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In this paper, we first give some historical background and trends in PV module technologies with a focus on the growing trend towards 'PV everywhere', mainly targeting improved aesthetics, dimensional freedom including curved surfaces, weight concerns and specific reliability testing. This section acts as an introductory review of the field. Then, in the following sections, we elaborate on two technological developments in this field where we are active: (i) multi‐wire interconnection and (ii) advanced encapsulation. In terms of multi‐wire interconnection, this technology offers improved aesthetics, a similar performance and dimensional freedom compared to the traditional tabbing‐stringing process, and the experiments show promising results on extended reliability testing, including thermal cycling, damp heat and humidity freeze, as well as high‐temperature storage. In terms of advanced encapsulation, we introduce our approach for curved surfaces using a double‐membrane laminator and present results on fabricating curved modules, targeting as demonstration examples on the one hand, glass–glass sunroofs, and on the other hand, lighter‐weight bonnets for automotive applications. We mix examples targeting building and automotive applications, to illustrate the variety of requirements (colours, curvature, weight, reliability, safety), although this variety within building and vehicle applications is probably as large as between them. [ABSTRACT FROM AUTHOR]

There is a growing interest in the development of microelectronics that can perform reliably and robustly at temperatures above 300 °C. Such devices require stable thermal properties, low thermal drift, and thermal cycling resistance. Conventional hybrid circuit technology demonstrates high‐temperature packages, but the high costs and lead time are significant drawbacks. In contrast, additive manufacturing processes, including aerosol jet printing (AJP), offer cost and time benefits, as well as 3D structures and embedded features. However, the properties and reliability of additive packaging materials at extreme temperatures are not well known. Herein, the reliability at temperatures up to 750 °C in terms of electrical performance and mechanical strength of aerosol jet printed gold thick films onto ceramic substrates are assessed. Thermal coefficient of resistance of printed gold films is measured. The electrical resistance stability and leakage current of printed gold structures are also characterized during over 100 h of aging at temperatures up to 750 °C. Finally, the mechanical adhesion strength of the printed gold films is evaluated after aging for 100 h at temperatures up to 750 °C. The adhesion of the printed gold to the ceramic substrates remains high after aging, very stable resistances and minimal leakage currents have been observed. [ABSTRACT FROM AUTHOR]

It is significant to promote reliability testing and assessment research of hydraulic cylinder which is the basis to improve reliability of the cylinder and pertinent machine system. In this study, a new comprehensive testing system for the reliability research of hydraulic cylinder has been developed, reliability testing of a hydraulic cylinder for precision production has been conducted using the test bench. With the obtained test data, parameters of the Weibull distribution function of the cylinder are estimated by means of the least square estimation method, thus, reliability distribution function and lifetime values of the cylinder under normal stress level are ultimately obtained. The developed new test bench and performed testing and analysis in this study would provide an excellent platform and reliability assessment approach for industry hydraulic cylinders. [ABSTRACT FROM AUTHOR]

Although ethylene vinyl acetate copolymer (EVA) is still the dominant PV encapsulant, polyolefins (PO) have gained market share in recent years. Like EVA, PO can be mixed with a cross-linking agent and chemically reacted during the lamination process to form polyolefin elastomers (POE). The cross-linked and therefore insoluble fraction of the encapsulation can be determined by extracting the soluble part of the material with a solvent. The degree of cross-linking, or gel content (GC), is determined from the mass ratio before and after extraction of the samples. The analytical methods for determining the GC value are described for example in IEC 62788-1-6 and the Chinese national standard GB/T29848-2018. We observe a significant difference between the test results of these two standards, with the GC values resulting from the GB standard test being significantly higher. This is particularly true in the low GC range. The main reason for this difference is the extraction time of 5 h specified in the GB standard, which is insufficient to ensure complete extraction of the non-crosslinked polymers at lower GC values. However, for certain POE materials the required minimum GC (50%-65%) is exactly in this range.

