It sounds like etchant is getting through the via tent. It is probably 
crystals that have built up or guide clips on the DES conveyors that are
piercing the resist. A thorough PM should do the trick.

Jeff Worth
IBM Austin


On Mon, 18 Dec 1995 [log in to unmask] wrote:

> We have experienced a random problem with three or four parts relative to rim
> voids.
> 
> In some cases it was part of the lot and in others it was the whole lot. 
> 
> They have been partial, full, top and or bottom. (no consistency) 
> 
> They are typically one to two mils down from the surface copper and one to
> three mils in height. 
> 
> They are not specific to any hole size. 
> 
> We use Dupont APG715 Dry Film, and develop on a Atotech/Chemcut horizontal
> system using Potassium Carbonate.
> 
> 
> 
> I would appreciate any suggestions, as to the cause.
> 
> 
> 
>