[time-nuts] Conducting Bench Top Material

[Scott Burris]

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_palmer at 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-bounces at febo.com [mailto:time-nuts- 
>>> bounces at 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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