Mouse bites can be described as a semi-circular nick or "bite" at the edge of
a circuit trace.  They can be found on both resist traces and plated traces,
even on pads and fingers.

In a print and etch process, mouse bites are generally caused by debris
laminated under the photoresist.  Residual pumice on the panel is a common
contributor.

The dirt under the resist creates a small air pocket.  If a circuit feature
fall over this pocket, the result after develop/etch can be a mouse bite.
 Similarly, deep scratches in the copper can be a cause.   Anything that
causes poor resist adhesion in localized spots can cause mouse bites.

Mouse bites can be imaged into the panel (dirt on the artwork or exposure
frame) however these are usually "repeaters" and are easy to trace.  A dent
in a lamination roll may also cause the problem -  again, if any pattern is
seen, this is a possible cause.

Mouse bites in Pattern Plate processes are most commonly caused by micro
bubbles in the acid plating tank.  Much has been written about this subject,
and your copper or resist vendor should be able to help with the problem.

Please contact me if I can be of further help.

Mark Dowding
Technical Service Manager
INSULECTRO
909-943-5758

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