[Amps] Tubes, transistors, and 'abuse'

[donroden at hiwaay.net]

Unless you have a perfect conductor under or part of your conductive  
mat, there will be differences as the mat is probed with a Fluke.
Don W4DNR

Quoting Al Kozakiewicz <akozak at hourglass.com>:

> In Jim's post there were five assertions of fact, one opinion, one  
> typo and a polite closing.  Was Don disagreeing with some or all of  
> them?
>
> Al
> AB2ZY
> ________________________________________
> From: Amps <amps-bounces at contesting.com> on behalf of Doug Ronald  
> <doug at dougronald.com>
> Sent: Tuesday, April 11, 2017 4:04 PM
> To: amps at contesting.com
> Subject: Re: [Amps] Tubes, transistors, and 'abuse'
>
> I just tested the anti-static mat in front of me with an ohmmeter, and was
> amazed to see the resistance was not linear with distance. The mat was on an
> insulating surface, and with the probes as close as possible without
> touching, I got 42 kilo ohm. At the opposite ends of the mat I got 56 kilo
> ohm. The mat is about 5 mm thick, and seems to be all the same uniform
> material. The backside behaved the same way. There may be some inner layer
> that is of much greater conductance - can't tell...
>
> -Doug W6DSR
>
> -----Original Message-----
> From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of
> donroden at hiwaay.net
> Sent: Tuesday, April 11, 2017 12:49 PM
> To: amps at contesting.com
> Subject: Re: [Amps] Tubes, transistors, and 'abuse'
>
> Disagree.
> Don W4DNR
>
>
> Quoting MU 4CX250B <4cx250b at miamioh.edu>:
>
>> Speaking of high resistance mats, an interesting property is that the
>> resistance between any two points on the map is the same, no matter
>> the distance between the points. In other words, it doesn't matter
>> whether you put your test probes a cm apart or 10cm apart, the
>> resistance will be the same. That's why the resistance of a flat mat
>> is always specified in ohms, unlike three-dimensional materials whose
>> resistivity is specified in ohm-cm. In two dimensions, resistance and
>> resistivity are the same thing.
>> 73,
>> Jim w8zr
>>
>> Sent from my iPhone
>>
>>> On Apr 11, 2017, at 12:42 PM, MU 4CX250B <4cx250b at miamioh.edu> wrote:
>>>
>>> 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 at 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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DonR