Thanks for your fast and helpful reply.

1. I do have more than 1 body, in fact I will have 3 bodies in total, one is the PC board, another two will be the IC chips that are mounted on the PC board, that is why I am asking that if I give the 2 surfaces with assigned thickness, when I try to give the material properties, I could assign it to the PC board and only one IC chip not the both, that is the problem that I could not solve, But considering that the two IC chips have almost the same material properties, I think it would not influence that much.

2. I am currently meet some problems on convergence issue, when I was doing the transient structural with my flexible PCB, if I turn on the large deflection, it will have some errors, I do use small time steps, but still have no idea why it will happen. while if I turn the large deflection off, there will be no errors and I am good to get the result, do you have and suggestion? I also attached the solver output file and the workbench file.

3. Sorry about my question about using sine or cosine function, hope it does not bother you. but very grateful for your amazing reply.

4. I have also done some research on nonlinear materials for the PCB, but I feel confused which nonlinear materials should I use in ANSYS, should I use the plasticity-multilinear isotropic Hardening? I think that will be the one that match the best with the model. besides it is not that easy to get some nonlinear materials for the PC board online, is it possible you could give me some help on it?