Leakage Current Measurements Research Articles

Thermal decomposition of binary mixtures of organic activators used in no-clean fluxes and impact on PCBA corrosion reliability

Purpose The purpose of this paper is to investigate the decomposition behavior of binary mixtures of organic activators commonly used in the no-clean wave flux systems upon their exposure to thermal treatments simulating wave soldering temperatures. The binary blends of activators were studied at varying ratios between the components. Design/methodology/approach Differential scanning calorimetry and thermogravimetric analysis were used to study the characteristics of weak organic acid (WOA) mixtures degradation as a function of temperature. The amount of residue left on the surface after the heat treatments was estimated by gravimetric measurements as a function of binary mixture type, temperature and exposure time. Ion chromatography analysis was used for understanding the relative difference between decomposition of activators in binary blends. The aggressivity of the left residue was assessed using the acidity indication gel test, and effect on reliability was investigated by DC leakage current measurement performed under varying humidity and potential bias conditions. Findings The results show that the typical range of temperatures experienced by electronics during the wave soldering process is not sufficient for the removal of significant activator amounts. If the residues contain binary mixture of WOAs, the final ratio between the components, the residue level and the corrosive effects depend on the relative decomposition behavior of individual components. Among the WOA investigated under the conventional wave soldering temperature, the evaporation and removal of succinic acid is more dominant compared to adipic and glutaric acids. Practical implications The findings are attributed to the chemistry of WOAs typically used as flux activators for wave soldering purposes. The results show the importance of controlling the WOA content and ratio between activating components in a flux formulation in relation to its tendencies for evaporation during soldering and the impact of its residues on electronics reliability. Originality/value The results show that the significant levels of flux residues can only be removed at significantly higher temperatures and longer exposure times compared to the conventional temperature range used for the wave soldering process. The potential corrosion issues related to insufficient flux residues removal will be determined by the residue amount, its composition and ratio between organic components. The proper time of thermal treatment and careful choice of fluxing formulation could ensure more climatically reliable product.

Effect of Pt3Pb on the permittivity and conductivity of lead zirconate titanate thin films

The evolution and interaction of buried interfaces during the synthesis of lead zirconate titanate (PZT) ferroelectric thin film devices have been previously predicted by density functional theory modeling and observed experimentally via in–situ structural characterization. Moreover, the formation and disappearance of an intermetallic phase (Pt3Pb) during the crystallization of the film has been identified as a key process expected to affect the resulting electrical properties of the devices. To elucidate this effect, a combination of direct current (leakage current measurements) and alternating current (impedance spectroscopy) characterization techniques are used to examine the electrical properties of sol–gel–derived PZT thin films. Films with the intermetallic phase exhibit a high potential barrier at the metal–insulator interface (0.83 eV) similar to the fully crystallized films (0.81 eV) and a lower current density than the films without the intermetallic phase, as shown in the Richardson plot. Impedance measurements also revealed that the conductivity of the films with the intermetallic phase, σ = 1.9 × 10−11 S cm−1, and the real part of the relative permittivity at 10 kHz, εr′=42, are lower than the other films (fully crystallized film: σ = 3.5 × 10−10 S cm−1 εr′=566, amorphous crystallized film: σ = 4.6 × 10−11 S cm−1 εr′=121). It is shown that these electrical characterization methods can serve as non–destructive examination tools to track the evolution of secondary phases during device synthesis and fabrication.

