Daan,

It is almost never the same in X and Y.  They will always be slightly
different due to the grain and non-grain (warp and weft) of the material.
We specify grain in a fixed dimension and have developed consistancy based
on that.



-----Original Message-----
From: d. terstegge [mailto:[log in to unmask]]
Sent: Tuesday, June 13, 2000 2:53 AM
To: [log in to unmask]
Subject: [TN] stretch and shrinkage of bare boards


I have a question for the fab-guys out there :

Is it likely for a bare board that shrinkage or expansion is different in X-
and Y-directions ? Or maybe even a stretch in X and a shrinkage in Y ?   Or
is it more common that both values are the same ?

The question behind this question is whether a pick&place machine that uses
only 2 fiducials can compensate for both dimensional inaccuracy and rotation
of the board in the conveyor. I think this is possible, but only if
dimensional changes in X and Y are equal.

Kind regards

Daan Terstegge
Unclassified mail
Personal website: http://surf.to/smtinfo

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