Thought I would offer my two cents worth on this issue. 1) When I order PCBs I expect them to match the data I send out to within the acceptable tolerance generally less than 20%, less than 10% variance preferred. 2) All final inspection is made to 1:1 originals generated from the unadjusted gerber files. 3) I do allow the fab. house to manipulate the data for process, knowing that they will adjust for etch, shrink, etc. I also only use any Fab. artwork for reference. -----Original Message----- From: Neel, Robert [mailto:[log in to unmask]] Sent: Thursday, February 15, 2001 2:18 PM To: [log in to unmask] Subject: [TN] design vs reality? Hi People, I've had technet streaming into my terminal for a couple of weeks now and thoroughly appreciate the background flow of information. I have a question for any interested participant: What causes a finished circuit board pattern/trace to deviate from the photoplot? I'm looking at the photoplot file of a critical section of a circuit board I'm trying to field. The plot file shows a pad-to-ground clearance of 20 mils. And yet when I slap a finished board under the scope, the pad-to-ground clearance measures 15-mils from one supplier and 10-mils from another. (The component center-to-center patterns are correct, so it's not a matter of scaling.) What gives? The assembly people are pounding on me to open-up the clearance, but, for the application constraints, and, by the book, the design clearances are fine. Is this correct? Will the finished PCB deviate so wildly from my plots? How much deviation can I expect? How much compliance can I demand? What's a reasonable difference between the photoplot file content and the finished board? (If you want to make my day, tell me they should match exactly. Then tell me why they might not match and by how much.) Thanks in advance. Robert ---------------------------------------------------------------------------- ----- 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 the following message: SET Technet NOMAIL 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 ---------------------------------------------------------------------------- ----- --------------------------------------------------------------------------------- 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 the following message: SET Technet NOMAIL 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 ---------------------------------------------------------------------------------