The 3 Big Goofs Print E-mail
Written by Max Clark   
Thursday, 01 March 2012 23:31

Tips for improving the design to fabrication handoff.

Engineers and printed circuit designers wipe copious amounts of sweat from their brows upon delivering PCB design data package to board fabricators. Their relief is often premature, however, as problems discovered by the fabricator result in resending data, lengthy phone calls, and in the worst case, a re-layout and respin of the board. Yet the errors PCB fabricators see most frequently can be easily found and fixed before data are delivered for manufacture.

Despite designers’ best efforts, fabricators have an elaborate and well-designed process to bring a design up to the level where they can manufacture a quality PCB at an acceptable yield. This process takes hours, even days. When errors are found, days can be wasted correcting those errors and getting a new data package to the fabricator. Here are three simple and common-sense tips to make the design-to-fabrication handoff much cleaner, and keep some sweat off your brow.

The consensus among fabricators is that three particular errors account for the majority of time wasted in the handoff to manufacturing. All, as one would expect, are substantially human errors and omissions. Altering the final signoff process on PCB designs to include these three checks could substantially lower the overall cost of a PCB.

Double-check data entry. Without exception, the leading issue fabricators have with design data is data entry errors. From misspelled file names to omitted or swapped components and reference designators, the possibilities are vast. In truth, most could be caught with a careful proofread and edit of all documentation. These types of errors are subtle for the design group to catch, even more so for a fabricator not nearly as familiar with the data.

For the most part, data entry errors are usually discovered and brought to the design group’s attention before fabrication begins. In that case, the cost is relatively low. But, as subtle as some errors may be, they can be missed until later in the process, costing time and possibly resulting in an expensive respin of the design. The solution for the design team is simple: Take the time to review the entire dataset and build it into the PCB release-to-manufacturing process.

Ensure all files use the same measurement granularity. Another surprisingly common problem is different measurement granularity in different files. For example, the granularity on the layout may be set to a considerably finer value than the drill pattern.

Again, fabricators have seen this frequently enough that they check for it and usually catch granularity problems before moving to production. In that case, again there are phone calls, regeneration of data, and delivery of a new data package to rectify the problem. This costs a moderate amount of time and money. However, the problem can slip by and not be found until board drilling begins. In this case, there is scrap and rework, in addition to lost weeks.
This problem can be avoided by verifying the granularity of all data and never just accepting default values.

Verify all files are included. The third most common problem is simply omitting necessary files from the data package sent to the fabricator. The first thing the fab checks is that all required files have been received. Too often, there are omissions of data required for manufacture.

This error is caught early in the process, but correction still requires phone calls, chasing down the correct files and resending. Several days are often lost in the process.

Design for manufacturing processes and tools are becoming more necessary to ensure products move efficiently from design to board fabrication to assembly and package integration. Some of these tools are fairly expensive and may take months or years to amortize. Adding the three common-sense steps described here to your handoff procedure could very well be three of the most-effective DfM steps available to ensure efficient, quick transfer of a PCB design to manufacturing.

Max Clark is product manager at Mentor Graphics, Valor division (mentor.com); This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Last Updated on Friday, 02 March 2012 18:59
 

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