High density interconnects and flexible hybrid assemblies for active biomedical implants

Advanced microtechnologies offer new opportunities for the development of a ctive implants that go beyond the design of pacemakers and cochlea implants . Examples of future implants include neural and muscular stimulators, impl antable drug delivery systems, intracorporal monitoring devices and body fl uid control systems. The active microimplants demand a high degree of devic e miniaturization without compromising on design flexibility and biocompati bility requirements. In need for integrating various microcomponents for a complex retina stimul ator device, we have developed a novel technique for microassembly and high -density interconnects employing flexible, ultra-thin polymer based substra tes. Pads for interconnections, conductive lines, and microelectrodes were embedded into the polyimide substrate as thin films. Photolithography and s puttering has been employed to pattern the microstructures. The novel "Micr oFlex interconnection (MFI)" technology was developed to achieve chip size package (CSP) dimensions without the requirement of using bumped flip chips (FC). The MFI is based on a rivet like approach that yields an electric an d mechanic contact between the pads on the flexible polyimide substrate and the bare chips or electronic components. Center to center bond pad distanc es smaller 100 mum were accomplished. The ultra thin substrates and the MFI technology was proved to be biocompat ible. Electrical and mechanical tests confirmed that interconnects and asse mbly of bare chips are reliable and durable. Based on our experience with t he retina stimulator implant, we defined design rules regarding the flexibl e substrate, the bond pads, and the embedded conductive tracks. It is concl uded that the MFI opens new venues for a novel generation of active implant s with advanced sensing, actuation, and signal processing properties.