paulmorriss
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Re: Cases and static

Mon Jan 30, 2012 5:04 pm

I used to work for an electronics firm and we were suitably paranoid about static - always wearing wrist straps when working with circuit boards etc. When it comes to cases, does it matter what the case is made of when it comes to preventing static damage? Does it matter how the PCB is fixed to the case?

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alexandru.cucu
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Re: Cases and static

Mon Jan 30, 2012 7:04 pm

There are so many electronics that have plastic cases. I don't think this is an issue if the board does not get near electrostatic charged object other than the one it has contact from the beginning.

The danger comes from the discharge, not from the charge itself.

Keep your cats away from the Raspberry Pi!!!
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dom
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Re: Cases and static

Mon Jan 30, 2012 8:34 pm

I wouldn't be too concerned about static. I've been manhandling boards like this for years - without a wriststrap, and have never known a board to be killed by static.

mobeyduck
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Re: Cases and static

Mon Jan 30, 2012 10:58 pm

And the board is cheaply replaceable its designed to be replaceable and destroyed.

But lets just hope "will it blend" waits for the 2nd batch

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rurwin
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Re: Cases and static

Mon Jan 30, 2012 11:19 pm

The story used to be that generally static does not kill a chip immediately unless it's a massive discharge. It just damages it enough that it dies a couple of weeks later.

But I have been very unkind to various devices over the years and very few of them have failed in any way. The danger is exaggerated, but wear a nylon shirt and run up and down a nylon carpet carrying a naked device, and you just might damage it.

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liz
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Re: Cases and static

Mon Jan 30, 2012 11:28 pm

One conference we were demoing the alpha boards at last year had a newly installed carpet. People kept coming up, index finger extended, and saying: "Oo! Is THAT the chip?" *Bzzzt.*

That particular board still works. So does the one that's spent the last six months in JamesH's backpack, the one I've taken on four (eight if you count returns) transatlantic flights in hand luggage, the one in the study that my cats occasionally nuzzle up to, and the one Dom fed power to through what turned out to be a piece of wet string he had accidentally mistaken for a USB cable. (Long story.) This is not a great dataset, but my feeling is that you've not got much to worry about.
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dom
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Re: Cases and static

Mon Jan 30, 2012 11:51 pm

This was the cable (in fact I bought two – they were only 99p when I bought them):

http://www.ebay.co.uk/itm/ws/e.....0744534601

Resistance of 5ohms. 5V in one end. Less than 4V out the other. R-Pi not very stable.

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Chromatix
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Re: Cases and static

Tue Jan 31, 2012 12:13 am

dom said:


This was the cable (in fact I bought two – they were only 99p when I bought them):

http://www.ebay.co.uk/itm/ws/e.....0744534601

Resistance of 5ohms. 5V in one end. Less than 4V out the other. R-Pi not very stable.


"Revolutionary 2-in-1 cable for charging power and transferring data simultaneously!"

See, that kind of breathlessly ignorant fluff is a red flag to me.
The key to knowledge is not to rely on people to teach you it.

bredman
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Re: Cases and static

Tue Jan 31, 2012 10:10 am

I have been handling circuit boards for years with no problems. In the beginning I used a wrist strap, but I don't know where it is now.

Maybe static isn't such a problem these days. Back in the 80s everybody had nylon carpets and polyester clothes.

So ditch the wrist strap and do your hardware hacking in the nude. Be careful of hot solder!

BFD
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Re: Cases and static

Tue Jan 31, 2012 11:50 am

A plastic case isn't necessarily a problem from an ESD perspective, after all most IC's are packaged in some form of plastic.

Some devices are more sensitive to ESD than others and damage from ESD events can be very latent.  Our lab does failure analysis on electronics and ESD damage can be observed using scanning electron microscopy (although it isn't always easy to find).  The most important ESD control principle is to always keep the printed circuit assembly and your body at the same potential (also the work surface).  This is usually accomplished with grounding (ground strap and static dissipative grounded work mat).  In the absence of an ESD workstation, touch something metal that is grounded before handling a printed circuit assembly and this will mitigate the risk.

Mark

Electronic Packaging/Fab

MarshallBanana
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Re: Cases and static

Tue Jan 31, 2012 2:00 pm

liz said:

 and the one Dom fed power to through what turned out to be a piece of wet string he had accidentally mistaken for a USB cable. (Long story.) 

i'd love to hear THAT story

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walney
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Re: Cases and static

Tue Jan 31, 2012 2:26 pm

liz said:

...the one in the study that my cats occasionally nuzzle up to...

If the cats have finished with it I'm sure that I can make good use of it...


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