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1996

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Subject:
FW: warped completed assemblies
From:
"Dill, Norm J" <[log in to unmask]>
Date:
Tue, 27 Aug 96 13:31:00 DST
Content-Type:
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Chet,
    A few years ago I had good results with reheating/cooling warped 
assembled
boards.  These boards were 8 x 10 inches with a warpage ranging from 1% up 
to 6%.  When the board was held (fixtured) flat and heated just long enough 
so that the entire core temp was just short of the Tg of the laminate, it 
worked well.  It was equally important to let it cool very sloowwly so that 
new stresses were not created.
    The fixture I used was made from 1/2 inch bar stock.  The board was 
clamped
onto the frame and extra short pieces were added as needed to push the 
center area flat.   The bar stock kept the board flat and allowed air 
circulation around both sides.
    Also, check the high temp rating on the mounted components.  Either 
remove the ones that will be damaged or run at a lower temp.  If your 
temperature is too low, the stresses within the laminate will not be fully 
relieved.

 ----------
From: [log in to unmask]
To: [log in to unmask]
Subject: warped completed assemblies
Date: Tuesday, August 27, 1996 10:36AM

     1. Does anyone know a way to straighten a completely stuffed board
     without damaging the components?


     2. How much of warp can be reliably corrected?

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