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The temperature uniformity of heater plates (HPs) should be sustained due to critical dimension uniformity and robust operation in high temperature processing of 300 mm wafers. It is very challenging to maintain the temperature uniformity of the HP despite the dynamic control of power inputs and temperatures. The packaged power terminals (PPTs) of the HPs may considerably affect their thermal reliability. Hence, the sophisticated thermal modellings and designs of the HPs and the PPTs are necessary. In this study, the finite element analysis (FEA) thermal models of the HP and the PPT were generated, experimentally validated, and employed for the analysis and the design. The influences of the heating element width, the heating element gap, and the zone gap on the thermal performance of the HP were investigated. The parametric influences of the substrate thickness on the thermal performance of the PPT were also explored. The results show that the effect of the heating element width on the temperature of the HP is almost negligible. The results have found that a sophisticated design of the heating elements may reduce the radial temperature difference of the HP by 56 % compared with the baseline case. The results suggest that the sophisticated design may enable both the simplified structure and the enhanced temperature uniformity of the HP.

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.

Many studies have been conducted to analyze and reduce mismatch loss (MML) in photovoltaic array. They have concluded that MML is typically less than 1% at installation and the economic loss is insignificant. In this study, long-term MML effect on photovoltaic array is explored quantitatively. An outdoor test has been conducted to verify that MML is increasing over time for a string of photovoltaic modules. The electrical parameters of the modules in the string are measured at the standard test condition (STC) before installation and after the exposure of 5.5 years. MML is estimated and compared for the data by two approaches; using a stochastic model and string simulating by a SPICE program. It is confirmed from the two methods that MML increases over time. Long-term MML model is developed based on the test data and several results from previous studies. The model expected that the MML keeps increasing over time and is substantial to the output of a solar power plant. The study reveals that MML could be a detrimental factor to the long-term maintenance of solar power plant.

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.

Water vapor ingress significantly impacts the performance and the long-term reliability of copper indium gallium selenide photovoltaic modules. A cost effective packaging method that can protect photovoltaic modules from the operating environment is critical to their widespread commercialization. Due to the sensitivity of both the copper indium gallium selenide cells and the electrodes to water vapor, they need an encapsulant with low water vapor permeation as well as side sealing materials, resulting in a high cost of manufacturing. Hence, a packaging strategy without sealing materials is proposed with new encapsulant materials. In this study, the overall amount of permeated water vapor through ionomer and polyvinyl butyral encapsulants was investigated and compared with widely used encapsulants such as ethylene vinyl acetate. The diffusion and solubility coefficients were calculated from the experimentally determined water vapor transmission rate in both transient and steady state transport regimes. To understand the permeation mechanism of water vapor through the encapsulant, the temperature dependence of the diffusion and solubility coefficients was investigated. Based on experimentally determined permeation properties, the amount of water vapor absorption and the ingress speed into the PV module under a continuously varying environment were investigated. Ethylene vinyl acetate shows its excellence among encapsulants, when simply considering ingress speed of water vapor (slower permeation), while ionomer dominantly outperforms other materials, when focusing on the total amount of water absorption (less permeation).

Key Words: Bendable Electronic Module(유연성전자모듈), Thermal and Hygroscopic Loading(열·습도복합하중), Autoclave Test(오토클레이브시험)초록: 이동용전자기기에적용가능한유연성전자모듈이롤투롤공정에의해개발되었다. 개발된전자모듈은모듈내의폴리이미드층이유연성기판역할을하고그사이에동선과이방성도전필름과박막실리콘칩과모듈의봉지재역할을하는접착재료로구성된다. 개발된유연성전자모듈의신뢰성을평가하기위하여일련의인증시험을수행하였다. 시험수행결과열·습도복합하중조건인오토클레이브시험후에시편모듈내에박리가발생하였다. 오토클레이브시험에서열과습기가유연성전자모듈에어떤응력을발생시키는지를범용유한요소프로그램으로연구하였다. 열·흡습복합하중조건에서열과흡습에의한영향을분리하여상대적으로평가해보기위하여오토클레이브조건중온도조건에해당하는121°C 온도조건만을적용하여해석을별도수행하고두결과를비교하였다. 또한비교해석결과를바탕으로유연성전자모듈의고장메커니즘을추정하였다.Abstract: A bendable electronic module is developed. In this module, thin silicon electronic chips areembedded in a polymer-based encapsulating adhesive between flexible copper-clad polyimide layers. Duringthe qualification test of a harshly thermal-hygroscopic complex loading condition, delaminations occur insidethe module layers. A finite element model is developed for the module. To investigate the effect ofhygroscopic stress on delamination, the results of the thermal and thermal-hygroscopic loads are compared.The analysis results reveal that the hygroscopic effect more strongly affects delamination than does thethermal effect. The potential failure mechanisms of the module are investigated based on the stress analysis.

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 bendable electronic module is developed for a mobile application by using a low-cost roll-to-roll manufacturing process. In the module, a thin silicon chip is embedded in a polymer-based encapsulating adhesive between flexible copper clad polyimide layers. A set of tests are conducted for the purpose of qualification: thermal shock, high temperature storage, and autoclave tests. During the autoclave test, delamination occurs at many places within the module layers. To investigate the failure mechanism, moisture diffusion analysis is conducted for the interior of the module under the autoclave test condition. For the analysis, the hygroscopic characteristics of the encapsulating materials are experimentally determined. Analysis results indicate the moisture saturation process in the interior of the module under the autoclave test condition.

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.

