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.

December 12th Meeting: Better than Blinky

blinkinglightsfromgoogleimagesPaul MacDougal will talk about alternatives to the classic Arduino beginning program and shares this summary:
“Blink is a great first example for Arduino programming, but a really bad example of embedded programming. With 99.9% of its time spent in delay(), nothing else can happen. This talk will show how to rewrite blink in several different ways to allow it to play nicely with other functions.”

Join Paul and others at NCSU for the regular meeting. More details on the “at NCSU” meeting page.

Notes about OSH Stencils

A few notes from listening to Brent of OSH Stencils: on The Amp Hour:

  • Planning to offer 1.6mm jigs to eliminate the error vis a visa common PCB thickness (hurray)
  • For those that didn’t know:
    • Offering high quality Kester solder paste (in checkout cart, as with the jigs)
    • Offering stainless steel as well as kapton (stainless steel are common 4mil thickness).
  • 5x5mil smallest feature size possible with kapton stencils. Minimum feature size for steel stencils is ONE MIL!
  • They see 70/30% split between 3mil and 5mil thickness of kapton. The 3mil is best for ordinary work, while the 5mil is appropriate for high power devices with large thermal pads, etc. where a lot of solder is needed. I can vouch for the fact that 5mil is a total disaster for fine pitch parts like a QFN package. Kapton in 4mil is unobtanium, which is why they don’t offer that thickness.
  • Name is OSH Stencils because Brent was originally going to collaborate with Laen of OSH Park, but a change in Laen’s circumstances caused them to remain separate entities and Laen was totally OK with the similarity of names.
  • Can reduce kapton stencil curl by “counter-rolling” the material and this will give temporary relief.
  • Started with hobby laser: That “exploded” the first week after starting business. Switched to Epilog 24 (roughly $30k)
  • Stainless steel stencils made with approx $300k LPKF fiber-based “flagship model” laser cutter
  • Have maintained 24 hour turn time from the beginning. They went with high end laser to be able to make *the best* stainless steel stencils. They are competitive by avoiding framed stencils and using a proprietary material loading system into the LPKF. Basic cost of framed stencil material is 5X the cost of raw. Could use “pneumatic frame” to simulate real frame, but that didn’t allow sheet sizes that were large enough to be cost effective.
  • Brent said their charter as they began making steel stencils was to offer the top quality at reasonable prices. He invited people to compare their metal stencils to Chinese stencils under a microscope as they consider potential “cost savings” by going off shore. (OSH Stencils is in the Salt Lake City area of Utah). The metal makeup is different. Most offshore vendors use “inexpensive stainless steel”. Looking at the apertures (the cutouts) you often see grooves to do with the kerf (diameter of laser beam). With low quality metals the edges of apertures have grooves making them look like washboards.  Also see minor warping and ripples in the Chinese metal.
  • Look for “exciting announcements” to do with the stencil process to be offered by OSH Stencils in coming months.
  • OSH Stencils makes stencils for customers that have nothing to do with electronics. Art projects, special “plates” for mechanical components, etc. They’re open to queries about whether your creative application can be handled by their equipment.