Physics of failure (PoF) based lifetime prediction of power electronics at the printed circuit board level

This paper presents the use of physics of failure (PoF) methodology to infer fast and accurate lifetime predictions for power electronics at the printed circuit board (PCB) level in early design stages. It is shown that the ability to accurately model silicon–metal layers, semiconductor packaging, printed circuit boards (PCBs), and assemblies allows, for instance, the prediction of solder fatigue failure due to thermal, mechanical, and manufacturing conditions. The technique allows a life-cycle prognosis of the PCB, taking into account the environmental stresses it will encounter during the period of operation. Primarily, it involves converting an electronic computer aided design (eCAD) circuit layout into computational fluid dynamic (CFD) and finite element analysis (FEA) models with accurate geometries. From this, stressors, such as thermal cycling, mechanical shock, natural frequency, and harmonic and random vibrations, are applied to understand PCB degradation, and semiconductor and capacitor wear, and accordingly provide a method for high-fidelity power PCB modelling, which can be subsequently used to facilitate virtual testing and digital twinning for aircraft systems and sub-system

Reliability study on avionics: feasibility study to determine mean time between failure (MTBF)

In general, the world faces an increase in the pressure to perform faster, better and cheaper, requiring engineers to predict accurately the reliability of products. In the early stages of the design process, these accurate predictions will contribute not only to a more robust and reliable product, but also will drive down the costs associated with redesigning the equipment/component, for example, when a product is already in production and a design error is found or as the result to improve the reliability obtained from operation. The number of electronic components, equipment and systems in an airplane increases with the new developments in technology. That is why it is imperative that manufacturer predict the failure rate and the mean time between failure of each equipment/component with the greatest accuracy. For this accuracy to be fulfilled, there are three methodologies: empirical (based on standards), failure mechanisms, and accelerated/life tests. The most common methodology is the use of standards. The main handbook/standard used in the electronics industry for the prediction of the mean time between failure is the MIL-HDBK-217F. However, at the present moment of technology development, this handbook is obsolete, as the predicted values are far from the reality. To overcome this problem, several companies from aeronautic and aerospace sector developed a standard called FIDES, which incorporate the three methodologies so that there was a significant improvement in predicting the probability of systems failure. By the fact that this standard is updated periodically and revised, it makes it one of the most suitable and accurate methods of predicting the probability of failure and mean time between failure for recent technologies. Therefore, this dissertation is based on this standard, using the methodology described alongside with the information and data retrieved in collaboration with Aeromec, for calculating the mean time between failure of electronic components, four integrated circuits. The final aim of this study is to establish a methodology to predict the mean time between failure of a specific component, giving to Aeromec a relevant process, namely the methodology implemented, to do the calculations for the equipment to be fitted on to an aircraft, and if feasible, then make adjustments to the aircraft maintenance programs under their responsibility The comparison of the results obtained was carried out by comparing it with an estimated value for the mean time between failure of the four integrated circuits done by Flight Data Systems with the “ReliaSoft” reliability prediction software. With this study it was found that the prediction of the mean time between failure for the four integrated circuits, carried out using the FIDES standard, is more optimistic and therefore with a longer/higher mean time between failure then the prediction made by Flight Data Systems with the MIL-HDBK-217F standard. This may be due to two factors: the MIL-HDBK-217F standard has not been reviewed and updated for new technologies since 1995, contrary to the FIDES standard; and the usage profile in Flight Data Systems prediction does not exactly match as the one in FIDES. For future works, the next step is to conduct a full study to assess the mean time between failure for a specific equipment, for example a primary flight display that has several different components, meaning estimate the mean time between failure for every component incorporated, and then the overall mean time between failure. This work could be done by Aeromec to assess the mean time between failure for the equipment that will be installed in to aircraft in maintenance.No momento presente o mundo enfrenta um aumento na pressão para que os trabalhos se executem de modo mais rápido, melhor e mais barato, exigindo que os engenheiros prevejam com precisão a fiabilidade dos produtos. Nas fases iniciais do processo de design do produto, essas previsões precisas contribuirão não só para um produto mais robusto e fiável, mas também reduzirão os custos associados a redesenhar o produto, por exemplo, quando o produto está em fase de manufatura e é encontrado um erro de design, ou face a necessidade de melhorar a fiabilidade detetada em sede de utilização. O número de componentes eletrónicos, equipamentos e sistemas numa aeronave, aumenta com os novos avanços na tecnologia. Por isso é imperativo que os fabricantes destes mesmos equipamentos eletrónicos prevejam com exatidão a probabilidade de falha e o tempo médio entre falhas de cada equipamento/componente. Para que esta exatidão seja elevada, existem três metodologias: empírica (baseada em standards), mecanismos de falha, e testes acelerados. A metodologia mais comum é a utilização de standards. Um dos primeiros standard desenvolvidos e mais reconhecido, principalmente na área militar, é o MIL-HDBK-217F, contudo no momento presente de desenvolvimento da tecnologia, encontra-se obsoleto, pois os valores de previsão são aquém da realidade. Para ultrapassar este problema, um consórcio de empresas da área de aeronáutica e aeroespacial desenvolveu o standard FIDES, agrupando as três metodologias para que houvesse uma melhoria significativa na previsão da probabilidade de falha de sistemas. Pelo facto de o standard FIDES ser periodicamente atualizado e revisto, faz deste um dos standards mais adaptados e precisos na previsão da probabilidade de falha e tempo médio entre falhas para tecnologias recentes. Assim sendo, esta dissertação tem por base o standard FIDES, conjugando a metodologia descrita para o cálculo da probabilidade de falha de componentes eletrónicos com a informação e dados recolhidos em colaboração com a empresa de manutenção Aeromec, para a realização do estudo do tempo médio entre falhas em quatro circuitos integrados. O objetivo final deste estudo é estabelecer uma metodologia que permita determinar o tempo médio entre falhas de um componente específico, fornecendo à empresa de manutenção Aeromec um processo relevante, nomeadamente a metodologia implementada, para o cálculo do tempo médio entre falhas dos equipamentos a serem instalados, e, se viável, permitir fazer ajustes aos programas de manutenção das aeronaves sob sua responsabilidade. A comparação dos resultados obtidos foi realizada através da comparação com um valor estimado para o tempo médio entre falhas dos circuitos integrados estudados por parte da empresa Flight Data Systems com o software para previsão do tempo médio entre falhas, denominado “ReliaSoft”. Com este estudo verificou-se que a previsão do tempo médio entre falhas para os quatro circuitos integrados, realizada recorrendo ao standard FIDES, é mais otimista e portanto com um tempo médio entre falhas mais longo do que o standard MIL-HDBK217F, utilizado para a mesma previsão por parte da empresa Flight Data Systems. Podendo isto dever-se a dois fatores: o standard MIL-HDBK-217F não ser revisto e atualizado para as novas tecnologias desde 1995, contrariamente ao standard FIDES; O perfil de utilização da previsão por parte da empresa Flight Data Systems não corresponder exatamente ao perfil de utilização no estudo. Em trabalhos futuros, o próximo passo será conduzir um estudo do tempo médio entre falhas para um equipamento específico, por exemplo um display primário de voo, recorrendo a metodologia apresentada neste estudo, estimando o tempo médio de falhas de cada componente incorporado no equipamento, para posterior cálculo do tempo médio entre falhas total. Este trabalho poderá ser realizado por parte da Aeromec para avaliar o tempo médio entre falhas para equipamentos a serem instalados em aeronaves a realizar manutenção

