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Date: | Fri, 29 Mar 96 13:22:00 EST |
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I few years ago I had good results with reheating/cooling assembled
warped boards. If the board was held (fixtured) in the correct position and
heated just long enough so that the core temp is 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.
You mentioned using weight with poor results. It would seem difficult
to evenly distribute weight an assembled board. Also, assuming the weight
only contacted parts of the board, the cooling rate would not be equal
becuase of the differences in thermal mass.
The fixture I used was made from 1/2 bar stock. The board was clamped
onto the frame and extra short pieces were added as needed to pull the
center area flat. The bar stock kept the board flat and allowed air
circulation around both sides.
Being assembled, check the high temp rating on the components. Either
remove the ones that will melt or run at a lower temp. If your temp. is too
low, the stresses within the laminate will not be fully relieved.
Norm Dill
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From: TechNet-request
To: TechNet Forum
Subject: Don't want to scrap it.
Date: Wednesday, March 27, 1996 12:06PM
Greetings,
Does anyone have a good procedure for removing a warp/twist from a pcb? I
am dealing with a .093 thick assembly that is 7 inches by 20 inches. The
board currenly has smt components placed and soldered (topside only) but,
the through hole components have not yet been mounted/soldered. I have
tried heating the board and letting it cool while applying weight, that did
not do the job. Any suggestions ? please respond.
Thanks,
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