Quantified reliability of aerospace optoelectronics

The attributes of and challenges in the recently suggested probabilistic design for reliability (PDfR) concept, and the role of its major constituents - failure oriented accelerated testing (FOAT) and physically meaningful predictive modeling (PM) - are addressed, advanced and discussed. The emphasis is on the application of the powerful and flexible Boltzmann-Arrhenius-Zhurkov (BAZ) model, and particularly on its multi-parametric aspect. The model can be effectively used to analyze and design optoelectronic (OE) devices and systems with the predicted, quantified, assured, and, if appropriate and cost-effective, even maintained probability of failure in the field. The numerical example is carried out for an OE system subjected to the combined action of the ionizing radiation and elevated voltage as the major stimuli (stressors). The measured leakage current is used as a suitable characteristic of the degree of degradation. It is concluded that the suggested methodology can be accepted as an effective means for the evaluation of the operational reliability of the aerospace electronics and OE systems and that the next generation of qualification testing (QT) specifications and best practices for such systems could be viewed and conducted as a “quasi-FOAT,” a sort of an “initial stage of FOAT” that adequately replicates the initial non-destructive segment of the previously conducted comprehensive “full-scale” FOAT

A unified multiple stress reliability model for microelectronic devices — Application to 1.55 μm DFB laser diode module for space validation

The establishment of European suppliers for DFB Laser Modules at 1.55 µm is considered to be essential in the context of future European space programs, where availability, cost and schedule are of primary concerns. Also, in order to minimize the risk, associated with such a development, the supplier will be requested to use components which have already been evaluated and/or validated and/or qualified for space applications. The Arrhenius model is an empirical equation able to model temperature acceleration failure modes and failure mechanisms. The Eyring model is a general representation of Arrhenius equation which takes into account additional stresses than temperature. The present paper suggests to take advantage of these existing theories and derives a unified multiple stress reliability model for electronic devices in order to quantify and predict their reliability figures when operating under multiple stress in harsh environment as for Aerospace, Space, Nuclear, Submarine, Transport or Ground. Application to DFB laser diode module technologies is analyzed and discussed based on evaluation test program under implementation

Collaborative Robotics: Application of Delphi Method

In the domain of collaborative robotics, it is often needed to make complex multiparametric choices or assessments that combine heterogeneous criteria, such as task performance, reliability, safety, and ergonomics. The Delphi method, a process of arriving at group consensus by providing experts with rounds of questionnaires, as well as the group response before each subsequent round, can be applied to solve this type of problems. The following Delphi method efforts are addressed in our analysis with application to finding appropriate criteria and their relative weights for the evaluation of the teleoperation task of a robotic platform: (1) Contribution of experts; (2) estimates using student\u27s distribution; and (3) decision making support using Fischer criterion. A consensus emerged among eight experts, who selected the criteria of duration, number of trajectory corrections, and feeling of the operator. Weights have been proposed for each criterion and statistical tools have been used to evaluate the consensus

FIBER OPTICS ENGINEERING: PHYSICAL DESIGN FOR RELIABILITY

The review part of the paper addresses analytical modeling in fiber optics engineering. Attributes and significance of predictive modeling are indicated and discussed. The review is based mostly on the author’s research conducted at Bell Laboratories, Physical Sciences and Engineering Research Division, Murray Hill, NJ, USA, during his tenure with Bell Labs for about twenty years, and, to a lesser extent, on his recent work in the field. The addressed topics include, but are not limited to, the following major fields: bare fibers; jacketed and dual-coated fibers; coated fibers experiencing thermal and/or mechanical loading; fibers soldered into ferrules or adhesively bonded into capillaries; roles of geometric and material non-linearity; dynamic response to shocks and vibrations; as well as possible applications of nano-materials in new generations of coating and cladding systems. The extension part is concerned with a new, fruitful and challenging direction in optical engineering- probabilistic design for reliability (PDfR) of opto-electronic and photonic systems, including fiber optics engineering. The rationale behind the PDfR concept is that the difference between a highly reliable optical fiber system and an insufficiently reliable one is “merely” in the level of the never-zero probability of failure. It is the author’s belief that when the operational reliability of an optical fiber system and product is imperative, the ability to predict, quantify, assure and, if possible and appropriate, even specify this reliability is highly desirable

Required Repair Time to Assure the Given/Specified Availability

International audienceA novel, simple, easy-to-use, flexible and physically meaningful methodology is suggested for the assessment of the required repair/restoration time, so that the object's/system's availability is swiftly restored, thereby keeping this availability on the specified/desirable/required level during the entire time of the system's operation. A working table for the time-dependent availability function is obtained for the following two major governing input variables: 1) the product of the anticipated failure rate of the system of interest and the time of operation and 2) the ratio of the intensity of the restoration process to the meantime to failure (MTTF). This intensity is simply reciprocal to the mean time to repair (MTTR). The general concept is illustrated by a practical example. Several extensions of this work are considered and indicated, and particularly the role of the human-system interaction ("human-in-the-loop") situations, when system's reliability and human performance contribute jointly to the never-100%-failure-free operation process. _____________________________________________________________________________

