Thermal Management

Thermal Relief Calculator

Spoke Design • Solderability Analysis

Design optimal thermal relief patterns for PCB pads connected to copper planes. Balance heat dissipation requirements with manufacturing solderability.

Thermal Relief Parameters

Outer Pad Diameter (mm)

Inner Diameter / Hole (mm)

Number of Spokes

Spoke Width (mm)

Copper Weight (oz)

Connected Plane Area (cm²)

Thermal Relief Analysis

Common Thermal Relief Configurations

Application	Spokes	Spoke Width	Solderability
Standard Via	4	0.25mm	Good
Power Pin	4	0.4mm	Marginal
Thermal Via	2	0.2mm	Excellent
Ground Pin	4	0.3mm	Good
High Current	4	0.5mm+	Poor (no relief)

*Ratings based on typical reflow soldering conditions. Wave soldering may require different configurations.

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 never reaches solder melting point
✗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

2️⃣

2-Spoke Pattern

Best for solderability. Use for thermal vias, non-power connections, and hand soldering applications. Creates maximum thermal isolation.

4️⃣

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).

Spoke Width Selection

0.2 - 0.25mm

Excellent solderability, low current

Vias, signals

0.25 - 0.35mm

Good balance, moderate current

General purpose

0.35 - 0.5mm

Marginal solderability, higher current

Power connections

>0.5mm

Poor solderability, use with caution

High current only

Related Calculators

Design your complete thermal management strategy with our other tools.

Via Current Calculator Pad Size Calculator

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.