FR4 Fiberglass vs Carbon Fiber Board: Insulation Material Comparison for Power Electronics

In power adapters, EV chargers, and inverters, the choice of insulation material directly impacts safety, thermal performance, and long-term reliability. This article compares FR4 fiberglass board and carbon fiber composite board across key parameters to help engineers make informed decisions.

Material Properties Comparison

Parameter	FR4 Fiberglass	Carbon Fiber Board	Notes
Base material	Epoxy + glass fiber	Epoxy + carbon fiber	-
Density	1.8-2.0 g/cm3	1.4-1.6 g/cm3	Carbon fiber is lighter
Thermal conductivity	0.3-0.4 W/mK	5-10 W/mK	Carbon fiber 15-30x better
Dielectric constant	4.2-4.8	6-12	FR4 has better insulation
Dielectric strength	20-30 kV/mm	10-15 kV/mm	FR4 is better for high voltage
Water absorption	0.1-0.2%	0.05-0.1%	Carbon fiber is more stable
CTE	14-16 ppm/C	2-4 ppm/C	Carbon fiber more stable
Tensile strength	300-400 MPa	600-800 MPa	Carbon fiber is stronger
Cost	Low	High (2-3x)	FR4 is more economical

Application Recommendations

FR4 Fiberglass: Recommended For

• Power adapter PCB mainboards - operating temp -40C to +130C, AC/DC mixed circuits
• EV charger insulation brackets - high voltage isolation requirements, insulation resistance >100 MOhm
• Inverter driver boards - IGBT/MOSFET drive circuits requiring stable dielectric properties
• Industrial control power supplies - harsh environments with high humidity

Carbon Fiber Board: Recommended For

• High-power heat dissipation structures - power density >10 W/cm3
• UAV power modules - weight-sensitive applications requiring high strength-to-weight ratio
• EV OBC/DC-DC converters - high power density designs requiring excellent thermal management
• High-frequency power supplies (>=500 kHz) - low CTE ensures dimensional stability

Key Parameter Analysis

1. Insulation Performance

FR4's dielectric constant (Dk) is approximately 4.5 with dielectric loss (Df) of about 0.02 at 1 MHz, providing stable insulation characteristics below 1 MHz frequency.

Insulation resistance (500V DC, 25C):
  FR4: > 10,000 MOhm.cm
  Carbon fiber: 1,000-5,000 MOhm.cm

Conclusion: FR4 is the safer choice for high-voltage isolation applications.

2. Thermal Management

Carbon fiber's thermal conductivity is 15-30x that of FR4, making it ideal for heat dissipation applications.

Thermal resistance (10mm x 10mm x 2mm sample):
  FR4: Rth = L/(k.A) = 0.002/(0.35 x 0.0001) = 57 C/W
  Carbon fiber: Rth = 0.002/(7 x 0.0001) = 2.9 C/W

Conclusion: Carbon fiber significantly reduces temperature rise in high-power applications.

3. Mechanical Performance

Carbon fiber composite's specific strength (strength/density) is 3-4x that of FR4, making it suitable for mechanical vibration and shock environments.

Flexural strength:
  FR4: 350-450 MPa
  Carbon fiber board: 700-900 MPa

Conclusion: Carbon fiber is preferred for vibration environments (automotive, portable devices).

4. Cost Analysis

Item	FR4	Carbon Fiber
Material cost (USD/kg)	2-4	12-22
Processing cost	Low	Medium
Standard availability	Abundant	Relatively limited

Conclusion: FR4 is the preferred choice for cost-sensitive products.

Selection Decision Flowchart

Start Selection
  |
  +-- Need high voltage isolation (>500V)?
  |     Yes --> Prefer FR4
  |     No  --> Continue
  |
  +-- Power density > 10 W/cm3?
  |     Yes --> Consider carbon fiber
  |     No  --> Continue
  |
  +-- Weight sensitive?
  |     Yes --> Consider carbon fiber
  |     No  --> Continue
  |
  +-- Cost sensitive?
  |     Yes --> Prefer FR4
  |     No  --> Choose based on other requirements
  |
  +-- Default recommendation: FR4

Chaorong Product Specifications

FR4 Fiberglass Board

Model	Thickness	Size	Color	UL Rating	Application
FR4-1.0	1.0mm	Custom	Green/Black	UL94 V-0	PCB substrate
FR4-1.5	1.5mm	Custom	Green/Black	UL94 V-0	Insulation spacer
FR4-2.0	2.0mm	Custom	Green/Black	UL94 V-0	Bracket/baffle
FR4-3.0	3.0mm	Custom	Green/Black	UL94 V-0	Structural parts

Carbon Fiber Board

Model	Thickness	Size	Finish	UL Rating	Application
CF-1.0	1.0mm	Custom	Glossy/Matte	UL94 V-1	Heat dissipation plate
CF-1.5	1.5mm	Custom	Glossy/Matte	UL94 V-1	Structural parts
CF-2.0	2.0mm	Custom	Glossy/Matte	UL94 V-1	Bracket

Quality Commitment: All products are tested with LCR meters (1 kHz-1 MHz), thermal cycling (-40°C to +125°C), and EMI pre-scan (9 kHz-30 MHz). Samples available within 3-5 business days.