초록:본논문에서는네트워크서버용컴퓨터주기판내장착된열방열시스템지지구조물에대한유한요소모델의솔더크리프특성을검증하였다. 열방열시스템은앵커구조물로지지되며앵커구조물은솔더를이용하여인쇄회로기판에장착된다. 컴퓨터내발생하는지속적인고온환경하에서솔더의크리핑이발생하고이는궁극적으로지지구조물의파괴로이어진다. 유한요소모델은솔더에발생하는응력분석과수명예측을위해사용되며, 솔더크리프특성을모사하기위하여Anand 크리프모델을적용하였다. 모델을검증하고교정하기위하여크리프시험을수행하였다. 시험은인쇄회로기판의변형을제외한솔더변형만을측정하기위하여특별한지그를설계하여수행하였다. 크리프시험결과를유한요소해석결과와비교하여Anand 크리프모델을검증하고교정을수행하였다. 교정된유한요소모델을이용하여열방열시스템구조물의보다정확한수명예측을수행할수있다.Abstract: The heat sink system for a main board in a network server computer is built on printed circuit board byan anchor structure, mounted by eutectic SnPb solder. The solder creeping is caused by a constant hightemperature condition in the computer and it eventually makes fatal failures. The FE model is used to calculate thestress and predict the life of soldered anchor in the computer. In the model, Anand constitutive equation isemployed to simulate creep characteristics of solder. The creep test is conducted to verify and calibrate the soldermodel. A special jig is designed to mitigate the flexure of printed circuit board and to get the creep deformationof solder only in the test. Test results are compared with analysis and calibration is conducted on Anand model’sconstants. Precise life prediction of soldered anchor in creep condition can be performed by this model

Large-scaled dye-sensitized solar cell (DSC) modules are recently developed for building-integrated photovoltaic (BIPV) applications. In the modules, two glasses with electrodes and dye are sealed together to prevent the leakage of liquid electrolyte. It is known that DSC modules deteriorate rapidly under high temperature conditions. Previous studies showed that expansion of liquid electrolyte in the module is the main reason for the degradation; the expansion of electrolyte induces the breakage of sealant material of DSC module in high temperature. This study investigates how the sealant curing process affects the integrity of DSC module in high temperature. Sealant samples are made up by several UV curing times. Shadow moire technique is used to measure the coefficient of thermal expansion (CTE) of the sealant samples. With the test results, finite element analyses are conducted to optimize the curing process time. It is finally suggested that the longer the curing time, the more robust the DSC module.

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.

We propose a novel hybrid approach to examine uncertain sources that cause variations in solder joint lifetimes and to predict statistical distributions of solder joint lifetimes under actual operating conditions. The uncertainty in input variables of a life prediction model is propagated to the output by an approximate integration method. The variations in the output are statistically compared to experimentally-measured lifetimes. A set of input variables that minimize the discrepancy between predicted and experimental results is obtained through the optimization technique. The proposed approach is implemented for chip resistor assemblies, and the fatigue life of solder joints under the actual operating conditions is predicted after calibration.

Large-scaled Dye-sensitized solar cell (DSC) modules are recently developed for BIPV applications. In the modules, two glasses with electrodes and dye are joined for electrolyte and sealed together to prevent the leakage of electrolyte. Test of the module in a high temperature environment discloses several symptoms of electrolyte leakage through sealing failure. A finite element model is developed for the DSC module to investigate the sealing failure from the different thermal expansions. The accuracy of the model is validated by experimenting the deformation patterns of the module in high temperature and comparing with the model results. Finally, the sensitivities of the cell width and glass thickness are studied and optimal configuration is suggested for preventing the sealing failure of DSC.

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.

Thermal cycling stress can result in fatigue cracks of interconnections between ribbon wires and the metallization of a photovoltaic (PV) module, thereby increasing its series resistance. Therefore, in this study, the thermal cycling (TC) history of PV modules exposed to two benchmark climate (Phoenix, AZ) has been derived employing corresponding meteorological data. Using the three parameters rain-flow counting algorithm, the number of TCs versus temperature change was calculated over one year. The number of rain-flow cycles was 935 in Phoenix. Furthermore, three types of accelerated tests were conducted to develop a lifetime prediction model. The Basquin equation was used to predict the number of cycles to failure, based on stress calculation. A finite element model for stress analysis was developed. Failure analysis shows that crack occurred at the solder joint after accelerated test.

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).

It has been reported that water vapor ingress and saturation of encapsulant materials dominantly impact on longterm reliability of copper indium gallium selenide PV cells. To understand diffusion mechanism of water vapor into PV module, diffusion coefficient and solubililty of various encapsulants and their temperature dependency were investigated. Based on experimentally determined permeation properties, governing equation for time dependent diffusion were solved using finite element method software to suggest design guideline for packaging of PV module for long-term reliability.

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.

For assurance more than 25 year lifetime of photovoltaic module, the reliability of components and material should be guaranteed. This study draws a conclusion of ribbon wire degradation mechanism among the materials under thermal cycling. The main degradation mechanism of ribbon wire the crack caused by coefficient of thermal expansion (CTE) mismatch between the module material and the ribbon wire solder. To demonstrate the degradation mechanism, thermal cycle test was designed and conducted with small photovoltaic module. The temperature cycle condition was (−) 45°C ∼ (+) 85°C and the dwell time was 20 minutes. Measurement was carried out every 100 cycles monitoring the series resistance (R s ) through dark I-V. The result shows that R s increases. After 1,000 cycles, the characteristics of Dark I-V and illuminated I-V were compared and analyzed. Failure mechanism analysis was conducted for the modules which decreased 20 % of P max . Water-jet techniques for cross-section and SEM were used to analyze the factor of resistance change and efficiency degradation. The degradation mechanism of ribbon wire was proved.

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.