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The intermittent failure is one of the causes of No-Fault-Found (NFF). Intermittent failure in electrical interconnections of avionics is intensively investigated. An avionics system vulnerable to the intermittent failure is identified and its mockup is constructed. Vibration and thermal cycling tests are conducted to generate intermittent failures in the interconnections of the mockup. Intermittent failures occur after the accelerated thermal cycling test in vibration environment. Failure analysis reveals a line of crack at the interconnection. The mechanism for the crack generation is explained by a numerical simulation. A hypothesis is suggested for the explanation of the occurrence of intermittent failure from the crack. A combined vibration and temperature test is conducted to verify the hypothesis. The test results follow the expectation of the hypothesis.

Solar cell modules are connected in series and parallel in a photovoltaic system. All the solar cell modules degrade over time and the most degraded module in a string decides the output level of the string. In this study, we suggest a health monitoring method which enables to detect the most degraded module in a string without separating the module from the string. The method places a non-transparent film on a module in a string to make an artificial shading effect and monitors the current-voltage curve of the string while placing the film to the next one. We show analytically that the most degraded module can be detected by comparing all the string current-voltage curves. We demonstrate the method on an outdoor photovoltaic string.

The lifetime of solar cell modules is an important factor in the reduction of solar energy costs. To enhance the lifetime of silicon solar cell module under thermal cycling, numerical analysis and optimization are conducted on a conventionally designed solar cell module. A series of sensitivity studies with a numerical model reveals the thicknesses of Cu and Si should be reduced to enhance the lifetime under thermal cycling. The lifetime of the reliability-enhanced design is expected to increase by 159% compared to that of the conventional module.

Dye-sensitized solar cell (DSC) is a promising candidate for the application in building-integrated photovoltaics (BIPV). At higher temperature above 85 °C, the reliability of the module has remained a major challenge yet. A large DSC module, sized 300 × 300 mm 2 , is developed. In the preliminary module design, the width of cell is 11 mm and the coefficients of temperature expansion (CTE) for sealant and electrolyte are 699 and 807 ppm/°C, respectively. The modules are stored in 85 °C. The power conversion efficiency of the modules drops rapidly in 100 h during the test. To analyze and enhance the module design in view of reliability, finite element model is developed for the module. Stress analysis reveals that high stresses in electrode cause the breakage of electrode and sealant in succession and the loss of electrolyte finally. From a parameter sensitivity analysis with the finite element model, it is identified that the maximum stress in electrode can decrease when the cell width increases. CTEs of sealant and electrolyte can be also optimized as analysis confirms that the maximum stress in electrode drops when the CTEs of sealant and electrolyte decrease. Based on the studies, new module design is formulated, which have the cell width of 18 mm and the CTEs of 277 and 656 ppm/°C for sealant and electrolyte, respectively. The new modules are tested in 85 °C and show much better lifetime than the preliminary one without the leakage of electrolyte.

A Glass-to-Glass (G2G) CuInxGa1-xSe2 (CIGS) solar cell module is a promising thin-film solar technology; however, it is highly sensitive to moisture-induced degradation. Many studies have been conducted on the lifetime prediction model of this technology. However, none of these studies considered the spatial effects of moisture propagation on degradation. This study introduced a novel method, the spatially distributed diode model (SDDM), and predicted the lifetime of G2G CIGS solar modules for moisture-induced degradation. We analyzed the diffusion of spatial moisture concentration on the CIGS solar modules and estimated the model parameters using degradation data. The proposed method can predict the lifetime of any size or shape of G2G CIGS module for moisture-induced degradation. Furthermore, the method can be used to envision a possible longer lifetime for the solar modules depending on the selection of physical appearance of the modules and installation location.

Recently, life prediction models for Pb-based and Pb-free solders used in chip resistor assemblies under thermal cycling have been introduced. The models suggest that the field lifetimes of Pb-free solders would be better than those of Pb-based solders when used for chip resistors under thermal cycling conditions, while the lifetime of the chip assemblies under accelerated test conditions show a reverse relationship. In this study, the prediction models were verified by applying the model to another research case. Finite element models were built, thermal cycling conditions were applied, and the energy densities were calculated. Finally, life prediction analysis was conducted for the cases where Pb-based and Pb-free solders were used. The prediction results were then compared with the test data of the case. It was verified that the predictions of the developed life cycle models are on the practical scale. † Corresponding Author, cw_han@keti.re.kr Ⓒ2016 The Korean Society of Mechanical Engineers

To enhance the reliability of the thin-film solar cell technologies, it is required to analyze and understand the moisture-induced degradation. In this study, the moisture induced degradation of glass-to-glass CIGS module are comprehensively analyzed. CIGS modules are fabricated and tested under damp-heat conditions with periodical measurement of the electrical characteristics. Individual layers of the module are also investigated experimentally and the moisture induced degradation is discussed. A modified method to extract the diode model parameters from degraded I–V curves is proposed and applied to the degraded data. Finally, the degradation rates are modelled and the effect of model parameters degradation on the power of module are quantitatively compared. It suggests that the power degradation of CIGS module under the damp-heat environment is more affected by the enhanced recombination of the absorber layer than the degradation of the metal layer or the leakage over layers.

