Environmental Stress Screening (ESS) - · PDF fileEnvironmental Stress Screening (ESS) What is ESS? ESS is a Product Development Process which involves the “precipitation and detection

Environmental Stress Screening (ESS)

Dr. Hong S. Liu, P.E.President

Quanta Laboratories

3199 De La Cruz Blvd., Santa Clara, CA 95054 (408) 988-0770 email: [email protected] website: www.quantalabs.com


Agenda

• What is ESS?• Why do ESS?• What is the ESS process?• When to do ESS?• ESS equipment considerations &

limitations• Examples of successful ESS applications• The ESS Process• Questions and answers


What is ESS?

ESS is a Product Development Process which involves the “precipitation and detection of hidden defects” by applying accelerated

stressed of vibration, thermal cycling or power cycling.


Multi-Level Screening Effectiveness

Product Failure Domain

Vibration Thermal-Cycling

Burn-InPower C

ycling

Electromigration


Typical Advanced Combined ESS Production Screen


Why do ESS?

• Finding Defects• Technical Benefits• Quality and Reliability Benefits• Financial Benefits


Vibration and Thermal ScreenDefective ComponentsBroken Components

Defective Solder JointsPCB Etch Defects

Particle ContaminationImproper Crimp or Pin Mating

Thermal ScreenWrong Component

Improperly Installed ComponentWire Insulation

Defective Harness TerminationComponent Parameter Drift

Hermetic Seal FailureChemical Contamination

Conformal CoatingWeak or Marginal Components

Folded IC LegsNo Solder Joints in IC though hole

Vibration ScreenMixed Assembly Defects

Two Components ShortingLoose Contact

Mechanical FlawsInadequately Secure High Mass Parts

DebrisPoorly Bonded Component

Loose HardwareChafed, Pinched Wires

Adjacent PCB’s, Parts rubbingCrystals

Loose Connectors Improperly Torqued Screws

Sticky RelaysWeak Circuit Breakers

Weak Switches

Finding DefectsPrecipitation of Defects by High Rate Thermal & Broadband Random Vibe


Technical Benefits

• Provides design technology edge over competition in world markets

• Discovers and allows correction of weaknesses in design during prototype phase prior to pre production phase

• Helps guarantee passing design specification qualification tests first time

• Reduces design cycle time and speeds corrective action for design and process problems

• Increases robustness of design


Quality and Reliability Benefits

• Improves quality and reliability via:

– Improved design – encouraging improved testability using advanced software, built-in-test, self-tests, boundary layer scan, external test access, etc. – Continuously validating consistency of manufacturing processes starting up front.

– Provides high degree of visibility to sources of quality and reliability problems in product or manufacturing processes

– Helps guarantee removal of latent [hidden] and intermittent defects in design and in marginally acceptable manufactured components from the product prior to delivery to the customer

– Higher mean time between failures (MTBF)

– Protects against shop personnel, technician turnover and inexperience


Financial and Marketing Benefits• Yields a high return on investment • Can increase profits• Forces product maturity and speeds product introduction (yields stabilized)• Decreases overall development costs• Maintains financial competitiveness in world markets, especially in the

future, and helps increase market share of a product line• Reduces proposal costs thereby offering a cost edge over competitor’s bid• Reduces overall testing costs during development, production and in field

trouble-shooting which, in some products, have jumped from about 10% of the total cost [life cycle cost] of a product to upwards of 30% of a product cost for complex electronics. This does not include additional test costs to resolve failures.

• Not only significant cost reductions but value added benefits accrue to production, test, quality, service organizations and to customers (lower warranty costs)

• Helps guarantee customer satisfaction thereby improving customerrelations

• Helps assure precise compliance with customer contract requirements


Return on Investment


What is the ESS Process

• Old methods of ESS

• Current approach of ESS

• Future trends of ESS


Old Methods of ESS

• Burn-in

• Temperature Cycling

• Vibration

• Shock


Current Approach for ESS

HALT = Highly Accelerated Life Testing [Engineering Development]• Separate High/Low Temperature Operation • Separate Vibration Step Stressing• Combined Vibration and Thermal Cycling

HASS = Highly Accelerated Stress Screening [Production Application]• Combined Vibration and Thermal Cycling,

2 to 5 Hours Per Process Run

POS = Proof of Screen [Engineering Development]• Combined Vibration and Thermal Cycling

10 ~ 30 Vibration Screens and Thermal Cycles


HALT Thermal Step Stress

45ºC•Increase/decrease temperature by no more than 40 °C per minute.•Stabilize temperature and functional test at each step•Note operational and design levels if limit is reached

-10ºC-20ºC

55ºC65ºC

-30ºC

75ºC

-40ºC-50ºC

85ºC95ºC

-60ºC

105ºC

-70ºC

25ºC


HALT - gRMS Table Input

7.5

18.4123.01

28.8736.08

45.1• Increase Vibration input by 25% increments, as you get higher up the scale you may want to step up in 10% increments.

• Record response of item.• Note Operational and Design Limit Levels.

14.73

11.78Point of stress where small increases in stress cause multiples failures. Must be well above expected field environment and provide sufficient failure margin to insure the population will survive.

