FR4 Epoxy Glass Laminate Sheet – Dielectric Strength & Selection Guide

Dielectric Strength and Selection Guide of FR4 Epoxy Glass Fiber Sheet 1. What Is Dielectric Strength of FR4? The d...

Dielectric Strength and Selection Guide of FR4 Epoxy Glass Fiber Sheet

1. What Is Dielectric Strength of FR4?

The dielectric strength of  FR4 epoxy glass fiber laminate sheet refers to its ability to withstand electric voltage without breakdown. It is one of the most critical parameters for evaluating insulation performance.

Under standard test conditions (ASTM D149), FR4 typically shows excellent dielectric properties:

👉 Conclusion: FR4 sheets offer a high dielectric strength of 16–20 kV/mm, ensuring reliable insulation performance in medium- and high-voltage electrical systems.

2. How to Select FR4 Sheet Based on Dielectric Strength

When selecting FR4 insulation sheets, it’s essential to consider working voltage, environmental conditions, and a proper safety factor.

(1) Determine the required insulation level

​Example:
Working voltage = 10 kV
Safety factor = 3
Dielectric strength = 18 kV/mm
→ Required thickness = 30 ÷ 18 ≈ 1.7 mm
Recommended: Use 2.0 mm FR4 sheet

(2) Consider operating environment

High humidity or temperature will reduce dielectric performance.

For long-term reliability, apply a safety factor ≥ 3.

For critical insulation, consider alternatives such as G10, G11, or UPGM203.

3. Recommended FR4 Sheet Thickness by Application

4. Summary

FR4 dielectric strength: 16–20 kV/mm

Selection factors: working voltage, environment, and safety factor

Advantage: High electrical insulation, flame resistance (UL94 V-0), and mechanical stability

FR4 epoxy sheets are ideal for transformers, switchgear, motors, PCB substrates, and high-voltage insulation systems.