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© 2004 – 2010 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
Introduction to
Design for Reliability (DfR) and
Design for Manufacturability
(DfM)
SMTA North Texas Chapter
November 4, 2016
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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
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o The foundation of a successful product is a robust design
o Provides margin
o Mitigates risk from defects
o Satisfies the customer
Why Design for Reliability (DfR)?
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When Do Mistakes Occur?
o Insufficient exchange of information between electrical
design and mechanical design
o Poor understanding of supplier limitations
o Customer expectations (reliability, lifetime, use
environment) are not incorporated into the new product
development (NPD) process
There can be many things that “you don’t
know you don’t know”
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List of DfR Tools and Techniques
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o Failure Mode Analysis
o Failure Mode Effect Analysis (FMEA), Fault Tree/Tolerance Analysis (FTA), Design Review by Failure Mode (DRBFM), Sneak Circuit Analysis (SCA)
o Reliability Prediction - Empirical
o Design Rules
o Design for Excellence
o Design for Manufacturability (DfM), Design for Testability (DfT)
o Tolerancing (Mechanical, Electrical)
o Simulation and Modeling (Stress)
o Thermal, Mechanical, Electrical/Circuit
o Simulation and Modeling (Damage)
o EMI/EMC, EOS/ESD, Physics of Failure, Derating
List of DfR Tools and Techniques
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o A process of identifying potential failure modes and
appropriate mitigations early in the design process
o Likely the most common DfR tool for reliability engineers
o These are generic DfR tools
o A Strength and Weakness
o Strength: Can provide amazing insight
o Weakness: Can be a boring, monotonous,
no-value, check-the-box activity
Failure Mode Analysis
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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 goals
o Use environment
o Dimensional constraints
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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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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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Electrical Environments
o Often very well defined in developed countries
o Introduction into developing countries can sometimes
cause surprises
o Rules of thumb
o China: Can have issues with grounding (connected to
rebar?)
o India: Numerous brownouts (several a day)
o Mexico: Voltage surges
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o Leader in surgical systems for eyecare
o Released latest system with foot pedal for ease of use
o Failed to realize how customers would use foot pedal
o Moving system across carpet without lifting up foot pedal created large static charges
o Using foot pedal to pull system caused cable/connector failures
Know Your Environment (Case Study)
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Thermal Environments (Case Study): 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
Te
mpe
ratu
re (
°C)
Container Temp (°C)
Outdoor Temp (°C)Temp.
Variation
Trucking
Container
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Dimensions
o Keep dimensions loose at this stage
o Large number of hardware mistakes driven by arbitrary size constraints
o Examples include poor interconnect strategies and poor choices in component selection
o Case study: Use of 0201 chip components
o Tight dimensional requirements push designer towards wholesale placement of 0201 components
o 0201 is not yet an appropriate technology for systems requiring reliability
o Result: Major issues at customers
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Part Selection
o The process of creating the bill of materials (BOM) during
the ‘virtual’ design process
o Before physical layout
o For some companies, this is during the creation of the
approved vendor list (AVL)
o Design-independent
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Part Selection (cont.)
o KIS: Keep it Simpleo New component technology can be very attractive
o Not always appropriate for high reliability embedded systems
o Be conservative
o Reality: Marketing hype FAR exceeds actual implementationo Component manufacturers typically use portable sales to boost
numbers
o Claim: We have built 100’s of millions of these components without a single return!
o Actuality: All sales were to two cell phone customers with lifetimes of 18 months
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Part Selection (cont.)
o Even when used by hi-rel companies, some modifications
may have been made
o Example: State-of-the-art crystal oscillator required specialized
assembly to avoid failures one to three years later in the field
o Prior examples of where care should have been taken
o New technologies: X5R dielectric, SiC diodes, etc.
o New packaging: Quad flat pack no lead (QFN), 0201, etc.
