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Old 8th Nov 2017, 7:40 pm   #16
duncanlowe
Nonode
 
Join Date: Jan 2016
Location: Stafford, Staffs. UK.
Posts: 2,529
Default Re: Cleaning and repairing a Corroded computer board

A few comments. Pure water wouldn't cause corrosion. The problem is it's very rare to find pure water. Generally it will be at a minimum rainwater which is not pure.

Then there's the problem of surface contaminants on the PCB possibly even from manufacture so even if you do add pure water its no longer pure. Not all fluxes are washable or require washing, some are what is known as self cleaning. In theory the soldering process renders them inert but that's not always the case. There is a specific kind of test known as ROSE that measures the equivalent value of NaCl in micrograms per square centimetre. Different types of application drive different cleanliness requirements.

Using PCBs in cars means we get to know a lot about this kind of problem because they are very humid places. Temperature changes combined with that humidity can cause significant condensation, and many items are permanently powered these days so you have a nice power supply to allow dendrites to grow and tracks to dissolve.

Of course if some muppet in the factory decides to use some random other flux they found and a paintbrush, you can be stuffed.
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