What is flux?
What type of flux should I use?
- No-clean flux is a good choice for soldering where cleaning is to be avoided. The light residue can be left on the board, or removed with a flux remover.
- Rosin activated flux (RA) provide excellent solderability in a wide variety of applications. It is best to remove the residue after soldering for aesthetics and avoid corrosion down-the-line.
- Rosin flux (R) or mildly activated rosin flux (RMA) can generally be left on the PCB after soldering unless the aesthetics are a problem.
- Water soluble flux (OA) is a very active flux engineered to be removed easily with DI water, like in a batch or in-line system. It can also be removed with isopropyl alcohol (IPA). It is very important to clean off water soluble flux residues because they are highly corrosive.
Do I need to add extra flux when soldering?
If soldering a simple connection, like 2 wires, or a thru-hole lead, the flux in a flux core solder should be enough. For more complex soldering techniques, like drag soldering multiple leads on a surface mount component, additional flux may need to be added. The flux is activated and consumed when it originally flows from the core. If the solder is worked further, like when you drag across multiple leads, you run the risk of cold joints or bridging without additional flux. While more seems like it should be better, take care not to over apply flux. Excess flux needs to be removed, especially if it isn’t fully activated by being heated to full soldering temperature.
How do I apply extra flux?
Flux can be painted on with an acid brush, applied with a needle bottle dispenser, or with a pen dispenser. While more seems like it should be better, take care not to over apply flux. Excess flux needs to be removed, especially if it isn’t fully activated by being heated to full soldering temperature.