Design for Manufacturing: Challenges & Opportunities

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9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
SMTA Capital Area Design for Manufacturing: Challenges & Opportunities
Cheryl Tulkoff, ASQ CRE
Senior Member of the Technical Staff
ctulkoff@dfrsolutions.com
May 16, 2013

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DfM Abstract
oIn the electronics industry. the quality and reliability of any product is highly dependent upon the capability of the manufacturing supplier, regardless of whether it is a contractor or a captured shop. Manufacturing issues are one of the top reasons that companies fail to meet warranty expectations, which can result in severe financial pain and eventual loss of market share. What a surprising number of engineers and managers fail to realize is that focusing on processes addresses only part of the issue. Design plays a critical role in the success or failure of manufacturing and assembly.
oDesigning printed boards today is more difficult than ever before because of the increased lead free process temperature requirements and associated changes required in manufacturing. Not only has the density of the electronic assembly increased, but many changes are taking place throughout the entire supply chain regarding the use of hazardous materials and the requirements for recycling. Much of the change is due to the European Union (EU) Directives regarding these issues. The RoHS and REACH directives have caused many suppliers to the industry to rethink their materials and processes. Thus, everyone designing or producing electronics has been or will be affected.
oThis course provides a comprehensive insight into the areas where design plays an important role in the manufacturing process. This workshop addresses the increasingly sophisticated PCB fabrication technologies and processes.

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Presentation Outline
MODULE 1: INTRODUCTIONS
oIntro to Design for Manufacturing
oKey Global DfM Guidelines
MODULE 2: INDUSTRY STANDARD DESIGN RULES (Reference)
oQuick View of Industry Standards
MODULE 3: OVERVIEW OF DFM TASKS
oTypes of Review Processes
oRoot Cause Problem Solving
oFailure Analysis (Reference)
MODULE 4: DfM - COMPONENT
Component Robustness
Temperature Sensitivity Level
Moisture Sensitivity Level
Pb-free Issues
MODULE 6: DfM - SOLDER
•General Soldering
•Lead Free Solder Alloy Update
•Hand Soldering
•Copper Dissolution
•Mixed Assembly

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Module 1: Introduction
Introduction to Design for Manufacturing (DfM)

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Design for Manufacturing (DfM)
oDefinition
oThe process of ensuring a design can be consistently manufactured by the designated supply chain with a minimum number of defects
oRequirements
oAn understanding of best practices (what fails during manufacturing?)
oAn understanding of the limitations of the supply chain

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DfM Failures
oDfM is often overlooked in the design process for some of the following reasons:
oDesign team often has poor insight into supply chain
oOriginal Equipment Manufacturer (OEM) requests no feedback on DfM from supply chain
oDfM feedback consists of standard rule checks (no insight)
oDfM activities at the OEM are not standardized or distributed

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oDfM is the process of proactively designing products to:
oOptimize all of the manufacturing functions: supplier selection and management, procurement, receiving, fabrication, assembly, quality control, operator training, shipping, delivery, service, and repair.
oAssure 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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oSuccessful DFM efforts require the integration of product design and process planning
oIf 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.
oIf 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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Module 2: Industry Standard Design Rules (Reference)

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Industry Standards – IPC, JEDEC, ISO…
oStart with industry standards where possible
oTried and true
oBut, represent only minimum acceptable requirements or concerns
oModify and extend as needed to customize for your product and environments!
oForums provide opportunities for free advice and feedback

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IPC Design Requirement/Guideline References
oIPC-2221- Generic Standard on Printed Board Design
oIPC-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.
o3 Performance Classes
oClass 1 General Electronic Products - consumer products,
oClass 2 Dedicated Service Electronic Products
oCommunications equipment, sophisticated business machine, instruments and military equipment where high performance, extended life and uninterrupted service is desired but is not critical.
oClass 3 High Reliability Electronic Products
oCommercial, 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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oGood quality is necessary but not SUFFICIENT to guarantee high reliability.
oClass 3 by itself does not guarantee high reliability
oA PCB or PCBA can be perfectly built to IPC Class 3 standards and still be totally unreliable in its final application.
oConsider two different PCB laminates both built to IPC Class 3 standards.
oBoth laminates are identical in all properties EXCEPT one laminate has a CTEz of 40 and the other has a CTEz of 60.
oThe 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.
oA CTEz 40 laminate built to IPC class 2 could be MORE reliable than the CTEz 60 laminate built to Class 3.
oAppropriate materials selection for the environment is key!
A Word on Quality, Reliability & Class 2 versus Class 3

