Question on annular ring and hole breakout.  Why does IPC 276 permit 
     breakout on outers on multilayers with PTHs?  I can understand 
     allowing it on inners, but not outers.  Breakout on outers means that 
     the pad associated with the hole does not cover all of the plated 
     through hole.  In outer layer processing the image of that pad 
     protects the hole copper during etch. If resist or resist plating does 
     not cover the holes during outer layer etch, won't the hole partially 
     etch out.  I can understand inners, but not outers.  Is the spec too 
     loose in this area?  I have seen boards with outer layer breakout with 
     partially etched out holes.
     
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______________________________ Reply Separator _________________________________
Subject: Re: registration equipt 
Author:  [log in to unmask] at Dell_UNIX
Date:    4/25/96 12:14 AM


Paul Waldner (Multiline Technology), 
     
Glad to hear from you again, Paul .  Yes your equipment makes it more 
possible to prevent breakouts.  In fact we could not get even close without 
some of it; however, we have designers pushing the 18 mil hole in the 25 mil 
land for the 10 layer multilayer and people trying to build them on the 18 x 
24 and the 24x 36 panel.and with a 1 or 2 mil annular ring.  Good luck even 
with the best equipment.  Realistically, many people are building to the the 
IPC-RB-276 class 2 specification which allows 90 degree breakout.  There has 
not been any problem that I am aware of except that the misregistration may 
cause shorting to a nearby trace.
     
Phil Hinton 
Hinton PWB Engineering 
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