[sdiy] electrosensitive devices

[Peter Grenader]

<<is it possible for a significant
> amount of static to transfer from say...my finger to an expensive cmos chip,
> without that audible "zap" sound?
> -steve>>

ABSOLUTELY!

I forgot the numbers, but the amount of charge you can hear/see is some
unbelievable amount higher than what will cause damage, even above what will
cause castasrophic failure.

Something along the power of 100.

If you hear it or see a zap when specifically touching a CMOS part, don't
even bother powering it up to see if it works, just go ahead and replace it.

Now, this is not to say that a static discharge of the that size will
automatically blip the CMOS -->  If you just touch a faceplate of a device
with CMOS in it, do not assume that that path made it's way to the part(s)
and that you've done them damage.  Even if the arc happened when touching a
jack which runs a direct line to the PCBA where those components are.

The static charge has got to run threw the device so that the charge of any
active pins are significantly different - this is what blows them.  All pins
must have the same charge to avoid damage.  This is what conductive foam
does.  it doesn't protect - it puts the pins at the same charge.

A pink poly bag does not protect, either - it just increases the surface
resistance so that the charge has less of a chance to make it to the
contents.  Nickel bags. like the ones Mouser use, DO protect, allowing a
discharge path of the arc around the contents, but not threw them.
Although only a few mils thick, this thin flash of nickel plating at the
inner layers of the nickel bags actually work like a faraday cage.

Hope this helps.

Peter


Stephen Beginwrote:

> One more question about static then...is it possible for a significant
> amount of static to transfer from say...my finger to an expensive cmos chip,
> without that audible "zap" sound?
> -steve
> 
> ----- Original Message -----
> From: "Peter Grenader" <petergrenader at mksound.com>
> To: "Stephen Begin" <trypannon at hotmail.com>; "synth"
> <synth-diy at dropmix.xs4all.nl>
> Sent: Friday, April 04, 2003 10:43 PM
> Subject: Re: [sdiy] electrosensitive devices
> 
> 
>> 
>> Many suppliers, Mouser among them, put a blanket control system on all
>> semiconductors.  It's less expensive for them to put all semi's into the
>> costly nickel plated anti static bags than it is to concoct some large
> scale
>> sorting/segregation system, because it has to carry not only to the final
>> shipment, but through their entire warehousing/receiving system as well.
>> You can only imagine how hard it would be to assure that all static
>> sensitive parts, and only those parts, received special handling
> procedures,
>> are kept in a separate stores locations, etc.
>> 
>> So,  if you are unsure which are and are not problematic for static, as
>> impractical as this may be, the best solution would be to carry out their
>> system in your lab and for you to treat everything as static sensitive as
>> well.   Yeah, I know...a drag.
>> 
>> Problem is, and this came up a few months ago...99.99999999 to the tenth %
>> of the failures from the initial static discharge is not catastrophic.  It
>> merely degrades the part so it will lean towards infant mortality
> somewhere
>> down the road.  And when it does, it's hard to determine if ESD was the
>> cause unless you pop the top off and have a look under an extremely
> powerful
>> microscope. Even more impractical in my book.
>> 
>> Two general rules of thumb will help you out a lot:
>> 
>> 1)  Treat static like a virus and take the necessary precautions to keep
> it
>> from spreading.
>> 
>> 2)  Get your hands around which parts are and are not susceptible and make
>> damn sure you at least keep them in foam when not in boards and wear a
>> ground strap when inserting them or when handling a board that has them
>> inserted, even if you are planning of fooling with those parts directly at
>> the time.
>> 
>> I worked for a company (Western Digital) whose first products were
>> controller LSI chips.  This is what they started off doing and what put
> them
>> on the map. This was years before they purchased the Tandon hard drive
>> division. You have no idea what you have to go through to create a truly
>> static free environment.  We're talking heels straps, nickel faraday bags,
>> heel straps, wrist wraps, conductive booties, grounded forklifts, grounded
>> storage racks, grounded soldering irons, air ionizers, conductive mats,
>> anitstatic spraying of work benches - it's a complete mess.
>> 
>> hope this helps - remember, it's not only 4000 series CMOS you have to
> worry
>> about!
>> 
>> Peter
>> 
>> 
>> 
>