Simulation Aided Testing Simulation Guided Testing · o Types of environmental conditions that can...

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Simulation Aided Testing

Simulation Guided Testing

DfR Solutions Webinar

James McLeish - 12/15/2016

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

o There are many guideline documents/standards on potential environmental conditions and the

static or dynamic stresses they apply that Electrical/Electronic (E/E) equipment need to endure.

These document also provide recommendations on how to apply functional performance and

reliability-durability life qualification test, examples: o MIL-STD-810 “Environmental Engineering Considerations and Laboratory Tests”

o SAE-J1455 “Environment Practices for Electronic Equipment in Heavy Duty Vehicles”

o IPC-SM-785 “Accelerated Reliability Testing of Surface Mount Solder Attachments”

o ISO-16750 “Road Vehicles – Environmental Conditions for E/E Equipment”

o IEC 60068 Series of Environmental Testing Method.

o Each of these documents provide valuable information on:

o Types of environmental conditions that can be encountered in various applications.

o How environmental stresses can disrupt the E/E performance & reliability.

o Recommendations on how to simulate these conditions in performance tests

o Accelerated Life Testing (ALT) i.e. Reliability-Durability Demonstration test guidelines

o However each of these documents advise that a significate degree of

tailoring is required to adapt the stress levels information to a specific application

and to correlate the duration of the test to the intended in service durability life.

INTRODUCTION

1


o These documents are good starting points for developing a reliability-durability

qualification test plan for E/E components and systems.

o BUT THEY ARE NOT COMPLETE TEST REQUIREMENTS

o Each of these documents advise that a significate degree of tailoring is required: o To adapt the stress levels information to a specific application and

o To correlate the duration of the test to the intended in service durability life.

o Organization interested in developing a test plan based still need to determine:o Test Duration in either time or number of test cycles.

o Pass/Fail Criteria.

o Sample Size – how many samples are necessary to demonstrate the reliability requirement or

to at least provide reasonable assurance on how the product will behave so that:

o Suppliers can provide the needed number of prototype parts for the test

o Lab personnel can determine the amount of test equipment that will be needed.

INTRODUCTION

2


o One of the most challenging aspects of developing an Accelerated Life Reliability-

Durability Qualification test is how long to run the test to simulate the expected usage

life of your product or system once the application appropriate test conditions are

determined.

o Electronic product are used in a wide range of environment conditions and service life

duration such as:

o For defense or aviation systems, 20-25 years

in a dynamic mobile environment are typical.

o For Industrial, power or telecom infrastructure equipment,

the usage life is typically 15-25 years in a fixed environment.

o The usage life for passenger cars and light trucks

is typically 10-15 year of environment exposure

and 100,000 to 200,000 usage miles.

o For heavy duty commercial trucks, the usage life is

typically at least 10 years of environmental exposure

and at least 1,000,000 miles of usage.

The Challenge of Test to Field Correlation

3


o The classical way to determine the duration of a life test for a product is a long and

expensive process of physical test to field correlation that involves:

1. Harvesting similar types of field aged electronics products from

equipment either still in service or from junk yards and documenting

what is known about where and how often the device was used

in order to determine an estimate of climatic stresses, exposure times

and operating time or cycles.

2. Performing first non-destructive, then destructive lab evaluations of

the field aged devices to characterize the types and degree of aging

degradation such as corrosion, wear & fatigue the device experience.

3. Run accelerate test experiments on material or sample test coupons

with periodic repeats of the degradation characterization evaluations

until finding where the test produces equivalent aging degradation.

This physical approach to test to field correlation projects typically

require at least 2-3 years of expensive effort.

