CAD design relies on not only the skill of the designer, but also the clarity of the design itself. Since designs are later translated into physical PCB components, it’s crucial for designs to be written in a way the CAD community can understand. CAD STEP (Standard for the Exchange of Product) files guide engineers in designing broadly useful and adaptable PCB components. While other design prototype file formats exist, STEP files are the de facto standard for PCB design.
What Are CAD STEP Files?
STEP files are an international file format for CAD data modeling and exchange. The formal name of this standard is ISO 10303-21, and it has existed since the 1980s. There have been some changes to the format over the years, but its focus has always been on a highly structured, human-readable format. The predictable structure of a STEP file makes it easy to parse in software. A STEP file version based on XML also exists, but the plain text version is more common among designers and software implementations. The format is especially useful because it includes model data, and contains information which assists in database indexing and application display. The STEP file standard integrates the EXPRESS data modeling language, which is another international standard. This data modeling language has a restricted character set and was inspired by programming languages. This means the data section is not quite as human-readable as the rest of a STEP file, but it still explains PCB design in an unambiguous way. Software reading and writing STEP files must integrate EXPRESS.
Many software products handling STEP files can convert between STEP files and other STEP models. Since many reputable products take various file formats as input and produce other formats as output, converting between formats is common in PCB design. All major CAD applications can handle STEP file imports, although they may expect different file extensions.
How Can Designers Find STEP Files for CAD Designs?
Like PCB footprints, it is possible to find published STEP files of lesser quality, and designers should be wary of these. Low quality STEP files may have missing or incorrect information. A clear indicator of a low-quality file is one not conforming to the established STEP standard. Keep in mind, a file conforming to the STEP standard may still be missing information. Since CAD designs vary widely, a designer’s next best defense against bad STEP files is to obtain those files from reputable sources. Designers can find models in datasheets, community forums, or search engines, among other sources. Highly curated groups of models are ideal because they are verified by professionals and often comply with more than one data modeling or electronics standard.
STEPCode is an open-source project of particular interest. Designers have relied on STEPCode for reliable STEP models for nearly three decades. Inspired by the NIST STEP Class library, which was developed in the mid-1990s, it has a wide variety of uses in CAD design. The project is a collection of open-source libraries, tools, and resources strictly complying with the STEP standard. It integrates standards-compliant models with plugins for multiple programming languages, has the ability to convert between formats, and provides fairly good documentation. It also contains easily accessible links to related standards such as data formats used in the oil and gas industries, a specialized STEP file standard used in the aerospace industry, and a production standard for the automotive industry. Any standard reusing part of the STEP standard can be read, manipulated, and verified with STEPCode. Parts of STEPCode are also used in other open-source projects, such as BRL-CAD and SCView.
Why Are STEP Files the Best Current Choice for CAD Design?
STEP files are the de facto standard for information transfer in CAD design, and all major CAD applications have the ability to use them. Some legacy formats—like IGES—are still in use, but the broad adoption of STEP has made those file types progressively less useful. The STEP standard has been updated multiple times, the most recent being in 2017, while some of the older standards are decades old and haven’t been updated to reflect modern design needs. While STEP and its data modeling language, EXPRESS, are not updated simultaneously, both have been updated within the last five years and have detailed documentation for easy adoption.
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