Recent growth of the insulated gate bipolar transistor (IGBT) module market has been driven largely by the increasing demand for an efficient way to control and distribute power in the field of renewable energy, hybrid/electric vehicles, and industrial equipment. For safety-critical and mission-critical applications, the reliability of IGBT modules is still a concern. Understanding the physics-of-failure of IGBT modules has been critical to the development of effective condition monitoring (CM) techniques as well as reliable prognostic methods. This review paper attempts to summarize past developments and recent advances in the area of CM and prognostics for IGBT modules. The improvement in material, fabrication, and structure is described. The CM techniques and prognostic methods proposed in the literature are presented. This paper concludes with recommendations for future research topics in the CM and prognostics areas.

Hybrid DC–DC converters for space applications should be designed for operation at full rated power within the military specification for temperature range of −55 to +125 °C. Hence, the thermal design is a crucial step in the design process of converter, ensuring that no component of the converter exceeds its rated maximum operating temperature. One of the objectives of this work is to guarantee that all electronic components operate below their maximum allowable temperature. For this purpose, a three dimensional model of a converter based on the finite element method was developed. Results based on numerical simulation were validated by experimental data from infrared camera. The total amount of dissipated power in every component was determined experimentally based on a prototype converter. In the case of a component with high power consumption, such as the field effect transistor, the increase in temperature was minimized by applying designed heat sink with a high-thermal-conductivity material.

Accelerated thermal cycling (ATC) tests are conducted for various chip resistor assemblies using the lead-based (SnPb) and lead-free (SnAgCu) solders. The corresponding life prediction models are developed by employing the well-established energy density approach. The life prediction model constants are obtained from the ATC test data. The models are utilized to predict the lifetimes of chip resistor assemblies under a mobile device field condition. The analysis indicates that the lead-free solder used in the chip resistor assembly would offer a longer lifetime under a field condition compared to the lead-based solder regardless of chip resistor types even when a reverse trend is observed in the ATC test results.

A vibration test coupon is prepared with nine plastic ball grid array packages on a printed circuit board using SnPb solders, and a random vibration test is conducted on the coupon. Life data from the test are analyzed, and it is shown that over the board, life data is location-dependent. For investigating this location dependency, a finite element model is developed and the equivalent stresses, which are defined based on the stress response functions at each node, are investigated. It is shown that one of the corner solder balls has the maximum equivalent stress at a package during the test. Finally, it is demonstrated that the maximum equivalent stress and durability life are inversely proportional.

DC/DC switching power converters are commonly used to generate a regulated DC output voltage with high efficiency. The DC/DC converter is composed of a PWM-IC (pulse width modulation-integrated circuit) controller, a MOSFET (metal-oxide semiconductor field effect transistor), inductor, capacitor, etc. It is shown that the variation of threshold voltage and the offset voltage in the electrical characteristics of PWM-IC increase by radiation effects in TID (Total Ionizing Dose) testing at the low energy rays using , and 4 heavy ions applied for SEL (Single Event Latch-up) make the PWM pulse unstable. Also, the output waveform for the given input in the DC/DC converter is observed by the simulation program with integrated circuit emphasis (SPICE). TID testing on PWM-IC is accomplished up to the total dose of 30 krad, and the cross section() versus LET() in the PWM operation is studied at SEL testing after implementation of the controller board.

This study investigates a solder interconnection failure of a 25-year-old crystalline silicon photovoltaic (c-Si PV) module and draws conclusions on the failure mechanism of the solder interconnection. The efficiency degradation of the 25-year-old c-Si PV module is –23%. Physical analysis of the solder interconnection failure finds solder to solder cracking and solder to Ag paste cracking. The main failure mechanism of the solder interconnection crack is caused by coefficient of thermal expansion (CTE) mismatch between the module material and the ribbon wire solder as shown by FMEA. To demonstrate the failure mechanism, a thermal cycle test is designed and conducted on a small c-Si PV module. The temperature cycle condition is −45 °C to 85 °C and the dwell time is 20 min. Measurements are carried out every 100 cycles monitoring the series resistance (Rs) through dark I – V . The result shows that Rs increases. After 1,000 cycles, the characteristics of dark I – V and light I – V are compared and analyzed. Failure mechanism analysis is conducted for the modules for which Pmax decreased with 20%. Water-jet techniques for cross-section and SEM are used to analyze the factor of resistance change and efficiency degradation. The failure mechanism of solder interconnection for c-Si PV Module is proved.

