Stiffness of PCB

[izax1]

I tried this in the materials forum, but since this is related to calculating natural frequencies I hope to get better responses here.

What is the Youngs modulus of a PCB (Printed Circuit Board). I have always assumed the the PCB is made from several layers 0/90 oriented layers of Continious Glass Fibre Plastic, and that no layers are oriented in 45 deg or any other directions. I need this to verify natural frequency of the PCB.

Thanks in advance

 

[Twoballcane]

Can you take a PCB and do a sine sweep to flush out Fn? Then from there you may calc backwards to E. But, in any case, I typically take G10's E and slightly thinner thickness than actual PCB for inertia. It will get you close to an Fn. Once you get the Fn, what will you do with it?

Tobalcane
"If you avoid failure, you also avoid success."

 

[izax1]

Thanks Twoballcane. Yes, I could do a sine sweep and find Fn, but I need this information to tune the FEM model to fit with the measured first two or three frequencies. If my material model in the FEM is not correct (twisting stiffness) then my whole idea of tuning will be complicated. It is alreday complicated enough even if my material model is correct.

 

[Twoballcane]

If you are trying to correlate the model to the data, you will have to "adjust" the E and also the constraints till you match data. You don't have to find specific material E, but adjust it till you get the right "stiffness". Once you get your model to "move" just like the real thing, you can move on to the next iteration of the design. You have to remember that FEM is math and code trying to predict dynamic modes, where the data is the real thing. Also, you can adjust your constraints to either free rotation for lowering the frequency or no rotation for raising the frequency.

Tobalcane
"If you avoid failure, you also avoid success."