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I've read a lot about people cleaning keyboards in the dishwasher. But how does the water damage electronics? Does it cause shorts on the ICs on the internal circuitry or physically get in the IC(which I can't see happening). So what actually happens?

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There are actually purpose-built circuit board washers used to clean excess flux. An example can be seen at this link – semaj May 11 '11 at 23:59
The bad stuff happens if the circuit is powered up while being submerged. Also, immersion for extended periods in water that is dirty, or excessively acidic or alkaline. I mean if you toss a circuit board into a river and then find it on an ocean beach somewhere, all bets are off. – Kaz Feb 23 at 5:22
By the way, in high school, I took apart a floppy disc (removed it from its plastic casing), and washed finger prints from it with soap and running water, then dried and resassembled. All data read perfectly. – Kaz Feb 23 at 5:23

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Many electronic assembly lines have a water cleaning machine in them. Basically it runs the PCB through it on a conveyor belt while spraying it with water. One smaller contract manufacturer I visited actually used standard dishwashers to clean PCB's (but had a closed water system, so no bad stuff made it into the sewer). In my lab, we use water soluble flux that must be cleaned with water, as the flux itself is very conductive. I simply rinse the PCB in the sink and dry it.

There are several important things to note when washing a PCB with water:

  1. The PCB should not be powered. This seems obvious, but people often forget about batteries for the real-time-clock and stuff. Sometimes the batteries will survive the washing step, but it's best to not tempt fate.

  2. The PCB should be completely dry before powering it up. This is the tricky one, since there are many small nooks and crannies for water to go into, and it doesn't evaporate quickly in those tight spaces. I'm in Colorado, where the humidity is often less than 30%, and I will either let the PCB drip dry for more than 24 hours or use a heat gun to speed things up. If you're in a more humid climate then extend the drying time accordingly.

  3. Some parts don't survive washing. Speakers, buzzers, and microphones are the big ones. Some switches and buttons don't like being washed either. Of course there are always exceptions.

  4. If your water has a high mineral content then you might want to do a "spot free rinse" using deionized or reverse-osmosis-ized water.

The #1 way water damages the electronics is by shorting things out while the power is on. The #2 way is by corrosion. Interestingly enough, it's not the water that does the damage but all the impurities that are dissolved in the water. Pure water doesn't do much (but look at it wrong and it'll get impurities). Of course, not powering on the device and drying it relatively quickly will prevent both of these problems.

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Compressed air is also a great way to dry wet, populated PCBs. Of course, it does require a compressor, but if you already have one, it's a great way to get everything really dry. – Connor Wolf May 12 '11 at 5:34
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Also, interesting fact: Pure water is actually a very good insulator (>18MΩ/cm, better than mineral oil, IIRC). However, pure water will actually fairly aggressively scavenge ions from whatever container it is in, so it is very hard to keep it pure. – Connor Wolf May 12 '11 at 5:38
@Fake Name You have to be a bit careful with compressed air, as it can create static zaps. Still, it can be quite useful. – David Kessner May 12 '11 at 13:20
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If the device is off and you are just using plain water it's not going to harm the device as long as you dry it off again before turning it on. Dishwashers work quite well for this, but you shouldn't put much soap into it (too much and the residue could stick to the PCB and cause problems.

If you run electronic equipment while it's wet then yes, it will short out. While water itself is not a conductor, any dissolved minerals/salts will make it very conductive. Since there are minerals in every form of tap or natural water it can be very bad for a computer.

That being said I've literally spilled an entire glass of water onto a working motherboard and it continued to work for the next 5 minutes while I saved my work and shut down. Dried it off and there was no damage.

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Note: Do not so this in a dishwasher that you also use for food. – Connor Wolf May 12 '11 at 5:35
@Fake Name Doing this once in a while isn't too bad. But I do run the dishwasher empty after, to clean it out. – David Kessner May 12 '11 at 13:21
I wouldn't use the dishwasher for cleaning flux or anything similar - just the grease and dirt in your keyboard. I don't see a problem with this, especially since it isn't a regular event. – charliehorse55 May 12 '11 at 15:35
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Years ago a friend asked me for a way to slightly illuminate a small river in a miniature diorama. There was almost no space to hide the little circuit (it was a PIC with internal oscillator that handled 3 red leds) and no time to rebuild that diorama part, so with just 3V of supply (to limitate water electrolysis) we simply submerged the circuit in the water reservoir. And as all provisional hacks, it worked for years without problems :-)

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