Burn-In Programs for Repairable Systems

Burn-in programs are often used for automotive or airplane engines in order to eliminate early failures due to ineffective adjustments and similar repairable sources of failure. We assume that there are two operating states: Good and Poor. Each has its own reliability characteristic, and neither necessarily has any statistical property that improves with bum-in. The purpose of the bum-in program is to uncover the Poor engines and then to repair them to the Good state. We calculate the mean time to failure of such engines when a burn-in program is used and derive conditions under which a burn-in program is justified.     

Analysis of burn-in time using the general law of reliability

Empirical lifetime distributions sometimes have a bathtub-shaped failure rate. This paper deals with some models having a bathtub-shaped failure rate. The root-mean-square criterion is proposed for selection of the best model. Besides two criteria of optimum burn-in time are proposed. The comparison of some models with the general law of reliability is given to determine a burn-in time in a number of examples.     

A nonparametric approach to estimate system burn-in time

System burn-in can get rid of more residual defects than component and subsystem burn-ins because incompatibility exists not only among components, but also among different subsystems and at the system level. There are two major disadvantages for performing the system burn-in: the high burn-in cost and the complicated failure rate function. This paper proposes a nonparametric approach to estimate the optimal system burn-in time. The Anderson-Darling statistic is used to check the constant failure rate (CFR), and the pool-adjacent-violator (PAV) algorithm is applied to “unimodalize” the failure rate curve. Given experimental data, the system burn-in time can be determined easily without going through complex parameter estimation and curve fittings     

Burn-in effect on yield

By removing infant mortalities, burn-in of semiconductor devices improves reliability. However, burn-in may affect the yield of semiconductor devices since defects grow during burn-in and some of them end up with yield loss. The amount of yield loss depends upon burn-in environments. Another burn-in effect is the yield gain. Since yield is a function of defect density, if some defects are detected and removed during burn-in, the yield of the post-burn-in process can be expected to increase. The amount of yield gain depends upon the number of defects removed during burn-in. In this paper we present yield loss and gain expressions and relate them with the reliability projection of semiconductor devices in order to determine burn-in time     

A relation model of gate oxide yield and reliability

The relationship between yield and reliability is obviously important for predicting and improving reliability during the early production stage, especially for new technologies. Previous research developed models to relate yield and reliability when reliability is defined as the probability of a device having no reliability defects. This definition of reliability is not a function of mission time and thus is not consistent with reliability estimated from the time-to-first-failure data which is commonly used. In this paper, we present a simple model to tie oxide yield to time-dependent reliability by combining the oxide time to breakdown model with a defect size distribution. We show that existing models become special cases when a single mission time is considered. As the proposed reliability function has a decreasing failure rate, the result is useful for a manufacturer seeking to find an optimal burn-in policy for burn-in temperature, burn-in voltage, and burn-in time.     

电子元器件老炼试验技术

老炼是对电子元器件施加应力,剔除有缺陷的元器件的过程。长时间的老炼会对一些原本健康的器件寿命产生影响,但是时间过短却又不能起到很好地剔除有缺陷的元器件的目的。在相关文章的基础上总结了哪类电子元器件适合进行老炼,以及元器件老炼时间的优化问题,提出电子元器件老炼的3个准则,电子元器件最优老炼时间的确定问题,以及元器件老炼发展方向。     

Relating integrated circuit yield and time-dependent reliability for various defect density distributions

The issue of developing a model to estimate field reliability from process yield has received a growing interest in recent years. Thus far, only Poisson and negative binomial relationships have been obtained, assuming that the number of yield defects is independent of the number of reliability defects in a device. In this paper, we derived explicit yield-reliability relationships for various defect density, such as Erlang, uniform, and triangle distributions, using a multinomial distribution to consider a correlation between the number of yield defects, and the number of reliability defects. The proposed model has advantages over previous models for any defect density distribution to determine the optimal burn-in time.     

Experimental Determination of a More Powerful Burn-In

This paper describes an experiment in which it was determined that burn-in could be made more powerful (i.e., capable of precipitating more failures in a given burn-in period) by reducing the time spent at the high temperature extreme. The number of failures precipitated in burn-in using a cycle consisting of a 2-hour non-operating cold soak and a 2-hour operating heat soak were compared to those precipitated using a 2-hour non-operating cold soak and a 4-hour operating heat soak. The shorter cycles precipitated as many failures as the longer, for an equal number of cycles. The fact that the shorter cycle required two-thirds the chamber time of the longer cycle equates to more cycles, and hence more failures removed, in a given burn-in period.     

