PCB Thermal Relief Calculator

Thermal relief spokes are the small copper bridges that connect a pad to a copper plane on a PCB — they reduce heat transfer during soldering and affect how much current the joint can carry. Enter your outer pad diameter, inner diameter/hole, spoke count, spoke width, copper weight, connected plane area, max current, and thermal conditions into the PCB Thermal Relief Calculator to get the thermal resistance of your relief pattern. Secondary outputs include current capacity, solderability rating, and maximum temperature.

mm

Outer diameter of the pad including thermal relief

mm

Drill hole diameter or inner opening

mm

Width of thermal relief spokes connecting pad to plane

cm²

Area of copper plane connected to the pad

A
°C
°C

Maximum allowable temperature rise above ambient

Results

Thermal Resistance

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Current Capacity

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Solderability Rating

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Maximum Temperature

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Results Table

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Frequently Asked Questions

Should all plane connections have thermal relief?

Not necessarily. High-current connections may need direct plane connection for maximum current carrying capacity, while signal pins typically benefit from thermal relief for better solderability.

How do thermal reliefs affect electrical performance?

Thermal reliefs slightly increase resistance and inductance compared to direct connections, but the impact is minimal for most applications. The improved solderability usually outweighs these small electrical compromises.

What about wave soldering vs reflow soldering?

Wave soldering typically requires more aggressive thermal relief (fewer or narrower spokes) due to longer heat exposure times. Reflow soldering can often use less aggressive relief patterns.

Can I use different spoke widths on different layers?

Yes, you can optimize spoke widths per layer based on current requirements and thermal management needs. Inner layers often need wider spokes due to reduced heat dissipation.

What is the optimal number of spokes for thermal relief?

Four spokes provide the best balance for most applications. Two spokes offer maximum thermal isolation but reduced mechanical strength, while six or eight spokes provide better current capacity but reduced thermal benefit.

How does copper weight affect thermal relief design?

Heavier copper (2oz+) conducts heat more effectively, requiring more aggressive thermal relief patterns. Lighter copper (0.5oz) may need less aggressive relief but has lower current carrying capacity.

What happens without thermal relief on ground connections?

Direct ground plane connections act as massive heat sinks, making it difficult to reach solder melting temperatures during assembly. This often results in cold solder joints and manufacturing defects.