Peter, Paul (& Mary?) -- (sorry!)
While I agree that conductive materials are great in the explosives
industry, you don't want to get carried away with conductive materials in
the electronics industry. Grounding conductors (surface resistivity
<1x10E5 ohms/square) and dissipative materials (surface resistivity
>1x10E5 - <1x10E12 ohms/square) will bleed the charges off to ground; the
higher the resistivity, the longer the discharge time (we're talking
milliseconds here). Grounding insulators (surface resistivity >1x10E12
ohms/square) is useless, as the charge is "static" at that point and will
not flow through the insulator to be bled off.
Using too much of a conductive material, in the wrong places, vs.
dissipative material can lead to other ESD failure modes (i.e. CDM -
Charged Device Model failures, where the charged device is then shorted
directly to ground through a grounded conductor, whereby an ESD event
occurs).
As for safety, operators are typically grounded through a 1 Megohm
resistor built into the wrist strap, or footstrap. In NO event should
the operator be connected directly to ground without the benefit of the
resistor (granted, there are some wrist straps with resistors rated at
less than 1 Megohm, for special applications). The 1 Megohm resistor is
there for operator safety, should the operator come into contact with 120
VAC, limiting the current to .12 milliamps. Operators working on high
voltage power supplies typically wear special wrist straps made for that
application, or more commonly, wear no wrist/foot straps at all.
Hope this helps.
Regards,
Glenn J. Saracino
Honeywell - Air Transport Systems
Quality Engineering
[log in to unmask]
-----Original Message-----
From: [log in to unmask]
Sent: Monday, March 30, 1998 7:50 PM
To: [log in to unmask]
Subject: Re: [TN] ESD
Peter ,
could you stress the difference between conductive/grounded and
dissipative ;
conductive regime being great in explosive manufacturing factories can
be deadly in electronics , especially the power segments of assembly and
test .
Too often I've seen really and truly personnel grounded without
slightest idea of principles and danger involved .
Thanks paul
>----------
>From: Peter Mariani[SMTP:[log in to unmask]]
>Sent: Tuesday, 31 March 1998 10:23
>To: [log in to unmask]
>Subject: Re: [TN] ESD
>
>I agree with Mr. Hamilton but it not always pratical to make everything
>conductive due to availability, cost or design requirements. PCB boards
and
>laminate for example are by design not conductive in many areas or in
most
>stages of manufacture. Grounding does not work unless the grounded item
is
>conductive.
>
>Ionization is a pratical cost effective tool to add to to the ESD tool
box
>along with training of the operators. To learn more about ESD and
>ionization visit http://www.electrostatics.com.
>
>
>
>At 04:58 PM 30-03-98 -0700, you wrote:
>>Fred,
>>
>>I am not clear from your message and I don't think the importance was
>>made strong enough in the answers I have seen so far.
>>
>>EVERYTHING MUST BE GROUNDED / CONDUCTIVE!! One loose cannon so to speak
>>can do all the harm. The tube, person, bag, table top, pop rivet gun,
>>rivet supply container, ......you get the picture, all of it must be
>>addressed for ESD. And don't forget the air. Then, after mounting,
don't
>>forget the device is now part of a PWBA. How is the PWBA handled????
>>etc., etc., etc.
>>
>>And speaking from experience, it is such fun to go after, because it
can
>>be so elusive. You can also get REALLY carried away in the protection
>>arena. However, the product may need it, and eventually you may be able
>>to back off the ESD activities once you better define each areas'
>>vulnerability.
>>
>>It may be worth it to get a specialist in to help you out.
>>
>>Best of luck to you, and I hope I have helped more than I have scared
>>you!
>>
>>Richard Hamilton
>>Clemar Mfg. / Rain Bird
>>[log in to unmask]
>>
>>> -----Original Message-----
>>> From: Fred Pescitelli [SMTP:[log in to unmask]]
>>> Sent: Monday, March 30, 1998 2:06 PM
>>> To: [log in to unmask]
>>> Subject: [TN] ESD
>>>
>>> All,
>>> We are having ESD problems with a particular FET, and are trying to
>>> track
>>> the problem down in our process. What is the proper procedure for
>>> transferring parts from a tube to an ESD bag? We are also using blind
>>> rivets to hold them down to a heatsink, can we be causing a problem
>>> there?
>>>
>>> Fred Pescitelli
>>> Phoenix Designs
>>> 1285 Turner Rd.
>>> Lilburn, GA 30047
>>>
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>
>
>Peter Mariani
>
>Ph. 215-513-0850
>Fx. 215-513-0855
>mailto:[log in to unmask]
>
>Visit http://www.electrostatics.com
>to learn more about static electricity
>
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