Batching plays an important role in semiconductor fabs, and it can lead to inefficiency if not treated with care. The performance of parallel batch processes is often approximated by the G/G/1-based approximate models. By carefully examining the existing models, the dependence between queueing time and wait-to-batch time has been identified. A new improved model for parallel batch systems is proposed to exploit this dependence. The computation of the new model is still simple and fast, but it gives better approximation by reducing the systematic error in earlier models which ignored the dependence between queueing time and wait-to-batch time.

We present an analytical approach for estimating the expected time for an automated material handling system (AMHS) to respond to move requests at loading stations in a vehicle-based, unidirectional, closed-loop AMHS. The expected response times are important for estimating the expected work-in-process (WIP) levels at the loading stations for design purposes, and for evaluating the performance of the AMHS as delayed response can impact the production cycle times. The expected response time approximation is validated by comparing the analytical model to the simulation results using a SEMATECH 300 mm hypothetical fab data set. Note to Practitioners - This paper describes an analytic method for estimating the average time for the AMHS to respond to lots ready for movement in a 300 mm wafer fab. The analysis is based on a large-scale model, requires standard solvers, and provides a very fast and reasonably accurate alternative to high-fidelity simulation. It is intended to support the early stage of fab design/redesign, allowing engineers to examine many different options before committing to the time and expense of simulation.

As the effective deployment of system production capacity and operational capability becomes critical for competitive semiconductor manufacturing, there is an increasing interest toward the development of a control framework which allows effective and efficient operation of the emerging 300 mm wafer fabs. In the paper, a colored Petri net-based approach is taken to develop such a distributed event-driven 300 mm fab controller. The key element of the proposed controller design is the distribution of control function, to the constituent components of the 300 mm fab, while maintaining the logical correctness and efficiency of the fab behavior. Furthermore, in order to achieve the viability of the resulting control scheme, the proposed approach seeks to incorporate detailed operational characteristics of the 300 mm fabs, including batching, setups, reworks, maintenance, machine failures, and complex resource allocation dynamics due to the routing flexibility and auxiliary resource sharing. The proposed approach is demonstrated through a small-scale example, modeling the operation of a 300 mm fab bay.

Semiconductor fabs are capital intensive. The rate of capital return heavily depends on their productivity. Accordingly, simulation has been adopted in many cases as a viable design and analysis tool to achieve better productivity. However, the gap between the simplistic simulation models and real complex systems has limited the confidence to apply simulation results directly to real systems. Ideally, the simulator should support the rapid modeling and fast execution of high-fidelity fab models in order to be able to provide more realistic simulation results. In this paper, we present our current research effort to develop a high-fidelity web-based simulator for the 300 mm wafer fabs. We take a model-view-control approach that allows us to develop modular and reusable fab simulation objects. The proposed approach is implemented as a distributed system that uses a message-based event synchronization mechanism to coordinate the simulation objects as well as to support distributed simulation execution. The presented simulator also provides a high quality VRML animation for visualization of real time paced simulation execution.

An ideal warehousing and distribution system has no inventory and operates with minimal handling. In an attempt to achieve this ideal, expert designers rely on their intuition, together with analytical models and procedures formalized over years of experience. Understanding the processes that experts employ to realize their designs can have great benefits, for instance, in developing computational tools to assist in design. We have conducted an ethnographic study of an expert design team during actual system design. In this paper, we describe our observations and a process model of design.

Design of warehousing and distribution systems is more an art than a science that reflects the cultures of particular design teams. Warehouses are often designed and operated by third party logistics companies with tight margins. Therefore, there is increased pressure to design warehouses that are flexible and adaptable, even while the available information is incomplete. Also, designers lack coherent and explicit models of information and function flow. The primary goal of the research discussed is to lay the foundation for developing such models. Working closely with expert designers, we have identified the key pieces of information and organized them in the form of an object model. Using this model, it should eventually be possible to provide relevant information to designers via context-sensitive (or 'ecological' or 'intelligent') displays. Upon further development, the model will be incorporated into an interactive system to assist in design. The authors describe the object model, and outline plans for implementing a design system.

Even though the methodologies for warehouse design are taught in traditional industrial engineering programs, students often find it difficult to develop the skills necessary to complete actual designs. The difficulty in translating the textbook knowledge of using the analytical and mathematical tools for design stem from their lack of experience in using such tools for designing warehouses of reasonable levels of fidelity compared to real systems. It is often very difficult to incorporate large datasets and the computational algorithms necessary during the different phases of warehouse design into the course material. As part of a larger research effort to develop a comprehensive collection of online teaching materials integrated into the undergraduate and graduate curricula, we have developed a warehouse design tutor in which additional functionality is constantly being added. Certain key details of the tutor are discussed in this paper.

A manufacturing facility can be viewed as a material flow network in which each node represents a delay (either for storage, transformation, or testing), and each arc represents a transport operation (which also may involve a significant delay). The loads on this material flow network result from the interaction of bills of materials, process plans, and production schedules, and are constrained by the capacities of the nodes and arcs. Efforts toward rapid prototyping have focussed on the specification of the material flow network, in particular, the selection of both processing and handling equipment and the layout of the facility. This work begins with the development of an engineering workstation environment for specifying automated guided vehicle system applications. This workstation employs AutoCad for creating the basic facility description, and for creating and modifying the configuration of the material handling system. By carefully defining blocks in the CAD system, it is possible to extract and post-process information about the design and certain constraints so that it is accessible to analytic routines outside the CAD package. The menu structure has been customized to make all the analysis and design routines accessible through the CAD menu.>

A method for performing preliminary, or rough-cut, design and analysis of automated guided vehicle (AGV) systems in which a large number of alternatives can be examined is described. The procedures are based on analytic models and are combined into an integrated engineering workstation environment. Also included in the workstation is a simulation/animation module which is used after the preliminary analysis is performed. The resulting system allows a complete study of an AGV system to be accomplished.>

A work flow control method is described for use in a flexible cell with limited buffer space where the objective is to maximize throughput rate in a stochastic environment. Control decisions are made at discrete points in time, using a linear programming-based optimization model. The proposed methodology has been compared to recently published methods using a hypothetical cell.

The concepts of flexible manufacturing are increasingly being applied within the electronics industry, particularly in the assembly of printed circuit boards. This paper discusses a class of problems which blur the traditional distinction between design and operation. Additionally, examples and solution methodologies are given for the class of problems under two distinct operating policies.