The problem is that the unpopulated boards meet the requirements -- they do not warp until the assembly process -- this does not violate the (6012) bare-board or the (4101) raw material acceptability specs...I suspect that the root-cause lays in the lamination, however there are many other factors that can influence of course -- but spec-wise, the bare-boards pass...Ian -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Lee Parker Sent: Thursday, July 12, 2007 2:27 PM To: [log in to unmask] Subject: Re: [TN] PCB Fab Question Regarding Bow and Twist Leland I would first characterize the boards using the parameters in the 620 document. If the boards are out of spec, I would inquire as to why these defective boards are being shipped. The cause is often best left to the manufacture (you would probably have to do an in-plant audit to begin to identify the root cause). The first place I would look is at the raw material; does it meet your specification. Best regards Lee J. L. Parker Ph.D. JLP Consultants LLC (804) 779 3389 -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Leland Woodall Sent: Thursday, July 12, 2007 12:03 PM To: [log in to unmask] Subject: [TN] PCB Fab Question Regarding Bow and Twist Everyone, I have a product that ran for almost a year with little or no problem. Recently we've started seeing unsoldered pins on a 256 pin QFP, and found the cause to be excessive twist in the board. We have verified that no changes have been made to our process. Reflow temps, cooling rates, conveyor speeds, rail parallelism, and transfers are all good. We've checked incoming raw material and found only slight deflection in a few specimens. A couple of examples: Incoming: 0.13 MM B reflow: 0.66 MM A reflow 1.98 MM We've identified assemblies that have excessive twist after each of the reflow operations, and our once good product is becoming an expensive stepchild. We cannot mount twisted boards into cases because of too much strain, and are forced to scrap this material. What in the PCB manufacturing process might have changed that would cause this scenario? Thanks in advance for your input. Leland --------------------------------------------------- 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 ----------------------------------------------------- RE: --------------------------------------------------- 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 ----------------------------------------------------- --------------------------------------------------- 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 -----------------------------------------------------