Root-Cause Analysis of HALT Failures - DfR Solutions slides pdfs... · Root-Cause Analysis of HALT Failures ... vibration and thermal cycling ... or ESS (environmental stress screening)

© 2004 - 2007 © 2004 - 2010 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com © 2004 – 2010

Root-Cause Analysis of HALT Failures

Cheryl Tulkoff and Greg Caswell

[email protected]

[email protected]

mailto:[email protected]

mailto:[email protected]

© 2004 - 2007 © 2004 - 2010 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com

“the process of seamlessly

cohesively integrating reliability

tools together to maximize

reliability and at the lowest

possible cost”

Reliability Integration


Reliability and Cost C

OS

T

RELIABILITY

TOTAL

COST

CURVE

RELIABILITY

PROGRAM

COSTS

WARRANTY

COSTS

OPTIMUM

COST

POINT

Use of the proper tools during the proper life cycle phase will

help to minimize total Life Cycle Cost (LCC).


o To minimize total Life Cycle Costs (LCC), a Reliability

Engineer must do two things:

o choose the best tools from all of the tools available and must

apply these tools at the proper phases of a product life cycle.

o properly integrate these tools together to assure that the

proper information is fed forward and backwards at the

proper times.

o Highly Accelerated Life Testing (HALT) is one reliability

tool that can assist with this process

Reliability vs. Cost, continued


o Highly Accelerated Life Testing (HALT)

o In HALT, a product is introduced to progressively higher stress

levels in order to quickly uncover design weaknesses, thereby

increasing the operating margins of the product, translating to

higher reliability.

Introduction to HALT


HALT Testing Overview

o Typically exposes the product to simultaneous vibration and thermal cycling

o Product is tested in operational mode while the vibration stress is increased with each thermal cycle

o Objective of the test is to cause failure of the product o Identifies the weakest link which can be then be

improved

o Test duration is typically less than a few weeks o On its own, this test is not able to predict the life of a

product (acceleration factor is not known)

o However, it is very useful when a product can be compared side-by-side with a previous generation of product with known reliability


Example HALT Test

o Functional testing is performed while the vibration is taking place

o This is important since intermittent opens can be found at this condition

o Vibration starts at 0 Grms and step up by 5 Grms each cycle until failure is

detected

o Failing units shall be analyzed carefully to find root cause failure


o Uncovers flaws typically not found before product

introduction

o Discovers and improves design margins

o Reduces overall development time and cost

o Provides information for developing accelerated

manufacturing screens (HASS)

HALT - Advantages over Traditional Testing


HALT versus Traditional Reliability Testing: Comparison

HALT

o Gathers info on product limitations

o Focus on Design Weaknesses

o 6 DoF (degrees of freedom) Vibration

o High Thermal Rate of Change

o Loosely Defined - Modified “On the Fly”

o Not a “Pass/Fail” Test

o Results used as basis for HASS or ESS (environmental stress screening)

Traditional

o Simulates Lifetime of use

o Focus on Finding Failures

o Single Axis Vibration

o Moderate Thermal Rate of Change

o Narrowly Defined - Rigidly Followed

o “Pass/Fail” Test

o Results typically not used in ESS


HALT

Highly Accelerated

Life Testing


o Value of HALT

o Rapidly discover design issues.

o Evaluate & improve design margins.

o Release mature product at market introduction.

o Reduce development time & cost.

o Evaluate cost reductions made to product.

o Developmental HALT is not really a test you pass or

fail, it is a process tool for the design engineers.

o There are no pre-established limits.

HALT - Highly Accelerated Life Test


HALT, How It Works

Start low and step up the

stress, testing the product

during the stressing


HALT, How It Works

Gradually increase

stress level until a

failure occurs


HALT, How It Works

Analyze

the failure


HALT, How It Works

Make

temporary

improvements


HALT, How It Works

Increase

stress and

start

process

over


HALT, How It Works


HALT, How It Works


HALT, How It Works


HALT, How It Works

Fundamental

Technological

Limit


Product

Operational

Specs

Stress

Upper

Oper.

Limit

Upper

Destruct

Limit

Lower

Destruct

Limit

Lower

Oper.

Limit

Margin Improvement Process


Product

Operational

Specs

Stress

Upper

Oper.

Limit

Upper

Destruct

Limit

Lower

Destruct

Limit

Lower

Oper.

Limit



Product

Operational

Specs

Stress

Upper

Oper.

Limit

Upper

Destruct

Limit

Lower

Destruct

Limit

Lower

Oper.

Limit



Product

Operational

Specs

Stress

Upper

Oper.