Application of electronic devices on automotive vehicles keeps increasing, and adoption of ball grid array (BGA) package is inevitable in the industry. Vibration loading to a vehicle provides another hazardous stress to the BGA assembly in addition to thermal one. In this paper, random vibration test on a daisy-chained BGA assembly is conducted with a real-time monitoring of resistance. BGA assemblies with leaded and lead-free solders are tested at once in the test. The changes of resistance before the occurrence of failure are investigated and a precursory resistance pattern before the failure of BGA assemblies is identified at the both solder types. Analyses on the failure locations confirm the localized failures on the BGA ball matrix. To investigate the generating mechanism of the precursory resistance pattern in the BGA assemblies, a numerical model of the mechanism is suggested and experimentally demonstrated. Based on the studies, a noble design of BGA assembly is suggested for the implementation of prognostics and health monitoring in vibration environment.

A thermal cycling test was conducted on a chip resistor solder joint with real-time failure monitoring. In order to study the failure mechanism of the chip resistor solder joint during the test, the resistance between both ends of the resistor was monitored until the occurrence of failure. It was observed that the monitored resistance first fluctuated linearly according to the temperature change. The initial variation in the resistance occurred at the time during the cycle when there was a decrease in temperature. A more significant change in the resistance followed after a certain number of cycles, during the time when there was an increase in the temperature. In order to explain the failure patterns of the solder joint, a mechanism for the solder failure was suggested, and its validity was proved through FE simulations. Based on the explained failure mechanism, it was shown that prognostics for the solder failure can be implemented by monitoring the resistance change in a thermal cycle condition.

Accelerated aging tests for induction motors with class E electrical insulation were conducted. The testing period exceeded one year and involved elevated temperatures, vibration, humidity, and voltage application. The activation energy of the aging process was estimated to be 0.72 ± 0.08 eV.

The heat sink assembly in a server station is anticipated to creep to fail at the solder joint under a constant load and temperature condition. To predict the lifetime of solder joint in the system, accelerated creep-rupture tests are conducted. Three loads of 4, 6, and 8 kg and temperatures of 35, 55, and 65 °C are selected for the tests. Larson–Miller model is adopted for the lifetime prediction, which requires tested lifetime data and stress analyses for the solder joint. An FE model for the stress analyses is developed and validated experimentally. Analyzed Larson–Miller constants show different tendency in the 8 kg load cases. Extensive failure analyses on the failed solder joints reveal the transition of failure mechanism at 8 kg load cases from the intergranular to the transgranular creep. Using only the validated test data of 4 and 6 kg load cases, creep lifetime prediction model for the solder joint in the heat sink assembly is developed and applied for a field condition.

High sensitivity shadow moire using non-zero order Talbot distances is proposed. A mathematical description for the contrast of shadow moire fringes produced by broad spectrum light is presented and its validity is corroborated experimentally. Using the non-zero order Talbot distances, the dynamic range is increased substantially and higher measurement sensitivity becomes practical, which has not been possible with the conventional shadow moire using the zero Talbot distance. Contour intervals in the range of 40 to 50 μm per fringe are practical. The critical parameters controlling fringe contrast are discussed and optical configurations for optimum contrast are suggested.

Three dimensional shape measurement techniques using optical methods are extensively applied in many fields of industry for product development and quality control. High resolution, fast measurement, large vertical and horizontal detecting area, and being applicable regardless of materials are valuable factors for the techniques. Recently there are strong demands to develop the technique which can measure specular and large surface quickly in production process for quality control purpose. Shadow moire can detect a large area due to the using a non-coherent light and measure in shorter time than scanning method but cannot be applied to specular surface. In the study, optical 3-D shape measurement technique based on shadow moire is proposed. By adapting UV light instead of visible white light in shadow moire, the new technique can measure even specular surface which was the limit of the existing shadow moire. Also it can take full advantage of the heritage of shadow moire; detecting a large area due to the using a non-coherent light and measuring in shorter time than scanning method. It can also increase vertical measuring range.

An electronic module was designed and developed to bend easily and repeatedly for a mobile application by a low-cost roll-to-roll manufacturing process [1]. The schematic diagram of the bendable module and its numerical model are shown at Fig.1. In the module, a thin silicon electronic chip is embedded in a polymer-based encapsuling adhesive between flexible copper clad polyimide (PI) layers. The thickness of silicon chip is 50 μm. Au bump is attached to the silicon and copper lines with anisotropic conductive film (ACF).

