Posted by
Gary Hvizdak on
Jun 03, 2010; 12:39pm
URL: http://elecraft.85.s1.nabble.com/Antistatic-work-mat-tp5132848p5134960.html
Thu Jun 3 06:05:49 EDT Pete Smith (N4ZR) wrote ...
"... what is to distinguish a "good" mat from one that won't really
provide the protection?"
--
Hi Pete,
A complete answer to your question will depend on the relative humidity
and on the susceptibility to ESD damage of the devices being handled. FYI,
the industry rates ESD sensitive devices into three classes based on their
susceptibility to damage:
o ESD Class 1 -- below 2,000 V
o ESD Class 2 -- 2,000 V to 4,000 V
o ESD Class 3 -- 4,000 V to 16,000 V
o Not ESD Sensitive -- above 16,000 V
Keep in mind that (WITH PROPER HANDLING) a sub-assembly may offer some
protection to the individual devices that comprise it, such that the overall
sub-assembly can withstand higher discharge voltages than the most sensitive
components that comprise it. This makes perfect sense since the highest
level assembly, i.e. a completed K3, is (generally) not ESD sensitive!
--- - - - ---
I also mentioned relative humidity in my opening sentence. FYI, at the
aerospace manufacturing facility (where I worked for ten years) even our
"good" mats were only adequate when the relative humidity was above 30%.
Below 30% RH "air ionizers" were also required at ESD work stations. These
devices aren't something you'll want to consider as they cost upwards of
$500! Oh, and they only "protect" a very small area, i.e. just a couple
square feet of work surface at most. That said, perhaps Elecraft would
consider using them in Aptos as an additional layer of protection?
--- - - - ---
In light of the above details, the best answer I can offer is that there
is an industry specification for the surface resistance of an ESD mat, which
is specified in the unusual unit "Ohms per square". Alan Bloom addressed
this subject in early April of this year. Please refer to his post in the
archives at
http://mailman.qth.net/pipermail/elecraft/2010-April/127988.html73,
Gary KI4GGX
K2 #4067
K3 #2724
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