10-Gbps signal propagation of high-density wiring interposer using photosensitive polyimide for 3D packaging

We have developed a high-density wiring interposer for 10-Gbps signal propagation using a photosensitive polyimide. We optimized the basic properties of the photosensitive polyimide film for the fabrication of the interposer. We experimentally confirmed that the high-density wiring interposer could be fabricated using the optimized polyimide and gold multilayered structure. Fine metal wirings were smoothly covered by the polyimide film, as confirmed by scanning electron microscopy (SEM) of the cross section of the fabricated balanced pair strip-line structure. From the high-resolution differential time domain reflectometry (TDR) measurement, the differential impedance Z_diff of a 12.5-mum-wide 12.4-mm-long balanced-pair strip-line was evaluated to be within 100 Omega plusmn 14.6 %. From the high-resolution differential time domain transmission (TDT) measurement, an insertion loss (S-parameter: S _dd21) of -2.96 dB at 10 GHz through the differential strip-line was evaluated. Finally, we confirmed eye diagram measurement at 10 Gbps through the differential strip-line on the fabricated interposer. The aperture size of the measured eye diagram at 10 Gbps was sufficient for ultrahigh-speed signal propagation