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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
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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
6SiTime Confidential – Do Not Distribute
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
7SiTime Confidential – Do Not Distribute
www.infineon.com
Package Lid
Hole Substrate with Leads
Cavity Package
MEMS Die
ASIC with Encapsulant
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
8SiTime Confidential – Do Not Distribute
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
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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???
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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
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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
13SiTime Confidential – Do Not Distribute
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
15SiTime 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
16SiTime Confidential – Do Not Distribute
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
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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
18SiTime Confidential – Do Not Distribute
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
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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
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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
• 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
22SiTime Confidential – Do Not Distribute
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
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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
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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
25SiTime Confidential – Do Not Distribute
Talk Summary
• 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
26SiTime Confidential – Do Not Distribute
27SiTime Confidential – Do Not Distribute
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
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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
29SiTime Confidential – Do Not Distribute
Peak Frequency Deviation (ppm)
29SiTime Confidential – Do Not Distribute
Shock Sensitivity Test ResultsDifferential XO, 500-g
SiTime
Frequency Stability (ppm)
30SiTime Confidential – Do Not Distribute
Frequency Stability (ppm)
Shock Sensitivity Test Results
Example Measurements
X - Blue
Y - Red
Z - Green
X - Blue
Y - Red
Z - Green
MEMS 1--SiTime
Frequency Stability (ppm)
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
• 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
31SiTime Confidential – Do Not Distribute
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
32SiTime Confidential – Do Not Distribute
Closing
• Thank You!
• Updated slides/questions/comments:• [email protected]
• Special Thanks• Carl Arft
• Dash Patel
• Sassan Tabatabaei
33SiTime Confidential – Do Not Distribute