When solder melts and forms a joint between two metal surfaces, it actually forms a metallurgical bond by chemically reacting with the other metal surfaces.
A good bond requires two things, a solder that is metallurgic ally compatible with the metals being bonded and good metal surfaces, free of oxides, dust, and grime that prevent good bonding. Grime and dust can easily be removed by cleaning or prevented with good storage techniques. Oxides, on the other hand need another approach.
Oxides form on almost all metals when oxygen reacts with the metal. On iron, oxidation is commonly called rust, but it happens to tin, aluminum, copper, silver, and nearly every metal used in electronics. Oxides make soldering much more difficult or even impossible, preventing a metallurgical bond with the solder. Oxidization happens all of the time, but happens much faster at higher temperatures, like when soldering Flux cleans metal surfaces and reacts with the oxide layer, leaving a surface primed for a good solder bond. Flux remains on the surface of the metal while soldering which prevents additional oxides from forming due to the high heat of soldering.
As with solder, there are several types of solder, each with key uses and some limitations as well.
Liquid Flux EF350 2.5L Container
Stannol Liquid Flux Container
The halogen-free activated No-Clean Flux EF350 guarantees outstanding wetting capability on different surfaces (e.g. OSP, Ni/Au, HAL, chemical Sn and chemical Ag) both with lead-free and solder alloys containing lead. Special additives have been integrated in the formulation of the flux to meet the requirements for the solder behavior of the flux and the electrical safety of the circuit board.SKU: 164151
Weller Electronic Flux 100ml
Liquid flux for fast and efficient soldering of electronic components also suitable for tin plating or solder pot dip tin plating. (Halogen free colophony liquid flux). The liquid flux remains on the soldered area, please use a suitable flux cleaner if a flux free board is required.SKU: T0051383199