Generating a 3D PCB in Pro/ENGINEER

By Keith Richman, Simplified Solutions Inc.

Integrating a printed circuit board into product design is vital when developing electronic devices. Although bundled with each license of Pro/ENGINEER, the Pro/ECAD interface remains vastly underutilized within the PTC product user community. Instead, many companies continue to struggle with the interface between their 2D electrical ECAD tools and Pro/ENGINEER. Others continue to pass “paper sketches” back and forth. 

In reality, the basic IDF (Intermediate Data Format) interface is extremely simple to use. Circuit board data typically originates in the 2D electrical world. A simple IDF export of EMN and EMP files from your company’s 2D ECAD tool provides the basic information required to generate a simplified version of your PCB. Specifically, the EMN file contains information about the physical PCB shape, keep-out areas, keep-in areas, and drilled holes, along with the location and orientation of each component. The EMP file, in contrast, contains information describing each component’s 2D size, height and shape.

In Pro/ENGINEER, all you have to do to import your PCB is

1.     Use the FILE–OPEN command and select the correct EMN file.

2.     Choose Assembly as the type. The PCB outline and component locations are then imported. 

3.     When prompted, choose the EMP file that contains the component profiles.

4.     A PCB similar to the one below will appear (Fig. 1)

Figure 1.

Adding 3D Information

But mechanical engineers need a lot more information to do their job right the first time. To create a 100% geometrically accurate PCB, the “block” components must be replaced with 3D models. The mechanism Pro/E provides to accomplish this task is a text file called the ecad_hint.map.

When you import an IDF (EMN) file, Pro/ENGINEER searches the ecad_hint.map file for a matching component called out in the EMN file. Pro/ENGINEER then replaces block geometry with a real 3D Pro/ENGINEER part. 

Here’s a sample component entry in an EMN file:

SOT-23 A-32788545     Q12                                         

15.0                 21.0                 0.0                   90.0       TOP       PLACED   

·       SOT-23 represents the ecad_name (typically a geometry package name)

·       A-32788545 represents the ecad_alt_name (often a company part number)

·       Q12 is the reference designator

·       15.0, 21.0, and 0.0 represent the component location with respect to the circuit board’s (0,0) point in the X, Y and Z directions. 

·       The 90.0 represents the orientation of the component

·       TOP is the side of the PCB on which the component resides.

·       PLACED (as opposed to unplaced) means this component will be populated upon import.

The entry in the ecad_hint.map file has the following format:

map_objects_by_name ->

ecad_name "SOT-23"

ecad_alt_name "A-32788545"

ecad_type ""

mcad_name "sot-3p290x130ll237h100"

mcad_type part

end

In this example, Pro/ENGINEER searches the ecad_hint.map for unique combinations of the ecad_name (SOT-23) and ecad_alt_name (A-32788545). Since a match was found, Pro/ENGINEER replaces the block geometry with a 3D part called sot-3p290x130ll237h100. Pro/ENGINEER assemblies can also be imported to a PCB by changing the mcad_type from part to assembly.

Orienting the Component

The next step in the process is to insure that the orientation of the ECAD geometry and Pro/ENGINEER geometry matches. If the coordinate systems do not match, the 3D component will be rotated with respect to the ECAD geometry when imported into Pro/ENGINEER. The center image in Figure 2 shows an overlay of the Pro/E 3D model and the ECAD geometry.

The coordinate systems for the ECAD and Pro/ENGINEER data must also be in the same location with respect to the component outline. The physical center of the part is often the best location for surface-mount components, while the center of Pin 1 often works best for through-hole components.

Importing a 3D Component

After connecting the EMN file entries to your 3D part using the ecad_hint.map file and verifying that the ECAD and MCAD components have the same orientation, you can import a component. To import a fully populated 3D PCB, all items in the EMN file should have:

·       A matching entry in the ecad_hint.map file containing the proper mcad_name.

·       A matching 3D model for the mcad_name that Pro/ENGINEER can locate during your PCB import. This model must have the proper coordinate system orientation and location.

The following configuration settings need to be added to your config.pro prior when importing your PCB:

ecad_mapping_file                                “Location of your ecad_hint.map”

ecad_comp_csys_def_name                   “ECAD component coordinate system name”

Once you have updated your configuration settings, use the same step for importing your improved PCB as for importing the PCB with the block components.

1.     Use the FILE–OPEN command and select the correct EMN File. 

2.     Choose Assembly as the type. 

3.     The PCB outline and component locations are imported.  This time, the 3D models called out by the ecad_hint.map appear, as shown in Figure 3. 

