Bridging the Gap Between ECAD and MCAD
Though difficult for smaller and medium sized companies, bridging the gap between these two functions has gotten a bit easier.
Mechanical CAD systems still serve a
different role from dedicated electrical CAD systems, which are
designed to lay out components on PCBs and calculate the routing of the
electrical connections between them. Both types of systems require
different skill sets from their operators, so it is unlikely that one
system to unify both types of design will become available in the near
future. There are, however, many reasons to try and improve the
communication between the two types of systems.The Advantages
First, let's look at the advantages for mechanical design. The
inclusion of accurate PCB models in a mechanical design can assist
mechanical designers in three main ways:
1. Physical constraints. By transferring an accurate model of the PCB
and its components accurately into a mechanical CAD system, users can
check for any potential collisions between the PCB and its
surroundings. In the case of a bidirectional link, the PCB shape or the
positions of components can be altered accordingly and the resulting
changes updated in the ECAD system.
2. Visualization and prototyping. CAD models are increasingly used for
visualization and sales use, often before the product itself has been
manufactured. The ability to show accurate PCBs with components in
visualizations or renderings adds an extra element of accuracy to the
image.
3. Analysis. 3D PCB models generated from ECAD data are increasingly
used for thermal analysis within mechanical CAD systems, especially in
the case of products with tight packaging constraints such as cellular
phones and PDAs where localized heat buildup can cause problems.
As well as bringing advantages to mechanical design, linking ECAD and
MCAD also helps the electrical design side of the process.
Increasingly, the outline shape of the PCB and the positions of the
components on it are driven by the shape of the product the PCB is
enclosed within. This is especially true of small electronic products
like phones and watches, but is increasingly a constraint on larger
products as product packaging becomes ever more critical.
By linking ECAD and MCAD, the PCB design process can be started in the
MCAD system by defining the shape of the PCB outline and the volumetric
areas where the electrical engineer is free to place components (known
as keep-out and keep-in areas).
The electrical engineer can then add the components and determine the
routing between them in the ECAD system, and pass the updated results
back to the MCAD system to update the mechanical model. If any problems
are noticed in the mechanical model, such as clashes or potential
thermal problems, the PCB can be modified in the MCAD system and the
updated data sent back to the ECAD system. This cycle continues until
the PCB design is optimized both electrically and mechanically.Linking the Two Systems
Having discussed the advantages of exchanging data between ECAD and
MCAD, let's take a look at the mechanism by which these systems can be
linked.
Intermediate data format (IDF) is the industry standard data exchange
format between ECAD and MCAD systems. IDF is an open file format
maintained by a group of ECAD and MCAD companies. Rather confusingly,
Each IDF file is actually two files-usually with the file suffixes
*.emn and *.emp, but other suffixes are used as well.
Most ECAD systems can read and write IDF files, either directly or with
an additional third-party translator. Most common 2D and 3D MCAD can
also read (and in some cases write) IDF files. Generally, any IDF
functionality built into MCAD systems is fairly limited, but additional
programs are available to add more powerful IDF functionality to most
common MCAD packages, such as SolidWorks and Inventor.
There are currently three versions of the IDF file format-2.0, 3.0, and
4.0. Most systems currently read and write the very similar IDF2.0 and
IDF3.0 formats. IDF4.0 is a much more detailed format currently only
supported by a few systems.
It's worth bearing in mind that the IDF format does not contain all the
information held in an ECAD systems proprietary file format. IDF
contains only the ECAD data of use to a MCAD system, such as the
physical size and shape of the board and its components. It is also (in
IDF2.0 and 3.0 form) a 2 1/2 D rather than 3D format. Components are
modeled as "skyscrapers"-their outline shape extruded to a height. In
most cases this simplified representation is fine, although more
advanced IDF translators such as CircuitWorks for SolidWorks can
substitute a fully detailed model in place of the simplified model data
contained in the IDF file.Getting More Information
More information about IDF and technical specs for the file format can
be found on www.intermedius.com. This site also contains a limited list
of the ECAD and MCAD systems that can read and write the format. The
list is by no means exhaustive and has not been updated recently, so
there is a good chance your ECAD and MCAD system may support the format
even if it is not listed. If in doubt, check the system's manual or
help file or contact your vendor. SolidWorks users can download a trial
copy of the CircuitWorks bidirectional IDF translator from www.circuitworks.net, or try the simple import-only CircuitWorks Lite IDF translator built into SolidWorks 2005.
