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October 2007

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Subject:
From:
Werner Engelmaier <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Wed, 3 Oct 2007 12:23:57 -0400
Content-Type:
text/plain
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text/plain (138 lines)
There is no reason why voids in non-conductive fills in PTVs are a 
problem. Kim's experience makes sense.

Werner

-----Original Message-----
From: Haynes, Kim <[log in to unmask]>
To: [log in to unmask]
Sent: Wed, Oct 3  12:12 PM
Subject: Re: [TN] Via plugging with LPI soldermask...

I hve watched this plug/tent discussion thread with interest.  I design
and build boards for multi-gigabit transmission rates in a lab
environment.  When I use conductive filling, I seem to have via problems
during thermal cycling device analysis.  When I use a non-conductive
epoxy, I do not have the problems.  I have not been able to prove this
hypothesis but I think the conductive fill has a different expansion
rate than the board and the small vias tend to crack.  The
non-conductive epoxy expands at about the same rate as the boards and I
do not seem to have the same failure rates from via cracking.  One of my
board fab shops is mil qual rated and they claim that the govt
inspectors do not even want conductive epoxy in the buildings.  It makes
them nervous because it could be used instead of the non-conductive
filler and they do not want any boards with silver epoxy.  I have been
searching to see if anyone has done controlled tests of conductive epoxy
versus non-conductive epoxy fills for via in pad technology.
Thanks,
Kim Haynes
Interface and Clock Products
High-Speed Serial Link Applications
Texas Instruments, Inc.
214-567-2057  Telephone


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ted Tontis
Sent: Wednesday, October 03, 2007 10:20 AM
To: [log in to unmask]
Subject: Re: [TN] Via plugging with LPI soldermask...

Bill,
    I used to specify in my manufacturing notes 'vias must be
plugged using LPI solder resist' I was told more then one once and from
different suppliers that they could not guarantee the vias would be 100%
'plugged'
using LPI. They would however guarantee that there would be LPI in the
via hole or that the LPI would tent over the via, leaving a void in the
center.
If I required 100% via fill I would have to require that they fill the
holes with some type of conductive filler.

Thank you,

Ted T

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Brooks,Bill
Sent: Tuesday, October 02, 2007 3:44 PM
To: [log in to unmask]
Subject: [TN] Via plugging with LPI soldermask...

Just a quick question...

When specifying 'plugged' vias using LPI soldermask... what is the
actual process used to accomplish this procedure? How do you make sure
the vias are plugged and what is the proper acceptance criteria used to
verify and inspect the finished results? What is an acceptable plugged
via vs. a reject? Is there a spec or standard that spells this out
process and inspection criteria and method for reference?

Thanks in advance...


Bill



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