My apologies...mind was on wicking. You are correct!
Rick

-----Original Message-----
From: Werner Engelmaier [mailto:[log in to unmask]]
Sent: Friday, December 07, 2001 12:43 AM
To: [log in to unmask]
Subject: Re: [TN] RESIN RECESSION


Hi Earl,
>Resin recedes back into the structure, away from the hole wall, during
thermal
>stress and returns to original geometry after cooling? Copper does not?
You got it backwards--I guess I did not describe it clearly enough. during
heating [thermal stress] the resin expands into the hole towards the hole
walls, not away from them {YES, I know a hole in a steel plate gets bigger
on
heating, but a PCB is not a steel plate, it is a resin matrix constrained in
2 directions by the glass reinforcements. You drill a hole in this and the
hole  gets smaller on heating}.
So, this inwards movement of the resin deforms the Cu inwards as well, and
some of this deformation is plastic. The adhesion of the Cu wlls to the
resin
 is not sufficient to pull the Cu walls back to their original position.
Smear removal or etch-back have nothing to do with this, plating thickness
and number of inner-layer lands do however.

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