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JEDEC/IPC Joint Standards
oJEDEC is the leading developer of standards for the solid-state industry. All JEDEC standards are available online, at no charge. www.jedec.org
oSome commonly referenced JEDEC/IPC Joint Standards standards:
oJ-STD-020D.01: JOINT IPC/JEDEC STANDARD FOR MOISTURE/REFLOW SENSITIVITY CLASSIFICATION FOR NONHERMETIC SOLID STATE SURFACE- MOUNT DEVICES:
oThis document identifies the classification level of nonhermetic solid-state surface mount devices (SMDs) that are sensitive to moisture-induced stress. It is used to determine what classification level should be used for initial reliability qualification. This revision now covers components to be processed at higher temperatures for lead-free assembly.
oJS9704 : IPC/JEDEC-9704: Printed Wiring Board (PWB) Strain Gage Test Guideline
oThis document describes specific guidelines for strain gage testing for Printed Wiring Board (PWB)assemblies. The suggested procedures enables board manufacturers to conduct required strain gage testing independently, and provides a quantitative method for measuring board flexure, and assessing risk levels. The topics covered include: Test setup and equipment; requirements; Strain measurement; Report format

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Module 3: Overview of DfM Tasks

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Common Types of DfM Review Processes
oInformal “Gut Check” Review
oPerformed by highly experienced engineers.
oDifficult with transition to original design manufacturers (ODM) in developing countries.
o“Tribal knowledge”
oFormal Design reviews
oInternal team
oExternal experts
oAutomated (electronic) design automation (ADA) software
oModules automate DfM rule checking.
oElectronic manufacturing service (EMS) providers
oPerform DfM as a service

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Design for Manufacturing (DfM)
oFormal DfM Reviews and Tools Sometimes Overlooked
oOrganization may lack specialized expertise.
oMore design organizations completely removed from manufacturing.
oDfM Reviews Needs to be Performed for:
oBare Board
oCircuit Board Assemblies
oChassis/Housing Integration Packaging
oSystem Assembly
oDfM Needs to be conducted in conjunction with the actual electronic assembly source.
oWhat is good DfM for one supplier and one set of assembly equipment may not be good for another.

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Use a Root Cause Problem Solving Methodology
oCritical that your organization has a formal root cause problem solving methodology used both internally and externally.
oThis is the best way to incorporate relevant material into your customized Design for Manufacturing and Sourcing guidelines.
oThis ties in closely with DfM Guideline #1: Know Your History!

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8D Problem Solving Methodology
oProblem Statement:
oSimply fixing the symptoms of a problem, more often than not, leads to band-aid solutions
oEnd up solving the same problem several times
oOther areas experience similar problems
oSolution:
oDo root cause analysis and follow through with permanent corrective actions on significant problems
oBreak the endless loop
oDrive Continuous Improvement
oSave money & efficiencies
oReap benefits beyond the discrete issue

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The 8 Disciplines (8D)
1.Create the Team
2.Problem Description and Data Analysis
3.Containment Actions
4.Perform Root Cause Analysis
5.Choose and Verify Corrective Action
6.Implement Corrective Action
7.Apply Lessons Learned
8.Celebrate Success / Close the Issue
(8D forms can also be used by suppliers. )

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Why is Failure Analysis Knowledge Important?
oThere are always more problems than resources!
oIf you don’t analyze, learn from, and prevent problems, you simply repeat them. Your list never gets smaller.

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General Words of Wisdom on Failure Analysis
oBefore spending time and money on Failure Analysis (FA), consider the following:
oConsider “order” carefully. Some actions will limit or eliminate the ability to perform additional tests.
oUnderstand the limitations and output of the tests selected.
oUse labs who can help you select and interpret tests for capabilities you don’t have.
oAvoid requesting a specific test. Describe the problem and define the data and output you need first.
oPursue multiple courses of action. There is rarely one test or one root cause that will solve your problem.
oConsider how the data will help solve the problem
oSome FA is just not worth doing!

