Advances in integrated circuit (IC) and package technologies, such as the increase of the number of metal layers and 3-D stacking technique, have paved the way for faster speed and higher performance in today's electronic products. However, continuing down-scaling in feature size poses crucial issues, such as the parasitic couplings between circuit elements and localized Joule heat dissipation. In this work, we introduce a systematic computational Electromagnetic (CEM)-thermal coupling approach capable of dealing with multiscale problems such as 3-D ICs and subsystems. A non-conformal finite element domain decomposition method is utilized to iterative the electrostatic, full-wave electromagnetic and thermal simulation. Moreover, we included preliminary numerical results demonstrating the effectiveness of the proposed approach.