High Reliability Applications Research Articles

Can Electrolytic Capacitors Meet the Demands of High Reliability Applications?

Abstract Electrolytic capacitors have long been identified as a weak link for long term high reliability applications. However, capacitor manufacturers have made significant improvements to the materials and manufacturing processes to enhance their reliability. This paper will discuss those changes, provide insight into the various failure mechanisms for electrolytic capacitors and describe appropriate accelerated tests to validate performance. We will take a deeper dive into the methodologies utilized to improve capacitor performance, e.g. foil purity and electrolyte volume. We will also discuss, from a reliability perspective, the impact of changing to a higher temperature electrolyte (from ethylene glycol to DMF, DMA and GBL) and also changes in the bung material (from butyl to EPDM). There are several environmental factors involved in the aging of electrolytic capacitors. Electrolyte loss due to drying out and leakage current due to oxide degradation are thermally related as is the self-heating associated with ripple current. The impact of the applied voltage level is also a driver as it can cause leakage current increases as well. All of these issues result in a capacitance decrease, an increase in ESR, and a change to the dissipation factor. Many other failure mechanisms associated with manufacturing will also be discussed.

Write-error rate of nanoscale magnetic tunnel junctions in the precessional regime

We investigate the write-error rate (WER) of spin-transfer torque (STT)-induced switching in nanoscale magnetic tunnel junctions (MTJs) for various pulse durations down to 3 ns. While the pulse duration dependence of switching current density shows a typical behavior of the precessional regime, WER vs current density is not described by an analytical solution known for the precessional regime. The measurement of WER as a function of magnetic field suggests that the WER is characterized by an effective damping constant, which is significantly larger than the value determined by ferromagnetic resonance. The current density dependence of WER is well reproduced by a macrospin model with thermal fluctuation using the effective damping constant. The obtained finding implies a larger relaxation rate and/or thermal agitation during STT switching, offering a previously unknown insight toward high-reliability memory applications.

Device-Sensor Assembly FEA Modeling to Support Kalman-Filter-Based Junction Temperature Monitoring

Junction temperature monitoring for power devices is an essential requirement for high-reliability applications. Temperature sensitive electrical parameters (TSEPs) are powerful tools in this process, but to achieve sufficient accuracy they require complex characterization procedures for each part, that can hardly be implemented in mass-produced converters. This paper proposes a combination of interdisciplinary approaches to ultimately solve this problem for power MOSFETs by an automated procedure that can occur in-place, with devices mounted and without any specific user intervention nor additional heating components. The TSEP exploited in this paper is the ON-state drain–source voltage of the power MOSFET. A wide-bandwidth ON-state voltage sensing circuit and a low-cost thermistor conditioning circuit to sense the case temperature of the device are presented and modeled. A lumped parameters thermal model of the system is given, and finite-element method (FEM) simulations are employed to obtain first-guess values for the unknown thermal network parameters, integrating information from the device datasheet. Finally, an observer based on the Kalman filter applied to the data collected from these sources is presented and evaluated experimentally. Performance is assessed with the use of thermal imaging techniques.

In-circuit fault tolerance for FPGAs using dynamic reconfiguration and virtual overlays

Reassuring fault tolerance in computing systems is an important problem in high-reliability applications. With the interest in commercial SRAM-based FPGAs in radiation environments, it is beneficial to provide runtime reconfigurable recovery from a failure. In this paper a virtual coarse-grained reconfigurable architecture is proposed, with an embedded on-demand fault-mitigation technique tailored for FPGA overlays. The proposed method performs spatial redundancy and run-time recovery. This approach can achieve up to 3 × faster run-time recovery with 20% less resources in FPGA devices, by providing integrated layers of fault mitigation.

Twofold Fail-Work Remedy for Reconfigurable Driver and Windings of Four-Phase Permanent Magnet Fault-Tolerant Motor System

In this paper, a novel multiphase reconfigurable and fault-tolerant drive converter topology is proposed for driver with fail-work capability, and fault-tolerant strategies are proposed for open-circuit and short-circuit faults in the single-phase windings, aiming to improve the motor drive system's fail-work ability in the high reliability applications. The drive converter topology can isolate open-circuit and short-circuit faults in power supplies, power devices, or switches. Then, it can reconfigure the drive circuit topology from independent H-bridge to star type by reconfigurable switches and power devices, according to the fault-type and the fault-tolerant truth tables. After reconfiguration, remedial operation will be utilized for open- and short-circuit faults of windings, so that the motor system has twofold fail-work capabilities in driver and windings. Finally, based on a series of experiments on a transit co-simulation model and test bench, the effectiveness and validity of fault-tolerant capability and the strategies are verified, and has twofold fail-work remedy.

