RF Characteristics of Through-Hole Interconnections Filled with Au-Sn Solder

Silicon through-hole interconnections filled with Au-Sn solder by Molten Metal Suction Method (MMSM) have been developed. They are expected to realize wafer-level package of various devices such as Micro Electro-Mechanical Systems (MEMS), RF devices and some sensors. In this paper, RF characteristics of the through-hole interconnections were examined. Co-planar type circuits including one signal line and two grand lines were used for the measurement. Each line has two through-hole interconnections connected electrically by Cu wiring. The diameter of the through-holes was 80 μm and the thickness of the substrate was 200 μm, respectively. S-parameter S₂₁ was measured from 0.1 GHz to 8 GHz. The thickness of SiO₂ insulation and the resistivity of the Si substrate were especially focused on. Transmission loss of 1.2 μm SiO₂ sample at 1 GHz was 0.86 dB and that of 0.1 μm SiO₂ sample was 3.7 dB, respectively. On the other hand, the transmission loss of 10 Ωcm sample at 1 GHz was 0.86 dB and that of 1000 Ωcm sample was 0.01 dB, respectively. From these results, it was appeared that RF transmission performance of the Si through-hole interconnections becomes superior as the thickness of SiO₂ was thicker and as the resistivity of the Si substrate becomes higher.