Post on 04-Aug-2020
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Design For Reliability at the Board Level
Raytheon Women in Engineering Lunch and Learn
March 11, 2014
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o What are you doing today?
o Specs?
o Handbooks?
How is this working for you?
Today
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Insanity
Einstein’s Definition of Insanity:
Doing the same thing over and over and over and over again
And expecting different results
It is time to stop the insanity!
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What is Design for Reliability (DFR)?
o Reliability is the measure of a product’s ability to
o …perform the specified function
o …at the customer (with their use environment)
o …over the desired lifetime
o Design for Reliability is a process for ensuring the
reliability of a product or system during the design
stage before physical prototype
o Often part of an overall Design for Excellence (DfX)
strategy (DFM, DFT, DFR, DFS)
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Why DFR Now?
o Product Differentiation
o As electronic technology reaches maturity, there is less separation in traditional metrics of price and performance
o Ensuring reliability is becoming increasingly difficulto Increasing complexity of
electronic circuits
o Increasing power requirements
o Introduction of new component and material technologies
o Introduction of less robust components (COTS)
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Why DFR? Leverage in Design Cost Control
70% of a Product’s Total Cost is Committed by Design
http://www.ami.ac.uk/courses/topics/0248_dfx/index.html
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Reduce Costs by Improving
Reliability Upfront
Why DFR? Earlier is Cheaper
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Faster time to market
Why DFR? Faster Time to Market
P. Smith and D. Reinertsen. Developing Products In Half The Time (New York Van Nostrand Reinhold. 1991). 4.
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How DFR? Implementation
o Many organizations have developed DfR Teams to
speed implementation
o Success is dependent upon team composition and gating
functions
o Challenges: Classic design teams consist of
electrical and mechanical engineers trained in the
‘science of success’
o DFR requires the right elements of personnel and tools
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o Component engineer
o Physics of failure expert (mechanical / materials)
o Manufacturing engineer
o Box level (harness, wiring, board-to-board connections)
o Board / Assembly
o Engineer cognizant of environmental legislation
o Thermal engineer (depending upon power requirements)
o Reliability engineer?
o Depends. Many classic reliability engineers provide NO
value in the design process due to over-emphasis on
statistical techniques and environmental testing
How DFR? Team Members
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How DFR? Timeline
Goal: Simultaneously
optimizing the design
Reality: Need for specific gating
activities (design reviews)
Ramp Up
Launch
&
Production
Start-Up
Production
Gate 1
Idea
Submission
Project
Charter
Gate 2
Business
Plan
Gate 3
Update Plan
& AR
Gate 4
Final Check
Gate 5
Process
Audit
Gate 6
Market
Research
Design
&
Development
Concept
Development
& Project
Planning
Concept
Feasibility
Idea
Generation
FunctionalPerformance
Design forReliability
Design forManufacture
Design forSourcing
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DFR Outline
o DfR at Concept / Block-Diagram Stage
o Specifications
o Part selection
o Derating and uprating
o Design for Manufacturability
o Reliability is only as good as what you make
o Wearout mechanisms and physics of failure
o Predicting degradation in today’s electronics
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Design For Reliability
At Concept: Specifications
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Concept / Block Diagram
o Can DFR mistakes occur at this stage?
o No………..and Yes
o Failure to capture and understand product
specifications at this stage lays the groundwork for
mistakes at schematic and layout
o Important specifications to capture at concept stage
o Reliability expectations
o Use environment
o Dimensional constraints
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o Typical reliability metrics
o Desired Lifetime / Product Performance
o Desired lifetime
o Defined as when the customer will be satisfied
o Should be actively used in development of part and product qualification
o Product performance
o Returns during the warranty period
o Survivability over lifetime at a set confidence level
o Try to avoid MTBF or MTTF
Reliability Goals
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Why is Desired Lifetime Important?F
ailu
re R
ate
Time
Electronics: 1960s, 1970s, 1980s
No wearout!
Electronics: Today and the Future
Wearout!
