Help pls - Silicone chip Hybrid Buck/Boost - SM/Linear PSU -white crud on joints - Page 1
Forum section: electronics / projects

author: v81
author_rank: Regular Contributor
timestamp: March 26, 2015, 07:53:46 am
content: Hi all,Am working on the project in title.After soldering the SMD parts i was resonably happy with the work (considering i'm a little rusty, and pin15&16 on the IC not counted).For the first time i used some stuff from Jaycar calledElectronic circuit board cleanerto clean the flux and crap off.This seemed to give a so so result and then the project was shelved until more parts arrived.Fast forward a few weeks and i ended up with a powdery white substance on the board around most of the solder joints.I have since scraped most of it away, and regret not taking a pic before i did so.Below is a pic as the board is now, is anyone able to shed some light on how i might clean this up and move forward?Comments appreciated.Cheers.

author: Asad
author_rank: Contributor
timestamp: March 26, 2015, 09:18:46 am
content: Looks like residue. Use some solvent like medium thinner or similar. Test it first with a cotton bud/swab before dunking the circuit in the stuff. Dry with air blower.

author: Unknown
author_rank: Unknown
timestamp: March 26, 2015, 09:46:49 am
content: Quote from: v81 on March 26, 2015, 07:53:46 amYeah, kinda crappy stuff that. It's mostly naptha / other light distillates with a bit of acetone & isopropyl (MSDS) - which is fine, except there's not enough acetone / alcohol in it to properly wash off the oils. If you want clean, you really need to wash off the residue afterwards with more acetone or isopropyl.(Strangely enough, it's a decent pot cleaner - though don't use it where the pots carry DC, or are in even a vaguely flammable environment.)

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 26, 2015, 04:18:02 pm
content: 1. If the solvent itself is not pure, it will leave a residue.2. If clean solvent isn't washed over the board repeatedly, it won't dissolve everything it can, or it will still contain some dissolved stuff.3. If the solvent is a low boiling point mix (like acetone and such), it will condense humidity from the air, which leaves an aqueous phase when the light solvent evaporates. When the water dries up, it leaves a slightly different pattern of residue. This can easily happen if you dry the board until it doesn't smell anymore.4. The less you leave on the board, the better. If possible, use compressed air to push the solvent off.Supposedly, the best cleaner for flux residue is something like ammonia and alcohol. Flux is an organic acid, so it's a very good idea.Whatever you use, don't forget to scrub gently (say with a toothbrush), wash repeatedly, and try to clear away as much used solvent as possible after each wash.For cleaning under SMT parts, ideally you'd have an ultrasonic bath, but just letting it soak for a long time will help greatly.Tim

author: marshallh
author_rank: Unknown
timestamp: March 26, 2015, 07:19:27 pm
content: Did you use water/noclean flux?

author: v81
author_rank: Regular Contributor
timestamp: March 27, 2015, 12:54:24 am
content: Appreciate the replies all,Quote from: blueskull on March 26, 2015, 09:32:17 amThe board was purchase from Silicone Chip magazine, not my design.I'm far to new at this to fully understand what you have said, but i will read up on it.Quote from: T3sl4co1l on March 26, 2015, 04:18:02 pmThat is an excellent list there.I was considering buying an air compressor soon, i'm using canned air at the moment.Quote from: marshallh on March 26, 2015, 07:19:27 pmOnly used flux on the LM5118 IC - it wasAim Solder NC-254.Given what i have on hand right now i have re-used the same Jaycar stuff, immediately followed by some Iso to wash the crap off.Not sure it is best course of action but i have a container that fits the board perfectly and i have it submerged in metho at the moment, swishing it back and forth over the board every so often.I'll pull it out later and give it a squirt with air.