Test Plan Development Webinar 9-19-13 - DfR Solutions Slides/Test... · 2018. 4. 2. · Mechanical...

© 2004 - 2007© 2004 - 20109000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com© 2004 – 2010

Test Plan Development using Physics of Failure: The DfR

Solutions Approach

Webinar: September 19, 2013

© 2004 - 2007© 2004 - 20109000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com

Introduction

o Agendao Introduction to Test Plan Development

o Testing Exampleso Introduction to Physics of Failure

o Wearout Examples o Methodology for Test Plan Development

o Define the Environmento Temp Cycles to Lifetimeo Test Exampleso Case Studies


Test Plan Development

o Product test plans are critical to the success of a new product or technologyo Stressful enough to identify defects

o Show correlation to a realistic environment

o DfR Solutions approacho Industry Standards + Physics of Failure

o 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!


o PoF Definition: The use of science (physics, chemistry, etc.) to capture an understanding of failure mechanisms and evaluate useful life under actual operating conditions

o Using PoF, design, perform, and interpret the results of accelerated life tests

o Starting at design stage

o Continuing throughout the lifecycle of the product

o Start with standard industry specifications

o Modify or exceed them

o Tailor test strategies specifically for the individual product design and materials, the use environment, and reliability needs

Physics of Failure (PoF)


Industry Testing Falls Short

o Limited degree of mechanism-appropriate testing

o Only at transition to new technology nodes

o Mechanism-specific coupons (not real devices)

o Test data is hidden from end-users

o Questionable JEDEC tests are promoted to OEMs

o Limited duration (1000 hrs) hides wearout behavior

o Use of simple activation energy, with incorrect assumption that all mechanisms are thermally activated, can result in overestimation of FIT by 100X or more


o 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:

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

o Failures May Occur:

o Prematurely

o Gradually

o Erratically

Physics of Failure Definitions


Critical Elements for Developing Robust Test Plans

o Test Objectives

o Comparison

o Qualification

o Validation

o Research

o Compliance

o Regulatory

o Failure analysis

o Elements

o Reliability Goals

o Design

o Materials

o Use Environment

o Budget

o Schedule

o Sample availability

o Practicality

o Risk


Define Reliability Goals

o Identify and document two key metricso Desired lifetime

o Defined as time the customer is satisfied with

o Should be actively used in development of part and product qualification

o Product performance

o Returns during the warranty period

o Survivability over lifetime at a set confidence level

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

8


Limitations of MTTF/MTBF

o MTBF/MTTF calculations tend to assume that failures are random in nature

o Provides no motivation for failure avoidance

o Easy to manipulate numbers

o Tweaks are made to reach desired MTBF

o E.g., quality factors for each component are modified

o Often misinterpreted

o 50K hour MTBF does not mean no failures in 50K hours

o Better fit towards logistics and procurement, not failure avoidance


Perspective on Desired Product Lifetimes

o Low-End Consumer Products (Toys, etc.)o Do they ever work?

o Cell Phones: 18 to 36 monthso Laptop Computers: 24 to 36 monthso Desktop Computers: 24 to 60 monthso Medical (External): 5 to 10 yearso Medical (Internal): 7 yearso High-End Servers: 7 to 10 yearso Industrial Controls: 7 to 15 yearso Appliances: 7 to 15 yearso Automotive: 10 to 15 years (warranty)o Avionics (Civil): 10 to 20 yearso Avionics (Military): 10 to 30 yearso Telecommunications: 10 to 30 yearso Solar 25 years (warranty)

10


Examples of Wear Out Failure Mechanisms

o Chemical / Contaminateo Moisture Penetrationo Electro-Chemical-Migration Driven

Dendritic Growth.o Conductive Filament Format (CFF)o Corrosiono Radiation Damage

o Mechanicalo Fatigueo Creepo Wear

o Electricalo Electro-Migration Driven

Molecular Diffusion & Inter Diffusiono Thermal Degradation

o When Over Stress Issue are Detected.

o Verify supplier’s are meeting material strength specs & purity expectation.

o Re-evaluate field loading / stress expectation used to design the part.

o Sort out stresses,

o Combined stress issues are often involved.

o Re-evaluate effectiveness of product durability testing

11


Desired Lifetime (IC Wearout)