An example of this approach is documented in the paper:

“Lab-Field Correlation For Automotive Electrical Connections” by F.W. O'Malia, et al, Delphi Automotive

Published in: Electrical Contacts - 2000. The Proceedings of the 46th IEEE Holm Conference on Electrical Contacts

(Cat. No.00CB37081). Ref: http://ieeexplore.ieee.org/document/889930/?reload=true

Classical Life Test Correlation

4

http://ieeexplore.ieee.org/document/889930/?reload=true


o Physics of Failure (PoF), also known as Reliability Physics,

o Is a scientific approach to failure research that identifies the failure mechanisms

of how and why failure occurs in various devices and products.

o This research has produced math models of aging-wear out failure mechanisms of

components and materials based on the Material Science principles of Stress Driven

Damage Accumulation in Materials.

o Provides a scientific basis for evaluating usage life and hazard risks of new materials,

structures, technologies and products under actual operating conditions.

o These failure mechanism models have been incorporated

into Computer Aided Engineering (CAE) software programs

that can preform durability simulations of new designs

in a virtual environment.

o To determine the rate of damage accumulation of materials

under stress that can identify when the failure point of an item

is reached and the reliability of products as they age under

either field or test usage and environmental conditions.

Physics of Failure Research Has Made Faster and More Accurate Accelerated Test to Field Correlation Possible

5

CA

E


1. Loads Elect. Chem.

Thermal, Mech... Individual or

combined, from environment &

usage act on materials & structure.

2. StressThe distribution/ transmission of loading forces

throughout the device.

6. Time to Mean Failure:(Damage Accumulation verses Yield Strength

A Function of: Stress Intensity, Material Properties, & Stress Exposure Cycles/Duration].

7. Project the Distribution About the Mean i.e. Rate of Failure (Fall out)

A function of variation in; Usage, Device Strength& Process Quality Control (i.e. latent defects).

3. StrainInstantaneous changes

(materials\structural) due to loading, different loads interact to contribute to a

single type of strain.

Knowledge of how/ which “Key Loads” act & interact is essential for “efficiently”developing good products,

processes & evaluations.

4. Damage Accumulation

(or Stress Aging)Permanent change

degradation retained after loads are removed. From small incremental damage, accumulated during periods/cycles

of stress exposure.

5. Failure Site & TypeTypically due to a designed in: stress concentrator , design weakness, material/process variation or defect.

Physics of Failure Wear Out: i.e. How Things Age & Wear out - The Material Science Principle of Stress Driven Damage Accumulation in Materials

6


o Modified Engelmaiero Semi-empirical analytical approacho Energy based fatigue

o Determine the strain range (Dg)o Where: C is a function of activation energy, temperature and dwell time,

LD is diagonal distance, a is CTE, DT of temperature cycle & h is solder joint height

o Determine the shear force applied at the solder jointo Where: F is shear force, LD is length, E is elastic modulus, A is the area, h is thickness,

G is shear modulus, and a is edge length of bond pad. o Subscripts: 1 is component, 2 is board, s is solder joint, c is bond pad, and b is boardo Takes into consideration foundation stiffness and both shear and axial loads

(Models of Leaded Components factor in lead stiffness / compliancy)

o Determine the strain energy dissipated in the solder joint

o Calculate N50 cycles-to-failure using:o An Energy Based model for SnPbo The Syed-Amkor model for SAC

Thermal Cycling Solder Fatigue Model (Modified Engelmaier – Leadless Device)

7

Th

LC

s

D DDD ag

D

aGGA

h

GA

h

AE

L

AE

LFLT

bcc

c

ss

sDDD

9

2

2211

12

aa

sA

FW DD g5.0

10019.0

D WN f

10006061.0

D WN f


o Determine applied stress applied (σ)

o Determine strain range (∆ε)

o Apply calibration constants

o Strain distribution factor, Kd(2.5 –5.0)

o PTH & Cu quality factor KQ(0 –10)

o Iteratively calculate cycles-to-failure (Nf50)

Plated Through Hole Via Barrel Cracking Thermal Cycling Fatigue Life Based On IPC TR-579

8


Sherlock ADA

PoF Predictions Just

Got Practical &

Accurate

An Award Winning

CAE App for

Physics of Failure

Durability Simulations &

Reliability Assessments

9000 Virginia Manor Rd Suite 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com10

o A Revolutionary Physics of Failure based CAE APP analysis tool

o First commercially available CAE program for performing Physics of Failure

Durability Simulations & Reliability Assessments on Electronic Products

o Predicts reliability-durability and identifies product failure risks

early in design process, quickly and accurately

o A tool for achieving ISO-26262 Functional Safety Requirements

o Develops highly reliable, E/E products faster and more efficiently

o Created in a highly automated CAE APP format

The Sherlock ADA (Automated Design Analysis) CAE APP


Steps of a Sherlock PoF CAE App Analysis

1) Design Capture – Circuit board CAD files provides the inputs to

the modeling software & calculation tools.

