What is IPC-2581?

The IPC-2581 standard defines a format for organizing and conveying printed circuit board designs from CAD tools to CAM systems for fabrication and assembly. The standard consolidates all aspects of a design, from layer descriptions through assembly and test details, into one file in one data format.

Why IPC-2581?

Most PCB designs are exported to manufacturers as a series of Gerber files that graphically describe the layers, combined with a drill file, a netlist, a board drawing, and a file of various notes and instructions. A bill-of-materials file and a file of coordinate data to drive pick-and-place machines are also included for assembly operations. None or few of those files except for the Gerber files share a common format. They are simply aggregated, compressed, and sent to the manufacturer to interpret.

When the conglomerated files arrive at the manufacturer, the staff first must identify the order of layers because among Gerber files, there is no convention on the design side for layer names, types (plane, signal, soldermask), or polarity. That typically consumes a quarter hour. If there is any uncertainty about how the layers are designated as received, the job must be sidelined until the designer can be reached for confirmation. When the layer order is resolved, the Gerber files and the information in the accompanying files must be translated to the format recognized by the fabricator’s CAM system, which is almost universally ODB++.

Valor Computerized Systems developed the ODB++ format two decades ago so that design data could be output from CAD platforms as a uniform hierarchy of files that could be downloaded and read directly by the CAM systems the company sold to PCB manufacturers. ODB++ can present a much richer description of a design than Gerber files can provide and eliminates the delays inherent with Gerbers because all the design files share a common format that requires no conversion to program production controls. Mentor Graphics acquired the company a few years ago and continues to market Valor CAM software.

PCB designs can be output in the ODB++ format from most CAD tools, not only those from Mentor Graphics. Nonetheless, Gerber-based design export remains the industry default by force of habit. Despite the advantages of ODB++ for design transfer, some CAD vendors have recently worried that their implementation of that format may become captive to future proprietary restrictions by Mentor Graphics, though there is no evidence at this time the firm intends to impose any such constraints. That uncertainty is responsible for the revitalization of the open-source standard IPC-2581, which in its original form was very similar to ODB++.

The IPC published Version B of the standard in October. Representatives from the nearly 50 companies who belong the IPC-2581 Consortium had revised the format structure to include detailed stackup definition including material types, and incorporated additional refinements enabling designers to express their build intent with even greater clarity. This open standard, which is free for implementation by any software developer, incorporates extensive attributes to pinpoint exactly what designers intend manufacturers to build.

IPC-2581 Consortium

IPC-2581 Consortium
IPC-2581 Consortium

As a Consortium member, Sierra Circuits endorses the IPC-2581B standard, which will accelerate manufacturing and assembly. It will enable design data to be downloaded without interpretation directly into CAM systems, thereby saving time and labor, compared with Gerber-based projects. Whether the industry embraces this intelligent format hinges on how faithfully the vendors of CAD tools, DFM software developers, and CAM system developers implement it. The first releases under IPC-2581B are anticipated in 2014.

The Limitations of Gerber-based Design Transfer:

  • A mix of files in different formats, which are incompatible with PCB manufacturing software
  • No convention for designating layers
  • Data can be misinterpreted

The Advantages of IPC-2581B:

  • All the data within a design can be exported in one file, in one format, from a CAD tool directly to a manufacturer’s CAM system
  • No intermediate data translation is required
  • Eliminates human errors
  • An open standard free from proprietary restrictions

How Does Revision B Extend the Standard?

  • Improves description of build intent with provisions for stack ordering, material types, technology attributes, stack-up composites
  • Expands BOM section to include stack up
  • Includes geometry object fill types, line types, user- defined primitives
  • Back-drilling support
  • Pin-one origin/orientation standard criteria
  • Pad-stack reference definitions
  • Z-axis definition, V-groove cavity/slot support
  • More notes on design intent can be added in the Spec section

Join the Consortium to Promote IPC-2581

  • Ask your company to become a corporate member
  • You can join personally as an individual associate member
  • Visit www.ipc2581.com to join