9.43

6

10 Min


Typical Advanced Combined ESS Production Screen


ESS Number of Repeated Cycles


Future Trends of ESS

• Most products will go through ESS• Standardized• Automated• Multi-Stress ESS Stimuli• Time and cost of ESS will be drastically

reduced


When to do ESS

Product Development

Pilot ProductionPrototype Production


Percentage Influence on Total Cost


ESS Equipment Considerations & Limitations

Types of equipment Available for ESS

– Electromagnetic shaker – single axis– Hydraulic shaker – single axis– Pneumatic hammer excited tables– Electromagnetic shaker with skewed table


Single Axis E-M shakers

• Principle of operation• Advantages:

– Readily available– Familiar to most engineers– Vibrational spectrum can be

programmed – Easy to mount test articles– Can be used for screening large

products

• Disadvantages:– Only excites the product in one axis at

a time– More test time is required for ESS


Single Axis Hydraulic Shaker

• Principle of operation• Advantages:

– Vibrational spectrum can be programmed– Vibrational levels are uniform throughout the whole mounting

surface– Easy to mount test article– Can be used for screening large

products

• Disadvantages:– Limited to lower frequency range– Only excites the product in one

axis at a time– More test time is required for ESS


Pneumatic Hammer Excited Tables• Principle of operation• Advantages:

– Relatively simple in mounting test articles– Can accommodate larger test articles

• Disadvantages:– Very large variation in vibrational levels at

different locations on the table– Input energy distribution does not provide the

optimum spectrum to precipitate product defects

– Relative magnitudes of the excited forces in X, Y & Z axes can not be controlled

– High equipment maintenance cost– Requires trained personnel to tune for different products– Large amount of water accumulated on the table during test which

can cause monitoring or operational failures


X, Y, Z Vibration Survey Comparison

System BSystem A

X = 56.89Y = 43.15Z = 38.90

X = 33.50Y = 26.30Z = 25.41

X = 45.71Y = 48.98Z = 19.05

X = 34.67Y = 35.08Z = 44.67

X = 21.13Y = 27.23Z = 46.77

X = 29.17Y = 51.29Z = 38.46

X = 53.70Y = 59.57Z = 34.67

X = 42.66Y = 31.99Z = 32.36

X = 51.29Y = 51.88Z = 31.62

1 2 3

654

7 8 9

X = 27.23Y = 20.18Z = 32.73

X = 32.73Y = 26.00Z = 31.62

X = 21.83Y = 30.90Z = 28.51

X = 17.99Y = 28.18Z = 25.70

X = 16.60Y = 19.72Z = 45.19

X = 21.63Y = 31.26Z = 39.36

X = 22.65Y = 29.51Z = 38.02

X = 30.55Y = 19.28Z = 42.66

X = 29.17Y = 21.88Z = 28.18

1 2 3

654

7 8 9


Pneumatic Hammer ESS System’s Spectrum

Note: Not enough energy to excite resonances at low frequencies


Pneumatic Hammer ESS Systems Spectrum

Note: Damaging energy level at high frequencies


Additional Information on Repetitive Shock Systems (RSS) ESS Chambers (AKA Pneumatic Hammer Systems (PHS)

In June 1994, Dr. Hobbs faxed Ed Howe and quoted as follows, “We have data on our shakers with a new vibrator mounting concept and some of it is supplied below…As you can see, the balance is much better than it used to be. (was up to 270% different across the bare table) I have found that a variation by a factor of two (200%) is well within the bounds of acceptability for HALT and HASS applications.”(Page 14, Test Engineering & Management 8/9, 1994, Howe, Dr. Liu)

“Some types of electronics materials and natural resonant frequencies damages domains which RSS and PHS Systems reach;” (Page 22, Test Engineering & Management Oct/Nov, 1998, Howe)

• 3,000 – 5,000 Hz for gold wirebonds• 4,000 – 8,000 Hz for 99% pure aluminum, 1 percent silicon wires • 10,000 Hz and above for most aluminum geometries• 5,000 – 10,000 Hz for transistor cans containing glass • 7,000 Hz for glassy pedestal transistor cans


E-M Shaker with Skewed Table


E-M Shaker with Skewed Table

Quanta’s Patented Skewed Fixture

Patent No:05650569


E-M Shaker with Skewed Table• Principle of operation• Advantages

– Vibrational levels are uniform throughout the whole test surface– Vibrational spectrum can be shaped to generate most effective

excitation energy to precipitate defects in the product– Relationships between the excitation forces in the three orthogonal axes

can be programmed– All three axes of the product are tested at the same time. Thus saving

test time and cost.– Low equipment maintenance costs– Can use temperature chamber and vibration table separately thus

reduce cost• Disadvantages:

– It is perceived that the in phase excitation forces in the three orthogonal axes are not as effective as independent phase forces

– Slightly more difficult to mount test articles.


Example of Glucometer


Example of Large Network Device


Example of Network System

Power Supply

1 2

PLP δ =AE

Therefore,AA1 = A2

δ 1 < δ 2L E1 = E2

P1 > P2

L1 << L2


Example of Medical Device


Example of GPS Tracking Device


Example of PC Board for Chip Fabrication System


Example of Network Device


The ESS Process

DesignHardware /Software

UUT StillOkay?

1

2

1

FabricatePrototype

InitiateHALT/ESS

Thermal Profiling(Mapping)

ConductThermal Stress

Screening

Find Problem &Correct It

Define Max &Min FunctionalTemperature

Select StartingIncrement Grms

Levels

DevelopHALT/ESS Plan

Increase orDecrease

Temperature

Select RampRate & Number

of Cycles

TempsReached Max

& Min?

VibrationProfiling

(Mapping)

ConductVibration StepStress (HALT)

IncreaseVibration Level


Failure LevelReached?UUT Okay?

2


Conduct Proof ofScreen UUT Okay? Conduct HASSVerify Product &

Table Uniformity

A B

C

D

FE

N

Y

N

Y

Y

N Y

N

Y

N

Questions?

Dr. Hong S. Liu, P.E.President

Quanta Laboratories

3199 De La Cruz Blvd.Santa Clara, CA 95054

[email protected]

Documents

Environmental Stress Screening (ESS) - · PDF fileEnvironmental Stress Screening (ESS) What is ESS? ESS is a Product Development Process which involves the “precipitation and detection