Describes flux-free soldering with formic acid HCOOH. The acid reduces the surface oxides, allowing the solder to wet the metal.

Formic acid is excellent at removing copper and tin oxides. Nickel oxides are possible with longer exposure times and high temperatures, while aluminum or steel is not attacked by formic acid.

Vacuum chambers are used in the soldering systems to create an oxygen-free atmosphere. The formic acid is usually introduced into the chamber in the form of an acid-nitrogen aerosol via a bubbler. Another form is the vaporization of the acid via a chemical vaporizer.

For optimum reduction, the product or acid should be at least 180°C warm. A reaction time of 2-3 minutes is usually required to reduce all surface oxides.