Reliability-Oriented Design of Electrical Machines: The Design Process for Machines' Insulation Systems MUST Evolve

As the world of transportation keeps moving toward greater electrification, the main design objectives in terms of power density and efficiency of system components are becoming increasingly important. Meanwhile, transportation applications are also very safety critical. The extra stresses being seen by important components, such as electrical machines (EMs) and their insulation systems, to achieve the required performances, are accelerating the degradation of components, making them less reliable and shorting their lives. In general, lifetime consumption and degradation of components, such as for insulation systems of EMs, is still assessed through statistical methods (i.e., recording the number of imposed cycles until failure of a built prototype). This is a very timeconsuming and expensive process. In the mobile applications, such assessments can be the major bottleneck in the development timeline of an electrical product, especially for certification

Moving Toward a Reliability-Oriented Design Approach of Low-Voltage Electrical Machines by Including Insulation Thermal Aging Considerations

© 2020 IEEE. Electrical machines (EMs) are required to consistently perform their intended mission over a specified timeframe. The move toward transportation electrification made the EMs' reliability an even stringent and predominant requirement, since a failure might cause severe economic losses, as well as endanger human lives. Traditionally, the design procedure of motors conceived for safety-critical applications mainly relies on over-engineering approaches. However, a paradigm shift is recently taking place and physics of failure approaches/methodologies are employed to meet the reliability figures, while delivering an optimal design. This article proposes and outlines a reliability-oriented design for low-voltage EMs. Thermal accelerated aging tests are preliminarily carried out on custom-built specimens. Once the aging trend of the turn-to-turn insulation system is assessed, the thermal endurance graph at several percentile values is determined and lifetime models are developed, for both constant and variable temperature operations. Finally, these models are used to predict the turn-to-turn insulation lifetime of motors meant for aerospace and automotive applications

