Understanding Best Practices in Test Plan Development January 24, - - PowerPoint PPT Presentation

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Understanding Best Practices in Test Plan Development

January 24, 2019 | Greg Caswell

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• Preparing a viable test plan involves several steps to properly identify

the requirements for the tests. This webinar will identify a methodology for this test plan approach. It will discuss the necessity for a BOM review to determine part limitations, assessing the field environmental conditions so they can be properly mapped to the tests implemented, and the impact of failure history, should it exist.

• Next, it is necessary to generate the acceleration factors for the test protocols.

Determining the acceleration factors involves identifying the failure mechanisms

• r the environments the unit has encountered. There are several formulas for

ascertaining the acceleration factor based on the anticipated failure

• mechanism. Several will be discussed.
• Next, identifying the correct activation energy for the materials being tested is

also critical. .7eV has classically been the activation energy for integrated circuits, but is not applicable for all device types.

• Finally, a test protocol that facilitates the accelerated testing is created. To do

so requires an understanding of the reliability metrics for the product (e.g. reliability requirement, life expectancy, confidence level, sample size) is

• needed. The test plan can then be formulated where the specific test conditions

and parameters are defined. These involve temperature range, humidity, cycles to failure, power (power cycling) and unusual stresses like dust or salt fog.

• This webinar will address this flow and provide insight into the approach to take

in developing your test plans.

2

Abstract

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• Determine Failure Mechanisms

− Review BOM, conduct product tear down if possible − Determine part limitations. What are the maximum stresses the product can handle in test? − Determine the field environmental conditions − Assess failure history if it exists

• The objective is to develop a test plan that does not stress the

assembly to a level where a failure might not be experienced in the field

3

Test Plan Approach

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Test Plan Development – Define Use Environment

• The critical first step is a good understanding of the shipping

and use environment for the product.

• Do you really understand the customer and how they use your

product (even the corner cases)?

• How well is the product protected during shipping (truck, ship,

plane, parachute, storage, etc.)?

• Do you have data or are you guessing?

− Temp/humidity, thermal cycling, ambient temp/operating temp. − Salt, sulfur, dust, fluids, etc. − Mechanical cycles (lid cycling, connector cycling, torsion, etc.)

4

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Test Plan Development – Define Use Environment

5

Container and Ambient Temperature

15.0 25.0 35.0 45.0 55.0 65.0 75.0 50 100 150 200 250 300 350 400 450 Hours Temperature (°C)

Container Temp (°C) Outdoor Temp (°C)

Temp. Variation In a Trucking Container

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Example of Failure Inducing Loads

6

• Temperature Cycling

– Tmax, Tmin, dwell, ramp times – T and Sustained Temperature – exposure time

• Humidity

– Controlled, condensation

• Corrosion

– Salt, corrosive gases (Cl2, etc.)

• Power cycling

– Duty cycles, power dissipation

• Electrical Loads

– Voltage, current, current density – Static and transient

• Electrical Noise
• Mechanical Bending (Static and Cyclic)

– Board-level strain

• Random Vibration

– PSD, exposure time, kurtosis

• Harmonic Vibration

– G and frequency

• Mechanical shock

– G, wave form, # of events

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Humidity / Moisture (Rules of Thumb)

• Non-condensing

− Standard during operation, even in outdoor applications − Due to power dissipation

• Condensing

− Can occur in sleep mode or non-powered − Driven by mounting configuration (attached to something at lower temperature?) − Driven by rapid change in environment − Can lead to standing water if condensation on housing

• Standing water

− Indirect spray, dripping water, submersion, etc. − Often driven by packaging

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Field Environment (BEST PRACTICE)

• Use standards when…

− Certain aspects of your environment are common − No access to use environment

• Measures when…

− Certain aspects of your environment are unique − Strong relationship with customer

• Do not mistake test specifications for the actual use environment

− Common mistake with vibration loads

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Test Plan Development

• Product test plans are critical

to the success of a new product or technology

• Stressful enough to identify

defects

• Show correlation to a realistic

environment

• DfR Solutions approach
• Industry Standards + Physics
• f Failure
• Results in an optimized test

plan that is acceptable to management and customers

• MIL-STD-810,
• MIL-HDBK-310,
• SAE J1211,
• IPC-SM-785,
• Telcordia GR3108,
• IEC 60721-3, etc.
• PoF!

