Document 6519742

Power Technology & Qualification
Why do Power Supplies Fail, and What
can be done about it?
Randy Malik, Rick Fishbune, Tim Daun-Lindberg,
Pat Frank, Eric Swenson, Dale Wilhite,
Charles Dishman, Brian Steenburgh
© 2005 IBM Corporation
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Power Technology & Qualification
Major Causes of Failure
“When power supplies fail, it isn’t because designers choose components
they know will fail; they often have insufficient information about the problems
that result from their choices.”
Components
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Power Supply Construction
HALT Tests
Control and Run Charts
3
2
1
0
1
–
–
4
5.
Failure Analysis
–
–
2
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Qualification & Testing
5
15
4.
High Humidity – chemicals
Conductive Metal Parts
Bugs
6
13
–
–
–
7
11
Environment
8
9
3.
Spacing on Board
Device Mounting on Heat Sinks
Placement of Components
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–
–
–
MOSFET
Ceramic
PolyP
Inductor
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Failure Rate
2.
Semiconductor Devices
Capacitors - Electrolytic, Ceramic, Poly Film
Magnetic Components
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–
–
–
3
1.
Time (month)
Root Cause Determination
Field failure data
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© 2004 IBM Corporation
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Power Technology & Qualification
MOSFET Construction Analysis
Electrical Components from two suppliers A and B are different. See Construction details
Figure 1 Supplier A: Delaminating between epoxy and lead frame
shown by red color. C-SEM front side
Figure 2 Supplier B No Delaminating
3
.
Figure 3 Supplier A: Voids between the die and lead
as represented by the white dots.
frame (die attach) are found
Figure 4 Wire bond Comparison Supplier A and Supplier Bi
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© 2004 IBM Corporation
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Power Technology & Qualification
MOSFET Failure = f (time)
MOSFET with the Soft Knee, Can’t run with the soft knee for long
Field Intensity
600
500
Ids
400
Ids - B
Ids - A
300
Soft Knee
200
100
650
600
550
500
450
400
350
300
250
200
150
-100
100
Crater
50
EPI Layer
0
0
Vds
Figure 1 : Craters on the EPI layer
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© 2004 IBM Corporation
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Power Technology & Qualification
MOSFETs from Supplier A and B
If you don’t know whether a component used in a product is robust or
not, how would you expect the product not to fail in the field?
A
B
Figure 1 Voltage Breakdown (BVdss) Distribution
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A
B
Figure 2 Leakage Current (Idss)
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© 2004 IBM Corporation
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Power Technology & Qualification
Electrolytic Capacitors
If you believe in plug and play , then learn to pray . Always Use Brand name quality Caps
Good capacitor brands
Rubycon
Nichicon
Panasonic
Sanyo
Nippon
United Chemi
Electrolyte formulation unstable, - hydrogen buildup inside the metal Can and failure in the field
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© 2004 IBM Corporation
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Power Technology & Qualification
Multilayer Ceramic Capacitors
Cut corners in cost, and then place them near corners, the result is obvious.
Figure 1. the corner of an MLCC, in
cross-section. The red arrows show
the cracked line
Figure 2. Close up of area
denoted by the red box in
figure 1. The crack bridges
between the conductors
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© 2004 IBM Corporation
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Power Technology & Qualification
Poly-Propylene Capacitors
Who says POLYP Capacitors don’t burn. When they do, they burn spectacularly
Burnt Polyp Capacitor
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1.
Flattened capacitors rely on heat and temperature to create a consolidated winding. This creates
stresses, particularly at the centre of the winding where the film is forced to fold through 180°.
2.
It is difficult to create consistent conditions for flattening, excessive pressure on some winding
and insufficient pressure on others due to film thickness variations.
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© 2004 IBM Corporation
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Power Technology & Qualification
Magnetic Components
Another Inductor Burnt, WOW! Did we learn anything here?
PFC Choke Burnt …. Two Powder Iron Chokes used in series
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© 2004 IBM Corporation
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Power Technology & Qualification
Zinc Whiskers and MOSFET Failures
WOW! Zinc Whiskers again! Remember the lessons learned.
Zinc Whisker
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© 2004 IBM Corporation
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Power Technology & Qualification
Roaches Infestation - Power Supply Failure
One thing is sure, nothing is Bug Proof
Roaches
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© 2004 IBM Corporation
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Power Technology & Qualification
Best Practices - Power Supply Construction
Good design can help to prevent manufacturing defects and service errors and to
reduce the need for non-value-adding inspection practices.
Heat
Heat Sink
Sink
G
G
D
D
Electrolytic
Electrolytic Capacitor
Capacitor
SS
Transformer
Transformer
PC
PC Window
Window
Inductor
Inductor
Figure 1 Power Supply Component Placement and PC windows
Heat Sink
Bond-Ply
Device 1
Device 2
Device 3
Figure 2 Heat Sink Assembly to mount semiconductor devices with no screws and no clips
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© 2004 IBM Corporation
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Power Technology & Qualification
PARETO Diagrams
Treating the symptoms is a short term relief, find the root cause and have a long term relief
35
30
25
20
15
10
5
0
MOSFET
Choke
Driver
Ceramic
Poly
Fan
Figure 1 Failed Components in the field
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10
8
6
4
2
0
HVMarginal
Bad Device
Driver Fail
Dust/Metal
Figure 2 Causes of MOSFET Failure
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© 2004 IBM Corporation
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Power Technology & Qualification
Relative Cost to fix a Problem
Relative cost
1000
100
10
1
Design
Assembly
Final Test
Field
Product Stage
The costs of preventing problems at the design stage are much lower than costs of
correcting problems that occur “ downstream”
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© 2004 IBM Corporation
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Power Technology & Qualification
Reliability and Learning Curve
1200
1200
1000
1000
800
800
600
Knowledge
Failure Rate
400
400
200
200
0
0
1
15
600
Knowledge
Failure rate ppm
Through a process of learning, knowledge is developed.
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3
4
5
6
7
8
9
10
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© 2004 IBM Corporation
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Power Technology & Qualification
PPM Defects for a Server Power Supply – Today and in Future
Cost being ($0.08/Watt), Quality will have a definite competitive advantage.
800
700
PPM - today
PPM- Future
PPM
600
500
400
300
200
Competitive Advantage
100
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21
19
17
15
13
11
9
7
5
3
1
0
Time - months
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© 2004 IBM Corporation
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Power Technology & Qualification
“Kaizen” – Journey of Continuous Improvement
Sustaining total quality requires viewing quality efforts as a journey, not an end.
R
If you can’t find the root
cause of failure, you can not
prevent it.
RootCause
Cause
Root
Determination
Determination
D
Q
MAN
Fail
Fail
Procurement
rs
60
0
a
Ye
Eliminating symptoms of
problems usually provides
only temporary relief;
eliminating root cause s
provides long-term relief.
Design
Design
Assembly
Assembly
& Qualification
P
W
System
System
FinalTest
Test
Final
S
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The purpose of the design review is to
stimulate discussion, raise questions,
and generate new ideas and solutions to
help designers anticipate problems
before they occur.
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How the data is collected,
analyzed, and to whom it is
presented, and if this does not
go to the right people … What a
waste of resources?
© 2004 IBM Corporation
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