High density electrical interconnections in liquid crystal polymer (LCP) substrates for retinal and neural prosthesis applications

Abstract

Retinal prostheses implemented by means of electrical stimulation of retinal ganglion cells have been previously demonstrated with 16 and 60 channel microstimulator arrays. Blind patients with severe retinal degeneration (e.g., retinitis pigmentosa (RP) have been able to use these devices to navigate and read large letters. However, to dramatically improve the effectiveness of such prostheses, and to enable a variety of neural stimulation implants, channel densities of 1000 per cm 2 and higher are highly desirable. This paper reports on a novel approach to an integrated bioelectronic package with high density electrical feedthroughs, capable of 1024 stimulator channels in a 5 mm × 5 mm area using liquid crystal polymer (LCP) substrates to enable implantable retinal prostheses.A novel fusion bonding process was demonstrated to achieve fine pitch interconnections with high adhesion strength and biocompatible metal-polymer interfaces. Helium leak rates of 1 × 10 -9 mbar-l/sec were measured for LCP samples without feedthroughs, representative of penetration through the bulk LCP film, and leak rates of < 5 × 10 -8 mbar-l/sec were measured for feedthrough array samples, comparable to leak rates demonstrated for glass substrates with metallized vias.

A Miniaturized, Eye-Conformable, and Long-Term Reliable Retinal Prosthesis Using Monolithic Fabrication of Liquid Crystal Polymer (LCP)

“…[55]. A recent study has revealed that a helium leakage rate of 1×10 -9 mbar-liter/s (~1×10 -9 atm-cm 3 /s) was measured for a 25-m-thick bulk LCP film, and less than 5×10 -8 mbar-liter/s (~5×10 -8 atm-cm 3 /s) was measured from the LCP film with a feedthrough array; these values are comparable to the leakage rate of glass substrates with metallized vias [56]. LCP encapsulation has been proven to provide superior long-term reliability than that of polyimide and parylene-C through accelerated soak tests [49].…”

A Polymer Cochlear Electrode Array: Atraumatic Deep Insertion, Tripolar Stimulation, and Long-Term Reliability

“…Although it has been argued whether helium leak tests can be used for polymer-based packages, as stated earlier, there have been a number of helium fine-leak-rate measurements of LCP encapsulations. High-density electrical interconnection feedthroughs, 1024-stimulator channels in a 5 mm × 5 mm area, are realized utilizing a novel fusion bonding process [126]. Helium leak rates of < 5×10 -8 mbar•l s -1 were measured, which is a reliable level compared to the leak rates of glass substrates with metallized vias.…”

Micro/Nano Technologies for High-Density Retinal Implant

“…It has been widely used in commercial products and allows mass production [40], but the manufacturing costs and risk of failure are rapidly increasing for high-density feedthroughs. Many efforts have been dedicated to increase package feedthrough and reliable bonding/joint using new processes and materials [26,27,28,29]. The second option is using one or several layers of biocompatible soft films as a hermetical coating, which has the advantages of being a small-size, light-weight, low-cost, and simple process with high flexibility [41], and has attracted a lot of research interest as an emerging technology enabling high-density, ultra-small medical implants.…”

“…Due to the biological incompatibility of Si substrate, higher density input/output (I/O) pins and peripheral circuit communication are required. There is a great demand in shrinking the implant size while increasing feedthrough counts [24,25,26,27], which has brought great challenges for packaging. Conventional direct packaging using plastic, metal, or ceramic cannot guarantee the long-term moisture-free environment for high-channel-count electronic devices.…”