Why do Power Supplies Fail, and What can be done about it?

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Felix Nicholson
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1 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

2 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. 1. Components Semiconductor Devices Capacitors - Electrolytic, Ceramic, Poly Film Magnetic Components 2. Power Supply Construction Spacing on Board Device Mounting on Heat Sinks Placement of Components 3. Environment High Humidity chemicals Conductive Metal Parts Bugs 4. Qualification & Testing HALT Tests Control and Run Charts 5. Failure Analysis Root Cause Determination Field failure data Failure Rate Time (month) MOSFET Ceramic PolyP Inductor /7/2005

C-SEM front side Figure 3 Supplier A: Voids

are found as represented by the white dots.

3 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 3 Supplier A: Voids between the die and lead frame (die attach) are found as represented by the white dots. Figure 2 Supplier B No Delaminating. Figure 4 Wire bond Comparison Supplier A and Supplier Bi 3 10/7/2005

4 MOSFET Failure = f (time) MOSFET with the Soft Knee, Can t run with the soft knee for long Field Intensity Ids Soft Knee Ids - B Ids - A EPI Layer Crater Figure 1 : Craters on the EPI layer Vds 4 10/7/2005

5 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 A B Figure 1 Voltage Breakdown (BVdss) Distribution Figure 2 Leakage Current (Idss) 5 10/7/2005

6 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 6 10/7/2005

the corner of an MLCC, in cross-section.

7 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 7 10/7/2005

8 Poly-Propylene Capacitors Who says POLYP Capacitors don t burn. When they do, they burn spectacularly Burnt Polyp Capacitor 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 It is difficult to create consistent conditions for flattening, excessive pressure on some winding and insufficient pressure on others due to film thickness variations. 8 10/7/2005

9 Magnetic Components Another Inductor Burnt, WOW! Did we learn anything here? PFC Choke Burnt. Two Powder Iron Chokes used in series 9 10/7/2005

10 Zinc Whiskers and MOSFET Failures WOW! Zinc Whiskers again! Remember the lessons learned. Zinc Whisker 10 10/7/2005

11 Roaches Infestation - Power Supply Failure One thing is sure, nothing is Bug Proof Roaches 11 10/7/2005

12 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 Sink GG DD SS Electrolytic Capacitor PC Window Transformer 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 12 10/7/2005

13 PARETO Diagrams Treating the symptoms is a short term relief, find the root cause and have a long term relief MOSFET Choke Driver Ceramic Poly Fan Figure 1 Failed Components in the field HVMarginal Bad Device Driver Fail Dust/Metal Figure 2 Causes of MOSFET Failure 13 10/7/2005

14 Relative Cost to fix a Problem 1000 Relative cost 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 14 10/7/2005

15 Reliability and Learning Curve Through a process of learning, knowledge is developed Failure rate ppm Knowledge Failure Rate Knowledge /7/2005

16 PPM Defects for a Server Power Supply Today and in Future Cost being ($0.08/Watt), Quality will have a definite competitive advantage PPM - today PPM- Future PPM Competitive Advantage Time - months 16 10/7/2005

17 Kaizen Journey of Continuous Improvement Sustaining total quality requires viewing quality efforts as a journey, not an end. If you can t find the root cause of failure, you can not prevent it. Root Root Cause Determination R Design 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. D MAN Q Eliminating symptoms of problems usually provides only temporary relief; eliminating root cause s provides long-term relief. Fail 600 Procurement & Qualification Years Assembly W P System S Final Test Final Test 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? 17 10/7/2005

17SCT002 DIRECT-COUPLED HIGH-VOLTAGE (1kV) CURRENT LIMITER 17SCT002 - PRELIMINARY SPECIFICATION - REVISION JUNE 3, 2017

17SCT002 DIRECT-COUPLED HIGH-VOLTAGE (1kV) CURRENT LIMITER 17SCT002 - PRELIMINARY SPECIFICATION - REVISION JUNE 3, 2017 Maximum Voltage... 1,100 V Zero External Components HV Current Sink Enabled by Direct-Coupled LV Control HV Sink Current Limited, independent of HV Low HV Idle Current DIE (TOP VIEW) Description The 17SCT002