Mixing rosin core solder with resin based flux - Page 1
Forum section: electronics / beginners

author: franksouto
author_rank: Newbie
timestamp: August 14, 2023, 05:16:06 pm
content: Hi all,I was thinking about buying those:* MG Chemicals 4880-18G RA solder wire* Chip Quik SMD291-10M REL0 no-clean tack fluxBut I realized the solder wire is rosin type (ROL) while the flux is resin based (REL).I understand that for applications like drag soldering, where the solder turns liquid in the iron tip (and the flux is burnt and evaporated) there should be no problem. But, is it possible that those two don't mix well in some cases and should be avoided?I was going to get those as part of a bigger order in Mouser, and those were the ones I considered the best given my budget (yes, I know some Kester wires may be better but the cheapest option in Mouser costs ~50€, and I didn't want to pay that much). So, if some other option available in Mouser, similarly priced, could be considered better for general soldering (both SMD and THT), any help would be appreciated.Thanks in advance.

author: EPAIII
author_rank: Super Contributor
timestamp: August 16, 2023, 06:13:43 am
content: No one is answering this so I will try.Heaven only knows how I worked in electronics for well over 45 years without ever giving even a pico second of thought to these nit-picky concerns. I just used rosin core solder and a tub of flux that was sold by the same manufacturer as that solder. That was it. And I almost never bothered to clean the flux off a PCB after soldering. Why, you ask. Well, if you are not careful, it can wash INTO parts with contacts and coat them with an insulating layer. When faced with a chance of corrosion 50 or 100 years from now vs. a relay or switch that positively stopped working NOW, just guess which way I decided was best. But people are going to be nit-picky about how a PCB looks.A bit of internet searching gave me some insight. Some sources state that rosin and resin are thesame thing: just different spelling. Others do make distinctions, but I was not able to find any that talked about problems from using both types together.To borrow from another area of human activity, I frankly think this is a "nothing burger". And if you want to worry about it further, I suggest that you do the internet research and write to or call some of the manufacturers of the various flux products.

author: franksouto
author_rank: Newbie
timestamp: August 16, 2023, 03:21:39 pm
content: Thanks for your reply!In fact, I only asked because when searching for advice on flux types, people would often talk about problems when mixing non-compatible fluxes. I did a little research before and read something like "rosin is resin but not all resin is rosin". However I thought that if they labelled it differently like REL0 or ROL0, maybe there could be some concern.I wouldn't be so worried about this, but were I live, it's very difficult to buy those things in a cheap manner so I wanted to be sure that I wasn't getting anything wrong.Best regards.

author: fichamba
author_rank: Contributor
timestamp: August 16, 2023, 03:55:08 pm
content: Hello:As EPAIII said, rosin and resin its exactly the same thing. The paste from pine trees which become solid if you leave it alone, like a stone (well, a crystal). Here in Spain we do have a lot of it. And of course, it is a nice protector for the solderings, once used. It prevents from oxidation. But, in fact, lately the good finish of the PCB is extremely taken into account. As EPAIII, I am in this business since I was 8 (now I'm 65, with a PhD in electronic engigeering...but I love the lab and the dust in my hands).It is true that for thinning cables, rosin (resin) is excelent. A previous bath in ro/esin will help you for the solder to flow (sometimes the flux contained in the core won't be enough). Personally, and for SMD rework, now I'm using AMTech flux. Thru the scope its easy to see components, due to its transparency. But for the rest of the soldering work (thru hole, tabs, tube amps, etc.) there is nothing like a goog Weller, roesin and 1mm solder wire (a good brand will be fine).Cheers to both.

author: janoc
author_rank: Super Contributor
timestamp: August 16, 2023, 07:18:21 pm
content: Quote from: EPAIII on August 16, 2023, 06:13:43 amThe corrosion is not an issue with rosin-based fluxes. Those only leave behind a sticky ugly mess but it is mostly harmless unless you care about leakage currents.However, if you are using one of the more modern fluxes (esp. those for lead free solder) then unless they are labeled "no-clean" you better do wash them off. Even the "no-clean" fluxes are corrosive if they haven't been activated by heat so you could get some residue somewhere that will cause problems later. The corrosion happens on the scale of a few years, certainly not "50 or 100 years from now" with those.

author: franksouto
author_rank: Newbie
timestamp: August 16, 2023, 09:04:27 pm
content: Quote from: fichamba on August 16, 2023, 03:55:08 pmThanks! By the way, where do you usually get your stuff from in Spain? I live in Portugal and usually I can only resort to online sites like Mouser where you can save the shipping costs with a bigger order, but I'm limited to their offering. I try not to buy stuff from sites like Aliexpress because I'm not sure about the quality.

author: EPAIII
author_rank: Super Contributor
timestamp: August 17, 2023, 05:33:31 am
content: Looks like I opened the flood gates. Good! Now we have a discussion.BTW,Idid not say that rosin and resin are exactly the same thing. What I said was, "Some sources state that rosin and resin are the same thing: just different spelling. Others do make distinctions, but I was not able to find any that talked about problems from using both types together."I can stand criticism and try to admit when I am wrong, but I do not like being misquoted. I am not enough of a chemist to judge the veracity of those statements that were made by others on the internet. I was only reporting what I read. And I was reporting two sides of the matter that are somewhat contradictory. I thought that was obvious in my post. I did not think I was settling the question and I welcome more discussion.

author: tooki
author_rank: Super Contributor
timestamp: August 17, 2023, 06:37:18 am
content: Even a cursory search of dictionaries and encyclopedias show that, as a general term, “resin” is a much broader term than “rosin” (which refers specifically to the stuff derived from tree sap). While they’re quite interchangeablein the context of electronics soldering flux, they certainly are not alternate spellings of the same word.

author: Ian.M
author_rank: Super Contributor
timestamp: August 17, 2023, 09:44:19 am
content: Its known that some of the components of rosin (colophony) can form copolymers with some other types of resin monomers. Therefore its possible that a mix of rosin and resin fluxes may, after heating to soldering temperatures, leave residue that is harder to remove than that from either flux on its own.However I don't have the background to assess whether this is a significant risk, in general or for the O.P's specific products, or if it is a problem, how severe it is likely to be, so if you need particularly clean PCBs, either you'd need to test the combination to assess the ease of cleaning its residue, or play safe, and order either only rosin based products (which are generally compatible) or resin based products from the same flux manufacturer with known compatibility.

author: John B
author_rank: Frequent Contributor
timestamp: August 17, 2023, 10:14:02 am
content: Careful though, some rosin fluxes aren't safe to leave as they are mildly conductive. I got caught out while using MG Chemicals 8342.