3D STEP Files and Component Footprints

August 6, 2019 First Page Sage

Haunted bridge in Indiana

 

Back during the early 1990s, a one-season-only television show called “Eerie, Indiana” completely captivated the dark comedy side of my personality. In particular, one episode appropriately titled “The Retainer” told about young Marshall’s friend Steve Konkalewski who had been given the largest retainer known to man. The retainer works as an antenna that picks up vibrations. Crosstalk and EMF were not issues with the retainer-turned-antenna. Instead, the oversized retainer allowed Steve to hear dog thoughts. And, as the story unfolds, the dogs are plotting a rebellion.

As far as I know, PCB design teams have never designed something that could interpret dog talks or dog language. Imagine what we could learn from a type of canine universal translator. However, before the introduction of STEP files, many design teams may have come close to rebellion because they could not share 3D models made with different CAD programs.

One STEP for man….

The introduction of the ISO-standard exchange format (ISO 10303-21) called Standard for the Exchange of Product Data (STEP or the .STP file extension) files quieted all signs of rebellion within the PCB design ranks. Peace reigns.

A STEP file simply contains three-dimensional data in a format that multiple programs can recognize. In fact, nearly all Electronic Computer-aided Design (ECAD) software tools recognize and use STEP files. When we consider that standard faucet parts do not exist, STEP files stand as a major achievement. Achieving interoperability between systems makes everything easier and faster as we move towards the goal of Design for Manufacturing (DFM).

The STEP file format divides into sections called a HEADER and DATA. Yes, I know, there’s not much imagination here. However, separating the STEP file into two sections works. While the HEADER has a fixed structure that consists of three-to-six groups arranged in a specific order, the DATA section contains encoded application data established in one scheme. The next table outlines the parts of the HEADER and DATA sections.

 

Basic STEP File Structure

HEADER Section

DATA Section

File Description

Instance Name

File Name

Instances of Single Entity Data Types

File Schema

Instances of Complex Data Types

File Population

Mapping of Attribute Values

Section Language

Mapping of Other Data Types

Section Context

 

 

Each of the subsections that make up the structure for the STEP file contain metadata. As an example, the File Description group contains version and conformance options. The File Name group includes the name of the exchange structure, a time stamp, the author name, and the name of the system originating the file. File Population provides governing schema and the governed sections.

On the DATA section side, the sections include references to unique naming formats that contribute to the exchange and encoding structures. For example, Mapping of Attribute Values and Mapping of Other Data Types refer to explicit attributes and the use of enumeration, Boolean, logical, string, and binary values as well as aggregate elements. All this allows to move high-quality standardized images from the ECAD domain to the Mechanical Computing Aided Design domain and a clear format that contains rich data. 

Having the ability to import STEP files from the ECAD domain into the MCAD domain allows us to check the physical clearance of components and enclosures. In addition, we can use the MCAD domain to turn, move, and otherwise manipulate the images to ensure that physical compatibility exists between the PCB, its components, connectors, and the enclosure. As a result, we move closer to satisfying the objectives set in the original design and to saving costs through DFM.

Footprints… Large Muddy Footprints on My New Rug

When we design PCBs, we follow best practices that help us to achieve the type of performance required by the original designer and the reliability and quality that ensure moving from design to fast production on schedule. Much of this involves following DFM guidelines established by fabricators and assembly houses. The transition from PCB design to fabricators and assembly houses requires a common language and understanding of needs.

 

integrated circuit on top of a larger circuit board panel

Working through circuit sizes and other various power needs makes documentation important

 

Following DFM guidelines takes us to standard created by the Association Connecting Electronics Industries (IPC). IPC-7351 establishes the “Generic Requirements for Surface Mount Design and Land Pattern Standards.” By using the standardized approach, design teams can speak the common language and achieve common understanding desired by fabricators and assembly houses. PCB design software applications rely on formulas and methods for calculating the land-pattern geometry for many different types of surface-mount components. With these calculations in hand, your design team determine if design rules align with the DFM guidelines.

Moving from ECAD to MCAD also relies on the use of component footprints that comply with IPC-7351 standards within your PCB design software. Having the ability to saving and previewing the generated IPC-compliant footprint model as a 3D STEP file allows your team to reuse and distribute the file. With this capability, your team can produce a fully rendered component body for the component or replace and existing 3D component body that members of the team built from preliminary 3D shapes.

Working through organizing documentation for your next PCB design is more than worth the trouble, especially if you have software that makes documenting your layout and analysis easy. OrCAD’s PCB Editor is one such software tool that can make your life easy in moving your design files where they need to go. 

If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts

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