From ESD Handbook ESD TR20.20 section 2.5 "Virtually all materials,
including water and dirt particles in the air, can be triboelectrically
charged." Per section 5.5.5 Tribocharging "Tribocharging from equipment can
be caused by conveyer belts, hardware sliding on surfaces, and moving fluids
(sprays) or solids (sandblasters). Moving gases that are free of
particulates, e.g. from air guns, fans, or heat guns do not tribocharge an
insulator or conductor. If rapid air movement causes parts or dust particles
to rub together, tribocharging might occur. Grounded conductive surfaces can
tribocharge an insulative surface. An insulative surface can charge an
ungrounded conductor, which is the greatest ESD hazard."
"There is sometimes a need to provide static control in a small defined area
or location. This may be done to provide static control within production
equipment, in mini-environments, or to facilitate particle removal from part
of a product. Ionizers used for this purpose may be blow-off guns or nozzles
that work with a supply of compressed air or nitrogen. They may use either
nuclear, soft x-ray or any of the previously described types of corona
ionization technology. It will be important to choose a method of ionization
and cleanliness of the gas supply that is appropriate to the work area."
[ESD handbook ESD TR20.20 section 5.3.6.5.2.4 Point-Of-Use Ionization]
Gene Felder
[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Thayer, Wayne - IIW
Sent: 2010 - 03 - 24 6:52 AM
To: [log in to unmask]
Subject: Re: [TN] air or nitrogen for drying
Many thanks for the insight and observations on this subject. This is VERY
helpful!
Wayne
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Hernefjord Ingemar
Sent: Wednesday, March 24, 2010 8:45 AM
To: [log in to unmask]
Subject: Re: [TN] air or nitrogen for drying
Then it's the dust that builds up the charge by friction, and not the air in
itself ?
We did not succeed to cause any charges with either nitrogen or air. Maybe
the speed of nitrogen was not enough. If so, what is the gas flow limit
which will cause electrostatic charge? Obviously, you dare walk with a board
in your hand or open a door. Air is never standing still. And the gas speed
is probably decreasing exponentially with the distance to the object. And
depending on the air nozzle diameter and geometry.
In some of our military electronic equipments that come home for
modification or general service, we have found the boards covered with
yellow dust from the desert. It's nearly impossible to stop it from getting
in. The fans for cooling are blowing the dust across the boards day and
night. Have never heard of ESD charging issues.
Interesting. Has anyone had semiconductor (e.g. 0.3 V gates)issues caused by
nitrogen blowing in the factory or dust in field, as described above?
Inge
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bob Landman
Sent: onsdag 24 mars 2010 13:13
To: [log in to unmask]
Subject: Re: [TN] air or nitrogen for drying
Googled the following:
ElectroStatic Discharge : PRACTICAL ANALOG SEMICONDUCTOR CIRCUITS Moving air
can also generate substantial staticcharges. When you blow dust off your
electronics their will be static generated. ...
www.allaboutcircuits.com/../1.html - Options
Moving air can also generate substantial static charges. When you blow dust
off your electronics their will be static generated. An industrial solution
to the problem to this issue is two fold: Firstly, air guns have a small,
well shielded radioactive material implanted within the airgun to ionize the
air. Ionized air is a conductor, and will bleed off static charges quite
well. Secondly, use high voltage electricity to ionize the air coming out of
a fan, which has the same effect as the air gun. This will effectively help
a workstation reduce the potential for ESD generation by a large amount.
-Bob Landman
Sent from my iPhone
On Mar 24, 2010, at 5:14 AM, Mike Fenner <[log in to unmask]> wrote:
> I'm not an ESD expert... so treat the following with caution, as it
> may not be the same situation.
>
> A similar concern was raised by a customer after I recommended forced
> air cooling after reflow. "Floating body charging" or similar words.
> Not being an expert and thinking this could be of more general
> concern, I got a static expert and his gear and we spent an
> interesting few hours with meters, ionizers, blowers, factory airlines
> and so on and found .....
> nothing.
> We rationalised that the stream carrying charges to the work, would
> similarly allow a path from the work. That accidental gas ionizing was
> no different (apart from the cash) to deliberate ionising.
>
> Does this make sense?
>
>
>
> Regards
>
> Mike
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Thayer, Wayne -
> IIW
> Sent: Tuesday, March 23, 2010 9:51 PM
> To: [log in to unmask]
> Subject: [TN] air or nitrogen for drying
>
> We have a number of "airbrush" low pressure nozzles around here for
> spraying solvents on reworked boards and for drying them off. I know
> that nozzles can create static, but I have had no problems to date and
> have had no problem with dust sticking to the boards when I dry them
> off this way.
>
> I haven't been able to find anything on trying to quantify static from
> nozzles used in this way. Does anyone have data? Moving to ionized
> blow-off for drying the boards would be painful, as that means yet
> more equipment in our small cleaning stations.
>
> Wayne Thayer
>
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