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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
oDestructive evaluation techniques
oDecapsulation
oPlasma etching
oCross-sectioning
oThermal imaging (liquid crystal; SQUID and IR also good after decap)
oSEM/EDX – Scanning Electron Microscope / Energy dispersive X-ray Spectroscopy
oSurface/depth profiling techniques: SIMS-Secondary Ion Mass Spectroscopy, Auger
oOBIC/EBIC
oFIB - Focused Ion Beam
oMechanical testing: wire pull, wire shear, solder ball shear, die shear
oOther characterization methods
oFTIR- Fourier Transform Infra-Red Spectroscopy
oIon chromatography
oDSC – Differential Scanning Calorimetry
oDMA/TMA – Thermo-mechanical analysis

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oMost critical step in the failure analysis process
oCan the reported failure mode be replicated?
oPersistent or intermittent?
oIntermittent failures often incorrectly diagnosed as no trouble found (NTF)
oLeast utilized to its fullest extent
oApproach dependent upon the product
oComponent
oBare substrate
oPCB assembly
oSometimes performed in combination with environmental exposure
oCharacterization over specified/expected temperature range
oCharacterization over specified / expected radiation range
oHumidity environment (re-introduction of moisture)
oNot intended to induce damage!
Electrical Characterization

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Failure Analysis Tools: Dye N Pry Capability
oAllows for quick (destructive) inspection for cracked or fractured solder joints under leadless components (BGAs, QFNs)
ohttp://www.electroiq.com/index/display/packaging- article- display/165957/articles/advanced-packaging/volume- 12/issue-1/features/solder- joint-failure-analysis.html

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Failure Analysis Dremel Tool – Induce Vibrations
oA Dremel tool can be used to induce local vibration during debugging
ohttp://www.dremel.com

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Module 4: Components
Component Robustness

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Robustness - Components
oConcerns
oPotential for latent defects after exposure to Pb-free reflow temperatures
o215°C - 220°C peak → 240°C - 260°C peak
oDrivers
oInitial observations of deformed or damaged components
oFailure of component manufacturers to update specifications
oComponents of particular interest
oAluminum electrolytic capacitors
oCeramic chip capacitors
oSurface mount connectors
oSpecialty components (RF, optoelectronic, etc.)

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Ceramic Capacitors (Thermal Shock Cracks)
oDue to excessive change in temperature
oReflow, cleaning, wave solder, rework
oInability of capacitor to relieve stresses during transient conditions.
oMaximum tensile stress occurs near end of termination
oDetermined through transient thermal analyses
oModel results validated through sectioning of ceramic capacitors exposed to thermal shock conditions
oThree manifestations
oVisually detectable (rare)
oElectrically detectable
oMicrocrack (worst-case)
NAMICS
AVX

47 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com
Thermal Shock Crack: Visually Detectable
AVX

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Thermal Shock Crack: Micro Crack
oVariations in voltage or temperature will drive crack propagation
oInduces a different failure mode
oIncrease in electrical resistance or decrease capacitance
DfR

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Corrective Actions: Design
oAvoid certain dimensions and materials
oMaximum case size for SnPb: 1210
oMaximum case size for SAC305: 0805
oMaximum thickness: 1.2 mm
oC0G, X7R preferred
oAdequate spacing from hand soldering operations
oUse manufacturer’s recommended bond pad dimensions or smaller
oSmaller bond pads reduce rate of thermal transfer

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Corrective Actions: Manufacturing
oReflow
oRoom temperature to preheat (max 2-3oC/sec)
oPreheat to at least 150oC
oPreheat to maximum temperature (max 4-5oC/sec)
oCooling (max 2-3oC/sec)
oIn conflict with profile from J-STD-020C (6oC/sec)
oMake sure assembly is less than 60oC before cleaning
oWave soldering
oMaintain belt speeds to a maximum of 1.2 to 1.5 meters/minute
oEliminate “cosmetic” touch up

Flex Cracking of Ceramic Capacitors (cont.)
o Excessive flexure of PCB
under ceramic chip capacitor
can induce cracking at the
terminations
o Pb-free more resistant to flex
cracking
o Correlates with Kemet results
(CARTS 2005)
o Rationale
o Smaller solder joints
o Residual compressive stresses
o Influence of bond pad
1.00 10.00
1.00
5.00
10.00
50.00
90.00
99.90
ReliaSoft's Weibull++ 6.0 - www.Weibull.c om
Probability - Weibull
Displacement (mm)
Unreliability, F(t)
6/13/2005 21:56
DfR Solut ions
Craig Hillman
Weibull
1812 SAC
W2 RRX - RRM MED
F=162 / S=0
        