A Gestão Ativa da Dívida Pública

A presente dissertação tem como objetivo de estudo, compreender como é feita a gestão da dívida pública, com especial atenção para a dívida pública portuguesa. Esta investigação foi feita com base nos relatórios anuais publicados pela Agência de Gestão de Tesouraria e da Dívida Pública-IGCP, E.P.E e pelo Tribunal de Contas, nas guidelines para a gestão da dívida pública publicados pelo Fundo Monetário Internacional e Banco Mundial, e através de uma entrevista com o Dr. Jorge Guedes, colaborador da Agência de Gestão de Tesouraria e da Dívida Pública-IGCP, E.P.E. Durante a dissertação procura-se mostrar quais os fatores a ter em conta para uma gestão eficiente da dívida pública, bem como a evolução que se tem verificado ao longo dos anos na gestão ativa da dívida pública portuguesa. O saldo da dívida nos últimos anos cresceu significativamente e com isso a gestão da dívida foi também evoluindo, de forma a manter a dívida sustentável. As emissões reais seguiram sempre o benchmark definido, demonstrando que a gestão da dívida foi sempre feita tendo em consideração todos os limites de risco impostos pela tutela. Em 2011 foi mesmo necessário assinar um acordo de ajuda externa (Programa de Assistência Económica e Financeira), tendo a partir dessa data, a gestão ativa da dívida perdido importância, visto que não dispomos de total autonomia para fazer as operações que se entendem convenientes. Com este estudo constata-se que a gestão da dívida pública tem evoluído de acordo com as condições macro-económicas e adaptando-se à conjuntura existente em cada momento.Esta dissertação permite observar a evolução de estratégias utilizadas na gestão da dívida ao longo dos últimos anos, bem como os valores atualizados respeitantes às emissões de títulos de dívida, à evolução do saldo da dívida e respetivos encargos

Predicted Stresses in a Ball-Grid-Array (BGA)/Column-Grid-Array (CGA) Assembly With a Low Modulus Solder at its Ends

A simple, easy-to-use and physically meaningful predictive model is suggested for the assessment of thermal stresses in a ball-grid-array or a column-grid-array with a low modulus solder material at the peripheral portions of the assembly. It is shown that the application of such a design can lead to a considerable relief in the interfacial stresses, even to an extent that inelastic strains in the solder joints could be avoided. If this happens, the fatigue strength of the bond and of the assembly as a whole will be improved dramatically: low-cycle fatigue conditions will be replaced by the elastic fatigue condition, and Palmgren–Minor rule of linear accumulation of damages could be used instead of one of the numerous Coffin–Manson models to assess the lifetime of the material

Could Application of Column-Grid-Array (CGA) Technology Result in Inelastic-Strain-Free State-of-Stress in Solder Material?

Physically meaningful and easy-to-use analytical stress model is developed for a short cylinder (beam) clamped at the ends and subjected to bending caused by the ends offset. The offset is due, in its turn, to an external lateral force that has to be determined from the known offset. It is envisioned that such a beam can adequately represent the state of stress in a column-grid-array (CGA) solder joint interconnection experiencing thermal loading due to the thermal expansion/contraction mismatch of the IC package and the printed circuit board (PCB). The CGA designs are characterized by considerably higher stand-off heights than ball-grid-array (BGA) systems. The offset Δ = lΔαΔt for a CGA solder joint located at the distance l from the mid-cross-section of the package/PCB assembly (the neutral point (DNP)), can be determined, in an approximate analysis, as a product of this distance and the “external” thermal mismatch strain ΔαΔt between the IC package and the printed circuit board (PCB). Here Δα is the difference in the effective coefficients of thermal expansion (CTE) of the PCB and package materials, and Δt is the change in temperature. The objective of the analysis is to demonstrate that the application of a CGA design, in which the solder joints are configured as short clamped–clamped beams, enables one not only to significantly relieve the thermally induced stresses, compared to the BGA system, but possibly to do that to an extent that the stresses in the solder material would remain within the elastic range. If this is achieved, the low-cycle-fatigue condition for the solder material will be replaced by the elastic-fatigue condition, thereby leading to a significantly longer fatigue lifetime of the joint. The elastic fatigue lifetime can be assessed, as is known, based on the Palmgren–Miner rule of linear accumulation of damages. Our analysis is limited therefore to elastic deformations

Predicted Stresses in Ball-Grid-Array (BGA) and Column-Grid-Array (CGA) Interconnections in a Mirror-Like Package Design

There is an obvious incentive for using bow-free (temperature change insensitive) assemblies in various areas of engineering, including electron device and electronic packaging fields. The induced stresses in a bow-free assembly could be, however, rather high, considerably higher than in an assembly, whose bow is not restricted. The simplest and trivial case of a bow-free assembly is a tri-component body, in which the inner component is sandwiched between two identical outer components (“mirror” structure), is addressed in our analysis, and a simple and physically meaningful analytical stress model is suggested. It is concluded that if acceptable stresses (below yield stress of the solder material) are achievable, a mirror (bow-free, temperature-change-insensitive) design should be preferred, because it results in an operationally stable performance of the system

Aerospace Mission Outcome: Predictive Modeling

Human-in-the-Loop (HITL)-related models can be applied in various aerospace vehicular problems, when human qualifications and performance are crucial and the ability to quantify them is therefore imperative; since nobody is perfect, these evaluations should preferably be done on a probabilistic basis. The suggested models can also be used in many other areas of applied science and engineering, not even necessarily vehicular engineering, when a human encounters an extraordinary situation and should possess a sufficiently high human capacity factor (HCF) to successfully cope with an elevated mental workload (MWL). The incentive for probabilistic predictive modeling and the rationale for such modeling is addressed in this article on the layman language level