Design for Reliability - SMTA
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Design for Affordability How to design for reliability and the importance and cost benefits of designing in reliability early in the life cycle. SMTA Nutmeg Chapter Tech Expo Walter Tomczykowski November 16, 2011
Transcript of Design for Reliability - SMTA
Design for Affordability How to design for reliability and the importance and cost benefits of designing in reliability early in the life cycle. SMTA Nutmeg Chapter Tech Expo Walter Tomczykowski
November 16, 2011
© 2004 - 2007 © 2004 - 2010
Outline
o How is Design for Affordability (DfA) defined?
o Design for Affordability Enablers
o Design for Reliability
o Design for Manufacturability
o Design for Supportability
o Summary
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© 2004 - 2007 © 2004 - 2010
Reduce Costs by Improving
Reliability Upfront
Design Costs
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o Traditional OEMs
spend almost 75%
of product development
costs on test-fail-fix
o Electronic OEMs that use design analysis tools shorten
or eliminate this feedback loop
o Hit development costs 82% more frequently
o Average 66% fewer re-spins
o Save up to $26,000 in re-spins
Gene Allen and Rick Jarman .Collaborative R&D; (New York John Wiley&Sons. Inc. 1999). 17.
Aberdeen Group, Printed Circuit Board Design Integrity: The Key to Successful PCB Development, 2007 http://new.marketwire.com/2.0/rel.jsp?id=730231
Design Costs
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Why DfA? Total Costs are Determined During Design
95% of the O&S Cost Drivers are Based on Decisions Made during Design.
Source: Architectural Design for Reliability, R. Cranwell and R. Hunter, Sandia Labs, 1997
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Timeline
Implement “Design for” Early
Simultaneously optimize the design
Conduct gating activities (design reviews)
Functional Performance
Design for Reliability
Design for Manufacture
Design for Supportability
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o The decisions made during the design and development process greatly influence the ultimate life cycle costs experienced by end users.
o DfR Solutions defines Design for Affordability as a comprehensive design strategy that includes: o Design for Reliability (DfR)
o Design for Manufacturability (DfM)
o Design for Supportability (DfS)
o DfA = 𝐷𝑓𝑅 + 𝐷𝑓𝑀 + 𝐷𝑓𝑆𝑀𝑖𝑙𝑒𝑠𝑡𝑜𝑛𝑒 𝐶
𝑀𝑖𝑙𝑒𝑠𝑡𝑜𝑛𝑒 𝐴
o = Optimized Total Ownership Cost
Design for Affordability (DfA)
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Optimized Total Ownership Cost ???
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Design for Reliability (DfR)
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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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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 engineers o 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 been 4X 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 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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o Growing complexity and vehicle electrification prompting a major change in design processes.
o Intense competitive pressure to improve efficiency & effectiveness to shortened development cycles and reduce costs.
o The combination of physical and virtual testing accelerates the product development process by early identification of deficiencies.
o Physics based models makes it easier to try out new designs, since evaluations can be performed without building physical prototypes.
o Simulations can be created and run in far less time & cost than building and testing physical prototype, models can than be quickly revised to evaluation alternative configurations and option content.
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Why the Automotive Industry Is Using More Virtual Computer Aided Engineering Methods
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Computer Aided Engineering Advancement Have Enabled
Reduced Dependence on Costly Physical D-B-T-F Testing.
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By 2004 GM was able to reduce vehicle road testing to the point that the southern portion of their
Mesa Az. Proving Grounds was sold. In 2006 the remaining northern 5 square miles, that formerly
operated with 1,200 people, was sold for Real Estate Development.
GM now operates with a much smaller DPG in Yuma Az.
and realized a significant reduction in structural costs.
Test CAE-M&S
As the use of CAE based
modeling & simulation methods
increase, dependence on physical
testing can be reduced and
refocused.
© 2004 - 2007 © 2004 - 2010
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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Why is Desired Lifetime Important? F
ail
ure
Rate
Time
Electronics: 1960s, 1970s, 1980s
No wearout!
