Reliability Analysis and Testing of Medical Devices. Minnetronix Case Studies

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Donald Lawson
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1 of Medical Devices Minnetronix Case Studies, QA Engineer Minnetronix Inc. ASTR 2013, Oct. 9-11, San Diego, CA

2 Background Using reliability testing and analysis during design and manufacturing Case studies Today s Presentation

3 Minnetronix Partner with medical device companies to design, test, and manufacture electro-mechanical medical devices High complexity class II and III devices 17 years experience QA engineer for many years. Perform design verification and reliability testing for many devices including heart pump controllers, sinus debriders, etc.

4 Medical Devices & Reliability Cannot tolerate field failures Patient safety Regulated environment Business financial ramifications

5 Learn About Reliability Early Design Phase Reliability assessment as part of the design process Production Phase - Stress screening of a device as part of the manufacturing process

6 Design Methods Determine reliability goals Reliability planning Mechanical stress analysis HALT at the component or system level Electrical component analysis Life testing

7 Production Methods Stress screening Trend analysis

8 Case Studies Case Study 1: Design Reliability - Single Board Computer reliability assessment Case Study 2: Design Reliability Mobile Power Unit reliability testing during DVT Case Study 3: Production Reliability - Stress screening of a device as part of the manufacturing process

9 Case Study 1 Medical Grade Single Board Computer design initiative component of a blood analysis device Determination of reliability goals Creation of reliability plan Testing to assess alpha reliability and what design changes were necessary for beta iteration

10 Case Study 1 SBC Reliability Goal: A mean time between failure (MTBF) of 5 years or approximately 20,000 hours of continuous use will be achieved.

11 SBC Reliability Plan Case Study 1 Step 1: Apply mechanical analysis tool (mechanical stress) Step 2: Perform HALT testing Step 3: Apply traditional MTBF component analysis (electrical stress)

12 Case Study 1 Step 1 - Mechanical Analysis Tool Used to provide feedback on early-stage design and layout Models board stack-up and components Simulates based on models, life cycle conditions

13 Simulation Input and Output Inputs CAD files that describe all layers, including drill file BOM and Pick & Place files Life cycle conditions Outputs Failure rates Problem areas Case Study 1

14 Performing the Analysis Set life cycle conditions Case Study 1 Temperature cycles Shocks Vibrations random and harmonic Used customer expectations of field conditions to generate the daily stresses on the board

15 Case Study 1 Running Simulations Simulations gave results on: Plated through hole fatigue Risk of CAF formation (migration of copper filaments) Solder joint lifetime (both thermal and vibration) Interconnect failures MTBF

16 Reliability Report Gives lifetime estimate Assigns modular scores Case Study 1 Highlights problem areas on the board due to thermal, vibration, and shock stresses Identifies components with shortest estimated lifetimes

17 Life Prediction Curve Case Study 1

18 Case Study 1 Vibration Analysis - Indicates components susceptible to vibration

19 Case Study 1 Step 2 HALT Subassembly Level HALT Find design problems early Different failure modes Allows more stringent testing Can validate efforts from ME Analysis Requires robust test setup

20 Case Study 1 Circuit Board HALT Testing

21 Circuit Board HALT Testing Specified limits prior to testing 5 to 45grms and -10 to 90C Uncover design weaknesses Critical findings incorporated in Beta design Sample size of N=3 No pass/fail criteria Case Study 1 Observe general error codes/flickering of display

22 Case Study 1 Circuit Board HALT Testing Robust test setup VGA screens outside of chamber for UI analysis Used HyperTerminal to gather data External power supplies powered boards Extensive labeling of cables

23 Case Study 1 Circuit Board HALT Testing Results: Reached 45 grms, -5C and 90C X-ray inspection of boards: BGA component on pad; no solder bridges No cracked solder joints Minimal signs of voiding at solder attachments Good electrical connections No visual issues with BGA components

24 Step 3 - MTBF Analysis Ops A La Carte Case Study 1 Sent BOM and Schematic Defined operational limit of 45C Room temp plus 20C internal rise of case Used HALT Calculator with testing results Comprehensive electrical stress analysis

25 Case Study 1 Conclusions Early design analysis assisted with layout and placement of PCB board HALT testing verified robustness of design MTBF calculations used to predict/verify life of design

26 Case Studies Case Study 1: Design Reliability - Single Board Computer reliability assessment Case Study 2: Design Reliability Mobile Power Unit reliability testing during DVT Case Study 3: Production Reliability - Stress screening of a device as part of the manufacturing process

27 Mobile Power Unit - Component to a life support device Portable device for use in a home environment Foreseeable rough use for the device Demands high reliability Case Study 2 Life testing during DVT to learn about reliability and design weakness before manufacturing.