Extending integrated-circuit yield-models to estimate early-life reliability

The integrated yield-reliability model for integrated circuits allows one to estimate the yield, following both wafer probe and burn-in testing. The model is based on the long observed clustering of defects and the experimentally verified relation between defects causing wafer probe failures, and defects causing infant mortality failures. The 2-parameter negative binomial distribution is used to describe the distribution of defects over a semiconductor wafer. The clustering parameter /spl alpha/, while known to play a key role in accurately determining wafer probe yields, is shown, for the first time, to play a similar role in determining burn-in fall-out. Numerical results indicate that the number of infant mortality failures predicted by the clustering model can differ appreciably from calculations that ignore clustering. This is particularly apparent when wafer probe yields are low, and clustering is high.     

半导体器件老炼筛选试验设计

老炼筛选试验是有效剔除内含固有工艺缺陷的半导体器件,以及保证半导体器件使用可靠性的重要途径。本文阐述了半导体器件早期失效的基本概念,并给出了半导体器件早期失效率的预计方法。在此基础上提出了半导体器件老炼筛选试验设计方法,以期最大限度地保证半导体器件出厂后的使用可靠性。     

On optimal burn-in procedures - a generalized model

Burn-in is a manufacturing technique that is intended to eliminate early failures. In this paper, burn-in procedures for a general failure model are considered. There are two types of failure in the general failure model. One is Type I failure (minor failure), which can be removed by a minimal repair or a complete repair; and the other is Type II failure (catastrophic failure), which can be removed only by a complete repair. During the burn-in process, two types of burn-in procedures are considered. In Burn-In Procedure I, the failed component is repaired completely regardless of the type of failure; whereas, in Burn-In Procedure II, only minimal repair is done for the Type I failure, and a complete repair is performed for the Type II failure. Under the model, various additive cost functions are considered. It is assumed that the component before undergoing the burn-in process has a bathtub-shaped failure rate function with the first change point t/sub 1/, and the second change point t/sub 2/. The two burn-in procedures are compared in cases when both the procedures are applicable. It is shown that the optimal burn-in time b/sup */ minimizing the cost function is always before t/sub 1/. It is also shown that a large initial failure rate justifies burn-in, i.e., b/sup */>0. The obtained results are applied to some examples.     

An extended model for optimal burn-in procedures

In this paper, the problem of determining optimal burn-in time is considered under the general failure model. There are two types of failure in the general failure model. One is Type I failure (minor failure) which can be removed by a minimal repair, and the other is Type II failure (catastrophic failure) which can be removed only by a complete repair. In the researches on optimal burn-in, the assumption of a bathtub shaped failure rate function is commonly adopted. In this paper, upper bounds for optimal burn-in times are obtained under a more general assumption on the shape of the failure rate function, which includes the bathtub shaped failure rate function as a special case.     

Reliability Enhancement Through Optimal Burn-In

Burn-in is an important screening method used in predicting, achieving, and enhancing field reliability. Although electronics burn-in has been studied qualitatively, no comprehensive quantitative approach exists for determining optimal burn-in periods. This paper presents a cost-optimization model from a system viewpoint, with burn-in periods for the components as the decision variables. This model is applied to an electronic product recently developed which uses many ICs. State-of-the-art ICs have high early-failure rates and long infant mortality periods. Proper use of burn-in reduces early failure rates and reduces system deployment costs. The total cost to be minimized is formulated as a function of the mean costs of the component, device burn-in, shop repair, and field repair, which in turn are functions of the mean number of failures during and after burn-in. Component and system reliability are constraints that have to be satisfied. The early device failures are assumed to have a Weibull distribution. The formulated problem, with failure rates and cost factors, is optimized. Some basic properties of reliability and cost functions are discussed.     

Dielectric breakdown distributions for void containing silicon substrates

Distributions of gate oxide failure in various types of silicon substrate materials have been investigated for a wide range of oxide thicknesses. Silicon substrates containing various well-characterized void distributions along with defect-free materials were tested using special low-series resistance capacitor structures. Results of both ramped field tests of variable ramp rate and constant field tests were performed and analyzed within the framework of Weibull statistics. Ramped field tests are not “time zero dielectric breakdown” tests as is commonly asserted. They can in fact be very useful in extrapolating time dependent failure. The same set of Weibull parameters can be used to describe both ramped field and constant field wearout tests if an appropriate model for the time dependent damage accumulation during the field ramp is used. There are implications for reliability predication and the burn-in screening of device populations containing such defects.     

