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 1 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 10 Power Supply Construction HALT Tests Control and Run Charts 3 2 1 0 1 – – 4 5. Failure Analysis – – 2 17 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 7 – – – MOSFET Ceramic PolyP Inductor 9 Failure Rate 2. Semiconductor Devices Capacitors - Electrolytic, Ceramic, Poly Film Magnetic Components 5 – – – 3 1. Time (month) Root Cause Determination Field failure data 10/7/2005 © 2004 IBM Corporation 2 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 10/7/2005 © 2004 IBM Corporation 3 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 4 10/7/2005 © 2004 IBM Corporation 4 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 5 A B Figure 2 Leakage Current (Idss) 10/7/2005 © 2004 IBM Corporation 5 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 6 10/7/2005 © 2004 IBM Corporation 6 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 7 10/7/2005 © 2004 IBM Corporation 7 Power Technology & Qualification Poly-Propylene Capacitors Who says POLYP Capacitors don’t burn. When they do, they burn spectacularly Burnt Polyp Capacitor 8 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. 10/7/2005 © 2004 IBM Corporation 8 Power Technology & Qualification 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 © 2004 IBM Corporation 9 Power Technology & Qualification Zinc Whiskers and MOSFET Failures WOW! Zinc Whiskers again! Remember the lessons learned. Zinc Whisker 10 10/7/2005 © 2004 IBM Corporation 10 Power Technology & Qualification Roaches Infestation - Power Supply Failure One thing is sure, nothing is Bug Proof Roaches 11 10/7/2005 © 2004 IBM Corporation 11 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 12 10/7/2005 © 2004 IBM Corporation 12 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 12 10 8 6 4 2 0 HVMarginal Bad Device Driver Fail Dust/Metal Figure 2 Causes of MOSFET Failure 13 10/7/2005 © 2004 IBM Corporation 13 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” 14 10/7/2005 © 2004 IBM Corporation 14 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. 2 3 4 5 6 7 8 9 10 10/7/2005 11 12 13 © 2004 IBM Corporation 15 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 23 21 19 17 15 13 11 9 7 5 3 1 0 Time - months 16 10/7/2005 © 2004 IBM Corporation 16 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 17 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. 10/7/2005 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 17