PART 8 • MEMS PACKAGING

The chip isn't done yet

A perfectly fabricated MEMS die is still useless until it's protected, wired up, and sealed into something you can actually ship.

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In this final part, you'll learn how a finished die becomes a real product — and why packaging often decides whether a MEMS device survives long enough to be useful.

Key idea: Fabrication builds the device. Packaging is what lets it survive contact with the real world.

WHY PACKAGING?

A connection to the outside world

Packaging builds the connection between a die and everything outside it — while selectively letting through only the parameters you actually care about.

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A pressure sensor needs pressure to reach the diaphragm. It does not need moisture, dust, or static charge to reach anything else.

TWO JOBS

Protect both directions

Protect the device

Electrical/magnetic isolation from moisture and electrolytes, mechanical protection, optical and thermal protection, chemical isolation.

Protect the environment

Contain toxic products, reduce host responses, and sterilize the device — all critical for BioMEMS.

Packaging isn't just a shield. Sometimes the device needs protecting from the world — and sometimes the world needs protecting from the device.

WHAT MAKES IT HARD

Everything, all at once

Hermetic sealing Vacuum or media compatibility for accelerometers, resonators

Cost & size Low cost, small footprint

Electrical interconnection Low voltage drop, cross-talk, and capacitive loading

Mechanical interconnection Mounting without adding undue stress

Precision alignment Especially critical for optical MEMS

A great package has to satisfy all of these requirements simultaneously — none of them are optional.

THE BIG PICTURE

Nine steps from die to shipped chip

1–3 Bonding, wafer sawing, pick and place

4–6 Die attach, wire bonding, encapsulation

7–9 Overmolding, trimming, final testing

Every one of these steps happens after the silicon fabrication you've already learned is complete.

STEP 1 • WAFER BONDING

Sealing at the wafer level

Direct Wafer Bonding

Polished wafers make intimate contact; Si atoms or SiO2 form a stable bond at 800–1200°C.

Anodic Bonding

A polished silicon wafer is bonded to glass at 180–500°C with 200–1000 volts applied.

Wafer bonding is how absolute pressure sensors get their sealed vacuum reference — bonded in, before the wafer is even diced.

UNIT 29 STUDY COMPLETE

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Ready for the Fab Challenges?

You've covered Why MEMS Packaging & the Big Picture.