Facing the headaches of early failures: A state-of-the-art review of burn-in decisions

System screening during electronic equipment manufacturing often cost-effective opportunities to remove and replace defective items. Burn-in is an important screening method used in predicting, achieving, and enhancing field reliability. Based on a simple calculation, we would expect the number of failures in the field to be a decreasing function of burn-in period. Especially, the expected number of failures drops significantly in the first part of the curve. Thus only a few hours of burn-in greatly reduces the failure rate, hence enhancing reliability. Qualitative studies on electronics burn-in have been done. It is well known that burn-in is costly. However, a comprehensive quantitative approach is lacking in the determination of optimal burn-in periods. This paper thoroughly reviews the studies of burn-in screenings applied to industrial products. Papers published in the past have been critically commented and systematically classified. This state-of-the-art review can serve as a guide in studying the burn-in problems.     

Circuit reliability simulator for interconnect, via, and contactelectromigration

A model for predicting Al interconnect and intermetallic contact/via electromigration time-to-failure under arbitrary current waveform is incorporated in a circuit electromigration reliability simulator. The simulator can (1) generate layout advisory for width and length of each interconnect, and the number of contacts and vias at each node in a circuit, and (2) estimate the overall circuit electromigration failure rate and/or cumulative percent failure as functions of time, temperature, voltage, frequency, and previous stress (e.g., burn-in)     

Cost Effective Burn-In and Replacement Times

Bum-in and replacement policies have been used to reduce the cost of maintaining a system function. Existing solutions to the burn-in and the combined burn-in, replacement problems are typically difficult to apply. A simpler solution to this problem is given. The only distributional property required is the reliability function. Thus either parametric or nonparametric estimates of reliability can be used in the solution. The nonparametric solution is appealing in the case of a combined burn-in and replacement policy because the U shaped failure rate makes parametric estimation of reliability difficult.     

Minimizing cost-functions related to both burn-in and field-operation under a generalized model

Summary and Conclusions-Burn-in is a method used to improve the quality of products. In field operation, only those units which survived the burn-in procedure will be used. This paper considers various additive cost structures related to both burn-in procedure and field operation under a general failure model. The general failure model includes two types of failures. Type I (minor) failure is removed by a minimal repair, whereas type II failure (catastrophic failure) is removed only by a complete repair (replacement). We introduce the following cost structures: (i) the expenses incurred until the first unit surviving burn-in is obtained; (ii) the minimal repair costs incurred over the life of the unit during field use; and (iii) either the gain proportional to the mean life of the unit in field operation or the expenditure due to replacement at a catastrophic failure during field operation. We also assume that, before undergoing the burn-in procedure, the unit has a bathtub-shaped failure rate function with change points t/sub 1/ & t/sub 2/. The optimal burn-in time b/sup */ for minimizing the cost function is demonstrated to be always less than t/sub 1/. Furthermore, a large initial failure rate is shown to justify burn-in, i.e. b/sup */>0. A numerical example is presented.     

一种星载电子产品老练试验加速因子估计方法

提出一种基于可靠性预计数据的星载电子产品老练试验加速因子的估计方法。在该方法中,温度对产品失效过程的影响通过器件失效率预计模型中的温度应力参数予以刻画。通过比较产品在工作环境温度与老练试验温度下的预计失效率数据来估计老练试验加速因子。该方法简单、易行,含义明确,有望增强可靠性评估结果与可靠性预计结果的可比性。     

Benefits of Integrated-Circuit Burn-In to Obtain High Reliability Parts

The technique of integrated circuit (IC) burn-in is applied industry-wide with the assumption that burned-in ICs have a much lower failure rate during operating life than ICs which are not burned-in. Several years ago this approach was valid for all ICs, but today burn-in procedures for some ICs provide little, if any, benefit. However, some customers still request burned-in ICs, assuming that this will produce better reliability. This paper provides historical data for linear ICs and presents a procedure to help the user determine if burn-in is worthwhile. An example for linear ICs where minimum benefit produced from burn-in is provided. By repeating this exercise with any other parts, the user can decide whether burn-in will decrease the failure rate appreciably for his application. This article deals specifically with decreases in failure rates through burn-in. It is not within the scope of this paper to describe general factors that could decrease failure rates.