Generating Component Outlines

One of the most common issues mechanical engineers run into when importing a PCB is lack of quality information from the ECAD side. For this reason, IDF allows the transfer of data to, as well as from, the electrical world.

From the top view of a 3D PCB, the geometric data should be identical to the 2D information in the ECAD tool. With this in mind, it often makes sense for mechanical engineers to define the PCB and component outlines in Pro/ENGINEER. ECAD drafting tools are not as sophisticated as Pro/E, and PCB designers often take much longer to produce less detailed outlines. This outline data can be exported through IDF and imported into ECAD by following these steps. 

1.     Create a protrusion using the surface that contacts the PCB as the sketching plane (Fig. 4a).

2.     Choose all external edges of the component as seen from a top view.  

3.     Extrude the protrusion to the top surface of the component (Fig. 4b). 

4.     Choose File, Save A Copy, select ECAD IDF (*.emn), and save the file (Fig. 4c).

5.     Import the EMN file into your ECAD software. 

Note:  The EMN file will not export if there is not a consistent cross section at every Z height.

Design Process for PCB Development

With mechanical engineers and PCB designers transferring data back and forth, it’s important to have a standard procedure for information exchange. Here is a good starting point for establishing your company’s own process for developing circuit board designs.

1.     The mechanical engineer creates the PCB board outline in Pro/ENGINEER and exports the file as an IDF EMN file.

2.     The PCB designer imports the PCB outline EMN file into the electrical design tool, places critical mechanical parts outside the PCB profile, and exports an EMN file.

3.     The mechanical engineer imports the EMN file back into Pro/ENGINEER, moves incorrectly placed components to the proper locations, and exports an EMN file.

4.     The PCB designer imports the EMN file, completes circuit layouts, etc., and exports an EMN file.

5.     The mechanical team imports the EMN file and performs analyses, including interference checks.

6.     The mechanical team and PCB designer go through an iterative process, checking and moving components until the PCB is ready for release.

Building a Library of 3D Components

Building 3D circuit boards in Pro/ENGINEER requires an organized library of components. Since most companies do not have dedicated resources for accomplishing this task, here are some resources for streamlining the creation of a 3D component library.

·       Many connector vendors provide IGES files and/or Pro/ENGINEER .prt files on their websites, which can be integrated into your library to save time and money. For example, Molex Inc. (www.molex.com) has thousands of connectors modeled in Pro/E. Other manufacturers such as Amp (www.amp.com) and Samtec (www.samtec.com) have IGES files available for a large percentage of their connector products.

·       Mechanical PCB components created in Pro/ENGINEER through the normal design process can also be added to your library. Components such as shields and contacts typically are designed and tooled based upon 3D models created by mechanical engineers. These same models can be integrated into a corporate library of components.

·       Electrical packages are typically used over and over. A one-time investment in modeling or acquiring these 3D models will pay dividends over the long haul. A library of 3D electrical packages modeled in Pro/ENGINEER can be found at www.simplifiedsolutionsinc.com.

Benefits of Using Pro/ECAD

With handheld products shrinking in size and product development cycles getting shorter, mechanical engineers need more detailed PCB information to get their designs right the first time. Pro/ECAD provides an easy-to-use interface for importing 3D Pro/ENGINEER components to improve the accuracy and speed of PCB design. Using more realistic 3D components makes the process more efficient in several ways:

·       Mechanical engineers work with the exact PCB geometry before the first circuit board is manufactured, minimizing costly tooling errors.

·       Interference checks reflect reality. Using more realistic geometric information often enhances shock and thermal analysis.

·       Product housings can be designed more accurately with the improved PCB information.

·       The detailed and accurate PCB information allows design of smaller, sleeker products.

·       ECAD design errors can often be caught before circuit boards are ordered.

·       Communication among PCB designers, mechanical engineers, industrial designers, engineering management, and marketing is vastly improved.

In sum, the upfront resources needed to generate 3D PCB geometric information more than pay for themselves over time.

Keith Richman is a mechanical engineer and chair of PTC/USER’s ECAD Technical Committee. He is also founder of Simplified Solutions Inc., which offers an extensive 3D electrical component library modeled in Pro/ENGINEER, along with time-saving tools for integrating components into PCB designs. This article is based on his presentation at the 2005 PTC/USER World Event. Keith can be reached at keith@simplifiedsolutionsinc.com.