Packaging materials are critical not only to maintain the performance of photovoltaic module in harsh environment but also to ensure the long-term stability of photovoltaic module. Among packaging materials, backsheet protects module from ultraviolet, dust, moisture, and other gases. Hence, to guarantee the lifetime of modules, backsheet should not fail for the same period of time. This paper presents results on the development of accelerated life test method and correlation study between actual use and accelerated field conditions. The main purpose of this study is to develop the method which can guarantee 25 year lifetime of backsheet.

This paper focuses on the effect of delamination on electrical performance in PV module, especially electrical loss of solar cell. Degradation mode of field aged crystalline-Si PV module has been investigated through visual microscope. Electrical performance was measured with solar simulator. Electroluminescence analysis was carried out for detecting defects of PV module. Delamination observed in the PV module has occurred at the interface between the encapsulant and the front surface of the solar cell and between the encapsulant and glass. Delamination was a main degradation mode of PV module. To describe the effect of delamination on the electrical performance, new analysis through line irradiance system for electrical mapping was used. Investigation of delamination indicated that new analysis is useful to describe the effect of delamination compared to the electroluminescence analysis.

Application of electronic devices in automotive industry keeps increasing and adoption of BGA assembly is inevitable in the industry. Vibrating environment in a vehicle provides another hazardous stress to the BGA assembly in addition to thermal one. In this study, random vibration tests on a daisy-chained BGA assembly have been conducted with real-time monitoring of resistance. The change of resistance before the occurrence of failure has been investigated and a precursory resistance change before the failure of BGA assemblies has been proposed. Analyses on the failure location have confirmed the localized failure pattern on the BGA matrix. Based on the studies, a noble design of BGA assemblies has been suggested for the implementation of prognostics and health monitoring in vibration environment.

Automotive industry faces social demands of advancing the performance and efficiency, which leads to the increasing development and adoption of vehicle electronic instrument. The properties of the Ball Grid Array (BGA) packages such as smaller size and higher I/O counts make them attractive for the automotive electronics application. The application of the BGA package raises doubts for the reliability in automotive harsh environment. Vibration environment originated from the engine or outside of a vehicle is one of the detrimental stress factors for the electronic instrument [1].Copyright © 2011 by ASME

Heat sink assembly for a main board in a server station is built on printed circuit board by an anchor system, mounted by eutectic SnPb solder. Constant high temperature condition in the station keeps solder creeping and makes it failed eventually. To calculate the stress and predict the life of soldered anchor in the station, an FE model of anchor system is built. As viscoplastic behavior of solder depends on several factors such as microstructure of solder, temperature, load, and loading rate, model characteristics should be verified before applying it to life prediction. In this study, Anand unified constitutive equation is adapted for solder modeling and its creep behavior is calibrated and verified based on creep tests.

An accelerated thermal cycling test to assess the reliability of lead-free solders at chip resistor has been conducted. Test results indicate that the life of lead-free solder at chip resistor (6432 mm type) could be worse than of SnPb solder in the accelerated thermal cycling condition (125/-50C). Based on the test results and some published data, life prediction model for the solders has been developed. The developed life prediction model consists of stress model and damage model. Stress model, which relates thermal cycling condition to damage at solder, includes FE model with Anand's constitutive equation for solders. Damage model, which relates the damage to life of solder, is based on Darveaux' crack growth approach. Developed life prediction model confirms worse reliability of lead-free solder than leaded solder in the accelerated thermal cycling condition but potentially predicts reverse results in the field condition. To predict the reliability of lead-free solder in the field condition, accelerated factor should be carefully calculated using life prediction model.

Phase-shifting in an achromatic configuration of moiré interferometry is explained. The rigorous diffraction theory defines the phase of diffracted beams in terms of the pitch and the relative position of a compensator grating. A numerical analysis proceeds to determine the total phase change between two diffracted beams that produce moiré fringes.

An exact solution for the intensity distribution of shadow moiré fringes produced by a broad spectrum light is presented. A mathematical study quantifies errors in fractional fringe orders determined by the phase-shifting technique, and its validity is corroborated experimentally. The errors vary cyclically as the distance between the reference grating and the specimen increases. The amplitude of the maximum error is approximately 0.017 fringe, which defines the theoretical limit of resolution enhancement offered by the phase-shifting technique.

The contrast of shadow moireat high-order Talbot distances is studied. An exact solution for the contrast of shadow moirefringes is developed from the diffraction phenomenon and its validity is corrobo- rated experimentally. The result is combined with an additional effect from the finite aperture of the camera to propose a complete expression for the contrast of shadow moirefringes. The results can guide the de- sign of shadow moireconfigurations with high-order Talbot distances for high-sensitivity measurements. © 2005 Society of Photo-Optical Instrumentation