Our friends at Rockwell have a chart in one of their presentations that show CTE of various common laminates up to a typical reflow temp. At room temp CTE of them is about 25ppm /degree C. But, by 150 C things get less predictable. And can be 75 ppm / degree. The thing is you are trying to attach a flex. What is its CTE. The difference between the two? It is important. Part two of your question The Z axis expansion of the woven substrate will be higher than the "x-y" advertized CTE. So, no I would not expect the material to shrink. What happens of the flex expands wildly above 100 C, you might think the substrate shrank . . . Guy -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Eric Christison Sent: Friday, July 02, 2010 11:12 AM To: [log in to unmask] Subject: [TN] Question about FR4 Curing I'm wondering about an issue we have with the dimensional stability of a substrate made of FR4. We're finding it's deforming during a flex attach operation, not by much but enough to cause us a problem. We use ACF and a hot bar. The substrate sees a temperature of 155 deg C for about 10 seconds. Someone suggested that the movement may be due to incomplete curing of the substrate. I'm wondering if a temperature of 150 deg C for 10 seconds is likley to have any effect at all on the matrix. If it did, would the volume of the matrix increase, decrease or stay much the same? I realise that we'll see deformation due the application of pressure as well but in some instances the substrate seems to be moving in the wrong direction. Thanks, -- Eric Christison Consumer& Micro group Imaging Division STMicroelectronics (R&D) Ltd 33 Pinkhill Edinburgh EH12 7BF United Kingdom Tel: +44 (0)131 336 6165 Fax: + 44 (0)131 336 6001 ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ --------------------------------------------------- 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 ----------------------------------------------------- ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ --------------------------------------------------- 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 -----------------------------------------------------