Hermeticity Charcacterization

Preditcting lifetime of a device by characterization of hermeticity as a measure of bonding quality

Most micro-electro-mechanical systems such as acceleration sensors, pressure sensors, gyroscopes or optical and fluidic elements consist of two or more bonded substrates. All devices share the demand on gas tightness at the bonded heterogeneous or homogeneous interfaces. A parameter to express the level of gas tightness is the hermeticity and thus the leakage rate. This value describes the change of pressure by time for a defined, encapsulated volume. Hence, the quality of the bonding interface needs to be characterized in order to predict the lifetime of a device, since a change of the internal atmosphere or pressure will influence the function of the device significantly and will cause a failure in worst case. Therefore, hermeticity characterization defines a crucial process within the production sequence of a MEMS or associated products.

Applicable Substrates

  • Wafer-Level packages (silicon, glass, ceramic, lithium niobate, lithium tantalite)
  • Chip sized package (QFN, TO, customer defined)

Characterization Techniques

Different measurement techniques have been established at Fraunhofer ENAS addressing different packages volumes and accuracy levels.

  • Techniques based on the utilization of a tracer gas (helium leakage test and spectrometric analyses)
  • The application of resonant microstructures with a pressure-dependent vibration characteristic