No abstract

Power system applications, such as street lighting, typically have a 10 year warranty. When these systems include electrolytic capacitors, it is important to choose a supplier that meets these requirements. Traditional lifetime testing of electrolytic capacitors to ascertain their life expectancy requires specialized equipment, is time consuming, labor intensive, and for most OEMs, is ultimately cost prohibitive. Electrolytic capacitors with the same capacitance and voltage ratings from different suppliers may be rated to the same lifetime, but historical data confirms that they can have significantly different operational expected lives. An accelerated testing methodology is needed to compare the reliability of electrolytic capacitors from different suppliers. DfR has developed an approach that reduces test times from thousands of hours to several weeks by taking advantage of two key behaviors of electrolytics. The first involves the rate at which capacitors lose electrolyte, which is fairly predictable at a given temperature and electrical stress. The second key behavior is the dependence of the equivalent series resistance (ESR) of electrolytic capacitors on the volume of liquid electrolyte. The approach that will be described in this paper will demonstrate a means of comparing the time to failure for comparable capacitors from different suppliers under the same conditions. Case studies will demonstrate how this method avoids the extended testing that is typically required.

This research compared the lifetime of similar aluminum electrolytic capacitors from different manufacturers using an accelerated life test, which consisted of critical weight loss testing and rate of weight loss testing. In critical weight loss testing, capacitors are perforated to speed up electrolyte evaporation and the equivalent series resistance (ESR) and weight are measured periodically to determine their relationship. In rate of weight loss testing, capacitors are subjected to final operating conditions (i.e. voltage and ripple current are applied) and the weight is periodically measured over the course of 500 hours. After test completion the relationship between ESR and weight loss is used to calculate the critical weight loss that occurs at datasheet-defined failure, which is typically a 200% increase in ESR. The rate of weight loss is extrapolated to the critical weight to estimate a time to failure that can be compared to other capacitors tested using the same accelerated approach. In this research, testing compared 450 V, 68 μF capacitors from Manufacturer A and Manufacturer B, and results indicated Manufacturer A had a significantly longer lifetime. Therefore, capacitors from Manufacturer A are more reliable than capacitors from Manufacturer B.

No abstract

Counterfeit components have been defined as a growing concern in recent years as demand increases for reducing costs. In fact the Department of Commerce has identified a 141% increase in the last three years alone. A counterfeit is any item that is not as it is represented with the intention to deceive its buyer or user. The misrepresentation is often driven by the known presence of defects or other inadequacies in regards to performance. Whether it is used for a commercial, medical or military application, a counterfeit component could cause catastrophic failure at a critical moment. The market for long life electronics, based on commercial off the shelf (COTS) parts, such as those used in medical, military, commercial depot repair, or long term use applications (e.g. street and traffic lights, photovoltaic systems), seems to create a perfect scenario for counterfeiters. With these products, components wear out and need to be replaced long before the overall product fails. The availability of these devices can be derived in many ways. For example, a typical manufacturer may render a component obsolete by changing the design, changing the functionality, or simply discontinuing manufacture. Also, the parts that are available after a design has been discontinued are often distributed by brokers who have very little control over the source or supply. Recycling of devices has also emerged as a means of creating counterfeit devices that are presented as new. And finally, as demand and price increase, the likelihood of counterfeits also increases. This paper will address the four unique sources of counterfeit components and insight into how they occur. Detection methodologies, such as visual inspection, mechanical robustness, X-Ray, XRF, C-SAM, Infrared Thermography, electrical characterization, decapsulation, and marking evaluations, will be compared and contrasted, as well as multiple examples of counterfeit parts identified by DfR.