[sdiy] OT: Where to get cheap ESD safe electronics parts drawers?

cheater00 cheater00 cheater00 at gmail.com
Sun Mar 12 14:01:27 CET 2017


Hi guys,

TL;DR:
1. ESD damage is insidious; it can be slight and make parts just act weird
or fail in months.
2. alu foil and conductive surfaces are just as bad for ESD damage as
insulative. You want dissipative. Don't line your drawers with alu foil.
3. Passives are easier to kill than chips.
4. You absolutely need to check ESD surfaces periodically so get a cheap
megger, they are difficult to make wrong.
5. ESD storage is cheap on alibaba.com and MOQs are low.
6. "I don't care about ESD" = "hold my beer".

Hugh's comment below is gold. When I went to a large electronics
manufacturing tradeshow a few years ago an ESD safety manufacturer rep made
exactly the same points and it made perfect sense: ESD damage can happen
without even trying, at low charges, and with the parts not getting fried -
instead they will act a bit weird, fail some time later, etc. As Hugh put
it, ESD damage is insidious.

They also made a second very imporrant point. When ESD damage happens it
happens in one of two ways:

1) the part receives charge from another object
2) the part gives up charge to another object

Both obviously create the same sort of damaging current. And obviously
parts can hold charge: semiconductors don't have internal high-impedance
shunts between the pins to let charge dissipate.

Thus came the second revelation: just as you don't want surfaces and
vessels made out of perfect insulators, which would build up charge and
give it to your part, you also don't want CONDUCTORS, which will short your
part (wither to ground or with itself) and create current that is not
limited. This will just as easily kill your parts.

The rep on the (huge) stand kept repeating that nervously and it was by far
the main point he wanted to carry across.

That is why ALUMINIUM FOIL IS BAD. Typed it in all caps so anyone who
doesn't read the whole mail still see this. Aluminium foil is conductive.
Do not use it to line your drawers. In addition to easily killing your
parts the instant they get shorted, you also end up making a huge
receptacle for any air-borne charges. And because the conductor is huge
now, amd cam reach very far into space, it will end up seeing large
voltages even from gradients that are locally very small - i.e. alu foil
AMPLIFIES ESD.

For a surface to be safe to parts (ESD Safe) it needs to be /dissipative/.
This means: not resistive enough to build up static charge, but not
conductive enough to allow unlimited current.

Here is a table of surface resistivities:

Conductive: 0..10^5 Ohm/sq
Dissipative: 10^5..10^11 Ohm/sq
Insulative: 10^11..inf Ohm/sq

Read this to understand the units: http://www.lxdinc.com/faq/ohms_per_square

So this brings us to the third point they were making, namely whether your
passives will be ok. Anyone who's read about how capacitors are made knows
those are easily damaged. Take tantalums: even the slightest imperfections
will result in resistove heating and result in a chain reaction and
destruction, maybe on a really hot summer day or under heavy load.
Electrolytic capacitors: the film inside is super thin. A tiny pinhole
through the insulator will easily create a shorted part. Capacitors are
generally rated up to 100s of volts and ESD is easily 0.5-tens of
kilovolts. When you go and stuff your capacitor into that alu foil
container you're likely to kill it just by discharging it.

As far as resistors go, this comment on a forum was good:

"A high enough voltage can cause normally insulating materials (like air)
to ionize and carry a current (like a spark). If air can ionize from ESD
voltages, you can imagine that insulating parts of resistors could too. ESD
can cause permanent damage to the resistor, either an extra conducting path
through a former insulator, or a open circuit because some conductor melted
(which would be thermal damage).

Theoretically, every resistor should have a maximum ESD voltage rating.
Many don't because they are large and robust. But very small resistors, and
resistors that are made on a silicon chip, can be damaged by ESD."

We can probably find ESD issues for all sorts of passives, including
inductors and the like, but let's stop here.

In general: unlike chips, passives have no built in ESD diodes and the
like., and are made out of flimsy layers of pixie dust.. no surprise they
can die.

The fourth point being made was that ESD safe equipment isn't. That is,
nothing is intrinsically ESD safe. Your surface might get dust on it and
then it starts building up charge, or it'll get oils deposited from the air
and it'll become insulative. So even if you get the best ESD surfaces and
storage, you need to check periodically. Given a megger is just a few dozen
bucks and much less than any sort of ESD safe storage or even a decent
rubber mat, the purchase is a no-brainer.

My final finding is that there is a lot of very cheap ESD tech on
alibaba.com. They have modular systems: stackable open bins, trays, boxes,
modular single drawers (for larger parts) and pill boxes (for tiny parts).
I think those are pretty good. If you don't trust them check with a megger,
which you should be doing *anyways*. Some sellers have fairly low MOQs of
e.g. 50 drawers which is less than one needs. I will now make a survey of
those and if it's in a sensible format I will post it here.

In general it's easily understandable people disregard ESD precautions.
Even knowing the stuff above I agreed with some of the points on the list
that I know were not the best ideas simply because it's soooo easy to
forget all this stuff until you really think about it for a while. But it's
important.


On Sun, 12 Mar 2017 01:50 Hugh Blemings, <hugh at blemings.org> wrote:

> Hiya,
>
> An interesting discussion on ESD... :)
>
> On 12/3/17 11:10, Tom Wiltshire wrote:
> >
> > On 11 Mar 2017, at 21:02, Andre Majorel <aym-htnys at teaser.fr> wrote:
> >> I've stuck TTL ICs into little pieces of black foam kept in
> >> ordinary plastic drawers but I'd be hesitant to do that for CMOS.
> >> Now, I keep ICs in wooden drawers, in foam or tubes cut to size.
> >> Wood might be an insulator but it doesn't seem to be as prone to
> >> build-up of electrostatic charge as untreated plastic. (Talking
> >> about plywood and solid wood here, not melamine-covered particle
> >> board.)
> >
> > I started out playing with CMOS and a 9-volt battery when I was a kid
> > and I'd never even heard of static precautions. I never killed
> > anything by static, but I grant you that the UK has a pretty damp
> > climate…
> >
> > I think the risk of chips dying from static is somewhat overplayed.
> > It's a good way to sell you more stuff, and perhaps in a production
> > environment where you're handling thousands each day the numbers
> > start to stack up, but for an individual? Seems unlikely.
> >
> > I'm quite willing to hear why that's all nonsense though.
>
> I'd be very reluctant to say "nonsense" among this erstwhile list but
> can offer this perspective;
>
> Many years ago I put basically the scenario outlined above to a good
> mate of mine who was also an EE of many years experience.
>
> Gav basically explained that the problem with ESD tends to be insidious.
>   Immediate failures are relatively rare, but at least have the
> advantage that the part is known bad then and there.
>
> Much more commonly though, the ESD causes non-catastrophic failure -
> only blows a little hole in the circuit elements if you like.  Thus the
> device continues to operate, but it's long term reliability is impaired
> and/or its performance degraded.
>
> The problem with "minor" damage then becomes one of statistically higher
> failure rates or weird behaviour in the field.
>
> He had some impressive electron microscope photos in a textbook that
> illustrated this, so long ago I've no idea the title, but this
> application note from Maxim is in a similar vein.
>
> https://www.maximintegrated.com/en/app-notes/index.mvp/id/4491
>
> The takeaway I had from this conversation that I've sought to work by
> ever since is to always take ESD precautions - static strap, mat on work
> bench, ESD foam for device storage, ground myself before touching even
> completed PCBAs etc.
>
> Hope this helps!
>
> Happy Hacking,
> Hugh
>
>
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