I've never said warpage, but twisting :-) 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: Joyce Koo <[log in to unmask]> Sender: TechNet <[log in to unmask]> Date: Thu, 29 Sep 2011 14:16:51 To: <[log in to unmask]> Reply-To: TechNet E-Mail Forum <[log in to unmask]>, Joyce Koo <[log in to unmask]> Subject: Re: [TN] Board question http://npil.kaist.ac.kr/pdf/foreign_journal/FJ_76.pdf -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of vladimir Igoshev Sent: Thursday, September 29, 2011 2:02 PM To: [log in to unmask] Subject: Re: [TN] Board question Hi Dave, I just measured it from the sections and they were pretty much identical and well balanced! 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: "David D. Hillman" <[log in to unmask]> Sender: TechNet <[log in to unmask]> Date: Thu, 29 Sep 2011 12:53:49 To: <[log in to unmask]> Reply-To: TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask] Subject: Re: [TN] Board question Hi Vlad - one other thing to check - is the pwb stack up "balanced"? Are all of the layers (both the dielectric and the copper) symmetrical with respect to the board thickness midpoint? Are you sure all of the thicknesses are equal? Dave Hillman Rockwell Collins [log in to unmask] "Vladimir Igoshev. PhD" <[log in to unmask]> Sent by: TechNet <[log in to unmask]> 09/29/2011 11:49 AM Please respond to TechNet E-Mail Forum <[log in to unmask]>; Please respond to "Vladimir Igoshev. PhD" <[log in to unmask]> To <[log in to unmask]> cc 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. 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