Moon-Hwan Chang

Light emitting diodes reliability review

The increasing demand for light emitting diodes (LEDs) has been driven by a number of application categories, including display backlighting, communications, medical services, signage, and general illumination. The construction of LEDs is somewhat similar to microelectronics, but there are functional requirements, materials, and interfaces in LEDs that make their failure modes and mechanisms unique. This paper presents a comprehensive review for industry and academic research on LED failure mechanisms and reliability to help LED developers and end-product manufacturers focus resources in an effective manner. The focus is on the reliability of LEDs at the die and package levels. The reliability information provided by the LED manufacturers is not at a mature enough stage to be useful to most consumers and end-product manufacturers. This paper provides the groundwork for an understanding of the reliability issues of LEDs across the supply chain. We provide an introduction to LEDs and present the key industries that use LEDs and LED applications. The construction details and fabrication steps of LEDs as they relate to failure mechanisms and reliability are discussed next. We then categorize LED failures into thirteen different groups related to semiconductor, interconnect, and package reliability issues. We then identify the relationships between failure causes and their associated mechanisms, issues in thermal standardization, and critical areas of investigation and development in LED technology and reliability.

Anomaly Detection of Light-Emitting Diodes Using the Similarity-Based Metric Test

Todays decreasing product development cycle time requires rapid and cost-effective reliability analysis and testing. Qualification is the process of demonstrating that a product is capable of meeting or exceeding specified requirements. Light-emitting diode (LED) qualification tests are often as long as 6000 h, but this length of time does not guarantee the typically required lifetime of 10 years or more. This paper presents a prognostics-based technique that reduces the LED qualification time. An anomaly detection technique called the similarity-based metric test is developed to identify anomalies without utilizing historical libraries of healthy and unhealthy data. The similarity-based metric test extracts features from the spectral power distributions (SPDs) using peak analysis, reduces the dimensionality of the features using principal component analysis, and partitions the data set of principal components into groups using a k-nearest neighbor (KNN)-kernel density-based clustering technique. A detection algorithm then evaluates the distances from the centroid of each cluster to each test point and detects anomalies when the distance is greater than the threshold. From this, the dominant degradation processes associated with the LED die and phosphors in the LED package can be identified. In our case study, anomalies were detected at less than 1200 h using the similarity-based metric test. Thus, our method could decrease the amount of LED qualification testing time by providing users with an earlier time to begin remaining useful life prediction without waiting 6000 h as required by industrial standards.

Failure Mechanisms and Reliability Issues in LEDs

The construction of LEDs is somewhat similar to microelectronics, but there are unique functional requirements, materials, and interfaces in LEDs that make their failure modes and mechanisms different. This chapter presents a definite, comprehensive and up-to-date guide to industry and academic research on LED failure mechanisms and reliability. It will help readers focus resources in an effective manner to assess and improve LED reliability for various current and future applications. In this review, we focus on the reliability of LEDs at the die and package levels. The reliability information provided by the LED manufacturers is not at a mature enough stage to be useful for the users of LEDs. This chapter provides groundwork for understanding of the reliability issues of LEDs. First, we present introduction about LED reliability and Physics of Failure (PoF) approach. We then categorize LED failures into 13 different groups related to semiconductor, interconnect, and package reliability issues. We close by identifying relationship between failure causes and associated mechanisms, issues in thermal standardization on LED reliability, critical areas of investigation, and development in LED technology and reliability.

Return on investment associated with PHM applied to an LED lighting system

Light emitting diode (LED) lighting systems have been implemented in a wide range of applications because they save money and are better for the environment than traditional lighting systems. However, the lack of information regarding LED reliability is a barrier to the further expansion of LED use. Prognostics and health management (PHM) techniques can be utilized to provide LED reliability information to remove this barrier. PHM can provide early warning of failures, reduce unscheduled maintenance events, extend the time interval of the maintenance cycle, and reduce the life cycle cost of LED lighting systems. This paper presents an evaluation of the return on investment from implementing PHM in LED lighting systems with different failure distributions. It also presents the results of a study comparing the life cycle cost of an LED lighting system maintained by unscheduled maintenance with the life cycle cost of the same system maintained using a PHM approach.

Introduction to LED Thermal Management and Reliability

Some like it hot, others do not. And those others for sure include the designers of products that contain light-emitting diodes (LEDs). This book is about thermal management of LEDs and especially LED applications. The main question to be addressed is: Why do we need thermal management? As Belady put it eloquently in 2001 [Belady and Minichiello, Electronics Cooling Magazine, May issue, 2003]: