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D. B. Shire, T. Salzer, W. K. Jones, R. Akhmechet, M. D. Gingerich, J. L. Wyatt, J. F. Rizzo; High Density Bonding to Next Generation Hermetic Packaging for the Boston Retinal Prosthesis. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3037.
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This work is related to the efforts of the Boston Retinal Implant Project to develop a sub-retinal prosthesis to restore vision to the blind.
Custom polyimide arrays with 69 Au micro-contacts, each 200 microns in diameter, were microfabricated and the contacts electroplated to a thickness of 40 microns. Meanwhile, screened and sintered Pt and Au bumps were patterned on 96% alumina substrates to match the contact pattern. Samples were joined together using a Kulicke & Soffa model 4522 bonder in TAB mode with the substrate heater set at 150 degrees C. Thermo-compression joints were made using a Small Precision Tools SPT 7645A-TI-0040-S-M tip.
Bond shear tests to the trial retinal implant feedthrough assemblies were performed using a XYZTec Condor 70 shear force tester. The thermo-compression bonds withstood up to 50 grams of force, indicating good quality bonding. Au to Au joining required less force and time than Au to Pt bonding. Optimization of the profiles of the electroplated contact pads and the sintered bumps on the electrode arrays and feedthrough discs respectively is expected to yield even greater bond strength. Polyimide mesh-reinforced contact pads were found to improve the integrity of the electrode array-feedthrough connections (see photo below).
The feasibility of high-density bonding of microfabricated electrode arrays to hermetic signal feedthrough arrays having 69 channels has been demonstrated. Such structures will form a key component in the next-generation Boston retinal prosthesis.
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