Electronics: Today and the Future
Wearout!
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o Manufacturer of network switches
wanted to understand potential costs of
switch from 3-yr warranty to
lifetime warranty
o Identified components that could experience wearout
o Fans, electrolytic capacitors, integrated circuits, solder joints, plated through
holes, ceramic capacitors, connectors, LEDs, overstressed components
o Performed circuit/thermal analysis to identify overstressed components
o Especially based on usage model (validated through internal DfR testing)
o Predicted reliability for each component based on validated algorithms
o Primarily conducted through Sherlock™
o Conducted component testing when necessary
Design Review: Network Switch
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o What is susceptible to long-term degradation in electronic designs?
o Ceramic Capacitors (oxygen vacancy migration)
o Integrated Circuits
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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© 2004 - 2007 © 2004 - 2010
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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“Let’s Use a COTS Board as a Solution”
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Know the Use 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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o Catastrophic damage to IGBT Module
o Used knowledge of electrical function to trace damage path
o Developed multiple theories, including defective wirebonding
o Identified root-cause as current inbalance at elevated temperatures
Failure Analysis of High Power DC-AC Power Inverter
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How to Implement DfR?
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 Systems Engineer
o Engineer cognizant of environmental legislation
o Thermal engineer (depending upon power requirements)
o Reliability engineer
o Understanding of design guidelines, physics of failure,
and systems lifecycle engineering experience
What Team Members are Needed for DfR?
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DfR Overview
o DfR at Concept / Block-Diagram Stage
o Specifications
o Part (Vendor) selection
o Benchmarking
o Derating and uprating
o Wearout mechanisms and physics of failure
o Predicting degradation in today’s electronics
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Concept / Block Diagram
o Can DfR mistakes occur at this stage?
o Failure to capture and understand product specifications at this stage lays the groundwork for future development mistakes
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 To mitigate misinterpretation, try to avoid MTBF or MTTF and focus on Annualized Failure Rate (AFR)
Reliability Goals
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Product Performance: Survivability
o Some companies set reliability goals based on survivability o Often bounded by confidence levels
o Example: 95% reliability with 90% confidence over 15 years
o Advantages o Helps set bounds on test time and sample size
o Does not assume a failure rate behavior (decreasing, increasing, steady-state)
o Disadvantages o 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 predictions
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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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 Simple o New component technology can be very attractive
o Not always appropriate for high reliability systems
o Be conservative
o Reality: Marketing hype far exceeds actual implementation o 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.
o Critical actions for part selection include critical
component identification and derating
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Component Ratings
o Definition
o A specification provided by
component manufacturers that
guides the user as to the
appropriate range of stresses
over which the component is
guaranteed to function
o Typical parameters
o Voltage
o Current
o Power
o Temperature
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o Derating is the practice of limiting stress on electronic parts to levels below the manufacturer’s specified ratings
o Guidelines can vary based upon environment (“severe, protected, normal” or “space, aircraft, ground”)
o One of the most common design for reliability (DfR) methods
o Goals of derating
o Maintain critical parameters during operation (i.e., functionality)
o Provide a margin of safety from deviant lots
o Achieve desired operating life (i.e., reliability)
o Sources of derating guidelines
o Governmental organizations and 3rd parties
o OEM’s
o Component manufacturers
o Derating is assessed through component stress analysis
Derating
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o Failure to perform component stress analysis can
result in higher warranty costs, potential recalls
o Eventual costs can be in the millions of dollars
o Perspective from Chief Technologist at major
Original Design Manufacturer (ODM)
Criticality of Component Stress Analysis
“…based on our experience, we believe a
significant number of field returns, and the majority
of no-trouble-founds (NTFs), are related to
overstressed components.”
