Specification management for the cost constraint optimisation in micro-electronic design Magali Mauchand1, Nicolas Perry2, Alain Bernard3 1.
[email protected] 2. IRCCyN - 1, rue de la Noë - BP 92 101 - 44321 Nantes CEDEX 03 –
[email protected] 3. IRCCyN - 1, rue de la Noë - BP 92 101 - 44321 Nantes CEDEX 03 –
[email protected]
ABSTRACT In preliminary design phase the integration of the economic constraints of a product is a hard engineering work since there is a real lack of dedicated tools. This article illustrates a specification software solution method making it possible to meet this need, applied to the micro-electronic field. 1 INTRODUCTION Needs for economic and technical product evaluation are compulsory in the design process. However methods for requirements expression used for apply integrated methods of costing are poorly developed on the market. In design it is essential to take relevant decisions and make a choice between several alternative solutions. It is crucial to emphasize the one that allows reaching the imposed objectives so much in term of cost, quality and time. Information and management systems must be developed in order to support the specification and so as to analyse the considered solutions. (Bachelet 1994, Perry 2003) The micro-electronic field is characteristic of firms said “fabless”, the design departments are located outside of the production sites and have few links with the latter. Also an operating mode must be set up in order to design circuits that should be feasible by the production line recommended for the manufacturing.
The main parameters of the life cycle of an electronic product of the public market are on the one hand its really short lifespan, on the other hand the very fast evolutions of technologies (shrink), and the last one the work requirements for phase lead (R&D). In electronics there are also systems at long lifespan such as the ones developed for military and aviation applications, etc. In these cases the design problem must include the system maintenance and allow a valorisation of the economic impact of decisions. (Riedel, 1999) Enterprises face the problematic of perpetual innovation with the renewal of technologies and world wide logistic integration to deliver customers all around the world. Consequently subcontracting capacities or competences became a common practice in micro-electronics. This article will illustrate these problems of specifications for the optimization of the costs constraints in micro-electronics design field, and more precisely the proposed method to approach these problems within the System Plus company. 2 MICRO-ELECTRONIC FIELD The aim of this article is to determine the bases on which decision-making tools can be built on to solve the economic problems which the designer faces without sufficient competences to answer it. The first step of this work is the generation of a cost estimate model. System Plus is a company that develop and edit software of cost estimation (costing) or sale price determination (pricing) in the micro-electronics field. It develops and/or sales four software solutions, which answer various aspects of the costing or pricing since the silicon wafer (microchips production) to the finished products (electronic boards). The description of a generic economic model used for the determination of the product industrial value is the goal of the thesis project carried out in collaboration between this company and IRCCyN. The experiment of micro-electronics parts, and more precisely the integrated circuits and the electronic boards, were highlighted by the development of software dedicated to these elements. It proves that this expert knowledge does not show through easily and "is hidden" within the heart of these applications. Software knowledge extraction and formalization is necessary to transcribe the infrastructure (basic elements) of the solutions (Du Preez 2005). They were tested and specified by experts of the technological field and experts in data processing. Obviously, this approach cannot be compared to the accounting method whose principal concern is the total result of the company. Here, the designer has to create a realizable (feasible) product and answering the whole of the technical specifications and constraints. Design is "the creative activity which consists in working out a project, or a part of the elements that compose it, on the basis of the expressed needs and means existing and technological possibilities with an aim of creating a product or a service" (GDT). All necessary information is available in order to establish a costing. But it remains to be able to put in adequacy their objectives with the costs of the product during its design. The distribution of the data-gathering sites (departments, services, continents) is a key-point approached in several writings such as those of Michael Wahl, (Whal and Al, 2000a - 2000b) who builds a cost model based on information. 3. CONSTRUCTION OF THE META-MODEL/CONCEPT
We promote, I and our research team, a common approach for facing knowledge-based engineering project illustrated in figure 1. The step of implementation, formalized in our methodology for the construction of models, is presented hereafter: Extraction Structuration Formalisation
Identification
Infrastructure Maintenance
Architecture Raffinement
Diffusion
Développement
Figure 1. Loop cycle of the integration step (Candlot et al., 2005) Let’s us first picture the background of the study. Four software solutions developed by company SYSTEM Plus are studied: 1. Virtual IC Fab is based on the simulation of a wafer fabrication plant in order to calculate its costs and its selling price. This software allows the creation of data bases to simulate a clean room. Its principal characteristics are: to be dedicated to the manufacture of wafer and the associated products (integrated circuits), supported by 3 key-fields in a company which are the knowledge of the production, the system of purchase and the design of the circuits. It carries out a simulation of the outputs and costs variations according to the parameter time, simulations of production costs calculations of the IC, simulations of the selling price according to the market fluctuations and creates a virtual wafer fabrication plant and calculates the wafer cost from real data. Moreover, a simulation on several levels of precision is realizable; it depends on the detail level of available information. 2. IC Puchaser is a computation software tool of costs and selling price estimate of integrated circuits. The cost calculations use parametric models extracted from analytical expertise. The passage from the costs to the selling prices is also based on parametric models. Thus, it has cost parameter generators, for example, an assistant of generation of manufacture technology like "Wafers", an assistant of cases generation. The Data base contains the following descriptive elements: technologies of wafer manufacture, encapsulation cases, wafer fabrication plants, component makers. The calculation carries out make it possible to follow the construction of the manufacturing costs and to have an estimate of the selling price. 3. SysCost aims to quantify with precision and speed the production cost of an electronic system (compound of a whole of boards or subsystems), to evaluate and control the costs of a project and to carry out a precise estimate. (Table 1) 4. WaCoFo is used to analyze and predict production costs of semiconductor technologies. It calculates a wafer cost over one defined period, based on the modelling of the manufacturing unit (Fabunit, Workshop, Workcenter description).