Limit

Upper

Destruct

Limit

Lower

Destruct

Limit

Lower

Oper.

Limit



Product

Operational

Specs

Stress

Upper

Oper.

Limit

Upper

Destruct

Limit

Lower

Destruct

Limit

Lower

Oper.

Limit


Operating

Margin

Destruct

Margin


o Combined stresses to technology limits

o Step stressing (individual and combined)

o Powered product with monitored tests

o Root cause failure analysis and appropriate corrective

action

HALT Implementation Requirements


Commonly Used HALT Equipment

o Combined

Temperature/Vibration

Equipment

o Pneumatic Vibration (to

provide the random

vibration) with Wide

Frequency Spectrum

o Fast Thermal Rates of Change

and Wide Thermal Range


o Planning a HALT

o Setting up for a HALT

o Executing a HALT

o Post Testing

Developing a HALT Process


o Meet with design engineers to discuss product.

o Determine stresses to apply.

o Determine number of samples available.

o Determine functional tests to run during Dev. HALT.

o Determine what parameters to monitor.

o Determine what constitutes a failure.

o Develop Test Plan

Planning a HALT

It is essential that the product being tested be fully exercised

and monitored throughout HALT for problem detection.


For each stress, we use the

Step Stress Approach

Continue until operating & destruct limits

of UUT (unit under test) are found or until test equipment

limits are reached.

Stimuli

Time (hour:minute)

D

C

B

A

0:00 0:10 0:20 0:30

Planning a HALT (cont.)


OTHER STIMULI:

• Voltage/frequency margining

• Power cycling

• Combined environment (Temp/Vib)

• Rapid transitions up to 60oC/min on the product

VIBRATION HIGH TEMP LOW TEMP

START

INCREMENT DWELL TIME

END

3-5 G’s

3-5 G’s 10 min* 10 min* 10 min*

5 to 10° C

+20° C +20° C

Destruct Limit or Test Equipment Limitation

STIMULI

5 to 10° C

* In addition to functional test time

Planning a HALT (cont.)


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 Design vibration fixture to ensure energy transmission to the

product (different from electrodynamic vibration fixtures).

o Design air ducting to ensure maximum thermal transitions on

the product.

o Tune chamber for product to be tested.

o Apply thermocouples to product to be tested.

o Setup all functional test equipment and cabling.

Setting up for HALT


o Begin with cold step stress and then hot step stress.

o Step in 10 °C increments, as approach “limits” reduce to 5 °C.

o Dwell time minimum of 10 minutes + time to run functional tests to ensure product is still functional. Start dwell once product reaches temperature setpoint, begin functional tests after 10 minute dwell.

o Continue until fundamental limit of technology is reached.

o If circuits have thermal safeties, ensure operation & then defeat to determine actual operating & destruct limits

o Apply additional product stresses during process:

o Power Supplies: Power cycling during cold step stress.

o Input voltage variation. Load variations.

o Frequency variation of clocks.

Executing a HALT (Thermal Step Stress)


o Transition temperature as fast as chamber will allow.

o Select temperature range within 5° of the operating limits found during thermal step stress.

o If product cannot withstand maximum thermal transitions, decrease transition rate by 10 °C per minute until operating limit is found.

o Continue series of transitions for a minimum of 10 minutes (or time it takes to run set of functional tests).

o Apply additional product stresses during process

Executing a HALT (Fast Thermal Transitions)


o Understand vibration response of product (i.e. how does product respond to increases in vibration input).

o Determine Grms increments (usually 3-5 Grms on product).

o Dwell time minimum of 10 minutes + time to run functional tests to ensure product is still functional. Start dwell once product reaches vibration setpoint.

o Continue until reach fundamental limit of technology.

o Apply additional product stresses during process.

Executing a HALT (Vibration Step Stress)


Power Spectral Density (measured on product on OVS-2.5HP)

Marker Fcn[Band Pwr]

Trace: D Strt: 0 Hz Stop: 3 kHz

Band:5.468 grms

32Hz 12.8kHzAVG: 20 X:288 Hz Y:2.82893 m*

Band:6.548 grms

Band:9.842 grms

X:288 Hz Y:176.027 u* 32Hz 12.8kHzAVG: 20

X:288 Hz Y:3.44536 m* 32Hz 12.8kHzAVG: 20

Band:4.488 grms

A: ROBOT BD

B: ROBOT ARM

X:288 Hz Y:1.19064 m*

Y* = grms^2/Hz100m*

10u*

LogMag

Y* = grms^2/Hz100m*

1u*

LogMag

C: R MOTOR

D: TABLE

Y* = grms^2/Hz1*

10u*

LogMag

Y* = grms^2/Hz1*

100n*

LogMag

32Hz 12.8kHzAVG: 20

Date: 03-14-97 Time: 09:46:00 AM

Y-AXIS

Z-AXIS

X-AXIS

Z-AXIS

Vibration Step Stress (cont.)