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“Let’s Use a COTS Board as a Solution”
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Define Reliability Goals
o Compatible with wide variety of reliability metrics
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Specify Environments
o Handles very complex environments
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Input Design Files
o Takes standard output files (Gerber / ODB)
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“Let’s Use a COTS Board as a Solution”
o Know the actual use (operating) environment
o Temperature
o Vibration
o Power
o Humidity
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PoF Vibration Results
Random Vibration Strain
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PoF Vibration Results
Random Vibration Strain
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Mount Point Added to Same COTS Board
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o Demonstrated to avionics customer that transition to Pb-free
would have a detrimental impact to product performance
o Driven by severe use environment
Case Study: Pb-Free Transition
SnPb Assembly SAC305 Assembly
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Design for Manufacturability (DfM)
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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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DfM Failures
o DfM is often overlooked in the design process
o Reasons
o Design team often has poor insight into supply chain
o OEM requests no feedback on DfM from supply chain
o DfM feedback consists of standard rule checks (no insight)
o DfM activities at the OEM are not standardized or distributed
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Criticality of DfM
o Failure to perform DfM increases the risk of a
defective product or lot reaching the end customer
o Warranty costs can be significant
o Perspective from a major Original Equipment
Manufacturer (OEM)
…we must fully address DfM <sic> to assure
successful product launches and continuing
volume production with acceptably low defect
levels.
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DfM Failures
o DfM is often overlooked in the design process
o Reasons
o Design team often has poor insight into supply chain (reverse
auction, anyone?)
o OEM requests no feedback on DfM from supply chain
o DfM feedback consists of standard rule checks (no insight)
o DfM activities at the OEM are not standardized or distributed
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Key Aspects of DfM
o Proactive
o Considers and optimizes all manufacturing functions
o Supplier selection and management, procurement, receiving,
fabrication, assembly, quality control, operator training, shipping,
delivery, service, and repair
o Assures that critical objectives are known, balanced,
monitored, and achieved
o Cost, quality, reliability, regulatory compliance, safety,
time-to-market, and customer satisfaction
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How to Implement DfM
o Successful DFM efforts require integration of product
design and process planning
o If existing processes are used, new products must be designed to
parameters and limitations of these processes (whether build is
internal or external)
o If new processes, then product and process need to be developed
concurrently and mindfully (carefully considering the risks
associated with “new”)
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Old Style Product Development - “Sequential Over The Wall”
o Before DfM, it was “We designed it” ~ “You build it!”
o Design engineers worked independently, then transferred designs “Over the Wall” to the next department or external to the company (CM).
o Eventually manufacturing has to assemble the product.
o Usually inherit a product not designed for their processes and too late to make changes.
o Manufacturing forced struggle to meet yield, quality, cost or delivery targets.
o Often required trial & error crisis management
o Followed by launch delays, then quality and reliability issues.
R & D
PRODUCT
ENRG. MANUF./
ASSEMBLY
DEALERS
DISTRIBUTORS
SERVICE
VALIDATION
TESTING
Requires 4.5 - 5
CHAMBER
Stress
Feedback Loops
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Case Study: No DfM
o Aerospace company o Two divisions
o Division A o PCB manufacturer is a top supplier.
o Division B o Wanted to blacklist the same
PCB manufacturer.
o On-site audit found no major process issues.
o Root-cause: No prior DfM engagement with supplier in Division B o Resulted in numerous
field issues.
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Key DfM Guidelines
o Foundation of a robust DfM system is a set of design guidelines and tasks
o Guidelines need to be customized to company’s culture, products, technologies and based on a solid understanding of the intended production system – whether internal or external
o “Top 10” DfM guidelines and tasks that are applicable to most companies
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“Top 10 DfM Guidelines”
1. Know Your History (Learn from the Past)
2. Standardize Design Methods
3. Simplify the Design – Parts Reduction
4. Design for Lean Processes
5. Eliminate Waste
6. Design for Parts Handling
7. Design for Joining and Fastening
8. Use Error Proofing Techniques
9. Design for Process Capabilities
10. Design for Test, Repair, and Serviceability
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DfM Guideline #1: Know Your History
“Those who do not learn from history are doomed to repeat it.”
