Introduction
In power electronics, industrial motors and transformers, the choice of insulation material directly affects product safety, reliability and service life. FR4, G10 and 3240 epoxy board are the three most common glass-fiber insulation materials. They look similar but differ significantly in performance and price. This guide compares them across composition, properties and application scenarios to help you make the right choice.
1. Material Basics
1.1 FR4
FR4 (Flame Retardant 4) is the most widely used PCB substrate material, made of epoxy resin reinforced with woven glass fiber cloth.
Key characteristics: UL94 V-0 flame rating · glass cloth styles 7628, 2116, 1080, etc. · usually green (also yellow and black) · standard thickness 0.8–3.0 mm.
Strengths: low cost with a mature supply chain · easy to cut and drill · stable electrical performance.
Limitations: moderate high-temperature performance (Tg around 130–140 °C) · less flexibility for large custom orders.
1.2 G10
G10 (Grade 10) has the same chemistry as FR4 (epoxy + glass cloth) but is a grade designed specifically for industrial use, built to the NEMA standard.
Key characteristics: NEMA LI 1-1998 · no flame retardant added (flame rating must be verified separately) · usually natural pale yellow · military-grade quality requirements.
Strengths: higher mechanical strength than FR4 · lower water absorption, better in humid environments · excellent dimensional stability.
Limitations: roughly 20–30% more expensive than FR4 · flame retardancy must be verified separately.
1.3 3240 Epoxy Board
3240 is the Chinese national grade code for epoxy board, built to the GB/T 1303 series standard, based on a phenolic-modified epoxy system.
Key characteristics: GB/T 1303.1-2009 · thickness 0.5–50 mm · yellow / tan color · phenolic-modified epoxy system.
Strengths: complete thickness range with ample stock of large sheets · better heat resistance than standard FR4 (about 155 °C) · excellent value for money.
Limitations: quality varies between manufacturers · slightly higher water absorption than G10.
2. Property Comparison
| Property | FR4 | G10 | 3240 Epoxy Board |
|---|---|---|---|
| Density (g/cm³) | 1.8–1.9 | 1.8–1.9 | 1.7–1.9 |
| Water absorption (%) | ≤ 0.10 | ≤ 0.05 | ≤ 0.10 |
| Flexural strength (MPa) | ≥ 340 | ≥ 400 | ≥ 350 |
| Tensile strength (MPa) | ≥ 300 | ≥ 350 | ≥ 300 |
| Dielectric strength (kV/mm) | ≥ 20 | ≥ 20 | ≥ 20 |
| Operating temperature (°C) | 130–140 | 130–140 | 150–155 |
| Flame rating | UL94 V-0 | None (additive optional) | UL94 V-0 |
| Typical applications | PCB, electronics | Military, industrial | Transformers, motors |
3. Application Scenarios
3.1 Power adapters
Recommended: FR4 or 3240. For 65–300 W power adapters, FR4 and 3240 are the most economical options: transformer insulation shims (2.0–3.0 mm), PCB standoffs (1.0–1.6 mm), heatsink insulation sheets (0.8–1.0 mm).
Tips: compact, high-density designs → thin FR4 (0.8–1.0 mm); high-power designs needing heat dissipation → thick 3240 (2.0–3.0 mm).
3.2 EV charging stations
Recommended: G10 or 3240. 7–22 kW charging stations demand more from insulation materials: high-voltage insulation shims (3.0 mm and above), electrical isolation plates (G10 is better thanks to lower water absorption), IGBT module insulation (G10 or high-Tg FR4).
Tips: indoor stations → 3240 for balanced cost; outdoor or humid environments → G10 for moisture resistance; DC fast chargers → G10 combined with epoxy potting.
3.3 Drones
Recommended: FR4 or carbon fiber composite. Weight and strength are critical for drones: frame plates (FR4, 2.0–3.0 mm), motor insulation shims (FR4, 0.8–1.0 mm), GPS mounts (carbon fiber, lighter).
Tips: consumer drones → 2.0 mm FR4; professional/industrial drones → carbon fiber composite; waterproofing requires surface coating.
3.4 Transformers and motors
Recommended: 3240 or G10. Transformers and motors demand high temperature resistance and mechanical strength: transformer insulation cylinders (3240 sheet or tube), motor slot insulation (thin G10, 0.5–1.0 mm), end-turn insulation shims (3240).
Tips: dry-type transformers → 3240 (155 °C); oil-immersed transformers → G10 (oil resistance); brushless motors → G10 insulation sheets.
4. Selection Decision Tree
Work through these questions in order:
1. Is UL94 V-0 flame retardancy required? Yes → G10 is out (unless flame-retardant grade is available). No → G10 is an option.
2. Operating temperature above 140 °C? Yes → choose 3240 (155 °C) or high-Tg FR4. No → all three work.
3. Humid or outdoor environment? Yes → prefer G10 (lowest water absorption). No → prefer FR4 (lowest cost).
4. Thick sections needed (>10 mm)? Yes → prefer 3240 (up to 50 mm). No → all three work.
5. Machining Notes
5.1 Cutting
Laser cutting: high precision, small heat-affected zone, good for complex shapes (FR4, G10). CNC precision cutting: no heat-affected zone, good for thick sheet (3240). Sawing: low cost, good for high-volume straight cuts.
5.2 Drilling
FR4 and G10 drill cleanly — use carbide bits. 3240 is more brittle: reduce spindle speed to prevent chipping. For micro holes, use specially ground bits.
5.3 Surface treatment
Silk screening: works directly on FR4 and 3240 surfaces. Anodizing: not applicable to epoxy laminates. Conformal coating: recommended in humid environments.
6. Quick Recommendations
| Application | Recommended material | Suggested size |
|---|---|---|
| Consumer electronics PCB | FR4 | 0.8–1.6 mm, green |
| Power adapters | FR4 or 3240 | 1.0–3.0 mm |
| EV charging stations | G10 or 3240 | 2.0–5.0 mm |
| Drone frames | FR4 or carbon fiber | 2.0–3.0 mm |
| Transformer insulation | 3240 | 3.0–10 mm |
| Military / high-end industrial | G10 | Custom to drawing |
Conclusion
FR4, G10 and 3240 each have their strengths — there is no absolute "best", only the most suitable choice. Weigh flame-retardancy requirements, operating temperature, humidity, mechanical strength and budget together.
Chaorong Electronics supplies the full range of epoxy laminates, supports custom machining from drawings or samples, and provides free selection support.