Tips for PCB Drilling and drill file

Tips for PCB Drilling and drill file

1.What file format should I send for my drill file?

Your Gerber files are used to print the images needed on your PCB. The copper patterns, solder mask reliefs, silkscreen, board outline and even fabrication notes should all be in 274X Gerber format. (We can also accept 274D Gerber or ODB++ formats).

The file that is used to program the CNC drilling equipment is not a Gerber file. It needs to be in Excellon CNC Drill File format. This is an industry standard format and all PCB layout software packages should be capable of creating this file. Some software packages automatically include this file during Gerber output and others need to be specifically generated as a separate step when creating your data. Contact your software support if you have questions regarding your software.

Use these settings when creating your drill file:

--Excellon Format

--ASCII Odd/None

--2.4 Trailing

--Zero Suppression

2.Where do I specify the drill sizes? In my fab notes, drill file or Gerber files?

If your CNC drill file is created correctly, your drill sizes should be included in the drill file. You may also opt to include a drill map and chart in a fab print. This not required but can be helpful to ensure the CNC drill file matches the drill map. Errors such as missing drill hits and incorrect drill sizes can be caught before manufacturing begins.

The fab print can be submitted in a Gerber layer and/or other common file type such as PDF, DOCX, TXT, etc. Including the fab print in a Gerber layer is highly since the drill map and drill file can be compared much more easily than if it was only in a PDF. Putting the fab print in Gerber format also guarantees that your notes will be seen when your board is tooled for production. Here is a common layout for a drill map and chart.

What drill sizes should I specify in my drill file?

Specify the size you'd like the holes to be when you receive the board. This is called the Finished Hole Size. With plated thru-holes (PTH), you don't need to account for plating in the barrel of the hole. We'll automatically compensate for the reduction of the hole caused by plating and use a slightly larger drill than you specify as your finished size. For non-plated thru-holes (NPTH), we will use the closest drill size available since we don't have to compensate for the copper plating.

How can I be sure I am asking for the correct size hole?

If the via is only used to pass signal to another layer, the hole can be quite small since a component lead doesn't need to physically fit into the hole. If spacing requirements are not a concern, use 12mil (0.3mm) holes or larger since they do not add cost to your design.
If your PTH is used as a component hole, make sure your specified size will be large enough for the component lead to fit inside the hole. Usually component manufacturers will state a recommended finished hole size on their datasheets, consult this first. If this isn't specifically stated in the datasheet, a good rule of thumb is to make the hole at least 10mils (.25mm) larger than the diameter of the lead that's going into the hole. The tolerance on a plated thru-hole (PTH) is +/- 3mils (+/- .0762mm). Keep in mind the lead on the component will also have a tolerance. If you have a perfect storm where your part is on the high end of its tolerance and the hole is on the low end, you'll need that extra room to fit your part into the hole.