I've been arguing with a colleague whether it is a sensible solution to clean dusty PCBs with compressed air. While I think this is the best solution (nothing touches the PCB), he claimed that spraying off the dust can cause ESD, because the charges that may have accumulated in the dust win't bleed off in the process (and it's better to leave everything as it is). I'm not really convinced by this argument and my (limited) knowledge of ESD production doesn't help getting peace of mind in this matter. What is your input?
Answer
IPC-A-610: Acceptability of Electronic Assemblies Section 3.1.2 mentions compressed air as a possible source of electrostatic discharge.
This forum post which claims to lay out the "Truths, myths, and flat out lies" about ESD notes that compressed air is a source of ESD due to the air rubbing against the air. But it claims that most of the charge is dissipated from the air particles before they hit the surface.
However, if you read the IPC spec, it talks about building up charge due to the air moving over insulating surfaces. So the charge will build up as it leaves the nozzle from air to air friction. Some (but not all) of that charge will dissipate as it travels to the board. But more charge will build up as the air moves across the laminate of the board itself.
The compressed air will defiantly have some charge as it leaves the can and it will build up more charge as is blows across the board. Whether or not the amount of charge is enough to damage your parts depends on a lot of factors. But it is very possible. When in doubt, test it.
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