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Design007-Sept2019

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24 DESIGN007 MAGAZINE I SEPTEMBER 2019 screenshots from the Reference Gerber Viewer illustrate the level of information carried in a current Gerber X2 file. The pad selected on the left is identified as a via pad, and the pad se- lected on the right is identified as a copper-de- fined SMD pad, and as pin 1 of R13 with net / IRQ-7. With Gerber X2, a designer can easily distinguish between a pin, via, and trace. As you can see, any claim that Gerber is "dumb" is wrong and misleading. Directories and Files Some detractors claim that Gerber's files and directories are awkward to use. But realisti- cally, a zipped directory with ODB++ files is no different from a zipped directory of Gerber files. Furthermore, a typical ODB++ package is not even a single directory but a complex di- rectory structure. To be fair, the IPC-2581 pack- age is a single file, even before zipping it. This can be seen as an advantage, but it can be seen as a disadvantage too. Individual layers—such as AOI or imaging—must often be accessed during fabrication, so storing these layers in separate files (as in Gerber and ODB++) makes their extraction easier and cleaner. DFM Other naysayers claim that it is not possible to generate full and meaningful DFM reports from Gerber files. Figure 2 shows part of a QED report generated by Ucamco soft- ware from a Gerber job. The first block shows the rings categorized by vias, laser vias, component pads, and mechanical pads. The last block shows the clearances to outline split by pads, tracks, and copper pours. Clearly, meaningful DFM reports can be generated from Gerber files. Evolution For some users, the fact that Gerber has—apparently—remained unchanged is another no-no. Apart from the fact that Gerber has in- deed evolved over its lifetime and continues to do so, let's go with this. Let's take the automotive industry's steering wheel. This has been, well, a wheel, since 1894 when Al- fred Vacheron took part in the Paris-Rouen race with a four-horsepower Panhard model that he fitted with a steering wheel instead of the then-popular tiller. It was such a great idea that within a decade, the vast majority of new cars had steering wheels. The round shape was a winner, and its position at the front of the car was a pretty good idea too. That was 125 years ago, and guess what? Steering wheels are still round, in the front, and used to direct cars. Nobody would say that they haven't evolved because they're not square or attached to the roof of the car. Steer- ing wheels have kept what works and have evolved with automotive steering and safety technology, integrating in-car entertainment and comfort features on the way. This is a bit like Gerber. Like the steering wheel, Gerber has stayed at the front, keeping what works, while the rest of this free, open format evolves to keep abreast of and drive beneficial devel- opments in PCB design and engineering. Why Use Gerber? One common question I hear is, "Why do designers still use Gerber?" I believe that de- signers have very solid grounds for their reluc- tance to drop what works in favor of a new for- mat. It is not that these new formats are bad— Figure 1: Output from a popular CAD system illustrates that Gerber X2 fully identifies pad types, sizes, nets, and pins.

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