Thermal Relief in PCB: What It Is and When to Use It

In PCB design, thermal relief is a pattern that connects a pad to a large copper area using thin traces instead of a solid connection. This helps control heat flow during soldering, making it easier to solder components without overheating the board.

How It Works

Thermal relief works like a small bridge between a pad and a large copper area on a PCB. Imagine trying to heat a metal plate with a small spot on it. If the spot is connected directly to a big metal area, the heat quickly spreads away, making it hard to heat the spot enough to solder. Thermal relief uses thin traces (called spokes) to connect the pad, which slows down heat flow.

This is similar to holding a hot pan by its handle instead of the whole pan. The handle is thinner and stops heat from spreading quickly, so it stays cooler. In PCBs, thermal relief helps the soldering iron heat the pad properly without the heat being lost to the big copper area.

Example

Here is a simple example of a thermal relief pattern in a PCB design file format (Gerber-like pseudocode). It shows a pad connected to a copper pour with four thin spokes instead of a solid fill.

pcb_design

PAD 1 AT (10,10) SIZE 1.5mm
COPPER_POUR AREA (5,5) TO (15,15)
THERMAL_RELIEF CONNECT PAD 1 WITH 4 SPOKES WIDTH 0.3mm

Output

Pad 1 connected to copper pour with four thin spokes of 0.3mm width, allowing controlled heat flow during soldering.

When to Use

Use thermal relief when a pad is connected to a large copper area like a ground or power plane. Without it, the large copper area acts like a heat sink, making soldering difficult because heat quickly escapes.

Thermal relief is especially useful for through-hole components and connectors where good solder joints are critical. It helps prevent cold solder joints and damage to components by controlling heat flow.

However, for high-current connections where low resistance is important, solid connections without thermal relief might be preferred.

Key Points

• Thermal relief connects pads to copper areas with thin spokes to control heat flow.
• It makes soldering easier by preventing heat from quickly escaping.
• Commonly used for ground and power planes in PCB design.
• Not always used for high-current paths where solid connections are needed.

Key Takeaways

Thermal relief uses thin traces to connect pads to large copper areas, controlling heat flow.

It helps soldering by preventing heat from dissipating too fast into copper planes.

Use thermal relief for ground and power planes to avoid cold solder joints.

Avoid thermal relief for high-current paths that need solid, low-resistance connections.