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KNOW YOUR ENVIRONMENT (CASE STUDY)

• Leader in surgical systems for eyecare

− Released latest system with foot pedal for ease of use

• Failed to realize how customers would use foot

pedal

− Moving system across carpet without lifting up foot pedal created large static charges − Using foot pedal to pull system caused cable/connector failures

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ELECTRICAL ENVIRONMENTS (CHARGING)

• Often well defined in developed countries

− Though, not as benign as always specified

• Introduction into developing countries can sometimes cause

surprises

• Rules of thumb

− China: Can have issues with grounding (connected to rebar?) − India: Numerous brownouts (several a day) − Mexico: Voltage surges

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• Beta Determination

12

Failure History

Beta = 2.7628 Rho = 97.4 Beta of 3 for EOL if test data not available

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13

Acceleration Factor

• Determine the Acceleration Factor formula to use

− The formula should be based on the failure mechanisms, but if not possible, then on the environments − Make it clear how the acceleration factor was determined − Determine the activation energy for the failure mechanism based on the materials involved.

• Research may be necessary to determine the most applicable

failure mechanisms depending on the environments.

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Using Sherlock

• In the Sherlock solder fatigue calculator you put in the information for the part most susceptible

to failure. In this case a 2512 chip resistor. The calculation on the left defines a diurnal thermal cycle from 20-40C. The right a test cycle from -20 to 85C with 1 hour at each

• extreme. The diurnal calculation is 135,132 cycles to failure while the test is 4358 cycles. The

acceleration is the diurnal divided by the test cycles = Af =31

14

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15

Arrhenius

• Widely used to describe variety of chemical reactions
• Limited to temperature effects

       = kT H A t f exp

A = scaling constant H = activation energy (eV) k = Boltzmann constant (8.62 x10-5 eV/K) T = temperature (K)

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16

Eyring

• Extension of Arrhenius equation

− Takes into account multiple stresses and synergy with temperature − Recommended by IPC SIR Handbook to determine acceleration factors for ECM

• Too comprehensive?

− Number of stresses undefined − Number of unknowns increases twice as fast as the number

• f stresses

− Stress functions undefined (natural log, exponential, linear)

      +       + +       + +  = 

2 1

exp S T E D S T C B kT H AT t f



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Peck

tlife = time to failure, A0 = material constant RH = relative humidity, n = empirical constant (2.66) Ea = activation energy, k = Boltzmann constant T = temperature, f(v) = voltage function (power law, ~1.5)

17

( )

kT E v f RH A t

a n life

− =

−

exp ) (

• Galvanic corrosion of aluminum bond pads in encapsulated

microcircuit

–

Based on Eyring model

• Review of previous research

–

Primary environments: 85/85, 110/85

–

Voltages: 5 to 70 VC

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• Derivation of how 24

temperature cycles = 1 year of

• peration
• Modified Engelmaier

− Semi-empirical analytical approach − Energy Based Fatigue

• Determine the strain range (g)
• C is a correlation factor that is

a function of dwell time and temperature, LD is diagonal distance,  is CTE, T is temperature cycle, h is solder joint height

Temp Cycles to Lifetime Correlation-Derivation Process

For electronics used outside with minimal power dissipation, the diurnal (daily) temperature cycle provides the primary degradation-inducing load

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Temp Cycles to Lifetime Correlation-Derivation Process

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Temp Cycles to Lifetime Correlation-Derivation Process

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Temp Cycles to Lifetime Correlation-Derivation Process

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Next Step

• Define the Reliability Metrics for the product

– Reliability in percentage (e.g. 95%) – Confidence in Test in percentage (e.g. 90%) – Life expectancy of the product in years – Sample Size available for test – Utilize the Beta and Acceleration Factors

• Define Test Recommendations

– Thermal Cycling – Temperature-Humidity-Bias – Vibration – Shock – Other

22

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Next Step

• Understand the customer limitations

− sample size − test duration − chamber capabilities − monitoring requirements

• Some testing protocols may be standards based to fit the

customers requirements

23

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• PoF Definition: The use of science (physics, chemistry, etc.) to

capture an understanding of failure mechanisms and evaluate useful life under actual operating conditions

