A Guide to Different Types of Solder Flux

1. A Guide to Different Types of Solder Flux Soldering is an essential part of electronics assembly, as it ensures proper connections of components on the printed circuit board. It requires the use of an appropriate solder, which can sometimes be administered with a flux to ensure good joints and avoid problems like bad connections and failure to create a reliable joint. To prevent bonding issues, the soldering process involves a flux agent to facilitate soldering. When choosing solder flux, you need to consider the kind of circuit board you are using, the type and density of electronic components that must be soldered, the solder ability of the metals for joining, and the soldering process. Flux is a form of chemical that is essential to the soldering and assembly of printed circuit boards, as it functions to keep the PCB’s surface clean before soldering. Its main function is not only for cleanliness, but the removal of any oxide that may form during the soldering process, too. Oxides present on a PCB are typically the reason for improperly formed joints, resulting in poor electricity flow and inefficient electrical conduction. With solder flux, you de-oxidize the metals for proper soldering and wetting. Activators found in a flux promote the wetting of molten solder on component terminations and surface mount lands, or on the lead by eliminating oxides and contaminants. There are different types of solder flux, which are formulated following J-STD-004 industry standards. Rosin flux is mainly made up of a refined natural resin from pine trees, and it is further classified into the following categories: 1. R (Rosin) flux - Primarily made of rosin and considered the least active, but virtually leaves no residue after the soldering process. 2. RMA (Rosin mildly activated) flux– Contains sufficient activators for cleaning plated or solder-coated lands. The component leads or terminators make the molten solder efficient in wetting those areas. 3. RA (rosin activated) flux– The most active but leaves a lot of residue. Solder flux is also classified as water-soluble and no-clean. The latter is exactly as the name describes—it does not require any cleaning post-soldering. Water soluble flux is otherwise referred to as OA (organic acid) flux, which is usually formulated with organic materials besides resin or rosin. When used, it generates good results due to good flux activity and efficient wetting action, which eliminates oxides to keep the surface clean for soldering. However, it tends to become too aggressive. So, users must be extra cautious during cleaning to prevent flux contamination.