(Solved) Flux or corrosion? - Page 1
Forum section: electronics / beginners

author: Mp3
author_rank: Frequent Contributor
timestamp: February 14, 2020, 12:37:23 pm
content: There are three images i took in this album below. The first showing how the pcb may already be corroding from all the flux on it. The second shows some problematic bridge jumpers between different PCBs to join those traces together, which needs to be replaced with either solid core wire or ribbon cable. The last picture shows the mess left behind after wiping the boards down with 99% isopropyl, which usually leaves boards spotless after it dries up.I have three questions, one corresponding to each of the three pictures in the album, and a more detailed explanation after the link.My first question is what you would do if you had to clean a board this dirty and gooey with decades old flux. I am considering taking a toothbrush and 99% isopropyl and really going at it. Additionally, it seems as though the flux is corroding some of the PCB already. I am curious if i should be taking some steps to mitigate this besides thoroughly cleaning and applying fresh solder.My second question is if it seems as though the traces appear to be damaged on the close-up of the bridge jumper connection. If i clean the solder off, it seems as though there are small holes in the board, so i may be able to put solid-core wire or ribbon cable straight in there. If not i suppose i will need to scratch away a bit of the surface to reveal fresh copper to solder to? My concern is the unit only functions properly for about a minute after freshly re-soldering all the connections, so i am worried there may be trace damage. However, i must try to hard-wire these junctions first and see if that solves it.My last question is if the residue left behind after solvent could be a problem.https://imgur.com/a/lsJ5QFpI am repairing this old synthesizer. Made early 80's. I have fixed two of them before. The main problem is there are these giant pcb's being connected with horrible jumper pins and it has been common knowledge for a long time that this is a major and prevalent point of failure in these units.The last couple i saw were not covered in flux. It was very simple to put fresh solder on these pins and voila, everything works nice and reliable again.This one seems to be drenched in its own flux. It seems like i can keep scrubbing at the board with 99% isopropyl alcohol and it keeps being fluxy. I have cleaned so much off the PCBs already and they're still filthy and covered in it. I even, after cleaning the bridge jumpers several times, would see the old flux bubbling away when attempting to resolder those connections.I am concerned the old flux bubbling away may have caused trace damage and if i should bother to scratch away a bit of either side of the trace and apply fresh solder to it from the wire i will be installing to replace these bridge jumpers.

author: ArthurDent
author_rank: Super Contributor
timestamp: February 14, 2020, 02:27:09 pm
content: I guess I don't see the problem with the flux on the board from what appears to be rosin core solder. You can remove the flux if you want but that generally isn't a problem. The only thing I see is that there wasn't solder flow on the pins on the right circuit board and you probably have cold solder joints that could cause the problems. You can see where the solder balled on the pins and didn't flow smoothly onto all the pads on the right board. I'd resolder all pins on the right side until you see good solder flow on the pins and the pads and forget about the flux unless it really bothers you knowing it's there.The highlighted bad solder connection in the drawing below looks like the soldering on the right of your photo.

author: Mp3
author_rank: Frequent Contributor
timestamp: February 15, 2020, 04:33:02 am
content: Quote from: ArthurDent on February 14, 2020, 02:27:09 pmThanks so much.It's a big relief to know the flux isn't a problem. I mistakenly thought it was corrosion due to the color. I appreciate it.