1995 2005 20150.1

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 µµµµm 0.25 µµµµm 130 nm 65 nm 35 nm

Process Variability

confidence bounds

Technology

(courtesy of J. Bernstein, UMD)


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

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

Desired Lifetime (Capacitor Wearout)


Desired Lifetime (Solder Wearout)

o Elimination of leaded devices

o Provides lower RC and higher package densities

o Reduces compliance

Cycles to failure

-40 to 125C QFP: >10,000 BGA: 3,000 to 8,000

QFN: 1,000 to 3,000CSP / Flip Chip:


PoF and Wearout

o What is susceptible to wearout in electronic designs?

o Ceramic Capacitors (dielectric breakdown)

o Electrolytic Capacitors (electrolyte evaporation, dielectric dissolution)

o Resistors (if improperly derated)

o Silver-Based Platings (if exposed to corrosive environments)

o Relays and other Electromechanical Components (wearout models not well developed)

o Connectors (if improperly specified and designed)

o Tin Whiskers

o Integrated Circuits (next generation feature size)

o Interconnects (Creep, Fatigue)

o Plated through holes

o Solder joints


Test Plan Development – Define Use Environment

o The critical first step is a good understanding of the shipping and use environment for the product.

o Do you really understand the customer and how they use your product (even the corner cases)?

o How well is the product protected during shipping (truck, ship, plane, parachute, storage, etc.)?

o Do you have data or are you guessing?

o Temp/humidity, thermal cycling, ambient temp/operating temp.

o Salt, sulfur, dust, fluids, etc.

o Mechanical cycles (lid cycling, connector cycling, torsion, etc.)

16


Failure Inducing Temperature: Transport & Storage

C o n t a i n e r a n d A m b i e n t T e m p e r a t u r e

1 5 . 0

2 5 . 0

3 5 . 0

4 5 . 0

5 5 . 0

6 5 . 0

7 5 . 0

0 5 0 1 0 0 1 5 0 2 0 0 2 5 0 3 0 0 3 5 0 4 0 0 4 5 0

H o u r s

Te

mpe

ratu

re (

°C)

C o n t a i n e r T e m p ( °C )

O u t d o o r T e m p ( °C )

Temp.

Variation

In a

Trucking

Container


Examples of Failure Inducing Loads• Temperature Cycling

– Tmax, Tmin, dwell, ramp times

• Sustained Temperature

– T and 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


o Derivation of how 24 temperature cycles = 1 year of operation

o Modified Engelmaiero Semi-empirical analytical approach

o Energy Based Fatigue

o Determine the strain range (∆γ)

o C is a correlation factor that is a function of dwell time and temperature, LD is diagonal distance, α 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


Temp Cycles to Lifetime Correlation-Derivation Process


Humidity / Moisture (Rules of Thumb)

o Non-condensing o Standard during operation, even in outdoor applications

o Due to power dissipation

o Condensingo Can occur in sleep mode or non-powered

o Driven by mounting configuration (attached to something at lower temperature?)

o Driven by rapid change in environment

o Can lead to standing water if condensation on housing

o Standing watero Indirect spray, dripping water, submersion, etc.

o Often driven by packaging


Test Plan Development

o Develop a comprehensive test plan

o Assemble boards at optimum conditions

o Rework specified components on some boards

o Visually inspect and electrically test

o C-SAM & X-ray inspect critical components on 5 or more boards (+3 reworked for BGAs)

o Use these boards for further reliability testing (TC, HALT, S&V)

o Perform failure analysis

o Compile results and review

© 2004 - 2007© 2004 - 20109000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com 25

Sorting Out Testing Methods, Brands and Different Approaches

HALT(Highly Accelerated Life Test)

Corrosion Testing

MFG, nitric acid test

CERT Combined Environment Reliability Test)

Shainin’s - Step Stress Probe

HASSHighly Accelerated Stress Screen)

HAST(Highly Accelerated Stress Test)

Entella’s - FMVT (Failure Mode

Verification Test)

Salt Spray

MEOST Mixed Environment & Operating Stress Test)

PoF-ALT(Physics of Failure based Accelerated Life Test)

STRIFE(Stress + Life)

PRD Product Ruggedization Development)