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o Low-End Consumer Products (Toys, etc.)
o Do they ever work?
o Cell Phones: 18 to 36 months
o Laptop Computers: 24 to 36 months
o Desktop Computers: 24 to 60 months
o Medical (External): 5 to 10 years
o Medical (Internal): 7 years
o High-End Servers: 7 to 10 years
o Industrial Controls: 7 to 15 years
o Appliances: 7 to 15 years
o Automotive: 10 to 15 years (warranty)
o Avionics (Civil): 10 to 20 years
o Avionics (Military): 10 to 30 years
o Telecommunications: 10 to 30 years
Desired Lifetime: Examples
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Product Performance: Warranty Returns
o Consumer Electronics
o Table on right
o Low Volume, Non Hi-Rel
o 1 to 2%
o Industrial Controls
o 500 to 2000 ppm (1st Year)
o Depends on complexity, production volumes, and risk sensitivity
o Automotive
o 1 to 5% (Electrical, 1st Year)
o Can also be reported as problems per 100 vehicles
ProductRepair rate (%)
[First 3 Yrs]
Desktop PC 37
Laptop PC 33
Refrigerator: side-by-side (with icemaker and
dispenser) 28
Washing machine 22
Refrigerator: top- and bottom-freezer (with icemaker) 17
Projection TV 16
Vacuum cleaner (excluding belt replacement) 13
Dishwasher 13
Clothes dryer 13
Microwave oven (over-the-range) 12
Electric range 11
Camcorder 8
Digital camera 8
Refrigerator: top- and bottom-freezer (without
icemaker) 8
TV: 30- to 36-inch 7
TV: 25- to 27-inch 5
Consumer Reports 2006
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Product Performance: Survivability
o Some companies set reliability goals based on survivabilityo Often bounded by confidence levels
o Example: 95% reliability with 90% confidence over 15 years
o Advantageso Helps set bounds on test time and sample size
o Does not assume a failure rate behavior (decreasing, increasing, steady-state)
o Disadvantageso Can be re-interpreted through mean time to failure (MTTF) or
mean time between failures (MTBF)
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Limitations of MTTF/MTBF
o MTBF/MTTF calculations tend to assume that failures are random in nature
o Provides no motivation for failure avoidance
o Easy to manipulate numbers
o Tweaks are made to reach desired MTBF
o E.g., quality factors for each component are modified
o Often misinterpreted
o 50K hour MTBF does not mean no failures in 50K hours
o Better fit towards logistics and procurement, not failure avoidance
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Identify Field Environment
o Approach 1: Use of standards
o MIL-STD-810,
o MIL-HDBK-310,
o SAE J1211,
o IPC-SM-785,
o Telcordia GR3108,
o IEC 60721-3, etc.
o Advantages
o No additional cost!
o Sometimes very comprehensive
o Agreement throughout the industry
o Missing information? Consider standards from other industries
o Disadvantages
o Most more than 20 years old
o Always less or greater than actual (by how much, unknown) IPC SM785
MIL HDBK310
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Field Environment (cont.)
o Approach 2: Based on actual measurements of similar products in similar environments
o Determine average and realistic worst-case
o Identify all failure-inducing loads
o Include all environments
o Manufacturing
o Transportation
o Storage
o Field
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Failure Inducing Loads
• Temperature Cycling
– Tmax, Tmin, dwell, ramp times
• Sustained Temperature
– T and exposure time
• Humidity
– Controlled, condensation
• Corrosion
– Salt, corrosive gases (Cl2, etc.)
• Power cycling
– Duty cycles, power dissipation
• Electrical Loads
– Voltage, current, current density
– Static and transient
• Electrical Noise
• Mechanical Bending (Static and Cyclic)
– Board-level strain
• Random Vibration
– PSD, exposure time, kurtosis
• Harmonic Vibration
– G and frequency
• Mechanical shock
– G, wave form, # of events
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Field Environment (Best Practice)
o Use standards when…
o Certain aspects of your environment are common
o No access to use environment
o Measure when…
o Certain aspects of your environment are unique
o Strong relationship with customer
o Do not mistake test specifications for the actual use
environment
o Common mistake with vibration loads
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Temperature: USA Worst-Case (Ambient)
TemperatureAvg. U.S.
CLIM Data
Avg. U.S.
Weighted by Registration
(Source: Confidential)
Phoenix
(hrs/yr)
U.S.