Effect of Filler Concentration on Tracking Resistance of ATH-Filled Silicone Rubber Nanocomposites

It is necessary for polymeric materials to have superior tracking resistance against various stress conditions for outdoor applications. In this study, the effect of nano-sized alumina tri-hydrate (ATH) particles on the tracking resistance of silicone rubber (SiR) is studied. Specimens with filler loadings of 1, 3, 5, 10, and 20 wt % are used for performance characterization. From the inclined plane test (IPT) results, apparent improvement in tracking resistance was achieved by mixing 3 wt % of nano-sized fillers, compared to unfilled specimens. ATH/SiR nanocomposites with 5 wt % loading showed comparable tracking performance to SiO2/SiR microcomposites with 20 wt % loading. For detailed analysis, measurements of surface contact angle (SCA) and surface leakage current, and thermo-gravimetric analysis (TGA) were performed. As the nano-ATH filler concentration increased, both thermal stability and leakage current characteristics were improved. Such results agreed with the tracking resistance performance by showing that thermal decomposition and surface charge transport is inhibited in ATH/SiR nanocomposites. Furthermore, performance improvement in nanocomposites was achieved, even at low filler loadings, compared to microcomposites. Meanwhile, the change in SCA was found to be rather limited, regardless of filler loading and filler size.

Detection of humidity ingress using online common‐mode insulation impedance‐monitoring system

Enhanced machine reliability through monitoring of its state of health is an emerging field of research. Ingress of contaminants such as moisture can effect electrical machine state of health and contribute to failure in winding insulation. This paper demonstrates the application of an online insulation health monitoring method to study the effect of moisture ingress on ground-wall insulation through practical experiment. The method, based on real-time high-frequency leakage current measurement, is implemented on a 2.83 kW machine during operation in open-loop configuration. The results are presented and discussed, demonstrating the feasibility of diagnosis of moisture ingress.

Exploring the Effect of Device Aging on Static Power Analysis Attacks

Vulnerability of cryptographic devices to side-channel analysis attacks, and in particular power analysis attacks has been extensively studied in the recent years. Among them, static power analysis attacks have become relevant with moving towards smaller technology nodes for which the static power is comparable to the dynamic power of a chip, or even dominant in future technology generations. The magnitude of the static power of a chip depends on the physical characteristics of transistors (e.g., the dimensions) as well as operating conditions (e.g., the temperature) and the electrical specifications such as the threshold voltage. In fact, the electrical specifications of transistors deviate from their originally intended ones during device lifetime due to aging mechanisms. Although device aging has been extensively investigated from reliability point of view, the impact of aging on the security of devices, and in particular on the vulnerability of devices to power analysis attacks are yet to be considered.This paper fills the gap and investigates how device aging can affect the susceptibility of a chip exposed to static power analysis attacks. To this end, we conduct both, simulation and practical experiments on real silicon. The experimental results are extracted from a realization of the PRESENT cipher fabricated using a 65nm commercial standard cell library. The results show that the amount of exploitable leakage through the static power consumption as a side channel is reduced when the device is aged. This can be considered as a positive development which can (even slightly) harden such static power analysis attacks. Additionally, this result is of great interest to static power side-channel adversaries since state-of-the-art leakage current measurements are conducted over long time periods under increased working temperatures and supply voltages to amplify the exploitable information, which certainly fuels aging-related device degradation.

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We present a defect spectroscopy technique to profile the energy and spatial distribution of defects within a material stack from leakage current (J-V), capacitance (C-V), and conductance (G-V) measurements. The technique relies on the concept of sensitivity maps (SMs) that identify the bandgap regions, where defects affect those electrical characteristics. The information provided by SMs are used to reproduce J-V, C-V, and G-V data measured at different temperatures and frequencies by means of physics-based simulations relying on an accurate description of carrier-defect interactions. The proposed defect spectroscopy technique is applied to ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -based metal-insulator-metal structures of different compositions for dynamic random-access memory capacitor applications. The origin of the observed voltage, temperature, and frequency dependencies of the I-V, C-V, and G-V data is understood, and the atomic structure of the relevant stack defects is identified.