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Part Selection (cont.)
o As technology progresses, functional performance has
become a limited aspect of the part selection process
o Other concerns are increasingly taking center stage
o Moisture sensitivity level (MSL)
o Temperature sensitivity level (PSL)
o Electrostatic discharge (ESD) classification
o Manufacturability (Design for Assembly)
o Plating material
o Lifetime / Long-term reliability
o Sometimes Physics of Failure is required
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Critical Components
o Most small to mid-size organizations do not have the resources to
perform a thorough part selection assessment on every part
o Does not excuse performing this activity
o Requires focusing on components critical to the design
o Critical Components: A narrowed list of components of most concern to
the OEM
o Sensitivity of the circuit to component performance
o Number of components within the circuit
o Output from FMEA / FTA
o Past experiences
o Complexity of the component
o Industry-wide experiences
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o With recent improvements in model development (typically biggest time sink), there are few limitations to rapid and robust electrical/thermal/mechanical/reliability simulations of electronic products
o Simulation and modeling allows organizations to
o Obtain deeper insight earlier in the design process
o Quantify price vs. performance for supplier and material selection
o Iteration and optimization at minimal cost
o Avoid ‘opinioneering’
o Substitute or replace test requirement
o Accurately predict field performance
o Faster time to market
When to do Simulation and Modeling?
9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com21
o EDA → Sherlock →
Flotherm → Sherlock →
Prediction: 8 hours
Simulation & Modeling Case Study – Virtual Power Cycling
3D Sherlock Model Thermal Analysis Results
Lifetime Prediction
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DfR Conclusions
o To avoid design mistakes, be aware that functionality is only the beginning
o Mechanical and thermal are just as important as electrical
o Maximize knowledge of your design as early in the product development process as possible
o Be aware of industry best practices
o Do not overly rely on supplier statementso Their view: Reliability is application dependent
o Design rules are a good start, but not the way to win!
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o Design for Manufacturability
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Design for Manufacturing (DfM)
o Definition
o The process of ensuring a design can be consistently
manufactured by the designated supply chain with a
minimum number of defects
o Requirements
o An understanding of best practices (what fails during
manufacturing?)
o An understanding of the limitations of the supply chain
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Introduction to Design for Manufacturing (DfM)
o DfM is the process of proactively designing products to:
o Optimize all of the manufacturing functions: supplier selection and management, procurement, receiving, fabrication, assembly, quality control, operator training, shipping, delivery, service, and repair.
o Assure that critical objectives of cost, quality, reliability, regulatory compliance, safety, time-to-market, and customer satisfaction are known, balanced, monitored, and achieved.
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Introduction to Design for Manufacturing (DfM)
o Successful DFM efforts require the integration of
product design and process planning
o If existing processes are used, new products must be
designed to the parameters and limitations of these
processes regardless of whether the product is build
internally or externally.
o If new processes are used, then the product and
process need to be developed carefully
considering the risks associated with “new”
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Why DfM? (cont.)
Reduce Costs by Improving Manufacturability
Upfront
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Industry Standards – IPC, JEDEC, ISO…
o Start with industry standards where possible
o Tried and true
o But, represent only minimum acceptable requirements or concerns
o Modify and extend as needed to customize for your product and environments!
o Forums provide opportunities for free advice and feedback
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IPC Design Requirement/Guideline References
o IPC-2221- Generic Standard on Printed Board Design
o IPC-2221A is the foundation design standard for all documents in the IPC-2220 series. It establishes the generic requirements for the design of printed boards and other forms of component mounting or interconnecting structures, whether single-sided, double-sided or multilayer.
o 3 Performance Classes
o Class 1 General Electronic Products - consumer products,
o Class 2 Dedicated Service Electronic Products
o Communications equipment, sophisticated business machine, instruments and military equipment where high performance, extended life and uninterrupted service is desired but is not critical.
o Class 3 High Reliability Electronic Products
o Commercial, industrial and military products where continued performance or performance on demand is critical and where high levels of assurance are required...
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o Good quality is necessary but not SUFFICIENT to guarantee high reliability.
o IPC Class 3 by itself does not guarantee high reliabilityo A PCB or PCBA can be perfectly built to IPC Class 3 standards and still
be totally unreliable in its final application.
o Consider two different PCB laminates both built to IPC Class 3 standards.
o Both laminates are identical in all properties EXCEPT one laminate has a CTEz of 40 and the other has a CTEz of 60.
o The vias in the laminate with the lower CTEz will be MORE reliable in a long term, aggressive thermal cycling environment than the CTEz 60 laminate.
o A CTEz 40 laminate built to IPC class 2 could be MORE reliable than the CTEz 60 laminate built to Class 3.
o Appropriate materials selection for the environment is key!
