NEMA FR5
NEMA FR5 is the high-temperature flame-retardant glass-epoxy laminate — woven E-glass cloth bonded with a high-Tg, halogenated epoxy resin system that delivers both UL94 V-0 flame retardancy and elevated-temperature mechanical performance, combining the flame-retardant chemistry of FR4 with a higher glass transition temperature analogous to G11.
TL;DR
| Property | Value |
|---|---|
| Parent material | Glass phenolic (epoxy grades) |
| Primary use | High-temp FR electrical insulation panels, PCB substrate at elevated temperature |
| Key spec | UL94 V-0; Tg ~170°C; continuous service ≥ 285°F |
| Standards | NEMA LI 1 (Grade FR5); MIL-I-24768/27; ASTM D709 |
Chemistry & Reinforcement
FR5 occupies the intersection of two requirements: high-temperature performance (like G11) and flame retardancy (like FR4):
- Reinforcement: Plain-weave woven E-glass cloth (same 7628-style fabric)
- Resin: Brominated (or phosphorus-based) high-Tg epoxy formulation providing UL94 V-0 rating and Tg ~170°C
- Color/finish: Natural/green tint; visually similar to FR4 and G10
- Density: ~1.80–1.92 g/cc
- Flame retardancy: UL94 V-0 — the laminate self-extinguishes within 10 seconds of ignition source removal
The flame-retardant additive system (typically tetrabromobisphenol-A or organophosphorus compounds in halogen-free formulations) lowers the Tg modestly versus unfilled high-Tg epoxy, but FR5 spec still achieves ~170°C Tg — significantly above FR4's ~130–140°C. This is the critical distinction: FR5 retains its modulus and flexural strength at temperatures that cause FR4 to soften.
FR5 vs. FR4: FR4 is a UL94 V-0, standard-Tg epoxy (~130°C). FR5 is UL94 V-0, high-Tg epoxy (~170°C). Never use them interchangeably in temperature-critical applications. FR5 vs. G11: G11 has a similar Tg (~170°C) but is NOT flame-retardant — it does not carry UL94 V-0. FR5 adds the flame-retardant chemistry on top of G11's thermal performance.
Key Properties
FR5's surprisingly high search volume (250/month, KD 0) suggests engineers actively seeking this grade are often upgrading from FR4 due to thermal failures in high-density power electronics. If your FR4 PCB substrate or insulation panel is softening or delaminating at operating temperature, FR5 is the direct NEMA upgrade path.
Typical Applications
FR5 is specified when FR4's thermal performance is insufficient and flame retardancy remains a code requirement:
- High-density power electronics boards — motor drives, power supplies, and inverter control boards operating in enclosures where winding temperatures exceed 130°C. FR5 maintains substrate rigidity where FR4 would warp or delaminate.
- Industrial control panel insulation plates — UL 508A panel shops specifying flame-retardant insulation panels for panels in Class F or H insulation systems require FR5 (or equivalent) for compliance.
- EV battery management system (BMS) substrates — automotive and industrial BMS boards increasingly specify FR5 or high-Tg FR4 (>170°C Tg) to survive battery thermal events.
- Transformer barrier boards (Class F/H) — where FR4 is required by a flame-spread specification but winding temperatures exceed its Tg.
- Server and telecom backplanes — high-power data center infrastructure where rack temperatures approach or exceed FR4's comfort zone.
- Defense and aerospace electronics — MIL-PRF-55110 or MIL-PRF-31032 qualified boards in avionics and ground equipment where both flame retardancy and thermal performance must be documented.
Standard Sizes
| Form | Common sizes |
|---|---|
| Sheet thickness | 1/32, 1/16, 1/8, 3/16, 1/4, 3/8, 1/2, 3/4, 1 in. |
| Sheet panel | 24 × 36 in., 48 × 96 in. |
| Rod diameter | 1/4 to 4 in. (limited stock; confirm availability) |
FR5 sheet is the primary form. Thinner sheets (1/32–1/8 in.) serve as PCB-analog substrate stock; thicker panels (1/4–1 in.) are used as structural insulation panels in industrial equipment.
Standards Reference
- NEMA LI 1 — Grade FR5 is defined with UL94 V-0 flame-retardancy requirement and elevated-temperature flexural retention in addition to standard dielectric and mechanical tests. NEMA LI 1-2020 is current.
- MIL-I-24768/27 — Military high-temperature flame-retardant glass-epoxy. Type GEEF (Glass-Epoxy, Elevated temperature, Flame-retardant). QPL certification required for defense programs.
- ASTM D709 — laminated thermosetting materials; D635 and D3801 (flame retardancy) are referenced.
- UL 94 — UL's Standard for Safety of Flammability of Plastic Materials; FR5 achieves V-0 classification.
- IEC 60893 — International: FR5 corresponds to HGW 2372.4 in the IEC laminate designation system.
Comparison to Neighbor Grades
| Feature | FR4 | FR5 | G11 | G10 |
|---|---|---|---|---|
| Flame retardant | Yes (V-0) | Yes (V-0) | No | No |
| Tg | ~130°C | ~170°C | ~170°C | ~130°C |
| Max service temp | 266°F | 285°F | 285°F | 266°F |
| Flexural strength (RT) | 55,000–60,000 psi | 58,000–65,000 psi | 60,000–65,000 psi | 55,000–60,000 psi |
| Dielectric strength | ≥400 V/mil | ≥400 V/mil | ≥400 V/mil | ≥400 V/mil |
| Cost | Moderate | Higher than FR4 | Similar to FR5 | Lowest |
Choose FR5 when: you need UL94 V-0 flame retardancy AND Tg ~170°C — the only standard NEMA grade delivering both. Choose FR4 when flame retardancy is required but service temperature stays below 266°F. See NEMA FR4 spec page. Choose G11 when high Tg is required but UL94 V-0 flame retardancy is not a code requirement. Choose G10 for the lowest-cost epoxy-glass laminate when neither flame retardancy nor high Tg is required.
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