Hi Ted,
I cannot agree with what you relate from that article as the causes of
HWPA and resin recession—if that were so, you would find them in
unprocessed PWBs. They are only found after exposure to soldering
temperatures, and result directly from the large CTEs of the resin
above Tg.
Werner
-----Original Message-----
From: Ted Tontis <[log in to unmask]>
To: [log in to unmask]; [log in to unmask]
Sent: Thu, Oct 4 5:45 PM
Subject: RE: [TN] Via plugging with LPI soldermask...
After reading Werners comments
about hole wall pull away and resin recession I remembered an article
in August
Circuittree that talked about HWPA and resin recession, they are two
different defects.
The two main causes of HWPA is copper plating the second is the
desmearing
process. If the rate of copper deposit is set too high it will lead to
a stressed
condition, causing the copper to pull itself away from the hole wall.
When
it comes to the desmearing process, the higher Tg materials seem to
react poorly
with the chemistry used. If the process isn’t under control the result
is
an inadequately prepared hole for the plating process. This results in
a
poorly plated hole that may look like a blister when cross sectioned.
As for resin recession, a
large portion of resin recession issues are related to uncured epoxy,
as the
epoxy cures it shrinks from around the plated hole. It is also possible
that an
aggressive desmearing process could lead to resin recession by
penetrating the
resin material.
Werner
thank you for your comments, after reading the article, it would seem
that
there is no relation between conductive epoxy and hole wall pull away
or resin
recession.
http://www.circuitree.com/CDA/Articles/Feature_Article/BNP_GUID_9-5-2006
_A_10000000000000141639
Thank you,
Ted T
From: [log in to unmask]
[mailto:[log in to unmask]]
Sent: Thursday, October 04, 2007
3:26 PM
To: [log in to unmask];
[log in to unmask]
Subject: Re: [TN] Via plugging
with LPI soldermask...
Hi Ted,
Is there any data that
suggests that conductive epoxies or fillers shouldn't be used at a
specific
aspect ratio?
A: No data like that in
the public domain, at least.
What are the chances
that the conductive epoxy is increasing hole wall pull away, damaging
the
barrel?
A: None, Hole wall pull
away, ot resin ressesion, is the result of hydro-static [actually
resin-static]
pressure surrounding the via barrel trying to collapse it, and partially
succeeding in terms of plastic deformation of the Cu barrel wall—putting
anything into the via reduces the collapsing depending on the CTE of
the fill
material.
Can non-conductive
fillers act as an insulator when it comes to heat transfer within the
barrel?
A: Non-conductive
filler will provide better heat transfer than air, but less than any
other type
of filler.
Werner
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