Copyright of Experimental Technology & Management is the property of Experimental Technology & Management Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• The reliability of high-power switches in Fast Discharge Unit (FDU) is very important for the safety operation of superconducting magnets. In this paper, the reliability and test number of FDU switches are discussed. • The FDU configuration characteristics of different types of superconducting magnets are introduced, and some explanation and calculation on reliability are provided. • The reliability interval estimation after a certain test number is discussed by using the binomial distribution theory. • The reliability conformance test based on the claimed reliability is discussed to derive the test number. High-power switches, as the important active part of Fast Discharge Unit (FDU) in Tokamak, are designed to interrupt the circuit current and transfer the quench energy for protecting expensive superconducting magnets. Hence, their reliability has always been highly underlined. In this paper, the reliability and test number of FDU switches are discussed, mainly including three issues. First, the FDU configuration characteristics of different types of superconducting magnets are introduced, and explanations and calculations on reliability are provided. Second, the reliability interval estimation after a certain test number is discussed by using the binomial distribution theory. Three, the compliance test based on the claimed reliability is studied, and two types of test plans are discussed and compared to derive the test number. The discussion in this paper focuses on the FDU switches and provides valuable guidance for their reliability test and assessment. [ABSTRACT FROM AUTHOR]

Advanced indentation techniques have been introduced to study the effects of multiple stresses on the transistor characteristics with using a cylindrical tip with various alignments. Particularly, controlling the cylinder tip orientation relative to the transistor channel direction is proposed to selectively strain the silicon channels in order to induce very different selectively controlled stresses. Several tip alignments allow to shift the stresses from uniaxial towards biaxial stress as well as to induce shear stress. Ring oscillator circuits based on NAND and NOR gates are used to monitor the stress effects on the characteristic circuit frequency as well as on the individual transistors. Finite Element simulations help to identify optimized setup properties for the targeted application. Comparison with previous indentation experiments derives the specific influence of each stress tensor component on the transistor characteristics. [ABSTRACT FROM AUTHOR]

In this paper, truncated lifetime testing is considered, and new single acceptance sampling plans (SASP) are proposed assuming that the lifetime distribution is the q-Weibull distribution of a product. Assuming a finite population size (limited population size, N); the inspection process for a single sampling plan is ASP(n,p) begins by choosing a simple random sample from a given lot, then based on pre-assigned quality standards, the manager will decide to reject the lot if some items fail to meet the pre-assigned quality standards. Since the population is limited; then this experiment meets the hypergeometric distribution assumptions. The hypergeometric theory is applied to compute the probability of acceptance, and the procedure is used to compute the minimum sample size and the operating characteristics of the sampling plans. Also, a real data analysis is given to illustrate the applicability of the proposed plan in the industry. [ABSTRACT FROM AUTHOR]

Minimum-cost reliability test durations based on gamma failure count data are found by solving mixed integer nonlinear programming problems. The optimal numbers of test units and failures allowed are also determined. A linear combination of test time and sample size is minimized assuming that producer and consumer risks are controlled. A quite accurate approximation of the smallest feasible acceptance number is deduced in closed-form. Moreover, a fast and efficient iterative algorithm is presented in order to obtain the optimal reliability demonstration test plan, which provides the best criterion to decide the acceptability of submitted lots and production processes. Furthermore, some descriptive analyses of the proposed inspection schemes, as well as applications of the developed methodology to the manufacturing of deep groove ball bearings, semiconductor lasers, and water pumps, are provided for illustrative and comparative purposes. [ABSTRACT FROM AUTHOR]

Summary: Embedded systems have high coupling and dependency among different hardware and software components in heterogeneous layers, which makes location and issue tracking in their testing difficult. Despite these poor verification conditions, even the most important reliability quality verification among embedded system characteristics is verified with insufficient sample size, typical test cases, and general test strategies, following limitations such as development costs and scheduling. As a result, shipments are highly likely to lead to various reliability quality problems because items have not been verified considering reliability quality characteristics. Hence, to address this gap, this study developed remote embedded device test framework on the cloud (RED‐TFC), which has an innovative reliability test manager component that can automatically perform various tests for the evaluation of reliability and performance of distributed shared devices by utilizing the cloud concept. RED‐TFC offers two key enhancements over existing testing services: (i) the adaptive sample scale for reliability test (ASRT), a feature that identifies the most appropriate sample size for performing functionality and reliability tests of remote verification targets connected to the RED‐TFC server; and (ii) the mass sample reliability test (MSRT), which uses a test case that is specific to reliability, with the sample size obtained by ASRT, to perform verification following the Markov prediction process. This paper analyses two Android smartphone models considered the most generic examples, including many embedded components, and presents a method of detecting a high number of reliability problems in smartphones using the proposed RED‐TFC and its implications. [ABSTRACT FROM AUTHOR]

