Bad news for you Daan,

The shrinkage is NOT the same for "X" and "Y". Simply because the weave is
not the same, this means that the resin contained with the weave will also
not be a constant in both direction. The copper on the surface also
influenced changes in the boards. Different materials have different
shrinkage / expansion factors.

Alain "use to do Fabs" Savard, B.Sc.
Chemical Process Analyst
CAE Electronics Ltd.
e-mail: [log in to unmask]

-----Original Message-----
From: d. terstegge [mailto:[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.

Daan Terstegge

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