Niobium flex cable for low temperature high density interconnects

This work describes the fabrication and characterization of a Niobium on polyimide flex cable suitable for sub-Kelvin temperatures. The processing used can be extended to high density interconnects and allows for direct integration with printed circuit boards. Several key parameters such as RRR, Tc, current carrying capability at 4 K and thermal conductivity in the range from 0.15 to 10 K have been measured. The average Tc was found to be 8.9 K, with a minimum of 8.3 K. Several samples allowed for more than 50 mA current at 4 K while remaining in the superconducting state. The thermal conductivity for this flex design is dominated by the polyimide, in our case Pyralin PI-2611,2 and is in good agreement with published thermal conductivity data for a polyimide called Upilex R.3

► We fabricated a highly miniaturized Niobium on Polyimide flex cable suitable of operation at mK level.
► We demonstrated a modified reflow process to solder these flex cables directly to PCB’s.
► We measured the current carrying capability of the Niobium on Polyimide flex cable.
► We measured the thermal coductivity of the Niobium on Polyimide flex cable in the region of 150 mK to 9 K.