Printed Circuit Design & Fab - October 2008 - (Page 28)

DESIGN toolS designers searching for part information and because it is easier to maintain from a librarian or corporate level. To see an overview concept of a database library system, see FiGurE 4. It should be noted that once a library system reaches the complexity of a database of parts that are complemented with graphic symbols and geometries for placement into the schematic and layout, chances are that this system will require at least one full-time librarian to manage the information. Library Maintenance Issues to Consider: Who Does It, and How? Once the file format of the library is tentatively decided, it is important to think through the maintenance processes. In a small team environment, it could be a group effort with one principal designer in charge of making sure no one introduces errors into the library. Or, one engineer could monitor the schematic information while one layout designer monitors the geometry information. In a medium to large design group, it is a good idea to hire at least one full- or part-time librarian to maintain all the information separately from the design groups. This helps prevent confusion that can occur from the number of people sharing information. In librarian-managed environments, designers are not allowed to put any new information into a library; they must request that the librarian add whatever is missing. The larger design groups tend to have two to three librarians. Typically, one librarian will manage the parts database information, and one or more librarians will manage the graphical symbol and geometry information. The reason this can become such a big job is because all of this information must be correct. For example, if a schematic symbol’s pin names and numbers do not directly correspond to its associated layout geometry, the layout designer will have no idea which signals are meant for which pins. In higher-level design systems, it is not even possible to place geometries that don’t have matching schematic pin and gate information. Given that this level of detail and verification is required to keep a library in order, it is easy to see why companies hire librarians to focus on the task, allowing designers to focus on the designs. The margin for error is greatly reduced if this division of labor is put in place from the beginning. The way in which the library’s versioning is structured can be influenced by who maintains it–librarians or designers. All library systems have versioning of some kind such as libraries, parts, symbols and geometry information. This is usually accomplished with direct file versioning systems, but it can also be accomplished through manually maintained copies. Before putting a library into motion, decide whether there will be only one library accessed by librarians and designers at the same time and backed up daily, or whether there will be a “release library” available to designers with incremental updates made by the librarians’ “development library,” either daily or weekly. Many larger companies have incremental, automated updating systems that run on a nightly basis while no one is attempting to 28 access information. Note that all of these options apply to flat file or database systems, so it is important to consider how data collisions may or may not occur in a specific design environment. Along with formatting and versioning considerations, another maintenance issue that often causes frustration for designers and librarians alike is how new part requests should be handled. When embarking on a new project, designers often need parts that are not found in the library. In loose library environments, designers can build their own part, symbol and geometry information and upload it to the main library for others to use. But as design teams get larger, this becomes an error-prone area that can cause designs to fail if a bad part is shared among many projects. In this environment, it becomes imperative not to allow designers to upload new information, but rather to have a librarian approve any new parts, symbols or geometries and publish them for general use. In this scenario, designers can request a new part and wait for the librarian, or they can make their request and then place a “dummy” symbol or geometry while they wait to get the approved symbol or geometry from the librarian. Using a “dummy” system places a shared responsibility on both designer and librarian and allows everyone to progress without having to wait for one another. The engineer or the designer may take a best guess when building the library symbol or geometry based on the established part information included. This “dummy” is then presented to the librarian, in full or partial form. While the engineer or designer continues on with his work, the librarian makes any adjustments necessary and publishes the approved part back to the main library. The engineer or designer can then replace any “dummy” information with the fully approved symbol or geometry information. While it is a proven fact that utilizing a central library will save design time, user confusion from not understanding how the library is intended to be managed can narrow the time savings window to the point that it no longer benefits the company. Not only is management of file and database information crucial, it is also of utmost importance to manage expectations and usage of that information. Rogue designers and engineers can tear apart a carefully planned library system in no time if they are not brought around to seeing the advantages of following the rules. The onus is placed on the managers and librarians to provide clear guidelines to maintain order among design teams. But there is no hard line in the sand; a library is a team effort to maintain, and it is entirely possible that the decisions made from the beginning may need to be reconsidered and tweaked once the library is put into action. A library is not simply a tool; it is a small building block on which a company can expand its success and profit. pCd&f abby Monaco is product manager with Intercept technology Inc. and can be reached at abby_monaco@intercept.com. OCTOBER 2008 printEd CirCuit dESign & fAB

Table of Contents Feed for the Digital Edition of Printed Circuit Design & Fab - October 2008

Printed Circuit Design & Fab - October 2008 Contents Our Line Market Watch Around the World Happenings Test and Inspection ROI Tip Jar Interconnect Strategies Final Finish Forum The New Wave in High-Speed Modeling The PCB Design Library Mixed Signal Design Considerations Modeling Conductor Surface Roughness Copper Erosion: The Influence of Metallurgy on Copper Dissolution The Wave of the Future Ad Index Building a Profitable Niche Marketplace Off the Shelf BGA Bulletin

Printed Circuit Design & Fab - October 2008

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