Creating manufacturing files that accurately reflect what the PCB designer wants to manufacture is a always a challenge, even for professional designers. However, by learning from others and avoiding the most common mistakes, a designer can speed up the turnaround time, reduce the chance of orders placed on hold, and complete PCB projects faster. The tutorial briefly presents the some common aspects and mistakes made with manufacturing files and recommendations to avoid them.

About Gerber files and aperture lists 
The Gerber files specify what to do and where. Additionally, the aperture list specifies what tool to use. A single comprehensive aperture list for all layers should be sent with the Gerber files, rather than a separate aperture list for each layer. Please note: an aperture list does not need to be sent with RS-274X format files. If you send RS-274D format, the manufacturer uses the aperture list in combination with the Gerber files to create the final artwork for fabrication.

Recommendation: One comprehensive aperture list for all layers, English Units is the best solution. The designer does not need to modify/save in other format, etc. the aperture list the CAD software outputs. An aperture list does not need to be sent with 274X format files. Absolute all PCB layout packages which generate as output files in RS-274D format also output an aperture list. Common extensions include .rep, .apt, and .apr. If you have difficulty outputting an aperture list, please use 274X format, in which the apewrture list is included into the Gerber file.

Missing Gerber Files
Unbelieveble at the first moment, there are cases in which the designers submit orders for PCB manufacturing and forget to attach their Gerber files. The situation is simmilar to that when a person wants to send somebody an e-mail with attachment but forgets to attach the file. 

Recommendation:  Gerber 274X or 274D, English units are preferable but nowadays metric units are coming in force worldwide. ODB++ files are acceptable; however, these files are in a new manufacturing format and it is possible to have problems at the interface with the manufacturer. It is possible to convert many other file formats to gerber. Announce the PCB manufacturer about any post-processing files in non-gerber formats.