Here's our answer to this question:
When working at an ESD protected workstation, is it acceptable for the use of
regular home fans while assembling product?
Answer:
There are two ESD control issues:
1) Is likely that portions of the fan is insulative generating
electrostatic charges and
by definition cannot be grounded.
2) Is not likely a problem that air is dirty enough having particles that
will tribocharge.
If fan is all conductive, it should be grounded. Per ANSI/ESD S20.20 Fundamental
Principle "All conductors in the environment, including personnel, must be
bonded or electrically connected and attached to a known ground".
Nonessential insulators must be removed. Per ANSI/ESD S20.20 Paragraph 6.2.3.1.
Protected Areas Requirement
"All nonessential insulators, such as those made of plastics and paper (e.g.
coffee cups, food wrappers and personal items) must be removed from the
workstation. Ionization or other charge mitigating techniques shall be used at
the workstation to neutralize electrostatic fields on all process essential
insulators if the electrostatic field is considered a threat."
However, if you deemed it an essential insulator, you must keep 12" away from
ESD sensitive products (or use ionization). ANSI/ESD S20.20 Paragraph 6.2.3.1.
Protected Areas Requirement
"Ionization or other charge mitigating techniques shall be used at the
workstation to neutralize electrostatic fields on all process essential
insulators if the electrostatic field is considered a threat." And Paragraph
6.2.3.2. Protected Areas Guidance "All process essential insulators that have
electrostatic fields that exceed 2,000 volts should be kept at a minimum
distance of 12 inches from ESDS items."
Does air tribocharge? Per ESD Handbook 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."
Gene Felder
[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis
Sent: 2007-03-13 2:39 AM
To: [log in to unmask]
Subject: Re: [TN] ESD control and fans
If the fan blades are in grounded bare metal, I don't think a problem
would occur, provided that the RH is maintained at 50% or more. If the
fan blades are plastic or are plasticised (including paint), then I
could foresee a potential problem (pun intended, to stop Dewey from
intervening!). However, like all ESD questions, have you ***measured***
the results? Anyone can say anything and be right or wrong. Only
measurements can justify any measure you take.
In any case, would not suitable airconditioning be a better solution?
Brian
Joel Alexander wrote:
> Has anyone had any experience assessing if personal fans could have an
> adverse effect on an ESD control program. We have ionizers on our
> compressed air sources used to clean or dry assemblies but we have no such
> policy for fans. We just transitions to lab coats with 13% carbonized
> nylon. Our policy when sitting is to wear a wrist strap that is tied into
> an approved ground or have the wrist strap connected to a shirt sleeve and
> your pocket button attached to an approved ground. Many employees
> complain that they are hot and I can see a lot more fans being used.
>
>
>
> Joel Alexander
> Quality Assurance Manager
> TT APSCO, INC.
>
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