Worst Case
(hrs/yr)
95F (35C) 0.375% 0.650% 11% (948) 13% (1,140)
105F (40.46C) 0.087% 0.050% 2.3% (198) 3.8% (331)
115F (46.11C) 0.008% 0.001% 0.02% (1.4) 0.1% (9)
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Temperature: Closed Containers
Container and Ambient Temperature
15.0
25.0
35.0
45.0
55.0
65.0
75.0
0 50 100 150 200 250 300 350 400 450
Hours
Tem
pe
ratu
re (
°C)
Container Temp (°C)
Outdoor Temp (°C)
Temp.
Variation
Trucking
Container
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Dimensions
o Keep dimensions loose at this stageo Large number of hardware mistakes driven by arbitrary size
constraintso Examples include poor interconnect strategies and poor
choices in component selection
o Case study: Use of 0201 chip componentso Tight dimensional requirements push designer towards
wholesale placement of 0201 componentso 0201 is not yet an appropriate technology for systems
requiring reliabilityo Result: Major issues at customers
o Use the Toyota approacho Except with sudden acceleration
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Toyota Approach
o Western engineers o Define several product concepts
o Select the one that has the most promise
o Draw up specifications and divide them into subsystems;
o Subsystems are designed, built and rolled up for system testing.
o Failures? Rework the specs and the designs accordingly (non-optimized and confusing endeavor)
o Toyota engineerso Efforts concentrated at lowest
possible design level
o Thorough understanding of the technology of a subsystem so it can be used appropriately in future designs
Toyota's development engineers have been4X as productive as U.S. counterparts.
Why?
Focus on learning as much as possible
Use of that knowledge to develop a stream of excellent products
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Toyota Example: Radiators
o Traditional approach: Design radiator for a specific vehicle based on mechanical specifications written for that vehicle
o Toyota approach: considers a range of radiator solutions based on cooling capacities and the cooling demands of various engines that might be used.
o How the radiator actually fits into a vehicle would be kept loose so that Toyota's knowledge of radiator technology could be used to create the optimum design
o Toyota's system is "test & design" rather than the traditional "design & test."
o Toyota engineers test at the fundamental knowledge level so they don't have to test at the later, more expensive stages of design and prototyping
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Traditional NPI Cycle
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NPI Cycle Using PoF Modeling
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o DfR Solutions: Leverages the knowledge and understanding of the processes and mechanisms that induce failure to predict reliability and improve product performance
o Army: An engineering-based approach to reliability that uses modeling and simulation to eliminate failures early in the design process by addressing root-cause failure mechanisms in a Computer-Aided- Engineering environment
o NASA-JPL: Modeling of failure mechanisms, based on science/engineering first principles, that support deterministic or probabilistic predictions of reliability and provide a scientific basis for determining the effectiveness of screens or inspections
What is Physics of Failure (PoF)?
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Physics of Failure (PoF) Modeling Dates back to 1960’s
211
2
2
1 11exp
TTK
E
V
V
t
t
B
a
n
)%063.0exp(~51.0~
exp RHkT
eVT f
aGGA
h
GA
h
AE
L
AE
LFLT
bcc
c
ss
s
9
2
221112
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Physics of Failure (cont.)
o Reliability is the measure of a product’s ability to
o …perform the specified function
o …at the customer (with their use environment)
o …over the desired lifetime
o Physics of failure therefore requires an understanding of
the design, desired lifetime and use environment
o Design: Architecture + Materials
o Desired lifetime: When the customer will be satisfied
o Use environment: Must include assembly, transportation,
storage, operation
o Translation: PoF takes more effort
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o What is susceptible to long-term degradation in electronic designs?
o Ceramic Capacitors (oxygen vacancy migration)
o Integrated Circuits (EM, TDDB, HCI, NBTI)
o Memory Devices (limited write cycles, read times)
o Electrolytic Capacitors (electrolyte evaporation)
o Resistors (if improperly derated)
o Silver-Based Platings (if exposed to corrosive environments)
o Relays and other Electromechanical Components
o Light Emitting Diodes (LEDs) and Laser Diodes
o Connectors (stress relaxation)
o Tin Whiskers
o Interconnects (Creep, Fatigue)
o Plated through holes
o Solder joints
PoF and Wearout
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Wearout Example – Integrated Circuits (ICs)
1995 2005 2015
0.1
1.0
10
100
1000
Year produced
Known trends for TDDB, EM and HCI degradation
(ref: extrapolated from ITRS roadmap)
Mean
Service
life, yrs.Computers
laptop/palm
cell phones
Airplanes
0.5 mm 0.25 mm 130 nm 65 nm 35 nm
Process Variability
confidence bounds
Technology
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o The majority of electronic failures are thermo-
mechanically related*
o By thermally induced stresses and strains
o Root caused to excessive differences in coefficient of
thermal expansion
Desired Lifetime (Solder Wearout)
*Wunderle, B. and B. Michel, “Progress
in Reliability Research in Micro and
Nano Region”, Microelectronics and
Reliability, V46, Issue 9-11, 2006.
