Packaging and Non-Hermetic Encapsulation Technology for Flip Chip on Implantable MEMS Devices

Abstract

We report here a successful demonstration of a flip-chip packaging approach for a microelectromechanical systems (MEMS) device with in-plane movable microelectrodes implanted in a rodent brain. The flip-chip processes were carried out using a custom-made apparatus that was capable of the following: 1) creating Ag epoxy microbumps for first-level interconnect; 2) aligning the die and the glass substrate; and 3) creating non-hermetic encapsulation (NHE). The completed flip-chip package had an assembled weight of only 0.5 g significantly less than the previously designed wire-bonded package of 4.5 g. The resistance of the Ag bumps was found to be negligible. The MEMS micro-electrodes were successfully tested for its mechanical movement with microactuators generating forces of 450 μN with a displacement resolution of 8.8 μm/step. An NHE on the front edge of the package was created by patterns of hydrophobic silicone microstructures to prevent contamination from cerebrospinal fluid while simultaneously allowing the microelectrodes to move in and out of the package boundary. The breakdown pressure of the NHE was found to be 80 cm of water, which is significantly (4.5–11 times) larger than normal human intracranial pressures. Bench top tests and in vivo tests of the MEMS flip-chip packages for up to 75 days showed reliable NHE for potential long-term implantation.

Engineering microscale systems for fully autonomous intracellular neural interfaces

“…The current microscale system has three independent movable microelectrodes. Chip-scale packaging and interconnect schemes using flip-chip-based strategies that we had reported earlier 28 can help realize multi-channel systems with tens or hundreds of independently movable microelectrodes.…”

“…Using conventional wire-bonding approaches for packaging, the system used in this study had a slightly large footprint (1.78 cm × 1.46 cm × 0.5 cm) for 3 independently movable GP microelectrodes. Using flip-chip-based packaging methods reported earlier, the size can be further reduced to chip-scale 28,40 and help realize higher channel counts (with tens and hundreds of GP microelectrodes) and throughput in future designs. Our current design accommodates 3 intracellular electrodes per chip, spaced approximately 800 μm apart.…”

Design of a Customized Multipurpose Nano-Enabled Implantable System for In-Vivo Theranostics

“…In that case, implantable devices for sensing and therapeutic purposes with active regions fully exposed to the physiological environment are a great challenge [ 89 ]. New approaches based on thin-film coating solutions are in progress to overcome these problems [ 90 , 91 ]. In Xie et al [ 90 ] a bilayer solution based on an atomic layer deposited (ALD) Al 2 O 3 combined with Parylene C for long-term encapsulation is presented, and in Sutanto et al [ 91 ], a packaging and non-hermetic encapsulation MEMS flip chip technology for implantable devices is developed.…”

Flip-Chip Based Packaging for Linear Ratcheting Microactuators Enables 3d Stacks of Moveble Microelectrodes for the Brain

“…Due to the risk of such contamination, the FLI are often moved hundreds of microns away from active MEMS structures increasing the form-factor of the device. We report here a novel low-temperature flip-chip based approach [7][8] using Ag epoxy or solder for FLI. FLI bumps with high aspect ratio (>2) can be made within 70 µm from active MEMS structures without any hindrance to MEMS function.…”

“…2. For more detail on this process, the reader is referred to our earlier report [7][8]. The key steps involved in the current flip-chip process are: 1.…”