Hi,

 

I just started playing with some 4 layer boards on an aluminum substrate. 

 

So I started looking at reflow profiles and holy cow do these PCBs bow when
hot. They are 5 inches long and I get a good 200mils + bow when hot. When
they cool back down they are flat again. So I looked up Al at about 22 ppm C
and FR4 about 15 ppm C.

 

I have a 2 inch connector along one side so I would expect 40 mils of bow.
Way too much to form reliable connections.

 

Has anyone got any ideas on how to deal with this? Bolt it down on something
to keep it flat?

 

Bob K.

 

 



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