I. Overview

In recent years, due to the rapid development of science and technology, the unqualified rate of products quickly decreases, such as electronics' failure rate was down to one thousandth part per million (ppm ,10-6 ) even a billionth of a (ppb ,10-9) from one percent in the past. Quality control way evolved to 6s control from 3s in the past. The unqualified rate under the steady-state of 3s control is 2.7 * 10-3 (0.27%), while under 6s is only 2.0 * 10-9 (two per 1 billion), refer to Figure 1. (Omit) This is the ultra-stringent quality requirements in the 21st century. As a result, a well-known expert in quality control of the United States Juran pointed out at the annual meeting of Quality Management Society in the United States as early as 1994: "The 21st century is the century of quality."

As we all know, implementation of the precautionary principle is the core of modern quality management and the essence. On such strict quality requirements, what kind of scientific methods to implement the precautionary principle and ensure that quality policy and objectives to be realized? This will refer to "SPC", "SPD" and "SPA".

II. What is SPC, SPD and SPA?

1. SPC
SPC is Statistical Process Control, first created in the 1920s by the United States Shewhart. SPC is the use of statistical techniques to monitor all stages in the process and find abnormal process, warn in a timely manner, so as to achieve quality assurance. The statistics generally refers to any technology can be applied to the mathematical statistical methods to control and map-based theory. However, SPC has its historical limitations, it can not tell what this unusual factors, where they took place, that can not be diagnosed, but it is an urgent need to diagnose the problem at the scene, or even there is no point to correct the abnormal.

2. SPD
SPD is Statistical Process Diagnosis first introduced in the 1980s by China's quality control expert Zhang Gongxu. In 1980, Zhang Gongxu put forward plans to elected control series. It is an important tool for the statistical diagnosis theory, laid the theoretical basis of statistical diagnosis. In 1982, Zhang Gongxu also put forward " two types of quality diagnostic theory", broke the traditional Shewhart quality control theory, opening up a new course for the quality of diagnosis. Since then, China has made "multiple diagnosis theory" and " two types of quality multi-diagnosis theory" to solve the multi-process, multi-indicator system of quality control and quality of diagnosis of the problem. Since then, SPC is up for SPD. SPD technology is the use of statistics to monitor and diagnose on the various stages of the process in order to shorten the abnormal diagnosis time, in order to take prompt corrective measures to reduce losses, reduce costs and ensure product quality. At present, on the basis of the above theory we have developed two kinds of diagnostic softwares. One is the application software SPCD2000 based on "two kinds of quality diagnosis theory", for the diagnosis of multi-process production lines of the processes; and the other is multiple diagnostic software DTTQ2000 based on "multiple diagnosis theory" and " two kinds of quality multi-diagnosis theory ", for the more relevant factors under the conditions of the diagnosis. At the same time, the latter also takes into account the influence of one process for the next process.