Well, i didn't think it takes less than two seconds to get pasted board
landed first sensitive component;
i'm still flabbergasted by longevity of this yarn ,
did i make it through to net with my last message about bottom (in pcb case)
mounted earthed carbon brush,
so commonly used to discharge running films in photo autolabs ?
(often with ionized instream)
Send one previously , came back with some message of unacceptability through
similarity (cute),
so i thought to send a hoy again .
Yo' can mound those wherever desired .
paul
-----Original Message-----
From: Cash, Alan [mailto:[log in to unmask]]
Sent: Saturday, 4 March 2000 10:28
To: [log in to unmask]
Subject: Re: [TN] ESD and Polyimide stencils...
The ionizer will not help due to the fact that it takes one to two seconds
to dissipate the built up charge, depending on its magnitude. Preventing
the generation of the charged field is the only way to prevent ESD damage to
susceptible components. See ANSI/ESD S20.20 for an ESD program guideline.
A clean gas stream hitting a pcb will not generate a static charge. The gas
must be full of particles in order to generate a charged field on an
insulator. The static charge comes from the person handling the pwb if they
are not grounded while transporting the pwb.
Al Cash
-----Original Message-----
From: Szilassi Zoltán [mailto:[log in to unmask]]
Sent: Friday, March 03, 2000 11:55 AM
To: [log in to unmask]
Subject: Re: [TN] ESD and Polyimide stencils...
Dear Techneters,
I'm very new in the forum, so here are some things about me. I'm working for
a small company in Hungary, which is selling all sorts of electronic
assembly machines, materials, services, basically everything, which can be
sold to electronic manufacturing companies. I'm mostly involved in the
technical support of our sales activities.
About the ESD problem with polimer stencils. I had the same kind of problem
at one of our customer's site, a CEM in Hungary. They were using Loctite
Varidot stencil for glue printing. (I do not know what sort of polymer is it
made of and also the company could not find it out.) After a while they have
realised, that some BGA packaged components would die during the printing
process. They have tried the ionic fan idea, but it did not give preffered
results. The final solution was to use metal stencil for this application.
The process is working fine ever since.
Questions:
They were using standard polyurethan sqeegee blades, not the one supplied by
Loctite. Does anyone has any experinece if the static charge buildup occures
if they use the Loctite blade for the Loctite stencil?
Why these stencil producing companies not use conductive polymers for such
an application?
Best regards
Zoltan Szilassi
-----Original Message-----
From: Murugan Vasudevan <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: kedd, február 29, 2000 4:11
Subject: [TN] ESD and Polyimide stencils...
>Hi all!
>With yesterday's discussion on Polyimide stencils and
>the associated ESD risk factors (Boy! I gotta admit
>that I was a little scared..oops after weeks of
>stencil design and evaluation, and assumption that it
>is the best we've got, now we end up fighting against
>ESD..), we decided to run a quick ESD test on our
>polyimide stencils..and here is what was observed.
>- The poly stencil, without doubt, is definitely more
>ESD prone than a metal one. Some places on the stencil
>was measured holding more than 2000v of charge. But,
>an interesting observation was that when the stencil
>is put on the printer and after a run or two, when the
>charge was measured again, it was very small (around
>100v). Something was discharging it and it was not the
>PC board. So it was a kinda mixed reaction that was
>observed. We dont want to take the risk of going ahead
>because, well, sometimes it may happen that the
>humidity falls, then these stencils would accumulate
>charges, and oops do i have to tell what'll happen!.
>We would be printing adhesives using this stencil on
>the bottom side, with ICs and lotta ESD sensitive
>stuff on the board.
>- One of the suggestions were to use an ionic fan
>(replace the regular fan on the rear of the printer
>with an ionic one), so that we can be safe from ESD
>problems, but..i was still kinda worried..and here i
>am!
>
>Any bouncing back of ideas/suggestions...???
>
>Regards,
>Murugan
>__________________________________________________
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>Talk to your friends online with Yahoo! Messenger.
>http://im.yahoo.com
>
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