Jack- We would drill the vias at 13.5 for a 25.0 mil pad, not 18.0. I really don't like to see the drilled hole to non-common conductor go below 9.0 mils, prefer 10.0 min. There is a cost associated with reducing the drill size below 13.5, tool costs and drill time increase due to reduced stack heights. At 10:18 4/26/2000 -0700, you wrote: >Sorry for the cross-post, but I couldn't decide if this was more of a >fabrication issue or a design issue. > >We typically remove unused pads from inner layers. (please don't change the >subject to warn me against removing inner-layer pads, that's not the issue I >need help with right now) >I am being asked to use the extra routing space that has been freed up by >the pads being removed. I have heard of this before but never tried it, and >frankly I'm a little worried about it. > >Somewhere I heard that the gap between traces to the drilled hole should be >something like 11-15mils, but that hardly makes sense from what we are >already doing. A 13mil via hole in a 25mil pad is probably drilled with an >18mil drill bit, right? If we were already using a 4mil clearance to the >25mil pads, then removing the pad still only leaves 7mils to the edge of the >drilled hole right? (sorry for all the numbers in one sentence) > >So how much extra routing space is there? I say virtually none. I can't >remember where I heard that drill to route should be 11-15mils, has that >become tighter these days? > >Anyway, that brings up another question. Maybe we can use smaller pads on >inner layers? That's yet another thing I've never tried.... Is there a rule >of thumb for that or am I just asking for trouble? > >Any responses will be greatly appreciated > >Jack > >############################################################## >TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c >############################################################## >To subscribe/unsubscribe, send a message to [log in to unmask] with following text in >the body: >To subscribe: SUBSCRIBE TECHNET <your full name> >To unsubscribe: SIGNOFF TECHNET >############################################################## >Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional >information. >If you need assistance - contact Keach Sasamori at [log in to unmask] or >847-509-9700 ext.5315 >############################################################## > Ian A. McMillan Engineer Herco Technology Ph# 858-679-2800 ext. 107 Fax# 858-679-7565 ############################################################## TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c ############################################################## To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TECHNET <your full name> To unsubscribe: SIGNOFF TECHNET ############################################################## Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information. If you need assistance - contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ##############################################################