What is MFC gas correction factor?

How K-factors relate calibration gas (usually N₂) to process gases, and how correction affects delivered flow in semiconductor gas panels.

Mass flow controllers are typically calibrated with a calibration gas—most often N₂—then corrected for other gases using a gas correction factor (K-factor) stored in the MFC firmware or gas panel software. The K-factor adjusts for differences in heat capacity and thermal conductivity that affect the thermal sensor used in most MFCs.

Why K-factors exist

Thermal MFCs infer mass flow from heat transfer to the gas stream. That heat transfer depends on gas properties, not only volumetric flow. Without correction, an MFC calibrated on N₂ would read incorrectly when flowing Ar, H₂, or specialty gases like NF₃ or SF₆.

Corrected flow ≈ Indicated flow × K-factor (gas) / K-factor (calibration gas)

Vendor K-factors are determined empirically per MFC model. Always use the gas name programmed in the tool software—not an approximate match.

Worked example — Mass-flow audit with MFC Gas Flow Unit Converter

Recipe specifies 200 sccm Ar carrier. After verifying K-factor is set to Ar in the gas panel, log mass flow for abatement reporting.

Converter: 200 sccm, gas Ar, To: g/min → 0.357 g/min.
Same 200 sccm on H₂ → 0.018 g/min—K-factor and density both matter for mass delivery.
If K-factor is left at N₂ while flowing Ar, indicated sccm may look correct on the MFC display but actual molar/mass delivery can be wrong—always verify with span check on the actual gas.

Common mistakes

Using N₂ K-factor for corrosive or specialty gases without vendor table entry
Confusing K-factor correction with sccm-to-kg/hr density conversion—they address different steps
Ignoring full-scale vs setpoint accuracy after K-factor is correct

See MFC calibration basics and Why MFC accuracy affects yield.