o Learn from the past o Process Yields, Returns, Corrective Actions, Recalls, etc.
o Develop and implement strategies to address and prevent recurrence of mistakes.
o Know and understand all problems and issues with current and past products with respect to: o Manufacturability / Delivery / Quality / Repairability / Regulatory / Recalls
o Especially critical if carrying over existing technologies into new designs.
o Best approach is to have an effective system for capturing and disseminating this historical knowledge throughout the organization (e.g., FRACAS)
o At minimum, initiate brain storming sessions (post-mortems) to collect lessons learned/best practices from all areas of the organization.
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DfM #2: Standardize Design Methods
o Standardize design, procurement, processes, assembly, equipment throughout organization
o Reduces overall cycle time.
o Simplifies training and tasks.
o Reduces repeated mistakes
o Improves opportunity for bulk discounts.
o Improves opportunity for automation and operation standardization.
o Don’t Redesign the Wheel
o Never custom design when you can buy off the shelf.
o Limit exotic or unique components.
o Higher prices due to low volumes and less supplier competition.
o Lower quality for exotic components.
o More opportunity for supply chain disruptions.
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DfM: Summary
o DfM is a process
o Earlier is always better
o Should be discussed at concept stage
o E.g.: Interconnect strategy (backplane vs. tiering vs. single board)
o Always be aware of the tradeoffs
o DfM vs. DfR vs. DfS (or DfT – test)
o Communication and knowledge are the core of DfM
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Design for Supportability (DfS)
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Design for Supportability
o The best design is not only reliable and
manufacturable, products must also be Designed for
Supportability (DfS).
o Designing products to be both reliable and
supportable is a critical step in the process one that
must be addressed if customers or end users have
repairable systems or products
o Completes the DfA equation: DfR + DfM + DfS
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“Top Ten DfS Logistics Design Elements”
o Baseline life cycle cost (estimated total ownership cost)
o Use environment verification
o Corrosion protection and mitigation
o Supplier benchmarking and vendor maturity and stability
o Maintenance planning, procedures, and real-time data collection, warrantees
o Prognostics and diagnostics
o Readiness based spares
o Open systems architecture, modular design, software re-use (includes overall design re-use)
o Technology refresh
o Obsolescence management (planning ahead)
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o Obsolescence management is a key driver
that also mitigates the risk of counterfeit parts.
o Best practices and lessons learned are well
documented.
o Planning ahead is key
o Left unchecked obsolescence will increase support
costs (and also developmement and production
costs)
o The First “M” in Diminishing Manufacturing Sources
and Material Shortages (Remember DfM)
Obsolescence Management
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o Automotive customer
evaluated replacement parts
o PoF modeling identifies risk of replacement before
prototype. Modified design accordingly
Design Change due to Obsolescence (DfS + DfR + DfM)
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Summary: DfA = integration of DfR + DfM+ DfS
o Practice design for excellence (DfX) to optimize affordability
o Design for reliability
o Design for manufacturability
o Design for supportability
o Use Automated Design Analysis
o Facilitates collaboration
o Implement tools and processes that allow in-depth assessment at
earliest stages in acquisition
o Remember the first “M” in DMSMS and practice DfM
o Know the quality and manufacturing of your suppliers
o Know your suppliers (mitigate risk of counterfeit)
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“Let’s Use a COTS Board as a Solution”
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With DfA = What Happens to Optimized Total Ownership Cost?
?
?
?
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Backup
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DfM #3: Simplify the Design - Parts Reduction
o Parts reduction is one of the best ways to reduce the cost of fabricating and assembling a product and increase quality and reliability. o Reduces parts costs.
o Reduces direct labor costs.
o Reduces process equipment.
o Reduces number or workstations.
o Fewer opportunities for defective parts.
o Fewer opportunities for assembly errors.
