Hi Russ

The most likely is you are having post-separation caused by the thermal
shock of a high temperature soldering or a very high temp. soldering.
I would make cross sections of some good holes and look at them whitout
etching. may be you also see some post separation that does not cause
complete failure but could cause that in the future. So the problem can be
also in your "good circuits".
If the circuit is very thick (more than 1/16") I would go to some higher Tg
material.
Other thing to check is in which components you are having the problem, if
these are very "big" heavy metal components they might be needing more heat
to solder and then the problem.
I also think it is worth to look at the design. Did you remove all non
functional pads in these holes and there are not enough "hangs" for the
holes, Is 5th layer a ground plane?
I don't think you could have a problem in the 6th (PS) layer.
Are there many grounds and vcc's? if this is the case you are heating to
much the board to solder, and again it will be good to have a higher Tg
material.
hope it helps
Roberto


At 12:03 PM 29/8/97 -0400, you wrote:
>I work in a material and failure analysis lab for Lockheed Martin.
>        We have a set of PCBs that are failing after hand soldering operations.
>Similar hand soldering operations on other boards are successful. Cross
>sections of the failed areas shows pad lifting and a seperation of the
>barrel and innerconnection on layer 5. The board is a 6 layer glass
>epoxy GFG board. Suspect problem with board material between layers 5 &
>6.
>        Looking for information on types of tests to run, printed material
>relating to testing PCBs, or other sources for information.
>        Thank You.
>
>        Russ Salvo
>
>
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Roberto Tulman
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