GNSS observations stochastic model influences all subsequent stages of data processing, from the possibility to reach the optimal parameters estimation, to the reliability and quality control of the solution. Nowadays, an uncontrolled use of GNSS stochastic models is common for both data processing and simulation missions, especially in commercial GNSS software packages. As a result, the variance–covariance matrices that are derived in the processing are inadequate and cause incorrect interpretations of the results. A proper method to evaluate the reliability of the stochastic model is needed to reflect the confidence level in statistic testing and simulation mission efforts. In this contribution, a novel method for evaluating the statistical nature of GNSS stochastic model is presented. The method relies on the deterministic nature of the integer ambiguity variable to examine and express the expected multinormal distribution of the double-difference adjustment results. The suggested method was used with a controlled experiment and 24 h of observations data to investigate how the statistical nature of the stochastic model is affected by different baseline lengths. The results indicate that as the baseline length increases, the stochastic model is less predictable and exposed to irregularities in the observation's precision. Additionally, the reliability of the integer ambiguity resolution success rate (SR) was tested as part of the stochastic model evaluation. The results show a dramatic degradation in the SR prediction level when using an inadequate stochastic model, which suggests using extra caution when handling this parameter unless high-confidence reliable stochastic model is available. [ABSTRACT FROM AUTHOR]

This paper examines the reliability of Structure from Motion (SfM) photogrammetry as a tool in the capture of forensic footwear marks. This is applicable to photogrammetry freeware DigTrace but is equally relevant to other SfM solutions. SfM simply requires a digital camera, a scale bar, and a selection of oblique photographs of the trace in question taken at the scene. The output is a digital three‐dimensional point cloud of the surface and any plastic trace thereon. The first section of this paper examines the reliability of photogrammetry to capture the same data when repeatedly used on one impression, while the second part assesses the impact of varying cameras. Using cloud to cloud comparisons that measure the distance between two‐point clouds, we assess the variability between models. The results highlight how little variability is evident and therefore speak to the accuracy and consistency of such techniques in the capture of three‐dimensional traces. Using this method, 3D footwear impressions can, in many substrates, be collected with a repeatability of 97% with any variation between models less than ~0.5 mm. [ABSTRACT FROM AUTHOR]

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Capability of high-speed and low-cost manufacturing makes the printing techniques a very promising approach for large-area flexible electronics mass manufacturing. Due to fast and intensive technology development, the lack of knowledge about the reliability and lifetime of printed electronics is obvious, requiring further investigation. Especially, the effect of torsional bending on lifetime is a mostly unexplored field of reliability testing. In this article, a torsional bending test of parallel printed silver conductors (0.3-, 0.5-mm pitch) on polymer substrate (polyethylene terephthalate, 125-μm thickness) was conducted and analyzed. According to the experimental results, torsional bending causes wear-out type failures in conductors and the length-to-width (LTW) ratio of the sample’s substrate was observed to have a significant impact on reliability. If the LTW ratio is smaller than 3, the lifetime of printed conductor seems to collapse and samples lasted for approximately only 17 bending cycles on average. Lifetime was improved by increasing the LTW ratio and samples withstood over hundreds of cycles with LTW ratio of higher than 15. However, the distance of a conductor from the edge of the substrate was not observed to have any significant influence on the reliability under torsional bending. [ABSTRACT FROM AUTHOR]

A reliable system is crucial in satisfying users' need, but the reliability is dependent on the varying effects of the test collection. The reliability is usually evaluated by the similarities of a set of system rankings to understand the impact of variations in relevance to judgments or effectiveness metrics. However, such evaluations do not indicate the reliability of individual system rankings. This study proposes a method to measure the reliability of individual retrieval systems based on their relative rankings. The Intraclass Correlation Coefficient (ICC) is used as a reliability measure of individual system ranks. Various combination of effectiveness metrics according to their clusters, selection of topic sizes, and Kendall's tau correlation coefficient with the gold standard are experimented. The metrics average precision (AP) and rank-biased precision (RBP) are suitable for measuring the reliability of system rankings and generalizing the outcome with other similar metrics. Highly reliable system rankings belong mostly to the top and mid performing systems and are strongly correlated with the gold standard system ranks. The proposed method can be replicated to other test collections as it utilizes relative ranking in measuring reliability. The study measures the ranking reliability of individual retrieval systems to indicate the level of reliability a user can consume from the retrieval system regardless of its performance. [ABSTRACT FROM AUTHOR]

