I should probably also say that the supplier was not able to reproduce the problem. They have a better temperature control in the cooling zone, compared to the ovens used over here by the customer. 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 Edwards <[log in to unmask]> Date: Thu, 29 Sep 2011 11:35:25 To: [log in to unmask]<[log in to unmask]>; [log in to unmask]<[log in to unmask]> Subject: RE: [TN] Board question When the PCB is run through the oven is it on rails or on the belt? The second question is, how long in the PCB about Tg? The third question is, is the thermal profile at the PCB surface the same for both sides? Paul Paul Edwards Process/Quality Engineering Surface Art Engineering -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of vladimir Igoshev Sent: Thursday, September 29, 2011 11:30 AM To: [log in to unmask] Subject: Re: [TN] Board question Thank you Phil, There was virtually no time difference between runs of the two different boards. I have to check the tabs, though. I'm holding off for the thermal analysis, as (as I said) it doesn't make much sense to me just now. Why would a board go back to normal if the laminate was undercured prior to the first run? 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: Phil Bavaro <[log in to unmask]> Sender: TechNet <[log in to unmask]> Date: Thu, 29 Sep 2011 11:03:23 To: <[log in to unmask]> Reply-To: TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask] Subject: Re: [TN] Board question Does it violate the spec for twist after the first reflow? Does it matter which side is run first? Internal layer thieving can cause this. Typically every supplier does their thieving differently. Does the panel have outside rails? Ask the supplier for their fab gerber used to actually make the panel. Usually since rails get discarded throw away piece, the board suppliers take liberties and modify the rail conductor fill to optimize their plating processes. You may see the outside conductors as identical but I have always noticed the thieving in panel rails vary between suppliers since it is not defined as part of the original pwb gerber. I am also not sure that you ran the two different supplier panels side by side through the oven at the same time but such a check would be good to do if it has been a long time since the "good" supplier boards have been run. Joyce also has the right idea....sometimes Tg is different if it is not a hard call out. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman Sent: Thursday, September 29, 2011 10:54 AM To: [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. 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