11

2) Life-Cycle Definition – define the reliability/durability

objectives and expected environmental & usage conditions

(Field or Test) that the device is needs to endure

3) Load Transformation – auto creates a Finite Element Analysis

to calculate and distribute the environmental and operational

loads across a PCBA to the individual parts & features.

5) Review Results/Risk Assessments - Multiple views, plots and

report formats to evaluate/share results & prioritizes risks which

allows product teams to revise the design to eliminate failure risk,

resulting in the creation of highly reliability products

4) PoF Durability Simulation/Reliability Analysis - Failure

Mechanisms algorithms applied to the model & stress conditions

to performs a design & application specific durability simulation

calculates life expectations, reliability distributions.

11


o In Addition to Producing Highly Reliable Product Designs,

The Sherlock ADA Durability Simulation CAE App can also be used to

design application specific optimize accelerated life tests.

o If the design has already been optimized for Reliability-Durability,

why is testing still needed?

o Traditionally Life Testing was the only way to achieve reliability-durability via

rounds of Physical of Design - Build - Test - Fix Reliability Growth Testing.

o While Sherlock can now be used to virtually optimize designs for reliability-durability,

it is still necessary to verify that suppliers and the assembly process are producing

to the designer expectations.

o However as designs are virtually optimized, testing no longer needs to be as extensive.

“Application Specific” test optimization can be used to design faster and more effect

durability-reliability test in conjunction with the design optimization.

Sherlock Based Reliability-Durability Qualification Test Optimization

12


Why are Application Specific Evaluations Needed?

- Because there is no Universal Acceleration Factor for Electronic Modules

E/E Module are Complex Assemblies of Hundred of Parts,

where each has their own life characteristics& Dozens of Different Components Types

is Challenging Accelerated Test Profiles that REALLY DO

Accelerate Time to Failure Testing For Actual

Failure Mechanism Have Been Demonstrated on

Test Coupons for Individual Component Types.

Excessive Accelerated Test Profiles that Produce

“Foolish Failures” (Not Application Relevant)

Have Also Been Demonstrated.

Practical REPEATABLE “Optimized” application

for Validation of REAL LIFE COMPLEX E/E

Assemblies of MANY DIFFERENT TYPE OF

COMPONENTS is A CHALLENGE.


o Because of Component Design Unique Factors that

Influence Thermal Cycling Solder Fatigue Life.

o Size & CTE of the PCBAs E/E Components

o Component Attachment System (Leaded, BGA, Bottom Terminate, Flip Chip . . . ).

o Size of Component Solder Joint and Pads.

o Fatigue characteristics of the Solder Material.

o Soldering Quality

o Relative to the CTE of the PCB determined by:

o The Material Properties of the Base Laminate Material (CTE & Tg).

o The Fiber Glass Fabric Weave that Constrains the CTE of the Base Laminae Epoxy

o The Copper Layout on Each Conductive Layer.

o The Thickness of Each Insulating and Conductive Layer in the PCB Stack Up

Why is Application Specific Testing Needed?

14


Single Sided Then Thru-hole

DIP Integrated Circuits

1970 ‘s- Today

~4 up to 68 I/O, 1” x 3.5”

Up to 10 Meg Hz Speeds.

1st Generation Quad Surface Mount

J Lead PLCC, 1982 - Today

~6 Up to 160 I/O, 1.5 in sq.,

Up to 100 Meg Hz Speeds

Source of Many Reliability Problems.

2nd Generation Quad Surface Mount

Fine Pitch Gull Wing I.C, 1993 - Today

~54 Up to 450 I/O, 1.75 in sq

Up to 250 Meg Hz Speeds

>10 Time the Life of J Lead in Auto ECMs.

Bump & Ball Grid Arrays ;Leadless Attachments

1996 - Today

~24 - 1000 I/O 1.2 in. sq

500+ 1000 Meg Hz Speeds.

