Printed Circuit Design & Fab - December 2007 - (Page 41)

TABLE 1. Common implementation strategies for DfM tools. STRENGTHS Standalone Application Machine local Might support multiple manufacturers Tool is always synched to correct DFM rules Close fab to rules association No additional money spent for tools Comes with your PCB design tool General purpose: can support multiple DFM sets More manageable reporting of spurious errors Certified by fab Interactive feedback during design WEAKNESSES Version mismatches in the field Requires software maintenance charges Too many spurious errors No Internet? No tool Too many spurious errors Inconsistent pricing models among providers Low fab to rules association Engineer writes own deck for each PCB fab Rules are only as good as the engineer writing them Rules only as detailed as the CAD tool/s DRC engine Web-based tool DRC Rule Engine Fab-supplied CAD Tool DRC rule deck systems go astray; these systems miss the opportunity to make meaningful design flow connections. The intent of DfM is to help engineers prevent or minimize the yield issues before they materialize. It’s easy to summarize sub-categories of failures and their likely place of occurrence. Manufacturing yield issues can be categorized into four combinations (FIGURE 3): Catastrophic vs. Parametric ■ Catastrophic – board design is nonfunctional ■ Parametric – board functions, but doesn’t perform to specification. Systemic vs. Statistical ■ Systemic – functionality does not work as planned in a consistent and reproducible way ■ Statistical – failures are seemingly random or do not correlate to another condition. The Standalone Conundrum Throughout the process of writing this article, a common opinion emerged that the standalone PCB DfM tools currently in wide availability work more like pre-engineering design validation tools than they do as an interactive resource for in-design decision-making. Given the pricing for these standalone DfM tools, it’s also clear that software companies are not aiming to sell their tools to the typical designer. Depending on features and installations, some standalone ftools can run as much as $100,000 – an amount that many firms are simply unable to absorb. “The current tools are thorough, but not all that helpful to the overall design flow,” says Joe Zaccari, vice president at Stilwell-Baker, when asked about the current state of PCB DfM. DECEMBER 2007 “You don’t get a lot of value from a tool that just tells you what you did wrong after the design is completed. It is much more efficient to work with ongoing feedback. We get better design results, higher yields and shorter design cycles when we can engage a customer using interactive methods.” This leaves standalone DfM tool developers in a lurch: the tool’s high cost means that the overall target market is limited to well-capitalized companies with enough PCB fabrication volume to justify the expense – PCB fabrication shops. Because the market niche is so narrow, PCB DfM standalone tool developers are required to charge a lot for their tools to cover the expense of creating them. In fact, some PCB fabricators have begun offering to run low- or no-cost DfM on anyone’s design, with the expectation that the customer will then place the order with the fabricator and help defray the cost of operating the DfM tool in the first place. their designs to the service via e-mail or website, and the DfM service responds by e-mailing a report containing the DfM issues identified. “They’ve got the idea right, but the implementation is wrong,” says Stilwell-Baker’s Zaccari of the web-based tools. “This is like emailing your word document to a spell checker service so you can get a list of misspelled words in under an hour. It is extremely inefficient as it requires redesign of the board for reasons that should have been known upfront.” CAD Tools: A Simple Solution Often Overlooked In an e-mail interview, Ed Rodledo, general manager of CadSoft USA, the US subsidiary of CadSoft GmBH, and maker of Eagle PCB Layout said, “There is another way. Use the DRC engine already built into your CAD system. Any commercial-grade design tool will have a DRC/DfM engine built in. Define the manufacturing rules there, and design interactively to the DfM restrictions published by your fab of choice.” Robledo seems to have company with this thinking. “A number of CAD tools support the concept of DRC or DfM rules files,” says Nancy Viter, The Next Stage in DfM Evolution: Web-Based Tools Wisely, some vendors are developing DfM tools that target the end user. Generally speaking, these tools are taking a web-based service application service provider approach, such as the Free DfM service from Advanced Circuits or the recently announced Control Center XP from UK-based fabricators Direct Logix and Artetch Circuits. A web-based model has its advantages such as easy distribution of bug fixes and the potential to be software-independent. However, it falls short on its ability to integrate tightly into the design flow, particularly when users interact with the tool by submitting Schematic Design Layout Design DfM Manufacture FIGURE 2. Key components in the DfM equation. PRINTED CIRCUIT DESIGN & FAB 41

Table of Contents Feed for the Digital Edition of Printed Circuit Design & Fab - December 2007

Printed Circuit Design & Fab - December 2007 Contents Our Line Market Watch Around the World Happenings ROI 2007 PCB Designer Salary Survey Interconnect Strategies Positive Plating RF Design Ad Index Noise Reduction Supply Chain DfM Off the Shelf Marketplace The Signal Doctor

Printed Circuit Design & Fab - December 2007

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.