Thermal Relief Calculator
Spoke Geometry
Work out thermal relief spoke geometry for PCB pads connected to copper planes. Thermal resistance and solderability are not calculated; confirm them with your fabricator.
Thermal Relief Parameters
Thermal Relief Analysis
Design conditions to confirm
Spoke width and count for a good solder joint depend on the fabricator, the CAD library rules and the part being soldered. This page does not publish rating tables because we have no source for them.
- Copper weight and the size of the connected plane
- Solder alloy and reflow or wave profile
- Thermal mass of the pad and component
- Current through the pad (spokes also limit current)
- Your fabricator's minimum spoke and gap dimensions
Why Thermal Relief is Important
Without Thermal Relief
Direct connection to copper plane acts as a massive heat sink:
- ✗Heat rapidly dissipates from pad
- ✗Pad may not reach solder melting temperature
- ✗Cold solder joints and defects
- ✗Longer soldering time damages components
With Thermal Relief
Spokes create thermal resistance while maintaining connection:
- ✓Heat concentrated at pad during soldering
- ✓Proper solder wetting and flow
- ✓Reliable solder joints
- ✓Electrical connection maintained
Thermal Relief Design Guidelines
2-Spoke Pattern
Best for solderability. Use for thermal vias, non-power connections, and hand soldering applications. Creates maximum thermal isolation.
4-Spoke Pattern
Standard for most applications. Better current capacity than 2-spoke. Use for ground/power pins with moderate current requirements.
No Relief
Direct connection for maximum current or heat dissipation. Use only with specialized soldering process (vapor phase, longer profiles).
Related Calculators
Design your complete thermal management strategy with our other tools.
Thermal Relief FAQ
Should all plane connections have thermal relief?
Not necessarily. High-current power connections may need direct connection for lower resistance. Signal vias and low-current connections should use thermal relief.
How do thermal reliefs affect electrical performance?
Thermal reliefs add resistance and inductance. For high-frequency signals, this can increase impedance discontinuities. For power, it increases voltage drop under load.
What about wave soldering vs reflow?
Wave soldering is more sensitive to thermal relief as it applies heat from one side only. Reflow heats the entire board, making it more forgiving of thermal mass.
Can I use different spoke widths on different layers?
Yes, this is common. Inner layers often use wider spokes for better current capacity, while outer layers use narrower spokes for better soldering access.
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