Yes, you are correct. sorry about missing that very important point.
 ----------
From: TechNet-request
To: TechNet-request; TechNet
Subject: Re[2]: ASSY: Post-wave Warpage
Date: Friday, May 17, 1996 14:42

     Whoa.  Before you bake your boards higher than their Tg, you must
     figure out if your components can stand that kind of temperature.  You
     may end up with a board full of melted connectors (generally 85C ~
     105C rated).  Tg may be in the 130C range.

     We have baked BARE boards to relieve warpage, but never a loaded
     board.

     Regards,

     Roger Held
     Hitachi Computer Products (America)


______________________________ Reply Separator
_________________________________
Subject: RE: ASSY: Post-wave Warpage
Author:  [log in to unmask] at Internet-HICAM-OK
Date:    5/17/96 1:43 PM



bake the board flat in an oven.  You must get the board above its glass
transition temperature.  Bake for a least 3 hrs. and allow a slow cool down
with the weight still applied.

Some warpadge occurs from the board design, random placement of holes in the 

board, bad distribution of copper layers or component weight.  If this is
the case a fixture that holds the boards shape may need to be developed for
wave process.

Other warpedge could be a warning sign that somthing in your process has
gone wrong.  To high a temperature, bad fixturing during wave etc....

Good luck
 ----------
From: TechNet-request
To: TechNet
Subject: ASSY: Post-wave Warpage
Date: Friday, May 17, 1996 12:28

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.