1812 SnPb
W2 RRX - RRM MED
F=90 / S=0
        
SnPb
SnAgCu

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Flex Cracking (Case Studies)
Screw Attachment
Board Depaneling
Connector Insertion
Heatsink Attachment

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Flex Cracking (cont.)
oDrivers
oDistance from flex point
oOrientation
oLength (most common at 1206 and above; observed in 0603)
oSolutions
oAvoid case sizes greater than 1206
oMaintain 30-60 mil spacing from flex point
oReorient parallel to flex point
oReplace with Flexicap (Syfer) or Soft Termination (AVX)
oReduce bond pad width to 80 to 100% of capacitor width
oMeasure board-level strain (maintain below 750 microstrain, below 500 microstrain preferred for Pb-free)

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Module 6: Solders General Soldering

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Process Capabilities Defects Rates for Soldering Processes
oDesigns that avoid manual soldering operations reduce defects.
oMain Issues: Insufficient solder or bonding, Missed joints, Heat Damage
oReflow soldering produces less defects that wave soldering.
oMain Issues: Solder Bridges, Solder Skips/Insufficient Solder, Missing Component
Defects Per Million (Joint) Opportunities (DPMO) Example 1,000 Joints/Board on 1,000 Boards
Solder Process
DPMO
Standard
Best in Class
Hand
5000
N/A
Wave
500
20 - 100
Reflow
50
<10

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Reflow Profile Optimization
oStart with paste manufacturer’s recommendations!
oPreheating Phase - Ramp & Soak vs. Straight Ramp preheating profiles
oRamp & Soak (soak period just below liquidus), more common, more forgiving.
oAllow flux solvents to fully evaporate and activate to deoxidize the surfaces to be soldered.
oAllows temperature equalization across the entire assembly.
oConsistent soldering and reduces tomb stoning.
oIf too long, flux may be consumed resulting in excessive oxidation.
oFlux may become volatile - producing solder balls or voiding defects.
oStraight Line is faster and causes less thermal damage to materials
oBut more susceptible to defect and quality variation, does not work as well on complex, dense assemblies.

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Reflow Profile Optimization
oPeak Temperature and Time at (above) Liquidus (TAL)
oA balance between being hot enough for long enough to achieve good consistent solder wetting and bonding for proper joint formation, across the entire assembly.
oYet as quickly as possible to prevent thermal damage to the components and board and to prevent excessive copper dissolution and excessive intermetallic growth.
oCooling Rate of SnAgCu effects the Microstructure & Bulk Intermetallics
oFaster cooling rates produce a finer, stronger microstructure and limits intermetallics.
oOverall Time (Costs & Efficiency)
oOverall throughput is determined the board size/complexity and the oven's heat transfer capabilities.
oRule of Thumb: 2-3 C/second ramp up and down rate

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PTH Soldering: Incomplete Hole Fill
oPoor solder hole fill can lead to solder joint cracks/failures. Can be caused by:
oInsufficient top side heating prevented solder from wicking up into PTH Barrel
oInsufficient flux or flux activity for the surface finish in use
oLack of thermal relief for large copper planes
oPCB hole wall integrity issues – voids, plating, contamination

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PTH Hole Fill & Thermal Relief
oUtilize thermal reliefs on all copper planes when practical
oReduces thermal transfer rate between PTH and copper plane
oAllows for easier solder joint formation during solder (especially for Pb-free)
oAllows for better hole fill
Copper
Plane
PTH
Laminate
Copper Spoke
Courtesy of D. Canfield (Excalibur Manufacturing)

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Module 6: Solders
Discussion of 2nd generation Pb-free alloys (e.g., SN100C)

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The Current State of Lead-Free
oComponent suppliers
oSAC305 still dominant, but with increasing introduction of low silver alloys (SAC205, SAC105, SAC0507)
oSolder Paste
oSAC305 still dominant
oWave and Rework
oSn07Cu+Ni (SN100C)
oSn07Cu+Co (SN100e)
oSn07Cu+Ni+Bi (K100LD)
oHASL PCB Coating
oSn07Cu+Ni (SN100C)