Power Spectral Density (measured on product on QRS410T)

Vibration Step Stress (cont.)


o Develop thermal profile using thermal operating limits, dwell times and transitions rates used during thermal step stress & fast thermal transitions.

o Incorporate additional product stresses into profile such as power cycling.

o The first run through the profile, run a constant vibration level of approx. 5 Grms. Step in same increments determined during vibration step stress.

o When reach higher Grms levels (approx. 20 Grms) add tickle vibration (approx. 5 Grms) to determine if failures were precipitated at high G level but only detectable at lower G level.

Executing a HALT (Combined Environment)


o Determine root cause of all failures that occurred.

o Meet with design engineers to discuss results of Developmental HALT and root cause analysis.

o Determine and implement corrective action.

o Perform Verification HALT to ensure problems fixed and new problems not introduced.

o Periodically evaluate product as it is subjected to engineering changes.

Post Testing


o Highly Accelerated Life Testing (HALT) is designed to induce product failure

o Requires effective root-cause analysis o Determination of failure site, failure mechanism, and root-

cause

o Absence prevents improvement in design margins; greatly reduces value of HALT process

o DfR Solutions takes a systematic approach to root-cause analysis o Proceeding from the least destructive to most destructive until

root-cause(s) are conclusively identified

o Process steps based upon failure information (failure mode, failure site, failure mechanism)

Failure Analysis (Motivation)

41

© 2004 - 2007 © 2004 - 2010 9000 Virginia Manor Rd Ste 290, Beltsville MD 20705 | 301-474-0607 | www.dfrsolutions.com 42

No Analysis? No Improvement!


Information Gathering

o Crucial first step in any failure analysis effort

o Use of standard nomenclature o Failure history

o When in HALT did the failure occur?

o Step stress testing, temperature cycling, vibration, combined

o What were the stresses being experienced by the product before failure?

o Temperature, vibration, combined

o Also electrical stresses

o Is there a specific change in design/bill of materials/manufacturing that is being assessed?

o Failure mode – the failure behavior experienced by the observer

o Failure site – the supposed location of the failure

o Failure mechanism – the mechanism initiating the failure (not root cause)


Failure History

o The stresses experienced before failure provides strong indication of potential failure site

o Temperature step stress testing tends to drive component issues

o High temperatures

o Driven by increase in leakage current (diode turn on) or increase in resistance (time delay)

o Semiconductors, power components

o Cold temperatures

o Primarily liquid electrolytic capacitors

o Cyclic stresses (temperature cycling, vibration) tend to drive interconnect issues

o Separable (sockets, press-fit connections, etc.)

o Permanent (solder joints)


Non-Destructive Evaluation (NDE)

o Designed to provide maximum information with minimal risk of damaging or destroying physical evidence

o Evaluation methods

o Electrical Characterization

o Visual Inspection

o Xray Microscopy

o Thermal Imaging

o SQUID Microscopy

o Acoustic Microscopy


o Most critical step in failure analysis (FA) process for

product subjected to HALT

o Especially for failures induced during temperature step stress

testing

o Recoverable failures (operational limits)

o Failure site can only determined through electrical

characterization and interpretation of changes in functional

behavior

o Permanent failures (destruct limits)

o Proceeds with a broader range of possible electrical

characterization techniques

Electrical Characterization

46


o JTAG (joint task action group) Boundary Scan

o Very accurate identification of failure site; rarely performed on failed units

o Oscilloscope

o Useful in probing operational circuitry

o Resistance measurements (manual) o Binary approach (best for an electrical open)

o Isolation of attached components

o Attempt to perform electrical characterization without component removal

o Parametric characterization

o Comparison of performance to datasheet specifications

o Curve tracer

o Valuable in characterizing diode, transistor, and resistance behavior

o Time domain reflectrometry (TDR)

o Measurement of phase shift of return signal can indicate location of electrical open

o Other characterization equipment

o LCR Meter, High resistance meter, low resistance meter, etc.