A. MacDiarmid, “Thermal Cycling Failures”, RIAC Journal,
Jan., 2011.
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o JEDEC JESD47 Guidelines for Component Qualification
o Requires 2300 cycles of 0 to 100C
o Testing often done on thin (down to 20 mil / 0.5 mm) coupons
o Testing on a thin coupons can extend lifetimes by
2X to 4X
o Current components may only survive
500 cycles of 0 to 100C
o This is less than 10% of the 6000
cycles recommended by IPC-9701
Industry Response to Solder Wearout?
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PoF Example: Solder Joint (SJ) Wearout
o Elimination of leaded devices
o Provides lower RC and higher package densities
o Reduced compliance
Cycles to failure
-40 to 125C QFP: >10,000 BGA: 3,000 to 8,000
QFN: 1,000 to 3,000CSP / Flip Chip: <1,000
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PoF Example: SnAgCu Life Model
o Modified Engelmaier
o Semi-empirical analytical approach
o Energy based fatigue
o Determine the strain range (g)
o C is a correction factor that is a function of dwell time
and temperature, LD is diagonal distance, is CTE, T
is temperature cycle, h is solder joint height
Th
LC
s
D g
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PoF Example – SAC Model (cont.)
o Determine the shear force applied to the solder joint
o F is shear force, L is length, E is elastic modulus, A is the area,
h is thickness, G is shear modulus, and a is edge length of
bond pad
o Subscripts: 1 is component, 2 is board, s is solder joint, c is
bond pad, and b is board
o Takes into consideration foundation stiffness and both
shear and axial loads
aGGA
h
GA
h
AE
L
AE
LFLT
bcc
c
ss
s
9
2
221112
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PoF Example – SAC Model (cont.)
o Determine the strain energy dissipated by the
solder joint
o Calculate cycles-to-failure (N50), using energy
based fatigue models for SAC developed by
Syed – Amkor
10019.0
WN f
sA
FW g5.0
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Validation – Chip Resistors
100
1000
10000
100 1000 10000
Cycles to Failure (Experimental)
Cy
cle
s t
o F
ailu
re (
Pre
dic
ted
)
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PoF Example – SAC Reliability (cont.)
o How to ensure 10 year life in a realistic
worst-case field environment for
industrial controls?
o American Southwest (Phoenix)
o Dominated by diurnal cycling
Month Cycles/Year Ramp Dwell Max. Temp (oC) Min. Temp. (
oC)
Jan.+Feb.+Dec. 90 6 hrs 6 hrs 20 5
March+November 60 6 hrs 6 hrs 25 10
April+October 60 6 hrs 6 hrs 30 15
May+September 60 6 hrs 6 hrs 35 20
June+July+August 90 6 hrs 6 hrs 40 25
+10C at max temperature due to solar loading
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PoF Example – SAC Reliability (cont.)
o Total damage in desert environment
over 10 years
o Total damage in one cycle of -40C to
85C test environment
o Total cycles at -40C to 85C to
replicate 10 yrs in desert
0.02604
0.00012
222 cycles
At 1 cycle/hour, approximately 1 day of test equals 1 year in the field
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PoF-Based Analysis a Reality?
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Results
47
Constant Failure Rate
Generic Actuarial MTBF Database
PTH Thermal
Cycling Fatigue
Wear Out
Thermal
Cycling
Solder
Fatigue
Wear Out
Vibration
Fatigue
Wear Out
Over All
Module
Combined
Risk
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Summary DFR at the Board Level
o To avoid design mistakes, be aware that functionality
is just the beginning
o Be aware of industry best practices
o Maximize knowledge of your design as early in the
product development process as possible
o Practice design for excellence (DfX)
o Design for Manufacturability
o Design for Test
o Design for Reliability
o Design for Sustainability
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Questions??Discussion
Tom O’Connor, DfR Solutions
301-640-5812
toconnor@dfrsolutions.com