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What are Solder Suppliers Promoting?
Company
Paste
Wire / Wave
Senju
ECO Solder (SAC305)
Nihon Genma
NP303 (SAC305),
NP601 (Sn8Zn3Bi)
NP303 (SAC305),
NP103 (SAC0307)
Metallic Resources
SAC305
SAC305,
SC995e (Sn05Cu+Co)
Koki
S3X (SAC305),
S3XNI58 (SAC305+Ni+In),
SB6N58 (Sn3.5Ag0.5Bi6In)
S3X (SAC305),
S03X7C (SAC0307+0.03Co)
Heraeus
SAC405
Cookson / Alpha Metals
SACX (SAC0307+Bi+0.1P+0.02RareEarth+0.01Sb)
Kester
K100LD (Sn07Cu+0.05Ni+Bi)
Qualitek
SN100e (Sn07Cu+0.05Co)
Nihon Superior
SN100C (Sn07Cu+0.05Ni+Ge)
AIM
SN100C (Sn07Cu+0.05Ni+Ge)
Indium
Indium5.1AT (SAC305)
N/A
Amtech
SAC305, Sn3.5Ag, Sn5Ag, Sn07Cu, Sn5Sb
Shenmao
SAC305 to SAC405, SAC305+0.06Ni+0.01Ge
Henkel
No preference
EFD
No preference
P. Kay Metals
No preference

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2nd Generation Pb-Free Solder (Thoughts)
oNi-modified SnCu and low silver SAC are the primary front runners
oBoth seem to display reliability behaviors between SAC305 and SnPb
oProliferation of custom alloys is unhealthy for the electronics industry
oToo much time spent on material identification, characterization, and risk assessment
oOne customer had SAC405, SAC387, SAC305, SAC105, SAC0307, and SAC125Ni on one board!
oAlmost no component manufacturers assess these new alloys from a physics of failure
oTest to spec mentality
oHuge risk for escapes

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Module 6: Solders
Hand Soldering Copper Dissolution Mixed Assembly

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oDesigned for hand soldering
oSIR data
oHalogen / halide free: Watch for definitions!
oSupplier – relationships, proximity
oLead finish
oSubstrate finish
oAcid number
oLead free or SnPb soldering?
oCompatibility with adjacent materials
oAdhesives, conformal coatings, etc.
Basic Hand Soldering Materials Selection Criteria

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oSize /type / pitch / plating of leads
oSubstrate finish / type – rigid, flex, ENIG, etc
oSpace between hand soldered leads and adjacent components and circuitry
oSize, shape, heat sinking of module at time of hand soldering
oCan unit and component be preheated?
Design Considerations

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oOperator variation is the norm. Training is critical!
oGeneral hand soldering tips:
oUse soldering irons with great thermal recovery - the lower the soldering temperature and the larger the tip, the less heat loss
oUse a high power soldering iron
oUse the largest tip commensurate with the size of the joint being soldered and available space
oCustom tips can be designed if needed.
oUse the largest cored solder wire diameter appropriate for the size of the joint and available space.
oAvoid the use of liquid fluxes
oTypical tip temperatures for Pb-free solder are ~700F with 2-5 seconds of contact time. Higher temps can damage boards and components.
Hand Soldering Process

Solder Tip Size and Cored Wire Size
Images courtesy of OK International
The diagram below shows why No-Clean Flux-cored solder seldom works as well as RMA-cored
solder:

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oConsider use of a portable preheater to shorten contact time and fully activate fluxes
ohttp://www.zeph.com/airbathseries.htm
oPreheat to 100 F or so
oVerify actual PCB and lead temperatures with small temp labels
ohttp://www.omega.com/toc_asp/sectionSC.asp?section=F&book=temperature
oUse solder preforms for repeatable joint size and flux volume – both PTH and SMT
Hand Soldering Tips

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oAlways avoid liquid flux if possible
oIf it’s truly needed:
oLook for methods to ensure precise delivery
oFlux pens are one method
oThe needle tip dispense bottles are not recommended.
oAvoid letting flux run under and around adjacent components.
oProvide some form of uniform heating to volatalize as much of the liquid as possible.
oSelect a flux designed and validated for hand soldering processes
oThis is probably NOT be the same material as your wave solder flux. Wave solder fluxes are designed to hold up through preheat and dual wave contact.
oReview surface insulation resistance (SIR) data
Use of Liquid Flux

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oTypical manual cleaning process:
oSome type of solvent spray is used to loosen flux residues and followed by hand cleaning using IPA and a soft bristle brush.
oThis type of manual cleaning process represents a reliability risk.
oSeveral studies have shown that SIR (surface insulation resistance) actually INCREASES when IPA and brushes are used in manual cleaning.
oBrushes are not routinely cleaned or maintained and become contamination transfer mechanisms.
oPoorly removed residues are more likely to experience corrosion failures than no clean flux residues left intact.
oIn rework and repair, if you can’t rinse, you can’t clean.
Manual Removal of Flux Residues: Not Recommended!

