Nuts & Volts - July 2004

In The Trenches

It’s easier to lay out the board yourself than to chase down elusive errors made by a machine.

Conclusion

It is important to do printed circuit board layout properly. It requires

common sense and attention to detail. Hopefully, this overview has provided some insights that will be useful to you. NV

PCB Files and Formats

Getting your PCB made commercially requires that you send your design via the Internet (there are a few exceptions). You will need the following files in “Gerber” format for a standard double-sided PCB: 1) top trace layout, 2) bottom trace layout, 3) silkscreen (if used), 4) soldermask (if used), 5) an aperture file, and 6) Excellon drill file. The Gerber format is a standard PCB format that virtually all layout software supports.

We’ve already discussed items 1 through 4. The Gerber files define the trace placement, but don’t specify the physical sizes. The aperture file does this with a short list of “flash codes.” Additionally, the Gerber files don’t specify the actual size of the holes to be drilled in the PCB. The Excellon drill file tells the manufacturer where the holes are and what size they are supposed to be. Drilling and etching are two separate procedures. When you send these files, be sure to add a short “Read Me” file that relates your file names to the physical parts of the PCB. This saves time and confusion.