Check your outerlayer resist laminator rolls immediately. 
If they are three months old or more change them out.  The rubber
durometer increases with age and eventually they do not conform to the
panel weave and you will have interfacial voids (tiny air bubbles) at the

low spots in the weave.  Nine times out of six that will fix this
problem.
 
On Sat, 31 Aug 1996 20:51:23 +0500 nss <[log in to unmask]> writes:
>We have been facing dificulty  in processing 4/4 mil,5/5mil ML 
>boards.There
>has been excessive defects particularly seepage shorts in outer layer
>only.This seepage shorts we have further analysed and noticed seeping 
>of
>COPPER and TIN plating. The copper thickness at the seeped location is 
>only
>around 5 microns, indicating that seepage or lifting of photoresist is
>occuring during the end of the plating cycle.
>All these seepages are creating multiple shorts.Our observation is 
>that it
>follows a definite pattern of the glass WEAVE TEXTURE.I am interested 
>to know
>1. any specific construction ie., specific glass styles to be used for 
>fine
>lines.
>2. any specs /ref., for acceptability of outer surface with respect to 
>WEAVE
>TEXTURE.
>3. any change in surface preparation wud improve (we have pumice 
>scrubbing
>in our existing process.)
>4.any checks exists to check photoresist adhesion .We use tape test, 
>is this
>an acceptable test procedure.
>
>Presently we are using vacuum aided computer controlled hydraulic
>electrically heated presses.,press param is 2 cycle ,8'kiss  
>50psi,90'cure
>300psi .
> 
>
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