The Packaging and Reliability Qualification of MEMS ... - SiTime.pdf · MEMS Oscillators: •...

The Packaging and Reliability Qualification of MEMS Resonator Devices

Pavan Gupta

Vice President, Operations

Yin-Chen Lu, Preston Galle

Quartz and MEMS Oscillators

Quartz Oscillators:

• Ceramic or metal package

• Quartz plate above driver circuit

• Built with special dedicated

processes in dedicated factories

MEMS Oscillators:

• Plastic QFN package

• Silicon MEMS die on CMOS die

• Built with standard processes in

standard IC and assembly factories

source: www.ecliptek.com

SiTime Confidential – Do Not Distribute 2

MEMS and Quartz Timing Applications

3

Computing-Storage

NetworkingIndustrial

Consumer

Wireless Telecom

Mobility

SiTime Confidential – Do Not Distribute

Talk Agenda

• MEMS Packaging Considerations

• SiTime Packaging Lessons Learned: MSL Delamination

• MEMS Reliability Qualification Considerations

• SiTime Qualification Lessons Learned 1: HTOL vs Aging

• SiTime Qualification Lessons Learned 2: Vibration Survivability vsSensitivity

4SiTime Confidential – Do Not Distribute

MEMS Packaging Considerations

• Understand requirements deeply• Application

• Customers

• Industry Standards

• Government Standards

• Minimize modifications to off-the-shelf packaging platforms

• Start Device/Package co-design as early in the development cycle as possible

• Customer implications

• MEMS device design and process implications

• ASIC design and process implications


MEMS Specific Package Modifications 1/2

• MEMS systems typically need 2 die in a package OR MEMS/Circuit integration

• MEMS/ASIC with a MEMS cap: Thick die stack• Thinner leadframe, die

• Thicker package mold cap

• Customized backgrinding, wafer dicing

• Low loop wirebonds


www.chipworks.com

1.4mm Thick!Industry

moving to thinner: <<1mm

Moldcap

Leadframe

MEMS/ASIC

MEMS Cap

Wirebonds

Side Xray of MEMS Accelerometer

MEMS Specific Package Modifications 2/2

• MEMS requiring exposure to the environment• Packages with holes

• Special package singulation

• Stress Sensitive MEMS• Cavity Packaging

• Low stress mold compound, encapsulant, DA epoxies

• Gel top

• All modifications require validation and qualification=Time+Money• Product performance and reliability impact

• Package performance and reliability impact


www.infineon.com

Package Lid

Hole Substrate with Leads

Cavity Package

MEMS Die

ASIC with Encapsulant

Talk Agenda







MEMS Packaging Considerations: SiTime

• Understand requirements deeply• Application: Commercial, Industrial, military timing

• Customers: comfortable with Quartz for timing. Wary of MEMS.

• Industry Standards: JEDEC, MIL-STD, concerns associated with Quartz reliability

• Government Standards: RoHS, REACH

• Minimize modifications to off-the-shelf packaging platforms• MEMS designed for standard IC packaging

• Process eliminates contamination sensitivity

• Design eliminates stress sensitivity

• Start Device/Package co-design design as early in the development cycle as possible

• Customer implications: Match Quartz package footprints using plastic packaging

• MEMS device design and process implications: packaging DFM rules used

• ASIC design and process implications: packaging DFM rules used


Using QFN to Look and Perform Like Quartz

10

Quartz Packaging QFN PackagingQuartz Mimicked using QFN

RectangularAu Plated Pads

Large Corner PadsNo Exposed Die PadMoisture Insensitive

Typically SquareSn Plated Leads

Small Perimeter PadsExposed Die Pad

Moisture Sensitive

DFNPPF Leadframe

Custom Lead DesignChip-On-Lead

Moisture Insensitive???


Look

Performance

Process

Materials

11

1. Copper lead frame 2. Mount CMOS chip 3. Mount MEMS resonator

4. Attach wire bonds 5. Mold plastic and singulate 6. Test and calibrate

Standard IC QFN Packaging Flow

• MEMS Designed for IC packaging and stress insensitivity

• QFN used with no MEMS specific modifications

• What could go wrong?SiTime Confidential – Do Not Distribute

Assembly Process Capability Looks Good.

Moisture Sensitivity?

Bottom Wire Pull: Cpk 1.9

Top Die Sheer: Cpk 2.0

Top Ball Sheer: Cpk 2.0

Top Wire Pull: Cpk 1.9

Bottom Ball Sheer: Cpk 2.4

Bottom Die Sheer: 88/88 >2kg


Moisture Sensitivity Level Classification

• All (plastic) packages must be classified for moisture sensitivity• Effect of moisture from the environment saturating the package that expand

rapidly when put through PCB solder reflow � “Popcorning”

• Goal is to determine uncontrolled shelf life of a package prior to solder reflow

• Classification process• Sample packages evaluated for mechanical integrity: visual and CSAM

• Samples exposed to moisture soak (See next slide for duration vs MSL level)

• Samples exposed to simulated solder reflow 3 times

• Samples re-evaluated for mechanical integrity: visual and CSAM

• Conduct full package qual on MSL preconditioned samples where appropriate

• MSL1/260 desirable• Unlimited shelf life � customer factory friendly

• No special packing required

• 0 Delamination desirable: synonymous with quality and reliability, can lead to

performance and reliability issues

• Quartz hermetic packages are MSL1/260


J-STD-20C: Moisture Sensitivity Level (MSL)

SiTime Confidential – Do Not Distribute 14

SiTime Packages MSL1 Compliant

• MSL1/260 compliant with 0 delamination after 3 construction iterations

• Every Iteration took 2-3mos to build and evaluate

• After final construction was chosen, full qualification had to be completed�3 more intense months


Talk Agenda







What is Qualification?

