Page 164 - Six Sigma for electronics design and manufacturing

Chapter
5
The Use of Six Sigma
with High- and Low-Volume
Products and Processes

One of the concerns about using six sigma is the volume of production.
There are two parts to this concern. The immediate reaction is that the
3.4 PPM defect rate associated with six sigma might imply that the vol-
ume of production has to be very large in order to properly assess this
high level of quality. The other concern is that the tools of six sigma
used for quality control and defect rate prediction might not apply be-
cause of the difficulty of properly obtaining statistical information such
as the standard deviation of the manufacturing variability of the pro-
duction process. Low-volume industries including defense, aerospace,
and medical, as well as their suppliers, share these concerns.
Several statistical tools will be discussed in this chapter in order to
allow for the use of six sigma in low-production environments, with
minimum uncertainties. They are based on sampling theory and dis-
tribution, and the relationships between samples and populations.
These tools are:

1. Process average and standard deviation calculations for samples
and populations. Section 5.1 will discuss the sample probability
distribution and its relationship to the parent population distribu-
tion. It gives examples of determining population standard devia-
tion and error based on sample sizes.
2. Determining process capability. Section 5.2 will discuss the
amount of data required to properly determine process capability.

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