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How to Choose the Right Flux and Solder

How to Choose the Right Flux and Solder

Kester solder with flux coreDoing your own electronics projects can be a fun and rewarding and these types of projects have something in common with making professional consumer electronics. That is, both require the use of solder and flux to secure the electronic components to a circuit board while ensuring electric conductivity. There are a few different types of solder all with different properties and this solder is usually used in conjunction with flux. While solder is kind of easily recognized, flux for electronics soldering is most commonly rosin, though other substances are sometimes used. This flux essentially cleans the metal connections and allows the solder to flow and melt properly to solidify an electronics connection. Try soldering without flux some time and you’ll see how important it is. Regardless of the type of project you’re doing, you want to make sure you’re using the right solder and flux for what you’re doing. But how do you choose the right flux and solder?

solder being appliedIt’s actually not that hard overall. Solder is pretty straight forward, but even so there are a number of different types to choose from. The most common type of solder is a 60/40 tin/lead alloy, but in the last few decades that has changed to reduce the amount of lead or remove it altogether as part of the “Reduction of Hazardous Substances” (RoHS) driven mainly by Europe. Solder with less lead tends to increase the amount of tin and/or add silver to it while lead free solder is typically made from some combination of tin and silver, which for obvious reasons costs more, though there is some solder that’s pretty much 100% tin. Each of these types of solder has a different melting point (or this chart) which is an important factor to consider when deciding upon which solder to use. There are situations where you want to choose a solder with a lower melting point because a higher melting point can sometimes damage electronic components.

rosin fluxSolder also has a few other options to consider. Firstly, there are different diameters to choose from, 0.02", and 0.04", 0.063" being the most common. The thicker, .063” is used for larger wires whereas the finer solder is obviously used for higher detail work and with smaller components. With these finer jobs it is important to use the thinner solder in a move to prevent bridging your solder joints by using too much. In addition to diameter, something else to consider is whether the solder is solid core or hollow with a flux core. One key thing to avoid is the use of acid core flux. The reason for that is because that’s used for plumbing and the acid will destroy and damage your components. Instead, rosin is the one to use and is honestly the most common, though there are other kinds. The benefit of having a rosin flux core while you’re soldering is it helps the solder flow more smoothly once it melts and reduces the amount of flux you have to apply before and during use.

Speaking of flux, as mentioned earlier, flux is an important part of any soldering job, because without it, the solder won’t flow well and it won’t stick as well to the metal you’re applying it to. In addition to making your melted solder flow, the flux’s main job is to clean the metal being soldered to ensure that when the solder hardens that it will stick and harden smoothly. Soldering that is done without the right amount of flux (and the right amount of solder) tends to result in sloppy connections, peaks and other undesirable things. In addition to rosin flux, you can use water soluble flux which can be cleaned with water, however its high acidity makes it something of an issue for most electronics work. No-clean flux is somewhat ironically named because to remove it you need to use special solvents. The name though stems from the fact that in theory you don’t need to clean it because its acidic properties are dormant until it’s heated and molten. That’s not personally an option to recommend, though there may be situations where it makes sense.

Soldering do's and dont's With these different types of solder and flux available it can be hard to choose the right one, however if you compare the available solder and flux with the needs of what you’re building you should be able to figure it out. Are you building something that you don’t want corroding? Use rosin flux with the appropriate cleaner afterwards. Do you have restrictions or concerns on lead? Use lead free solder. Small detailed work or larger piece? Choose the right diameter solder. Are your circuits sensitive to heat? Get solder with a lower melting point. Do you want your soldering to be easy? Use flux core solder with a little extra flux applied on the side. You’ll find that rosin flux and 60/40 solder will do most jobs and if you have special considerations make a different choice from there.

Choosing the right flux and solder is relatively straight forward and it’s important to choose something that will be easy to apply to create a clean solder connection. Regardless of what type you end up using you want to make sure to have proper ventilation and clean the flux from the circuits and your hands when you’re done. While the danger of lead poisoning is low you want to be careful to wash your hands when you finish and ventilation takes away the slightly acrid vapors put off by the smoking flux. When you’re ready to start working with solder we recommend choosing a high quality solder for best results, Kester and MG Chemicals being two of the brands we know make a great product you can rely on.

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