• Using PoF, design, perform, and interpret the results of

accelerated life tests

− Starting at design stage − Continuing throughout the lifecycle of the product

• Start with standard industry specifications

− Modify or exceed them − Tailor test strategies specifically for the individual product design and materials, the use environment, and reliability needs

Physics of Failure (PoF)

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• Failure of a physical device or structure (i.e. hardware)

can be attributed to the gradual or rapid degradation of the material(s) in the device in response to the stress or combination of stresses the device is exposed to, such as:

− Thermal, Electrical, Chemical, Moisture, Vibration, Shock, Mechanical Loads . . .

• Failures May Occur:

− Prematurely − Gradually − Erratically

Physics of Failure Definitions

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Desired Lifetime (IC Wearout)

1995 2005 2015 0.1 1.0 10 100 1000 Year produced Known trends for TDDB, EM and HCI degradation

(ref: extrapolated from ITRS roadmap)

Mean Service life, yrs. Computers laptop/palm cell phones Airplanes

0.5 mm 0.25 mm 130 nm 65 nm 35 nm

Process Variability confidence bounds

Technology

(courtesy of J. Bernstein, UMD)

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Desired Lifetime (Capacitor Wearout)

• Ceramic chip capacitors with high capacitance / volume (C/V) ratios

– Can fail in less than one year when operated at rated voltage and temperature

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Desired Lifetime (Solder Wearout)

• Elimination of leaded devices

− Provides lower RC and higher package densities − Reduces compliance

Cycles to failure

• 40 to 125C

QFP: >10,000 BGA: 3,000 to 8,000 QFN: 1,000 to 3,000 CSP / Flip Chip: <1,000

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Examples of Wear Out Failure Mechanisms

• Chemical / Contaminate

− Moisture Penetration − Electro-Chemical-Migration Driven Dendritic Growth. − Conductive Filament Format (CFF) − Corrosion − Radiation Damage

• Mechanical

− Fatigue − Creep − Wear

• Electrical

− Electro-Migration Driven Molecular Diffusion & Inter Diffusion − Thermal Degradation

29

• When Over Stress Issues are

Detected.

− Verify supplier’s are meeting material strength specs & purity expectation − Re-evaluate field loading / stress expectation used to design the part − Sort out stresses

›

Combined stress issues are

• ften involved

− Re-evaluate effectiveness of product durability testing

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PoF and Wearout

• What is susceptible to wearout in electronic designs?

− Ceramic Capacitors (dielectric breakdown) − Electrolytic Capacitors (electrolyte evaporation, dielectric dissolution) − Resistors (if improperly derated) − Silver-Based Platings (if exposed to corrosive environments) − Relays and other Electromechanical Components (wearout models not well developed) − Connectors (if improperly specified and designed) − Tin Whiskers − Integrated Circuits (next generation feature size) − Interconnects (Creep, Fatigue)

›

Plated through holes

›

Solder joints

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Critical Elements for Developing Robust Test Plans

• Test Objectives

− Comparison − Qualification − Validation − Research − Compliance − Regulatory − Failure analysis

• Elements
• Reliability Goals
• Design
• Materials
• Use Environment
• Budget
• Schedule
• Sample availability
• Practicality
• Risk

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Define Reliability Goals

• Identify and document two key metrics

− Desired lifetime

›

Defined as time the customer is satisfied with

›

Should be actively used in development of part and product qualification

− Product performance

›

Returns during the warranty period

›

Survivability over lifetime at a set confidence level

›

MTBF or MTTF (try to avoid unless required by customer)

32

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Perspective on Desired Product Lifetimes

33

• Low-End Consumer Products (Toys, etc.)

− Do they ever work?

• Cell Phones:

18 to 36 months

• Laptop Computers:

24 to 48 months

• Desktop Computers:

24 to 60 months

• Medical (External):

5 to 10 years

• Medical (Internal):

7 years

• High-End Servers:

7 to 10 years

• Industrial Controls:

7 to 15 years

• Appliances:

7 to 15 years

• Automotive:

10 to 15 years (warranty)

• Avionics (Civil):

10 to 20 years

• Avionics (Military):

10 to 30 years

• Telecommunications:

10 to 30 years

• Solar:

25 years (warranty)

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HOW MANY SAMPLES?

