You will get these marks whenever the mask is under tack-dried. The mask
skin dries ,so when you place the artwork on top and draw down the vacum
,it pushes on the soft -wet ink leaving the marks you describe

On Sat, 21 Feb 1998, Padmanabha Anandapuram Halappa wrote:

>      Fellow Technetters,
>
>
>      Does any one ever came across depression mark on Printed Circuit Board
>      during Solder mask Exposing?How does this marks eppears and how to
>      overcome this problem?
>
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