There are many applications, especially in high-volume soldering, where furnace soldering produces consistent and satisfactory results. Furnace or oven heating should be considered under the following circumstances:
(1) When entire assemblies can be brought to the soldering temperature without damage to any of the components
(2) When production is sufficiently great to allow expenditure for jigs and fixtures to hold the parts during soldering
(3) When the assembly is complicated, making other heating methods impractical
Furnace or oven soldering is usually carried out with inorganic fluxes because of the temperature and time requirements. The use of a reducing atmosphere in the oven allows joints to be made with less aggressive types of fluxes, depending on the metal and solder combination. The use of inert atmospheres will prevent further oxidation of the parts but still requires adequate and appropriate fluxing. It is often advantageous to accelerate the cooling of the parts on their removal from the oven. An air blast has been found satisfactory.
Furnaces should be equipped with adequate temperature controls since the flow of solder has an optimum temperature range, depending upon the flux used. The optimum heating condition exists when the heating capacity of the furnace is sufficient to heat the parts rapidly under controlled flux application.