• The one question that is the most difficult to answer
• Reality is driven by resource limitations

− Most (~85%) companies subject less than 10 samples through any accelerated life test − Some (~10%) will test a larger number (16-24) to failure so as to

• btain good distribution behavior

− Few (~5%) actually perform a statistical analysis of sample size

›

Many more ‘want to’, but adjust when calculated sample size is larger than attainable

34

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Test Plan Development

• Develop a comprehensive test plan
• Assemble boards at optimum conditions
• Rework specified components on some boards
• Visually inspect and electrically test
• C-SAM & X-ray inspect critical components on 5 or more

boards (+3 reworked for BGAs)

• Use these boards for further reliability testing (TC, HALT, S&V)
• Perform failure analysis
• Compile results and review

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Temperature/Humidity/Bias

• Determine if environment is condensing or non-condensing
• Condensing

− Cyclic humidity testing is more relevant − Repeated applications of condensation events leads to wearout type behavior ( > 1) over time − Initial condensation events “weaken” the circuit by inducing dissolution of conductor material − MIL-STD-810, IEC 60068-2-30, IPC TM-650 2.6.3.1 / 2.6.3.4

• Non-condensing

− Best practice is to perform step stress approach − 40C/93%RH for 500 hours at bias, DfR has found that 3 weeks at this environment will drive ECM failures if they are going to occur

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37

Thermal Cycle Testing

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

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

− Thermal Cycling Key Parameters:

›

Thermo-mechanical expansion/contraction is the force that drives material damage accumulation stress aging.

• Primary Aging Factors are:

High End Temp., High to Low Temp. Difference & # of Cycles. Correlation to Number of Cycles, Not the Time Duration

• Secondary Aging Factors are:

Hot Dwell Time & Change Rate.

• Limit Factors (to Avoid Foolish Failures) are:

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

Note: PROFILES MUST BE BASED ON Temperatures as are measured at the components on the PCB (Not Chamber Settings) and must include Self heating and Thermal Lag Effects

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• From IPC-SM-785 - Guidelines for Accelerated Reliability

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

− Temperature Cycling Continued:

› Max Temp. MUST NOT EXCEED:

• The (Tg - Glass Transition Temp.) of the substrate/PWB. Material properties dramatically

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

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

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

IMPORTANT.

• Hot Dwell is more important than Cold Dwell - needed to realize creep damage.
• Hot Dwell under a TENSILE LOAD causes faster attachment aging rates then Compressive

Load.

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

› 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

• Because Metal becomes a structure (do not creep) < 50% absolute (K) Melting

temperature

• Eutectic Solder Melts at 183ºC +> 456ºK,
• 50% = 228ºK => - 44ºC

Thermal cycling Testing (continued)

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HALT Testing

• A typical HALT test exposes the product to

simultaneous vibration and thermal cycling. The product is tested in the operational mode while the vibration stress is increased with each thermal cycle.

• The objective of the test is to cause failure of the

product thus identifying the weakest link which can be then be improved. The test duration is typically less than a week. On its own, this test is not able to predict the life of a product (acceleration factor is not known). However, it is very useful when a product can be compared side-by-side with a previous generation

• f product with known reliability.

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Temperature Cycling/Vibration

• Best Practice: Based on acceleration factor derived from end-
• f-life simulation

− Most common: Based on specification provided by the customer

• Best Practice: Continuous functionality testing

− Most common: Periodic functionality test − Avoid: Functionality test before and after testing (relatively worthless)

• Best Practice: Test to failure (provides data for continuous

improvement)

− Most common: Test to life (based on acceleration factor) or test to spec (based on specification)

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41

Two Types of Circuit Board Related Vibration Durability Issues

• Board in Resonance

–

• Components. Shaken Off/Fatigued

by Board Motion.

›

By Flexing Attachment Features

• Components In Resonance.

–

Components Shake/Fatigue themselves apart or

• ff the Board.

