Design for excellence – shortly DFX – encompasses methods, design guidelines and checklists for the improvement of products and processes which can lower costs in several phases of the product lifecycle.
DFX, Design for Excellence, includes methods, design guidelines and checklists for product and process improvements which can offer decisive cost benefits in different phases of the product life cycle. Some motivating factors to use DFX include an optimum time-to-market, optimized test coverage and error diagnosis, minimal test costs and new investments as well as the ability to reach the profit zone more quickly.
The simultaneous approach – to already implement DFX aspects in product development and to take into account the accompanying production and test solution right in the early test phase is one of the core points of DFX. In Fig 1, the traditional product launch, with a separate, sequential process for design and process development is shown (red curve, without DFX). With the approach of analyzing DFX and product development simultaneously (blue curve), an earlier market launch is achieved and the profit zone is reached earlier as well. These correlations and model examples of different DFX disciplines should be illustrated below.
DFT – Design for Testing: Communication is essential
Like in every success story, the application of Design for Testing requires rules and the earliest possible and cooperative communication of the players, in this case product development and test engineering. Here the ideal time is the early design phase of a new product or the start of a redesign or a cost reduction cycle for an existing product. The CAD product data container serves as the input variable for the analysis. Some DFT checklists can already be applied data like in a circuit diagrams or in an initial layout. In principle, an analysis can already be performed on a block diagram level and feedback can already be provided in terms of testability aspects.
The checklists are the "DFT chapter" for the test engineers and include the proven solutions with many test challenges and the widest range of product approaches. Improvement points are added to the early design documents and product requirements where such things as minimum distances for test points to components, a fast and seamless on-board program sequence and the reduction of external equipment through self-testing features offer a gain for end customers, also in field applications.
Due to this early coordination, the specialists involved know the project-specific requirements and technical framework conditions and create an optimum for test coverage in this scope through the appropriate technical measures.
DFT analysis: How to choose the best possible test concept
The DFT analysis shows the selection of the optimum test concept. Here additional key parameters of the project are integrated into the process such as annual and lifetime count, product complexity and market (industry, automotive, medicine, etc.), embedded programming and software download strategy, material costs, repair strategy, rejection costs etc.
The initial input variables of the tool-based DFT analysis are formed by the CAD product data container. The second variable describes the process characteristics of the individual production location. This characteristic includes a minimized error frequency in the assembly process and the implemented error detection capabilities such as paste AOI and X-ray inspection - in terms of the component housing forms and component types (IC's, resistors, condensers, diodes etc.).
Through several iteration cycles with deviating test process configurations, the optimum test product can be simulated for a product. The calculated drop, which must be calculated from the next step, is listed for every process step. This is of interest particularly for the development of the functional test systems in order to especially close the calculated test coverage gaps and to simultaneously implement any dual review which may be required, only in the desired scope.
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