On October 16, 2013, the IPC published Revision B of IPC-2581, the data format the standards organization has developed to convey PCB designs from CAD tools to board manufacturers’ CAM platforms. How will that standard benefit designers, since it’s simply a protocol for organizing and presenting designs for fabrication? The answer is clarity, and time to market.
IPC-2581B aggregates all elements of a design, every aspect from layer description through assembly, into one file, in one format. It will speed fabrication, assembly, and testing.
Close to 90 percent of the designs Sierra Circuits has fabricated to date arrived as Gerber files that graphically defined the layers, bundled with a drill file and a netlist, a board drawing, and a readme text with various notes and instructions. Most of those Gerber files are in the RS-274X extended format, though some are in the outdated RS-274D format (yes, we continue to get those occasionally). There’s also assembly, which requires a BOM file and a file of component coordinates for driving pick-and-place machines. The conglomeration of disparate files for each design, none or few of which except for the Gerbers share a common format, resulted in good boards. Nonetheless, consider how those files had to be processed to drive the CAM systems that guide production.
When a board manufacturer receives Gerbers, someone in front-end engineering has to identify the order of layers, because with Gerbers there is no fixed rule on the design side for naming layers, their types (plane, signal, soldermask), or polarity. Usually that takes 15 minutes or so per job, time that seems negligible unless you are a quickturn manufacturer of prototypes who receives a hundred or more orders daily. However, if there is a question about whatever arbitrary designations were applied to the layers as received, the job must be put on hold until the designer can be reached. When a project has advanced to the prototype stage at an OEM, there’s often a large investment and precious time riding on the quick receipt of assembled boards for testing, debugging, and possibly design revision in time to meet the deadline for a product introduction. Any delay in fabricating the prototype boards jeopardizes that critical schedule.
Design Software and File Formats
Valor CAM software is nearly universal among PCB manufacturers for driving production equipment. Valor Computerized Systems originated the data format native to that software, ODB++, nearly two decades ago. ODB++ was developed as a vehicle to transmit the design information from CAD tools to CAM systems in a common, ordered format encompassing layer graphic data, drill data, the stackup, the netlist, a BOM, component coordinates, and any other information needed for manufacture. The data, consolidated in a single format, are contained among a hierarchy of files and folders that can be delivered and downloaded to CAM systems in one smooth process. This is in contrast to Gerbers and their accompanying mix of files in different formats.
Mentor Graphics bought Valor Computerized Systems in 2010 and continues to improve and market Valor CAM software. Even though ODB++ can provide a much more detailed description of a design than Gerbers can present, and even though a great many CAD tools, not only those from Mentor, can output a design in ODB++ format, and even though a design captured in ODB++ format requires much less time to load into CAM systems, Gerbers remain the habitual default. Only ten percent of the designs Sierra Circuits has manufactured to date were delivered in ODB++ format.
Despite the advantages of ODB++ for design transfer, some CAD vendors worry that their implementations of ODB++ may become captive to future proprietary conditions by Mentor, though there is no evidence at this time that Mentor intends to impose any such restrictions. 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 First U.S. PCB Manufacturer to Fab from An IPC-2581 Design
IPC-2581B incorporates a rich set of attributes to explain precisely what PCB designers expect manufacturers to build. Pay close attention to this standard. CAD and CAM software releases implementing the updated format will be available in 2014. IPC-2581B aggregates all elements of a design, every aspect from layer description through assembly, into one file, in one format. It will speed fabrication, assembly, and testing. Like Gerbers or ODB++, the success of IPC-2581B depends on how faithfully software developers implement the format. Sierra Circuits intends to evaluate various IPC-2581B software releases as they become available next year.
Meanwhile, Sierra Circuits is the first U.S. PCB manufacturer to fabricate a board exclusively from a design delivered in the IPC-2581 format. We found no bugs in the design file we received from Fujitsu Network Communications. Fujitsu and Sierra Circuits are both members of the IPC-2581 consortium responsible for updating the standard and actively endorse the widespread adoption of the standard. The demonstration project is a 12-layer network line card.
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For more information on IPC-2581, check out our IPC-2581 Tech Talk video.