Overview

There are many issues that need to be considered in any system design. What I hope I have been able to highlight is the need to consider the subject holistically, taking the widest possible view of a "system." Personally, I would include the materials supply and any downstream processes into my holistic view. The reason for this is that the substrate and any pretreatments can affect the process and the resultant product. Also variations in the process, although they may produce a product within a desired specification, may also generate variations in any downstream process. If the following downstream process is to be carried out by a customer, you may or may not, know of all their problems and so believe that the product is consistent and reproducible, even when it is not.

I am sure that many of us have suffered from a supplier changing their manufacturing process and not disclosing the fact. Nominally, the product meets the same specification and so it is deemed not necessary to inform customers of the changes. However, it is sometimes the case that some of the required functionality of the substrate may never have been described in the specification. This requirement may only come to light once the changes in the manufacturing process have changed this functionality and been highlighted as a problem in the vacuum deposition process.

If we are not to fall into this trap, we need to understand the processes both upstream and downstream of our own process...