Steve,

One factor can be ground planes or large areas of foil in or on the boards.
This is one of the reasons that many people now use a mesh style ground
plane... unless you are purposely trying to create a huge capacitor.

Are you running the same "recipe" as the last time the board was run?

And yes, it could be something to do with the construction of the FR4.

Regards,

Phil Nutting
Manufacturing Engineer
Kaiser Systems, Inc.

-----Original Message-----
From: Stephen R. Gregory [mailto:[log in to unmask]]
Sent: Thursday, March 23, 2000 12:42 PM
To: [log in to unmask]
Subject: [TN] Warped Boards...


Hi ya'll!

I've been wave soldering an assembly today and they've warped on me...not
coming off the wave, but as they cool down.

They come off the wave nice and flat, but curl up along all three edges
except for the one edge where there's a right angle connector along the
length of the edge and secured in with three screws. I'd bet if the
connector
wasn't there, that edge would curl too. I use a titanium stiffener on the
back edge of the board when waving it, and tried to see if I left it on
while
it was cooling might prevent the curling..but it still curls.
The board thickness by the way is .062" and about 10" X 12"

I've been told that when these boards were built in the past, and they're
pretty sure they didn't have this problem...

What could cause this? I know how the layers are stacked makes a difference.
But if I'm to believe that this problem wasn't there the last time the
boards
were built, the layer stack-up shouldn't be an issue.

Could it be something the way the weave of fiber cloth in the different
layers are oriented to each other?

Trying to figure this out...

-Steve Gregory-

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