The Packaging and Reliability Qualification of MEMS Resonator Devices

The Packaging and Reliability Qualification of MEMS Resonator Devices Pavan Gupta Vice President, Operations Yin-Chen Lu, Preston Galle

Quartz and MEMS Oscillators source: www.ecliptek.com 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 2

MEMS and Quartz Timing Applications Consumer Computing-Storage Mobility Industrial Networking Wireless Telecom 3

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 vs Sensitivity 4

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 5

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 Moldcap MEMS Cap 1.4mm Thick! Industry moving to thinner: <<1mm Wirebonds MEMS/ASIC Leadframe Side Xray of MEMS Accelerometer www.chipworks.com 6

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 Package Lid MEMS Die ASIC with Encapsulant Cavity Package Hole Substrate with Leads All modifications require validation and qualification=time+money Product performance and reliability impact Package performance and reliability impact www.infineon.com 7

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 9

Using QFN to Look and Perform Like Quartz Quartz Packaging Quartz Mimicked using QFN QFN Packaging Look Process Rectangular Au Plated Pads Large Corner Pads No Exposed Die Pad Moisture Insensitive Performance DFN PPF Leadframe Custom Lead Design Chip-On-Lead Moisture Insensitive??? Materials Typically Square Sn Plated Leads Small Perimeter Pads Exposed Die Pad Moisture Sensitive 10

Standard IC QFN Packaging Flow 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 MEMS Designed for IC packaging and stress insensitivity QFN used with no MEMS specific modifications What could go wrong? 11

Assembly Process Capability Looks Good. Moisture Sensitivity? Top Ball Sheer: C pk 2.0 Top Wire Pull: C pk 1.9 Top Die Sheer: C pk 2.0 Bottom Die Sheer: 88/88 >2kg Bottom Ball Sheer: C pk 2.4 Bottom Wire Pull: C pk 1.9 12

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 13

J-STD-20C: Moisture Sensitivity Level (MSL) 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 15

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 17

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 18

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 19

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 20

Qualification Plan Example for Oscillators JEDEC/MIL-STD Tests 1 2 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 1 2 Aging Shock sensitivity Vibration sensitivity 21

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 240 DUTs HTOL Board Edge Connector/Backplane HTOL Oven 23

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 24

Aging Stations 85 C Rack 25 C Rack Measurement equipment mounted into rack Power Supplies 2 chassis + 8 128W modules 85 C Oven 25 C Oven UPSs 2 head units + 8 battery packs 25

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 vs Sensitivity 26

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 27

Mechanical Shock Sensitivity Test Setup Z Y Reference pin 1 mark for orientation Vertical drop on guide rail Z Continuous Time Interval Analyzer X X, Y Controller Shock Tester Power Supply 28

Shock Sensitivity Test Results Differential XO, 500-g Peak Frequency Deviation (ppm) SiTime 29

Shock Sensitivity Test Results Example Measurements Frequency Stability (ppm) MEMS 1--SiTime X - Blue Y - Red Z - Green Frequency Stability (ppm) Quartz Saw 2 X - Blue Y - Red Z - Green Frequency Stability (ppm) MEMS 2 X - Blue Y - Red Z - Green Frequency Stability (ppm) Quartz 4 X - Blue Y - Red Z - Green 30

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 32

Closing Thank You! Updated slides/questions/comments: pg@sitime.com Special Thanks Carl Arft Dash Patel Sassan Tabatabaei 33