SOLUTION

The functions of flux in soldering are to activate the cleaned metal surfaces to be joined, protect that cleaned surface during heating processes, and be available to protect the molten solder at the proper processing temperature.

Fluxes may be classified into three groups:

(1). Inorganic fluxes (most active):- This class of flux includes inorganic acids and salts. These fluxes are used where conditions require rapid and highly active fluxing action. They can be applied as solutions, pastes or dry salts.

(2). Organic fluxes (moderately active):- They are active at soldering temperatures, but the period of activity is short because of their susceptibility to thermal decomposition. Organic fluxes are particularly useful in applications where controlled quantities of flux can be applied and where sufficient heat can be used to fully decompose or volatilize the corrosive constituents.

Zinc chloride commonly called “Killed Spirits” of Salts and forms the base for more commercially produced fluxes. A good genera flux suitable for mild steel, brass, copper, ternplate, and Tinplate

(3). Rosin fluxes (least active):-  Rosin fluxes possess important physical and chemical properties which make them particularly suitable for use in the electrical industry.