Micro‐LEDs are attracting more and more attention recently due to the excellent electrical and optical properties. The performance of Micro‐LEDs in different environment becomes very important in order to meet the requirement of various applications or even multi‐function mode. However, for display, we found the reflection of ambient light from metal electrode will reduce the contrast ration seriously. Therefore, more researches have be done to solve this problem and maximize the strengths of Micro‐LEDs. Here, we report the fabrication of Micro‐LEDs with varied size from 200um pitch to 20um pitch. The devices performance under different environment have been tested, showing great stability and reliability. Besides, the ambient contrast ratio (ACR) has been investigated, and a reflection elimination method has been proposed as well. Besides, according to the comparison between mini‐LED display and Micro‐LED display, the relationship between metal electrode design and light reflection has been investigated. And a trade‐off method has also been proposed, showing great potential to improve the performance of Micro‐LED display. [ABSTRACT FROM AUTHOR]

Background: Subjective assessment of right ventricular (RV) function by neonatal echocardiography lacks validation. Incorrect diagnostic assignment in patients with suspected pulmonary hypertension (PH) may lead to unnecessary treatment or missed treatment opportunities. Methods: Six evaluators (experts [n = 3], novice [n = 3]) were asked to independently rate RV characteristics (global function, dilation, and septal flattening) based on standardized echocardiography images. We randomly selected 60 infants, ≥35 weeks gestation at birth, of whom 30 were clinically unwell with acute pulmonary hypertension (aPH) and 30 were healthy controls. aPH was defined by echocardiography presence of right‐left shunting across transitional shunts or elevated right ventricular systolic pressure as estimated by the magnitude of the regurgitant jet across the tricuspid valve with impaired oxygenation. Inter‐rater comparative evaluation within groups and between groups was performed using Kappa statistics. Results: Global agreement between evaluators for subjective assessment of RV function (0.3 [0.03], P < 0.001), size (0.14 [0.02], P < 0.001), and septal flattening (0.2 [0.02], P < 0.001) was uniformly poor. Agreement in RV function assessment was marginally better for both expert (0.32 [0.08], P < 0.001 vs 0.13 [0.081], and P < 0.001) and novice (0.4 [0.08], P < 0.001 vs 0.06 [0.07], and P < 0.001) evaluators. Overall, the diagnosis of aPH vs control was misclassified in 18% of cases. Conclusion: This study demonstrated significant variability in qualitative assessment of RV size and function by trained evaluators, regardless of level of expertise attained. The reliability of objective measures of RV hemodynamics requires prospective evaluation. [ABSTRACT FROM AUTHOR]

Electrolytic capacitors are widely used in the dc link of variable frequency drives (VFDs). Their reliability has a significant impact on VFD performance and lifetime. Typically, the lifetime of electrolytic capacitors is specified in vendors’ datasheets at the rated continuous dc voltage and at the rated ripple current at one fixed frequency, under rated temperature, and humidity conditions. In order to analyze and verify their life time specified in the datasheet, a test fixture is needed to apply both adjustable dc-bias voltage and ac ripple current at a specific frequency. In this paper, two portable test fixtures with low kVA requirements are proposed for electrolytic capacitor reliability testing for different dc-bias voltage. The test fixtures can easily be scaled to test large capacitors with high ripple current rating. Multiple capacitor samples or entire capacitor bank assemblies used in VFDs can be tested. Design details of the test fixtures and reliability test results are provided. [ABSTRACT FROM AUTHOR]

Micro‐LEDs are attracting more and more attention recently due to the excellent electrical and optical properties. The performance of Micro‐LEDs in different environment becomes very important in order to meet the requirement of various applications or even multi‐function mode. However, for display, we found the reflection of ambient light from metal electrode will reduce the contrast ration seriously. Therefore, more researches have be done to solve this problem and maximize the strengths of Micro‐LEDs. Here, we report the fabrication of Micro‐LEDs with varied size from 200um pitch to 20um pitch. The devices performance under different environment have been tested, showing great stability and reliability. Besides, the ambient contrast ratio (ACR) has been investigated, and a reflection elimination method has been proposed as well. Besides, according to the comparison between mini‐LED display and Micro‐LED display, the relationship between metal electrode design and light reflection has been investigated. And a trade‐off method has also been proposed, showing great potential to improve the performance of Micro‐LED display. [ABSTRACT FROM AUTHOR]