–

Especially Large, Tall Cantilever Devices 3 Med. Sized Alum CAPS 1 Small Long Leaded Snsr 1 Hall Effect Sensor. 1 Large Coil Assembly

PC Board Lead Motion

• Flexed Down
• Normal
• Flexed up

Bending Lead Wires Stressed Solder Joint

Displacement

Gull Wing I.C.

• Time to Failure Determine by

Intensity/Frequency of Stress Verses Strength of Material

Log (Number of Cycles to Failure) Log (Peak Strain) Solder Fatigue Life

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Temperature Cycling + Power Cycling

• Product qualification based
• n power cycling

− Acceleration is simply through an increase in frequency − Acceleration factors greater than 120 easily attainable

10 20 30 40 50 60 12:00 AM 4:48 AM 9:36 AM 2:24 PM 7:12 PM 12:00 AM

Time Temperature

• 0.45

• Combined testing should be

performed at both hot and cold dwells

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Mechanical Shock / Drop Testing

• Heavily based on military and

industry specifications

− Random events difficult to capture and characterize

• Primary driver for failure is out-
• f-plane displacement

− Similar to vibration

• Solder joint failure sensitive to

intermetallic thickness

− Preconditioning may be appropriate − Correlation to field environment based on Arrhenius equation and activation energy of 0.5 eV

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Mechanical Shock

• Experienced during both shipping and installation
• Options

− IEC 60068-2-31 (mentioned in IEC 61298)

›

Four drops (one per edge)

›

Drop from 25, 50, or 100 mm

›

Angled at 30º

• IEC 60068-2-27

− 50G peak load with 11 millisecond pulse

• MIL-STD-810

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Product Qualification (other)

• Mixed Flowing Gas (MFG)

− Used to simulate corrosive mechanisms found in equipment exposed to industrial environments − Consists of Cl2, H2S, SO2, and NOx − Most commonly used for connectors or products used in particularly corrosive environments (under sink, paper processing, etc.)

• Salt Spray
• Water Spray
• EMI/EMC – IEC 61000-X for series of applicable tests
• ESD
• High Temperature Operating Life (HTOL) IEC60068-2-2
• UV Exposure – ASTM G154-06

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Test Plan Development

• Identify the specific recommendations for the customer’s

application and requirements

• Identify the specific test conditions and parameters

− Temperature range − Humidity − Thermal Cycles − Power

• Identify the test duration – including any ramp rates, and

dwells

• Define “failure” for each test

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Test Plan Development

• Utilize Weibull ++ to perform calculations

− In this example we used the acceleration factor for the 2512 resistor previously calculated. − We used a 95% reliability metric, 80% confidence level, 10 year life expectancy, 50 samples and a Beta of 3 as we have no failure history. − The output is that a 100 day test will equate to 10 years in the field.

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Case Study 1-Industrial Application

• Environments tend to be high humidity (95%RH)

− Test data suggests the unit will not be exposed to high humidity while running because of the equipment’s inherent ability to dehumidify the enclosure − Concern is that in some environments the equipment will operate less frequently and could get “soaked” with humidity while dormant

• Environments commonly seaside

− Salt an absolute concern

• Among other things, typical chemicals used in exposure testing:

Acetic Acid (Glacial) Acetone Ammonium Hydroxide (20 percent by weight) ASTM reference fuel C Diethyl Ether Furfural Ethylene Dichloride Ethyl Acetate n-Hexane Methanol 2-Nitropropane Toluene

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Case Study 1: Equipment Description: Conformal Coating

• Conformal Coating

− Acrylic resin − Thickness: Wet thickness: 200-250µm, Dry thickness: 50-60µm. How applied: dip coating.

