Q: We need to remove RMA solder flux on indium/lead soldered sub assemblies. Most aqueous cleaners attack this solder.
A: Generally speaking, indium lead solders are alkali resistant solders. Rosin mildly activated (RMA) flux traditionally consists of rosin, solvent, and a small amount of activator. The RMA solder flux is best cleaned by alkaline/saponifying cleaners with no chelating agents, halides or conductive metal cations such as sodium. Our Alconox Inc. cleaner, Detergent 8® Low-Foaming Ion-Free Detergent is a great choice.
The ion-free formulation also ensures safety when cleaning circuit boards or other electronics that could be short circuited by even the most minute amounts of residual ions. Because Detergent 8 is cation free, it cannot leave conductive residues.
The organic amine in Detergent 8 cleaner forms a water soluble soap with the rosin. We recommend using a 3% Detergent 8 solution for ultrasonic immersion cleaning or a 5% Detergent 8 solution for manual cleaning of indium/lead soldered sub assemblies. Solutions should be warm and thoroughly rinsed, typically with DI water.
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