Hello Brian.  Years ago Joe Keller wrote some articles regarding the filling
of plated through holes.  Those articles should be available through some
library research on hole filling.  As a past chairman of the IPC Plated
Through Hole Fill Task group, I can state without a doubt that two factions
existed in the market place regarding plated through hole filling. The
commercial business without a doubt wanted to take whatever happened, if it
did not fill so be it, it was reliable and no one had any information
otherwise.  The military position was that the hole had to be filled or
massive failures would occur.  

At the time the military was concerned with corner cracks of the pth which
is why they demanded top side fillets. Investigations at the time reflected
thin plating at the knee which was an exposed intermetallic layer which
prevented the solder from flowing over to the top side of the pad.  Some
manufacturers went as far as to electroplate a lead coating over the copper,
then plated it with tin/lead so the weak knee phenomena would not appear.
All this effort was expensive and the commercial users would have none of it
at the time.  SMOBC products exhibited the weak knee phenomena even more
than the tin/lead electroplate fused process which created more division
amoungst the users.

The bottom line was and still is that the issue is still unresolved and that
individual manufacturers are doing their own research to determine what is
good for their unique products.

In your comments regarding thick boards, the problem is even more difficult
to answer.  I would suggest also investigating the work Roger Wild did at
IBM for plated through hole filling.  I seem to think that an empty or
partially filled hole was more ductile therefor lasted longer than a filled
hole.  Roger also did some work on reworking plated through holes and found
that any hole filled with solder after the initial soldering operation was
weaken and would fail faster than an untouched plated through hole.

So where am I going with this.  Do a library search on Wild from IBM and
Keller, perhaps from some old Nepcon Procedings.

Good luck 

Leo Lambert
EPTAC
At 05:16 PM 10/14/96 PST, brianwada wrote:
>
>Brian Wada
>Solectron    [log in to unmask]
>
>Does anyone recall the article sometime back in the 80's or later on Plated
>Through Hole Solder Quality pertaining to solder fill with leads or voids
>with leads correlated to solder joint reliability.  NASA or Aerojet may be
>the author.  Printed wiring boards are increasing in thickness greater than
>.092 inches and the question of whether solder fill or lead to pth wall
>solder joint affects or impacts reliablity.
>
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