Soldering fluxes

The requirements of a good soldering flux are:

1. It must remain liquid at soldering temperature.

2. In its liquid state it must act as a cover over the joint and exclude the air.

3. It must dissolve any oxide film present on the surfaces being joined.

4. It should be readily displaced from the metal surfaces by molten solder.

Fluxes used for soft soldering operations may be classified as active or inactive (passive).

The active fluxes will quickly dissolve the oxide film on a metal and, at the same time act as a barrier to prevent further oxidation.

All active fluxes have a corrosive action. Although any active flux residue which is present along the edges of the joint after soldering may at first appear to be dry and harmless, it must he removed as soon as the soldering has been completed. These apparently dry flux residues which remain after soldering absorb water readily from the atmosphere. Within a few hours any active flux residue, if not removed, will become wet spots at which corrosion will take place rapidly. Corrosive flux residues may be removed by washing in hot water containing a few drops of hydrochloric acid, rinsing in a hot dilute soda solution, and finally in hot water to remove the salts formed. If only hot water is available, the soldered part should be thoroughly rinsed.

The inactive fluxes protect a previously cleaned metal surface and have little effect on oxides.

Because of the difficulty of avoiding corrosion the use of active fluxes is banned in electrical and other work that cannot be washed effectively.

Дата добавления: 2015-07-25