Rick Apart from the obvious causes of shorts, fine shorts which are difficult to see can be caused by over etching. This leaves overhanging copper which then breaks away during subsequent brushing prior to solder mask application. These slivers of copper are almost imposible to detect after solder mask without a current tracer. Pumice cleaning will only cause this problem in extreme cases of over etching and is therefore more reliable. Inner layer shorts are more commonly due to photo tooling or registration errors unless they are plated and etched (buried vias) in which case the above could apply. Good luck -- Paul Gould Teknacron Circuits Ltd EMail [log in to unmask]