So looking at ESD mat material at Digikey, there appears to be a
bewildering array of choices. Elastomer, rubber, vinyl,
thermoplastic, laminate, foam rubber, and polyethelene.
Any guidelines about what to choose?
Scott
On Jan 25, 2010, at 11:59 AM, Ed Palmer <ed_pal...@sasktel.net> wrote:
I've still got a paper copy of an HP Bench Brief from 1983 that was
one of my first introductions to the dangers of ESD. I've used a
wrist strap and antistatic mat since then. ESD protection in the
ICs has improved since then, but I think that the article is still
mostly applicable today.
http://www.hparchive.com/Bench_Briefs/HP-Bench-Briefs-1983-03-05.pdf
Ed
Lux, Jim (337C) wrote:
-----Original Message-----
From: time-nuts-boun...@febo.com [mailto:time-nuts-
boun...@febo.com] On Behalf Of Charles P. Steinmetz
Sent: Monday, January 25, 2010 10:27 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Conducting Bench Top Material
Bruce wrote:
Although over the years the non-conductive top has been an asset
in
avoiding short circuits, etc., I am concerned about static
discharges when
handling modern semiconductors. Would it make sense to spray
the Masonite
with a weak copper sulphate or similar solution so as to make
the masonite
slightly conductive, but not so conductive that 155 VAC
connections
could not
safely rest upon it? Is there a better-suited material that
could be used
to replace the Masonite?
One generally looks for static-dissipative surfaces, rather than
conductive surfaces. 1 Megohm/square, for instance. The idea is to
keep everything isopotential as charge drops onto things, not to
rigorously establish a common voltage.
I notice that many folks who have contributed on this thread use
anti-static benchtops, but I have never found it necessary (and I
try
to keep the RH in my house under 45% -- it is generally 20% or less
in the winter). I've been fooling with static-sensitive parts for
35
years and haven't lost one to static yet
You haven't lost one *that you know of*. It also depends on the
kinds of parts you're working with. There are some that are quite
sensitive AND which don't fail outright, but just degrade
performance a bit when they take a hit. It also depends on the
energy behind the hit, of course. An example might be the
MiniCircuits ERA-4 or ERA-5 (just because I happen to have the data
sheet handy). Take a look at the later pages in the report, and
you can see where the gain changes slightly as a result of 100V ESD
hits (see page 6, where you can see gain dropping about 1.5 dB over
8 pulses, with about 0.1dB per hit.)
As they say at the end of the report:
The new amplifier ERA-4XSM shows gradual degradation in the gain
and the
device voltage. That fact is not so bad. Even with the multiple
stress a customer
would rather have gradual changes then catastrophic failure. The
amplifier
withstands a single 100V ESD pulse, or 3 pulses at 50V.
http://www.minicircuits.com/pages/pdfs/an60028.pdf
----
When we (JPL) do site visits to vendors, lackadaisical approaches
to ESD handling are one of the common problems. For us, who are
building just one or two of something that's going to be going
somewhere where repair isn't an option, latent damage and gradual
degradation are a big deal.
It's really a "habit" thing that everyone has to get used to.
That's why even nuts and bolts come in ESD packaging (even though
they're obviously ESD immune): it gets people in the mindset of
"come in the area, put on the wrist strap". Back in the 70s, when
ESD processes started to be used, they would have multiple
categories of parts, some which needed ESD precautions (CMOS parts,
DRAMs,etc.) and some which didn't (resistors, capacitors). It was
found that workers would be working with something in one category,
and the habits would carry over to the others, so the industry, in
general, went to the "everything is ESD sensitive" approach.
The *worst* offenders for ESD are the engineers (like those of us
reading the list!), because they actually know what parts are
sensitive and which aren't, and tend to take shortcuts with the non-
sensitive parts. Which works, sort of, until they guess wrong, and
cook something. "Hey, why is the NF on this LNA 0.2 dB higher than
it was yesterday?"
jim
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