Advanced Hermetic Feedthrough and Packaging Technology for the Boston Retinal Prosthesis

Abstract

 

Purpose

 

This work is related to the efforts of the Boston Retinal Implant Project to develop a sub-retinal prosthesis to restore useful vision to the blind. This poster focuses on high density signal feedthrough advancements for the Boston visual prosthesis, and manufacturing and assembly methods for the miniature implantable packages.

 

Methods

 

Cofired ceramic discs with platinum-based signal feedthroughs were also fabricated to mate with 2-piece, 11mm diameter custom-machined and laser-welded titanium micro-enclosures. These discs were fabricated by precision punching of 100-150 micron diameter vias in 100 micron thick green alumina tape, followed by via filling with Pt-based conductive ink. The layers of tape were isostatically laminated and then fired at 1550 °C. In a subsequent assembly step, flexible iridium oxide - based electrode arrays for sub-retinal stimulation were joined to these feedthrough disc assemblies by thermo-compression bonding.

 

Results

 

Radiographic analysis, helium leak testing, high pressure burst testing, and precision metallography of all joints were performed. Parts were measured for electrical resistance (approx. 5 mΩ/via) and hermeticty. SEM and cross-section analysis were used for alignment verification. Thermo-compression bonds made between the feedthrough discs and electrode arrays had an average shear strength of more than 50 grams force, indicating good quality bonding. Helium leak rates of better than 1.0x10E-09 standard cc He / second were measured and compared with a calibrated leak rate standard of the same value. Finished assemblies had specialized titanium suture arms attached by laser welding, and completed units were subsequently implanted in Yucatan mini-pig animal models.

 

Conclusions

 

High-quality, repeatable hermetic feedthrough fabrication and assembly processes for miniature, implantable retinal prostheses have been demonstrated, and microfabricated electrode arrays having 256+ channels were successfully bonded to the package exterior. To our knowledge, this is a higher number by of hard-wired electrode connections via hermetic feedthrough assembles that deliver stimulus currents than in any available neural prosthetic device.

 

 

Cross section of a portion of a platinum filled conductive feedthrough in a co-fired alumina ceramic disc, showing an absence of voids. The feedthrough disc is a key component of the Boston Retinal Prosthesis.

 

Keywords: 696 retinal degenerations: hereditary • 412 age-related macular degeneration • 549 image processing