FR-3
ASTM D709 Grade FR-3
FR-3 is a flame-retardant epoxy-impregnated paper laminate to ASTM D709 (Grade FR-3), stocked as standard, cold-punch, hot-punch, halogen-free and single- or double-sided copper-clad sheet.
Reference datasheet — FR-3 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
FR-3 grades and fills
FR-3 is supplied in 3 conditions, soft to hard.
Compare all 3 grades and fillsHide
| Grade · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness |
|---|---|---|---|---|---|
Cold-punch grade | Pick when boards up to ~1.6 mm must be punched on unheated tooling in high-volume consumer production. | 85 | 1.4 | 100 HRM | |
Halogen-free flame-retardant FR-3 | Choose for RoHS-plus/halogen-free customer specifications (Br+Cl each < 900 ppm) at a small price premium. | 90 | 1.2 | 103 HRM | |
Hot-punch grade | Pick for thicker sheet or the crispest hole edges; requires preheated blanks/dies but gives higher rigidity and Tg. | 105 | 1.1 | 110 HRM |
Supply forms, finishes and certifications
Ways FR-3 is supplied — form, process route, surface or paperwork — without a datasheet of their own. The property values above apply.
| Option | What it is | Type |
|---|---|---|
CCL-1S | Single-sided copper-clad FR-3 | Surface finish |
CCL-2S | Double-sided copper-clad FR-3 | Surface finish |
STDDefault | Standard unclad FR-3 epoxy-paper laminate sheet | Standard supply |
What is FR-3?
FR-3 is a flame-retardant epoxy-impregnated paper laminate to ASTM D709 (Grade FR-3), stocked as standard, cold-punch, hot-punch, halogen-free and single- or double-sided copper-clad sheet. Density is about 1.45 g/cm³ with service to 105 °C and a machinability score of 80, so it punches, shears and drills far more easily than glass-epoxy while offering better mechanical and electrical properties than FR-2 at lower cost than FR-4. The paper core still wicks moisture at cut edges and limits thermal and plated-through-hole performance, so FR-4 remains the choice for multilayer or high-reliability boards. FR-3 has a density of 1.45 g/cm³ (0.0524 lb/in³), lighter than 59% of composite grades. Its glass-transition temperature is 115°C (239 °F). FR-3 has a tensile strength of 95 MPa (13.8 ksi), weaker than 69% of composite grades. Elongation at break is 1.2% and the elastic modulus is 9 GPa (1.31 Msi).
What is FR-3 used for?
- single/double-sided PCBs
- punched electrical insulation parts
- terminal strips
Advantages
- Easy to machine — 80/100, better than 85% of composite grades
Limitations
- Limited service temperature — 105°C (221 °F), worse than 90% of composite grades
- Hard to polish — 20/100, worse than 90% of composite grades
- Degrades in UV without stabilisers — 25/100, worse than 86% of composite grades
FR-3 properties
Typical room-temperature values; bars are the position among composite grades.
Physical4
FR-3 has a density of 1.45 g/cm³ (0.0524 lb/in³), lighter than 59% of composite grades. Its glass-transition temperature is 115°C (239 °F).
Mechanical10
FR-3 has a tensile strength of 95 MPa (13.8 ksi), weaker than 69% of composite grades. Elongation at break is 1.2% and the elastic modulus is 9 GPa (1.31 Msi).
Thermal8
FR-3 is rated for continuous service to 105°C (221 °F). It conducts heat at 0.28 W/m·K (0.162 BTU/hr·ft·°F), worse than 71% of composite grades. Thermal expansion is 20 µm/m·K (11.1 µin/in·°F).
Electrical7
FR-3 is an electrical insulator with a dielectric strength of 18 kV/mm (457.2 V/mil) and a resistivity of 1×10¹¹ Ω·m.
Chemical & Environmental3
Corrosion resistance is very good (70/100), worse than 64% of composite grades. UV resistance is poor.
