Hi Bryan,

I'm Curious as to what Class copper you are using on the Inner layers. We have
found that in the past that class-1 copper would not cut it, and switched to
Class-3 Copper which is more ductile. This practically eliminated foil
cracking.

Regards,
Les
>  From: Bryan Kerr +44 1383 822131 ext 4409 <[log in to unmask]>, on 2/25/99
>  4:58 PM:
>  On this subject, I have recently been investigating an open circuit problem
>  with a multilayer board and have found a small, but significant, level of
>  foil
>  cracking at the hole / inner layer interface with no apparent reason. There
>  are
>  no unused pads and I had already been pondering whether the lack of these
>  "dummy" pads could result in more stress on the inner layer junctions during
>  thermal shock - 288 C for 10 seconds. Maybe any weaknesses in the junction
>  are
>  more likely to result in fracture if there are no dummy pads ?
>  Comments, anybody.
>
>  Bryan
>
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