Constraints imposed on the tasks and resources required to implement them are essential for executing the tasks mentioned. Semiconductor process engineers face the unique challenge chemical engineering dictionary pdf transforming raw materials into high-tech devices. To produce these and other semiconductor devices, semiconductor process engineers rely heavily on interconnected physical and chemical processes. A prominent example of these combined processes is the use of ultra-violet photo-lithography which is then followed by wet etching, the process of creating an IC pattern that is transferred onto an organic coating and etched onto the underlying semiconductor chip.
Process Engineers are generally involved in the development, scaling, and quality control of new semiconductor processes from lab bench to manufacturing floor. The CPRET representation integrates the process Mission and Environment in order to offer an external standpoint. Note: process definition and modeling are interdependent notions but different the one from the other. Natural conditions and external factors impacting a process. Purpose of the process tailored to a given environment.
This definition requires a process description to include the Constraints, Products, Resources, Input Elements and Transformations. Imposed conditions, rules or regulations. All whatever is generated by transformations. Human resources, energy, time and other means required to carry out the transformations. Elements submitted to transformations for producing the products. Operations organized according to a logic aimed at optimizing the attainment of specific products from the input elements, with the allocated resources and on compliance with the imposed constraints.
The purpose of the following examples is to illustrate the definitions with concrete cases. These examples come from the Engineering field but also from other fields to show that the CPRET definition of processes is not limited to the System Engineering context. The CPRET formalized definition systematically addresses the input Elements, Transformations, and Products but also the other essential components of a Process, namely the Constraints and Resources. Among the resources, note the specificity of the Resource-Time component which passes inexorably and irreversibly, with problems of synchronization and sequencing. This definition states that environment is an external factor which cannot be avoided: as a matter of fact, a process is always interdependent with other phenomena including other processes. This page was last edited on 6 March 2017, at 06:04. Steam and liquid water are two different forms of the same chemical substance, water.
It cannot be separated into components by physical separation methods, i. However, in practice, no substance is entirely pure, and chemical purity is specified according to the intended use of the chemical. UV light, showing how the chemical interacts dynamically with its solvent environment. In law, “chemical substances” may include both pure substances and mixtures with a defined composition or manufacturing process. Therefore, although the exact chemical identity is unknown, identification can be made to a sufficient accuracy. The CAS index also includes mixtures. However, there are some controversies regarding this definition mainly because the large number of chemical substances reported in chemistry literature need to be indexed.