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_1
0000000000000141639 

 

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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