design for manufacturing: challenges & opportunities

1 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

[email protected]

May 16, 2013


DfM Abstract

o In 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.

o Designing 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.

o This 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.


Presentation Outline

MODULE 1: INTRODUCTIONS

o Intro to Design for Manufacturing

o Key Global DfM Guidelines

MODULE 2: INDUSTRY STANDARD

DESIGN RULES (Reference)

o Quick View of Industry Standards

MODULE 3: OVERVIEW OF DFM

TASKS

o Types of Review Processes

o Root Cause Problem Solving

o Failure 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


Module 1: Introduction

Introduction to Design for Manufacturing (DfM)


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


DfM Failures

o DfM is often overlooked in the design process for some

of the following reasons:

o Design team often has poor insight into supply chain

o Original Equipment Manufacturer (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



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.



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”


Why DfM? (cont.)

Reduce Costs by Improving

Manufacturability Upfront


Module 2: Industry

Standard Design Rules

(Reference)


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


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...


o Good quality is necessary but not SUFFICIENT to guarantee high reliability.

o Class 3 by itself does not guarantee high reliability

o 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 & Class 2 versus Class 3


JEDEC/IPC Joint Standards

o JEDEC is the leading developer of standards for the solid-state industry. All JEDEC standards are available online, at no charge. www.jedec.org

o Some commonly referenced JEDEC/IPC Joint Standards standards:

o J-STD-020D.01: JOINT IPC/JEDEC STANDARD FOR MOISTURE/REFLOW SENSITIVITY CLASSIFICATION FOR NONHERMETIC SOLID STATE SURFACE-MOUNT DEVICES:

o This 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.

o JS9704 : IPC/JEDEC-9704: Printed Wiring Board (PWB) Strain Gage Test Guideline

o This 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

http://www.jedec.org/


Module 3: Overview of DfM Tasks


Common Types of DfM Review Processes

o Informal “Gut Check” Review o Performed by highly experienced engineers.

o Difficult with transition to original design

manufacturers (ODM) in developing countries.

o “Tribal knowledge”

o Formal Design reviews o 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


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.


Use a Root Cause Problem Solving Methodology

o Critical that your organization has a formal root cause

problem solving methodology used both internally

and externally.

o This is the best way to incorporate relevant material into

your customized Design for Manufacturing and Sourcing

guidelines.

o This ties in closely with DfM Guideline #1: Know Your

History!


8D Problem Solving Methodology

oProblem Statement:

o Simply fixing the symptoms of a problem, more often than not,

leads to band-aid solutions

o End up solving the same problem several times

o Other areas experience similar problems

oSolution:

o Do root cause analysis and follow through with permanent

corrective actions on significant problems

o Break the endless loop

o Drive Continuous Improvement

o Save money & efficiencies

o Reap benefits beyond the discrete issue


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. )


Why is Failure Analysis Knowledge Important?

o There are always more problems than resources!

o If you don’t analyze, learn from, and prevent

problems, you simply repeat them. Your list never gets

smaller.


General Words of Wisdom on Failure Analysis

o Before spending time and money on Failure Analysis (FA),

consider the following:

o Consider “order” carefully. Some actions will limit or eliminate the

ability to perform additional tests.

o Understand the limitations and output of the tests selected.

o Use labs who can help you select and interpret tests for capabilities you

don’t have.

o Avoid requesting a specific test. Describe the problem and define the

data and output you need first.

o Pursue multiple courses of action. There is rarely one test or one root

cause that will solve your problem.

o Consider how the data will help solve the problem

o Some FA is just not worth doing!

39 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com 39

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


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


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


Failure Analysis Tools: Dye N Pry Capability

o Allows for quick (destructive) inspection for cracked or fractured solder joints under leadless components (BGAs, QFNs)

o http://www.electroiq.com/index/display/packaging-article-display/165957/articles/advanced-packaging/volume-12/issue-1/features/solder-joint-failure-analysis.html

http://www.electroiq.com/index/display/packaging-article-display/165957/articles/advanced-packaging/volume-12/issue-1/features/solder-joint-failure-analysis.html




















Failure Analysis Dremel Tool – Induce Vibrations

o A Dremel tool can be used to

induce local vibration during

debugging

o http://www.dremel.com

http://www.dremel.com


Module 4: Components

Component Robustness


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.)


