Why should you care how data are output from your CAD tool after you’ve completed your design, provided that the design is sound and the description is thorough?
UPDATE: Read about IPC-2581 set to retire Gerber files across the board!
Whether you send Gerbers to your manufacturer (along with a drill file, netlist, BOM, board drawing and readme text), a zipped ODB++ file, or a file in the IPC-2581 format when it’s finalized, what’s the difference?
How your design data are formatted determines how easily—and perhaps how successfully—your manufacturer can interpret exactly what you intend to have built. Nearly 90% of the orders my company receives for fabrication and assembly are Gerber-based, even though it was more than 15 years ago that Valor introduced the ODB++ format for intelligently describing designs at the manufacturing level.
Each zipped ODB++ file, if complete, consolidates all the information needed for a board to be manufactured and assembled, and it can be directly loaded into the front-end CAM system.
We would much rather receive ODB++ data, which our CAM tools can analyze in a fraction of the time required to convert and review Gerbers and their accompanying files. But of course, like other manufacturers, we are happy to accommodate our customers’ preferences.
I’m not alone in emphasizing the benefits of the richer data in the ODB++ format when compared to Gerber data. Whereas Gerbers convey merely the outlines and locations of features layer by layer, ODB++ data identify the features and enable their sizes, shapes, and positions to be adjusted locally or globally to simplify manufacture and ensure good boards.
Gerbers are no more than simple graphic representations, and are therefore hard to physically edit: A round pad is just a filled drawn circle completely independent of all other such circles. However, ODB++ defines pads as pads. For example, if necessary during CAM review, one, some, or all 10- mil pads can be enlarged to 12 mils.
Manufacturers do make slight adjustments in coordination with customers to preserve the integrity of designs. When our Valor system reveals something in a design that would compromise manufacture—such as traces that are too close together or holes that are too big for pads—and it could be resolved with a minor edit, the system automatically checks the edit against the netlist to confirm that change has no effect elsewhere. Each zipped ODB++ file, if complete, consolidates all the information needed for a board to be manufactured and assembled, and it can be directly loaded into the front-end CAM system, which will in turn output the programs to drive all the process equipment—nice, clean and easy. When we receive a design described by Gerbers and the accompanying files, we convert these files so they can be loaded into our system for review. That takes time. You can appreciate why a quickturn manufacturer would favor production formats that streamline transferring designs to fabrication.
Like ODB++, the evolving IPC-2581 standard is an intelligent format for delivering all the data needed to automate PCB manufacturing, assembly and testing, all in one unified file. Unlike ODB++, which has been proprietary to Mentor Graphics since that company purchased Valor several years ago, IPC-2581 will be open to implementation by anyone, with no license required.
ODB++ has been so widely imported by CAD and CAM vendors that it has become a virtual standard, and as far as I know, no burdensome restrictions are imposed on those vendors licensing ODB++. But I understand why some people may be nervous about relying on a captive de facto standard. Why Mentor Graphics might be reluctant to cheerlead the IPC effort is equally simple to comprehend. From the Mentor (Valor) perspective, why on Earth is there a need for another standard that will simply require conversion to ODB++ and therefore invite errors?
My company actively supports the IPC effort, while recommending the use of ODB++ by our customers because it saves both of us time and uncertainty. IPC introduced the open 2581 standard many years ago, long after my company started business, and there has been little clamor among customers to bring designs to us in that format. However, I am willing to bet that a truly open standard eventually will prevail.
Incidentally, regarding format uniformity, in the 1990s my company compared the Gerber data from several EDA tools for a reference design and found the outputs differed in accuracy and in the size of the data set. There’s no guarantee that the ODB++ files output by various platforms would exactly coincide either. My company has volunteered to build a reference design on behalf of the IPC-2581 Consortium when the CAM software is available for testing. We also intend to compare the results of a design output in Gerber, ODB++, and IPC-2581. I’ll let you know what happens.