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While “Design for Manufacture” (DFM) tools have been an ongoing innovation in the electronic design automation and computer-aided design sectors of the electronics industry, they have surprisingly not enjoyed such prevalence with their close relative, printed circuit board design. DFM technology has only recently become a critical component in a PCB’s design to manufacturing process. Previously, designers were forced to make underinformed decisions resulting in significant rework and missed market opportunities. New DFM methodology helps designers incorporate manufacturing knowledge during the initial design process, preventing, or minimizing,yield issues while saving time and money. The role of DFM DFM is about creating the detailed documentation necessary to deliver accurate, easily reproducible end products. More specifically, it means hitting the center of your allowed process windows so a process deviation does not end up hurting yield. In a recent industry white paper, semiconductor software firm Synopsys made the following observations: Design for manufacturing is about connections … connections within the design flow; connections within the manufacturing flow; and most importantly, connections between designand manufacturing. These connections are required to address fundamental issues associated with yield loss intoday’s leading edge products and are key to a robust DFMsolution. Figure 1 illustrates this point: 
A project’s ultimate process window is the intersection of all process windows in a design to manufacturing flow. Major misalignments are the fault of missed connections throughout the process, resulting in poor yields and necessary redesign. When DFM is not involved throughout the design to manufacturing process, end products have a much higher rate of failure due to yield issues. The intent of DFM is to minimize these issues before they materialize. Yield issues are summarized by the following types of failure and the likely place of occurrence within a two-by-two matrixshown in figure 2: 
• Catastrophic – board design is non-functional • Parametric – board functions, but does not perform to specification • Systemic – functionality does not work as planned in a consistent and reproducible way • Statistical – failures are seemingly random or does not correlate to another condition Design teams are increasingly looking to DFM tools as a methodology to 1) capture and describe these process window relationships, 2) compare these relationships to their designs in quantifiable ways, and 3) report this information back to the designer so they can reduce oreliminate specific yield issues. Shift in methodology PCB Design tools have been available on the market almost since the dawn of the CAD/EDA industry. The exact emergence of PCB design rule check and DFM tools differs upon what tools are included, but it is the general consensus that DFM checkers for PCBs were available in the later 1980’s. The DFM tools’ ultimate role of providing a continuous feedback loop for the engineering team is a job that human can no longer execute utilizing only older DFM methods. Current design complexities, shorter design cycles and increased levels of outsourcing have forced a shift in DFM methodology. As a result, three major implementation styles for DFM tools have emerged: standalone tools, Webbased tools, and interactive tools. • Standalone client Installed directly to the user’s PC or network, a standalone tool’s architecture parallels the traditional batchrun tools feeding two main input files, the design artwork and the rules specifications against which to check. As illustrated in figure 3 standalone tools tend to fit in at the end of the design flow, when the PCB is almost complete. Errors are then reported in a text based report, with an optional graphical overlay of some fashion identifying what can be expected to be a large number of design violations, warnings, and suggestions. Design teams then employ any number of strategies to manage the information returned. • Web based tools Web based tools can have a variety of implementation styles, mainly batch oriented, but with varying levels of interaction with the user. Web based batch: accessed through an email connection, users send their Gerber files to a tool operator who runs the check with a rule deck they maintain. The tool operator then sends an error report back to the user. Much like the old process of handing Formula Translation Language (FORTRAN) card decks to a mainframe computer center operator; this process is not ideal. Web based interactive: users install a client application on their local computer to perform DFM checks against a web server’s definitions and the files maintained by the tool operator. Each check begins by a query and possibly a download of the latest version of the user specified rule deck. ASP model: users upload their design files, select the process definitions to use for verification, and execute the verification on the server’s CPU accesses via a browser. New functionality is distributed immediately to all users of the tool. Currently, no web based interactive tools areavailable. 
• Interactive tools
Because the cost of fixing a design flaw increases in geometric proportion to how late in the design cycle the flaw is identified, it is safe to say errors found early are cheaper to fix. It is this very thinking that drives the development of interactive DFM tools to give engineers insight into how their design choices will impact yields and therefore enable them to make more robust design decisions or, at least, perform well calculated risks (figure 4). An interactive solution contains a checker engine or executable, directly accessible from the editing tool running in real time, or functioning as a command explicitly invoked as needed. Checker engines are a general purpose tool, using a parameter file, more commonly referred to as a rule deck, to define the specifics for a process. Interactive DFM tools reside on the client work station insulating the user Figure 3: Design process flow utilizing back end standalone DFM tools. from Internet fiascos but limiting the amount of accessible data storage. Database content is managed through either a client-resident tool or a hosted database depending on thenature of the content. 
Looking ahead Recognizing the importance of DFM tools in respect to the designers that use their software and their manufacturing partners, Sunstone Circuits recently pioneered an interactive rule deck approach. The company collaborated with Cadsoft and Altium to provide DFM rule decks that accurately and completely implement Sunstone’s design rules. Designers load the rule decks onto their CAD systems and design directly to Sunstone’s manufacturing processes. This has enabled them to focus on more critical aspects of their design, reducing manufacturing difficulties during downstream assembly processes and yield issues. As tools continue to develop, Sunstone expects DFM’s current boundaries to expand for inclusion of more sophisticated checks and availability of part-specific lifecycle information within the design process in innovative ways. PCB designers are innovators, and DFM tools allow them to capitalize on alternative approaches and experimentation. It is only a matter of time before another valuable innovationis discovered in part due to the guidance of DFM tools. | 
