ESD Best Practices and Compressed Air Use.

this blast of air, in addition to possibly physically damaging board component soldering connections...

That's a strong blast of air! I'm not familiar with high pressure air guns, but it's not that hard to remove ESD as a concern in a manufacturing operation. If you've done all you say, and are still having board failures, I would look somewhere else for the problem.

PS - You can buy inexpensive ESD meters that will tell you whether you are getting a static charge from your air guns. When in doubt, measure.

Yes, ionized air can be a problem and it seems like you're on the way with that. There are a few other less obvious items that come in as the next rank of improvements.

Many people use laminated plastic work instructions, or plastic sleeves for production charts, PWBs often arrive vacuum packed inplastic film, inside cartons that have styrene foam used to prevent damage, people's clothing can be a significant issue as well as the covering on your seats. Standing operators should have TWO footstraps, or ideally ESD suitable shoes/boots, as often they can stand with the strapped foot out of contact with the ground. Computer monitors are also damned awful for static charge, exhaust fans on your electrical cabinets, even your nitrogen feed lines can create static as well as your fume extraction and remember that static to a metal object that is outside the environment will conduct static inside the room. (Like compressed air lines, or even building hardware.)

ESD is a bit like photography, "The more you find out, the more you find out you don't know."

Shop air can be 100% OK from an ESD point (if it is dry). If there are any water molecules, specifically drops, in the air stream, you can get 100's or 1000's of static volts onto your circuitry. If you have high RH in the area and the air driers have not been purged, sometimes you may get water molecules or drops in the air flow and that is the problem. We call that particle-laden air.

The dry air will not create a charge, but it will not remove one, either. Since the circuit boards are made out of some dielectric material (FR-4, or similar), it is considered a process-essential insulator. The ionizing air guns work great and they do remove the charge on the insulators, such as the circuit boards. However, they require dry air. Some people use Nitrogen as the air supply. The other mistakes were covered by you and the others that have replied.

Jay Skolnik, PE, CPI (ESD Auditor, Consultant, IPC Certified Instructor)

www.skolnik-tech.com

You can also refer to sections 3.1, 3.2, and 3.3 of IPC-A-610D. Table 3.1 specifically mentions compressed air as a source of ESD as well as some other hand tools.

Some other helpful documents referenced in J-STD-001D would be:

ANSI/ESD S3.1 Ionization

ANSI/ESD S20.20 Development of an ESD control program.