Dust test


Environment Definition (Example)

o Flow monitor on oil pipelines

o Environment descriptiono Outside in housing (exposed to direct sunlight)

o On continuously (low power dissipation)

o Fluid flow on pipelines creates vibration

o Shock during shipping and installation

o Optimized approacho Temperature: Use of Phoenix environment

o Thermal:o Imaging outside of the housing; thermocouple on hottest components

in housing

o Vibration: Measurements with friendly customers

o Shock: IEC 60068-2-27


Constant Temperature Testing

o Typically do not recommend long-term constant temperature testing

o Failure mechanisms tend to be well known and designed for (TDDB (Time Dependent Dielectric Breakdown), Electromigration, etc.)

o Potential for future need once sub-100 nm technology incorporated into military electronics

o Intel recently launched a 22 nm device (soon 14 nm)

o Acceleration factor tends to be relatively low (long test time to qualify field performance)


Temperature/Humidity/Bias

o Determine if environment is condensing or non-condensing

o Condensingo Cyclic humidity testing is more relevant

o Repeated applications of condensation events leads to wearout type behavior (β > 1) over time

o Initial condensation events “weaken” the circuit by inducing dissolution of conductor material

o MIL-STD-810, IEC 60068-2-30, IPC TM-650 2.6.3.1 / 2.6.3.4

o Non-condensingo Best practice is to perform step stress approach

o 40C/93%RH for 72 hours at bias followed by 65C/88%RH for 72 hours at bias


Thermal Cycle Testing

o From IPC-SM-785 - Guidelines for Accelerated Reliability Testing & Solder Joint Reliability (SJR) Theory & Application - John Lau.

o Thermal Cycling Key Parameters:

o Thermo-mechanical expansion/contraction is the force that drivesmaterial damage accumulation stress aging.

o Primary Aging Factors are: High End Temp., High to Low Temp. Difference & # of Cycles.Correlation to Number of Cycles, Not the Time Duration

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 are measured at the components on the PCB (Not Chamber Settings) and must include Self heating and Thermal Lag Effects


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/PWB. 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 energyo Because Metal becomes a structure (do not creep) < 50% absolute (K) Melting temperatureo Eutectic Solder Melts at 183ºC +> 456ºK, o 50% = 228ºK => - 44ºC

Thermal cycling Testing (continued)


HALT Testing

o 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.

o 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 of product with known reliability.


Temperature Cycling/Vibration

o Best Practice: Based on acceleration factor derived from end-of-life simulationo Most common: Based on specification provided by the customer

o Best Practice: Continuous functionality testingo Most common: Periodic functionality test

o Avoid: Functionality test before and after testing (relatively worthless)

o Best Practice: Test to failure (provides data for continuous improvement)o Most common: Test to life (based on acceleration factor) or test to spec (based on specification)


Two Types of Circuit Board Related Vibration Durability Issues

o Board in Resonance

o Components. Shaken Off/Fatigued by Board Motion.

o By Flexing Attachment Features

o Components In Resonance.o Components Shake/Fatigue themselves apart or off the Board.

o Especially Large, Tall Cantilever Devices3 Med. Sized Alum CAPS1 Small Long Leaded Snsr1 Hall Effect Sensor.1 Large Coil Assembly

PC Board

Lead Motion- Flexed Down- Normal- Flexed up

Bending Lead WiresStressed 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


Temperature Cycling + Power Cycling

o Product qualification based on power cycling

o Time to failure for SnPb solder is relatively independent of dwell

o Acceleration is simply through an increase in frequency

o Acceleration factors greater than 120 easily attainable

0

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

Te

mp

era

ture

-0.45

0.05

0.55

1.05

1.55

2.05

o Combined testing should be performed at both hot and cold dwells


Mechanical Shock / Drop Testing

o Heavily based on military andindustry specificationso Random events difficult to capture and characterize

o Primary driver for failure is out-of-plane displacemento Similar to vibration

o Solder joint failure sensitive to intermetallic thicknesso Preconditioning may be appropriate

o Correlation to field environment based on Arrhenius equation and activation energy of 0.5 eV