MICROELECTRONIC RELIABILITY MODELS FOR MORE THAN MOORE NANOTECHNOLOGY PRODUCTS

Disruptive technologies face a lack of Reliability Engineering Standards and Physics of Failure (PoF) heritage. Devices based on GaN, SiC, Optoelectronics or Deep-Submicron nanotechnologies or 3D packaging techniques for example are suffering a vital absence of screening methods, qualification and reliability standards when anticipated to be used in Hi-Rel application. To prepare the HiRel industry for just-in-time COTS, reliability engineers must define proper and improved models to guarantee infant mortality free, long term robust equipment that is capable of surviving harsh environments without failure. Furthermore, time-to-market constraints require the shortest possible time for qualification. Breakthroughs technologies are generally industrialized for short life consumer application (typically smartphone or new PCs with less than 3 years lifecycle). How shall we qualify these innovative technologies in long term Hi-Rel equipment operation? More Than Moore law is the paradigm of updating what are now obsolete, inadequate screening methods and reliability models and Standards to meet these demands. A State of the Art overview on Quality Assurance, Reliability Standards and Test Methods is presented in order to question how they must be adapted, harmonized and rearranged. Here, we quantify failure rate models formulated for multiple loads and incorporating multiple failure mechanisms to disentangle existing reliability models to fit the 4.0 industry needs

System Level Reliability Assessment of Short Duty Electric Drives for Aerospace

The reliability performance of electrical machines and power electronics converters are generally verified separately, even if the two components are meant to be part of the same electric drive. Depending on the application, however, it might be necessary that the whole drive fulfils a certain reliability target, which is pre-defined by the application itself. An appropriate design approach should involve joint efforts between machine and converter designers, so that the final product is as optimized as possible, while still satisfying reliability constraints. In this work, a system level reliability study for short duty electric drives is proposed and implemented, using an aerospace electromechanical actuator as case-study. Concepts of statistical post-processing for the lifetime prediction of power modules are discussed throughout. Additionally, accelerated lifetime tests on electrical machine windings are performed for predicting the motor insulation’s time to failure. For the short duty aerospace drive under investigation, i.e. case-study, it is finally verified that the power electronics converter represents the reliability bottleneck

Detection of Interconnect Failure Precursors using RF Impedance Analysis

Many failures in electronics result from the loss of electrical continuity of common board-level interconnects such as solder joints. Measurement methods based on DC resistance such as event detectors and data-loggers have long been used by the electronics industry to monitor the reliability of interconnects during reliability testing. DC resistance is well-suited for characterizing electrical continuity, such as identifying an open circuit, but it is not useful for detecting a partially degraded interconnect. Degradation of interconnects, such as cracking of solder joints due to fatigue or shock loading, usually initiates at an exterior surface and propagates towards the interior. A partially degraded interconnect can cause the RF impedance to increase due to the skin effect, a phenomenon wherein signal propagation at frequencies above several hundred MHz is concentrated at the surface of a conductor. Therefore, RF impedance exhibits greater sensitivity compared to DC resistance in detecting early stages of interconnect degradation and provides a means to prevent and predict an important cause of electronics failures. This research identifies the applicability of RF impedance as a means of a failure precursor that allows for prognostics on interconnect degradation based on electrical measurement. It also compares the ability of RF impedance with that of DC resistance to detect early stages of interconnect degradation, and to predict the remaining life of an interconnect. To this end, RF impedance and DC resistance of a test circuit were simultaneously monitored during interconnect stress testing. The test vehicle included an impedance-controlled circuit board on which a surface mount component was soldered using two solder joints at the end terminations. During stress testing, the RF impedance exhibited a gradual non-linear increase in response to the early stages of solder joint cracking while the DC resistance remained constant. The gradual increase in RF impedance was trended using prognostic algorithms in order to predict the time to failure of solder joints. This prognostic approach successfully predicted solder joint remaining life with a prediction error of less than 3%. Furthermore, it was demonstrated both theoretically and experimentally that the RF impedance analysis was able to distinguish between two competing interconnect failure mechanisms: solder joint cracking and pad cratering. These results indicate that RF impedance provides reliable interconnect failure precursors that can be used to predict interconnect failures. Since the performance of high speed devices is adversely affected by early stages of interconnect degradation, RF impedance analysis has the potential to provide improved reliability assessment for these devices, as well as accurate failure prediction for current and future electronics

Modelling the impact of refinishing processes on COTS components for use in aerospace applications

Commercial off the shelf components (COTS) are being adopted by electronic equipment manufacturers for use in aerospace applications. To ensure that these components meet the quality and reliability standards, refinishing processes, such as hot solder dip and laser deballing/reballing, are used to replace component lead-free solder terminations with tin–lead solder. These processes provide a risk mitigation strategy against tin whiskers induced short circuit failures. Being an additional step to the subsequent PCB assembly process it is important that this additional process does not impose significant thermo-mechanical stress which can impact subsequent reliability. As part of a major study in collaboration with industry partners, process models have been developed to predict the thermo-mechanical behaviour of components when subjected to the refinishing process. This paper details the techniques used to provide model input data (e.g., process parameters and package geometric/materials data) as well as the development and application of these modelling techniques to the refinishing process