Mark:  As far as I know the most definitive study done on this was about 10
years ago by Roger Wild of the IBM house (Federal Systems Divison I think).
He found (if memory serves me correctly and that is always a little "iffy"),
by monitoring for failures during extended thermal cycling, that an unfilled
pth was the most reliable, a pth hole with 100% solder fill was next most
reliable, and a pth with 50% solder fill was next most reliable.  An epoxy
filled hole was in the data somewhere, but I don't remember where.  Seems
like the reliability difference between the 50% and 100% hole fill was
concluded to be attributable to the 100% fill cresting over the (topside)
knee of the pth and thereby providing some Z-axis reinforcement.  My guess
would be that 75% hole fill would fall into the reduced reliabilty arena
associated with 50% hole fill.  The practice of filling the hole is dubious
from the standpoint of achieving a reliabiltiy improvement.  What is the
end-item thermal environment of the pwa.  I no longer have a copy of the
report, you might call the IBM Tech. Library and see if it is available
through them.    Regards, Jim Moffitt/EMPF


At 01:03 PM 10/10/96 CDT, you wrote:
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>From: Mark Weiler <[log in to unmask]>
>To: [log in to unmask]
>Message-Id: <@m400gw.dell.com>
>Subject: Through Hole wave Vs. rework
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>     
>     We are building a board that has 8 layers with multiple ground planes,
this 
>     combined with Entek plus coating and a no clean process is making it 
>     difficult to optimize the wave solder profile to get 100% fill with a 
>     fillet on all pins on the top side of the board.
>     
>     The IPC A-610 rev B specification calls out 75% fill as being acceptable 
>     (table 4-1, pg. 52) on through hole solder joints. We are pushing our 
>     subcontractors to get 100% fill with a fillet on each pin.
>     
>     Since we are setting our expectations to 100% fill on these solder joints 
>     the subcontractor is having to touch up some of the solder joints to meet 
>     this requirement (they are touching up the pin from the solder side
letting 
>     the solder flow through the board to the top)    Thus my question...
>     
>     Is a solder joint that is 75% filled over the wave stronger (more
reliable) 
>     than a solder joint that has been touched up to get to 100% with a
fillet? 
>     
>     What is the effect to long term reliability of touching up a through hole 
>     solder joint?
>     
>     I would really like some reference material on this subject if anyone
has a 
>     source.
>     
>     Thanks,
>     
>     Mark Weiler
>     [log in to unmask]
>     512-728-8323
>
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