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2010 | Buch

Introduction Kapitel lesen Erstes Kapitel lesen

Reliability Physics and Engineering

Time-To-Failure Modeling

verfasst von: J.W. McPherson

Verlag: Springer US

Enthalten in: Springer Professional "Wirtschaft+Technik" , Springer Professional "Technik"

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Über dieses Buch

All engineers could bene?t from at least one course in reliability physics and engineering. It is very likely that, starting with your very ?rst engineering po- tion, you will be asked — how long is your newly developed device expected to last? This text was designed to help you to answer this fundamentally important question. All materials and devices are expected to degrade with time, so it is very natural to ask — how long will the product last? The evidence for material/device degradation is apparently everywhere in nature. A fresh coating of paint on a house will eventually crack and peel. Doors in a new home can become stuck due to the shifting of the foundation. The new ?nish on an automobile will oxidize with time. The tight tolerances associated with ?nely meshed gears will deteriorate with time. Critical parameters associated with hi- precision semiconductor devices (threshold voltages, drive currents, interconnect resistances, capacitor leakages, etc.) will degrade with time. In order to und- stand the lifetime of the material/device, it is important to understand the reliability physics (kinetics) for each of the potential failure mechanisms and then be able to develop the required reliability engineering methods that can be used to prevent, or at least minimize the occurrence of, device failure.