Dependence of thin film transistor characteristics on low-angle grain boundaries of (100)-oriented polycrystalline silicon thin films

Parallel and perpendicular n-channel and p-channel TFTs were developed on highly (100)-oriented polycrystalline silicon thin films that had low-angle grain boundaries. The n-channel TFTs exhibited excellent characteristics. A low leakage current of 10−11 A μm−1, an ON/OFF current ratio of 106, and a sub-threshold slope of 114 mV dec−1 were observed in the perpendicular TFT. These values were better than those of parallel TFT, however, its electron field effect mobility of 480 cm2 V−1 s−1 was twice smaller than that of parallel TFT. The cross low-angle grain boundaries strongly impacted on TFTs’ performance and Their barrier potential was calculated from the measured leakage current of parallel and perpendicular TFTs based on Levinson equation. Contrastingly, characteristics of parallel and perpendicular p-channel TFTs were similar due to uninfluenced by grain boundaries. An averaged hole field effect mobility of 148 cm2 V−1 s−1 was observed with dominantly (100)-oriented silicon crystals.

Failure analysis of BMC insulators used for third rail traction system

Bulk molding compound (BMC) or Glass Reinforced plastic (GRP) composite insulators are extensively used for the third rail electric traction system. The performance of these insulators primarily depends on the local environmental conditions that cause degradation over a period of time. Degradation leads to partial arcing which grow more severe and can generate combustion that ignites flammable debris, smoke including fires resulting in service interruptions and safety risks of the third rail traction system. In the present investigations, exhaustive analysis is conducted to understand the root cause of degradation and arcing on the field aged insulators rated for 750Vdc. Leakage current and surface resistance measurements are conducted under dry, wet and contaminated conditions. Further to better interpret Physico-chemical analysis are conducted using Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray (EDAX) and Fourier Transform Infra-Red (FTIR) spectroscopy to investigate surface morphology and chemical changes in the samples, also Thermo-Gravimetric Analysis (TGA) is performed to find the thermal characteristics of the insulator. Interesting results obtained from the investigations clearly present evidence to loss of epoxy material from the bulk eventually leading to the exposure of glass fibers causing degradation, arcing and failure of the insulators. The study further highlights the essential procedures to be edopted to locate, isolate, and better anticipate failures of BMC insulators used in third rail traction system.

Exploration of Properties of Organic Insulation Materials in Power System

In order to effectively monitor the leakage current on the surface of organic materials, based on the existing research status, the relevant research results at home and abroad are analysed profoundly, and a more advanced system is designed to measure and monitor the leakage current on the surface of organic materials. The hardware circuit (main control circuit, differential amplifier circuit, filter circuit, power supply circuit and communication interface circuit) and software system (main program, data acquisition subroutine, data processing subroutine, communication subroutine, etc.) of the monitoring system are designed, respectively. Generally speaking, some researches are carried out on the carbonization and leakage current measurement of organic materials, and it also lays a theoretical foundation for the follow-up related research.

Crystalline beryllium oxide on Si (100) deposited using E-beam evaporator and thermal oxidation

The growth characteristics and electrical properties of thin films of crystalline beryllium oxide (BeO) on Si (100) substrates grown using electron beam evaporation (EBE) are described. To expand the commercial viability of BeO, a combination of EBE with thermal oxidation was optimized to facilitate its use in nanoscale semiconductor devices. The surfaces of the EBE BeO films were found to be smooth with limited quantities of native oxides or metal silicates, as determined using atomic force measurements and X-ray photoelectron spectroscopy, respectively. Moreover, high-resolution transmission electron microscopy revealed that the films were highly crystalline. Excellent insulator properties, including a dielectric constant of 6.77 and a breakdown voltage of 8.3 MV/cm, were deduced from a series of capacitance–voltage and leakage current measurements. Reflection electron energy loss spectroscopy and ultraviolet photoelectron spectroscopy indicated that the films exhibited a high band gap of 8.6 eV and a high conduction band offset of 3.43 eV. Collectively, these results indicate that EBE BeO films hold promise for use as electrical insulators in Si CMOS and nanoscale device applications.

