Ah, Wise move on your part, Manfred. I wouldn't wear it either! Your
former boss needed higher level Technical Support!
Jim
Sent from my iPhone
> On Apr 11, 2017, at 12:39 PM, Manfred Mornhinweg <manfred@ludens.cl> wrote:
>
> Jim,
>
>> Manfred, I think you are worrying needlessly. A grounding wrist strap
>> connects to the mat, not to the device under test. ESD mats typically have a
>> resistance in the 10E7-10E8 ohm range. The mat on my workbench has a
>> resistance too high to measure with my Fluke 87-V. The mats discharge static
>> buildup, but neither they nor the wrist strap pose any safety hazard.
>
> Fine then. But the straps that one boss at the job wanted me to wear were all
> metal. Indeed they connected to the mat - but to a metal frame surrounding
> the static dissipative (highly resistive) material, and that frame was
> grounded. In the end, that wrist strap was grounded with a very low
> resistance, and I refused to wear that, for safety reasons.
>
>> I have lost MOSFETS from not taking adequate ESD measures. Some of the older
>> devices, especially, are very easily burned out.
>
> There are some that don't have the built-in zener protection - those are
> indeed fragile. Laser diodes (or rather their built-in photodiodes, I think)
> are also said to be very sensitive to static. I have handled such devices
> with no more precautions than the basic ones, and never lost any.
>
>> There's a reason all semiconductor distributers (Mouser, Digikey, etc.) pack
>> their components in ESD envelopes!
>
> Yes, and that's actually a good thing to do, and I do it too, when I ship
> something sensitive. My fundamental point instead is that thoughtlessly used
> grounding straps and the like can CAUSE more risk to the parts than they help
> prevent! I have seen people who put on such a grounding strap, next to their
> static-safe workbench, and then think that nothing bad can happen. Then they
> reach over to a drawer and withdraw a MOSFET by the gate terminal, and !ZAP!,
> they discharge the entire drawer through that MOSFET! My practice instead is
> to first get hold of the drawer, to put myself at its potential, then pick up
> the MOSFET by anything but its gate terminal, then walk over to my desk,
> touch the desk, then place the MOSFET on it. In doing so, I have already
> double safety in it: By avoiding to touch the gate first, and by equalizing
> the potential between myself, the desk, the MOSFET, and anything else, in a
> safe way.
>
> Most of this caution exceeds what's needed, but as you say, it's smart to be
> careful. And I would add that it's good to be smart! In the sense of thinking
> where static charges will form, what can be charged relative to what, which
> items could carry significant leakage current, and so on, and then acting
> accordingly. That's much safer than using a mat, a strap, and stopping to
> think about the matter, which is what I have witnessed some people doing!
>
> Manfred
>
> ========================
> Visit my hobby homepage!
> http://ludens.cl
> ========================
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