46

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 manifestations o Visually detectable (rare)

o Electrically detectable

o Microcrack (worst-case)

NAMICS

AVX


47

Thermal Shock Crack: Visually Detectable

AVX


Thermal Shock Crack: Micro Crack

o Variations in voltage or temperature will drive crack propagation

o Induces a different failure mode

o Increase in electrical resistance or decrease capacitance

DfR


49

Corrective Actions: Design

o Avoid certain dimensions and materials

o Maximum case size for SnPb: 1210

o Maximum case size for SAC305: 0805

o Maximum thickness: 1.2 mm

o C0G, X7R preferred

o Adequate spacing from hand soldering operations

o Use manufacturer’s recommended bond pad dimensions or smaller

o Smaller bond pads reduce rate of thermal transfer


50

Corrective Actions: Manufacturing

o Reflow

o Room temperature to preheat (max 2-3oC/sec)

o Preheat to at least 150oC

o Preheat to maximum temperature (max 4-5oC/sec)

o Cooling (max 2-3oC/sec)

o In conflict with profile from J-STD-020C (6oC/sec)

o Make sure assembly is less than 60oC before cleaning

o Wave soldering

o Maintain belt speeds to a maximum of 1.2 to 1.5 meters/minute

o Eliminate “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

R eliaSoft's W eibull++ 6.0 - w w w .W eibull.c om

Probability - Weibull

Displacement (mm)

Unre

liability

, F(t

)

6/13/2005 21:56DfR SolutionsCraig Hillman

Weibull1812 SAC

W2 RRX - RRM MEDF=162 / S=0

1812 SnPb

W2 RRX - RRM MEDF=90 / S=0

SnPb

SnAgCu


Flex Cracking (Case Studies) Screw Attachment Board Depaneling

Connector Insertion Heatsink Attachment


Flex Cracking (cont.)

o Drivers

o Distance from flex point

o Orientation

o Length (most common at 1206 and above; observed in 0603)

o Solutions

o Avoid case sizes greater than 1206

o Maintain 30-60 mil spacing from flex point

o Reorient parallel to flex point

o Replace with Flexicap (Syfer) or Soft Termination (AVX)

o Reduce bond pad width to 80 to 100% of capacitor width

o Measure board-level strain (maintain below 750 microstrain, below

500 microstrain preferred for Pb-free)


Module 6: Solders

General Soldering


Process Capabilities Defects Rates for Soldering Processes

o Designs that avoid manual soldering operations reduce defects. o Main Issues: Insufficient solder or bonding, Missed joints, Heat Damage

o Reflow soldering produces less defects that wave soldering. o Main 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


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.


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


PTH Soldering: Incomplete Hole Fill

o Poor solder hole fill can lead to solder joint cracks/failures. Can be caused by: o Insufficient top side heating prevented solder from wicking up into PTH Barrel

o Insufficient flux or flux activity for the surface finish in use

o Lack of thermal relief for large copper planes

o PCB hole wall integrity issues – voids, plating, contamination


PTH Hole Fill & Thermal Relief

o Utilize thermal reliefs on all copper planes when practical

o Reduces thermal transfer rate between PTH and copper plane

o Allows for easier solder joint formation during solder (especially for Pb-free)

o Allows for better hole fill

Copper

Plane

PTH

Laminate

Copper

Spoke

Courtesy of D. Canfield (Excalibur Manufacturing)


Module 6: Solders

Discussion of 2nd generation Pb-free alloys (e.g.,

SN100C)


