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Date: Wed, 8 May 1996 16:42:40 -0400
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Subject: Fab:Re: Breakout at innerconnect
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Eugenio 

We all have had for many years a gut feeling that breakouts at the internal
connection between the hole and the conductor is bad/bad/bad.  IPC-RB-276
restricts the breakout at this point on Class 3 but is silent on Class 1 and
2.  We who have manufactured boards know that in the complex board unless
the
lands are elongated or pear shaped the likelyhood of breakout at these
points
are not infrequent.  I have done failure-cause on many that did have via
breakouts at the interconnect and have not seen a failure related to the
interconnect that occurred at a breakout unless other holes without breakout
exhibited the same failure mode.  Their does not seem to be a published
analysis on the subject where a good DOE was done and statisically
evaluated.
Most testing that I am aware of appears to be random short quick-looks and
move on.  

I have heard that in some recent evaluations by the post separation group
that the innerconnects that did not have an annular ring (landless vias)
were
better than those that did.   

The Military Specification MIL-P-55110 does not allow breakout at the
innerconnect; however, the coupon called for testing this on the internal
layer does not have internal connections at the holes; therefore, is not
directly evaluated but is secondarily determined by annular ring
measurement.
.  

The landless via is being increasing used with good results and will
probably
be the way of the future. If any of the other subsribers have though on
breakouts at internal interconnects please log on.

Phil Hinton 
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======== Fwd by: Tony King / N ========
Phil,

When we as manufacturers finally look at where we have come, what the
various  specifications require to build "acceptable" product and where the
future technology seems to be going, we wonder how in the world we got here.
Its another case of "you cant get here from there", or so it seems. We have
specifications arise which REQUIRE etchback to guarantee product integrity
for example, but gradually it is realized that desmear works just as well,
after all you dont need to build a tank to drive down the street, a car
works just as well. The controversy over pink ring, aesthetics or defective.
How much product was scrapped over the years on the possibility that pink
ring was a defect or indicator of a possible process problem... We now look
at the driving force to reduce pad size to free valuable design real estate
yet maintain the same annular ring specifications imposed on previous
designs.  Padless vias ???  Is it now time to step back and look at our
"progress" over the years ???  Look back to multi wire product, a system of
manufacture used for years and still in use where thin wire is laminated
into multiple layers and then drilled. Landless vias... how far have we come
and where are we going...

Tony King
Elexsys International
603-886-0066