Three-beams spring interconnects for long-term high density flexible electrode arrays

This work reports on the development and characterization of novel spring interconnects on polyimide electrodes array that overcome mechanical reliability issues of flexible substrates in implant assembly. The spring is composed of three arcuate beams, which start from a central junction and end on outer annulus boundary metal. The dimensions of the spring beams (each about 25 μm wide) and the central junction (about 25 μm in diameter) allow for Microflex bonding overcoming larger vertical distances provided by thicker inter-contact insulating gasket. These interconnections reduce the buckling and warpage of the flexible arrays by mechanically decoupling of the bulk material and the substrate. The method allows reliable gasket-underfilling, a crucial element for long-term electrical integrity of the individual electrical connections. This novel interconnect technology proved suitability for long-term applications according to MIL STD 883 testing. No open-circuits but very minor changes in contact resistance of spring-pads were observed during 300 hours storage at 300 °C temperature (from 0.557 Ω to 0.542 Ω) as well as after vibration tests for 144 hours (from 0.868 Ω to 0.865 Ω).