Life Varies w/Size & Conf.

No Lead Chip Scale Packaging (NLCSP)

(LCCC, QFN, DFN, SON, LGA)

2002 - Today

~8 - 480 I/O, .75 in SQ, Gigi Hz Speeds

Can have significantly reduces life


o Newer Bottom Terminated QFN ICs are designed to have thin packages & low profile solder joints which make them less durable than previous IC packages

o A design that make thin & light portable consumer electronics possible o But such low profile solder joints have high CTE Mismatch Expansion-Contraction

shearing angle stresses which Reduces Durability Capabilities

• The IC Industry is prioritizing development of new ICs in QFN packages

o The High Reliability/ Harsh Environment industry needs to be able to able to accurately Evaluate & Validate which EE component package types are suitable for their application

Each EE Component Type and Size has its own Life Characteristics

Example: Comparing Thermal Cycling Durability of IC Packages

Laminated BGAs:

TTCL: 3,000 to 8,000FNL CSP:

TTCL: 1,000 to 3,000

*TTCL = Typical Thermal Cycle Life

During -40° to +125°C Testing

Package

Type

Typical Thermal Cycles to Failure

(-40C to 125C)

QFP >10,000

BGA 3,000 – 8,000

QFN 1,000-3,000

Gull Wing Leaded QFPs

TTCL: >10,000


o Because Thermal Cycling Detects More Defects &

Triggers Thermal Expansion/Contraction Mismatch Stress Driven

Failure Mechanisms that many E/E Components are Susceptible to.

Why is Thermal Mechanical Cycling a Fundamental Aspect

or E/E Durability Testing

IEST – Survey of Stress Screen Results

Source: http://www.istgroup.com/english/3_service/03_01_detail.php?MID

=2&SID=55&ID=156

JPL 83-76 NASA Flight Electronic Environmental

Stress Screening Survey –Source: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/198

40013934.pdf

http://www.istgroup.com/english/3_service/03_01_detail.php?MID=2&SID=55&ID=156

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19840013934.pdf


o The Simulation Guided Testing analysis is based on the Material Science Principles of

Stress Driven Damage Accumulation in Materials (a.k.a Stress Aging).

o Physics of Failure mechanism models used these principles to determine the rate of damage

accumulation & when the failure point of an item is reached. o Explained on the following slides

o The process involved creating a CAE models of a module’s PCBA(s) in the

Sherlock ADA durability simulation program.

o A durability simulation is run using the module’s expected in service operating stress

conditions to determine the amount of accumulated damage life consumption the

module would experience over its expected usage life.

o A 2nd durability simulation is then run using the stress conditions the module will experience

under the stress profile of the Accelerated Life Test (ALT). o The results of the 2nd durability simulation are evaluated to determine how long it takes for the test to

accumulate an amount of stress aging (damage accumulation) that is equivalent to the life time of in

service usage produced in the first durability simulation.

o This define how long the Higher Stress Levels/Faster Stress Cycles in the Accelerate Life Test need to run

to correlate the life test to the expected in field service conditions.

SIMULATION GUIDED TESTING EVALUATION PROCEDURE to Correlate Test Duration to Expected Field Durability Life

18


2) CAE Durability Simulation Determines Stress Failure Level & Time to Failure

Relative to Design Life Requirements.

SGT - Simulated Guided Testing For Designing

an Accurate, Optimized Accelerated Life Test from Knowledge Field Conditions.

Time or # of Usage Cycles

AccumulatedStrain

Damage

Accelerated Test Time to Failure

1) CAE Durability Simulation of Field Conditions Determine Stress/Strain

Driven Damage Accumulation Rate Under Expected Field Conditions

XX

Design Life Goal

3) Rerun the Durability Simulation Under the Accelerated Test Conditions to Determine the Accelerated Time to

Reach the Equivalent Level of Damage Accumulation that Correlates to Field Failures

Determination of Worst - Best Variation

Range Is Also Possible


5) PoF Computer Simulation Calculates Time to Reach Failure Pt. Relative to Design Life Requirements.

