Printed Circuit Design & Fab - February 2009 - (Page 38)

LAYOUT toolS do You reallY Want a Better autorouter? Complex constraints require integrated autorouting that gives the designer the control to deliver productivity gains. by RoB IRWIN Asking PCB designers whether they would like a better autorouter may seem akin to asking children whether they’d like an ice cream - a rhetorical questions with an obvious answer. Perhaps some better question are what do designers mean when they say they want a better autorouter? What criteria define better autorouting? And how can the benefits of automating the routing process best be delivered to designers? The answers to these questions are not so straightforward. We need to examine the role of autorouting in the context of the overall PCB design process and look at the changing nature of board design and electronics in general to get to the answers. It’s a digital world. Electronics started off as an analog discipline. The requirements placed on board design by the technology of the time were modest by today’s standards, and hand routing was an accepted and relatively efficient process, even when done mechanically using tape and tracing paper. The widespread use of computer-based board design applications through the 1980s allowed significant gains to be made in design efficiency and the complexity and quality of boards that could be produced. Digital technology changed this significantly. It increased signal density and introduced new challenges, such as the need to route groups of eight, 16, 32 or more signals along a single path. This was tedious and repetitive to do manually, even in a computer-based layout package, and as the prevalence and complexity of digital boards increased, board designers began to get bogged down in the digital detail. It was into this landscape that stand-alone autorouting applications were born and began to be used as a 38 common part of the board design process. As layer and pin counts increased and package pin densities skyrocketed with the advent of surface mount technology, early gridded maze routers gave way to shape-based ‘gridless’ technology. More recently, topological path mapping algorithms have been used to cope with unusual board geometries and component orientations. The 1990s saw the autorouter rise to a level of prominence as a design tool, and the technology has become progressively better and easier to use. But there is a problem. Traditionally, autorouters have been developed as stand-alone applications. Typical PCB layout software, however, also includes the ability to route connections. So, there is an uneasy relationship that has developed between the two. Over the last decade, we have seen this manifest into a significant convergence of the two design spaces. On the one hand, stand-alone autorouters have acquired features that allow them to be used in a more interactive fashion, as well as the ability to manually route connections within the autorouting space. On the other hand, PCB layout software has become far more intelligent in its approach to routing and the level of automation available in the routing features offered (FiGurE 1). Converging Paths This is not a power struggle between autorouters and layout software. Instead, it is a natural reflection of the general convergence of electronics design technologies and the fact that board design is no longer a simple drafting process. Increasingly, it requires a high degree of engineering input in order to achieve an optimal outcome. What once was considered a simple connection, FEBRUARY 2009 printEd CirCuit dESign & fAB

Table of Contents Feed for the Digital Edition of Printed Circuit Design & Fab - February 2009

Printed Circuit Design & Fab - February 2009 Contents Our Line Market Watch Around the World Happenings ROI Tip Jar BGA Bulletin Interconnect Strategies Final Finsh Forum Defects Database Embedded Active Components In Multilayer LCP Packages Simulation: The Need for Speed Advanced Registration Systems The DC Design Squeeze Ad Index Do You Really Want a Better Autorouter? Designing With Conductive Materials, Part 1 Off th eShelf Marketplace On the Forefront

Printed Circuit Design & Fab - February 2009

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