Lee and Ashok,
While it is sometimes common practice to earth ground an ESD safe bench,
resistance is required to reduce hazardous shock exposure of operators
should they come in contact with an available voltage source at the bench.
Additionally, the resistance level is as specified considering the common
potential resource of 115VAC (solderin irons, lights, etc) and should there
be higher potentials available, the resistance value will need to be
reassessed. Increase in available voltage potentials requires equivalent
increase in resistance value to provide operator protection from a path to
ground. A 1M ohm resistance is inadequate if there is a 300 V resource at
the bench. While assessing the aspects of a correct ESD bench it is
important to keep in mind the possibility of parallel ground paths which
reduce the effective resistence. MIL-HDBK-263 contains detailed information
concerning these topics.
It is also important to provide a decay characteristic for applied voltage
potentials to bleed off without creating as great a potential for damage to
sensitive components that could be in the path of a potential surge in it's
effort to seek ground potential.
EIA 625 as an ESD standard applies well to component environments but other
standards such as the previous MIL-STD-1686 (with support of MIL-HDBK-263)
and ESDA S20.20 may provide additional information that is useful for
product assembly operations. IPC-A-610C has updated ESD information as well
as graphics for ESD bench attachment.
As for the attachments the major requirement is that it be rugged enough to
withstand production environments and be monitored or tested to prevent
processing equipment in a potential ESD hazard environments. Again the Mil
Specs recommend at least a half watt resistor and I would add a protective
covering to support the lead attachments (shrink sleeving)as well. A plus
would be sleeving that allows visual inspection.
Contact me if I can be of any assistance.
Mel Parrish
201 Cedar Road
Mullica Hill, NJ 08062
[log in to unmask]
856 223 5828
----- Original Message -----
From: Lee Whiteman <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, May 23, 2000 5:36 PM
Subject: Re: [TN] Question on EIA-625 : Technical specs of Grounding
resistor
> >From my experience, one does not require a grounding resistor on table
mats
> / floor mats. In fact, I've connected them directly into earth ground.
>
> According to EIA-625, Figure 1 (page 8), the resistors for the static
> dissipative work surfaces (R2) and the ESD protective floor mats (R3) are
> optional. If you are using R2 and R3, the values should be specified by
the
> ESD equipment manufacturer. I don't think there are any special
requirements
> (wattage, material of construction, etc.) for this resistor.
>
> Lee Whiteman
> Senior Manufacturing Engineer
> ACI / EMPF
> Telephone: (610) 362-1200; Ext. 208
> FAX: (610) 362-1290
> E-Mail: [log in to unmask]
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Ashok Dhawan
> Sent: Tuesday, May 23, 2000 6:51 PM
> To: [log in to unmask]
> Subject: [TN] Question on EIA-625 : Technical specs of Grounding
resistor
>
> << File: adhawan.vcf >> For grounding Table Mats/ Floor Mats and
> workstations, does grounding
> resistor need special
> characteristics e.g. Wattage, material of
> construction, etc.
> We intend to use 1M Ohms resistor. EIA-625 does refer
> to EOS/ESD-S6.1 standard (
> paragraph 7) for grounding details, if anyone has
> that details on that.
>
> Thanks in advance for advice.
>
> Ashok
>
> --
>
> Ashok Dhawan P.Eng
> Engineering
> C-Mac Electronic Systems Inc.
> 1455 Mountain Avenue
> Winnipeg, Manitoba R2X 2Y9
> Canada
> Phone: (204) 631-7208
> Fax: (204) 631-7294
> E-mail: [log in to unmask]
> www.cmac.ca
>
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