It's to do with the plating of the barrel in a multilayer board. When the hole is drilled, the external surfaces have complete copper coverage and so the annular ring isn't evident until after imaging and etching. Hence you can add the thickness of the plating to the pad size for an annular ring requirement. On the inner layers, imaging and etching have already been completed so when the hole is drilled, it needs to 'see' enough copper around the hole so that the plating of the barrel makes good contact to the innerlayer pad. That hole size is the drilled hole, but the final hole size is the one specified by the designer and relies on an oversize drilled hole to be plated up. So the annular ring is specified 'worst case', which is before plating. Andy K. Sychip Inc Office (972) 202 8852 -----Original Message----- From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Stan Radzio Sent: Wednesday, December 10, 2003 10:34 AM To: [log in to unmask] Subject: Re: [DC] Manufacture adjusting Gerber's Gary, I was following you right up to the point where you said "for inner layers". I don't mind looking like an idiot asking questions that are obvious to everyone else. Could you explain why you are using the drill hole size versus the finished hole size on inner versus outer layers? Said another way: what is the manufacturing process that you are accommodating with this design decision? Thanks, -Stan -----Original Message----- From: Gary Ferrari [mailto:[log in to unmask]] Sent: Tuesday, December 09, 2003 5:12 PM To: [log in to unmask] Subject: Re: [DC] Manufacture adjusting Gerber's Ted, The board fabricator always drills with a larger drill bit to compensate for shrinkage of the laminate. This is why the designer uses the drilled hole size when calculating lands for inner layers. The finished hole size is used for calculating outer layer land sizes. The board fabricator is not requred to automatically adjust inappropriate spacing. They usually will contact the designer and explain the problem. That is, if you use a decent board fabricator. Regards, Gary ------------------------------------------------------------------------ --------- DesignerCouncil 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 DesignerCouncil. To set a vacation stop for delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ------------------------------------------------------------------------ --------- ------------------------------------------------------------------------ --------- DesignerCouncil 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 DesignerCouncil. To set a vacation stop for delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ------------------------------------------------------------------------ --------- --------------------------------------------------------------------------------- DesignerCouncil 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 DesignerCouncil. To set a vacation stop for delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------