How to Calculate Thermal Resistance of PCB: Simple Guide
To calculate the
thermal resistance of a PCB, use the formula R = t / (k × A), where t is the thickness of the PCB, k is the thermal conductivity of the PCB material, and A is the cross-sectional area for heat flow. This gives the resistance in °C/W, showing how well the PCB resists heat flow.Syntax
The basic formula to calculate thermal resistance of a PCB is:
R = t / (k × A)
- R: Thermal resistance (°C/W)
- t: Thickness of the PCB (meters)
- k: Thermal conductivity of PCB material (W/m·K)
- A: Cross-sectional area for heat flow (square meters)
This formula assumes steady-state heat flow through the PCB thickness.
plaintext
R = t / (k * A)
Example
This example calculates the thermal resistance of a PCB that is 1.6 mm thick, made of FR4 material with thermal conductivity 0.3 W/m·K, and has a heat flow area of 0.01 m².
python
thickness_m = 0.0016 # 1.6 mm in meters thermal_conductivity = 0.3 # W/m·K for FR4 area_m2 = 0.01 # 10 cm x 10 cm area thermal_resistance = thickness_m / (thermal_conductivity * area_m2) print(f"Thermal Resistance: {thermal_resistance:.4f} °C/W")
Output
Thermal Resistance: 0.5333 °C/W
Common Pitfalls
- Using incorrect units for thickness or area can cause wrong results; always convert to meters and square meters.
- Ignoring the thermal conductivity value of the specific PCB material leads to inaccurate calculations.
- Assuming uniform heat flow area when heat spreads unevenly can misrepresent thermal resistance.
- Not accounting for additional heat paths like copper layers or vias can underestimate heat dissipation.
python
wrong_thickness = 1.6 # Using mm instead of meters k = 0.3 area = 0.01 # Wrong calculation (units mismatch) wrong_R = wrong_thickness / (k * area) # Correct calculation correct_thickness = 0.0016 correct_R = correct_thickness / (k * area) print(f"Wrong R: {wrong_R}") print(f"Correct R: {correct_R}")
Output
Wrong R: 533.3333333333334
Correct R: 0.5333333333333333
Quick Reference
| Parameter | Description | Typical Units |
|---|---|---|
| t | PCB thickness | meters (m) |
| k | Thermal conductivity of PCB material | W/m·K |
| A | Cross-sectional heat flow area | square meters (m²) |
| R | Thermal resistance | °C/W |
Key Takeaways
Always convert PCB thickness and area to meters and square meters before calculation.
Use the correct thermal conductivity value for your PCB material.
Thermal resistance shows how well the PCB resists heat flow; lower values mean better heat dissipation.
Consider copper layers and vias as they affect overall thermal resistance.
Check units carefully to avoid large calculation errors.