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Natnael Masresha Zerihun

Teardown of a Commercial MEMS Pressure Sensor

Heterogeneous Integration course, SSIs M.Sc. · Autumn 2024 · Academic project · Group of 4

X-ray, optical, and SEM/EDS analysis of an ST piezoresistive pressure sensor, identifying its wafer-bonding technology and package construction.

  • SEM
  • EDS
  • Failure analysis
  • Packaging
  • MEMS

Overview

A failure-analysis style investigation of an ST LPS22HD barometric pressure sensor: how is the vacuum cavity sealed, how is the die attached and wired, and what is the package actually made of?

Technical approach

  • X-ray imaging of the intact package, then cross-sectioning
  • Optical microscopy and SEM imaging with EDS elemental analysis
  • EDS line scans across the die-to-cap seal, matched against phase diagrams

Results

  • Identified aluminium-germanium eutectic wafer bonding as the cavity seal from the EDS line scans and the Al-Ge phase diagram
  • Characterized the solder intermetallics, gold-wire to aluminium-pad bonds, and the multilayer PCB substrate
  • The sensing membrane itself was lost during dicing, documented as an honest limitation of the cross-sectioning approach

Media

Labeled optical cross-section of the pressure sensor package
Package cross-section under the optical microscope: membrane part and seals, ASICs, solder joints, and PCB layers.
SEM image of the pressure sensor die cross-section
SEM view of the cross-sectioned die stack (50x).