Mechanical Shock

o Experienced during both shipping and installation

o Options

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

o Four drops (one per edge)

o Drop from 25, 50, or 100 mm

o Angled at 30º

o IEC 60068-2-27

o 50G peak load with 11 millisecond pulse

o MIL-STD-810


Product Qualification (other)

o Mixed Flowing Gas (MFG)

o Used to simulate corrosive mechanisms found in equipment exposed to industrial environments

o Consists of Cl2, H2S, SO2, and NOx

o Most commonly used for connectors or products used in particularly corrosive environments (under sink, paper processing, etc.)

o Salt Spray

o Water Spray

o EMI/EMC

o ESD


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

o 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

o Concern is that in some environments the equipment will operate less frequently and could get “soaked” with humidity while dormant

o Environments commonly seaside

o Salt an absolute concern

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

Case Study 1-Industrial Application

Acetic Acid (Glacial)

Acetone

Ammonium Hydroxide

(20 percent by weight)

ASTM reference fuel C

Diethyl Ether

Methyl Ethyl Ketone

Furfural

Ethylene Dichloride

Ethyl Acetate

n-Hexane

Methanol

2-Nitropropane

Toluene


o Conformal Coating

o Acrylic resin

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

o This coating material is designed for use on boards having no-clean flux residue

Case Study 1: Equipment Description: Conformal Coating


o Reliability Objectives

o Demonstrate lifetime of 10 years

o Zero (0) test failures out of a sample size of 6

Case Study 1 - Objectives


o There are a large number of potential failure mechanisms that can be accelerated on the electronics

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

o Based on this activation energy, testing at 105C provides a 26X acceleration factor over 55C operating

o Ten (10) year life can be demonstrated by testing for 3309 hours

Case Study 1 -Constant Temperature


o 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 (uncontrolled indoor in Phoenix, AZ)

o 24 one hour cycles equals 365 diurnal cycleso Cycle is 20 minute dwells with ramps covering 10 minuteso 48 cycles of -40C / 85C = 2 years in the fieldo 64 cycles of -10C / 85C o 84 cycles of 30C / 85C

o Using:

o 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.

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

Case Study 1 - Temperature Cycling


o 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.

o 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


o Three primary concerns with ‘air-induced’ corrosion in the environments definedo Industrial gases

o Relative humidity / condensation

o Salt spray

o Industrial Gaseso Due to its presence in industrial locations, may wish to consider mixed flowing gas (MFG) testing

o Appropriate specification is EIA-364-65, class IIA for 4 days (2 years equivalent) (336 hours for 10 year life equivalent)

o NOTE: This is an expensive test and not a standard test among industrial control equipment

Case Study 1 - Corrosion – Air


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

o There is also an IEC equivalent, IEC 60512-6

o Recommend MIL-STD to cover military customers

o 96 hour duration

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

Case Study 1 - Corrosion – Salt Spray


o There is no universal algorithm for deriving an acceleration factor for exposure to elevated moisture conditionso Because of this limitation, most OEMs use standard test conditions to evaluate the robustness of

designs when exposed to elevated moisture for long periods of time

o Cycling the temperature and humidity will drive condensation of water inside the unit (especially when the equipment is off). o This test method will assess conductive anodic filament (CAF) formation, effectiveness of the PCB

conformal coating, and the robustness of the hardware

o DfR believes that the most appropriate test method is IEC 61215 10.12 (humidity freeze conditions) and 10.13 (damp heat). o This test methodology is called out by ASTM E1171-09, which was created to assess the

robustness of solar panelso The IEC tests call out 10 humidity freeze cycles (-40C/60C) followed by 1000 hours at

85°C/85%RH

o Power cycling the electronics is recommended as it would create a worst case situation

Case Study 1 - Proposed Test Plan: Humidity Cycling


o Provide a Test Plan that will ascertain the ability of the connectors in the Unit to meet a 99% reliability with 90% confidence level using a small sample size

o Used Norris-Landzberg to calculate Acceleration Factor

o Used Weibull Analysis to project test duration

o Input 99% reliability requirement

o Input 90% confidence level

o Input 7 year operational life requirement

o Input sample size (32 will be required)

Case Study 2 – Connector Reliability Test

Plan


Temperature 0°C to 50°C

Humidity 0% to 95% relative humidity noncondensing

Altitude To 10,000 feet

Case Study 2 - Device Environments

Operating Environment

Device Mechanical Strength

IEC 601-1, subclause 21a and b

IEC 601-1 subclause 21.5

Temperature -5°C to 55°C

Humidity 5% to 95% noncondensingAltitude To 10,000 feet

Storage Environment


o Both connectors are Surface Mounted onto the printed circuit boards and then mated.

