Let's dive today into the world of solder flux!
We've covered in past blog posts that different metals require different prep in order to become solderable. A necessary component to this prep is the use of flux to break down the oxide layer that forms when the metal molecules in your component are exposed to oxygen. A flux is made essentially of two ingredients, an activator, which is an acid that will break down the oxide layer, and a solid, which coats the surface of your components preventing further exposure to oxygen that might allow that oxide layer to reform. While there are degrees of strength when it comes to fluxes, you will generally see them labeled as one of the following categories;
Rosin, No Clean, Water Soluble.
We can break them down.
Rosin
Rosin is one of the most used flux types on the market, you will see it categorized often as Type R (and then RMA and RA which we will discuss in a bit). It's actually derived naturally from the resin of pine trees. To quickly touch on this, just because I think it's interesting, resin is a substance that occurs only in pine trees, or trees in the Pinaceae family. So you will not find it in deciduous trees. The process involves collecting this resin, which effectively acts as a scab when pine trees are injured, congealing on an distressed area of the trees outer bark and protecting it from outside forces while the tree heals. It's interesting to note that this substance is not the same as tree sap, which is more viscous and serves a different purpose for the tree it comes from. Once the resin is collected from a tree, it goes through a multiphase refining process to remove imperfections, and is then dissolved in a solvent, often Isopropyl Alcohol, to be used as a flux. The naturally occurring acidic properties make it useful for breaking down that pesky oxide layer. To increase the effectiveness of the flux, activators can be added. You will see this noted as RMA or RA, Rosin Mildly activated and Rosin Activated. Mildly Activated is, as the name suggests, more mild than Rosin Activated, the latter of which is more suited for tougher to solder more oxidized components. It is important to remember that the more activators you add, the more corrosive the flux becomes and the more important it is to clean the residue left over to make sure the board and components aren't negatively impacted.
No Clean
No Clean flux is a category of flux that is designed to leave residue that doesn't require cleaning. The flux itself works much the same as the rosin fluxes but is formulated to leave non corrosive residue, where essentially the corrosive activators are encased and inactive after the residue dries. The idea being that if we remove the cleaning process it will make production more efficient. As with all things, this type of flux does come with some drawbacks, as the residue itself is, counterintuitively, more difficult to clean than rosin. Being that you can leave it on the board, this is not a huge deal, but in practice this residue left behind can lead to some issues. For starters, the cosmetic look of a board that has visible flux residue can be troublesome if you are selling parts that you want to look nice for consumers. It can also collect dust and other debris that could interfere with the functionality of the board. Because the activators are being encapsulated to prevent corrosion, they can be released during repair or rework and if left uncleaned can corrode the circuits. For these reasons, there are a number of cases in which the No Clean ends up being cleaned anyway. For this you can use specific flux removal products such as ES835 which is useful in removing all rosin based fluxes, including those are of the No Clean variety.
Water Soluble
While the name gives a bit away about what makes this type of flux unique, there is quite a bit more to it than just dissolving in water. They contain organic acids, halogenated (containing chlorine or bromine) compounds, amides, and monobasic and dibasic organic salts and are more active than the previous two types we've discussed. For this reason, you may need to use this on older products that need extra effort to deoxidize or just metals that have less solderability. However, the corrosiveness of these solders require them to be cleaned completely off the surface of the board after soldering otherwise it will deteriorate.
Overall, there is a flux designed for each specific project you can imagine. While I think it's important to do your own research to make sure you select the right flux for what you're trying to do, I hope this will give a general outline to point you in the right direction.
Now, I'd like to quickly go over some of the specific fluxes that you'll find here on the site.
You will find that the solders we have available for purchase are flux cored wire solder. Which means that there is flux contained in the wire itself, that is released during the soldering process.
Some of the fluxes you'll find in the solders are as follows:
Kester 44
this is a RA (Rosin Activated) solder flux, many consider it to be the industry standard, Kester describes it's instant acting wetting performance as its stand out feature. Because it is a more activated flux, it is extremely effective but does need to be cleaned well after use.
Kester 48
This is another RA flux that builds upon the 44, it is specifically designed for use with lead free solders. Since lead free typically has a higher melting point than leaded, a more specialized flux is also required.
Kester 245
This is a no clean flux, designed to leave less residue that doesn't need to be cleaned like the previous rosin based fluxes. Behaves similarly to an RMA flux.
Kester 275
Similar to the 245, this is a no clean flux that leaves a clear residue that doesn't need to be cleaned after soldering. On this site you will see it in the Lead Free solder wires.
Kester 285
This is a RMA mildly activated solder flux that is designed to be more effective than ordinary RMA fluxes, with Kester describing it as comparable to a RA flux. It is designed for projects require use of a RMA flux but increased solderability is necessary.
Kester 331
This is kester's water soluble flux core, its an organic flux that is designed to be more effective than Rosin fluxes for use on difficult to solder materials. Can be cleaned with a heated water rinse. Deionized water is recommended.
Some of the fluxes that we sell separately in the form of pens are as followed:
Kester 186
This is the liquid flux counterpart to the 285 RMA solder, designed for when RMA flux is required but a flux more closely aligned with RA is needed.
Kester 951
This is a zero halogen no clean flux designed to leave minimal residue that does not require cleaning.
Kester 2331 zx
This is the liquid counterpart to the 331, a water soluble flux designed for tough to solder materials.