• This coating material is designed for use on boards having no-

clean flux residue

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• Reliability Objectives

− Demonstrate lifetime of 10 years − Zero (0) test failures out of a sample size of 6

Case Study 1 - Objectives

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• There are a large number of potential failure mechanisms that

can be accelerated on the electronics

− To handle this variability, the electronics industry has typically assigned an ‘average’ activation energy of 0.7eV

• Based on this activation energy, testing at 105C provides a

26X acceleration factor over 55C operating

− Ten (10) year life can be demonstrated by testing for 3309 hours or 138 days

Case Study 1 -Constant Temperature

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• For air temperature variation, prior analyses performed by DfR has

found that 24 cycles of -40C / 85C is equivalent to 1 year in a realistic worst-case industrial environment (in Phoenix, AZ)

• 24 one hour cycles equals 365 diurnal cycles

− Cycle is 20 minute dwells with ramps covering 10 minutes − 48 cycles of -40C / 85C = 2 years in the field − 64 cycles of -10C / 85C − 84 cycles of 30C / 85C − Using:

• Provides insight into solder joint fatigue, plated through hole fatigue

that results from differences in thermal expansion between the components and the printed circuit board.

• A sample size of six (6) should be sufficient for this test

Case Study 1 - Temperature Cycling

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• Test standard IEC 60529 can be utilized to test the electronics

for resistance to dust and water ingress. In the dust test method 13.4 talcum powder is used as the dust medium. Condition 5, category 2 is recommended (no pressure differential between the enclosure and the chamber). Test duration is 8 hours and a sample size of 3 is recommended.

• DfR also recommended that a thermal coupling test be

performed where the temperature rise of the electronics is monitored as the dust clogs the system.

Case Study 1 - Dust and Water Ingress

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• Three primary concerns with ‘air-induced’ corrosion in the

environments defined

− Industrial gases − Relative humidity / condensation − Salt spray

• Industrial Gases

− Due to its presence in industrial locations, may wish to consider mixed flowing gas (MFG) testing − Appropriate specification is EIA-364-65, class IIA for 4 days (2 years equivalent) (336 hours for 10 year life equivalent) − NOTE: This is an expensive test and not a standard test among industrial control equipment

Case Study 1 - Corrosion – Air

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Case Study 1 - Corrosion – Salt Spray

• The standard for this test is MIL-STD-810, Method 509.5

− There is also an IEC equivalent, IEC 60512-6 − Recommend MIL-STD to cover military customers

• 96 hour duration

− Unit is typically not operational during these test, but must function after the test is completed

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Case Study 1 - Proposed Test Plan: Humidity Cycling

• There is no universal algorithm for deriving an acceleration factor

for exposure to elevated moisture conditions

− Because of this limitation, most OEMS use standard test conditions to evaluate the robustness of designs when exposed to elevated moisture for long periods

• f time
• Cycling the temperature and humidity will drive condensation of

water inside the unit (especially when the equipment is off).

− This test method will assess conductive anodic filament (CAF) formation, effectiveness of the PCB conformal coating, and the robustness of the hardware

• DfR believes that the most appropriate test method is IEC 61215

10.12 (humidity freeze conditions) and 10.13 (damp heat

− This test methodology is called out by ASTM e1 171-09, which was created to assess the robustness of the hardware − The IEC tests call out 10 humidity freeze cycles (-40C/60C) followed by 1000 hours at 85ºC/85%RH

• Power Cycling the electronics is recommended as it would create a

worst case situation

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• Hard Drive Testing

− Customer’s reliability goal was an annualized failure rate (AFR) of <0.5%

›

AFR should be calculated using disk drive wearout parameters and not an arbitrary MTBF number

›

Drive constituent and wearout mechanism

• Bearings, platter, axle – mechanical shock and high temperatures
• Bearing lubrication – high temperatures, low temperatures, and humidity
• Platter – electro-magnetic field
• Armature, head, slider – mechanical shock, wearout from use (load-unload process)

Outside the Box Test Plans

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• Utilization inefficiency can be defined as the excess number of times the

disk drive performs this 7-step load-unload routine:

1.

Motor acceleration

2.

Slider loading

3.

Track following

4.

Armature sweeping

5.

Track following

6.

Slider unloading

7.

Motor deceleration

• Reducing the number of times the disk drive performs this routine extends

the drive’s life. Most high reliability disk drives are spec’d for 500k- 600k load-unload (LUL) cycles.

• Customer stated that the disk drive will contain their system’s operating

system and act as a data logging storage device. This means that they can control, with software, how often the disk drive spins down by enabling a “capacity assessment” or “lookup” routine.

