Flexible Chip-Scale Package and Interconnect for Implantable MEMS Movable Microelectrodes for the Brain

Abstract

We report here a novel approach called MEMS microflex interconnect (MMFI) technology for packaging a new generation of Bio-MEMS devices that involve movable microelectrodes implanted in brain tissue. MMFI addresses the need for (i) operating space for movable parts and (ii) flexible interconnects for mechanical isolation. We fabricated a thin polyimide substrate with embedded bond-pads, vias, and conducting traces for the interconnect with a backside dry etch, so that the flexible substrate can act as a thin-film cap for the MEMS package. A double gold stud bump rivet bonding mechanism was used to form electrical connections to the chip and also to provide a spacing of approximately 15-20 µm for the movable parts. The MMFI approach achieved a chip scale package (CSP) that is lightweight, biocompatible, having flexible interconnects, without an underfill. Reliability tests demonstrated minimal increases of 0.35 mΩ, 0.23 mΩ and 0.15 mΩ in mean contact resistances under high humidity, thermal cycling, and thermal shock conditions respectively. High temperature tests resulted in an increase in resistance of > 90 mΩ when aluminum bond pads were used, but an increase of ~ 4.2 mΩ with gold bond pads. The mean-time-to-failure (MTTF) was estimated to be at least one year under physiological conditions. We conclude that MMFI technology is a feasible and reliable approach for packaging and interconnecting Bio-MEMS devices.

Reliability of spring interconnects for high channel-count polyimide electrode arrays

“…A similar behavior has been reported previously for MEMS microflex for chip-scale bonding [23]. However, no failure in the tested interconnects was observed due to 'Kirkendall's' effect or 'Horsting' voids [21,23]. A possible reason could be that the gold metallization on the rigid substrate was screen printed and cured at 950 °C.…”

A Comprehensive Study on Design Trends and Future Scope of Implantable Drug Delivery Systems

“…Several challenges that are faced while designing an IDDS are effective drug deliver strategy, operating time [26][27], drug reservoir size and loading volume [28], biocompatibility [29], location of implant [30] Drug concentration decision making based on the physiological needs of a patient and temporary or permanent mental and physical states of patient is difficult to achieve as human body is very complex and non-linearity in responses is also high. Risks include designing malfunctions that can cause over or under infusion of drug.…”

A Cardiovascular Occlusion Method Based on the Use of a Smart Hydrogel

“…The microelectrodes were fabricated on a glass substrate for mechanical support as shown in Fig 2a. Polyimide pre-cursor (PI-2611, HD Microsystems) was spin-coated and then imidized in a nitrogen oven at 350ºC resulting in a uniform 5 µm thick polyimide layer [21,22]. Polyimide was chosen as the flexible substrate because of its biocompatibility and favorable processing properties and low water adsorption.…”