mmW characterization of wafer level passivation for 3D silicon interposer

The fabrication of a smart interposer for millimeter wave applications is described in this article. The process flow and fabrication steps are presented. A special focus is made on the electrical characterization of a specific backend routing lines and the wafer level molding material laminated on the interposer. RF properties up to 67 GHz are reported: the backend routing CPW lines exhibit an attenuation loss of 0.5 dB/mm at 60 GHz while the addition of 200 μm molding layer is adding an extra 0.1 dB/mm loss. The relative effective permittivity on the CPW is evaluated at 3.5 and 4.7 without and with molding respectively. The relative and intrinsic dielectric permittivity of the 200 μm molding compound is evaluated at 3.9 and is relatively stable up to 67 GHz. This paves the way to further developments on silicon for mmW applications.