Everything should be made as simple as possible, but not one bit
simpler. - Albert Einstein
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DfM #3: Parts Reduction (cont.)
o Can also reduce structural costs. o Fewer parts rippling through the organization reduces the work
load for every department at every level.
o Fewer items to be processed by: o Product Development
o Engineering, Purchasing, Development/Test Labs.
o Manufacturing Support
o Inventory Warehousing, Material Handling, Service Parts.
o Quality Management.
o Manufacturing facilities
o Facility Size, Equipment, Processing/Assembly Time & Labor
o Provides more opportunities for process automation.
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DfM #3: Methods for Parts Reduction
o Method 1: Parts Commonality via Multi-Use/Multi-Functional Parts
o Develop an approved vendor list (AVL), aka preferred parts lists or standardized bill of materials (S-BOM), to encourage different products lines to share common parts.
o Designer CAD/CAE systems can be configured to access preferred designs and parts catalogs.
o Use of one-piece structures
o From injection molding, extrusions, castings and powder metals or similar fabrication techniques instead of bolt/glue together multi part assemblies.
o Establish part families of similar parts based on proven materials, architecture and technologies that are scaled for size or functionality
o Use multi-functional parts:
o An electric conductor that also serves as a structural member,
o A cover or base plate that also serves as a heat sink
o Incorporate guiding, aligning, or self-fixturing features into housing and structures.
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DfM #3: Methods for Parts Reduction
o Method 2: Modular design.
o Can push DfM issues farther down the supply chain
o Use complete modules and subassemblies, instead of designing, fabricating and assembling everything yourself or on one platform
o Advantages o Manufactured and tested before final assembly.
o Facilitate the use of standard components to minimize product variations.
o Add flexibility to product update in the redesign process
o Mitigates obsolescence risks
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DfM #4: Design for Lean Processes
Fundamental Principle of Lean
Anything that does not add value to
the product is waste and must be
reduced or eliminated
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DfM #4: Design for Lean Processes
o Lean supply, fabrication and assembly processes are
essential design considerations.
o Simple lean fabrication/processing/assembly is more likely to
be done quickly and correctly
o Right part at the right station at the right time
o Reduced throughput time equals faster time to market and
lower costs (reduced labor hours and faster turns).
o Designs that are easy to assemble manually will be more
easily automated.
o Assembly that is automated will be more uniform, more
reliable, and of higher quality.
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DfM #4: Design for Lean (cont.)
o Develop and use standard guidelines appropriate for the process: o Common hole sizes, lines, and spacings o Standard soldering temperature profiles o Standard handling (e.g., avoid MSL > 3 components)
o For assembly - design for human factors – the “Visual” Factory o Allow for visual, audio and/or tactile feedback to ensure correct assembly
operations. o Makes it obvious to follow the correct process flow. o Bottlenecks and problems are more easily identified
o Provide adequate access clearances for tools and hands.
o Design in self aligning and self guiding features such as tapered parts, guide pins or groves.
o Design work to use standard tools and settings: crimpers, splicers, cutters, solder iron tips, drill bit sizes, torque settings, wire sizes o Minimizes tool clutter and decision making on what to use
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DfM #5: Eliminate Waste
o Seven Types of Waste 1. Overproduction
Build more than required, before required.
2. Waiting
Stop build to look for parts, tools, material, information
3. Transportation/Moving
Moving material, parts, tooling
Transferring product between locations, into/out of racks
4. Process Inefficiencies
Unnecessary operations, too many inspections, not building to customer spec
5. Inventories/Storage
Excess raw material, excess WIP
6. Unnecessary Motions
Walking, climbing, bending, searching, identifying
7. Defective products
Low Yields, mistakes leading to large reworks, sorting, inspection
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DfM #6: Design for Parts Handling
o Minimize handling to correctly position, orient, and place parts and avoid multiple or complex assembly orientations.
o Use symmetrical parts. o When non-symmetrical parts are needed, use keying features
to ensure proper orientation. o Make orienting and mating parts as visually obvious as possible.