Solders: Copper Dissolution
o The reduction or elimination of surface copper conductors
due to repeated exposure to Sn-based solders
o Significant concern for
industries that perform
extensive rework
o Telecom, military,
avionics
Bath, iNEMI
ENIG Plating
60 sec. exposure
274ºC solder fountain

Solders: Copper Dissolution (cont.)
o PTH knee is the point of
greatest plating reduction
o Primarily a rework/repair
issue
o Celestica identified significant
risk with >1X rework
o Already having a detrimental
effect
o Major OEM unable to repair
ball grid arrays (BGAs) S. Zweigart, Solectron

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Copper Dissolution (Contact Time)
oContact time is the major driver
oSome indications of a 25-30 second limit
oPreheat and pot temp. seem to have a lesser effect
oOptimum conditions (for SAC)
oContact time (max): 47 sec. (cumulative)
oPreheat temperature: 140-150°C
oPot temperature: 260-265°C
A Study of Copper Dissolution During Pb-Free PTH Rework Using a Thermally Massive Test Vehicle , C. Hamilton (May 2007)

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Solutions to Cu Dissolution
oOption 1: restriction on rework
oNumber of reworks or contact time
oOption 2: solder material
oIndications that SNC can decrease dissolution rates
oReduced diffusion rate through Sn-Ni-Cu intermetallics
oOption 3: board plating
oSome considering ENIG
oSome considering SNC HASL
A Study of Copper Dissolution During Pb-Free PTH Rework Using a Thermally Massive Test Vehicle , C. Hamilton (May 2007)

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Mixed Assembly
oPrimarily refers to Pb-free BGAs assembled using SnPb eutectic solder paste
oWhy?
oArea array devices (e.g., ball grid array, chip scale package) with eutectic solder balls are becoming obsolete
oMilitary, avionics, telecommunications, industrial do not want to transition to Pb-free…yet
UIC

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Mixed Assembly: Reflow
•Initial studies focused on peak temperature
•Identified melt temperature of solder ball as critical parameter
•217°C for SAC305
•Ensured ball collapse and intermixing
•Recommendations
•Minimum peak reflow temperature of 220°C
•Reflow temperatures below 220°C may result in poor assembly yields and/or inadequate interconnect reliability
•For increased margin, >225 to 245°C peak

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Mixed Assembly: Solder Joint Morphology
Motorola

Mixed Assembly: Solder Joint Morphology
Richard Coyle,et al), “THERMAL FATIGUE RELIABILITY
AND MICROSTRUCTURAL CHARACTERIZATION OF A
LARGE,HIGH DENSITY BALL GRID ARRAY WITH
BACKWARD COMPATIBLE ASSEMBLY”, SMTAI 2012
W. Fox et al, “DEVELOPMENT OF PROCESSING
PARAMETERS FOR SOLDERING LEAD-FREE BALL GRID
ARRAYS USING TIN-LEAD SOLDER”, SMTAI 2012
Better mixing appears to enhance reliability

Increasing Heat Increases Ball Strength
W. Fox, B. Gumpert, and L. Woody (Lockheed Martin), “DEVELOPMENT OF
PROCESSING PARAMETERS FOR
SOLDERING LEAD-FREE BALL GRID ARRAYS USING TIN-LEAD SOLDER”, SMTAI 2012,
p878-885, Orlando,
Florida, October 14-18, 2012

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Impact of Peak Temp & % Pb Dissolution on Fatigue Life
oFatigue life begins to increase at 217 C
oIncreases until the maximum temperature of 224°C is reached.
oAfter 217 C, higher peak temperature = higher fatigue life.
oFatigue life does not increase until ~ 85% Pb dissolution
oTo maximize fatigue life, require at least 85% dissolution
Mudasir Ahmad, Kuo-Chuan Liu, Gnyaneshwar Ramakrishna, and Jie Xue (Cisco), ” IMPACT OF BACKWARDS COMPATIBLE ASSEMBLY ON BGA THERMOMECHANICAL RELIABILITY AND MECHANICAL SHOCK, PRE- AND POST-AGING”, SMTAI 2008, p306-321, Orlando, Florida, August 17-21, 2008

