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September 2007

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Subject:
From:
"Brooks,Bill" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Brooks,Bill
Date:
Wed, 19 Sep 2007 10:12:55 -0700
Content-Type:
text/plain
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text/plain (90 lines)
One board manufacturing house we use draws the LPI into the via holes with a
vacuum filling them entirely before screening the material onto the board
surface... then they expose the boards for imaging and develop... 
I believe they must have some technique for exposing the LPI material in the
holes to make it solidify but I am not the board fabricator... 
The distinction required to get this process was changing my notes to say
'plugged' vias instead of 'tented' vias. 

So far it has been working very well. 

Bill

 

-----Original Message-----
From: Whittaker, Dewey (EHCOE) [mailto:[log in to unmask]] 
Sent: Wednesday, September 19, 2007 10:02 AM
To: [log in to unmask]
Subject: Re: [TN] Via Plugging

Yes, but as an esteemed member of this forum and an Icon of the Industry
says" It depends". If you are looking for long term reliability and
can't tolerate any open or exposed vias, there are only three methods.
Capped and covered [dry film SM cap covered by a LPISM (SMOBC)]; POFV
[plated over filled via (could be a SM material for the filler followed
by a LPISM over the copper if access not needed)]; and a plugged or
filled via (could be a SM material) covered by a LPISM (SMOBC).
The new revision of IPC-SM-840 deals with a lot of the acceptance
criteria, but there are additional requirements that have already been
proven out. 
If you don't care because it is not a functional requirement and only a
processing aid for test or assembly, then anything will work.
Dewey

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bill Dworak
Sent: Wednesday, September 19, 2007 9:37 AM
To: [log in to unmask]
Subject: [TN] Via Plugging

Does any one know of a  better way to plug vias with LPI  ratehr than
just the old standard method that will cover and plug the entire surface
of a PCB? I am being told that it is "industry Standard" to have about a
10% non plugged ratio. Any help will be welcome. 


   Bill Dworak


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