Hybrid gate dielectrics: a comparative study between polyvinyl alcohol/ $$\hbox {SiO}_{2}$$ SiO 2 nanocomposite and pure polyvinyl alcohol thin-film transistors

Polyvinyl alcohol (PVA) thin films as polymer gate dielectrics, with and without \(\hbox {SiO}_{2}\) nanoparticles were fabricated using spin-coating. Surface roughness and hydrophilicity of PVA and PVA/\(\hbox {SiO}_{2}\) thin films were studied by contact-angle measurements and atomic force microscopy. The dielectric properties were characterized via capacitance and leakage-current measurements on metal–insulator–metal structures. In order to further investigate the application potential of such materials as a replacement for conventional inorganic dielectrics such as \(\hbox {SiO}_{2}\) in organic thin-film transistors, devices were fabricated based on these polymers using \(\upalpha \), \(\upomega \)-dihexylquaterthiophene as an active layer. Performance of the devices was realized by electrical measurements and Kelvin probe force microscopy. All transistors showed hole and electron mobilities in the low-voltage range. PVA/\(\hbox {SiO}_{2}\) films showed larger capacitance, less hydrophilicity, rougher surfaces and considerable leakage currents compared with those with neat PVA. Although integrating nanoparticles modified surface electronic properties and showed a shift in surface potential as observed in Kelvin probe force measurements, it appears that non-polymeric and neat polymeric dielectric materials could still be a privilege to nanocomposite polymeric dielectrics for optoelectronic applications.

A Leakage Current Forecast of the Polymeric Insulator Using ANFIS Method Based on LabView Pre-processed Thermal Image

This paper reports estimates of leaky currents based on Thermal (Infrared) images of polymer insulators using LabVIEW as preliminary data from the ANFIS method for the purpose of condition-based non-contact monitoring. In this study, images of very high contaminated polymer insulators were taken using the FLIR-A600 thermal camera series. The laboratory pollution performance test is carried out in accordance with the standards of IEC 60507 with an 18 kV AC voltage. The pollution severity is indicated because the ESDD value is very high contaminated and the relative humidity conditions are maintained at the range of 85% RH to 95% RH and temperature at 28°C. Humidity and temperature are maintained through a mist-producing container that is connected to a controlled polymer isolator test container using an Arduino microcontroller with temperature and humidity sensors. LabVIEW is used to calculate the percentage of RGB color from a thermal image related to a certain measured leakage current. This RGB data is training data for ANFIS to predict leaky currents. The results show that this method is able to predict current leakage without spending time to reach RMSE 0.00008. By adding a calculation to determine the condition of the insulator in the category of Safe, Maintenance or Hazard so that the Field Technician can decide whether the insulator must be replaced or not. With a non-contact method that only through thermal analysis of polymer insulators can accelerate the process of checking the condition of the insulator.

Effect of Organic Solvents on the Electrochemical Performance of Sodium‐Ion Hybrid Capacitors

AbstractA comparative study on the ionic conductivity of carbonate‐ and ether‐based electrolytes was performed, which showed that the ionic conductivity was strongly affected by the dielectric constant of the organic solvent. The relationship between the physicochemical properties of a liquid electrolyte and the cycling performance of sodium‐ion hybrid capacitors (SICs) was assessed by comparing the electrochemical characteristics of SICs assembled with a negative activated carbon electrode and a positive Na3V2(PO4)3 electrode. Cyclic voltammetry, leakage current measurements, and electrochemical impedance spectroscopy results demonstrated that the good cycling performance of SICs with carbonate‐based electrolytes can be ascribed to their superior electrochemical stability, large amounts of free ions, and favorable electrochemical reaction kinetics. An SIC employing an electrolyte consisting of 1.0 M NaClO4 in ethylene carbonate/propylene carbonate exhibited a good rate capability and delivered a high initial discharge capacity of 98.7 mAh g−1 with a capacity retention of 90.8 % after 1000 cycles at a constant current density of 500 mA g−1.

