Heat Spreader Sizing Calculator
Work out heat spreader sizing instantly with clear inputs, formula shown and shareable results.
About Heat Spreader Sizing Calculator
Heat spreads laterally through a spreader at roughly 45 degrees, so a 3 mm copper lid over a 13 mm die presents about 19 mm of area to the heatsink — nearly twice the flux reduction. Beyond that the spreading resistance of the material itself limits any further benefit.
Formula
Heat spreading
spreader side = die side + 2 x thickness x tan(45 degrees); flux reduction = spreader area / die area
Worked example
With the default values below, Heat Spreader Sizing Calculator returns Recommended spreader area of 377. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Power to spread
- 95 W
- Die area
- 180 mm²
- Spreader thickness
- 3 mm
- Spreader conductivity
- 390 W/m·K
Results
- Recommended spreader area
- 377 mm²
- Spreading thermal resistance
- 0.09556 °C/W
- Spreader side length
- 19.42 mm
- Heat flux reduction
- 2.09 x
Step by step
- 1Values used
- 2Heat spreading
- 3Recommended spreader area= 377 mm²
- 4Spreading thermal resistance= 0.09556 °C/W
- 5Spreader side length= 19.42 mm
- 6Heat flux reduction= 2.09 x
Assumptions and limits
- The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 5 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
Why not use a very large spreader?
Beyond about a 45 degree spread cone the extra area receives little heat, because in-plane conduction resistance dominates. Thicker copper helps more than wider copper.
Why copper rather than aluminium?
Copper conducts about twice as well (390 versus 200 W/m·K), which matters most in the spreading layer where flux density is highest.
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