title: 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 450μN with a displacement resolution of 8.8μm/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 andin vivotests of the MEMS flip-chip packages for up to 75 days showed reliable NHE for potential long-term implantation.
authors.affiliation: School of Biological and Health Systems Engineering, Arizona State University, Tempe, AZ 85287-9709 USA.
authors.forename: Jemmy
authors.initials: J
authors.lastname: Sutanto
authors.affiliation: School of Biological and Health Systems Engineering, Arizona State University, Tempe, AZ 85287-9709 USA.
authors.forename: Sindhu
authors.initials: S
authors.lastname: Anand
authors.affiliation: School of Biological and Health Systems Engineering, Arizona State University, Tempe, AZ 85287-9709 USA.
authors.forename: Arati
authors.initials: A
authors.lastname: Sridharan
authors.affiliation: School of Biological and Health Systems Engineering, Arizona State University, Tempe, AZ 85287-9709 USA.
authors.forename: Robert
authors.initials: R
authors.lastname: Korb
authors.affiliation: School of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, AZ 85287-5706 USA.
authors.forename: Li
authors.initials: L
authors.lastname: Zhou
authors.affiliation: Sandia National Laboratory, Albuquerque, NM 87185 USA.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Baker
authors.affiliation: Sandia National Laboratory, Albuquerque, NM 87185 USA.
authors.forename: Murat
authors.initials: M
authors.lastname: Okandan
authors.affiliation: School of Biological and Health Systems Engineering, Arizona State University, Tempe, AZ 85287-9709 USA.
authors.forename: Jit
authors.initials: J
authors.lastname: Muthuswamy
keywords: Actuators; biomedical microelectromechanical systems (MEMS) (bio-MEMS); flip chip; hydrophobic silicone; microactuators