来几个资料关于Bathtub Curve的介绍。
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Region (I) 被称为早夭期（Infancy period）
这个阶段产品的 failure rate 快速下降，造成失效的原因在于IC设计和生产过程中的缺陷；
Region (II) 被称为使用期（Useful life period）在这个阶段产品的failure rate保持稳定，失效的原因往往是随机的，比如温度变化等等；
Region (III) 被称为磨耗期（Wear-Out period）
在这个阶段failure rate 会快速升高，失效的原因就是产品的长期使用所造成的老化等。
认识了典型IC产品的生命周期，我们就可以看到，Reliability的问题就是要力图将处于早夭期failure的产品去除并估算其良率，预计产品的使用期，并且找到failure的原因，尤其是在IC生产，封装，存储等方面出现的问题所造成的失效原因。
david_zw at 2009-6-18 18:59:01先来几个资料关于Bathtub Curve的介绍。
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Figure 3 shows that the curve follows a classic bathtub shape [9] (although this is a generalization). The curve consists of three distinct regions: Early Life, Useful Life, and Wear-out. Each region is characterized separately with potential failures classified as quality failures, random failures, and wear-out failures, respectively.
The early life failures can be process related, such as defect-induced, and would be characterized by a decreasing failure rate. The wear-out failures, on the other hand, are inherent process limitations and are generally well characterized before process release. These failures would be due to oxide wear-out, electromigration, and hot electron effects, all of which limit the life of the product. They generally have an increasing failure rate. Random failures occur for a variety of reasons and usually account for only
a very small number of failures. They are characterized by a constant failure rate. The ideal shape to the curve is to have a very long useful life period and a low amount of quality defects.
david_zw at 2009-6-18 19:01:41先来几个资料关于Bathtub Curve的介绍。
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"Initial failures" are considered to occur when a latent defect is formed, for example, during the device production process and then becomes manifest under the stress of operation. For example, a defect can be formed by having tiny particles in a chip in the production process, resulting in a device failure later. The failure rate tends to decrease with time because only devices having latent defects will fail, and these devices are gradually removed.
"Random failures" occur once devices having latent defects have already failed and been removed. In this period, the remaining high-quality devices operate stably. The failures that occur during this period can usually be attributed to randomly occurring excessive stress, such as power surges, and software errors. This group also includes devices susceptible to remains of initial failures (long-life failures).
"Wear-out failures" occur due to the aging of devices from wear and fatigue. The failure rate tends to increase rapidly in this period. Semiconductor devices are therefore designed so that wear-out failures will not occur during their guaranteed lifetime.
Accordingly, for the production of highly reliable semiconductor devices, it is important to reduce the initial failure rate to ensure the long life, or durability against wear-out failures.
To reduce the initial failure rate and thereby improve reliability, Renesas has implemented
advanced quality controls and quality improvement activities as well as screening procedures, including electrical characteristics testing and burn-in tests. Furthermore, to provide the necessary product durability for the service life of products, the company has been building in reliability starting with the design and development stages. In addition, it carries out reliability design, design review, and other activities to ensure reliability, and also conducts reliability testing.