Sustainability2
Producing a kilogram of FR-3 takes about 90 MJ of energy and emits 5 kg of CO₂ — less than 75% of composite grades.
Manufacturability2
FR-3's machinability is very good (80/100, better than 85% of composite grades).
Common Calculations4
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the composite family
Yield strength against density for every composite grade FabDigit runs. FR-3 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with FR-3
Is FR-3 easy to machine?
Drills, routs and shears easily but the cured epoxy/paper is mildly abrasive — use carbide tools, high speed and vacuum dust extraction; edges fuzz if feeds are too low.
Can FR-3 be welded?
Not weldable; join by bonding with epoxy adhesive or by mechanical fastening/riveting.
Can FR-3 be formed, bent or molded?
Supplied as a fully cured thermoset laminate — it cannot be reformed; blanking and holes are made by cold or hot punching (hot punch 60–100 °C for thicker sheet) or by routing.
FR-3 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| cellulose (kraft) paper reinforcementmultiple plies of resin-impregnated paper | 45 – 60 | 55 |
| brominated flame retardant (TBBPA-based)absent in halogen-free HF variant | 2 – 6 | 4 |
| inorganic fillers / curing agents | 0 – 5 | 2 |
| copper foil (clad grades only)18–70 µm electrodeposited foil, one or both faces | 0 – 15 | 0 |
| epoxy resin binderoften DGEBA cured with dicy/novolac; may be phenolic-modified | ≥ 35 (balance) |
What surface finishes work on FR-3?
Cut edges should be sealed or varnished to limit moisture wicking into the paper core; clad grades take standard etch, HASL/OSP and solder mask, though bath temperatures must be kept moderate.
Equivalent designations
Standards and trade names that resolve to FR-3 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- ASTM
- D709 Grade FR-3
How much does FR-3 cost?
FR-3 is a premium-cost composite ($$$), cheaper than about 51% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
FR-3 — frequently asked
What is FR-3 used for?
FR-3 is typically used for single/double-sided PCBs, punched electrical insulation parts and terminal strips. In short: punchable epoxy-paper substrate; stronger than FR-2; cheaper than glass-epoxy FR-4.
What is the tensile strength of FR-3?
FR-3 has a typical tensile strength of 95 MPa (13.8 ksi) — weaker than 69% of composite grades. Strength varies by condition: see the 3 listed tempers.
Is FR-3 easy to machine?
Yes — machinability is rated very good (80/100, better than 85% of composite grades). Drills, routs and shears easily but the cured epoxy/paper is mildly abrasive — use carbide tools, high speed and vacuum dust extraction; edges fuzz if feeds are too low.
Can FR-3 be welded?
Not weldable; join by bonding with epoxy adhesive or by mechanical fastening/riveting.
What surface finishes work on FR-3?
Cut edges should be sealed or varnished to limit moisture wicking into the paper core; clad grades take standard etch, HASL/OSP and solder mask, though bath temperatures must be kept moderate.
Can FR-3 be formed, bent or molded?
Supplied as a fully cured thermoset laminate — it cannot be reformed; blanking and holes are made by cold or hot punching (hot punch 60–100 °C for thicker sheet) or by routing.
What is the maximum service temperature of FR-3?
FR-3 is rated for continuous use to about 105°C (221 °F), and briefly to 150°C. Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
How much does FR-3 cost?
FR-3 is a premium-cost composite ($$$), cheaper than about 51% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- ASTM D709 — Standard Specification for Laminated Thermosetting Materials — ASTM International (2017)
- NEMA LI 1 — Industrial Laminated Thermosetting Products — NEMA (1998)
- UL 94 / UL 796 flammability and PCB material requirements — UL Solutions (2023)
- IPC-TM-650 test methods for laminate electrical and physical properties — IPC (2022)
- Paper-based copper clad laminate (FR-1/FR-2/FR-3) datasheets — Kingboard / Shengyi (2023)
- Printed Circuits Handbook — base material properties — McGraw-Hill (2016)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.