Buying good solder. What rosin core to buy? - Page 1
Forum section: electronics / beginners

author: RiRaRi
author_rank: Regular Contributor
timestamp: February 27, 2025, 03:41:50 pm
content: Hello. I have been soldering for some time now but recently it got to my attention that there are multiple rosin cores: R, RMA, RA. Also, this applies with external flux which should be used. I got recommendation that Kester 44 is good solder for my application which is vintage audio. However, since i do not work with highly oxidized PCB and wires i think RMA would be the best. Kester 44 is RA. I use Weller R additional flux. Will the solder joint separate if i do not use activation? Also Kester 44 datasheet is confusing, it says: "Do not apply the solder directly to the soldering iron tip, doing so will shorten the life of the soldering tip" and "Additional liquid flux should only be used as a last resort". Can anyone clear things up about this for us beginners?

author: tooki
author_rank: Super Contributor
timestamp: February 28, 2025, 12:36:28 am
content: I’m moving my reply to this thread (and modifying it a bit); I suggest you delete your reply in the other thread as well, since it’s a necropost to a 6 year old thread.People have been using Kester 44 for the better part of a century, mostly without cleaning. It’s safe to leave on, in that it does not cause corrosion, and its conductivity is low enough for normal applications.I’m a bit puzzled about the “don’t apply directly to the tip” line, too, insofar as you never apply solder to the tip when making joints (you heat the joint and apply solder to the joint, not the tip), except that you must tin the tip with solder before (and ideally after!) use.Anyway, Kester 44 (technically ROM1, which most closely aligns to RMA, but Kester classifies it as RA. However, its residues are non-corrosive and explicitly are safe to leave on for most purposes) is the same stuff people were using when your vintage gear was made. And it’s a fantastically good solder. I use it daily at work.I recommend the size-66 flux core (~3% flux) when using thinner diameters like 0.032”/0.8mm or smaller.

author: Konkedout
author_rank: Frequent Contributor
timestamp: February 28, 2025, 04:44:40 am
content: Quote from: tooki on February 28, 2025, 12:36:28 amYES I also like to use the Kester 44. I am no expert on the chemistry, but I have been soldering for about 60 years. I think that the flux is "mildly activated". I can tell that it works much better than the ordinary rosin core solder. The other thing...often it is helpful to apply flux before soldering. For example do you ever try to solder bare copper wire? I have flux in paste form and also in a "pen" which is good to apply to SMT extended pads before putting down the component and soldering it. I have never seen evidence of corrosion from the Kester 44 solder.I like to use the 0.040 inch diameter solder for the medium-larger components, and I think I am using 0.020 inch diameter for fine work.

author: Whales
author_rank: Super Contributor
timestamp: February 28, 2025, 05:55:33 am
content: Quote from: RiRaRi on February 27, 2025, 03:41:50 pmWe can only guess. You have to judge the quality of the joints by visually inspecting them after you finish soldering.If your joints end up bad then you don't have to change solder. Instead you can add more flux externally or (for more serious corrosion) mechanically remove it with steel wool or similar. Changing solder might be easier if you are working with bad surfaces regularly, however.

author: Simmed
author_rank: Frequent Contributor
timestamp: February 28, 2025, 06:41:00 am
content: Quote from: RiRaRi on February 27, 2025, 03:41:50 pmthe additional question after that would bewhich 1 will wash off completely with simple 70/90% IPAor which 1 will require special post washing process

author: RiRaRi
author_rank: Regular Contributor
timestamp: February 28, 2025, 04:18:04 pm
content: Thank you all for advice and clearing things up. Going to buy 44. What about "Additional liquid flux should only be used as a last resort" which is in Kester 44 datasheet? I always or almost always use additional rosin flux which works great. Do you use additional liquid flux with this solder?

author: tooki
author_rank: Super Contributor
timestamp: February 28, 2025, 05:55:08 pm
content: Quote from: RiRaRi on February 28, 2025, 04:18:04 pmDepends on what you’re doing. But for most things it’s not needed. I generally use additional flux when doing rework, or for the types of soldering procedures where no new solder is added. But for ordinary through-hole joints, tinning wire, etc. it isn’t needed.

author: tooki
author_rank: Super Contributor
timestamp: February 28, 2025, 06:05:29 pm
content: Quote from: Simmed on February 28, 2025, 06:41:00 amKester 44 comes off ok, but not perfectly, with 95%+ IPA.I wish people would stop recommending straight IPA as flux cleaner: solvent blends work much better. Commercial flux removers are really good. For non-delicate components, a mix of alcohol and acetone is extremely effective.But there’s also a lot to be said for water-based cleaning. Commercial saponifying cleaners like the Electrolube Safewash series (or the chemically similar ZEP floor wax stripper, which is far cheaper, but not designed for electronics) work very well, especially in an ultrasonic bath.I now use ultrasonic whenever possible (i.e. when all components are safe to submerge and are not sensitive to ultrasound), as it makes quick work of flux, doing especially well at flux residues underneath components, where hand cleaning struggles. Depending on the situation, I use either Safewash Super (SWAS) or alcohol (we have tons of ethanol at work so I use that), in either case in a smaller container suspended in the ultrasonic bath filled with water; that avoids needing huge volumes of cleaner or solvent, and avoids the significant danger of large amounts of flammable solvent, heated, in a device that tends to encourage aerosolization.