Low Profile Packaging for MEMS Aero-Acoustic Sensors.
Abstract: This thesis
explores both a semi-automated conductive ink process and modifications to Draper
Laboratory's i-UHD (Integrated - Ultra High Density) process for packaging MEMS devices.
These methods are applied to packaging MEMS acoustic sensors for wind tunnel testing.
The primary advantage of these methods is a reduction in surface topology between the
package and the integrated MEMS ... read moresensors. In these particular applications, the sensor
records surface pressure and shear stress under the turbulent boundary layer. In order
to avoid self-noise effects or other modifications to the boundary layer structure
associated with surface roughness, the interface between the MEMS sensor and its package
must be as close to planar as possible. The thickness of the viscous sub layer below the
turbulent boundary layer is the upper bound on allowable surface topology. For wind
tunnel flows at free stream velocities between 20 and 200 m/s and plate lengths on the
order of half a meter, the Reynolds number is between 105 and 107. This suggests that
the viscous wall unit will be on the order of 1 to 35 micrometers. The viscous sub layer
is approximately 5 wall units thick, so surface topologies of between 5 and 175
micrometers are desired . A previous packaging approach using gold wire bonds with
Computer Numerical Controlled (CNC) machined epoxy fill resulted in a minimum surface
topology of greater than 100 micrometers. In addition, for large arrays of MEMS
microphones, yield issues were dominated by wire bond integrity problems. These two
issues were the primary motivation for using Draper's i-UHD process and developing the
low profile conductive ink process. However, the process is generally useful and can be
applied to the packaging of various types of sensor systems that require low profile
Thesis (M.S.)--Tufts University, 2012.
Submitted to the Dept. of Mechanical Engineering.
Advisor: Robert White.
Committee: Robert White, Brian Smith, Livia Racz, and Anil Saigal.
Keywords: Packaging, Acoustics, and Mechanical engineering.read less