MEMS Packaging & Damping Mechanisms ד " ר דן סתר תכן וייצור התקנים מיקרומכניים

MEMS PackagingMEMS Packaging

& Damping Mechanisms& Damping Mechanisms

ד"ר דן סתר תכן וייצור התקנים מיקרומכניים


Wafer -> Chip First Level Package : Chip-

Scale-Packaging (Single or Multi-chip Module) .

Second Level Package : PCB or Card.

Third Level Package : Mother Board

Electronic Packaging HierarchyElectronic Packaging Hierarchy


Step 1: Wafer Dicing Step 2: Die Placement Step 3: Die Attach Step 4: Wire Bonding Step 5: Encapsulation/Molding Step 6: Lead Forming Step 7: Solder Bumping Step 8: Package Inspection Step 9: Package Test Step 10: Laser Marking Step 11: Singulation

Step 12: Packing and Shipping

Typical Packaging Flow - ElectronicsTypical Packaging Flow - Electronics




Applications : air bag and rollover detection sensors for automotive applications.

Hermetically Sealing and Protection from : corrosion , moisture, and debris , contamination.

“Stress Free” Package

Wafer level packaging protection involves an extra fabrication process where the micro-machine wafer is bonded to a second wafer which has appropriate cavities etched into it.

MEMS PackagingMEMS Packaging

MEMS - PackagingMEMS - Packaging


Functions of MEMS Packages:

* Mechanical Support

* Protection From Environment

* Electrical Connection to Other System Components

* Thermal Considerations

MEMS MEMS –– Packaging (cont.) Packaging (cont.)ד"ר דן סתר תכן וייצור התקנים מיקרומכניים

Types of MEMS Packages

* Metal Packages

* Ceramic Packages

* Thin-Film Multilayer Packages

* Plastic Packages


Package-to-MEMS Attachment: Die Attachment


Chip Scale Packaging

* Flip Chip

Controlled Collapse Chip Connection (C4) is an interconnect technology developed by IBM during the 1960s as an alternative to manual wire bonding.

Often called "flip-chip," C4 attaches a chip with the circuitry facing the substrate. C4 uses solder bumps (C4 Bumps) deposited through a Bump Mask onto wettable chip pads that connect to matching wettable substrate pads (Figure 8-4). MEMS technology initially may not use flip chip packaging but the drive toward miniaturization may necessitate its incorporation into future designs.


* Flip Chip (cont.)


The primary advantage of C4 is its enabling characteristics. Specific advantages include:

Size and weight reduction

Applicability for existing chip designs

Increased I/0 capability

Performance enhancement

Increased production capability

Rework/chip replacement

Key considerations include:

Additional wafer processing vs. wire bond

Supplemental design groundrules

Wafer probe complexity for array bump patterns

Unique thermal considerations


Wire BondingWire Bonding


Tape Automated BondingTape Automated Bonding


BGA PackageBGA Package

Ball Grid Array is a surface mount chip package that uses a grid of solder balls as its connectors. It is noted for its compact size, high lead count and low inductance, which allows lower voltages to be used. BGAs come in plastic and ceramic varieties. It essentially has evolved from the C4 technology whereas more I/Os can be utilized in the same area as in a peripherally leaded package (or chip). The CBGA and PBGA are not truly Chip Scale Packaging but the evolution to the BGA has come out of the experience the industry has gained from the CBGA and PBGA packages.


BGA PackageBGA Package


BGA PackageBGA PackageThe uBGA package is constructed utilizing a thin, flexible circuit tape for its substrate

and low stress elastomer for die attachment. The die is mounted face down and its electrical

pads are connected to the substrate in a method similar to TAB bonding. After bonding these

leads to the die, the leads are encapsulated with an epoxy material for protection. Solder balls

are attached to pads on the bottom of the substrate, in a rectangular matrix similar to other BGA

packages. The backside of the die is exposed allowing heat sinking if required for thermal

applications. Ball pitches available today are 0.50, 0.75, 0.80, and 1.0 mm. Other features and

benefits include: 0.9 mm mounted height, excellent electrical and moisture performance, 63/37

Sn/Pb solder balls, and full in-house design services.


Solder Solder BumpsBumps


MCM (Multi-Chip-Modules)MCM (Multi-Chip-Modules)



Failure by Stiction and Wear.

Delamination.

Environmentally induce failures

Cyclic mechanical fatigue

Dampening Effect.

Packaging and development of testing methodologies .

Typical MEMS Packaging Failure ModesTypical MEMS Packaging Failure Modes


WLP for MEMS PackagingWLP for MEMS Packaging


WLP for MEMS PackagingWLP for MEMS Packaging

“Recent Development in WLP” - AMKOR

“Wafer level “Hermetic” packaging for sensors / MEMS” - MOTOROLA

ד"ר דן סתר ריסון במיקרומערכות הנדסת מיקרומערכות

Damping in MicrosystmesDamping in MicrosystmesThere are two main damping mechanisms in Mycrosystems:

The motion of a free standing planeThe motion of a free standing plane

A cantilever or a membrane, moving in a fluid without any interaction with another solid body. The damping is mainly due to the fluid properties such as: viscosity, density, pressure and temperature.

The relative motion of planes in the fluidThe relative motion of planes in the fluid

Planes (micorostructures) that are moving one raltive to the other in the fluid:Perpendicular motion: Electrostatic motion perpendicular to the

substrate, Tuning fork beams.

Parallel motion: Comb Drive.

The damping is influenced mainly by the gap size between the solid surfaces, the fluid properties, the pressure and the motion amplitude.


The 1 DOF SystemThe 1 DOF SystemQ: The quality factor:Q: The quality factor:Equation of motion:

Solution The natural frequency:

mF

C

K

tFKXXCXm sin0 tFKXXCXm sin0

22

1

1

2;sin)(

n

ntgtRtX

22

1

1

2;sin)(

n

ntgtRtX

m

Kn

The damping ratio:Km

C

2

Non dimensional definition of the state solution: tR

KF

Xd sin

0 tR

KF

Xd sin

0

Rd is the dimensionless response factor

Non velocity solution: tRKF

Xv sin

0

tR

KF

Xv sin

0


Lower damping Q increasing. The “quality” of the system is higher

2

1

nQ

2

1

nQ

2/max/ dvR

RV, Rd(RV)max ; (Rd)max

n

In microsystems high Q values are needed:

103 < Q < 105


Damping of the motion of a free standing planeDamping of the motion of a free standing plane

The low pressure region: The surrounding damping is negligible relative to the inner damping in the material.

Empirical Q f(P)

The molecular region: The damping mechanism is due to momentum transfer between single molecules of the surrounding and the solid.

The high pressure region: Continuity region. The damping is due to pressure, viscosity – drag.


Damping of the relative motion of surfaces in a fluidDamping of the relative motion of surfaces in a fluid

* The pressure regions , the properties of flow and the damping mechanism is determined by the “Knudsen no”:

mn h

K

– The mean free path between the moledules

hm – Mean thickness of the fluid layer or the nominal gap between the surfaces.

2a – Length of the membrane side

hm

aaP

P 0

The index 0 indicates the value for 1 atm:

0 (1 atm) = 9.3510-6 [cm] for air

hm < Kn > 1 The molecular region

<hm < 100 10-2 < Kn < 1 Knudsen flow

hm > 100 Kn < 10-2 Continuity





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MEMS Packaging & Damping Mechanisms ד " ר דן סתר תכן וייצור התקנים מיקרומכניים