Compressive sensing based random access for machine type communications considering tradeoff between link performance and latency

Machine type communications (MTC) in the next generation of mobile communication systems require a new random access scheme to handle massive access with low signaling overhead and latency. The recently developed compressive sensing multi-user detection (CS-MUD) supports joint activity and data detection by exploiting the sparsity of device activity. In this paper, we adopt the CS-based random access scheme by assigning the unique identification sequences to distinguish the different sensor nodes and employ group orthogonal matching pursuit least square (GOMP-LS) and weighted iteration (WI) GOMP algorithms based on the conventional GOMP with respect to high-reliability and low-latency applications. In addition, to further reduce computational complexity and latency, we introduce a low complexity WIGOMP with inverse Cholesky factorization (WIGOMP-ICF). Based on the simulation results and analysis, we can observe that the proposed three algorithms are promising to support different services requirements for MTC by considering high reliability, low latency, and computational complexity.

Life prediction of copper wire bonds in commercial devices using principal component analysis (PCA)

Copper has been widely adopted as a viable alternative to gold for wire bonding, due to its lower cost, better electrical and thermal conductivity, lower tendency for wire sweep due to a higher modulus and slower intermetallic compound (IMC) formation with aluminum bond-pad. However, these IMCs can cause an increase in resistance and separation between bonding interface which causes an open circuit. Wire bond and component reliability must consider all factors in combination with the change of wire bond materials and processes. How can users of off-the-shelf components determine the effects of wire bond material changes on the reliability of the components in their systems? How will these changes affect high reliability applications such as automotive, military and harsh environments?Although physics-of-failure based models can represent the failure mechanisms individually, the complex nature of the mixed failure mechanism has inhibited development of an analytical equation to represent it. In addition, geometrical and material characteristics of the entire package along with bonding process parameters play a crucial role in magnitude of stress experienced by these bonds, portraying difficulty in developing one such equation for use to all copper wire bonded devices. This study has aimed to develop a data-based predictive method based on the principal component analysis technique to provide an estimate of the wire bond time to failure for plastic encapsulate components. Extensive thermal cycling experiments have been performed on multiple commercial devices to obtain training data for the model. This method of wire bond fatigue and failure prediction is an adaptive technique which can achieve greater accuracy as more data is added. This method aims to provide a life-time estimate of copper wire bonded component with inputs such as initial geometrical, material properties, and wire bond related attributes for a specific package.

Reliability Analysis of the 300W GaInP/GaAs/Ge Solar Cell Array Using PCM

Spacecraft requires sufficient power in orbit to perform its mission. So as to comply with system requirements, the sufficient power should be made by a solar cell array by photovoltaic power conversion. A life time of space program depends on its mission considering parts reliability and parts grade. Based on the mission life time, power equipment might be designed to meet specifications. In outer space, solar cell array might generate the dc power by photovoltaic conversion effects and GaInP/GaAs/Ge solar cells are used in this study. Space programs that require more than five years should select parts for high reliability applications. Therefore, reliability analysis for high reliability applications should be performed to check its fulfilment of the requirements. This program should also require more five years for its mission and we performed its analysis using parts count method (PCM) for its reliability. Finally, we performed reliability analysis and obtained quantitative figures found out 99.9%. In this study, we presented the reliability analysis of the 300W GaInP/GaAs/Ge solar cell array.

Improved Control Strategy for Fault-Tolerant Flux-Switching Permanent-Magnet Machine Under Short-Circuit Condition

Fault-tolerant flux-switching permanent magnet (FTFSPM) machines are suitable for high-reliability applications owing to their good fault-tolerant capability and relatively high torque density. Under a short-circuit fault, the torque ripple caused by the short-circuit current of the FTFSPM machine affects the steady-state performance of the system; in addition, the traditional proportional–integral (PI) controller of the speed loop can hardly guarantee the optimal dynamic performance of the speed. In this study, to solve these two problems, an improved control strategy that can offer two improvements for the FTFSPM machine under the short-circuit condition is investigated. As the first improvement, on the basis of analysis of the torque ripple caused by the short-circuit current, the feed-forward control is employed to reduce the torque ripple. As the second improvement, on the basis of analysis of the influence of the speed loop PI parameters on the system dynamic performance, a torque integral balance-control method is proposed. This algorithm can make the speed and the electromagnetic torque converge simultaneously after only one adjustment of the speed. Thus, the best possible dynamic response for the speed can be achieved. Experimental results verify the correctness and effectiveness of the improved control strategy.