o Use parts oriented in magazines, tape, reels or strips or use parts designed to consistently orient themselves when fed into a process
o Reduce and avoid parts that can be easily damaged, bent, or broken.
o Parts should be designed with surfaces that can be grasped, placed or fixtured. o Reduces the need for temporary fastening and complex fixtures.
o Begin assembly with a large base component with a low center of gravity. Assembly should proceed vertically with other parts added on top o Exception: avoid upward orientation of debris /contamination sensitive features. o Prevent dust or moisture from falling into electrical, hydraulic, pneumatic connector or lines
o Use appropriate and safe packaging for parts but minimize the creation of waste
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DfM #7: Design for Joining & Fastening
o Design for efficient joining and fastening.
o Fasteners increase the cost of manufacturing, handling and feeding operations.
o Screws, bolts, nuts and washers are time-consuming to assemble & difficult to automate.
o Increased potential for defects (missing and improper assembly).
o Avoid threaded fasteners when possible, consider alternative,
o Consider the use of snap-fit.
o Evaluate adhesive bonding techniques.
o Where fasteners used, minimize variety o Use guidelines and standardize fasteners to
minimize the number, size, and variation.
o Self-tapping and chamfered screws are preferred.
o Use captive fasteners when possible.
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DfM #8: Use Error Proofing Techniques
o Mistakes will happen, What can go wrong will go wrong.
o Anticipate and Eliminate opportunities for error
o Use error proofing techniques in product design and assembly
o Make the correct assembly process visually obvious, well-defined and clear cut. Remove confusion and interpretation.
o Have written instructions in one location only – no competing docs
o Minimize wording in instructions. Use pictures, icons, photos
o Key unique parts so that they can be inserted only in the correct location.
o Use notches, asymmetrical holes and stops to mistake-proof the assembly process.
o Design verifiability into the product and its components.
o Sight, Sound or Feel - use visual, audio, tactile feedback
o Use color coding
o Electronic products can be designed to contain self-test diagnostics
o Avoid or simplify adjustments or modifications
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DfM #8: Error Proofing (example)
o All polarized SMT and through-hole components should be placed in the same orientation and in only one axis.
o This facilitates easier visual inspection.
o Where this is not practical, try to group components in the same orientation
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DfM #9: Design for Process Capabilities
o Make use of specific production DFM guidelines or know the process capabilities of the production equipment
o Avoid unnecessarily tight tolerances and tolerances that are beyond the inherent capability of the manufacturing processes or operators in a continuous production situation. Tighter is not always better!
o Perform tolerance stack up analyses on multiple, connected processes and parts.
o Determine when new production process capabilities are needed
o Allow time to develop/optimize new processes
o Determine optimal process parameters
o Establish controlled processes.
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DfM #10: Design for Test, Repair, & Serviceability
Defects will occur. Design for ease of test and repair will make these processes more efficient, cost effective, and reliable.
o Use recommended component spacing to allow for safe repair or replacement
o Design in diagnostics, self tests, meaningful error messages, and diagnostic interfaces.
o ESD Considerations - provide warning labels and appropriate workstations where needed.
o Standardize approaches and methods.
o Minimize parts variety, minimize tools/special tools needed
o Minimize disassembly steps to access replaceable/repairable Items.
o Consider unfastening and refastening, disassembly and reassembly issues.
o Use self-fastening and self-jigging features when possible.
o Consider impact of adhesives, coating, and potting
o Wiring/Hose Interconnection – consider disconnect and reconnect capabilities.
Failed products are often returned to the manufacturer for service and failure analysis. Where possible, use the production test equipment/setup for returns analysis.
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DfM #10: Example
o If BGA's are on both sides of the board, it is not recommended that the BGA's are positioned on top of each other. o This method makes rework of a BGA extremely difficult.
o Also makes x-ray inspection of solder balls very difficult
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Additional Questions ?
o Walter Tomczykowski
o 5110 Roanoke Place
o College Park, MD 20740
o 301-474-0607
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