PCB thermal management: copper, thermal vias and aluminium boards
Where the heat goes, what you can do about it in the layout, and when it is time to move from FR4 to an aluminium board.
Heat leaves the board in three ways
A component dissipates power as heat. On the board that heat travels through the copper and the laminate, spreads sideways, and leaves by convection and radiation from the surfaces, or through a heatsink or the enclosure. The layout decides how easily the heat can spread, so thermal design starts on the PCB, long before a heatsink is chosen.
Use copper where the heat is
Copper conducts heat roughly a thousand times better than FR4. Three levers follow from that:
- Copper area. Connect the thermal pad of a power component to a large copper area, not to a thin trace. Larger area means lower temperature rise.
- Copper weight. 35 µm is the usual choice; 70 µm carries more current and spreads heat better in the same area. We produce 18, 35, 50 and 70 µm (see the copper thickness guide).
- Inner planes. On multilayer boards, inner copper layers act as heat spreaders when the thermal vias connect to them.
Mind the compromise: a heavy copper layer needs wider spacing, and a large pad connected to a plane can solder poorly unless it is relieved with thermal spokes where manual or reflow soldering requires it.
Thermal vias
Vias under a thermal pad move heat from the top layer to a plane or to the opposite side. As a typical starting point:
| Parameter | Typical value |
|---|---|
| Drill diameter | 0.3 mm |
| Pitch | about 1.0 to 1.2 mm |
| Placement | grid under the thermal pad |
| Connection | to a copper plane or a large area on the other side |
Open vias under a pad can draw solder away from the joint during assembly. Check with your assembler whether they want the vias reduced in number, offset, or covered with solder mask. Our limits for holes are in the guide on vias and hole sizes.
Board thickness and material
Thinner boards have a shorter vertical path, but the heat still has to spread sideways through copper. Standard FR4 has low thermal conductivity, so the copper does most of the work. For the standard thicknesses see PCB thickness.
When to choose an aluminium board
If a component dissipates more heat than copper area and vias can handle, as with LEDs or power stages, an aluminium board (IMS, insulated metal substrate) conducts heat into the metal base and from there to a heatsink or housing. It has one copper layer and a thin dielectric between copper and aluminium. Read FR4 versus aluminium for the comparison and aluminium boards for LEDs for design rules.
Layout rules that help
- Place high-power parts apart from heat-sensitive ones.
- Keep heat-generating components away from board edges where the board is clamped, unless the edge is the intended thermal path.
- Do not place all hot parts in one corner; spread them.
- Use wide traces and planes for power; they carry both current and heat (see trace width and current).
- Verify the result on a prototype with a thermal camera or thermocouple, not only by calculation.
Calculate the price of your board with the price calculator, or send us the files for review.
Frequently asked questions
How many thermal vias do I need under a component?
There is no fixed number; it depends on the power and the copper area they connect to. A grid with a 0.3 mm drill and a pitch of about 1.0 to 1.2 mm is a common starting point. Confirm the result by measuring a prototype.
When is an aluminium board better than FR4?
When the heat cannot be spread by copper and vias alone, for example with LEDs or power components. An aluminium board conducts heat into the metal base, but it has a single copper layer.
Does thicker copper help with heat?
Yes. Thicker copper spreads heat better and carries more current, but it needs wider spacing between traces. We offer 18, 35, 50 and 70 µm.
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