Mixed Assembly: Temp Cycling Results
10 100 1,000 8,000
0.03
0.3
3
30
99
SnAgCu/SnPb
SnAgCu/SnAgCu
SnPb
Cycles to Failure
Cumulative Failure (%)
HP: 0 to 100ºC, 214ºC Peak Temp

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Mixed Assembly & Voiding
oBGA voiding is common in mixed assembly
oIndium Corp. studied behavior under
o217C Peak T (Low)
o240 C Peak T (High)

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Indium Corp Study Conclusions
oMixed systems have less voiding at low temp
oMixed systems had higher voiding than lead-free systems when reflowed at high temp
oSome ways to reduce voiding
oSolder paste formulation less prone to have voiding
oMechanical shielding fixture (temperature)
oLonger soaking profile
oNitrogen reflow atmosphere

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Mixed Assembly: Conclusions
oA potentially lower risk than complete transition to Pb-free
oImportant note: more studies on vibration and shock performance should be performed
oThe preferred approach for some high reliability manufacturers (military, telecom):
oAcceptance of mixed assembly could be driven by GEIA- STD-0005-1

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Mixed Assembly: Alternatives
oOther options on dealing with Pb-free BGAs other than mixing with SnPb
oPlacement post-reflow
oReballing
oTwo flux options
oApplication of Pb-free solder paste
oApplication of flux preform
oTwo soldering options
oHot air (manual)
oLaser soldering (automatic)

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Reballing BGAs
oHas been shown to be reliable in several studies
o“Reballed components exhibited adequate performance and can be recommended as a solution for the mixed system assembly process.”
Intermetallic Structure of reballed BGAs
RELIABILITY ASSESSMENT OF REBALLED BGAs J. Li1, S. Poranki1, M. Abtew2, R. Kinyanjui2, Ph.D., and K. Srihari1,

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Ongoing DfM Learning Opportunities
oSome ideas for low cost continuing education inside and outside of your company
oE-Learning at dfrsolutions.com
oOrganize “Your Company Days”, Poster Sessions, Demos
oUse internal electronic bulletin boards an resources
oBrown Bags &” Lunch and Learns” from your internal gurus and from your suppliers
oPCB
oContract Manufacturers
oElectronics Materials - paste, fluxes, cleaners

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Summary
oDfM is a proven, cost-effective strategic methodology.
oEarly effective cross functional involvement:
oReduces overall product development time (less changes, spins, problem solving)
oResults in a smoother production launch.
oSpeeds time to market.
oReduces overall costs.
oDesigned right the first time.
oBuild right the first time = less rework, scrap, and warranty costs.
oImproved quality and reliability results in:
oHigher customer satisfaction.
oReduced warranty costs.

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Instructor Biography
Cheryl Tulkoff has over 22 years of experience in electronics manufacturing with an emphasis on failure analysis and reliability. She has worked throughout the electronics manufacturing life cycle beginning with semiconductor fabrication processes, into printed circuit board fabrication and assembly, through functional and reliability testing, and culminating in the analysis and evaluation of field returns. She has also managed no clean and RoHS-compliant conversion programs and has developed and managed comprehensive reliability programs.
Cheryl earned her Bachelor of Mechanical Engineering degree from Georgia Tech. She is a published author, experienced public speaker and trainer and a Senior member of both ASQ and IEEE. She has held leadership positions in the IEEE Central Texas Chapter, IEEE WIE (Women In Engineering), and IEEE ASTR (Accelerated Stress Testing and Reliability) sections. She chaired the annual IEEE ASTR workshop for four years, is an ASQ Certified Reliability Engineer and a member of SMTA and iMAPS.
She has a strong passion for pre-college STEM (Science, Technology, Engineering, and Math) outreach and volunteers with several organizations that specialize in encouraging pre-college students to pursue careers in these fields.

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Contact Information
•Questions?
•Contact Cheryl Tulkoff, ctulkoff@dfrsolutions.com, 512-913-8624
•askdfr@dfrsolutions.com
•www.dfrsolutions.com
•Connect with me in LinkedIn as well!

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