The Current State of Lead-Free

o Component suppliers o SAC305 still dominant, but with increasing introduction of low

silver alloys (SAC205, SAC105, SAC0507)

o Solder Paste o SAC305 still dominant

o Wave and Rework o Sn07Cu+Ni (SN100C)

o Sn07Cu+Co (SN100e)

o Sn07Cu+Ni+Bi (K100LD)

o HASL PCB Coating o Sn07Cu+Ni (SN100C)


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


2nd Generation Pb-Free Solder (Thoughts)

o Ni-modified SnCu and low silver SAC are the primary front runners

o Both seem to display reliability behaviors between SAC305 and SnPb

o Proliferation of custom alloys is unhealthy for the electronics industry

o Too much time spent on material identification, characterization, and risk assessment

o One customer had SAC405, SAC387, SAC305, SAC105, SAC0307, and SAC125Ni on one board!

o Almost no component manufacturers assess these new alloys from a physics of failure

o Test to spec mentality

o Huge risk for escapes


Module 6: Solders

Hand Soldering

Copper Dissolution

Mixed Assembly


o Designed for hand soldering

o SIR data

o Halogen / halide free: Watch for definitions!

o Supplier – relationships, proximity

o Lead finish

o Substrate finish

o Acid number

o Lead free or SnPb soldering?

o Compatibility with adjacent materials

o Adhesives, conformal coatings, etc.

Basic Hand Soldering Materials Selection Criteria


o Size /type / pitch / plating of leads

o Substrate finish / type – rigid, flex, ENIG, etc

o Space between hand soldered leads and adjacent

components and circuitry

o Size, shape, heat sinking of module at time of hand

soldering

o Can unit and component be preheated?

Design Considerations


o Operator variation is the norm. Training is critical!

o General hand soldering tips:

o Use soldering irons with great thermal recovery - the lower the soldering temperature and the larger the tip, the less heat loss

o Use a high power soldering iron

o Use the largest tip commensurate with the size of the joint being soldered and available space

o Custom tips can be designed if needed.

o Use the largest cored solder wire diameter appropriate for the size of the joint and available space.

o Avoid the use of liquid fluxes

o Typical 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:


o Consider use of a portable preheater

to shorten contact time and fully

activate fluxes

o http://www.zeph.com/airbathseries.ht

m

o Preheat to 100 F or so

o Verify actual PCB and lead temperatures

with small temp labels

o http://www.omega.com/toc_asp/secti

onSC.asp?section=F&book=temperatur

e

o Use solder preforms for repeatable joint

size and flux volume – both PTH and SMT

Hand Soldering Tips

http://www.zeph.com/airbathseries.htm



http://www.omega.com/toc_asp/sectionSC.asp?section=F&book=temperature





o Always avoid liquid flux if possible

o If it’s truly needed:

o Look for methods to ensure precise delivery

o Flux pens are one method

o The needle tip dispense bottles are not recommended.

o Avoid letting flux run under and around adjacent components.

o Provide some form of uniform heating to volatalize as much of the liquid as possible.

o Select a flux designed and validated for hand soldering processes

o This 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.

o Review surface insulation resistance (SIR) data

Use of Liquid Flux


o Typical manual cleaning process:

o Some type of solvent spray is used to loosen flux residues and followed by hand cleaning using IPA and a soft bristle brush.

o This type of manual cleaning process represents a reliability risk.

o Several studies have shown that SIR (surface insulation resistance) actually INCREASES when IPA and brushes are used in manual cleaning.

o Brushes are not routinely cleaned or maintained and become contamination transfer mechanisms.

o Poorly removed residues are more likely to experience corrosion failures than no clean flux residues left intact.

o In rework and repair, if you can’t rinse, you can’t clean.

Manual Removal of Flux Residues: Not Recommended!