SAT - Simulation Aided Test to Field Correlation

– For Interpreting Field Reliability From Accelerated Durability Test Results

Time or # of Usage Cycles

AccumulatedStrain or Damage

Accelerated Test Time to Failure

1) Overstress Testing Identifies 1st Part(s) to Fail & Accelerated Test Time To Failure.

4) PoF Computer Simulation of Rate of Strain/Damage Accumulated

During Expected Field Conditions &Range Over Build Variation

XX

Required Design

Life 2) Rate of Damage Accumulated,

Failure Point During Test

3) Worst - Best Variation Range


o An OEM requires a reliability of at least 97% (<3% Failure risks) over a 10 year

durability period for an electronic module and defined a thermal cycling reliability-

durability demonstrated to demonstrate compliance to this requirement.

o This test was more severe than the E/E module supplier had previously received from the

OEM for similar E/E modules.

o The supplier experienced failures on this test that appeared to prevented compliance

to the OEM’s 97R requirement.

o The supplier requested DfR to use the Sherlock program and the Simulated Aided Testing

process to determine the field reliability demonstrated on the Test.

o A 3D model of the electronic module was created in the Sherlock CAE environment

o The OEM’s definition of annual thermal cycling events was used to model the 10 year thermal

cycling field profile.

o The Sherlock SAT analysis determined that the OEM’s 10 year life test actually correlated to

20.2 year of field life and

o The 10 years field life was actually achieved at 49% of the test time

o At this point the demonstrated failure risk was 1.8% (a reliability of 98.2%).

o From this analysis the OEM accepted that the reliability requirement was achieved and

adjusted the test requirement for future programs.

Simulated Aided Test to Field Correlation – Case Study

21


Test to Field Correlation – Case Study Results.

The Sherlock SAT analysis found

Test to Field Correlation is 2.02

The 13.9% failure risked demonstrated

over the duration of the test was correlated

to ~20.2 years in the field.

Test to Field Correlation is 2.017

The 3% Failure Point was found to occurs at 59%

of the test time which correlated to ~11.9 years

under field conditions .

Field

Test

The Equivalence of 10 Years of

Field Usage was calculated to

occurs at ~49% of the Thermal

Cycle Testing


Defining the Mission Profile in Terms of Stresses Experienced by the Product

- Is an Essential Challenge in Developing an Accelerated Life Test

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Hrs

)

Time At Temperature Hours Over 10 Years

Number of Thermal Cycles Over 10 Years

20-

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(Deg F)

Peak Temp. Band

(Deg F)

Examples of Life Time Field Environmental Thermal Profiles


Test Acceleration Correlates to a Material’s Elastic, Plastic and Yield/Fracture Point Properties

o Material N-S Curve (Number of Life Cycle at a Stress Level) (Transposed S-N) .

Excessive Plastic Deformation

Elastic Region

Plastic Region

Fracture Point

Low Stress~ Near “Infinite”

Life Region

Plastic Region Provides Useful

Acceleration Factors

Foolish Failure Region INVALID TEST REGION

High (log)

Numberof

Cycles

Low

Low Stress (log) High

o Can be Correlated to

the Stress - Strain

Yield Curve.

Low STRAIN in/in High

High

STRESS(psi)

Low


Additional Guidelines for Optimizing Electronic Module Accelerated Testing

While Avoiding Foolish Failures Risks

o Requirements Developed from:o IPC-SM-785 - Guidelines for Accelerated Reliability Testing &

o Solder Joint Reliability (SJR) Theory & Application - John Lau.

oThermal Cycling Key Parameters:

o Thermo-mechanical expansion/contraction is the force

that drives solder fatigue damage accumulation (i.e. stress aging).

o Primary Aging Factors are:

High End Temp., High to Low Temp. Difference & # of Cycles.

o Secondary Aging Factors are:

Hot Dwell Time & Change Rate.

o Limit Factors (to Avoid Foolish Failures) are:

High End Temp., Change Rate & Min. Hot Dwell Time.

Note: PROFILES MUST BE BASED ON Temperatures as measured on the PCB

(Not Chamber Settings) and must include Self heating and Thermal Lag Effects


Guidelines for Electronic Module AST to Avoid Foolish Failures

Part I - Without Simulation Guidance.

