March, 2014
www.us-tech.com
Guidelines for Ensuring PCB Manufacturability
By Nolan Johnson, CAD/EDA Manager, Sunstone Circuits, Inc., Mulino, OR
although modern circuit boards are being asked to deliver more perform- ance and more functionality in small- er and smaller pieces of real estate. The need for smaller, more-complex circuit boards for smartphones, com- puter tablets, and other hand-held electronic devices continues to grow and drive the need for smaller and more highly integrated PCBs. As a result, the use of Design for Manu- facturability (DFM) plays a more important role than ever in the elec- tronic production process. With the continued miniaturization of prod- ucts, many designs push the physi- cal limits of PCB manufacturability, inviting poor performance or even failure. But by following some straightforward guidelines, it is pos- sible to apply DFM methods to in- crease the manufacturability of even these smaller, more complex circuit boards. Addressing the issue of design
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tools early in a manufacturing process can help to prevent manu- facturability problems. The use of DFM plans ahead for the manufac- turing process, considering yield and other manufacturing issues that affect cost and quality. Designers can use multiple de-
sign tool types to create DFM-opti- mized designs. Each tool type is best suited to a particular usage. When usage requirements call for the best performance with the most thor- ough rule checking, standalone DFM tools are generally preferred since these tools offer the most ex- tensive capabilities for finding DFM rule-set violations. Unfortunately, such back-end tools can also form bottlenecks that slow manufactur- ing processes. When use require- ments call for the most efficient de- sign process, interactive DFM tools provide increased efficiency, al- though using such tools can also in- terrupt the design process. Interac- tive DFM tools provide insight into how to design for improved yield or manufacturability, helping design- ers to make more robust design de- cisions.
Back-End DFM Tools For a process that does not em-
ploy a real-time DFM tool, integrat- ing a back-end DFM tool into the de- sign workflow can be a benefit. A back-end tool can identify what’s ex- pected to be a large number of de- sign violations, warnings, and sug- gestions. To manage the informa- tion that is returned from a back- end tool, three common processes are available. The first option involves the use
of fewer full-functionality, full-design checking runs and longer result-re- view phases. Such an approach is thorough and identifies more produc- tion errors overall, but can still suffer the risk of missing a critical error. The second option involves running full-functionality check on portions of a design, with one full-design check at the end of a run for a final check.
See at APEX, Booth 2285
ules for designing printed-cir- cuit boards (PCBs) have changed little over the years,
This approach is commonly used for reviewing modular designs, although the technique is less comprehensive
involves the use of more review itera- tions using focused-functionality runs, with more short design reviews.
Use of Design for Manufacturability (DFM) plays a more important role than ever in the electronic production process as continued miniaturization of products pushes the physical limits of PCB manufacturability.
than the first approach and can miss errors and violations. The first option
This third option is the most effective approach of the three options, offering
just-in-time rule checking and mini- mizing chances of performing rework on a design. Even for a design process that
has been built around a DFM philos- ophy, pitfalls can occur. By better un- derstanding these potential process problems, they can be overcome and invaluable process time can be saved. For example, a common process prob- lem is poor communication with a
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