Case Study 2 - Connector Description


o -40 to +85°C Temperature Cycling Test, Norris Landzberg equation

o Field temperature change ∆To ≈ 30°C, ∆Tt ≈ 125°Ctt = 1 hour, to = 24 hour, Tmax,o = 50°C, Tmax,t = 85°C

o Acceleration factor = 12.5 cycles in the field is equivalent to 1 cycle under test, 2555 (assumed 1 thermal cycle per day) field operation cycles is 204 cycles under test.

o Achieving the 16.15 year duration derived from Weibull indicates that 471 cycles (β =2.3)would provide assurance that the connectors can achieve the 99% reliability requirement with a 90% confidence level, using 32 samples.

Case Study 2 - Temperature Cycling

−

∆

∆==

too

t

o

t

t

o

TTt

t

T

T

N

NAF

max,max,

136.00.2

111414exp


o If we raise the maximum test temperature to 125C, which is the maximum temperature for the connectors we can significantly reduce the test time. (-40 to +125C cycle)o Field temperature change ∆To ≈ 30°C, ∆Tt ≈ 165°C

tt = 1 hour, to = 24 hour, Tmax,o = 50°C, Tmax,t = 125°C

o Acceleration factor = 31.15 cycles in the field is equivalent to 1 cycle under test, 2555 (assumed 1 thermal cycle per day) field operation cycles is 82 cycles under test.

o Achieving the 16.15 year duration derived from Weibull indicates that 190 cycles would provide assurance that the connectors can achieve the 99% reliability requirement with a 90% confidence level, using 32 samples.

Case Study 2 - Temperature Cycling (Pushing the Extremes)


o DfR then followed the temperature cycling with a 7 day

humidity/cycling test using the same samples to ascertain the

robustness of the conformal coating or potting. This method

does not attempt to duplicate the temperature/humidity

environment but rather, it provides a generally stressful

situation that is intended to reveal problem areas with

materials, in this case, the conformal coating.

o DfR recommends a Temperature/Humidity/Bias test for 168

hours at 85C and 85%RH. This would have to be done on live

units to properly bias them. This test will determine whether

there are problems with the connectors or any other element of

the product.

Case Study 2 - Temperature/Humidity/Bias


o Only 2 things can happen to connectors at altitude.

o They can outgas

o They will run hotter than at ground level.

o DfR does not feel that an altitude test is absolutely necessary, but would recommend that three units be subjected to a test that simulates 10,000 feet of altitude (equivalent to the inside of a commercial jet liner (8,000 ft)). This would require fully operational units to ascertain if issues from heat rise occur.

o Test duration should be one hour.

Case Study 2 - Altitude


o The Vibration Requirement called out by the customer looks to be an adequate test to verify the robustness of the connector interface.

o For ME EQUIPMENT and its parts, including mounting ACCESSORIES, broad-band random vibration test in accordance with IEC 60068-2-64:2008, using the following conditions:o NOTE 5 This represents Class 7M1 and 7M2 as described in IEC/TR 60721-4-7:2001.o – acceleration amplitude:o – 10 Hz to 100 Hz: 1,0 (m/s2)2/Hz,o – 100 Hz to 200 Hz: –3 db per octave,o – 200 Hz to 2 000 Hz: 0,5 (m/s2)2/Hz,o – duration: 30 min per perpendicular axis (3 total).

Case Study 2 - Vibration


o The Shock test called out in the Customer Specification appears to be an adequate test for the test plan.

o Shock testing should also be performed per IEC 60601-1-11.

o Shock test in accordance with IEC 60068-2-27:2008, using the following conditions:o This represents Class 7M2 as described in IEC/TR 60721-4-7:2001.

o test type: Type 2;

o - peak acceleration: 300 m/s2 (30 g),

o - duration: 6 ms,

o - pulse shape: half-sine,

o - number of shocks: 3 shocks per direction per axis (18 total).

