Hi Paul, How could I practically do? Vladimir SENTEC Testing Laboratory Inc. 11 Canadian Road, Unit 7. Scarborough, ON M1R 5G1 Tel: (416) 899-1882 Fax: (905) 882-8812 www.sentec.ca -----Original Message----- From: Paul Reid <[log in to unmask]> Sender: TechNet <[log in to unmask]> Date: Thu, 29 Sep 2011 13:41:27 To: <[log in to unmask]> Reply-To: TechNet E-Mail Forum <[log in to unmask]>, Paul Reid <[log in to unmask]> Subject: Re: [TN] Board question Hi Vladimir, Some times the warp and weft of the material is coming into play. The warp is the direction of the weave that the glass fibres were in tension; the weft is the direction in which the glass fibres where under less tension, where more compliant to go around the glass had tight as with the warp. Placing the warp in one direction can cause the boards to bow and twist. I would check out the weft direction of each layer from each layer. Best regards, Paul Reid Program Coordinator PWB Inc, Work 613 596 4244, ext 229 Home 613 839 7794 _____ From: TechNet on behalf of Vladimir Igoshev. PhD Sent: Thu 29/09/2011 12:49 PM To: [log in to unmask] Subject: [TN] Board question Hi TechNetters, I have a question for board gurus, as I'm almost lost. Here is a story. A panel of four simple 4 layers FR4 twists after going through the first side re-flow and flatten out after the second side is re-flowed. It does the same thing with and without the components placed. The panels are from new vendor and the old ones had never exhibited the problem. What confused me is that both boards (from both of the vendors) were built identically: dielectric layers and Cu layers are look identical thickness- wise. There are no signs of resin recession or delamination in cross-sections which could have pointed out at incomplete curing. Glass bundles look also identical. What else it could be? Any suggestions are deeply appreciated. -- Best regards, Vladimir Igoshev. PhD mailto:[log in to unmask] SENTEC Testing Laboratory Inc. 11 Canadian Road, Unit 7. Scarborough, ON M1R 5G1 Tel: (416) 899-1882 Fax: (905) 882-8812 www.sentec.ca ______________________________________________________________________ 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 16.0 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 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 16.0 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 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 16.0 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 For additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------