The board often requires to be cleaned down with a spray solvent, but you have to be careful what you use, it must not attack plastics, inks, paints or component surfaces or PCB coatings. In the USA the product I would trust for this is "CO Contact Cleaner" made by CRC (In AU I uses a similar product called "circuit board and contact cleaner" made by motortech, but it's basically the same)
(These products replaced trichloroethylene, which was used to replace carbon tetrachloride which is a wonderful degreaser/cleaner that was banned after it was found to cause cancer in the dry cleaning industry- a bit OT but there was a great episode of Lost in Space where Will Robinson travelled back to Earth in a time machine built by aliens, and bought a bottle of carbon tet from a hardware store to help fix the Jupiter 2) I could still buy carbon tet myself from the pharmacy, up till about 1975, it is fantastic for cleaning grease off rubber parts.
The CO cleaner is applied by a small tube attached to the nozzle , the high velocity jet of it will displace dust and dirt from the surfaces under most IC's and flush it out of PCB connectors. You might use half a can of it or more on a mobo. As this happens the mobo starts to cool down and water from the atmosphere will start to condense on it.In places as suggested it might need a light brush as well. So after it is clean you need to hold the PCB in a stream of flowing air at or above ambient temperature, to evaporate the H20. The output vents of a home air conditioner work fine, but if you use a hair dryer, have it on low heat and the nozzle well away from the PCB at least 1 foot, you don't want to overheat any part of the PCB, only blow slightly warm air over it until the water droplets have evaporated.
However, if an electrolytic cap has leaked on the board, the contact cleaner (a non polar solvent)will sometimes not satisfactorily wash off the electrolyte, especially if the PCB coating is the non glossy type. A warm stream of deionised water ( a polar solvent) is required to wash over a for at least 10 to 20 minutes, then a spray with the CO contact clear to help displace the water then an air dry.
Once the board is cleaned and dry, it's not over yet there is more......It is very unwise to leave any of the connector pins on any of the board's connectors dry and fully degreased like this, they then will be vulnerable to corrosion and in the case of plugs/ sockets , card edge connectors wear from excessive friction when cards and plugs etc are fitted and re-fitted. The connection surfaces need protection and lubrication. There are products made by Caig chemicals to help, for example "Pro-Gold", I have found though that WD-40 is perfect, spray it sparingly into the edge connectors for the cards and all other electrical connectors. It coats the metal surfaces, prevents corrosion and lubricates them. It can be applied to the surfaces of IC pins (the CPU).
Some CPU's with gold plated pins (like the Athlon types) which go in ZIF sockets get intermittent connections.
Gold over time gets a clear invisible insulating coat over it that does not break down at low voltages, so in contact systems, where there is no sliding force (and surface scratching) this includes ZIF IC sockets, or the types of touch contacts seen in items like Tek oscilloscope attenuators or the target connection eletrodes in vintage tube cameras, resistance develops and causes intermittent behaviour. However, in sliding contact systems, like card edge connectors, it's not usually a problem as this breaks through the microscopically thin surface layer.
For example on Athlon 64+ CPU's and similar ones, it's important to place the CPU in a small bath of CO contact cleaner, brush the pins gently with a small artists brush for 10 minutes or more (to remove the invisible coating) then spray the pins with WD-40 and leave to dry for 10 min, leaving a thin coat of WD-40.
It's more difficult to get this oxide off the ZIF socket,but if small cardboard spacers about 0.5mm thick are used under the corners of the IC, then partially close the ZIF socket arm until there is just a little contact on the IC's pins, remove the spaces and push the IC home. The small amount of sliding friction and movement helps to break through the layer on the ZIF sockets pins. So if you have any computer problems that are intermittent like failure to POST, and the CPU is a gold plated pin ZIF socket type, this may be the problem. In single tube color video cameras, when this happens the series resistance at the preamp input from the target electrode results in a LPF forming, the 7MHz color carrier is lost and the output picture goes green. In Tek scopes the attenuators where the zero sliding for gold contacts are uses simply go open circuit or intermittent. The problem in worse in low voltage systems, like 1.5V powered CPU's. Higher applied voltages tend to break down the thin surface layer on the gold.
Finally, about WD-40 and pcb's : WD-40 is compatible with practically every component on a PCB, so there are pcb's, that after cleaning can be entirely coated with it and wiped down, leaving all the exposed metal on components and IC pins protected from future corrosion. However, there are a couple of exceptions to watch out for, If there are any stickers, WD 40 will soften their glue. There is one type of PCB component not compatible with WD-40, not that the WD40 damages it, but WD-40 is an insulator which has a dielectric constant. If it is sprayed onto small PCB adjustable ceramic capacitors, like the sort used in RF circuits, or sometime to set a crystal frequency on some computer pcb's or in attenuators in scopes etc, it alters the capacitance and plays havoc with the adjustments, so never put WD-40 on on that type of PCB component.
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