Characterization of Low-Inductance Microcoaxial Cables for Power Distribution

Low-impedance microcoaxial cables have been developed to supply power to microchips. These uniquely low-inductance cables are enabled by a very thin dielectric compared with a conventional 50-Ω cable. These cables will be used in a novel packaging platform in which traditional interconnects are replaced by microscale coaxial cables. This method saves time and cost for small production volumes and custom electronics, compared with high density interconnects and silicon interposer technologies. These microcoaxial cables are designed to have minimal impedance to meet the stringent power supply requirements of today's electronics. As a concrete example, we consider a Kintex 7 Field-Programmable Gate Array (FPGA). To power this chip with interconnect lengths of 25 mm and a voltage ripple less than 30 mV, a resistance of 3.20–6.40 mΩ/mm and an inductance of 12–15 pH/mm is needed. The tight voltage ripple constraint is what makes this device challenging to design power distribution for. One cable fabricated by Draper, to achieve these power requirements, is the focus of this article. The Draper cable consists of a 127-μm Copper core, 12-μm polyesterimide dielectric layer, and 55-μm gold shield. The measured resistance per unit length at DC, inductance per unit length, capacitance per unit length, and characteristic impedance of the Draper cable are 2.0 mΩ/mm, 40 pH/mm, 118 pF/mm, and 6.56 Ω, respectively.