from 0.5 mm to 50 mm and matte or gloss surfaces. Custom cutting and CNC machining to drawing are available for production runs.
Frequently Asked Questions (FAQS)
1. What is the difference between FR4 and G10?
Both are woven glass-epoxy laminates. G10 (IEC 60893 EPGC201) is the base grade; FR4 (EPGC202) adds brominated flame retardants to achieve a UL 94 V-0 rating. Mechanical and electrical properties are otherwise very similar, and the two designations are often used interchangeably in commercial supply.
2. What thickness range and standard sheet sizes are stocked?
Thickness runs from 0.5 mm to 50 mm, with standard sheet sizes of 1020×1220 mm and 1220×2440 mm. Custom sizes and CNC-machined parts cut to drawing are available on order.
3. Is FR4 suitable as a PCB substrate?
Yes. FR4 is the most common rigid PCB substrate thanks to its stable dielectric constant (around 4.4-5.0 at 1 MHz), high volume resistivity, low water absorption, and good drilling and routing behavior.
4. What flammability rating does FR4 meet?
FR4 is rated UL 94 V-0, meaning it self-extinguishes after ignition with short burning time and no flaming drips. This is a defining requirement for electrical and electronic applications.
5. Can FR4 sheets be CNC machined?
Yes. FR4 machines well on CNC routers, milling, drilling, and waterjet equipment using carbide tooling. Because it is thermoset, it cuts rather than melts; sharp tooling and dust extraction are recommended to keep glass dust controlled.
6. What is the maximum operating temperature?
Standard FR4 has a glass transition temperature around 135-140°C and a continuous operating ceiling near 130°C (Insulation Class B). High-Tg FR4 and FR5 grades raise continuous service temperature for hotter environments.
7. How are FR4 sheets packaged for shipment?
Sheets are protected with PE film, separated to prevent surface scratching, and secured on export pallets or in wooden crates suitable for container freight. Machined parts are individually protected to guard finished edges and surfaces.
