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John Whitehurst
Reliability Analysis and Testing
of Medical Devices
John Whitehurst, QA Engineer
Minnetronix Inc.
ASTR 2013, Oct. 9-11, San Diego, CA
Reliability Analysis and Testing of
Medical Devices
Minnetronix Case Studies
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
Background
Using reliability testing and analysis during design
and manufacturing
Case studies
ASTR 2013 Oct 9-11, San Diego, CA
Today’s Presentation
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
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
John Whitehurst
QA engineer for many years. Perform design
verification and reliability testing for many devices
including heart pump controllers, sinus debriders, etc.
ASTR 2013 Oct 9-11, San Diego, CA
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
Medical Devices & Reliability
Cannot tolerate field failures
• Patient safety
• Regulated environment
• Business financial ramifications
ASTR 2013 Oct 9-11, San Diego, CA
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
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
ASTR 2013 Oct 9-11, San Diego, CA
John Whitehurst
Reliability Analysis and Testing
of Medical Devices ASTR 2013 Oct 9-11, San Diego, CA
Design Methods
Determine reliability goals
Reliability planning
• Mechanical stress analysis
• HALT at the component or
system level
• Electrical component analysis
• Life testing
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
Production Methods
Stress screening
Trend analysis
ASTR 2013 Oct 9-11, San Diego, CA
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
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
ASTR 2013 Oct 9-11, San Diego, CA
Case Studies
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
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
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 1
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
SBC Reliability Goal: “A mean time between failure
(MTBF) of 5 years or approximately 20,000 hours
of continuous use will be achieved.”
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 1
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
SBC Reliability Plan
Step 1: Apply mechanical analysis tool
(mechanical stress)
Step 2: Perform HALT testing
Step 3: Apply traditional MTBF component
analysis (electrical stress)
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 1
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
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
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 1
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
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
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 1
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
Performing the Analysis
Set life cycle conditions
Temperature cycles
Shocks
Vibrations – random and harmonic
Used customer expectations of field conditions to
generate the “daily stresses” on the board
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 1
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
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
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 1
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
Reliability Report
Gives lifetime estimate
Assigns modular scores
Highlights “problem areas” on the board due to
thermal, vibration, and shock stresses
Identifies components with shortest estimated
lifetimes
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 1
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
Life Prediction Curve
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 1
John Whitehurst
Reliability Analysis and Testing
of Medical Devices ASTR 2013 Oct 9-11, San Diego, CA
Case Study 1
Vibration Analysis - Indicates components susceptible to
vibration
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
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
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 1
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
Circuit Board
HALT Testing
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 1
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
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
• Observe general error codes/flickering of display
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 1
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
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
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 1
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
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
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 1
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
Step 3 - MTBF Analysis
Ops A La Carte
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
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 1
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
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
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 1 Conclusions
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
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
ASTR 2013 Oct 9-11, San Diego, CA
Case Studies
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
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
Life testing during DVT to learn about reliability and
design weakness before manufacturing.
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 2
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
Mobile Power Unit - Design Reliability
Cable Flex Testing – 95/95
System Level Life Testing – 2 Years
Cycle Testing – 1460 Cycles
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 2
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
Cable Flex Testing
Reliability Target: 95/95
Pull Force: 31 Lbs.
Sample Size (Single Failure):
95
(reduced to 20 samples X5)
Raw Cable, Strain Relief &
Housing
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 2
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
System Level Life Testing
Reliability Target: 90/80 @ 2 years
Test Environment: 55C @ 846 Hrs
(Arrhenius model – 10.35 AF)
Sample Size (Single Failure): 30
Continuous Monitoring of outputs
(loaded)
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 2
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
Cycle Testing – Critical Features
Battery, AC Power & Alarm Cycled
Reliability Target: 90/80 @ 2 years (1460 Cycles)
Simulated power cycling, alarm activation & VAD connect
/ disconnect
Sample Size (Single Failure): 30
Continuous Monitoring of outputs
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 2
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
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
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 2 Conclusions
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
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
ASTR 2013 Oct 9-11, San Diego, CA
Case Studies
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
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
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 3
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
Electronic failure mechanisms include infant
mortality as well as wear out.
Environmental stress screens (ESS) can be used to
reduce infant mortality failures
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 3
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
What is ESS?
Use accelerated stress to detect latent faults
Vibration
Thermal Cycling
Power Cycling
Goal: find devices with latent faults prior to shipping
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 3
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
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
Case Study 3
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
Random Vibration
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 3
Board Level Assembly
& TestRI
Top Level Assembly,
Test & Calibration
Thermal/Power
Cycling
Final Inspection Shipping
Random Vibration
• Board Level Screen – Random Vibration
• Boards unpowered during vibration
• Functional test post vibration exposure
• Heavy burden – external testing
• Yielded few faults
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
Thermal/Power Cycling
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 3
System Level Screen – Thermal/Power
Cycling Units powered on/off during thermal cycling
Continuous monitoring
Lowest burden – in-house equipment
Cost effective screen
Board Level Assembly
& TestRI
Top Level Assembly,
Test & Calibration
Thermal/Power
Cycling
Final Inspection Shipping
Random Vibration
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
Thermal Cycling Profile
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 3
-60
-40
-20
0
20
40
60
80
100
0 1000 2000 3000 4000 5000 6000
Thermal Cycling
Thermal transition rates: 5C/min
Thermal limits: +80C & -40C
10 Minute dwell times
12 – 14 Thermal Cycles
Powered off at temperature extremes
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
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
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 3
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
System Qualification 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).
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 3
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
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
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 3
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
Screen Effectiveness / End
Of Life
Process monitoring
Number of thermal cycles
increased to 14
Analyzed life consumed –
Less than 1%
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 3
0 2 4 6 8 10 12
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
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)
ASTR 2013 Oct 9-11, San Diego, CA
Case Study 3 Conclusions
John Whitehurst
Reliability Analysis and Testing
of Medical Devices
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
Uncover faults not caught during board level
ASTR 2013 Oct 9-11, San Diego, CA
In Summary…
John Whitehurst
Reliability Analysis and Testing
of Medical Devices ASTR 2013 Oct 9-11, San Diego, CA
Questions/Comments?
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