No-Clean Solder Flux Chemistry and Temperature Effects on Humidity-Related Reliability of Electronics

The use of no-clean flux technology for the wave soldering process of a printed circuit board assembly (PCBA) influences the humidity-related robustness of the electronic devices due to the ionic residues remaining on the PCBA surface after soldering. This paper investigates the effect of various no-clean solder flux chemistries on the formation of a water layer on the PCBA surface studied as a function of climatic conditions relevant for the electronics industry. The activating part of the commercial flux formulations used for the investigations was based on single weak organic acid (WOA) and WOA mixtures. The hygroscopic nature of flux residues, reflecting their ability to uptake moisture and lead to water film build-up, was investigated using the gravimetric moisture sorption test and AC electrochemical impedance. The effect of flux composition and ambient climatic conditions on the corrosion reliability was studied using DC leakage current measurements upon varying potential bias, humidity, and temperature levels. The study shows that solder flux residues containing a mixture of WOA activators in their formulation facilitate the formation of water layer on the PCBA surface at lower humidity levels, compared to the residues composed of a single activator, and absorb a higher amount of moisture. Corrosion occurrence is accelerated by the presence of highly hygroscopic residues of WOA mixtures, compared to significantly less corrosive contaminants comprised of single activator. Increasing ambient temperature enhances moisture interaction with flux residues and changes its deliquescent behaviour, leading to the formation of a thicker water layer and severe ion-induced corrosion at lower humidity levels.

Development and Experimental Evaluation of Leakage Current Measurement Sensor for Electrical Power Apparatus

Abstract Leakage current measurement plays an important role in determining the healthiness of high voltage insulation of a power apparatus. High voltage (HV) insulation degrades due to electrical, thermal and mechanical ageing and their cumulative effects, and thus the leakage current of the insulation increase over a period of time. The accurate and real time measurement of leakage current enables the utilities to on-line access the healthiness of the insulation. This paper describes about the design, development, calibration and testing of a novel non-contact type passive leakage current sensor which can be used for monitoring of various electrical devices based on the analysis of the leakage current captured by the sensor. The developed sensor has been successfully used for measurement of leakage current in oil-filled HV bushings as well as in gas insulated surge arresters. The sensitivity of the developed sensor as per its design can be in the order of few milli amperes in case of bushing and in the order few micro amperes for surge arrester monitoring. The paper also reported a novel design of bushing adapter-sensor assembly for on-line measuring the leakage current in HV bushings without using the conventional capacitive or resistive tapping based measurements. Further, results covering experimental leakage current measurement on a 420 kV bushing using the developed adapter sensor assembly have also been presented. To establish capabilities of the developed sensor with optimized design parameters, laboratory measurements of leakage current on 420 kV and 145 kV GIS surge arresters have also been carried out and reported in the paper. Third harmonic content of surge arrester leakage current has also been estimated in-line with IEC requirement to assess the healthiness of the surge arrester. Finally, suitability of the developed sensor for leakage current measurement of above power apparatus equipment has also been analyzed and discussed.

A new experimental method to estimate the leakage current in the solid oxide fuel cell with a mixed ionic and electronic conducting electrolyte

The leakage current in a solid oxide fuel cell with a mixed ionic and electronic conducting electrolyte considerably depresses its performance, and current studies mainly focus on the theoretical analysis by numerical models due to the difficulty in the measurement of leakage current. In this paper, a new experimental method to online estimate the leakage current is developed. In this method, the electronic current can be directly measured at theoretical voltage and the electronic conductivity coefficient of the electrolyte can be calculated by this electronic current; the electronic current at the open circuit can be calculated by operating conditions, and the electronic current at any condition can be calculated by the voltage and external current. This experimental method is verified by comparing with other experimental data in the literature and numerical results of a 1D polarization model. The electronic conductivity coefficient of this method shows same order of magnitude to the experimental data. The electronic current at any condition calculated by this method shows good agreement with the model results. The comparison results manifest that this experimental method can be used to online estimate the leakage current and electronic conductivity of the electrolyte.

