Sub-THz flexible interconnection technology based on polyimide transmission lines

We present a novel flexible interconnection technology for sub-THz packaging applications. The interconnect consists of a 50 Ω-transmission line, fabricated on polyimide substrate with a single Au conductor layer. It also provides an under-bump-metallization (UBM) to enable flip-chip bonding. A transmission loss of less than 1.7 dB/mm and a reflection coefficient lower than -17 dB at 220 GHz have been achieved using a coplanar waveguide structure. The dielectric constant and the loss tangent were measured both for the W- and D-band up to 170 GHz, using the Fabry-Perot resonator technique. The measured relative dielectric constant and the loss tangent are 3.54-3.61 and 0.004 - 0.005, respectively.