Mechanical CAD integration
Why does this matter?
At the first Design Automation Conference (DAC), held in 1964, computer-assisted electronic design was merely one part of the programme and it was not seen as a major user of compute power at the time. For many years, the primary application seen for EDA was analogue modelling. In 1964, the content was largely about 3D mechanical design: Ivan Sutherland described his Sketchpad concept, one of the first attempts to build a graphical user interface for computers.
Slowly, mechanical computer-aided design (MCAD) fell away from the DAC programme as mechanical CAD developers found other venues to discuss their technology. And the links between the two worlds remained almost severed for decades. Manual processes appeared to work well enough. Circuitry could be constrained to fit a certain board size and when most components could be expected to project no more than millimetres from the surface. Tall electrolytic capacitors might cause concern in terms of height clearance but this was relatively easy to accommodate in most systems with some care exercised by the designers.
Advanced users have repeatedly called out for a better integration between electrical and mechanical CAD. US space agency NASA has been one of the driving forces for better cooperation, organising conferences to discuss how best to share data between different types of CAD tool. A growing number of users are now encountering similar problems to those faced by NASA.
The pressure on electronics companies to produce more stylish products and squeeze complex assemblies such as image sensors and displays alongside other components into tight spaces has reawakened interest in links between EDA and MCAD tools. Concerns over heat flow are also driving the demand for closer integration.
To work effectively, these tools need accurate models of component placement and structure to be able to work out how hot air will flow around boards and heatsinks and follow conducted heat through the copper traces and around cutouts in the PCBs themselves.
What is being done?
The available open standards come from US-based organisation PDES in the form of the STEP AP210 and AP214 specifications. Part of the problem with the STEP standards is that they were defined with the idea that tools would support them natively. For backwards compatibility, tools vendors prefer to retain their own file formats and convert data for use with other tools.
Mentor and PTC decided to adopt and promote a later iteration of the STEP work. Taking requirements from a series of workshops held in 2005, the ProSTEP iVIP group worked on a data-exchange format, EDMD, based on the XML language used in internet software that took many of the elements of AP210 and AP214. Ultimately, this resulted in the IDX format, although a number of other vendors favour the older IDF format, which is also supported by Pro/Engineer among other mechanical CAD tools.
Altium’s software can export PCB data to the mainstream STEP format as well as generating its own 3D visuals to show how a physical board will look. Zuken, which worked on the AP210 and AP214 specifications together with Mentor with the help of STEP specialist LKSoft, instead built direct links to Dassault Systèmes’ Catia V5 software from its CR-5000 PCB design package.
Some free tools have added 3D links. Distributors such as Farnell and RS Components have built databases of 3D models of components and put support for them into their own software. RS Components’ DesignSpark will export IDF files and the 3D component shapes the company has produced can be used in free mechanical CAD tools such as Google’s SketchUp. In 2013, RS licensed a version of SpaceClaim’s solid-modeling software that can import IDF files from PCB design tools and currently offers it for free download. In the future, SpaceClaim aims to add IDF export to support round-trip updating of PCB component placement from the MCAD domain and this will be added to the RS DesignSpark Mechanical tool.
Farnell’s Eagle will export design files and generate 3D models in SketchUp. Alternatively, there is the option to use Eagle3D in the paid-for Pro release of the PCB design software.
Risk factors
The primary risks involved with the current state of MCAD integration remain those of fragmentation and the reliance, in some cases, on relatively old standards that do not necessarily make it easy to iterate designs between two groups. Some of these drawbacks can be addressed in the tools through the use of additional metadata but a lack of cross-industry standardisation could prove problematic.
Although the free tools may prove attractive for some users, they have drawbacks. For SketchUp, Google is concentrating mainly on the Collada format developed, which was conceived originally for interactive 3D modelling and animation rather than engineering. These formats describe surfaces well but not internal function or behaviour, which may be sufficient for passing data onto to airflow analysis tools but may not be adequate for organisations that need to perform electromechanical integration and who will focus on MCAD tools such as SolidWorks.