Abstract By using micro-electro-mechanical systems (MEMS), this work develops flexible four-in-one (temperature, voltage, current and flow) micro sensors on a flexible substrate. The flexible four-in-one micro sensors use polyimide as the protective layer, owing to its high temperature resistance. This paper will involve designing and fabricating the flexible four-in-one micro sensors and low-temperature proton exchange membrane fuel cell (LP-PEMFC). A programmable thermal shock tester and a programmable temperature and humidity tester were used to simulate the inner environment of the LP-PEMFC. The calibration curves reveal repeatability and highly linear of the flexible four-in-one micro sensors. After calibrated and its reliability confirmed, the flexible four-in-one micro sensors are inserted into the LP-PEMFC for local microcosmic measurement. In particular, the inside data and performance are monitored to optimize the performance and extend the life of a fuel cell. Highlights • Home-made four-in-one flexible micro sensor can be placed anywhere in a low-temperature proton exchange membrane fuel cell. • Four-in-one flexible micro sensors are four functions, compactness, acid corrosion resistance, good temperature tolerance, quick response. • In-situ diagnosis local temperature, voltage, current and flow information of a low-temperature proton exchange membrane fuel cell. [ABSTRACT FROM AUTHOR]

To ensure sufficient thermal performance within electric vehicle (EV) batteries, thermal interface materials (TIMs), such as pastes or adhesives, are widely used to fill thermally insulating voids between cells and cooling components. However, TIMs are composite materials that are subject to degradation over the battery's lifetime. Using TIMs for battery applications is a new and emerging topic, creating the need to rapidly acquire knowledge about appropriate lifetime testing and evaluation methods, in close collaboration with the battery manufacturers. This paper reviews suitable methods for durability testing as well as basic modeling approaches which allow for the transfer of laboratory results to the longtime behavior of interface materials during a vehicle's lifetime. [ABSTRACT FROM AUTHOR]

In this paper, the influence of microwave curing on the reliability of a representative electronic package is examined by reliability testing and measurement of residual stresses. A LM358 voltage regulator die was mounted to an open quad flat no-leads (QFN) package for reliability testing. For the stress measurement, a specifically designed stress measurement die was mounted to the QFN package. The chips were encapsulated with Hysol EO1080 thermosetting polymer material. Curing was performed using an open-ended microwave oven system equipped with in situ temperature control. Three different temperature profiles for microwave curing were selected according to the requested degree of cure and chemical composition of the cured material. A convection cure profile was selected for the control group samples. Temperature cycle tests and highly accelerated stress tests (HAST) were performed on a total number of 80 chips. Ninety-five QFN packages with stress measurement chips were also manufactured. The increased lifetime expectancy of the microwave-cured packaged chips was experimentally demonstrated and measured between the 62% and 149% increased lifetime expectancies after temperature cycle test (TCT), and between 63% and 331% after a HAST and TCT compared to conventionally cured packages. The analysis of specifically designed stress test chips showed significantly lower residual stresses ranging from 26 to 58.3 MPa within the microwave-cured packages compared to conventionally cured packaged chips, which displayed residual stresses ranging from 54 to 80.5 MPa. Therefore, this paper provides additional confidence in the industrial relevance of the microwave curing system and its advantages compared to the traditional convection oven systems. [ABSTRACT FROM AUTHOR]

Non-destructive electrical characterization was performed to detect copper migration in a degraded through-silicon via structure after various stressing conditions, such as elevated temperature exposure, temperature cycling, and electrical biasing. They were performed either independently or as a combination with electrical bias for comparison. Variations in the electrical characteristics reflect the presence of copper. The electrical characteristics were also able to monitor the transport of copper ions from an applied electric field. Physical failure analysis was performed to verify the presence of migrated copper, correlating with the changes observed during electrical measurement. With this understanding, reliability assessments become possible where this paper seeks to value add to verify the influence of Cu migration on the conduction mechanism and time-dependent dielectric breakdown (TDDB) lifetime, in which there is currently a lack in understanding. The conduction mechanism was fitted with experimental data before and after degradation and it was deduced that the Poole–Frenkel conduction mechanism is the dominant mechanism after degradation. However, this is dependent on the copper oxidation state which was verified to change over time from Cu2O to CuO by X-ray photoelectron spectroscopy. TDDB experiments were also performed based on this understanding and found that the presence of copper may accelerate or decelerate time to failure. TDDB lifetime was fitted experimentally and is found to be in good agreement with the $\sqrt {E} $ model. It was verified experimentally by measuring the time to failure at low ${E}$ -field within reasonable failure time, rather than extrapolating from data at high field. [ABSTRACT FROM AUTHOR]

