Agree. You beat me to make the point. Or you can check the layout and go beat the layout guy before repair it if the signature on the dwg are clear enough. Some time, you will find some surprise: the layout was used for different materials. -------------------------- Sent using BlackBerry ----- Original Message ----- From: TechNet <[log in to unmask]> To: [log in to unmask] <[log in to unmask]> Sent: Mon Feb 01 15:03:01 2010 Subject: Re: [TN] IPC-7721 LESSONS LEARNED Steve, From an outsiders [microelectronics oriented] point of view it would seem that the layer to layer copper coverage variance would have the most to do with warpage. Like you say, you could force it flat for P&P, but the sucker is most certain to warp again during reflow. I bet that is when you beat on the layout guys! Glad you are feeling a bit better! Steve C -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory Sent: Monday, February 01, 2010 2:50 PM To: [log in to unmask] Subject: Re: [TN] IPC-7721 LESSONS LEARNED Lee, In my experience of straightening warped/twisted bare board, I've done it by putting solder bars on top of the board and then baking them like the -7721 says, then cooling them with the bars remaining on top. The board will be flat for printing and pick and place, but it's been my experience that most of the time the board will re-warp during reflow. Steve -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Lee Whiteman Sent: Monday, February 01, 2010 2:20 PM To: [log in to unmask] Subject: Re: [TN] IPC-7721 LESSONS LEARNED No - These are bare unpopulated boards. Lee Whiteman, PMP Senior Member Engineering Staff L-3 Communications East Telephone: (856) 338-3508 FAX: (856) 338-2906 E-Mail: [log in to unmask] -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Paul Edwards Sent: Monday, February 01, 2010 2:19 PM To: [log in to unmask] Subject: Re: [TN] IPC-7721 LESSONS LEARNED Lee, Are these populated PCBs? Paul Paul Edwards Surface Art Engineering -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Lee Whiteman Sent: Monday, February 01, 2010 7:07 AM To: [log in to unmask] Subject: [TN] IPC-7721 LESSONS LEARNED We got some boards that are warped (bent & twisted that exceeded the flatness requirements per the J-STD-001). IPC-7721 has a repair procedure for warped boards. I'm getting a copy of IPC-7721 so I can familiarize myself with the process. In the meantime, does anyone have any "lessons learned" from using this procedure? THANKS. 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