This paper describes a method to design mmW PAs, by modeling the electromagnetic behavior of all the passive structures and the layout interconnections using a 3D-EM solver. It allows the optimization of the quality factor of capacitors (Q-factors > 20 can be obtained at 80GHz), the access points and arrangement of the power transistor cells. The method is applied to the design and optimization of an E-Band PA implemented in a 55nm SiGe BiCMOS technology. The PA presents a maximum power gain of 21.7dB at 74GHz, with a 3-dB bandwidth covering from 72.6 to 75.6GHz. The maximum output P1dB is 13.8dBm at 75GHz and the peak PAE is 14.1%.