A Predictive Model for Thermal Conductivity of Nano-Ag Sintered Interconnect for a SiC Die

Nano-Ag sintering technology is a promising die attach method for power semiconductors in high reliability and high temperature (i.e. 300°C) applications. However, the present predictive models for thermal conductivity of multiphase materials are not suitable for the porous sintered Ag due to the model limitations of low porosity, i.e. < 10%, and simple pore geometry (sphere or ellipsoid). In this paper, an extension differential scheme (EDS) model based on the classical differential scheme (DS) approach has been developed. The thermal conductivity of the microporous Ag die attach layer on a SiC device was developed by measuring seven different sintering parameters that are fitted with the model. The finite element method (FEM) was also employed to analyze the influence of different factors. The results indicate that the EDS model has better adaptability and accuracy, which will be important for implementation of this new die attach material and technology.

A New Control Strategy of 5-Phase PM Motor under Open-Circuited Phase Based on High Order Sliding Mode and Current References Real-Time Generation

The high quality of electrical power in high power and high reliability applications is a crucial necessity even under fault mode function. However, in these conditions, the quality of the torque is a key feature. To overcome this problem, the multiphase permanent magnet (PM) motors seems to be a very attractive choice. In order to highlight the robustness and reliability of this technology, this paper investigates the control of a five-phase PM motor under an open circuited phase fault conditions. Moreover, a High Order Sliding Mode (HOSM) controller combined to an optimal reference current generation is tested and compared to a PID controller under fault mode conditions. This original control strategy is proposed for faulted conditions. Compared to classical fault tolerant control, this strategy allows a better dynamic tracking of the non-sinusoidal reference currents and leads to a smooth torque with minimal losses even in severe fault conditions. To validate the proposed control strategy, simulation, and experimental results are presented and discussed.

Distributed SDN Deployment in Backbone Networks for Low-Delay and High-Reliability Applications

Internet applications, such as video streaming, critical-mission, and health applications, require real-time or near real-time data delivery. In this context, Software Defined Networking (SDN) has been introduced to simplify the network management providing a more dynamic and flexible configuration based on centralizing the network intelligence. One of the main challenges in SDN applications consists of selecting the number of deployed SDN controllers, and their locations, towards improving the network performance in terms of low delay and high reliability. Traditional k-center and 􀀀-median methods have been fairly successful in reducing propagation latency, but ignore other important network aspects such as reliability. This paper proposes a new approach for controller placement that addresses both network reliability and reducing network delay. The proposed heuristic algorithm focuses on four different robustness functions, viz, algebraic connectivity (AC), network criticality (NC), load centrality (LC), and communicability, and has been applied in four different real-world physical networks, for performance evaluation based on degree-, closeness-, and betweenness-based centrality-based attacks. Experimental results show that the proposed controller selection algorithms based on AC, NC, LC, and communicability, achieve a high network resilience and low C2C delays, outperforming the latest, widely-used baseline methods, such as 􀀀-median and 􀀀-center ones, especially when using the NC method.

Investigation of a Fault-Tolerant Control Method for a Multiport Dual-Stator Doubly Salient Electromagnetic Machine Drive

A novel fault-tolerant inverter topology of the multiport dual-stator doubly salient electromagnetic machine (MDDSEM) drive is proposed in this paper for high reliability applications such as automotive and aerospace industries. The proposed topology adopts four diverter switches to reconnect the floating phase windings under the fault conditions and reconfigures the dual inverter to be a five-leg inverter; the output performance could be maintained after a single-phase open-circuit or short-circuit fault of the dual inverter. Compared with the traditional fault-tolerant method of the dual inverter for the MDDSEM, the lower cost and smaller volume of the proposed fault-tolerant system can be achieved. The operation principle and the optimized commutation method of the five-leg inverter for the MDDSEM are analyzed to eliminate the unexpected phase current drop so that the torque performance in the fault-tolerant mode could be improved. The effectiveness and feasibility of the proposed fault-tolerant topology and control strategies are verified by the simulation and experimental results of a 24/16-pole MDDSEM that includes both steady-state and dynamic processes with the standard angle control method and the advanced angle control method.