Table 1. Enters and outputs of the SysCost tool Inputs Flow, assembly schedules Bill Of Material (BOM) DB Purchases
Outputs Assembly and test costs Raw cost Manufacturing cost Selling price
We tried to tackle this problem with the search of a global model which would take into account all the concepts and rules which are in the existing software and making it possible to restore it. Methods of production costs modelling at the conceptual design stage were developed. In (Rehman and Al, 1998), a methodology implementing expert knowledge at production and design level is presented. Moreover, the studies undertaken in the field of the foundry can provide enrichments for the development step of the cost estimate model. (Delplace, 2004 and Perry and Al, 2004) First the meta-model; the first stage of the implemented methodology consists in the extraction of the cost estimate models from the tools. Then an abstraction phase leads to the construction of a meta-model common to the various solutions suggested by the company System Plus. The last phase consists in reinforcing the semantics contained in the meta-model to extend the application fields. The first methodological phase deals with the infrastructure modelling of System Plus applications; they integrate the very first constrained that were specified by the customers needs (first specification of the tools) and new concepts and models (each specific application make them integrating models whose aims varied from the original) (cf. table 2): - Cost calculation models configured within the software are parametric models or analytical models, - Models of production flows take into account different degrees of complexity, - Different scales of product (of the electronic chart to the chip), - Multi or mono products sites. Table 2. Studied software application characteristics Virtual IC Fab IC Purchaser Sys.Cost WaCoFo
Application field Semiconductor Semiconductor Electronic board Semiconductor
Cost method Analytic Parametric Analytic Analytic
Product scale Micro Micro and Multi Macro Micro
Enterprise Multi-products Mono-product Mono-product Multi-products
Flow structure Complex Complex Linear Complex
Thus the field infrastructure is consisted in the whole of the calculation methods contained in the software solutions and the attributes of the products in their context. Their formalization and their refinement make it possible to obtain the architecture of a more homogeneous and more complete cost model. The concepts of activity and process, entity and article, resources (material and human) and of course costs and selling price are a representative panel of the main extracted concepts. This list is not exhaustive. An interaction exists between the industrial concepts and the prospective scientific tools. Various scientific researches are concerned with the set of themes implemented here such as the management of production, the management control (Mévellec and Al, 1998 and 2000). In addition, it appears that concepts are employed in several tools without being directly
definable. The expert language masks the real semantics of the concepts. It is important to ensure coherence between the latter (as well as the models which represent them) mainly on the aspects of coverings the fields, constraints, contexts... It is essential to represent the bonds between the concepts. With this purpose, two aspects have to be approached: - a static approach (the concept definition and bonds formalization by a diagram of class), - a dynamic approach (the use of the concepts thought a sequence diagram or a SADT diagram). The integration phase concretizes the models and the concepts included in all the tools published by System Plus and makes it possible to confront the various partial approaches (realized by using a diagram of class). It is also necessary to take into account the processes of usage of these concepts and the calculation methods in the System Plus tools (such as for example a SADT diagram identifying the specific needs with each considered stage of the project life cycle). At this level a first methodological approach of deployment and use of the tool is formalized. In the second phase, the architecture development relies on a semantic analysis that enriches and consolidates the meta-model so as to make it independent of a particular industrial sector. In addition, the methodological step of suggested use is re-examined and enriched to be independent of a specific application. An experiment feedback and a confrontation with other industrial branches must make it possible to test its robustness. Interpretations of the final model are preconditioned by the fact that various methods and software tools were already developed. However they do not presuppose of the final development that remains to be defined. Thus, all the model development is carried out in interaction with the modelling of these various applications. The implementation of Architecture is thus closely related to the maturity of the comprehension of the Infrastructure. 4. CONCLUSION AND OUTLINES The steps presented in this article have a double objective: - To structure the models and the concepts handled in the various tools developed by the System Plus company, as well on the level of the cost models as on the level of the dataprocessing development, - To structure the meta-model of cost estimate of industrial products independently of its industrial branch. This study having begun after the development of the software applications supporting these problems, it benefits from this first generalization. The suggested methodological step, already tested, guides the construction of the implemented thesis postulate. The prospects for this work relate to two aspects: - On the one hand, to continue to confront general methodology proposed by a real case for improving it if necessary or judging its robustness, - In addition, to apply the general approach of modelling recommended in this work to various industrial sectors to identify the lacks and to consolidate the generic approach; the definition of indicators and their measurement remain to be realized. This can take place only by the identification of partners and real applications. REFERENCES 1
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