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IC Thermal Copper Area Calculator | NextPCB
 

IC Thermal Copper Area Calculator

Estimate how much PCB copper pour you need to act as a heatsink under a power IC or surface-mount package, from power dissipation, junction temperature limit, and ambient temperature.

Thermal Parameters

W

The power the device needs to dissipate as heat (not its total input power).

°C
°C

Uses a natural-convection copper-pour approximation for a single 1oz copper layer. See the FAQ for what this model does and doesn't account for.

Estimated Copper Area Needed

IC side copper pour heatsink (illustrative, top view)

Required Copper Area

0.00 cm²

≈ a 0.00 cm square copper pour under the package

Req. θJA

0.00 °C/W

Temp Rise (ΔT)

0.00 °C

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Calculation Reference

This calculator uses a widely circulated rule-of-thumb approximation for sizing a natural-convection PCB copper pour as a simple heatsink under surface-mount power packages. The required thermal resistance is derived from your temperature budget, then converted to a copper area.

  • ΔT = Tj − Ta, your available temperature budget
  • θJA = ΔT / Pc, the thermal resistance you need to hit
θJA (°C/W) = 50 / √Area(cm²)
Area (cm²) = ( 50 / θJA )²
A commonly cited empirical approximation for single-layer, ~1oz copper, natural convection. Treat as an order-of-magnitude estimate — see the FAQ.

Frequently Asked Questions

What does this calculator actually estimate?

It estimates how much PCB copper pour area, acting as a simple natural-convection heatsink, you'd need under an IC or power package so the junction temperature stays under your target limit at a given power dissipation. It's meant for early-stage, back-of-envelope sizing before you commit to a layout, not as a substitute for thermal simulation or measurement.

Where does the formula come from, and how accurate is it?

This calculator uses a widely circulated rule-of-thumb approximation, θJA (°C/W) = 50 / √Area(cm²), which is commonly cited in application notes for sizing PCB copper heatsinks under SOT-223, DPAK, and similar surface-mount power packages. It's a simplified empirical fit, not a first-principles calculation, and published constants for this kind of estimate vary meaningfully across sources depending on copper weight, board layer count, and airflow, so treat the result as an order-of-magnitude starting point rather than a guaranteed number.

What does this calculator not account for?

It assumes natural convection (no fan), roughly 1oz copper, and a copper pour that isn't blocked by nearby components, and it doesn't account for copper weight beyond that baseline, the number of layers connected to the pour, thermal vias, solder mask coverage, or heat from neighboring parts. Heavier copper, additional layers tied together with vias, and airflow can all meaningfully reduce your real thermal resistance below what this simple formula predicts, while a crowded layout or thin single-layer copper can make it worse.

What is θJA (junction-to-ambient thermal resistance)?

θJA describes how many degrees Celsius the junction temperature rises above ambient for every watt of power the device dissipates, combining every step in the heat path from the die through the package and, in this case, out into the copper pour and surrounding air. A lower θJA means the part can dissipate more power for the same allowable temperature rise, which is why adding copper area (which lowers θJA) is one of the simplest ways to raise a surface-mount part's usable power rating.

Do thermal vias help even though they're not part of this calculation?

Yes. Adding an array of thermal vias under or near the package, connecting the top copper pour to internal or bottom-layer copper, is one of the most effective ways to lower real-world thermal resistance beyond what a single-layer copper pour alone achieves, since it lets heat spread into additional layers rather than being limited to the top surface. This calculator doesn't model vias, so treat its area estimate as a conservative single-layer baseline that thermal vias can improve on. See our Via Current Calculator for sizing the vias themselves.

Should I trust this for a final, shipping design?

Use it to get a rough starting footprint during early layout planning, then verify the real design with your component's datasheet thermal data, a thermal simulation tool, or physical prototype measurement, especially if the part is running close to its power or temperature limits. The variability across published empirical formulas in this space means a simple square-root rule is a reasonable first guess, not a certified thermal analysis.

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