Decoupled Vector Space Decomposition Based Space Vector Modulation for Dual Three-Phase Three-Level Motor Drives

In this paper, a novel space vector modulation (SVM) strategy is proposed and designed for dual three-phase three-level motor drives based on vector space decomposition (VSD), which could be applied for high-power and high-reliability applications. The key of the proposed method is to design two decoupled groups of voltage vector candidates for synthesis on α − β subspace and x − y subspace, respectively. The two decoupled groups of voltage vectors will synthesize respective voltage references on α − β subspace and x − y subspace, while having no impact on each other. The redundant small voltage vectors and zero-sequence voltage vectors are utilized to mitigate voltage oscillation in midpoint of dc link and suppress zero-sequence current component for dual three-phase windings with a common neutral. For comparison, another VSD-SVM strategy is designed based on traditional solution, which cannot offer closed-loop control on x − y subspace. Both simulation and experiments have been given to verify that the proposed decoupled VSD-SVM can suppress harmonic components on x − y subspace besides tracking torque components on α − β subspace. Furthermore, the harmonic performance of the proposed decoupled VSD-SVM has been compared with the traditional VSD-SVM strategy and the carrier disposition based pulsewidth modulation.

Evolutionary Fault Tolerance Method Based on Virtual Reconfigurable Circuit With Neural Network Architecture

With the continuous development of computer and electronics, the idea of artificial intelligence has been integrating into the fault tolerance research. As a valuable and prospective intelligent fault tolerance technique in high reliability and high safety applications, the evolvable hardware fault tolerance technique is becoming an important and widely applicable method. However, this technique confronts two difficult problems: evolved circuit scale and evolution efficiency. Toward these problems, we present a programmable architecture called neural network architecture-based virtual reconfigurable circuit (NNA-VRC), and an evolutionary fault tolerance method based on this programmable architecture. The NNA-VRC-based evolution method simplifies the structure and configuration of programmable architecture, avoids illegal interconnections during the circuit evolution, and implements high level (module level) evolution. The experiments of this paper show that a function module scale circuit is evolved efficiently. Furthermore, NNA-VRC-based evolution method can recovery from many injected fault patterns, behaving a strong feature of fault tolerance.

Field-oriented control and direct torque control for a five-phase fault-tolerant flux-switching permanent-magnet motor

This paper presents a comparative performance analysis of a new five-phase fault-tolerant flux-switching permanent-magnet(FT-FSPM) motor for high-reliability applications under the two most popular control schemes, namely, field-oriented control(FOC) and direct torque control(DTC) based on stator-flux orientation. Firstly, the new motor topology and structural characteristics are briefly presented. Secondly, the d- and q-axis for the FT-FSPM motor are defined, which is crucial to the mathematical model and control scheme, and the mathematical models are derived. Then, two control schemes, i.e., FOC and DTC, and the main system are proposed. The operational principles of the two control schemes are presented, and space vector pulse width modulation(SVPWM) based on four neighboring vectors is adopted to reduce current harmonics and torque ripples. Finally, the simulated and experimental results are given, and performance analysis of the two control schemes are compared and discussed. The results reveal that FOC scheme has the sinusoidal phase current and low torque ripples, while the DTC scheme has fast dynamic response, verifying the effectiveness of the two proposed control schemes. This paper is a primary investigation for more possible improvements in the control schemes of the five-phase FS-FTPM motor.

