Thanks for your helpful and patient reply
some other question still need your advice,
1. if I turn on the large deflection there will have nonlinear solution, if I turn it off, does it means that it is linear case?
besides, what is the meaning of turning on the nonlinear effect and thermal strain effect?
2. as you mentioned that even though I do not apply the nonlinear materials but with only linear isotropic material properties, I could still get the nonlinear vibration effect with only geometrical nonlinearity. is the reason that the geometrical had already included the nonlinear stress-strain relationship like the COMSOL example you sent it to me a few days ago which told me that the geometrical nonlinearity will also cause the stress-stiffening?
3. you are right, the IC chips are mounted on the opposite side of the PC board, therefore, my 2D model with assigned thickness could handle PC board with only one chip not both, that is why I could not make it perfect. besides when I was doing the mesh within the ANSYS, it shows me two IC chips, does it means that I will have 2 IC chips with the same material properties?
As I marked in the green color, There are only two surfaces that could be given the thickness, therefore it should have the PC board and only one chip, but from the view of mesh, it is 3 bodies(PC board and 2 IC chips). Do you know why?