Kelley Rountree, RTI International

Join Kelley Rountree of RTI International at the LED A.R.T. Symposium


Abstract: Mimicking Real LED Lamp Stress Factors: Thermal Cycling in Luminaries and Lamp Failure Analysis

The present work provides insight to common failure locations and mechanisms for commercial LED lamps exposed to elevated temperature (caused by common-use application in enclosed ceiling fixtures or recessed downlights, for example) and thermal cycling (due to switching). The commercially available LED lamp models were operated to maximize the total number of cycles experienced by the device under test (provided that the temperature reached 95% of the upper and lower stabilization points on each cycle), and configurations were chosen to approximate field conditions. Thermal, photometric, and maintenance parameters were used to monitor the standard lumen depreciation and abrupt failure of 627 individual lamps. Over a fifteen-month period, 130 lamps completely failed and an additional 24 lamps were intermittent failures; these details are available in a separate report. Failed lamps were then disassembled to reveal driver components and LED package types for further testing including electrical, and in some cases thermal. Examination of the failed lamps identified interconnect issues including solder failure and degraded electrical contacts as primary failure modes. Solder failure and board/component discoloration were found to be localized, with location varying based upon driver topology (e.g., buck, flyback, boost) and LED packaging type. For example, through-hole component solder failure, particularly for transformer, capacitor, and transistor components, was dominant in flyback topologies while LED solder failure prevailed in boost topologies. Component and visible signs of LED degradation were also observed for over half of the samples. These failure mechanisms likely stem from the high heat produced by compact LED lamp drivers in the different test configurations, in particular the recessed and enclosed ceiling luminaires. Moving forward, it will be important for industry to address localized heat caused by switch cycles and improve solder technique in these high-stress locations.


About Kelley Rountree :

Kelley Rountree received her education and professional training at the University of Pittsburgh (with Prof. Alexander Star) and the University of North Carolina at Chapel Hill (with Prof. Jillian Dempsey). Kelley worked to develop an in situ method to determine charge transfer driving force in quantum dot assemblies. This work led to an interest in electronics and later employment at Pine Research Instrumentation, an electrochemical equipment manufacturer, and as an electrical engineering instructor at Duke TIP. Kelley recently joined the staff at RTI International to work on solid-state lighting projects.