A three-dimensionally interconnected metal-spring network in a silicone matrix as a resilient and electrically conducting composite material

Isotropic, highly resilient and electrically conducting composites in the form of a copper-spring three-dimensional network embedded in a silicone matrix were developed for use as electrical and thermal contact materials. The springs were made from 63 μm diameter copper wires and were coated and interconnected by Sn-Pb solder. The springs used were long coils, intersecting and interconnected to one another to form a three-dimensional network. Composites were fabricated by infiltration of a silicone resin into a preform of springs. A volume resistivity of 5 × 10^-4 Ω cm, a contact resistivity with copper of 0.016 Ω cm² at ≥ 0.03 MPa, and a permanent set of 0.6% after compresssion at 0.4 MPa were achieved in a silicone-matrix composite containing 3.1 volume% Cu springs and 2.9 volume% solder (i.e., 6.00 volume% total filler); the volume resistivity was not affected by heating in air at 130-150°C for 7 days, nor by immersion in water for 7 days. The volume resistivity values of composites containing from 4.17 to 6.00 volume% total filler were equal to three times the corresponding calculated values for composites containing unidirectional and continuous fibres, indicating that the filler was indeed a continuous three-dimensional network.