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
Environmental Stress Screening (ESS)
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
Environmental Stress Screening (ESS)
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.
Environmental Stress Screening (ESS)
Multi-Level Screening Effectiveness
Product Failure Domain
Vibration Thermal-Cycling
Burn-InPower C
ycling
Electromigration
Environmental Stress Screening (ESS)
Typical Advanced Combined ESS Production Screen
Environmental Stress Screening (ESS)
Why do ESS?
• Finding Defects• Technical Benefits• Quality and Reliability Benefits• Financial Benefits
Environmental Stress Screening (ESS)
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
Environmental Stress Screening (ESS)
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
Environmental Stress Screening (ESS)
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
Environmental Stress Screening (ESS)
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
Environmental Stress Screening (ESS)
Return on Investment
Environmental Stress Screening (ESS)
What is the ESS Process
• Old methods of ESS
• Current approach of ESS
• Future trends of ESS
Environmental Stress Screening (ESS)
Old Methods of ESS
• Burn-in
• Temperature Cycling
• Vibration
• Shock
Environmental Stress Screening (ESS)
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
Environmental Stress Screening (ESS)
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
Environmental Stress Screening (ESS)
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
Environmental Stress Screening (ESS)
Typical Advanced Combined ESS Production Screen
Environmental Stress Screening (ESS)
ESS Number of Repeated Cycles
Environmental Stress Screening (ESS)
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
Environmental Stress Screening (ESS)
When to do ESS
Product Development
Pilot ProductionPrototype Production
Environmental Stress Screening (ESS)
Percentage Influence on Total Cost
Environmental Stress Screening (ESS)
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
Environmental Stress Screening (ESS)
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
Environmental Stress Screening (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
Environmental Stress Screening (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
Environmental Stress Screening (ESS)
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
Environmental Stress Screening (ESS)
Pneumatic Hammer ESS System’s Spectrum
Note: Not enough energy to excite resonances at low frequencies
Environmental Stress Screening (ESS)
Pneumatic Hammer ESS Systems Spectrum
Note: Damaging energy level at high frequencies
Environmental Stress Screening (ESS)
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
Environmental Stress Screening (ESS)
E-M Shaker with Skewed Table
Environmental Stress Screening (ESS)
E-M Shaker with Skewed Table
Quanta’s Patented Skewed Fixture
Patent No:05650569
Environmental Stress Screening (ESS)
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.
Environmental Stress Screening (ESS)
Example of Glucometer
Environmental Stress Screening (ESS)
Example of Large Network Device
Environmental Stress Screening (ESS)
Example of Network System
Power Supply
1 2
PLP δ =AE
Therefore,AA1 = A2
δ 1 < δ 2L E1 = E2
P1 > P2
L1 << L2
Environmental Stress Screening (ESS)
Example of Medical Device
Environmental Stress Screening (ESS)
Example of GPS Tracking Device
Environmental Stress Screening (ESS)
Example of PC Board for Chip Fabrication System
Environmental Stress Screening (ESS)
Example of Network Device
Environmental Stress Screening (ESS)
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
Find Problem &Correct It
Failure LevelReached?UUT Okay?
2
Find Problem &Correct It
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