28 Case Study 2 Mobile Power Unit - Design Reliability Cable Flex Testing 95/95 System Level Life Testing 2 Years Cycle Testing 1460 Cycles

29 Cable Flex Testing Reliability Target: 95/95 Pull Force: 31 Lbs. Case Study 2 Sample Size (Single Failure): 95 (reduced to 20 samples X5) Raw Cable, Strain Relief & Housing

30 Case Study 2 System Level Life Testing Reliability Target: 2 years Test Environment: 846 Hrs (Arrhenius model AF) Sample Size (Single Failure): 30 Continuous Monitoring of outputs (loaded)

31 Case Study 2 Cycle Testing Critical Features Battery, AC Power & Alarm Cycled Reliability Target: 2 years (1460 Cycles) Simulated power cycling, alarm activation & VAD connect / disconnect Sample Size (Single Failure): 30 Continuous Monitoring of outputs

32 Case Study 2 Conclusions Battery capacity better than expected Flex testing drove a design update to the shielding Had to compensate for thermal rise from test units during life test exposure

33 Case Studies Case Study 1: Design Reliability - Single Board Computer reliability assessment Case Study 2: Design Reliability Mobile Power Unit reliability testing during DVT Case Study 3: Production Reliability - Stress screening of a device as part of the manufacturing process

34 Case Study 3 Class III life support device Small enclosure, primarily electronics and display Learning about reliability in manufacturing Manufacturing screen to remove early stage failures, infant mortality, of device before entering the field

35 Case Study 3 Electronic failure mechanisms include infant mortality as well as wear out. Environmental stress screens (ESS) can be used to reduce infant mortality failures

36 What is ESS? Use accelerated stress to detect latent faults Vibration Thermal Cycling Power Cycling Case Study 3 Goal: find devices with latent faults prior to shipping

37 Case Study 3 Manufacturing Screen Plan Decide approach System level screen thermal/power cycling Board level screen random vibration Minimize risk of potential damage to device under test (DUT) Design scalable test fixture Automated data collection Limited sample sizes initially (clinical trials) Process analysis Use data to verify and track failures

38 Case Study 3 Random Vibration Board Level Assembly & Test RI Top Level Assembly, Test & Calibration Final Inspection Shipping Random Vibration Thermal/Power Cycling Board Level Screen Random Vibration Boards unpowered during vibration Functional test post vibration exposure Heavy burden external testing Yielded few faults

39 Thermal/Power Cycling Case Study 3 Board Level Assembly & Test RI Top Level Assembly, Test & Calibration Final Inspection Shipping Random Vibration Thermal/Power Cycling System Level Screen Thermal/Power Cycling Units powered on/off during thermal cycling Continuous monitoring Lowest burden in-house equipment Cost effective screen

40 Thermal Cycling Profile -60 Case Study Thermal Cycling Thermal transition rates: 5C/min Thermal limits: +80C & -40C 10 Minute dwell times Thermal Cycles Powered off at temperature extremes

41 Thermal Cycling Maintain a consistent screen environment Thermal modeling Good (constant) air circulation Mounting trays can restrict or direct air flow Augment air circulation Robust screen environment Case Study 3

42 System Qualification Case Study 3 Screen Validation Effectiveness / End of Life Qualified For Intended Use Test System Design Documentation Identify intended use and audience Requirements System & software Risk Management Identify associated risks and control measures Design documents (schematics, drawings, software, BOM) Configuration Management Test Procedures and Expected Results Installation, Calibration and Maintenance detail Record of results from qualification activities (Report).

43 Process Monitoring Mechanical Vibration Board level screen failed to detect latent faults. Removed the screen Thermal Cycling System level screen catches latent faults. Improved this screen Case Study 3

44 Screen Effectiveness / End Of Life Process monitoring Number of thermal cycles increased to 14 Analyzed life consumed Less than 1% Case Study

45 Case Study 3 Conclusions Faults detected and removed prior to field release Poor solder connections of Large components BGA components RTC battery PCBA connectors Open VIA Failed components (RTC, diodes, caps) LCD failure (custom LCD)

46 Reliability as part of design Uncover design weaknesses Done early in design Stress board outside operational limits Reliability as part of production Done during manufacturing process Reduce infant mortality In Summary Uncover faults not caught during board level

47 Questions/Comments?

Opportunities for HALT/HASS in designing robust electronics

Opportunities for HALT/HASS in designing robust electronics Isabelle Vervenne Flanders Mechatronics Engineering Centre Katholieke Hogeschool Brugge-Oostende Outline Introduction HALT HASS/HASA Predominant