Printed Circuit Design & Fab - March 2009 - (Page 24) dfm Manufacturing Compliance: It’s YOUR JOB A concurrent approach to design that considers manufacturing limitations will reduce errors, lower costs and improve time-to-market. by hAPPy hoLDEN and DANIEL SMITh In today’s tense economic environment, companies that have not outsourced their PCB design value their designers as an integral project team member. As “first to market,” “quality first” and other positive expressions permeate your office, how can you, as a PCB designer, personally help your company’s short-term survival and long-term growth? One opportunity is by frequently using manufacturing analysis tools throughout the PCB design process to identify fabrication and assembly problems (especially after an ECO is introduced into the design). Eliminating these manufacturing problems as they are found will significantly improve your chances of shipping out the PCB design on or ahead of a project’s schedule, as well as minimizing initial in-house inspection of your build package at the fabrication and assembly houses. The traditional PCB fabrication and EDA industries have adapted incrementally to the evolutionary development of printed circuit boards over the last few decades, without significant technological discontinuity. From the demands for high-end consumer products such as cellular telephones, to the medical field and reaching into Aero/ Military products, all have revolution24 ized the PCB industry. No longer are the traditional design and fabrication methodologies sufficient. These types of products must be made faster, lighter and smaller, with less cost and higher quality. This high-tech density revolution has created the need for OEMs to embrace high density interconnect (HDI) technology. However, the arrival of HDI circuits now represents a discontinuity in technology for PCB fabricators and the EDA industry—due to the sudden reductions in dimensional scale. HDI products go beyond the scope of traditional PCB fab- rication processes. The changes in build architectures no longer match up with the database structures and the assumptions that were inherent in previous generations of CAD/CAM systems. The One-Pass PCB Design Process Extreme miniaturization trends place new demands on verification of designs such that manufacturing concerns must be addressed concurrently in the design flow. fIGure 1 represents an ideal process for design while continually validating the designs’ manufacturabil- taBLe 1. Manufacturability issues from design artwork. phYSIcAL ARtwORK ISSue Acid traps (photo-resist slivers) Pin holes Copper slivers Starved / isolated thermals Soldermask (S/M) slivers (web) S/M to trace spacing S/M coverage Solder bridging Legend on pads DeScRIptION Of ISSue Small pieces of photo-resist that have minimum adhesion and can break off, resulting in plating or redeposits Small openings in planes or pours that can result in loss of adhesion Small features that may lose adhesion and break off Copper legs for thermals that are cut off from the rest of the plane Small S/M features too tiny to image and adhere properly Small spacings that create S/M slivers Features left open that could result in solder bridging Small gaps between soldered features without S/M that could bridge solder Silkscreen or legend on surface mount technology (SMT) lands MARCH 2009 PRINTED CIRCUIT DESIGN & FAB
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