We Are in the Field of PCB Manufacturing and Are Using About 800 Components. How Should We Decide the Opportunities During Calculation of Sigma Value?

Simply stated, an opportunity is merely a set of conditions favorable to some end. In view of the two possible fates of a (critical to quality) CTQ – success or failure – we have the idea of a yield opportunity and that of a defect opportunity. Since one is merely the flip side of the other (as they are mutually exclusive), we choose most frequently to use the form defect opportunity in recognition of certain quality conventions.

From an industrial or commercial perspective, the set of conditions just mentioned can be associated with a set of performance standards.  For example, we can offer a set of performance standards in the form of a range, often given as LSL < T < USL. In this form, a potential opportunity can be fully described by the relation Op = f (LSL, T, USL), where Op is the potential opportunity, LSL is the lower specification limit, T is the target value (nominal specification) and USL is the upper specification limit. In addition, the operational condition of the corresponding process distribution (defined by the mean and standard deviation) must be made known or rationally estimated, and then mated or otherwise contrasted to the performance specifications so as to place the opportunity in a kinetic state.

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Thus, a kinetic opportunity can be fully prescribed by the simple relation Ok = f (LSL, T, USL, m, s), where m  is the corresponding process mean, and s is the standard deviation of the corresponding process. Essentially, this relation infers that a kinetic opportunity can only be created when these five key factors are mechanistically interacted or otherwise interrelated in real time and space. From a different angle, we can say that a kinetic opportunity can be brought forth into real time and space only when the performance specification of a given design feature is married or otherwise operationally mated to its corresponding process capability (process distribution). Only then can a probability of success or failure be rationally estimated, declared or consequentially established.

It should go without saying that if any of the underlying conditions are fully absent, unknown or not established, a kinetic opportunity cannot be declared. However, a potential opportunity can be acknowledged. For example, if the performance specifications USL, T and LSL do in fact exist, but the corresponding mean and standard deviation are both unknown or have not been empirically estimated and made relational to the specifications, then the opportunity would only exist in a potential state. As a result, it would not be possible to estimate the probability of a nonconformance to standard. In other words, if an opportunity does not kinetically exist in real time and space, it should not be counted among those that do exist (for reporting purposes).

On the other hand, if the opportunity is kinetic, but the performance is not regularly assessed or otherwise measured and reported, the opportunity would be declared as passive in nature. Consequently, it should not be included among those opportunities that are active by nature (regularly measured and reported). Thus, we have the operational guideline that says: a defect opportunity should only be counted if it is regularly assessed (measured in terms of conformance to standards) and subsequently reported for purposes of quality management. This is to say the opportunity must not only be kinetic, it must be active as well.