The Flux Coefficient (FC) is a measure of the dielectric properties of a solder paste. Due to no-clean solder pastes having slow flux-powder interactions, the powder-flux interface is typically not visible in a timely manner through the Electrochemical Impedance Spectroscopy (EIS) measurement by the Vision MARK-1. Therefore, the FC is typically tracked in no-clean solder pastes.
The properties measured by the FC are defined as the conductivity/ion mobility and polarizability of the bulk flux media. A smaller FC value could indicate a more conductive flux media or an active flux. A larger FC value could indicate a less conductive flux media or a less active flux. The FC correlates well with viscosity and probability of solder balling after reflow.