We recommend conductive flooring < 1 x 10E6 ohms (as defined in ANSI/ESD
S7.1).  This is so one can meet ANSI/ESD S20.10 Table 2 Flooring/Footwear
Method 1 required limit of < 3.5 x 10E7 ohms.  Now or in the future.
However, the required limit is only < 1 x 10E9 ohms per ANSI/ESD S20.20
Table 3.

There is currently no floor lower limit, however the ESD Association floor
working group is likely to add it at 2.5 x 10E4 ohms in the next update of
S7.1.  See page 10 of "Threshold" at
http://www.esda.org/documents/Threshold_JulyAug2010.pdf
WG7.0 - Flooring.
"Members of the WG met with TAS on Saturday to discuss a lower limit of 2.5
x 104E4 in the definition of conductive floor materials in the glossary.
There will also be a proposed change to the definition of dissipative floor
materials at a later date."

You are correct regarding worksurfaces.  The requirement is only < 1 x 10E9
ohms per ANSI/ESD S20.20 Table 3.

However, there is a worksurface lower limit recommendation.  Per ANSI/ESD
S4.1 section 8
"RESISTANCE GUIDELINES
Due to a wide variety of applications for worksurfaces, specific
requirements that could be broadly applied are difficult to determine.
However, the following set of guidelines can be used as a starting point for
establishing local requirements for the resistance of worksurfaces:
- Resistance-to-groundable point 1 x 10E6 to 1 x 10E9 ohms
- Resistance from point to point >/= 1 megohm [1 x 10E6 ohms]
These guidelines represent a range of resistance that has generally been
proven to provide protection in the manufacturing environment. They also are
loosely based on models for the effects of ESD on devices. It should be
noted that worksurfaces with point-to-point resistances below 1 megohm may
be a hazard where exposed voltage may contact the user or the worksurface."

The ESD Handbook ESD TR20.20 states in Worksurface section 5.3.1.7
Electrical Considerations "When worksurface materials are being selected,
consideration should be given to possible CDM [Charged Device Model] damage
to ESD sensitive products. If CDM damage is a concern, then setting a lower
resistance limit for the worksurface should be considered. Typically, the
lower limit for these types of worksurfaces is 1 x 10E6 ohms."

S20.20 lists ESD TR53 as the test method for Compliance Verification.  It
can be purchased at www.ESDA.org.  Since it details simplified test
procedure, we recommend that users reference ESD TR53 in their written ESD
control plan and not S4.1 or S7.1 which primarily detail test procedures for
independent test labs.

Gene Felder
[log in to unmask]


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Rob Strecker
Sent: 2010 - 07 - 08 8:44 AM
To: [log in to unmask]
Subject: [TN] ESD Mat Standards

Hello Technetters,



I am in the process of sourcing out new static mats for our company,
table and floor mats.  We have the ESD S20.20-2007 standard as well as
ESD S4.1-2006 and ESD S7.1-2005.



In S4.1 RTG is 1M - 1G ohms and RTT is >= 1M ohm, this is fairly simple
and most table mats fall within this range.  However in S7.1 for floor
material it's not so clear.  There is no mention of RTG or RTT values.



In S20.20 it states product qualification for work surface and flooring,
required limits of < 1G ohm (is that for RTG or RTT).  So does the lower
limit of 1M for RTG really matter??  What about RTT?? (I am only talking
about product qualification not compliance verification)



Many floor mats/runner I have looked at are 1K - 100K ohms RTG & RTT.
These mats have been tested using S7.1 but what are the pass/fail
limits?  What is the RTG and RTT for floor material?  S7.1 looks more
like a test method than a standard stating limits.



Any help would be appreciated.



Thanks



Rob


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