o Sometimes requires re-introduction of environmental stresses

o Especially elevated temperatures

Electrical Characterization Techniques

47


o Latest innovations

o Digital detector, laminography, nanofocus resolution, oblique viewing

o Greatest potential

o Solder joint failures under area array devices

o Problem

o Difficult to identify microcracks that occur during fatigue/fracture of the solder

o Can detect voiding or poor wetting

o Provides evidence of root-cause of failures during the application of cyclic stresses

Xray and HALT

48


o Best for component failures

o Especially increases in elevated leakage

currents

o Rarely used

o Electrical characterization often provides

more rapid identification of failure site and

more definitive information on failure

mode

o However, can provide evidence of

excessive temperature rise due to power

dissipation

o Can identify root-cause of failures at

temperatures below expectations

Thermal Imaging and HALT

49


SQUID Microscopy

Current flow in devices produce a magnetic field

SQUID uses a highly sensitive magnetic detector (superconductor) to resolve these fields

Magnetic field image is converted to a current density image, allowing for fault location

Resolution

500 nA, 300 nm

Dependent on working distance (requires a flat sample)


SQUID Microscopy

Critical technology for detecting package level electrical shorts

Much more rapid failure site resolution

Absolute confirmation of shorting path

Thermal imaging induces damage


Failure Analysis: Temperature Tools

o Cold Spray and hot

plates to simulate fails

at temperature

extremes


Failure Analysis Dremel Tool – Induce Vibrations

o A Dremel tool can be

used to induce local

vibration during

debugging

o http://www.dremel.com

http://www.dremel.com


Sherlock Analysis

o Sherlock Automated Design Analysis™ can be used to assess the validity of failure mechanism

o Can provide prediction of modes shapes and stresses during vibration

o Compare prediction to observation

o Were vibration loads sufficient to fail the interconnect?

o Were defects identified during failure analysis?

o If answers to one and two are no, maybe issue with test procedure

o Important: Can not be used for combined environment (temperature cycling + vibration)

o Too complex

340 Hz (369 Hz) 806 Hz, (715 Hz) 945 Hz, (910 Hz)


NDE and HALT

o Failure site identification is best performed through

electrical characterization, visual inspection, and an

understanding of failure mechanisms

o NDE techniques are most useful in the second phase of

failure analysis, when root-cause must be determined


Root-Cause Evaluation

o Appropriate point to evaluate information obtained o Requires understanding of failure mechanisms and root-cause

o Inappropriate technique could destroy evidence

o Use of failure analysis tools to direct destructive phase of process o Fault tree analysis (FTA)

o Fishbone diagram

o Stress vs. Strength

o Failure modes and effects analysis (FMEA)? o Useful for design review; rarely used in failure analysis

process


o Used once approximate failure site has been

determined

FTA (cont.)

57

Ceramic Capacitor

Failure

Insufficient Capacitance

Dielectric Formulation

Crack Propagation

Solder Joint Open

Elevated Leakage Current

Crack Propagation

Surface Insulation

Resistance


Fishbone Diagram (Ishikawa)

o Useful in identifying all potential influences that could

drive product failure

o Can result in overcommitment of resources


Stress vs. Strength

59

Fiber/resin separation

Copper/resin separation

Hollow fibers

Misregistration of PTHs/Vias

Copper wicking

Drilling damage

Separation of PTH wall from epoxy resin

Higher voltage

Higher moisture concentration

Tighter conductor spacing

Higher ion concentration in epoxy resin


Destructive Evaluation

o Used when information obtained during NDE is

insufficient to conclusively identify root-cause of failure

o Primarily consists of two techniques

o Cross-sectioning

o Decapsulation/delidding


o Critical for interconnect failures (cyclic stresses)

Cross-Sectioning and HALT

61


Cross-Sectioning

o Identify the area of interest (failure site)

o Remove the area of interest

o Diamond-encrusted blades are preferred (minimizes surface damage)

o Band saw, high and low speed diamond saw

o Plunge cuts preferred (minimizes damage to surrounding PCBA)

o Mount sample

o Prevents relative movement / improves handling

o Use room-temperature cured epoxy

o Plane of interest should be near the surface of sample

o Excessive removal of material increases likelihood of non-planarity, overheating, and loss of root-cause information


Grinding/Polishing

o Rough grinding

o Used to approach the area of interest

o Involves application of 60 to 400 grit of SiC paper

o Rough polishing

o Used to remove damage introduced during grinding

o Involves 600 to 1200 grit of SiC paper

o Fine polishing/etching

o Used to reveal microstructural elements

o Involves use of polishing media one micron and finer

Grit

(Silicon Carbide)

Particle Size

(microns)

