[Amps] Tubes, transistors, and 'abuse'

[donroden at hiwaay.net]

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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