72

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


Copper Dissolution (Contact Time)

o Contact time is the major driver o Some indications of a 25-30 second limit

o Preheat and pot temp. seem to have a lesser effect

o Optimum conditions (for SAC) o Contact time (max): 47 sec. (cumulative)

o Preheat temperature: 140-150°C

o Pot temperature: 260-265°C A Study of Copper Dissolution During Pb-Free PTH Rework Using a Thermally

Massive Test Vehicle , C. Hamilton (May 2007)


Solutions to Cu Dissolution

o Option 1: restriction on rework

o Number of reworks or contact time

o Option 2: solder material

o Indications that SNC can decrease dissolution rates

o Reduced diffusion rate through Sn-Ni-Cu intermetallics

o Option 3: board plating

o Some considering ENIG

o Some considering SNC HASL

A Study of Copper Dissolution During Pb-Free PTH Rework Using a Thermally

Massive Test Vehicle , C. Hamilton (May 2007)


Mixed Assembly

o Primarily refers to Pb-free

BGAs assembled using

SnPb eutectic solder paste

o Why?

o Area array devices (e.g.,

ball grid array, chip scale

package) with eutectic

solder balls are becoming

obsolete

o Military, avionics,

telecommunications,

industrial do not want to

transition to Pb-free…yet

UIC


77

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


78

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


Impact of Peak Temp & % Pb Dissolution on Fatigue

Life o Fatigue life begins to

increase at 217 C

o Increases until the maximum temperature of 224°C is reached.

o After 217 C, higher peak temperature = higher fatigue life.

o Fatigue life does not increase until ~ 85% Pb dissolution

o To 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

100 1,000 8,00010

0.03

0.3

3

30

99

SnAgCu/SnPb

SnAgCu/SnAgCu

SnPb

Cycles to FailureC

um

ula

tive

Fa

ilu

re (

%)

100 1,000 8,00010

0.03

0.3

3

30

99

SnAgCu/SnPb

SnAgCu/SnAgCu

SnPb

100 1,000 8,00010

0.03

0.3

3

30

99

100 1,000 8,00010

0.03

0.3

3

30

99

SnAgCu/SnPb

SnAgCu/SnAgCu

SnPb

Cycles to FailureC

um

ula

tive

Fa

ilu

re (

%)

HP: 0 to 100ºC, 214ºC Peak Temp


Mixed Assembly & Voiding

o BGA voiding is common

in mixed assembly

o Indium Corp. studied

behavior under

o 217C Peak T (Low)

o 240 C Peak T (High)


Indium Corp Study Conclusions

o Mixed systems have less voiding at low temp

o Mixed systems had higher voiding than lead-free systems

when reflowed at high temp

o Some ways to reduce voiding

o Solder paste formulation less prone to have voiding

o Mechanical shielding fixture (temperature)

o Longer soaking profile

o Nitrogen reflow atmosphere


Mixed Assembly: Conclusions

o A potentially lower risk than complete transition to Pb-free

o Important note: more studies on vibration and shock

performance should be performed

o The preferred approach for some high reliability

manufacturers (military, telecom):

o Acceptance of mixed assembly could be driven by GEIA-

STD-0005-1


Mixed Assembly: Alternatives

o Other options on dealing with Pb-free BGAs other than mixing with SnPb o Placement post-reflow

o Reballing

o Two flux options o Application of Pb-free solder paste

o Application of flux preform

o Two soldering options o Hot air (manual)

o Laser soldering (automatic)


Reballing BGAs

o Has 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,


Ongoing DfM Learning Opportunities

o Some ideas for low cost continuing education inside and

outside of your company

o E-Learning at dfrsolutions.com

o Organize “Your Company Days”, Poster Sessions, Demos

o Use internal electronic bulletin boards an resources

o Brown Bags &” Lunch and Learns” from your internal gurus

and from your suppliers

o PCB

o Contract Manufacturers

o Electronics Materials - paste, fluxes, cleaners


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.


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.


Contact Information

• Questions?

• Contact Cheryl Tulkoff, [email protected],

512-913-8624

• [email protected]

• www.dfrsolutions.com

• Connect with me in LinkedIn as well!

http://www.dfrsolutions.com/