FR4 Epoxy Sheet Heat Resistance Rating & Selection Guide

Time: 11-18 2025 Auther: Xujue Electrical

1.Heat Resistance Rating of FR4 (Accurate Version) FR4 epoxy sheet is a composite material made from epoxy resin and...

1.Heat Resistance Rating of FR4 (Accurate Version)

FR4 epoxy sheet is a composite material made from epoxy resin and woven fiberglass cloth. Its thermal capability mainly depends on the resin system, Tg, and curing process.

fr4 glass fiber sheet

Continuous Working Temperature of FR4: 130–150°C

Type of FR4	Continuous Operating Temperature	Thermal Class	Notes
Standard FR4	110–130°C	Class B (130°C)	Used in general-purpose PCBs and electrical insulation parts
Enhanced / Modified FR4	130–150°C	Close to Class F (155°C)	Used for electrical insulation structural parts
High Tg FR4 (Tg150 / Tg170)	≈150°C (not exceeding 160°C)	Not an H-class material	High Tg ≠ high continuous operating temperature

Important Clarification

High Tg FR4 (e.g., Tg170) does NOT mean it can operate continuously at 170°C.

Tg (glass transition temperature) indicates the temperature at which the resin starts to soften

It is not the allowable long-term operating temperature

Even high-Tg FR4 typically supports only ≤150°C continuous usage

2. Thermal Resistance Comparison With Similar Materials

To help engineers make decisions quickly, below is a comparison between FR4 and other common insulation laminates:

Material	Continuous Temperature	Thermal Class	Characteristics
FR4	130–150°C	B ~ F	Low cost, good machinability, widely used
G10	130°C	B	Good mechanical strength, moderate heat resistance
EPGC203	155°C	F	Widely used in electrical and power equipment
G11	180°C	H	High temperature & high reliability applications
EPGC204	180–200°C	H	Premium high-temperature laminate

3. How to Select FR4 for Engineering Applications

Below is a practical decision-making process used by engineers.

1) Selection by Temperature (Most Critical)

Application Temperature	FR4 Applicable?	Recommended Material
≤120°C	✔ Fully suitable	Standard FR4
120–140°C	✔ Use enhanced FR4	Modified FR4
140–155°C	⚠ Borderline, near performance limit	EPGC203 recommended
155–180°C	✘ Not suitable	G11
≥180°C	✘ Forbidden	H-class or PI-based insulation

2) Selection by Voltage Level

Voltage Level	FR4 Suitability	Notes
Low voltage ≤1kV	✔ Very suitable	PCB, low-voltage insulation
Medium voltage 3–12kV	✔ With high-quality FR4	Use ≥3–5mm thickness
24–40kV	⚠ Not recommended	Use EPGC203 or G11
≥66kV	✘ Not suitable	Requires high-voltage pressboard/laminate

3) Selection by Mechanical Load

FR4 has moderate mechanical strength. For heavy-load applications, it is not recommended.

Load Level	FR4 Suitable?
Light load (electronic parts, PCB)	✔
Medium load (general support pieces)	✔ with thicker FR4
Heavy load (transformer clamping plates, structural supports)	✘ Use EPGC203 / G11

4) Selection by Application Scenario

Application	Recommended Material	Reason
PCB, control boards	FR4	Standard application
Low-voltage insulation	FR4	Adequate thermal capability
Switchgear partition (medium voltage)	Thick FR4 / EPGC203	Depends on voltage level
Transformer clamping parts	❌ Not FR4	Insufficient strength & heat resistance
Inverters, power modules	High Tg FR4	Suitable if temperature rise is controlled
Energy storage systems, PV	EPGC203	Higher safety requirement
High-temperature motors, transformers	G11 / EPGC204	H-class needed

4. One Sentence Summary for Engineers

FR4’s reliable heat resistance: 130–150°C.
Do NOT use FR4 for >150°C, high-voltage, or heavy-load environments.
For improved reliability → EPGC203 (155°C)
For high-temperature 160–180°C → G11 (180°C)

FR4 epoxy sheet factory warehouse

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