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Added some notes about the gerber files.

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Salvador E. Tropea 2020-11-06 17:12:55 -03:00
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@ -33,6 +33,7 @@ To learn more about KiBot variants visit the [example repo](https://inti-cmnb.gi
* [Filters and variants](#filters-and-variants)
* [Usage](#usage)
* [Installation](#installation)
* [Notes about Gerber format](#notes-about-gerber-format)
* [Usage for CI/CD](#usage-for-cicd)
* [Github Actions](#usage-of-github-actions)
* [Credits](#credits)
@ -605,6 +606,46 @@ kibot --help-outputs > /dev/null
- Run the script *src/kibot*
## Notes about Gerber format
I found this topic poorly documented and quite complex. So here is what I know, feel free to send me any corrections.
Note that this is a very dynamic topic and this text was written in november 2020.
The gerber format is controlled by [Ucamco](https://www.ucamco.com/en/), a leading manufacturer of equipment and software for PCB fabrication.
Even when this isn't an open standard they release the spec for free and interact with Jean-Pierre Charras (father of KiCad).
So KiCad support for gerber format is really updated.
The gerber format evolved with time, here are the versions I know:
* **RS-274D** obsolete version of the format.
* **RS-274X** (aka **X1**) this is the *extended* version of the format. Is the most widely supported, but has some limitations.
* **X2** this is the format currently recommended by Ucamco and the default for modern KiCad versions.
This extension adds important meta-data to the files. It helps CAM operators to know what's every drawing in the image.
So you know which are pads, tracks, etc. And also more interesting information: impedance controlled tracks, the role of each file, etc.
Using X2 you can know what is each file without the need of special names or file extensions.
KiCad can generate drill files using X2.
* **X3** this is the current draft. One interesting addition is the *Components* role.
These files replaces the position files, adding important information about the footprint.
In addition to them is the spec for the **Gerber Job** file. This file was introduced between X2 and X3, and is used to group all the gerber files.
The *gbrjob* file contains all the missing stack-up information.
KiCad 5 can generate X1, X2 and gerber job files, including drill information in gerber format.
KiCad 5.99 (6.0 pre-release) can also generate X3 files (position files in gerber format).
As you can see the idea of Ucamco is to unify all fabrication information in one format.
The **X2** format was designed in a way that software that fully implement **X1** can just ignore the added meta-data.
In an ideal world you shouldn't bother about it and generate **X2** files. Just use the **gbr** file extension and a *gbrjob* file.
The problem is with poorly implemented CAM tools. In particular **CAM350**, used by various important cheap China manufacturers.
This software has known issues interpretating aperture macros and some X2 data.
If your manufacturer has problems with your files check the following:
* Put gerber, drill and position files in the same directory.
* Disable **X2** extensions (`use_gerber_x2_attributes` set to `false`)
* Use arcaic role mechanism (`use_protel_extensions` set to `true`)
* Disable **aperture macros** (KiCad 6 only: `disable_aperture_macros` set to `true`)
## Usage for CI/CD
When using a GitHub or GitLab repo you can use KiBot to generate all the needed stuff each time you commit a change to the schematic and/or PCB file.