CASE STUDY

Packaging built on the wafer itself

Wafer-level packaging via thermally released metal-organic membranes builds the entire package in four phases, without ever leaving the wafer.

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Instead of bonding a separate lid, this process grows the protective cavity right on top of the finished device.

PHASE 1 & 2

Cavity, then cap

Phase 1: Cavity formation A sacrificial layer forms a cavity, 1–100 µm tall, over the MEMS's moving parts

Phase 2: Polymer cap A compliant, photo-definable polymer covers the device; bond pads are opened by patterning it

At this stage, the cavity is still full of sacrificial material — nothing is free to move yet.

PHASE 3 & 4

Phase 3: Decomposition Heating to 180–260°C thermally decomposes the sacrificial polymer, forming the air cavity

Phase 4: Metallization A conformal metal coating hermetically seals the package, with a thin insulator maintaining isolation

This exact process was used to package the University of Michigan and Delphi polysilicon ring gyroscope.

WORKED EXAMPLE

1. Fabricate Build the MEMS structure, as in earlier units

2. Seal or bond Wafer-bond a cap, or build an on-wafer membrane package

3. Dice Cut individual dies apart

4. Attach Pick, place, and attach the die to its substrate

5. Interconnect Wire-bond or flip-chip bond it electrically

6. Encapsulate Seal it against corrosion and damage

7. Test Verify it survived the entire process

Fabrication builds the device once. Packaging is what has to work every single time it ships.

UNIT 33 STUDY COMPLETE

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You've covered Wafer-Level Packaging Case Study.