High Performance Etchable RoHS Compliant Thick Film Gold Conductor

Abstract The thick film paste manufacturers are expected to produce conductors which are lead and cadmium free, yet have excellent fired film properties and the same performance and properties as the cadmium and lead containing formulations. The fired film surface of these conductors must be defect free (i.e. imperfections, pills, agglomerates) after multiple firing steps and must perform on dielectric as well as substrates from different suppliers. Typically, the thick film gold conductors are used in high reliability applications such as medical devices, military applications, and high frequency circuits, which require robust performance at high and low temperatures, in chemically aggressive environments, or extremely humid conditions. As circuits decrease in size and become more complex, the thick film gold properties become increasingly critical. The challenge is to develop an alternative gold conductor formulation, which can print and resolve fine features (down to 4 mil lines and spaces) as well as have the ability to be etched for higher density circuit designs (down to 1–2 mil lines and spaces). Gold conductors are typically used in conjunction with other high temperature thick films so good performance after multiple firings was also a targeted requirement. Heraeus has been proactive for the past decade in the development of thick film products that are both RoHS (lead and cadmium free) as well as REACH compliant. This paper discusses the experiments that were performed in order to understand the contribution of gold powder, organic and inorganic system to improve the fired film performance. These formulations were compared against existing gold conductors including the high performance gold conductor options as well as other available standard gold conductor options. Thin wire bonding trials including both gold and aluminum wire are used to compare influences of raw materials which includes high volume wire bonding reliability including failure modes and aged wire bond adhesion at elevated temperature exposures (300°C) for extended periods of time. In order to analyze fired film morphology and link this up to wire bond performance, SEM images of the conductor surface and cross sections were conducted. These studies resulted in a newly developed thick film gold conductor paste for use in a wide variety of applications. We present wire-bonding data with gold and aluminum wire and reliability results on both 96% Al2O3 ceramic substrates as well as on top of standard dielectrics.

Integration of Satellite and 5G Networks

The articles in this special section focus on the integration of satellite and 5G networks. This is an important topic to help advance the technologies to support the 5G communications. It is expected that satellites will provide the necessary coverage for effective means to reach areas beyond terrestrial coverage, to passengers in trains, aircrafts, and vessels, and cover urban areas; provide resilience as an integral part of the 5G ecosystem; and be ideal for high-reliability applications. For these reasons, this issue is a humble contribution to advancing this technology.

A Torque Impulse Balance Control for Multi-Tooth Fault Tolerant Switched-Flux Machines under Open-Circuit Fault

The multi-tooth fault tolerant switched-flux machines (MTFTSFM) providing both excellent fault tolerant capability and relatively high torque density are good choices for high reliability applications. A rapid control of the electromagnetic torque under open-circuit fault can always be achieved by the direct torque control with voltage vector reconstruction (RDTC); however, with respect to the rotor speed, its dynamic performance is still impacted by the proportion-integration (PI) parameters. Therefore, a torque impulse balance control (TIBC) is investigated in this paper for the MTFTSFM under open-circuit fault to obtain excellent dynamic performance of the rotor speed. During the dynamic state, the electromagnetic torque and the speed can converge at the same time after only one adjustment of the speed by using the optimized voltage vector sequence based on torque impulse balance, thus, achieving the best possible dynamic process for the speed. The TIBC method is carried out on an MTFTSPM machine system, and the correctness and effectiveness are verified.

Flip-Chip (FC) and Fine-Pitch-Ball-Grid-Array (FPBGA) Underfills for Application in Aerospace Electronics—Brief Review

In this review, some major aspects of the current underfill technologies for flip-chip (FC) and fine-pitch-ball-grid-array (FPBGA), including chip-size packaging (CSP), are addressed, with an emphasis on applications, such as aerospace electronics, for which high reliability level is imperative. The following aspects of the FC and FPGGA technologies are considered: attributes of the FC and FPBGA structures and technologies; underfill-induced stresses; the roles of the glass transition temperature (Tg) of the underfill materials; some major attributes of the lead-free solder systems with underfill; reliability-related issues; thermal fatigue of the underfilled solder joints; warpage-related issues; attributes of accelerated life testing of solder joint interconnections with underfills; and predictive modeling, both finite-element-analysis (FEA)-based and analytical (“mathematical”). It is concluded particularly that the application of the quantitative assessments of the effect of the fabrication techniques on the reliability of solder materials, when high reliability is imperative, is critical and that all the three types of research tools that an aerospace reliability engineer has at his/her disposal, should be pursued, when appropriate and possible: experimental/testing, finite-element-analysis(FEA) simulations, and the “old-fashioned” analytical (“mathematical”) modeling. These two modeling techniques are based on different assumptions, and if the computed data obtained using these techniques result in the close output information, then there is a good reason to believe that this information is both accurate and trustworthy. This effort is particularly important for high-reliability FC and FPBGA applications, such as aerospace electronics, as the aerospace IC packages become more complex, and the requirements for their failure-free operations become more stringent.