240 50

320 29

400 17

600 9

800 7

1200 3


o Use of acid to remove encapsulant and expose internal workings of the package

o Used to analyze on-die failures

o Primarily driven by hot step stress test

o Interconnect issues, primarily wirebonds, that can be discovered during temperature cycling, are best initially investigated using cross-sectioning

o Further characterization, using mechanical testing, will require decapsulation

Decapsulation and HALT

64


Case Study -- Cold Step Stress Test

o Mass flow meter

o Recoverable failure at -30C

o Failure mode

o Loss of communication

o No permanent failures observed

o Results of electrical characterization / functional testing

o Insufficient filtering of electrolytic capacitors (rated at 105C)

o Parametric testing identified drop in capacitance at -35C

o Freezing of the electrolyte

o Corrective actions that were considered

o Switch from liquid electrolytic capacitor to tantalum capacitor

o Switch from 105C rated to 85C rated (reduced lifetime)

o Increase capacitance from 3.3 uF to 47 uF

o Extends range as well as improves filtering


Cold Step Stress Test (cont.)

o Subsequent testing on production units identified an additional failure mode

o Initiated at approximately -5C

o Out of specification on line voltages, corrupting micros in the unit

o Incorrect resistor values

o Resistors were removed and replaced with different values

o Units passed remaining cold step stress test

o Of interest, the unit used for the initial HALT did not demonstrate these cold temperature problems, showing impact of component variability on product performance

o Identifying design margins!

o Subject sufficient number of samples to HALT process


Case Study -- Hot Step Stress Test

o Mass flow meter

o Permanent failure at 140C

o Failure site

o Catch diode for a switching power supply

o Failure mechanisms

o Electrical short (< 1 ohm). Operating junction temp for that part is -65C to 125C.

o Diode was replaced and the unit was functional after exposure at 140C. Temperature was stepped up to 150C, where nonfunctional failure reoccurred


Hot Step Stress Test (Example)

Hello Craig,

We found that an Optical-Isolator started getting noisy at higher temperatures. The communication link stopped updating at 50C because digital data (1's and 0's) were getting through, but at a reduced amplitude. Thus, some of the 1's were being misinterpreted as 0's by the foundation fieldbus communication card.

We solved the problem by getting a better Opto-isolator with a higher current gain.

Best regards,

Jim


o Application of vibration, starting at 5g and increasing

in 5g increments

o First failure noted at 30g

o Failure site identified as connector solder joints

o Insufficient flow through

o After touch up unit survived up to 40g

o Incorrect approach to failure analysis

o Unit was fixed as soon as a problem was detected

o Root-cause unable to be identified

o Design for reliability? Design for manufacturing? Processing

defect?

Case Study -- Vibration

69


o Failure after exposure to vibration

o Electrical characterization indicated electrical open under

area array device

o Confirmed through cross-sectioning

Case Study – Desktop Computer

70


o Validity of failure mechanism?

o Additional observation of separated leads on electrolytic capacitors

o Occurrence of failure mechanism was strongly dependent upon the orientation of the leads

o Lead planes oriented along the board length most likely to fail

o Vibration test may not have applied random loads

o Potential issues with HALT table or fixture

Issues with HALT

71


When FA and HALT?

o Failure analysis can be a time intensive process

o Hold up in product release while awaiting results

o The use of FA should be selective and should provide

maximum value


FA and HALT (cont.)

o Product

o When product design or functionality is revolutionary, perform FA on all failures

o When product design or functionality is evolutionary, perform FA selectively

o Temperature Step Stress Test

o When recoverable failure occurs between the operational and storage specifications

o Specified to operate between 0 to 70C

o Specified for storage between -40 to 100C

o E.g., recoverable failure occurs at 90C

o When permanent failure occurs within 10C of cold temperature storage specification or within 20C of hot temperature storage specification


FA and HALT (Cyclic Stresses)

o Delineation between when to perform FA less definitive

o General rule o Temperature cycling should not induce any failures, unless

using custom designed interconnect

o Use prior behavior to guide failure analysis in vibration or combined

o Failure on previous designs is always the electrolytic capacitor at 20g’s

o Identification of processing defect can be a design issue! o Design for manufacturing


Conclusion

o HALT can be an important step in best practice

reliability activities

o Use can be extremely limited without root-cause

analysis

o Value-added root-cause analysis requires

understanding of failure mechanisms and the stresses

that drive them

o Sufficient knowledge base allows for optimization of

resources and rapid feedback

Documents

Root-Cause Analysis of HALT Failures - DfR Solutions slides pdfs... · Root-Cause Analysis of HALT Failures ... vibration and thermal cycling ... or ESS (environmental stress screening)