We had some boards with a warpage problem.  MFRing made up some fancy board 
carriers that held the boards flat during the process.  Also, they may have 
tweaked the process (temperature profiles etc.).  I don't know which (if it 
was either of these) fix actually solved the problem.



At 12:00 AM 2002-04-04 -0800, you wrote:

>A number of different ways to even out copper coverage on layers on
>opposing sides of board were mentioned, and these are probably aimed
>at solving residual stresses left in the board.  That sounds good, but may
>be difficult to accomplish, dpending on board density, etc.
>
>One thing that comes to mind is that the boards come out of the laminating
>press flat, go through all the additional steps in PCB fabrication OK, but
>then warp when YOU process them to attach components.  Are you sure
>you have to heat the boards as hot, for as long as you are doing, to get
>good soldering?  That may have something to do with it.
>
>Finally, could you give the boards some mechanical support during the reflow
>soldering?  Making some simple metal frames that hold the board edges
>during the entire time it is heated might keep them flat as they cool.
>
>Jon
>



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