Kevin, The supplier is right to ask if you have stated you want the laminate at class A tolerance. If you want your 10% for this particular material you should specify class B or C. IPC 4101/B section 1.1.4, and table 3.7 regards Dougal -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Kevin Glidden Sent: 09 January 2009 13:42 To: [log in to unmask] Subject: [TN] PCB thickness tolerance question...Am I losing it? We have a small PCB that is less than 2" x 2" square. Material is IPC-4101/21 FR4 with 2 oz copper. 2 layers. Finish is Tin-Lead HASL. Total thickness is specified as .040" +/- .005", and the supplier is requesting increase to .040" +/- .006". Is it me, or is +/- .006" excessive for a 2 layer .040" thick PCB? I was always taught a "rule of thumb" that the PCB thickness tolerance is +/- 10% of the specified nominal thickness. Is this a bad "rule of thumb"? Even +/- .005" is 12.5%! Is this a sign of a problem with the supplier's process? Thanks! Kevin Glidden Manufacturing Engineer Luminescent Systems Inc. --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/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 847-615-7100 ext.2815 ----------------------------------------------------- Stevenage Circuits Limited. Registered office: Caxton Way, Stevenage, Hertfordshire, SG1 2DF. Registered in England under company number 1059497. The views of the author may not necessarily represent those of Stevenage Circuits Ltd. This message may contain information and/or data that is confidential and legally privileged. It is intended solely for the addressee(s) only. If you are not the intended recipient you are notified that any use, publication, reproduction or dissemination is strictly prohibited. In such an event, please contact the sender by return e-mail and destroy this and all copies of this message and/or data. Please be aware that the integrity of this email cannot be guaranteed, as it is not a safe and secure medium for communication. --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/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 847-615-7100 ext.2815 -----------------------------------------------------