PCB Board Cleaning: Pure Isopropyl vs MG Cleaner

Here’s a breakout board that got a lot of hand soldering with three different kinds of flux. Plain 91% isopropyl was used after rework using AIM 280 “no clean”  (the watery stuff), which, if used copiously, definitely needs cleaning if you care about appearance. In this case, even scrubbing with a nice (Adafruit) ESD-safe brush would not remove the flux completely as can be seen with this first picture below. The gray cast that’s most pronounced in the lower right corner shows this “can’t clean” flux layer:

Several rework episodes later, the board had seen lots of the NC flux, but also Chipquik SMD 291 “Tack Flux N/C”, which, in my experience, is never “no clean” except perhaps in the sense of “the electrical connections won’t eventually short out with this stuff”.  From an aesthetic perspective the layer of goo left behind in many cases is simply not nice. Finally, I got lazy with a brute force desoldering method involving braid and old style rosin flux and that stuff is of course just plain nasty. So here’s the very sad “before” photo after the shunt resistor and other parts had been messed with a few times:

For this case a bit of MG Flux Remover was put into the bottom of a jar, the board was put below the surface, and the jar was swished around for a while. Some exceptionally bad looking, black “baked rosin flux” bits were scrubbed off and then the board got another few seconds in the jar. Then the flux remover was washed off with pure  isopropyl to get the “gunk in solution” level down to zero. (This cheap squirt bottle from Rite Aid works very well for this). Then after the board had dried it looked like this:

The result was superb: no gray splodges or any other stains. Notice the very tired traces missing solder mask in places. This is what comes of too vigorous scrubbing. The flux remover looks unchanged and I’m expecting that in the tightly sealed jar it has a lot of use left.

I was expecting the remover to have evil stuff in it and was surprised to find it’s  ethanol, isopropyl alcolhol, and ethyl acetate. The latter is found in small quantities in wine (and many homebrew beers). But despite the familiar chemicals I use lots of ventilation for this kind of task.

Thanks to Shane Trent for letting me “try out his jug”.


May 8th meeting: well pumps, shade trees, and hot solar

There are a few things to share from this month’s meeting :

  • Folks compared notes about participation at RARSFest last month. The “non-commerical” aspect of Triembed folk’s participation at the next RARSFest is expected to be free. Whoever takes the lead on preparing for the next one can arrange this and get “just the right spot” for tables if they contact the organizers early in the process (4-6 weeks ahead).
  • Shane Trent passed a heavy duty patent law exam and is now a seriously useful resource for area developers wanting to invest in IP via the patent process. Congrats, Shane!
  • Paul MacDougal shared his setup for remotely detecting potential freezups of his well pump.
  • Chip McClelland showed an air temperature logging addition to his repertoire of park service tools being embedded at Umstead. This will allow the park staff to measure the cooling effect of newly planted shade trees.  Chip also passed around his full custom battery management board for folks to admire (built at Pete’s shop).
  • Pete described tests of the Silvertel AG103 Maximum Power Point Tracking solar powered battery charger board and a ten watt Ecoworthy solar panel being prepared for the “Little Library” Jeff Crews (of Splatspace) built and installed at the Durham Scrap Exchange.