Product Ruggedization Development

o From IPC-SM-785 - Guidelines for Accelerated Reliability Testing &

Solder Joint Reliability (SJR) Theory & Application - John Lau.

o Temperature Cycling Continued:o Max Temp. MUST NOT EXCEED:

o The (Tg - Glass Transition Temp.) of the substrate. Material properties dramatically change above the Tg

invalidation the tests. (Tg for FR4 PCB 125-135’C).

o The Lowest Re-Crystalization Temperature of the Plastics used in the Device.

o Temp. Dwell Time (MEASURED on the PCB/COMPONENTS IS VERY IMPORTANT.

o Hot Dwell is more important than Cold Dwell - needed to realize creep damage.

o Hot Dwell under a TENSILE LOAD causes faster attachment aging rates then Compressive Load.

o For FR4 PCB Tensile Loading occurs at Hot Temperatures.)

o Practical Min. Temp. - Cooling Parts below 50% of the Absolute Temp. melting point

of a metal is not value added (wasted time and expensive cooling energy

o Because Metal becomes a structures (do not creep) < 50% absolute (K) Melting temperature

o Eutectic Solder Melts at 183ºC +> 456ºK,

o 50% = 228ºK => - 44ºC


ALT Profile of BCM Run # 4 (Final)w/ shroud -50 to +120 @ Low Power

(added resistors to reduce currents on FETs)

22.9

33.3

51.6

87.5

57.4

33.6

-11.7

-24

4.3

38

65.6

85.8

95.1101.2 101.3

85.5

101.9

105.3

-37.3

-36.6

-38.8

-30-33.3

-60

-50

-40

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Time (min)

Tem

p (

C)

Temp profile near FET Tg (PWB) min. operational temp (Pl. Hs)

Tg (PWB) & Pl. Hs recrystallization temp =120'C12 min. dwell

operational temp

strain gage: -75C to 175C

Accelerometer: -51C to 121C

data collected on

11-19-99

Chamber Setting

-50 to +120 @ 36 min/cyc

Ramp @ 28.33 'C/min

(170'c in 6 min.)

Hot Dwell = 12 min

Cold Dwell = 12 min

5 @ 12.5 'C/Min

5 @ 3.3 'C/Min

~=> 3 @ 103

6 @ -19.5 'C/Min

5 @ -5 'C/Min

Avg 10 @ ~8 'C/Min

Avg 15 @ 9.33 'C/Min

8 @ 14.66 'C/Min

4 @ 5.75

'C/Min

7 @ -37'C

Avg 11 @ -12.5 'C/Min

Need to Understand the Dynamics of the Parts Temperature Relative to Chamber Temperature,

The Temperature that Penetrates into the Parts & PCB

is More Important Than the Chamber Temperature


Difference Between Powered Temperature Cycling & Thermal Shock

Accumulated strain energy density in one cycle

period for thermal shock & thermal cycling.Ref: Effects of Dwell Time and Ramp Rate

on Lead-Free Solder Joints

Fan, Raiser & Vasudevan - Intel Corporation

o Thermal Shock Occurs when the PCBA Experiences

Thermal Ramp Rates of 20-30°C per minute o (Ref. IPC-SM-785) Guidelines for Accelerated Reliability Testing of SM

Solder Attachments.

o Powered Thermal Cycles (PTC) produces a more even

heating/cooling response across a PCBA than Thermal Shock. o Plus the sampled can be monitored for proper operation.

o But PTC cycles are slower which increases time & cost.

o TS is a cheaper test to run that has a much faster ramp rate that

imposes more damage (faster aging) per cycle than PTC.o In many E/E Devices TS cycles can be faster than PTC cycles

o But parts can not be activated and monitored when cycling

between hot and cold chambers.

o Depending on the component type & profile TS with PbFree Solder is

1.5-1.8 times more damaging per cycle than PTC .

o Running ~1/2-2/3 of life under Thermal Shock speeds up the testo Any failures that occur this early in life consumption are treated as

Early Life/Infant Mortality Quality Defects not wear out issues.

o Running the last ~1/2-1/3 of life active under PTC o Enables detection of when wear out failures occur which allows the

time or cycle to failure info to be used in reliability calculations.