Inhaltsverzeichnis

Frontmatter
Chapter 1. Introduction
Abstract
It is very frustrating (and often very expensive) to buy a device only to have it to fail with time. However, all devices (from integrated circuits to automobile tires) are fabricated from materials that will tend to degrade with time. The materials degradation will continue until some critical device parameter can no longer meet the required specification for proper device functionality. At this point, one usually says: the device has failed. This failure could be due to an increase in capacitor leakage (in the case of the integrated circuits) or the inability of an automobile tire to hold proper pressure (blowout). Materials degradation and eventual device failure are the subjects of reliability physics and engineering. Reliability physics is normally associated with understanding the kinetics of failure mechanisms. Reliability engineering is usually associated with establishing: proper design rules, robust materials selection criteria, and good manufacturing guidelines for reliable device fabrication and use.
J.W. McPherson
Chapter 2. Materials and Device Degradation
Abstract
Degradation is seemingly fundamental to all things in nature. Often this is described as one of the consequences of the Second Law of Thermodynamics — entropy (disorder) of isolated systems will tend to increase with time. 1 The evidence for degradation is apparently everywhere in nature. A fresh coating of paint on a house will eventually crack and peel. The finish on a new automobile will oxidize with time. The tight tolerances associated with finely meshed gears will deteriorate with time. The critical parameters associated with precision semiconductor devices (threshold voltages, drive currents, interconnect resistances, capacitor leakage, etc.) will degrade with time. In order to understand the useful lifetime of the device, it is important to be able to model how critically important material/device parameters degrade with time.
J.W. McPherson
Chapter 3. From Material/Device Degradation to Time-To-Failure
Abstract
In the previous chapter, it was suggested that material/device degradation will occur with time and that this continuing degradation will eventually cause device failure. Methods were presented in Chapter 2 which can be used for modeling the time-dependence of degradation. The question that we would like to address in this chapter is --- how does one go from the time-dependence of degradation to the time-to-failure for the device? The time-to-failure equations are critically important, for device failure-mechanisms, and will be the focus of the remaining chapters in this book.
J.W. McPherson
Chapter 4. Time-To-Failure Modeling
Abstract
All materials tend to degrade, and will eventually fail, with time. For example, metals tend to creep and fatigue; dielectrics tend to trap charge and breakdown; paint tends to crack and peel; polymers tend to lose their elasticity and become more brittle, teeth tend to decay and fracture; etc. All devices (electrical, mechanical, electromechanical, biomechanical, bioelectrical, etc.) will tend to degrade with time and eventually fail. The rate of degradation and eventual time-to-failure will depend on the electrical, thermal, mechanical and chemical environments to which the device is exposed.
J.W. McPherson
Chapter 5. Gaussian Statistics — An Overview
Abstract
The Gaussian distribution (normal or bell-shaped distribution) is a widely used statistical distribution and it is generally used as the foundation for statistical quality control. Simply measuring the time-zero values of a parameter (resistor values, mechanical tolerances, children heights, class grades on a test, etc.) can result in a distribution of values which can be described by a normal distribution.
J.W. McPherson
Chapter 6. Time-To-Failure Statistics
Abstract
When nearly identically processed materials/devices are placed under the same set of stress conditions, they will not fail exactly at the same time. An explanation for this occurrence is that slight differences can exist in the materials microstructure, even for materials/devices processed nearly identically. This means that not only are we interested in time-to-failure but, more precisely, we are interested in the distribution of times-to-failure. Once the distribution of times-to-failure is established, then one can construct a probability density function f(t) which will permit one to calculate the probability of observing a failure in any arbitrary time interval between t and t + dt, as is illustrated in Figure 6.1.
J.W. McPherson
Chapter 7. Failure Rate Modeling
Abstract
For a collection of devices, it is critically important to be able to understand the expected failure rate for the devices. For the supplier of such devices, the expected failure rate will be an important indicator of future warranty liability. For the customer, the expected failure rate will be an important indicator of future satisfaction. For mission-critical applications, it is of paramount importance for one to know that the expected failure rate will be extremely low.
J.W. McPherson
Chapter 8. Accelerated Degradation
Abstract
Generally, materials/devices exist in metastable states. These states are referred to as being metastable because they are only apparently stable. Metastable states will change/degrade with time. The rate of degradation of the materials (and eventual time-to-failure for the device) can be accelerated by an elevated stress (e.g., mechanical stress, electrical stress, electrochemical stress, etc.) and/or elevated temperature.
J.W. McPherson
Chapter 9. Acceleration Factor Modeling
Abstract
In reliability physics and engineering, the development and use of the acceleration factor is fundamentally important to the theory of accelerated testing. The acceleration factor permits one to take time-to-failure data, very rapidly under accelerated stress conditions, and then to be able to extrapolate the accelerated time-to-failure results (into the future) for a given set of operational conditions. Since experimental determination of the acceleration factor could actually take many years, the acceleration factor must be modeled using the time-to-failure (TF) models introduced in Chapter 4. Since the acceleration factor must be modeled, it brings up another important question — how does one build some conservatism into the models, without being too conservative?
J.W. McPherson
Chapter 10. Ramp-to-Failure Testing
Abstract
Engineers are constantly confronted with time issues. Applying a constant stress and waiting for failure can be very time consuming. Thus, it is only natural to ask the question — does a rapid time-zero test exist that can be used on a routine sampling basis to monitor the reliability of the materials/devices? The answer to this question is often yes and it is called the ramp-to-failure test. While the test is destructive in nature (one has to sacrifice materials/devices), it is generally much more rapid than conventional constant-stress time-to-failure tests. The relative quickness of the test also enables the gathering of more data and thus the gathering of better statistics.
J.W. McPherson
Chapter 11. Time-To-Failure Models for Selected Failure Mechanisms in Integrated Circuits
Abstract
Advanced integrated circuits (ICs) are very complex, both in terms of their design and in their usage of many dissimilar materials (semiconductors, insulators, metals, plastic molding compounds, etc.). For cost reductions per device and improved performance, scaling of device geometries has played a critically important role in the success of semiconductors. This scaling (where device geometries are generally reduced by 0.7x for each new technology node and tend to conform to Moore’s Law) has caused the electric fields in the materials to rise (bringing the materials ever closer to their breakdown strength) and current densities in the metallization to rise causing electromigration (EM) concerns.
J.W. McPherson
Chapter 12. Time-To-Failure Models for Selected Failure Mechanisms in Mechanical Engineering
Abstract
The mechanical properties of materials are related to the fundamental bonding strengths of the constituent atoms in the solid and any bonding defects which might form. A molecular model is presented so that primary bond formation mechanisms (ionic, covalent, and metallic) can be better understood. How these bonds form and respond to mechanical-stress/loading is very important for engineering applications. A discussion of elasticity, plasticity and bond breakage is presented. The theoretical strengths of most molecular bonds in a crystal are seldom realized because of crystalline defects limiting the ultimate strength of the materials. Important crystalline defects such as vacancies, dislocations, and grain boundaries are discussed. These crystalline defects can play critically important roles as time-to-failure models are developed for: creep, fatigue, crack propagation, thermal expansion mismatch, corrosion and stress-corrosion cracking.
J.W. McPherson
Chapter 13. Conversion of Dynamical Stresses into Effective Static Values
Abstract
The time-to-failure models which were developed in the previous chapters assume that the stress remains constant with time until the material fails. Even when we discussed fatigue (a failure mechanism caused by a cyclical stress), it was assumed that the stress range Δσ remained constant with time. However, seldom is the applied stress constant with time, as illustrated in Fig. 13.1. In integrated circuits, the currents and fields are continually changing during operation and generally depend on the frequency of operation. In mechanical devices, the mechanical stress usually varies with time (the mechanical stress in a metal light pole changes with wind direction and with wind speed while the mechanical stress in the shaft of a rotor changes with the number of rpm). Therefore, a question naturally arises: how does one convert dynamical stresses (time-dependent stresses) ξ(t) into an effective static form ξ effective so that all of the previously developed time-to-failure models can be used? This chapter presents a methodology for that conversion.
J.W. McPherson
Chapter 14. Increasing the Reliability of Device/Product Designs
Abstract
Design engineers are continually asked reliability questions such as: (1) how long is your newly designed device/product expected to last and (2) how can you make cost-effective design changes to improve the reliability robustness of the device? Often the designer will attempt to answer these questions by stating a safety factor χ which was used for a design
J.W. McPherson
Erratum to: Materials and Device Degradation
J.W. McPherson
Backmatter
Metadaten
Titel
Reliability Physics and Engineering
verfasst von
J.W. McPherson
Copyright-Jahr
2010
Verlag
Springer US
Electronic ISBN
978-1-4419-6348-2
Print ISBN
978-1-4419-6347-5
DOI
https://doi.org/10.1007/978-1-4419-6348-2

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