Most fluxes nowadays are “no-clean”, which encompasses a huge range of flux formulations whose only shared characteristic is that their residues don’t need to be cleaned. As a consequence of their reduced use, far fewer rosin fluxes are made now, so they’re becoming harder (not impossible, before anyone jumps down my throat…) to find, especially here in Europe. Rosin fluxes tend to not stand up as well to the higher temperatures of lead-free soldering, which is one reason why rosin fluxes aren’t used as much as they used to be. You can buy liquid rosin flux, or liquid flux of other types. for example bga flux gel : the msds (in Polish but scroll down to page 3 ) ex 10-25% rosin reacted with acrylic acid, <10% 2-decyltetradecanoic acid, <10% Carboxylic acids, <10% 2-hexyldecanoate, <10% 2-ethylimidazole, <5% succinic acid and <5% castor oil You can buy most of these chemicals but minimum quantities are kind of big, considering the percentages you need I recommend checking out MSDS for various gel fluxes to see what they use to make them gel like. it's available at Amazon, food grade stuff, like $10 for 12 ounces/340g bag that will last for tens of liters of liquid flux: For gels. They sell on TME.eu 500g bags of colophony preactivated with 2.5% adipic acid for less than 5 EUR plus shipping : So you can just add isopropyl alcohol and optionally benzoic acid. For example a liquid flux I often use - Topnik TK83 by AG Termopasty is made according to the MSDS with <25% rosin, <75% isopropyl alcohol and <5% each of benzoic acid and adipic acid. I actually mentioned to another person this morning that you can make your own flux by buying colophony (pure rosin) and mix it with isopropyl alcohol and optionally with acids that make the flux more active. You can do the work with liquid flux as well, it's just going all over the place more easily. for example let's say in SMD, when you want to clean the pads for a soic or a qfn part, you may apply a bit of flux over the pads so that you can then bring some solder into a cup solder tip (used often for drag soldering), tin the pads, then clean the pads with solder wick (to remove the old solder plus freshly applied solder), apply flux again and now tin the pads again with just the fresh solder. Gels and pastes are good for when you need some flux and don't want it flowing it around. but it can be cleaned usually with isopropyl alcohol or acetone or flux removers if you don't want reside on the circuit board. Rosin flux is relatively mild and active only when it's heated up, and helps make better solder joints and in general it's not needed to removed from the circuit board as it's not conductive. The flux inside the solder is supposed to become liquid as it heats up from the solder iron tip, drop on the leads or pads your want to solder and attack the surfaces and corrode the oxides and shit so that when you bring the actual solder, the solder metal has a chance to chemically combine with the metals on the pads or leads and make a strong connection. and it's possible to have the solder iron tip too hot and actually burn the flux before it gets a chance to activate and do its job. It's not always enough, it depends on the parts you want to solder, how old and oxidized they are. typically 1 to 3% flux depending on diameter of wire and other factors. ![]() Modern solder wires have some amount of flux in them. NOW - a big question: What's wrong with the Rosin? If I go my old way and solder with the rosin solution in spirit - is there anything wrong with that? Last question: To make a paste like flux is it possible to mix the ethanol alcohol, rosin and Vaseline (petroleum jelly)? Will it work as a paste flux? ![]() ![]() Remember, those warnings are copied over to the Chinese made fake stuff but since it exists on the original ones as well it must be twice as bad! Nevertheless people quote those warnings and continue to use it. However, there is a warning on those plastic jars: Don't use at home, it's toxic, harmful, so on. Amtech, Kingbo, you name it, are being the most popular ones but despite the fact they are fake people buy them in tonnes and enjoy soldering with them. Now, when I'm returning to the hobby I find the majority use some sort of paste flux that comes from China in syringes or plastic jars. I fact I tried to solder with the rosin core solder only and it didn't work just as good as it worked with the rosin solution added. To make it short: I used rosin core solder then BUT! - I was taught at that time (remember, it was over 30 years ago) not to rely solely on the rosin core solder but use spirit (alcohol) soluble rosin at every solder point in addition to the rosin activated flux and I did exactly that. Last time I seriously touched my iron, it was 32 years ago when I soldered-assembled and setup a clone of the ZX Spectrum Z80 MPU based computer.
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