Over the years I've used a lot of different chemicals for removing flux from a board after soldering.
In a pinch I once tried to use brake cleaner (sold in automotive parts stores). It turned out to be the best thing I ever used. A 2 second spray cleaned the board with no residue and no leftover flux. Of course, you want to do this outside. Hold the board with the side to be cleaned at a 45 degree angle so that you're spraying upward to the board. (this way the spray runs off the board and not onto the component side). So far I haven't had any issues with the spray melting plastics or circuit board varnishes or silkscreen, so I am really happy with the results.
On this same line. I use, ultrasound bath with isopropyl. Submerge the board after soldering, let it clean for a few minutes. Take it out and dry it. They come out like fresh from the factory.
I use a very cheap jewelry cleaner something like $28 - 20€, there are some semi-pro baths for about $40 - 56€.
There are different kinds of brake cleaner. I've used CRC #05089 which is primarily tetrachloroethylene; this is non-flammable and doesn't seem to attack any plastics, works well as noted. OTOH, CRC #05088 contains methanol, acetone, toluene and heptane, so very flammable and while I haven't used it, I'd think it would be very rough on plastic and paint. So YMMV. Know what you've got and use it safely (definitely outside if you don't happen to have a fume hood, and that's not the one over the stove ;))
I've found regular denatured alcohol works very well. Although it's flammable it's not particularly toxic. I just pour a little in a pan and use an old toothbrush to clean the board.
99% isopropyl alcohol (IPA) works even better than the "regular" stuff, which is generally 70%, while still being readily available at grocery stores (at least here).
I'm surprised about the isopropyl alcohol+ultrasonic cleaner approach, as I believe flammable liquids should not be used with ultrasonic cleaning due to the potential for fire/explosion. YMMV.
The thing to watch out for with cleaners like "brake cleaner" is not inhaling the nasty fumes. I'd much rather inhale a bit of IPA than tetrachloroethylene, toluene, or heptane. Especially on a regular basis.
In all cases, ventilation is highly recommended.
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fm:
Submerge the board after soldering, let it clean for a few minutes. Take it out and dry it. They come out like fresh from the factory.
Is there a problem with getting the components "wet" with the alcohol?
I've been spraying with an aerosol can of flux cleaner, scrubbing with a bristle brush, then rinse/scrub with distilled water. Repeat. This is very time consuming, and I'd rather just soak the boards like you do. But I've been hesitant to really let the components get soaked since I don't know whether this will cause problems.
Nope, soaking is fine. Commercial cleaning involves submersion in ultrasonic baths or pressure wash in a dishwasher-type device. In all cases, all the parts get thoroughly wet.
As long as you dry the PCB and components fully (put them in your oven on the lowest setting...really) there should be no problem. Air drying is not good enough for some components (e.g., microphones, pressure sensors, etc. where water can get into crevices). Note, however, that some household ovens' lowest setting is above the temperature rating of electrolytic caps (85C) so you have to be careful.
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Some parts aren't suited for washing, I found this out the hard way with a tact switch (and read it, later, in the datasheet ). After cleaning the flux from the board, the switch didn't work. I imagine some flux-bearing solvent got into the switch and deposited it there so that the switch contacts were insulated.
I use solder with a no-clean flux. So removing flux really has no benefit other than aesthetics. Still, I do like the looks better, so sometimes I'll clean the flux off, depending on the mood I'm in XD
Ultrasonic bath doesn't get warm at all. If you are concerned, just use in a open space well ventilated place (that is what I do). Alternatively you can dilute to 50%. Distilled water is another option, but it depends on the type of flux used.
RuggedCircuits:
As long as you dry the PCB and components fully (put them in your oven on the lowest setting...really) there should be no problem. Air drying is not good enough for some components (e.g., microphones, pressure sensors, etc. where water can get into crevices). Note, however, that some household ovens' lowest setting is above the temperature rating of electrolytic caps (85C) so you have to be careful.
I have a PID controller on my toaster/reflow oven that'll maintain a low temperature for drying. I was thinking somewhere around 65C should be OK.
). After cleaning the flux from the board, the switch didn't work. I imagine some flux-bearing solvent got into the switch and deposited it there so that the switch contacts were insulated.