To my knowledge there is no default tolerance for board thickness in IPC specifications. The previous post sending you to IPC-T-50 won't help because it defines terms and definitions, but does not contain any specifications. The other post about IPC-4101 applies to bare laminate, but not directly to the finished PCB. IPC-4101 is used by the board fabricators to specify to the raw material suppliers what they want to purchase for laminate, but does not directly apply to the finished PCB. If you have a multilayer PCB, then it won't help you with the tolerance on thickness for prepreg dielectrics, only cores/laminates. The copper thickness specifications only specify minimums, so you won't know the average or the maximum values of those through IPC specifications. So you were correct in turning to IPC-A-600 and IPC-6012 for the finished PCB requirements. Look at Section 3.4 on Printed Board Dimensional Requirements. "All dimensional characteristics such as...thickness...shall be as specified in the procurement documentation." So it must be listed on the fabrication drawing. I hope this helps. --------------------------------------------------- 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 -----------------------------------------------------