Annealing studies of irradiated p-type sensors designed for the upgrade of ATLAS phase-II strip tracker

The upgrade of the LHC to the High Luminosity LHC will challenge the silicon strip detector performance with high fluence and long operation time. Sensors have been designed and tests on charge collection and electrical performance have been carried out in order to evaluate their behaviour. Besides that, it is important to understand and predict the long-term evolution of the sensor properties. In this work, detailed studies on the annealing behaviour of ATLAS12 strip sensors designed by the ITK Strip Sensor Working Group and irradiated from 5×1013neqcm−2 to 2×1015neqcm−2 are presented. Systematic charge collection and leakage current measurements have been carried out during the annealing process until break-down or the appearance of charge multiplication. The annealing was carried out, separating the sensors into two groups being either annealed at 23°C or 60°C. Sensors showing charge multiplication have been then kept at high voltage for a long time in order to monitor their stability. The difference in the annealing behaviour between the two temperatures has been analysed and compared to similar measurements on n-type sensors and with a theoretical model. From the impedance measurements for the samples irradiated to low fluences it was possible to extract the effective doping concentration. This was compared to similar measurements on n-type sensors and with a theoretical model.

Insulator string leakage current-monitoring sensor based on fiber Bragg grating.

A novel insulator string leakage current-monitoring sensor based on a fiber Bragg grating (FBG), cantilever beam, and spiral coil is demonstrated. The spiral coil is used to convert the leakage current into the force exerted on the cantilever structure, which is obtained by measuring the strain of the FBG. Experimental results show that the linear regression correlation coefficient is 0.99964. In addition, although the leakage current measurement is not sufficiently accurate, the 50-Hz component measurement is accurate. The sensor is suitable for use as an insulator string flashover warning and has promising prospects for future grid security protection applications.

Investigation on the degradation indicators of short-circuit tests in 1.2 kV SiC MOSFET power modules

This paper provides a comprehensive investigation on both static characteristics and short-circuit performance of 1.2 kV SiC MOSFET power modules with 2nd generation planar technology. The experimental approach is based on the static characteristics measurements and the short-circuit tests with gradual increase of pulse time duration. If any variation of the static characteristics appears, the time duration of next short-circuit tests would keep the same with the last pulse duration (approach 1) or increase continuously (approach 2). The results of the short-circuit waveforms show a gate degradation which is further confirmed with the measurement of the gate leakage current. Additionally, other degradation indicators, including positive shift of threshold voltage, drain leakage current and on-state resistance increase are evidenced and discussed in this paper. These can be used for early prediction of the degradation and failure in the short-circuit conditions.

Humidity-related failures in electronics: effect of binary mixtures of weak organic acid activators

The ionic residues of activator compounds used in the no-clean solder flux systems often remain on a Printed Circuit Board Assembly surface after the soldering process and may compromise the corrosion reliability of electronic device upon exposure to humid environment. The solder flux formulations contain weak organic acids (WOAs) activators of different types, sometimes present in the form of mixtures of varying compositions. This paper presents the results of parametric hygroscopicity studies of binary mixtures of weak organic acids that simulate the activating part of the typical no-clean solder flux formulation. Three types of binary blends of varying ratios between the acids were tested: adipic:succinic, adipic:glutaric, and succinic:glutaric. The hygroscopic and corrosive behaviour of the mixtures were investigated under relative humidity (RH) varying from 30 to ~ 99% and at test temperatures of 25 °C, 40 °C, and 60 °C. The moisture sorption and desorption isotherms were determined using a gravimetric method, while AC electrochemical impedance was employed for monitoring the solid–liquid transition of residues. The influence of residues on corrosion reliability was investigated using DC leakage current measurements on a contaminated surface insulation resistance comb patterns with tin solder alloy. The results of corrosion testing were correlated with hygroscopicity studies and visualized by ex-situ colorimetric analysis using a tin ion indicator in a gel. The results show that the critical humidity level for moisture absorption shifts to lower RH values for mixtures, compared to pure WOAs. Water absorption behaviour varied based on the relative content of WOAs in the mixtures and ambient temperature, which also influenced the leak currents and electrochemical migration.