Microelectromechanical systems combine small mechanical structures with electrical sensing or actuation. Their package must protect the device while preserving the physical behavior that makes it useful. Start a packaging brief by identifying what must reach the device, what must be excluded and which conditions must remain stable over time.
Start with the physical function
A resonating structure may need a controlled low-pressure cavity to limit gas damping. An infrared device needs a suitable optical path. A microphone needs acoustic access, and a pressure sensor needs a defined pressure interface. These examples lead to different package architectures and different verification questions.
Fraunhofer ISIT's wafer-level packaging work describes vacuum capping of microsensors, actuators and microoptical components, including infrared windows. Its examples show how joining materials and functional access belong in the same design decision.
On a narrow screen, scroll the table horizontally. Keyboard users can focus it and use the arrow keys.
| Requirement | Design question | Evidence to retain |
|---|---|---|
| Mechanical motion | Is there clearance through operation and shock? | Geometry, travel limits and functional response |
| Controlled atmosphere | Which pressure or gas composition must persist? | Initial condition, leak/outgassing model and aged response |
| External sensing access | What must pass through a window, port or membrane? | Transmission or transfer behavior in the intended environment |
| Electrical connection | How do signals cross the package boundary? | Continuity, parasitics, insulation and seal compatibility |
Choose the bond as part of the device process
Wafer-level packaging forms protective structures before individual devices are separated. The sequence can reduce repeated handling, but the bond process must fit the device's thermal budget, surfaces and alignment needs. Ask how the lid, seal ring and electrical feedthroughs are made and inspected.
Fraunhofer IZM's hermetic packaging example describes components sealed in inert atmosphere or vacuum using a dedicated soldering process. It is evidence for a particular construction, not a universal recipe. Compare candidate bonds by their compatible materials, process temperature, surface requirements and demonstrated device results.
Include stress from the package, contamination introduced during assembly, outgassing from internal materials and any getter strategy in the review. A package that initially functions can still drift as its internal environment changes. Set the acceptable change from the device requirement.
Combine seal evidence with functional evidence
Ask the test specialist how the selected leak method applies to the cavity volume, gas and expected leak range. Record the method's sensitivity and interpretation limits. Bond strength, visible bond continuity and electrical continuity answer different questions from cavity retention.
Measure relevant device behavior before packaging, after packaging and after defined exposures. Preserve temperature, drive conditions and fixture identity. ISIT describes using resonator Q-factor behavior in a specialized fine-leak method; applying that principle requires a device-specific relationship between damping and cavity conditions.
Fictional screen: a resonator's Q decreases from 10,000 to 9,000 after aging, a 10% change. Investigate the environment, readout and package using controls. The observation alone does not establish a leak rate or cavity pressure.
Qualify the construction and its changes
Approve the combined device, lid, bond, cavity and test method using repeated, traceable builds. Define what triggers review: new seal material, revised thermal cycle, changed feedthrough or altered cleaning. Keep the initial measurements and failure analysis with the released process. For electrical measurement planning, use the semiconductor parametric-testing guide.
Use the working record
Download the editable mems packaging brief. Save a copy, complete the actual requirements and evidence fields, and review open issues with the responsible owner. The plain-text record includes instructions, units where needed, the fictional example, and source references.