ROGER HELD wrote:
> 
>      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.

Just a quick correction:  While I may not be up to speed on the latest materials 
used for multilayers, the Tg for double sided materials starts at 130C and can go 
to 150C for materials sold as "FR-4" depending on the laminate supplier.

> 
>      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.
> 

Don Vischulis
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