Implantable micromachined electrode arrays, in the short term, are highly valuable research tools, and in the long run will have a great impact on rehabilitation of patients with various disabilities. In a chronic system, an interconnect forms the critical link between the micro electrode to the external world through a percutaneous connector. University of Michigan has integrated their probes with miniature, flexible, multilead silicon ribbon interconnects. The critical issue is that the ribbons are inherently fragile being made from thinned down silicon, and are prone to breakage as a result of the mechanical stresses created by tissue contraction during the healing process. To overcome these limitations, a polyimide flex cable and a discrete connector are being investigated. Preliminary testing of polyimide cables has indicated that it is unsuitable for chronic implants. The proposed effort will focus on replacing polyimide ribbon cables and discrete connectors with an integrated rigid flex circuit made out of a class of biocompatible materials known as liquid crystal polymers (LCP) with a unique combination of properties. Compared to polyimides, LCPs absorb virtually no moisture and not susceptible to hydrolysis. The ribbon cable and the connector are fabricated as one piece. Integrating the connector with the flex cable represents a major advancement compared to the current hybrid approach. This eliminates one level of interconnections, and results in a much smaller percutaneous connector compared to current discrete connectors. Ultimately, the cable will be bonded to the neural probe with a planar flip-chip bond, eliminating the need for wire bonds. Elimination of wire bonds will reduce the profile height and eliminate a major reliability concern.
The proposed technology development will enable the broader acceptance and use of micro probe/stimulator technology. Although at present this is a niche market with several hundred probes are being distributed by University of Michigan on a monthly basis, the packaging technology is expected to enable its wide spread application in neurophysiology and in the treatment of chronic neural disorders such as paralysis, deafness and blindness.
