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26 The PCB Design Magazine • September 2017 far too overdesigned' and complex, thus adding a lot of unnecessary costs and complexity. The D&B DFM/A methodology was used concurrently with the physical design to point out complexities and provided feedback on how to simplify. It was also used to benchmark competitor's products. The DFM/A method- ology was focused on "Doing it right the first time." This was not a design rule checker, and a lot more useful than "best practices," although these are useful tools. This is where I get my definition of DFM or DFX. CAM software, including DRCs, are activi- ties that take place after the design is finished. We found one EDA supplier, Zuken, that had "design advisor" software for signal integrity, which they gained when they acquired Racal- Redac. This software resided on the screen and provided real-time feedback on SI as they rout- ed traces by taking variables from the database and doing a real-time simulation. Metrics are an important part of DFX, and D&B created some very useful ones. But we had to develop metrics for the PCB (complexity in- dex, density, connections/sq. inch, wiring capa- bility), PC design (layout efficiency, routability index, wiring demand, first pass yield), and SMT assembly (average leads/sq. inch). We were focused on taking manufacturing performance in fab and assembly, and feeding this data back to design and layout. This data would then drive the predictive tools advising designers on best practices and what-to-do- next. As design's horizon is very short com- pared to the life of a product. This data had to reside in the product data management (PDM) enterprise software and not in the EDA tools. Like the D&B methodology, the key attribute was "predictive metrics and models" powered by real manufacturing performance. Thus, predictive engineering or Design for Competitive Advantage (DFCA) emerged as a better definition of DFM or DFX, because every- one was using the term DFM to refer to design rule checks, which occur after the fact and are not predictive. To support this predictive arena for PCB and assemblies, we developed eight processes: 1. The DFM Manual: A design document that provided: 1. Electrical performance, mate- Design Managers Design Engineers Manufacturing Engineers Quality Assurance Personnel PC Layout/ Drafters Manufacturability Objectives Analysis Calculate Score (METRICS) Evaluate Opportunities Brainstorm Select Approach & Execute Parts List Process Requirements Assembly Motions Mfg. Capability Iterate Figure 1: Dewhurst & Boothroyd DFMA software. Figure 2: The benefits of metrics as a common design language. Figure 3: The process to develop a manufactur- ability metric as a substitute for opinions. THE HISTORY OF PREDICTIVE ENGINEERING

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