Peter, Comumn is an old hi reliability, Class III term, synonomous with column when wrong key depressed while typing, eating, drinking (probably this one mostly as Bud), and reading at same time. Wasn't it 275, can't find my copy now, that had the famous three comumns as preferred, standard, and reduced producibility. Anyway, I still use the three as guidlines today but having evolved from reduced to preferred over the very long time I've been designing and building these type boards. At any rate 5:1 works fine. I still stick with my previous views concerning non-functional pad removal as being totally acceptable. My previous comments brought up the old requirements for two plies of prepreg per dielectric thickness minimum meaning resin rich material was always present in high layer count (over 8) MLB's. Because it was so rich, it "pushed" and "pulled" its way into and out of hole walls effecting separation and such. Now, in the single ply world, this is not as much a factor or concern, as the resin to glass ratios are nearly balanced so much less movement is apparent. Also, I belive 2221 talks to Class III plating thickness requirements as 25 um minimum. What is that table? MoonMan --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site http://www.ipc.org/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------