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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