A Word on Quality, Reliability & IPC Class 2 versus Class 3
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Common Types of DfM Review Processes
o Informal “Gut Check” Reviewo Performed by highly experienced engineers.
o Difficult with transition to original design
manufacturers (ODM) in developing countries.
o “Tribal knowledge”
o Formal Design reviewso Internal team
o External experts
o Automated (electronic) design
automation
(ADA) software o Modules automate DfM rule checking.
o Electronic manufacturing
service (EMS) providers o Perform DfM as a service
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Design for Manufacturing (DfM)
o Formal DfM Reviews and Tools Sometimes Overlooked
o Organization may lack specialized expertise.
o More design organizations completely removed from manufacturing.
o DfM Reviews Needs to be Performed for:
o Bare Board
o Circuit Board Assemblies
o Chassis/Housing Integration Packaging
o System Assembly
o DfM Needs to be conducted in conjunction with the actual electronic assembly source.
o What is good DfM for one supplier and one set of assembly equipment may not be good for another.
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Failure Analysis Techniques
� Returned parts failure analysis always starts with Non-Destructive
Evaluation (NDE)
� Designed to obtain maximum information with minimal risk of damaging
or destroying physical evidence
� Emphasize the use of simple tools first!
� (Generally) non-destructive techniques:
� Visual Inspection
� Electrical Characterization
� Time Domain Reflectometry (TDR)
� Acoustic Microscopy (SAM)
� X-ray Microscopy
� Thermal Imaging (Infra-red camera)
� Superconducting Quantum Interfering Device (SQUID) Microscopy
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Failure Analysis Techniques
o Destructive evaluation techniques
o Decapsulation
o Plasma etching
o Cross-sectioning
o Thermal imaging (liquid crystal; SQUID and IR also good after decap)
o SEM/EDX – Scanning Electron Microscope / Energy dispersive X-ray Spectroscopy
o Surface/depth profiling techniques: SIMS-Secondary Ion Mass Spectroscopy, Auger
o OBIC/EBIC
o FIB - Focused Ion Beam
o Mechanical testing: wire pull, wire shear, solder ball shear, die shear
o Other characterization methods
o FTIR- Fourier Transform Infra-Red Spectroscopy
o Ion chromatography
o DSC – Differential Scanning Calorimetry
o DMA/TMA – Thermo-mechanical analysis
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o Most critical step in the failure analysis process
o Can the reported failure mode be replicated?
o Persistent or intermittent?
o Intermittent failures often incorrectly diagnosed as no trouble found (NTF)
o Least utilized to its fullest extent
o Approach dependent upon the product
o Component
o Bare substrate
o PCB assembly
o Sometimes performed in combination with environmental exposure
o Characterization over specified/expected temperature range
o Characterization over specified / expected radiation range
o Humidity environment (re-introduction of moisture)
o Not intended to induce damage!
Electrical Characterization
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Robustness - Components
o Concerns
o Potential for latent defects after exposure to Pb-free reflow temperatures
o 215°C - 220°C peak → 240°C - 260°C peak
o Drivers
o Initial observations of deformed or damaged components
o Failure of component manufacturers to update specifications
o Components of particular interest
o Aluminum electrolytic capacitors
o Ceramic chip capacitors
o Surface mount connectors
o Specialty components (RF, optoelectronic, etc.)
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Ceramic Capacitors (Thermal Shock Cracks)
o Due to excessive change in temperature o Reflow, cleaning, wave solder, rework
o Inability of capacitor to relieve stresses during transient conditions.
o Maximum tensile stress occurs near end of termination o Determined through transient
thermal analyses
o Model results validated through sectioning of ceramic capacitors exposed to thermal shock conditions
o Three manifestationso Visually detectable (rare)
o Electrically detectable
o Microcrack (worst-case)
NAMICS
AVX
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o Tend to be overly focused on
drop, but excessive flexure
can occur at multiple points
post-assembly
Mechanical Shock Events
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Flex Cracking
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o Review/perform ICT strain evaluation at fixture mfg and in process: 500 us, IPC 9701 and 9704 specs, critical for QFN, CSP, and BGA
o http://www.rematek.com/download_center/board_stress_analysis.pdf
o To reduce the pressures exerted on a PCB, the first and simplest solution is to reduce the probes forces, when this is possible.