Considerations for the Effects of Combined Environments

Dealing with Combined Environment conditions o In reality the environmental conditions occur simultaneously however correlating a combined Environment

test is very difficult.

o Sequence of Testing - In general, both specs recommends placing the most severe environmental testing

last (i.e. … shock & vibration).

o Temperature cycling is often performed first to condition the test article to function mechanically.

In Reality, Traditionally Product Validation Testing is Typically:

o Optimized for scheduling & efficiency of test personnel & equipment.o Separate prototypes groups are tested in the Mechanical Lab, the Thermal Lab, Environmental lab . .

. etc., by separate test specialists.

o This duplicates pieces of the product operating experience.

o But misses the interaction or key stresses that product field failure.

o An answer to the management question of:

“Our products passed the test plan, So why do they it fail in the field?

o Typically encourages specialization of test personnel. o Instead of total product durability specialists.

o Potential for over specialization.

o Success test format.o Emphasizes passing the “Good Enough to Start Production” test.

o Instead of finding potential product weaknesses.

o Impossible to demonstrate a field reliability.


Physics of Failure Basics – Field Failure Often Occur because of Stress Interactions

that are Not Replicated Under Traditional Single Stress Test Formats o Different Environmental & Usage Load Conditions Work in Combination

to Produce Failure Mechanisms.

o Solder Cracks: Range & Number of Thermal Cycles, with

Wire bond/ with Shock/Vibration @ Temperature .

Lead Fatigue STRAIN the SOLDER JOINTS, BOND WIRES& LEADS.

o Diffusion: Usage & Storage time with Chip Die Temperature &

Material Interactions.

o Organic Growths: Time @ Humidity level & Temp., Organic Contaminates.

o Electromigration: Time @ Humidity., Voltage/Current & Ionic Contaminates,

(Dendrite Growths) Geometry layout, Sometimes Temp. & Material Interaction

o CFF (Conductive Time @ PCB Humidity Penetration & Temp., Voltage Diff.,

Filament Formation) PCB Material & Layout, Freq. of Hollow Fiber Defects.

o Corrosion: Time @ Humidity & Temperature, Material Interactions &

Sometimes Voltage, and Salt Contamination .

o This Test Grouping Organization Results in an Enhanced

“Failure Mechanism Susceptibility Detection” Testing Capability


COMBINED THERMAL AND VIBRATION STRAIN- IMPACT TO PRINTED CIRCUIT BOARD LIFE

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VIBRATION STRAIN TRANSMITTED TO FAILURE SITE

THERMAL STRAIN

TRANSMITTED

TO FAILURE

SITE

THERMAL AND VIBRATION STRAIN TRANSMITTED ON TO PWA

& IMPACT TO SOLDER DURABILITY LIFE

VIBRATION STRAIN

TRANSMITTED TO FAILURE SITE

THERMAL STRAIN

(Elastic & Inelastic)

TRANSMITTED

TO FAILURE SITE


o In reality environmental conditions occur simultaneously

o However correlating a combined Environment test is very difficult.

o Sequence of Testing - In general environmental testing specs recommends

placing the most severe environmental testing last in a test sequence

(i.e. …shock & vibration).

o Temperature cycling is often performed first to condition the test article to function

mechanically.

o i.e. “Shake after Bake” approach that assures that after a lifetime of

thermo-mechanical life consumption an E/E module still has adequate

strength to endure the stresses of mechanical vibration

Considerations for the Effects of Combined Environment

32


o In this presentation we had discussed how Physics of Failure knowledge

and the Failure Mechanism Models in the CAE Durability Simulations

of the Sherlock ADA CAE APP in addition to being used to optimize the

Reliability – Durability capabilities of an E/E Product.

o (i.e. Design for Reliability).

o Can also be used to optimize Accelerated Life Qualification Testing of

E/E product resulting in faster test with greater accuracy for detect failure

susceptibilities.

In Conclusion

33


Questions & Discussion

Thank you for your attention.

Any questions?

For More Information or

Assistance in Developing an Optimize Test Plan

Contact:

[email protected]

301-640-5819

mailto:[email protected]

Simulation Aided Testing Simulation Guided Testing · o Types of environmental conditions that can...

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