Probabilistic Design For Reliability Concept Research Articles

Analytical Modeling of Electronic and Photonic Materials Reliability: Perspective and Extension

Abstract The objective of this review is twofold: to show materials scientists, mechanical engineers, and reliability physicists not involved in electronics, photonics, microelectronic-mechanical-systems (MEMS), or MOEMS (optical MEMS) engineering what kind of value they could bring to this important “high-tech” area, as well as to demonstrate to “high-tech” engineers how they could benefit from the application of what has been developed, for many years, in the general field of physical design for reliability of materials and structures employed in various fields of engineering and applied science and what could be effectively applied to their body of knowledge. Accordingly, in the perspective part of the review, some critical and even paradoxical, i.e., a priori nonobvious, problems encountered in microelectronics and photonics materials science, reliability physics, and structural analysis are addressed using what could be called analytical (“mathematical”) modeling. The extension part has to do with some specific, mostly aerospace, recent applications of the probabilistic design for reliability concept and analytical modeling effort.

Aerospace Electronics Reliability Must be Quantified to be Assured: Application of the Probabilistic Design for Reliability Concept

Aerospace Electronics Reliability Must be Quantified to be Assured: Application of the Probabilistic Design for Reliability Concept

What could and should be done differently: failure-oriented-accelerated-testing (FOAT) and its role in making an aerospace electronics device into a product

High operational reliability of an electronic material or a device intended for aerospace applications is critical, and, in the author’s opinion, cannot be assured, if the underlying physics of failure is not well understood and the never-zero probability of failure is not predicted and made adequate for the particular material, device and application. The situation is the same in some other areas of electronics materials engineering, such as military, medical, or long-haul communications, where high level of reliability is required. The situation is different in today’s commercial electronics, where cost and time-to-market are typically more important than high reliability. Failure-oriented-accelerated-testing (FOAT) of aerospace electronics materials and products and its role in making a viable device into a reliable product is addressed and discussed vs. very popular today highly-accelerated-life-testing (HALT). The differences of the two accelerated test procedures and objectives is briefly discussed. FOAT is an essential part of the recently suggested probabilistic design for reliability (PDfR) approach in electronics engineering. It is argued that high (adequate) reliability level of aerospace electronics materials and devices cannot be achieved and assured, if their never-zero probability-of-failure is not quantified for the given (anticipated) combination of the loading conditions (stresses, stimuli) and time in operation. It is the application of the FOAT, the heart of the highly effective and highly flexible PDfR concept, that should be employed and mastered, when high reliability of a material or a device is imperative. The general concepts are illustrated by numerical examples. They are based on an analytical modeling approach, as the FOAT models are.

Static fatigue lifetime of optical fibers assessed using Boltzmann–Arrhenius–Zhurkov (BAZ) model

The recently suggested probabilistic design-for-reliability (PDfR) concept and particularly its physically meaningful and flexible Boltzmann–Arrhenius–Zhurkov (BAZ) model, can be effectively employed as an attractive replacement of the widely used today purely empirical and physically unsubstantiated power law relationship for assessing the static fatigue (delayed fracture) lifetime of optical silica fibers. In this analysis the BAZ model is employed to estimate the static fatigue lifetime of an optical silica fiber under the combined action of tensile loading and an elevated temperature. The PDfR concept has its experimental basis in the highly-focused and highly-cost-effective failure-oriented accelerated testing (FOAT). Accordingly, it is shown how the PDfR concept, BAZ model and FOAT data can be effectively used, when there is a need to assess the long-term tensile strength (static fatigue life) of a coated optical fiber subjected to the combined action of tensile loading and elevated temperature. Although the role of elevated humidity might be insignificant owing to the elevated temperature conditions, this role can be accounted for, if there is a need for that, as well, by using multi-parametric BAZ model. Since the principle of superposition does not work in reliability engineering, all the three stressors, namely, the elevated temperature, tensile stress and relative humidity, should be applied concurrently to the specimen under test, and their coupling, if any, should and could be considered by the FOAT based on the BAZ model. The numerical example is carried out, however, for the case when only the elevated temperature and tensile stress are applied. The results of the analysis can be employed in the design and testing of optical silica fibers.

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.

Could electronics reliability be predicted, quantified and assured?

Application of the consistent, comprehensive and physically meaningful probabilistic design for reliability (PDfR) concept can not only help to understand the physics-of-failure of an electronic product, but, most importantly, can enable one to predict, quantify and assure its failure-free performance in the field. The use of the PDfR concept can be helpful also in the development and implementation of the new generation of the most feasible and effective qualification test (QT) methodologies, practices and specifications. The major ten PDfR requirements (“commandments”) for the predicted, quantified and assured reliability of an electronic or a photonic product could be formulated as follows:(1)PDfR approach is an effective means for improving the state-of-the-art in the field, having in mind that nothing is perfect, and that the difference between an unreliable product and a robust one is “merely” in the level of the never-zero probability of failure (PoF).(2)The best electronic product is, in effect, the best compromise between the needs for its reliability, cost effectiveness and time-to-market (completion) for a particular product and application.(3)Reliability cannot be low, need not be higher than necessary, but, for a cost-effective and a timely product, has to be adequate for a particular product and application.(4)When reliability is imperative, ability to quantify it is a must, especially if optimization is considered: no optimization is possible, of course, if the product’s reliability characteristics of interest are not quantified.(5)One cannot design a product with predicted, quantified, optimized and assured reliability by limiting the effort to the highly accelerated life testing (HALT): HALT can test the reliability limits and perhaps to ruggedize the product, but does not quantify reliability.(6)Reliability is conceived at the design stage and should be taken care of, first of all, at this stage, when a “genetically healthy” product is supposed to be created; if the reliability of the product is taken care at this stage, then the subsequent fabrication, qualification and prognostics-and-health-monitoring (PHM) stages will have much better chances to succeed.(7)Reliability evaluations and assurances cannot be delayed until the product is fabricated and shipped to the customer, i.e., cannot be left to the PHM stage: it is too late at this stage to change the design or the materials for improved reliability; that is why, when high reliability is critical (e.g., in the aerospace and military electronics), users have to re-qualify devices to assess their (remaining) useful lifetime (RUL) and to use redundancy in an attempt to build a reliable system out of insufficiently reliable components.(8)Design, fabrication, testing, qualification and PHM efforts should consider, and be specific for, particular products and their most likely actual or at least anticipated applications.(9)Highly cost-effective and highly focused failure oriented accelerated testing (FOAT) geared to a particular pre-determined relevant reliability model and aimed at understanding the physics of failure anticipated by this model is an important constituent part of the PDfR concept and effort.(10)Effective, easy-to-use and physically meaningful predictive modeling (PM) is another important constituent of the PDfR approach; in combination with FOAT, it is a powerful means to carry out meaningful sensitivity analyses (SA), so that the operational reliability of the product is effectively predicted, quantified and assured (“principle of practical confidence”). Analytical (“mathematical”) modeling occupies a special place in the modeling effort, because of its compactness and explicit indication on “what affects what” and what could possibly be done to improve the product’s performance.In the write-up that follows the above requirements (“commandments”) are addressed and discussed in detail.