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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