Flux Information & Solderability

Soldering process requires clean surfaces so the base metal is well exposed to the molten solder. During soldering operation, fluxes do the following:

  1.    Remove the oxide films on the base metal.
  2.    Momentarily prevent further formation of oxide films.
  3.    Lower the surface tension of the solder to promote wetting.

Fluxes need to be removed after the soldering process since they tend to be corrosive. If they are not properly cleaned, they will eventually corrode the metals being joined, leading to product failures. For environmental reasons, the least aggressive flux should be chosen to do the job. A range of No Clean Fluxes are available that does not require cleaning.

 

Solderability

Base Metal

Remarks

Excellent

Tin
Gold
Silver
Palladium
Rhodium

Noble metals dissolve easily in solders. Care must be taken because the solder joint can be brittle.

Good

Copper
Bronze
Brass
Lead
Nickel-Silver
Beryllium-Copper

High thermal conductivity of these metals requires high heat input during soldering. Oxidizes quickly so proper flux must be used

Fair

Carbon Steels
Low-Alloy Steels
Zinc
Nickel

Solder joints become brittle in sulfur-rich environments. Avoid higher temperatures in the presence of lubricants (which contain sulfur).

Poor

Aluminum
Aluminum-Bronze

Tough oxides on the surface prevent wetting (formation of the inter-metallic layers). Solders have to be specially selected to avoid galvanic corrosion problems.

High-Alloy Steels
Stainless Steels

Too much chromium oxide the surface needs to be cleaned with an aggressive flux.

Very Difficult

Cast Iron
Chromium
Titanium
Tantalum

Require pre-plating with a solderable metal.