What Is FR4 Fiberglass Board?
FR4 is a composite material made of woven fiberglass cloth impregnated with epoxy resin and cured under heat and pressure. The "FR" stands for flame-retardant and "4" denotes the grade. It is the worldwide workhorse insulating substrate for printed circuit boards and for structural insulation components. With its balanced mechanical strength, electrical insulation and dimensional stability, FR4 is widely used in power adapters, chargers, new-energy charging piles and power tools.
Key Parameters Explained
TG Value (Glass Transition Temperature)
The glass transition temperature (TG) is the point above which the epoxy softens and loses rigidity. Common commercial grades are 130 °C, 140 °C and 150 °C. Higher TG means better heat resistance, lower moisture absorption and improved dimensional stability under lead-free reflow.
Water Absorption
FR4 typically exhibits water absorption of less than 0.1% over 24 hours at 23 °C, which protects insulation resistance in humid environments.
Breakdown Voltage
The perpendicular dielectric strength of standard FR4 is greater than 20 kV/mm, providing robust creepage and clearance for mains-voltage insulation.
Peel Strength
Copper foil peel strength is normally ≥ 1.4 N/mm, ensuring reliable conductor bonding in etched or plated applications.
| Property | Typical FR4 value | Note |
|---|---|---|
| TG value | 130 / 140 / 150 °C | Higher = better heat resistance |
| Water absorption | < 0.1% | 24 h @ 23 °C |
| Breakdown voltage | ≥ 20 kV/mm | Perpendicular |
| Peel strength | ≥ 1.4 N/mm | Copper foil |
| Flammability | UL94 V-0 | Self-extinguishing |
| Dielectric constant | 4.2 – 4.8 | @ 1 MHz |
Critical Insulation Ratings
FR4 vs 3240 vs G10
Engineers often compare FR4 with related laminates:
| Material | Resin | Flame class | TG | Typical use |
|---|---|---|---|---|
| FR4 | Epoxy | UL94 V-0 | 130–150 °C | PCB & insulation |
| 3240 (EPGC201) | Epoxy | V-0 / HB | 130–140 °C | Mechanical & insulation |
| G10 | Epoxy | HB (non-halogen FR optional) | 130 °C | Structural, no flame req. |
In short, FR4 adds the flame-retardant requirement on top of G10-class mechanical performance, while 3240 is the Chinese GB/T equivalent with similar epoxy chemistry. For power-supply insulation that must pass safety certification, FR4 (V-0) is the safe default.
Thickness Range & Custom Cutting
We supply FR4 sheet and machined parts from 0.3 mm to 3.0 mm thickness, with CNC, punching and routing to customer drawings. Thin 0.3–0.5 mm sheets are ideal for precise insulating spacers, while thicker plates serve as structural barriers.
Typical Applications
- Power adapter main-circuit insulation — barrier plates, bobbins, terminal shields.
- New-energy charging piles — high-voltage isolation panels.
- Power tools — motor insulation and switch supports.
- Industrial control — relay and contactor insulation.
Selection Recommendations
How to Choose the Right FR4
- High-voltage designs: select high TG (≥150 °C) and verify breakdown voltage margin.
- High-power designs: use thicker plates for mechanical and thermal robustness.
- Precision parts: specify 0.3–0.5 mm thin sheet with tight tolerance cutting.
Handling, Storage and Moisture Sensitivity
Although FR4 absorbs less than 0.1% water, prolonged exposure to high humidity can raise surface leakage current. Store sheets flat in sealed packaging below 70% RH and, for critical safety barriers, bake at 120 °C for about two hours before lamination or conformal coating. Avoid direct contact with aggressive solvents that could attack the epoxy surface, and wear eye protection when routing glass-reinforced material because the dust is abrasive.
Machining Tips
FR4 machines cleanly with carbide tooling. Use sharp drill bits at 3000–12000 rpm with a light feed to prevent fraying of the glass edges, and rout with a down-cut spiral bit for burr-free profiles. Deburr lightly with 600-grit paper. Because the material is abrasive, expect faster tool wear than with acrylic or aluminum and plan tool changes accordingly to keep tolerances tight.
Quality Certification and Traceability
For power-supply safety, request material with UL recognition to UL94 V-0 and a certificate of compliance referencing IEC 61249 or IPC-4101. Lot traceability, TG verification by differential scanning calorimetry, and dielectric-strength sampling protect your certification audit and field reliability. Chaorong supplies these documents with every shipment so your quality team can close the traceability loop.
Combining FR4 With Other Insulators
In compact adapters, FR4 often works alongside mating insulators such as PET film, silicone sleeves and the common mode choke bobbin. Define clear creepage and clearance budgets per IEC 62368-1, and let the FR4 barrier carry the highest-voltage isolation while thinner films handle local spacing. This layered approach yields a robust, certifiable insulation system at minimal cost.
Typical Failure Modes and How to Avoid Them
FR4 failures in power supplies usually trace to moisture absorption, delamination under thermal shock, or insufficient creepage at high voltage. Keep the material dry before soldering, avoid thermal gradients above the TG, and route high-voltage traces with generous clearance. Where safety isolation is critical, specify reinforced thickness and verify with a hi-pot test rather than assuming the datasheet margin survives reflow.
Application Example: 65 W GaN Adapter Isolation
A 65 W GaN charger switching at high frequency needs a thin yet robust barrier between primary and secondary sides. A 0.5–0.8 mm FR4 spacer with high TG (150 °C) and verified breakdown voltage provides isolation while fitting a slim enclosure. Combined with a molded insulation sleeve, it passes both functional and reinforced insulation tests.
Environmental and RoHS Compliance
Modern FR4 is halogen-free and RoHS compliant, with low halogen content and minimal outgassing. Request the material declaration for REACH and conflict-minerals reporting if your product ships to the EU or North America. Chaorong maintains up-to-date compliance documentation for audit readiness.
Standards and Grade Cross-Reference
FR4 is covered by IPC-4101 and IEC 61249; in China it aligns with GB/T 1303. When specifying, call out the TG class, flame rating and copper weight so suppliers quote like-for-like. Chaorong can supply FR4 matching IPC-4101/21, 24 or 26 slash sheets, with certificates on request.
Why Choose Chaorong
Chaorong supplies UL94 V-0 FR4 fiberglass board with full material certification, cut and machined to your drawings. We hold common thicknesses in stock and support rapid prototyping for power-supply insulation projects.
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