Abstract Background Health care researchers working in the Arabian Gulf need information on how to optimize recruitment and retention of study participants in extremely culturally diverse settings. Implemented in Doha, Qatar in 2012 with 4 language groups, namely Arabic, English, Hindi, and Urdu, this research documents persons’ responses to recruitment, consent, follow-up, and reminder procedures during psychometric testing of the Multicultural Assessment Instrument (MAI), a novel self- or interviewer-administered survey. Methods Bilingual research assistants recruited adults in outpatient clinics by approaching persons in particular who appeared to be from a target language group. Participants completed the MAI, a second acculturation instrument used for content-validity assessment, and a demographics questionnaire. Participants were asked to take the MAI again in 2–3 weeks, in person or by post, to assess test-retest reliability. Recruitment data were analyzed by using nonparametric statistics. Results Of 1503 persons approached during recruitment, 400 enrolled (27 %)—100 per language group. The enrollment rates in the language groups were: Arabic-32 %; English-33 %; Hindi-18 %; Urdu-30 %. The groups varied somewhat in their preferences regarding consent procedure, follow-up survey administration, contact mode for follow-up reminders, and disclosure of personal mailing address (for postal follow-up). Over all, telephone was the preferred medium for follow-up reminders. Of 64 persons who accepted a research assistant’s invitation for in-person follow-up, 40 participants completed the interview (follow-up rate, 63 %); among 126 persons in the postal group with a deliverable address, 29 participants mailed back a completed follow-up survey (response rate, 23 %). Conclusions Researchers in the Arabian Gulf face challenges to successfully identify, enroll, and retain eligible study participants. Although bilingual assistants—often from the persons’ own culture—recruited face-to-face, and our questionnaire contained no health care-related content, many persons were reluctant to participate. This occurrence was observed especially at follow-up, particularly among participants who had agreed to follow-up by post.

Several electronic applications must withstand elevated temperatures during their lifetime. Materials and packages for use in high temperatures have been designed, but they are often very expensive, have limited compatibility with materials, structures, and processing techniques, and are less readily available than traditional materials. Thus, there is an increasing interest in using low-cost polymer materials in high temperature applications. This paper studies the performance and reliability of sensor structures attached with anisotropically conductive adhesive film (ACF) on two different organic printed circuit board (PCB) materials: FR-4 and Rogers. The test samples were aged at 200 °C and 240 °C and monitored electrically during the test. Material characterization techniques were also used to analyze the behavior of the materials. Rogers PCB was observed to be more stable at high temperatures in spite of degradation observed, especially during the first 120 h of aging. The electrical reliability was very good with Rogers. At 200 °C, the failures occurred after 2000 h of testing, and even at 240 °C the interconnections were functional for 400 h. The study indicates that, even though these ACFs were not designed for use in high temperatures, with stable PCB material they are promising interconnection materials at elevated temperatures, especially at 200 °C. However, the fragility of the structure due to material degradation may cause reliability problems in long-term high temperature exposure.

The advantages of light emitting diodes (LEDs) over previous light sources and their continuous spread in lighting applications is now indisputable. Still, proper modelling of their lifespan offers additional design possibilities, enhanced reliability, and additional energy-saving opportunities. Accurate and rapid multi-physics system level simulations could be performed in Spice compatible environments, revealing the optical, electrical and even the thermal operating parameters, provided, that the compact thermal model of the prevailing luminaire and the appropriate elapsed lifetime dependent multi-domain models of the applied LEDs are available. The work described in this article takes steps in this direction in by extending an existing multi-domain LED model in order to simulate the major effect of the elapsed operating time of LEDs used. Our approach is based on the LM-80-08 testing method, supplemented by additional specific thermal measurements. A detailed description of the TM-21-11 type extrapolation method is provided in this paper along with an extensive overview of the possible aging models that could be used for practice-oriented LED lifetime estimations.