• Validate that a product or process will do what is intended• In manufacturing � Process qualification

• Over time � Reliability qualification

• In application � Performance qualification

• Reliability qualification answers• Failure rate over time?

• What causes it to fail?

• How will it fail?

• “Text Book” qual plan can come from JEDEC/MIL-STD• Good starting point: needs interpretation to apply to any particular product

• Customers recognize such a plan as important but will require more/other tests

• Technology matters to understand potential sensitivities or weaknesses


http://www.weibull.com

MEMS Qualification Considerations

• Understand Requirements• Application

• Customer

• Industry

• Government

• Understand Data Reporting Requirements• Pass/Fail only?

• Parametrics?

• Drift from pull to pull?

• Over temperature, VDD, process?

• Cpk on critical parameters?

• Design qual plan as early as possible in product development cycle• Customer implications

• MEMS device implications

• ASIC implications


MEMS Qualification Considerations

• Understand Requirements• Application: Industrial of Commercial general purpose timing using MEMS

• Customer: comfortable with Quartz for timing. Wary of MEMS.

• Industry: JEDEC, MIL-STD, historical reliability concerns associated with Quartz

• Government: RoHS, REACH

• Understand Data Reporting Requirements• Pass/Fail only? Yes, for some stresses.

• Parametrics? Yes, for some stresses.

• Drift? Yes, for some stresses

• Over temperature, VDD, process? Yes, for some customers

• Cpk on critical parameters? Yes, for some data.

• Design qual plan as early as possible in product development cycle• Customer implications: Reporting must be thought through prior to qual start

• MEMS device implications: designed for critical parameter monitoring

• ASIC implications: CMOS designed for critical parameter monitoring


What goes into a good qual plan?

• Part number of qual units• Package body size, number of leads

• Packaging packaging vendor

• Stress Name

• Stress Condition

• Sample Size, # lots

• Pass/Fail criteria

• Qual location

• Testing methodology• Static or dynamic data collection

• Pre testing

• Post testing

• Pulls and/or hours


Qualification Plan Example for Oscillators

21

• JEDEC/MIL-STD Tests• MSL1 Preconditioning

• HTOL

• HTS

• HAST

• PCT

• TC

• ESD, LU

• Shock survivability

• Vibration survivability

• Customer Specific • PCB Temp Cycling

• PCB Bend Test

• Package Core Body Test

• Terminal Peel Strength

• Application Specific• Aging

• Shock sensitivity

• Vibration sensitivitySiTime Confidential – Do Not Distribute

1

1

2

2

Talk Agenda







High Temperature Operating Life (HTOL)• Purpose: To determine the operating lifetime of a product

• Meant to accelerate, through high temperature and VDD• Time-dependent Dielectric Breakdown, Electromigration

• Hot carrier effects, charge effects, Mobile ionic contamination

• Data retention capability of NVM

• Description of test: • Test samples (ATE)

• Place parts in Burn-in oven at 125C ambient and worst case VDD

• Pull parts at 168hrs and test the samples

• Place back in oven

• Repeat at 500hrs, 1000hrs, …

• Static: No data is collected during stress

23

HTOL Board HTOL Oven240 DUTs Edge Connector/Backplane


Dynamic Aging Methodology Developed

to Meet Customers Requirements

• Requirement: continuously

measure frequency for greater than

1yr and at 2 different temperatures

• MIL-PRF-55310E compliant

• 2 Aging Systems• 25C, 85C

• 100s of DUTS/oven

• Package size and vendor diversity

• Continuous Frequency Measurement

• GPS disciplined freq reference

• Continuous Vdd and Temp monitoring

• UPS power backup

• Running continuously


Aging Stations

85 C

Oven

25 C

Oven

25 C RackMeasurement equipment

mounted into rack

85 C

Rack

UPSs2 head units +8 battery packs

Power Supplies2 chassis +

8 128W modules


Talk Summary








Static vs Dynamic Tests of Shock Effects

• Nearly all electronics experience mechanical shock during use

• Effect on clock oscillators• Solder joint failure in PCB assembly

• Damage of Quartz of MEMS resonators or packages in the clock oscillator

• Instantaneous frequency spike on shock

• How to evaluate clock oscillators sensitivity to shock• Static testing: test functionality before and after exposure to shock

• Dynamic testing: Compare peak frequency deviation DURING shock


Mechanical Shock Sensitivity Test Setup

Controller Shock

Tester

Vertical drop

on guide rail

Continuous Time Interval Analyzer

Power Supply

X

Y

Z Reference pin 1 mark for orientation

Z

X, Y


Peak Frequency Deviation (ppm)


Shock Sensitivity Test ResultsDifferential XO, 500-g

SiTime

Frequency Stability (ppm)



Shock Sensitivity Test Results

Example Measurements

X - Blue

Y - Red

Z - Green

X - Blue

Y - Red

Z - Green

MEMS 1--SiTime


X - Blue

Y - Red

Z - Green

Quartz 4

Frequency Stability (ppm) X - Blue

Y - Red

Z - Green

MEMS 2

Quartz Saw 2

Talk Agenda• MEMS Packaging Considerations






Talk Summary

• Deeply understand packaging and qualification requirements

• Start package and qual plan development as early as possible

• Packaging:• Minimize modifications to off-the-shelf packaging platforms

• Evaluate and qualify any departures

• Qualification:• Customer and application specific studies can require a lot of resources

• Pay particular attention to data reporting requirements


Closing

• Thank You!

• Updated slides/questions/comments:• [email protected]

• Special Thanks• Carl Arft

• Dash Patel

• Sassan Tabatabaei


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