Refers to a silvery haze that forms around the solder joint on the substrate during formic acid soldering. The reason for this is tin formates which are formed together with the formic acid if the process settings are incorrect. The formates detach from the solder and are deposited on the circuit carrier. There they decompose into tin and leave behind the so-called tin fog or tin dust that appears as a silvery discoloration on the substrate.

A lower concentration of formic acid or a reduction in the exposure time and temperature will help.