Case Study 2 - Shock


o The Cycle Count for the Connects has been defined as 35 typical and a worst case of100 with the male connector being replaced every 55 days.

o DfR’s concern is not with the mating interfaces but rather with fatigue of the SMT solder joints

o DfR recommends a simple insertion/withdrawal test where the male and female connectors are removed and reinserted 300 times and then visually inspected to see if there is any solder joint cracking occurring. (Periodic visual inspections are recommended)

Case Study 2 - Insertion/Withdrawal of the Connectors


o Hard Drive Testingo Customer’s reliability goal was an annualized failure rate (AFR) of


o Utilization inefficiency can be defined as the excess number of times the disk drive performs this 7-step load-unload routine:1. Motor acceleration2. Slider loading3. Track following4. Armature sweeping5. Track following6. Slider unloading7. Motor deceleration

o 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.

o 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


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

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

o Array analyzed: 100%, 50%, 25%, 10%, 5%, 2.5%, 1%, and 0.5%

o Data logging interval considers a LUL cycle to write data to the drive

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

o 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


o Electrolytic Capacitor Wearout Behavioro Wear-out is caused by electrolyte diffusion through the end seal

o Increased temperature increases rate of diffusion

o As electrolyte volume decreases, ESR increases

o 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 = 0.0239xR² = 0.9975

0

2

4

6

0 200 400

Weight Loss (mg)

Time (hrs)

Average Weight Loss Over Time 2

y = 0.0062xR² = 0.98250

0.5

1

1.5

0 200

Weight Loss (mg)

Time (hrs)


y = 0.004xR² = 0.9904

0

0.5

1

0 100 200 300

Weight Loss (mg)

Time (hrs)


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


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

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

o Modeled using an exponential function

o Data fits well to model

Results: Rate of Weight Loss Temperature Dependence

y = 7E-05e0.053x

R² = 0.9919

0

0.005

0.01

0.015

0.02

0 20 40 60 80 100

Rate of Weight Loss (mg/hr)

Temperature (°C)

Rate of Weight Loss Temperature Dependence


o Exponential function fits relationship between mass loss and % increase in ESRo Models a sharp increase in ESR after a given mass loss

o 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

0

200

400

600

800

1000

0 500 1000 1500 2000 2500

% Inc ESR

Weight Loss (mg)

% Increase in ESR with Weight Loss


o If failure is defined as a 200% increase in ESR, then characteristic life for the aluminum electrolytic capacitors tested is:

o 58,100 hours at 105°C

o 248,000 hours at 85°C

o 349,000 hours at 76°C

o 1,870,000 hours at 45°C, based on rate of weight loss temperature dependence

Discussion: Characteristic Lifetime Estimates


o Effective failure analysis is critical to reliability!

o Without identifying the root causes of failure, true corrective action cannot be implemented

o Risk of repeat occurrence increases

o Use a systematic approach to failure analysis

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

o Techniques based upon the failure information specific to the problem.

o Failure history, failure mode, failure site, failure mechanism

Don’t Overlook Failure Analysis!


Case Study: Test Plan Dev & Industry Standards Failures

o Immersion silver (ImAg) introduced in the 1990’s as the ‘universal finish’

o Benefitso Excellent flatness, low cost, long-term storage

o Problemo Sulfur reacts with silver

o Induces creeping corrosion


ImAg (Creeping Corrosion)

o Failures observed within monthso Sulfur-based gases attacked exposed immersion silver

o Non-directional migration (creeping corrosion)

o Occurred primarily in environments with high sulfur levelso Rubber manufacturing

o Gasoline refineries

o Waste treatment plants


Findings

o Analysis identified copper as the creeping element (not silver)

o Cross-sections identified corrosion sites near areas with no or minimal immersion silvero Galvanic reaction was initiating and accelerating corrosion behavior

o What went wrong?


PoF and Testing

o Failure #1

o Test coupons were not representative of actual product

o No solder mask defined pads, no plated through holes

o Failure #2

o Industry test environments are limited to 70%RH (chamber limitations)

o Actual use environment can be more severe

Telcordia


PoF and Immersion Silver

o The Final Failure?

o Acknowledging the reactivity of silver with sulfur and moving beyond ‘test to spec’ to truly capture potential risks

o The ‘physics’ was not well enough understood before the new material was released


THANKSContact Information:

Greg Caswell

DfR Solutions

301-640-5825

[email protected]

Date post:	30-Jan-2021
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