Soldering terminology

Breakdown products of flux left behind on the solder joint after soldering. Because they usually contain corrosive substances, their presence can jeopardize the long-term load capacity of the solder joint. Residues may also absorb moisture in a hygroscopic environment, leading to the formation of conductive connections between conductor tracks and to the migration of copper and tin as a consequence. There is high demand for fluxes which break down into residues that do not require the use of CFC- based cleaners, but are easily removed with water. Such fluxes are referred to as water-soluble fluxes, although, strictly speaking, the name "flux which forms water- soluble residues" would be more accurate. Since residues complicate the verification with a bed of nails tester, they should be removed as far as possible. However, RMA fluxes do not require cleaning. If residues are not removed, their surface insulation resistance (SIR) must be tested at temperatures up to around 100 °C in a humid atmosphere as they may cause even the substances isolating at room temperature to lose their insulating ability when the solder joint heats up.