Together again

Separated almost at birth, electronic and mechanical CAD are close to reaching an understanding.

When the first Design Automation Conference (DAC) was held in 1964, electronic design was only one part of the agenda. Engineers turned up to hear about early software that would analyse aircraft space-frames or perform rudimentary 3D mechanical design. Ivan Sutherland reprised a talk about the Sketchpad, one of the first attempts to build a graphical user interface for computers.

It took some years for DAC to mutate into a conference aimed purely at electronics design. Slowly, the mechanical elements of computer-aided design (CAD) fell away, partly because the idea of automation in design looked most tractable in the 2D world of electronics. The earliest computer tools for design were the forerunners of the Spice analogue simulation language and printed-circuit board layout software. Mechanical CAD focused on drafting with far less emphasis on the automation concepts that would drive the electronics business, at least until techniques such as finite-element analysis came along.

Mechanical and electrical CAD were not just separated between academic conferences. The commercial worlds went their separate ways - linked by manual processes. Some companies saw a future in making the link between electrical and mechanical CAD but found limited enthusiasm among customers. When it picked up the remains of the Dazix business in the early 1990s, Intergraph saw an opportunity to bring together the two worlds. But the idea did not take off.

Looking at the products of the time, it is not hard to see why. In many cases, the enclosure was designed around the needs of the electronic system. If they looked like bricks, it was for a reason: it was the easiest way to contend with components mounted on PCBs. There were plenty of airgaps to cope with the varying height of heatsinks, connectors and add-in cards.

Some isolated areas of design did find common ground between the electrical and mechanical worlds. In the avionics and automotive sectors, specialist companies created cable-harness design software. In high-volume markets, software helped optimise PCB layouts for production. Tall components would be moved, or moved later in the insertion sequence to keep the robotic placement heads moving at top speed - a tall component placed early could slow down the insertion of other parts.

Better integration

Some 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, 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.

John Isaac, director of systems market development at Mentor Graphics, says: "What is driving the integration is the demand for high performance in smaller spaces and situations where the interaction between the PCB and the enclosure from an interference or assembly point of view is critical.

"Customers want to achieve higher performance in smaller places with minimal cooling. With today's handhelds, it is becoming more critical."

Smaller spaces leave less room for error and, if you start using the chassis for cooling as well as vibration protection, close cooperation between the two design teams is essential. The problem, claims Pawel Chadzynski, vice president of product management at mechanical CAD company Parametric Technology (PTC), is that the current level of communication is not quick enough to catch problems. "You need to be able to communicate incremental decisions quickly. You can't wait two weeks to perform a verification at the end."

Isaac agrees: "It's the incremental changes that need to be negotiated. If you need to change the board outline, that is a negotiation. I can't just do it."

There are ways to share information between the electrical and mechanical domains. PDES, a US-based organisation that has provided many of the key standards for mechanical CAD interoperability used in the automotive and aerospace sectors, stepped in to forge links to the electrical world with the STEP AP210 and AP214 specifications. Despite being available for more than five years, software vendors have not used these formats to store design data.

Part of the problem with the STEP standards is that they were defined with the idea that tools would support them natively. For the most part, vendors want to stick with their own native file formats and translate data between them. Altium's software can export PCB data to the mainstream STEP format, so that 3D mechanical software can show how a physical board will look. Zuken, which worked on the AP210 and AP214 specifications and Mentor with the help of STEP specialist LKSoft, has used direct links to Dassault Systèmes' Catia V5 software from its CR-5000 PCB design package.

Mentor and PTC adopted a later iteration of the STEP work. Taking requirements from a series of workshops held in 2005, the ProSTEP iVIP group worked on EDMD, a data-exchange format based on the XML language used in Internet software that took many of the elements of AP210 and AP214.

"Design changes can be expressed in an XML data model that are not specific to any tool. We created a programmatic way to describe change between a 2D and a 3D system. We don't need to know what the tools do, just that they can read and write an open format," says Chadzynski.

Although only two companies have publicly committed to EDMD, Isaac insists it is open: "It so happens that Mentor and PTC are the first to pick this up."

A spokeswoman for Zuken told E&T that the company is evaluating whether support for EDMD is a direction that it might pursue, although the software vendor is not actively working on it at the moment. Altium is also not currently working on supporting EDMD.

Isaac says, potentially, a lot of information can be passed between the mechanical and electrical domains. "There are hundreds if not thousands of constructs in these systems. We tried to identify which were the most likely to change in the course of a project. They turned out to be components, board outlines and mounting holes and a few others. The initial standard identified those."

One issue facing Mentor and PTC is the availability of component libraries. "Unless you spend the time to define them, each component is just a box," says Isaac.

Standard packages are easy to support but building libraries will have to be taken on by users until manufacturers and distributors provide their own. Forty years since the two branches of CAD went their separate ways, a bond is being formed even if the tools will not merge.

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