HDD Testing Approach

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• AFR was calculated using two utilization criteria: Inefficiency and Data logging

interval − Inefficiency consists of the percentage of time the operating system starts and stops the hard drive during normal, non-data logging use

›

Array analyzed: 100%, 50%, 25%, 10%, 5%, 2.5%, 1%, and 0.5% − Data logging interval considers a LUL cycle to write data to the drive

›

Array analyzed: 1hr, 30min, 15min, 10min, 5min, 1min, 30sec, and 10sec

• A combination of these two criteria, High-to-low inefficiency and long-to-short

intervals, were weighted against a total LUL cycle count of 600k cycles for the drive

HDD Results

Total Load-Unload Cycles 6.00E+05 0.01% 0.01% 0.03% 0.04% 0.09% 0.44% 0.87% 2.59% 0.5% Inefficency 43.8 87.6 175.2 262.8 525.6 2628 5256 15768 Yearly: 8760 17520 35040 52560 105120 525600 1051200 3153600 Hourly: 1 2 4 6 12 60 120 360 Datalogging Cycle: 1 hr 30 min 15 min 10 min 5 min 1 min 30 sec 10 sec Utilization Breakdown by Load-Unload Cycles Annualized Failure Rate (AFR) by Load-Unload Routine Utilization

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• Electrolytic Capacitor Wearout Behavior

− Wear-out is caused by electrolyte diffusion through the end seal

›

Increased temperature increases rate of diffusion

›

As electrolyte volume decreases, ESR increases

− DfR Solutions used temperature dependent rate of weight loss testing and critical weight loss dependence on % ESR increase(failure identified as 200%) to predict characteristic life of capacitors

Sometimes New Testing Approaches are Required

y = 0.0239x R² = 0.9975 2 4 6 200 400

Weight Loss (mg) Time (hrs)

Average Weight Loss Over Time 2

y = 0.0062x R² = 0.9825 0.5 1 1.5 200

Weight Loss (mg) Time (hrs)

Average Weight Loss Over Time 2

y = 0.004x R² = 0.9904 0.5 1 100 200 300

Weight Loss (mg) Time (hrs)

Average Weight Loss Over Time 2

105C=0.0258 mg of electrolyte/hour 85C=0.00605 mg of electrolyte/hour 76C=0.0043 mg of electrolyte/hour

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• Based on rates at 105°C, 85°C, and 76°C

− Expected rate at 45°C 0.0008 mg of electrolyte/hr

• Modeled using an exponential function

− Data fits well to model

Results: Rate of Weight Loss Temperature Dependence

y = 7E-05e0.053x R² = 0.9919

0.005 0.01 0.015 0.02 20 40 60 80 100

Rate of Weight Loss (mg/hr) Temperature (°C)

Rate of Weight Loss Temperature Dependence

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• Exponential function fits relationship between mass loss and %

increase in ESR

− Models a sharp increase in ESR after a given mass loss

• Sharp increase in ESR is seen around critical weight loss of 1500 mg

Results: % Increase in ESR with Weight Loss

y = 3.4859e0.0027x R² = 0.88 200 400 600 800 1000 500 1000 1500 2000 2500

% Inc ESR Weight Loss (mg)

% Increase in ESR with Weight Loss

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• If failure is defined as a 200% increase in ESR, then

characteristic life for the aluminum electrolytic capacitors tested is:

− 58,100 hours at 105°C − 248,000 hours at 85°C − 349,000 hours at 76°C − 1,870,000 hours at 45°C, based on rate of weight loss temperature dependence

Discussion: Characteristic Lifetime Estimates

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• Effective failure analysis is critical to reliability!
• Without identifying the root causes of failure, true

corrective action cannot be implemented

− Risk of repeat occurrence increases

• Use a systematic approach to failure analysis

− Proceed from non-destructive to destructive methods until all root causes are identified.

• Techniques based upon the failure information specific to

the problem.

− Failure history, failure mode, failure site, failure mechanism

Don’t Overlook Failure Analysis!

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THANKS

Contact Information:

Greg Caswell DfR Solutions 301-640-5825 443-834-9284 (cell) gcaswell@dfrsolutions.com