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EETE JAN 2016

degisn & prdoucts Circuit analyiss & bdeug Avoiding the costs of inadequate ECAD/ MCAD & design data management By Robert Huxel It is a truism that only a part of a design engineer’s time, in the course of his or her daily tasks, is spent actually designing. Sometimes that proportion can be frustratingly small; of the time spent carrying out ancillary functions, managing information can account for a large part. Automation – as with all applications of information technology – can make a big difference, but only when the systems applied are properly focussed on the task in hand. Printed board design can be viewed as the pivotal design function. Looked at in one direction, it both defines and is constrained by the overall format of the final product: there is an exchange of information with the mechanical world (ECAD to MCAD in terms of design systems) that relates to the external dimensions of the product, and to how the electronic assemblies are packaged within the outer casing. From another perspective, the PCB is where all of the work that goes into circuit design is focussed; and to that can be added everything that goes into component selection and procurement; plus all the effort that is invested in verification in the electrical, mechanical and thermal domains. All of these aspects represent information that has to be sourced, maintained and exchanged between a variety of systems. Viewed from that high level, it is clearly desirable that the various stages of, and tools used in, the design process should access common data formats and exchange information in as seamless a fashion as True ECAD/MCAD collaboration gives designers visibility into incremental design changes. Both designers can see component placement changes simultaneously and make any necessary alterations in response. possible. The reality that many engineers have been used to working with, however, falls some way short of that ideal. The interface between mechanical and electrical (PCB) design environments is a well-known case in point. The PCB, in all three dimensions, must fit in some form of enclosure. The available space may be pre-allocated, or it may be designed around the PCB. In either case, development demands an exchange – in practice, repeated exchanges or iterations – between mechanical and electrical design spaces. Over time, a variety of off-the-shelf and “home-built” systems have evolved to facilitate this exchange; where files are passed back and forth between ECAD and MCAD, two file formats have been in common use. IDF (Intermediate File Format) is long established but falls short of passing comprehensive geometry. It is not a full 3D representation, rather a layout or footprint plus height of individual components (from component models, of which more later). STEP (Standard for The Exchange of Product model data) takes things forward a stage with a true 3D representation of design data and can be used for PCBs, components, mechanical assemblies/housings, and any other design files which may be collaborated on by multiple designers using different programs. But this still involves exporting and importing files between software packages, with all that implies for version control and the opportunities for error. There are benefits, and limitations, associated with using STEP for bi-directional transfer between programs. Native 3D PCB editing tools running within ECAD software for mechanical design, or at least alignment, placement, and export of 3D mechanical models, allow much of the work to be done in a single software package. Altium Designer, for instance, includes capabilities for aligning 3D component models to footprints, modelling and clearance checking for housings/ enclosures, and if necessary, standard exports of complex PCB features for MCAD interfacing. More recently, Altium created a new PCB tool that comprehensively integrates PCB data with full 3D CAD in SolidWorks. The true costs of not having a coherent link between ECAD and MCAD can be considerable. They can manifest themselves as missed schedules and extended time-to market; inefficient Robert Huxel is Technical Marketing Manager EMEA at Altium - www.altium.com 30 Electronic Engineering Times Europe January 2016 www.electronics-eetimes.com


EETE JAN 2016
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