o Secondly, the positioning of the fingers/stoppers must be optimized to control the probe forces. But this is often very difficult to achieve. Mechanically, the stoppers must be located exactly under the pressure fingers to avoid the creation of shear points
ICT Strain: Fixture & Process Analysis
40
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o The most common method for PCB Panel Singulation is to use V-grooved
boards and a system as shown below to slice though the boards at the
grooves.
o If the PCBs in the panel are not properly supported, then mechanical
stress cracks can occur in MLCC capacitors.
What Can Cause Cracked Capacitors-Mechanical Stress?
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Aluminum Electrolytic Capacitors – Failure
Criteria
Capacitance Change Within +/- 20% of initial value
Dissipation Factor Not more than 200% of the specified value
Leakage Current Initial specific value or less
Failure criteria defined in manufacturer
datasheets.
Dissipation factor is proportional to equivalent
series resistance (ESR), so >200% increase in ESR is
classified as failed.
Increase in
leakage current
Increase in
dissipation factor
(ESR); Decrease in
capacitance
Detailed internal
construction of an Al ECap
from EPCOS.
9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com43
Apply rated
ripple and bias
at rated
temperature.
Oven and
ripple current
heating causes
electrolyte
evaporation.
Turn off
electricity and
cool to room
temperature.
Life Test – Traditional (& Accelerated: Rate of Weight Loss)
e-
e-
Measure ESR
Did ESR have a
>200%
increase from
the initial
value?
No. Continue
testing.
Yes. Testing
is complete.
e-
e-
Weight: 1.432 g
Weigh.
Electrical
characterization
.
PCB PCB PCB
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Life Test – Trends in Traditional Data
We
igh
t Lo
ss
Time (hours)40002000 30001000
Time (hours)40002000 30001000
%In
cre
ase
ES
R
200%
400%
600%
800%
VariableImpact on Rate
of Weight Loss
Ambient temperature
Applied ripple current
Heat dissipation
Space between bung and can
Linear throughout entire test
lifetime of an Al ECap population.Exponential behavior that is relatively
constant until approach time to failure.
Variable
Impact on
Critical Weight
Loss
Electrolyte stability
Initial ESR measurement
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1. Critical weight loss at 200% increase in ESR is calculated
using the ESR-Weight Loss curve
2. Rate of weight loss is extrapolated to the critical weight
loss and the corresponding time is recorded as the
accelerated test lifetime
Life Test– Accelerated Calculations
We
igh
t Lo
ss
Time (hours)40002000 30001000
Weight Loss
%In
cre
ase
ES
R
200%
400%
600%
800%
Critical weight loss
Critical weight loss
Accelerated test lifetime
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o Supplier ARate of Weight Loss ≈ ½ Supplier BRate of Weight Loss
o Supplier A capacitors have a better seal between the can and bung
Accelerated Life Test – Suppliers A & B Rate of Weight Loss
450 V, 68 µF
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Accelerated Life Test – Suppliers A & B Critical Weight Loss
450 V, 68 µF
o Supplier ACritical Weight Loss ≈ Supplier BCritical Weight Loss
o Chemical stability of Supplier A and Supplier B electrolyte is comparable
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o Accelerated life test results indicate that the Supplier A
Al ECap is more reliable than Supplier B
o This is opposite of what the datasheet lifetimes suggest
Accelerated Life Test – Suppliers A & B Comparison
Supplie
r
Minimum Accelerated
Lifetime (hours)
Maximum Accelerated
Lifetime (hours)
Datasheet
Lifetime (hours)
A 21,130 29,140 10,000
B 12,540 16,030 >15,000
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Peak Temperature Ratings
o AKA: ‘Temperature Sensitivity Level’ (TSL)
o Some component manufacturers are not
certifying their components to a peak temperature of
260ºC
o 260ºC is industry default for ‘worst-case’ peak
Pb-free reflow temperature
o Why lower than 260ºC?
