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-In
g
lin
c
Cy
on
r
i
t
e
ra
w
g
o
i
P
om
r
t
c
Ele
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)
Finding Defects
Precipitation of Defects by High Rate Thermal & Broadband Random Vibe
Vibration Screen
Thermal Screen
Vibration and Thermal Screen Mixed Assembly Defects
Wrong Component
Two Components Shorting
Improperly Installed Component Defective Components
Broken Components
Loose Contact
Wire Insulation
Mechanical Flaws
Defective Harness Termination Defective Solder Joints
PCB Etch Defects Inadequately Secure High Mass Parts
Component Parameter Drift
Particle Contamination
Debris
Hermetic Seal Failure
Chemical Contamination Improper Crimp or Pin Mating Poorly Bonded Component
Loose Hardware
Conformal Coating
Chafed, Pinched Wires
Weak or Marginal Components
Adjacent PCB’s, Parts rubbing
Folded IC Legs
Crystals
No Solder Joints in IC though hole
Loose Connectors
Improperly Torqued Screws
Sticky Relays
Weak Circuit Breakers
Weak Switches
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 customer
relations
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
105ºC
95ºC
85ºC
75ºC
65ºC
55ºC
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
25ºC
-10ºC
-20ºC
-30ºC
-40ºC
-50ºC
-60ºC
-70ºC
Environmental Stress Screening (ESS)
HALT - gRMS Table Input
•
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.
28.87
Note Operational and Design Limit Levels.
•
•
45.1
36.08
23.01
18.41
14.73
11.78
9.43
7.5
6
10
Min
Point 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.
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
Prototype
Pilot
Production
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 B
System A
1
X = 21.83
Y = 30.90
Z = 28.51
4
2
X = 32.73
Y = 26.00
Z = 31.62
5
3
X = 27.23
Y = 20.18
Z = 32.73
6
1
X = 45.71
Y = 48.98
Z = 19.05
4
2
X = 33.50
Y = 26.30
Z = 25.41
5
3
X = 56.89
Y = 43.15
Z = 38.90
6
X = 17.99
Y = 28.18
Z = 25.70
X = 16.60
Y = 19.72
Z = 45.19
X = 21.63
Y = 31.26
Z = 39.36
X = 34.67
Y = 35.08
Z = 44.67
X = 21.13
Y = 27.23
Z = 46.77
X = 29.17
Y = 51.29
Z = 38.46
7
8
9
7
8
9
X = 29.17
Y = 21.88
Z = 28.18
X = 30.55
Y = 19.28
Z = 42.66
X = 22.65
Y = 29.51
Z = 38.02
X = 51.29
Y = 51.88
Z = 31.62
X = 42.66
Y = 31.99
Z = 32.36
X = 53.70
Y = 59.57
Z = 34.67
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
P
2
δ =
PL
AE
A
A1 = A2
L
E1 = E2
P1 > P2
L1 << L2
Therefore,
δ1<δ2
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
Design
Hardware /
Software
Fabricate
Prototype
Initiate
HALT/ESS
Conduct
Thermal Stress
Screening
Thermal Profiling
(Mapping)
A
UUT Still
Okay?
B
Define Max &
Min Functional
Temperature
Find Problem &
Correct It
Y
Increase or
Decrease
Temperature
N
Temps
Reached Max
& Min?
C
Y
Develop
HALT/ESS Plan
Select Ramp
Rate & Number
of Cycles
Select Starting
Increment Grms
Levels
Vibration
Profiling
(Mapping)
1
Conduct
Vibration Step
Stress (HALT)
UUT Okay?
D
Find Problem &
Correct It
2
N
UUT Okay?
E
Find Problem &
Correct It
Y
Failure Level
Reached?
N
N
Conduct Proof of
Screen
Y
Verify Product &
Table Uniformity
Conduct HASS
F
Y
2
1
N
Increase
Vibration Level
Questions?
Dr. Hong S. Liu, P.E.
President
Quanta Laboratories
408-988-0770
[email protected]
www.quantalabs.com
3199 De La Cruz Blvd.
Santa Clara, CA 95054