Why do Power Supplies Fail, and What can be done about it? › procurement › proweb.nsf... · Root Cause Determination AssemblyAssembly System System Final TestFinal Test Procurement

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Power Technology & Qualification

© 2005 IBM Corporation

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

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© 2004 IBM Corporation2 10/7/2005

Major Causes of Failure

1.1. CComponentsomponents– Semiconductor Devices– Capacitors - Electrolytic, Ceramic, Poly Film– Magnetic Components

2.2. PPower Supply Constructionower Supply Construction– Spacing on Board– Device Mounting on Heat Sinks– Placement of Components

3.3. EnvironmentEnvironment– High Humidity – chemicals – Conductive Metal Parts – Bugs

4.4. Qualification & TestingQualification & Testing– HALT Tests– Control and Run Charts

5.5. Failure AnalysisFailure Analysis– Root Cause Determination– Field failure data

“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.”

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MOSFETCeramicPolyPInductor

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MOSFET Construction Analysis

Figure 1 Supplier A: Delaminating between epoxy and lead frame shown by red color. C-SEM front side

Figure 2 Supplier B No Delaminating .

Figure 3 Supplier A: Voids between the die and lead frame (die attach) are foundas represented by the white dots.

Electrical Components from two suppliers A and B are different. See Construction details

Figure 4 Wire bond Comparison Supplier A and Supplier Bi

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MOSFET Failure = f (time)

CraterEPI Layer

Field Intensity

Figure 1 : Craters on the EPI layer

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Soft Knee

MOSFET with the Soft Knee, Can’t run with the soft knee for long

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MOSFETs from Supplier A and B

Figure 1 Voltage Breakdown (BVdss) Distribution Figure 2 Leakage Current (Idss)

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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

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Electrolytic Capacitors

Good capacitor brands

Rubycon

Nichicon

Panasonic

Sanyo

Nippon

United Chemi

If you believe in plug and play , then learn to pray . Always Use Brand name quality Caps

Electrolyte formulation unstable, - hydrogen buildup inside the metal Can and failure in the field

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Multilayer Ceramic Capacitors Cut corners in cost, and then place them near corners, the result is obvious.

Figure 2. Close up of area denoted by the red box in figure 1. The crack bridges between the conductors

Figure 1. the corner of an MLCC, in cross-section. The red arrows show the cracked line

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Poly-Propylene Capacitors

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.

Burnt Polyp Capacitor

Who says POLYP Capacitors don’t burn. When they do, they burn spectacularly

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Magnetic Components

PFC Choke Burnt …. Two Powder Iron Chokes used in series

Another Inductor Burnt, WOW! Did we learn anything here?

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Zinc Whiskers and MOSFET Failures

Zinc Whisker

WOW! Zinc Whiskers again! Remember the lessons learned.

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Roaches Infestation - Power Supply Failure

Roaches

One thing is sure, nothing is Bug Proof

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Best Practices - Power Supply Construction

DD SSGG

PC WindowPC Window

Heat SinkHeat Sink

Electrolytic CapacitorElectrolytic Capacitor

TransformerTransformer

InductorInductor

Heat Sink

Bond-PlyDevice 1 Device 2 Device 3

Figure 1 Power Supply Component Placement and PC windows

Figure 2 Heat Sink Assembly to mount semiconductor devices with no screws and no clips

Good design can help to prevent manufacturing defects and service errors and to reduce the need for non-value-adding inspection practices.

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PARETO Diagrams

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HVMarginal Bad Device Driver Fail Dust/Metal

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MOSFET Choke Driver Ceramic Poly Fan

Figure 1 Failed Components in the field

Figure 2 Causes of MOSFET Failure

Treating the symptoms is a short term relief, find the root cause and have a long term relief

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Relative Cost to fix a Problem

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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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KnowledgeFailure Rate

Reliability and Learning CurveThrough a process of learning, knowledge is developed.

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PPM

PPM - todayPPM- Future

PPM Defects for a Server Power Supply – Today and in Future

Competitive Advantage

Cost being ($0.08/Watt), Quality will have a definite competitive advantage.

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“Kaizen” – Journey of Continuous Improvement

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Root Cause

DeterminationRoot Cause

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Final TestFinal TestSystem System

Procurement

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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.

If you can’t find the root cause of failure, you can not prevent it.

Eliminating symptoms of problems usually provides only temporary relief; eliminating root cause s provides long-term relief.

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?

Sustaining total quality requires viewing quality efforts as a journey, not an end.

600

MAN

Years

Documents

Why do Power Supplies Fail, and What can be done about it? › procurement › proweb.nsf... · Root Cause Determination AssemblyAssembly System System Final TestFinal Test Procurement