FR4 Breakdown Voltage: FR4 is the most widely used material for Printed Circuit Boards (PCBs) due to its excellent balance of mechanical strength, electrical insulation, and cost-effectiveness. One of the critical properties of FR4 is its breakdown voltage, which determines its ability to withstand high electrical stress without failure.

Understanding FR4 breakdown voltage is essential for designing high-reliability PCBs, especially in applications involving high voltage, power electronics, and industrial control systems.

FR4 Breakdown Voltage

2. What Is Breakdown Voltage?

Breakdown voltage is the voltage at which an insulating material loses its dielectric properties and allows current to pass through, leading to electrical failure. For PCBs, this means the voltage level at which FR4 insulation collapses, causing short circuits or damage to electronic components.

Factors Affecting Breakdown Voltage

Several factors influence the breakdown voltage of FR4 PCBs:

Material Thickness: Thicker FR4 materials have higher breakdown voltages.

Moisture Absorption: Higher humidity levels reduce breakdown voltage.

Operating Temperature: Extreme temperatures can degrade dielectric strength.

Manufacturing Quality: Impurities and defects in FR4 affect insulation performance.

3. Typical Breakdown Voltage of FR4

FR4 materials have high dielectric strength, typically measured in kilovolts per millimeter (kV/mm).

Note: These values are approximate and depend on specific FR4 material grades and testing conditions.

4. How FR4 Breakdown Voltage Affects PCB Design

High-Voltage PCB Design Considerations

Adequate Clearance & Creepage Distance: Maintain sufficient spacing between high-voltage traces.

Thicker FR4 Layers: Increase breakdown voltage by using thicker dielectric layers.

Conformal Coating: Apply coatings to improve insulation in harsh environments.

Moisture Protection: Use high-quality FR4 with low water absorption to maintain insulation strength.

Applications Requiring High Breakdown Voltage

Power Supply PCBs: Transformers, converters, and inverters.

Industrial Control Systems: High-voltage circuits in automation and robotics.

Automotive Electronics: Electric vehicle (EV) power modules.

Medical Devices: Isolation circuits in diagnostic and imaging equipment.

5. Breakdown Voltage Testing Methods

To ensure reliability, manufacturers test FR4 breakdown voltage using standardized methods such as ASTM D149 and IEC 60243.

Common Testing Procedures

Dielectric Strength Test – Applies increasing voltage to an FR4 PCB sample until breakdown occurs.

High-Potential (Hi-Pot) Test – Checks insulation by applying high voltage for a specified duration.

Surface & Volume Resistivity Tests – Measures resistance to prevent leakage currents.

6. Conclusion

FR4’s breakdown voltage is critical to PCB performance in high-voltage applications. The right material thickness, optimized PCB layout, and thorough testing ensure safe operation and reliability.

When precision matters, SQPCB is your partner for high-voltage and industrial PCB projects. We combine cutting-edge production lines, in-house process control, and a wealth of PCB engineering experience to deliver consistent, industry-compliant results.

7. FAQs about FR4 Breakdown Voltage

Q1: What is the typical breakdown voltage per millimeter for FR4?
A1: FR4 typically offers around 37–40 kV/mm, depending on grade and test conditions.

Q2: Does moisture significantly affect FR4 breakdown voltage?
A2: Yes. FR4 absorbs moisture over time, and higher humidity can lower breakdown voltage by several kilovolts.

Q3: Can conformal coating increase breakdown voltage?
A3: It can’t change the inherent FR4 breakdown voltage, but it improves surface insulation and environmental resistance, reducing leakage paths.

Q4: Is thicker FR4 always better for high-voltage applications?
A4: Thicker FR4 generally increases breakdown voltage, but designers must also balance weight, cost, and mechanical constraints.

Q5: How does manufacturing quality affect breakdown voltage?
A5: Impurities, voids, and poor lamination can weaken dielectric strength. High-quality processes, like those at SQPCB, ensure maximum insulation performance.

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