Saul,
What we have done may not be suitable for you. Anyway, I will still tell you my
method.
I think of crazy idea sometimes..Please note this is not proper way of
handling the board, but it is a quick-fix for us. (May not work for your
board). 
We place the board on top of the wave-solder preheater (we are using pallet
machine). Once the board has reached about 130 deg. cel, bring the board,
and place on 2 toothpicks. Then use 2 long bars, (weighs about 500 to 750
gram) and place near along the side of the board. 

See detail below ...

  t - refers to small toothpick that place at the center of the board.
  xxxxxxx - refers to the bar that place along the side of the board. In
this way, it 
                   presses the board sideway downwards.

             x                            x
         ----x--------------t-------------x----
         |   x                            x   |
         |   x                            x   |     
         |   x                            x   |
         |   x                            x   |
         |   x                            x   |
         ----x--------------t-------------x----
             x                            x

Note: Be careful not to damage the components. In this process, it requires
very 
careful way of handling...And try to place where there is no or little
component.

If you still don't understand what I talking or drawing, I could fax your a
drawing...

How to "minimise" it, is possible, you can start making pallet that your
board fix and sit well on it, and make sure you don't take out the board
after wave. Let it cool down, at least to room temperature before you take
it out from the pallet. By the way, the pallet should have a gripper as to
hold the board well during cooldown.

How to eliminate, talk to the board designer (may be you have a better
luck). So far, for us, there is no possibility to get rid of it. We are
getting all kinds of boards.

Anyway, good luck. ... In case you have an idea how to eliminate, please do
let me know.

Poh Kong Hui
Nera Electronics

----------------------------------------------------------------------------
------------------------------------------------------------

At 12:28 5/17/96 EDT, you wrote:
>Can anyone give me some suggestions on returning a board to flat after it has
>gone over the wave?
>
>I have a new customer who has been using someone else to solder his boards and
>is experiencing warpage after it has been wave soldered.  The board measures 16
>cm x 23.5 cm with two (2) 96-pin connectors (.100" spacing) along the 23.5 cm
>side of the board.  He said the other shop's solder pot is about 480
degrees and
>it is assumed they are running the board with the short side in the grippers so
>as to avoid hand-soldering the 96-pin connectors since they hang off the
egde of
>the board.
>
>Some additional data:
>I.C. orientation: 33 run east-west, 11 run north-south, 1 PLL.  There is one
>20-mil pitch SMT QFP device on the board.  The QFP is the only SMT device
on the
>board.
>
>Any ideas on how to avoid the warpage in the first place and when you do have
>it, how to eliminate it?
>
>Thanks to all who may contribute.
>
>