Views: 0 Author: Site Editor Publish Time: 2025-07-07 Origin: Site
Flame‑retardant laminates are the backbone of safe, reliable insulation in electrical and electronic assemblies. While FR‑4 reigns supreme in high‑performance PCBs, NEMA grades FR‑1 through FR‑3 offer cost‑effective, punchable alternatives, and the latest FR‑5 grade delivers enhanced high‑temperature and mechanical performance. This guide demystifies each grade—FR‑1, FR‑2, FR‑3, FR‑4, and FR‑5—so you can match material characteristics to your project’s thermal, electrical, and fabrication needs.
FR‑1 & FR‑2: Alpha‑cellulose (cotton linter) paper with phenolic‐based flame‑retardant resin.
FR‑3: Same paper substrate, upgraded to an epoxy‐based flame‑retardant resin for improved moisture and dielectric performance.
FR‑4: Woven glass fabric saturated with brominated epoxy resin—offering exceptional structural rigidity and electrical insulation.
FR‑5: 7628 fiberglass cloth bonded with a high‑TG, brominated epoxy resin. Engineered for high mechanical strength under elevated temperatures.
| Grade | UL 94 Rating | Continuous‑Use Temperature |
| FR‑1 | V‑1 | Up to 130 °C |
| FR‑2 | V‑1 | 75 °C (≤0.062″) / 105 °C (>0.062″) |
| FR‑3 | V‑1 | 90 °C (≤0.062″) / 110 °C (>0.062″) |
| FR‑4 | V‑0 | 130–140 °C |
| FR-5 | V-0 | 155 °C |
FR‑5 meets UL 94 V‑0 for complete self‑extinguishing behavior and sustains 50% of its flexural strength at 150 °C (E‑1/150).
FR‑4 & FR‑5: Excellent resistance to water absorption and aggressive chemicals—ideal for outdoor, rail, and aerospace environments.
FR‑3: Good moisture and chemical resistance, outperforming FR‑1/FR‑2 thanks to epoxy chemistry.
FR‑1/FR‑2: Fair moisture resistance; phenolic plasticizers may leach in harsh chemical or UV‑exposed settings.
| Property | FR‑1 | FR‑2 | FR‑3 | FR‑4 | FR-5 |
| Dielectric Properties | Basic (no RF) | Good – RF compatible | Good – RF compatible | Excellent – RF/high‑freq | Excellent – up to 35 kV |
| Mechanical Strength | Fair | Fair | Fair to Good | High | Very High |
FR‑5: Exceptional dielectric breakdown (≥35 kV) and tensile strength (~380 MPa) make it suitable for high‑voltage and structural insulating components.
| Grade | Fabrication | Relative Cost vs FR‑4 |
| FR‑1 | Heated punching | Low |
| FR‑2 | Ambient punching | Low |
| FR‑3 | Easy punching | Moderate |
| FR‑4 | CNC machining/drilling | High |
| FR-5 | CNC machining/drilling | Premium |
FR‑5 is machinable only (drilling, routing). Its superior performance commands a premium price compared to FR‑4.
FR‑1: Inexpensive switchgear and motor spacers (non‑RF).
FR‑2: Appliance insulation and moderate‑frequency circuitry.
FR‑3: Industrial controls, moderate‑frequency modules in humid environments.
FR‑4: High‑density PCBs, RF/microwave devices, aerospace and automotive electronics.
FR‑5: High‑temperature circuit boards, rail‑vehicle fire‑safety components, structural insulators in aerospace and transport.
| Grade | Standards Met |
| FR‑1 | MIL‑I‑24768/24, IEC 60893 PF CP 205 |
| FR‑2 | MIL‑I‑24768/25, IEC 60893 PF CP 308 |
| FR‑3 | MIL‑I‑24768/26, IEC 60893 EP CP 201 |
| FR‑4 | MIL‑I‑24768/27, IEC 61249‑2‑4 |
| FR-5 | NEMA LI‑1 Grade FR5, IEC 60893 EPGC204, GB/T 1303.2‑2009, EN 45545‑2 |
From punch‑friendly phenolic paper grades (FR‑1, FR‑2) to epoxy glass laminates (FR‑3, FR‑4) and the latest high‑performance FR‑5, each flame‑retardant laminate aligns with distinct thermal, electrical, and fabrication demands. FR‑5 extends the envelope with higher continuous‑use temperatures, superior mechanical integrity, and robust electrical insulation—perfect for mission‑critical, high‑voltage, and harsh‑environment applications. Map your project requirements against this expanded material matrix to ensure optimal performance and cost efficiency.
