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8 MEMS Packaging

•Ken Gilleo PhD•ET-Trends LLC

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Packaging Classification

Packaging Classification

1. Package discrete MEMS device (non-WLP)

2. Partial WLP; pre-packaging; e.g. capping

3. Total WLP

Bond protective wafers with vias

Bond protective wafers with vias in MEMS

Integrated package with 2nd-level connectors

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Hermetic PackagingHermetic Packaging

• Metal

• Ceramic

• Combinations

Plastic has not “proven” hermeticity – passing leak test is not enough;Result is generally a Near-Hermetic Package (NHP)

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OPEN INSERT FILLPlastic

Conductor Insert

Plastic Molded PackagePlastic Molded PackageMetal Lead Fame (MLF)

Thermoplastic

Quantum Leap Packaging

RJR Polymers

RJR Polymers

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PCB Fabricated Enclosures

PCB Fabricated Enclosures

• Fabricated PCB substrate; BGA, QFN

• Add walls; various methods used

• Die attach & wire bond chip (s)

• Seal lid

• Singulate

Used for non-hermetic MEMS such as microphones

Knowles Electronics

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Ported Flip Chip BGA

Ported Flip Chip BGAEncapsulant

MEMS FLIP CHIP

Light pipe or gas accessUnderfill

Dam

Selective; semipermeable membrane, etc.

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WLP ProcessesWLP Processes• Wafer preparation

MEMS release step Coat (polymer), treat; anti-stiction, other

• Wafer bonding Apply adhesive if required Bond

• Singulation; cap, MEMS, both

• Secondary packaging if required

• Test

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Partial WLP: Pre-Packaging

Partial WLP: Pre-Packaging

• Form package components Caps in wafer Couplings, fittings, ports, or none

• Assemble Place sub-components Wafer bonding

• Move to final packaging process Capped wafer is transportable Packaging foundry may handle

Popular for inertial sensors;

accelerometers, gyro.

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MEMS Wafer

Cap

Printed Adhesive Wallsor use etched features

Wafer-Level CappingWafer-Level Capping(1) Print Adhesive

(2) Bond

(3) Singulate; may be complex

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WL “Cap & Mold”WL “Cap & Mold”

2. Attach & bond device

1. Apply cap to device or wafer;solder, weld, bond.

3. Conventional overmolding or dispensed encapsulant

MEMS Chip

Cap

Vacuum

Seal

After singulation steps

Cross-section

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Lid Sealing/BondingLid Sealing/Bonding

• Used for virtually all cavity packages

• WL lid bonding is called “capping”

• Many methods, old and new

• Wafer bonding & lid seal can share methods

Can use many of the same methods as wafer bonding

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1. Form sheet of polymer film or resin

2. Cut or mold into matrix; laser or die

3. Bond tack to lens disk

4. Flip lens/LCP array and align to wafer

5. Seal/bond to wafer with laser,such as near-IR

6. Singulate by sawing

Wafer-Level with Polymer Films

Wafer-Level with Polymer Films

Laser spot or diode bar line

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Total WLPTotal WLP

• Electrical pass-through; e.g.; TSV

• Enclosure

• Interconnect to PCB (2nd-level)

• Controlled atmosphere as required

• Non-electrical I/Os as required

• General package attributes

Processes must provide:

TSV = Through Silicon Vias

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Interconnect for WLInterconnect for WL

1. Through chip (drill & fill; plasma, RIE)

2. Route conductors over/under

Same methods been adopted & developed for 3D stacked chips

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Integral CapsIntegral Caps

• Form capping structure

• Clean

• Vacuum or gas environment

• Seal port

• Singulate

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Fabricate Caps on Wafer(Hexal MicroMold Process)

Fabricate Caps on Wafer(Hexal MicroMold Process)

• Etch Recess

• Deep Etch

• Deposit sacrificial & pattern

• Plate Au bumps & seal

• Release

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Micro Cap AssemblyMicro Cap Assembly

• Transfer caps to MEMS

• Align

• Bond

• Separate

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Sacrificial

Integrated PackageIntegrated Package

Base

MEMS Structure

Deposited Layer

EvacuateSeal

…or add port or coupling

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Device-Specific Packages

Device-Specific Packages

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This type of machine can be used to selectively encapsulate MEMS- one like this is used on ink jet cartridges. Courtesy of Speedline

Ink Jet “Gun”

I-TAB package

Ink Jet “Gun”

I-TAB package

MEMS bare die

MEMS

Encapsulation

EncapsulationSelective

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Pressure PackagesPressure Packages

Bishnu Gogoi, Motorola

Motorola Unibody Package

Cost can be too high

Protective Coating; e.g.; Parylene

Corrosion can occur under the coating in harsh environments

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Bio-MEMS & Fluidics Packaging

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Bio-MEMS ChallengeBio-MEMS Challenge• Biocompatibility; inert

• Sample into pressurized system

• Variety of energy transfer modes

• Interfaces in hostile environments

• Protection within life system

• Remakable couplings

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Fluid Coupling Technology

Fluid Coupling Technology

• Fluidic MEMS device (s)

• Inter-chip coupling as required

• Auxiliary unit connections

• Through-package fluidic interface

• Electrical I/Os and 2nd-level

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Fluid Coupling DesignFluid Coupling Design

Ellis Meng; California Institute of Technology

Materials: silicon, polymersProcesses: bulk etching, RIE

Bulk Coupler AssemblyPlastic Insertion Using Cryogenics

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BioMEMS

BioMEMS

IME Singapore

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Plug-inMEMS

Plug-inMEMS

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Session SummarySession Summary• MEMS is a major packaging challenge

• Typically device-specific

• Often application-specific

• Result is non-standard, high customization

• Trend Discrete pWLP full-WLP

• More WLP in the future

• Some MEMS packaging suppliers evolving