Thermal Via Array Calculator
Thermal resistance of a via grid under a QFN/PowerPAD — per-via θ from geometry, divided across the array.
The array only helps if BOTH ends connect to real copper: a solid pad on top and a spreading pour or plane below. Diminishing returns set in once via resistance drops below the spreading resistance of the planes (~5–10 °C/W) — that's why 9–25 vias under a QFN is the sweet spot, not 100. Use 0.3 mm holes: small enough to limit solder wicking, big enough to plate well.
Disclaimer: This tool is for general informational and estimation purposes only and is not professional financial, tax, accounting or legal advice. All figures are estimates — verify with a qualified professional before making decisions. Read the full disclaimer.
Thermal Via Array Calculator computes the thermal resistance of a via grid carrying heat through the board — free, instant and private in your browser. Designers cooling QFN/PowerPAD parts into a bottom-side pour or chassis use it to skip the datasheet algebra: type your numbers, read the answer with the substituted formula shown step by step, and share an exact permalink of the calculation.
About Thermal Via Array Calculator
Thermal Via Array Calculator computes the thermal resistance of a via grid carrying heat through the board using the standard engineering relation: θ(via) = L/(k·π·(d+t)·t) per via, divided by the count for the array. Worked live: nine 0.3 mm vias with 25 µm plating through 1.6 mm FR-4 give ~20 °C/W — 2 W drops ~40 °C across the board. The result recalculates on every keystroke, the worked-example panel shows your numbers substituted into the formula, and the Copy permalink button encodes the inputs in the URL so a colleague opens exactly your calculation. Everything runs client-side — nothing you type leaves your device.
How to use Thermal Via Array Calculator
- 1Enter your values — the tool starts with realistic defaults for this exact use case, so the worked example is meaningful immediately.
- 2Read the live result and the worked-example panel, which substitutes your numbers into the formula step by step.
- 3Adjust any input to compare scenarios, then use Copy result or Copy permalink to share the calculation.
Why use Thermal Via Array Calculator?
- ✓Implements the real formula — θ(via) = L/(k·π·(d+t)·t) per via, divided by the count for the array — with the substitution shown, not a black box
- ✓Built for designers cooling QFN/PowerPAD parts into a bottom-side pour or chassis
- ✓Copy result and permalink buttons — share the exact calculation in a README, forum answer or design review
- ✓100% free, no sign-up, runs entirely in your browser (works offline once loaded)
Frequently asked questions
How do you calculate thermal via array?+
The thermal resistance of a via grid carrying heat through the board follows θ(via) = L/(k·π·(d+t)·t) per via, divided by the count for the array. For example, nine 0.3 mm vias with 25 µm plating through 1.6 mm FR-4 give ~20 °C/W — 2 W drops ~40 °C across the board. The calculator applies the same relation and shows the substituted arithmetic so you can verify every step.
How many thermal vias should go under a QFN pad?+
A 3×3 grid of 0.3 mm vias suits most 1–3 W parts; 5×5 for power stages. Beyond that, returns diminish because plane spreading resistance (~5–10 °C/W) starts dominating. Tight pitch (0.8–1 mm) matters more than raw count.
Will solder wick down the vias and starve the joint?+
Open 0.3 mm vias wick a little — usually acceptable; bigger holes wick badly. High-reliability flows use filled-and-capped (via-in-pad) or tent the bottom side. For hand assembly, small open vias plus a touch more paste is the pragmatic norm.
Is the Thermal Via Array Calculator free and private?+
Yes — completely free with no sign-up or usage limits, and it runs entirely in your browser: the values you enter are never uploaded or stored on a server.
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