o Industry specification
o Technology/Packaging limitation
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Moisture Sensitivity Level (MSL)
o Popcorning controlled through moisture sensitivity levels (MSL)
o Defined by IPC/JEDEC documents J-STD-020D.1 and J-STD-033B
o Higher profile in the industry due to transition to Pb-free and more aggressive packaging
o Higher die/package ratios
o Multiple die (i.e., stacked die)
o Larger components
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MSL: Typical Issues and Action Items
o Identify your maximum MSLo Driven by contract manufacturer
(CM) capability and OEM risk aversion
o Majority limit between MSL3 and MSL4 (survey of the MSD Council of SMTA, 2004)
o High volume, low mix: tends towards MSL4Low volume, high mix: tends towards MSL3
o Not all datasheets list MSLo Can be buried in reference or quality documents
o Ensure that listed MSL conforms to latest version of J-STD-020
Cogiscan
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Future of Contamination / Cleanliness
o Continued reductions in pitch between conductors will make future packaging more susceptible
o Increased use of leadless packages (QFN, land grid array, etc.) results in reduction in standoff
o Will reduce efficiency of cleaning, which may lead to increased concentration of contaminants
o Increased product sales into countries with polluted and tropical environments (East Asia, South Asia, etc.)
o ECM occurrence very sensitive to ambient humidity conditions
o Pb-Free and smaller bond pads
o Require more aggressive flux formulations
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Nominal Ionic Levels
o Bare printed circuit boards (PCBs)
o Chloride: 0.2 to 1 µg/inch2 (average of 0.5 to 1)
o Bromide: 1.0 to 5 µg/inch2 (average of 3 to 4)
o Assembled board (PCBA)
o Chloride: 0.2 to 1 µg/inch2 (average of 0.5 to 1)
o Bromide: 2.5 to 7 µg/inch2 (average of 5 to 7)
o Weak organic acids: 50 to 150 µg/inch2 (average of 120)
o Higher levels
o Corrosion/ECM issues at levels above 2 (typically 5 to 10)
o Corrosion/ECM issues at levels above 10 (typically 15 to 25)
o Corrosion/ECM issues at levels above 200 (typically 400)
o General rule
o Dependent upon board materials and complexity
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Reflow Profile Optimization
o Start with paste manufacturer’s recommendations!
o Preheating Phase - Ramp & Soak vs. Straight Ramp preheating profiles
o Ramp & Soak (soak period just below liquidus), more common, more
forgiving.
o Allow flux solvents to fully evaporate and activate to deoxidize the
surfaces to be soldered.
o Allows temperature equalization across the entire assembly.
o Consistent soldering and reduces tomb stoning.
o If too long, flux may be consumed resulting in excessive oxidation.
o Flux may become volatile - producing solder balls or voiding
defects.
o Straight Line is faster and causes less thermal damage to materials
o But more susceptible to defect and quality variation, does not work as
well on complex, dense assemblies.
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Reflow Profile Optimization
o Peak Temperature and Time at (above) Liquidus (TAL)
o A balance between being hot enough for long enough to achieve good
consistent solder wetting and bonding for proper joint formation, across
the entire assembly.
o Yet as quickly as possible to prevent thermal damage to the components
and board and to prevent excessive copper dissolution and excessive
intermetallic growth.
o Cooling Rate of SnAgCu effects the Microstructure & Bulk Intermetallics
o Faster cooling rates produce a finer, stronger microstructure and limits
intermetallics.
o Overall Time (Costs & Efficiency)
o Overall throughput is determined the board size/complexity and the
oven's heat transfer capabilities.
o Rule of Thumb: 2-3 C/second ramp up and down rate
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Summary
o DfM is a proven, cost-effective strategic methodology.
o Early effective cross functional involvement:
o Reduces overall product development time (less changes, spins, problem solving)
o Results in a smoother production launch.
o Speeds time to market.
o Reduces overall costs.
o Designed right the first time.
o Build right the first time = less rework, scrap, and warranty costs.
o Improved quality and reliability results in:
o Higher customer satisfaction.
o Reduced warranty costs.
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Contact Information
• Questions?
• Contact Greg Caswell, [email protected],
301-640-5825- office 443-834-9284 - cell
• www.dfrsolutions.com
• Connect with me in LinkedIn as well!
