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PCB Designing using Kicad (Part 11/12)

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PCB Design Gerber Files:

Gerber files are like ‘universal language’ for PCB designs.  It is the family of the file format used by the PCB industry software to describe the connections, drilling, and milling data. Gerber format is an open vector format for 2D images. The standard file extension is “.GRB”  and the current Gerber format is – 274X.

Common problems with Gerber files and solutions:

 
S.No Problem Description Solution

1

 Obsolete file format Gerber file has mainly two formats, 274D and 274X. In 274D, Aperture list is required while in 274X Apertures are embedded into the files. ODB++  is also a Gerber format.  In these formats 274X is the preferred format, since the Apertures are embedded into Gerber files.  
2 Confusing file labels The board layers are labeled in Gerber files as “.GBL” , “.GBS” and so on. The finding board layers with these labels are very confusing. Providing a text label in the Gerber file data is a better way to indicate the files and layers representation.
3 Fabrication Drawing files A fab drawing contains the overall dimensions of the board, cut outs, special routing, file names, thickness, and material names related information. If there is any simple mistake, it may lead to a big Error in fabrication of the PCB. When we have to work with an outside vendor, we have to carefully check these files, before sending them.  
4 Drill format Drill formats do not have a proper format; we have to guess that by trial and error.  In format, the header must include the information about drill file. It’s a short way to convey the information within the drill file. 
5 Registration of the layers Manual file alignment of the layers is necessary because some files may have layers at different datum alignment.  If possible, having the Gerber files registered to a common data point is recommended.
6 Vector fills Layers with shield area come filled with 1 or 2 mil vectors. This causes the Gerber file to be larger in size. And we need to contourize the data. Filling areas by using “raster” and “contour” is recommended.
7 Composite layers To create one layer, some design software use composite layers.  Like Embedded traces use three layers to create one layer. 1. Plane layer, 2. Clearance layer, 3. Trace layer.  Three layers should combine, and then we can get  a single Gerber layer.

How to create Gerber files:

Creating Gerber files is different in different software. Like, in eagle cad we can generate Gerber files by using CAM processor, but it is different in KiCad.

To generate Gerber file in Kicad follow these  steps:

1.       Open file menu and select plot option. (In PCB new window).

2.       A plot dialogue box will appear on the screen as shown below.

 
Screenshot of Plot Dialogue Box in KIcad
 
Fig. 1: Screenshot of Plot Dialogue Box in KIcad
 

1.       Select “plot format” as Gerber.

2.       Select the required layers in layers list.

EX: front copper layer, bottom copper layer, front and back silk screens, Mask layers, Edge cuts, etc.

3.       Leave output directory blank, it will save out Gerber file default Project folder. But if you need to create a separate folder, then select path.

4.       In “options” default boxes are checked, if we need any other options we can select and check.

5.       Now press the “plot button” at the bottom side of the window. After this, select “Generate drill file”.

6.       A dialogue box will appear with the name of “Drill file generation”.

7.       Leave output directory (we selected any path in plot window, select same path).

8.       Settings are very important in this window, mainly,

·         Drill units (inches)

·         Zeros format(suppress leading zeros)

·         Options(minimal header)

·         Drill origin (Absolute)

 
Screenshot of Drill Files Generation Window on KIcad
 
Fig. 2: Screenshot of Drill Files Generation Window on KIcad
 

1.       Now click on “Drill file” button and close the window.

2.       Now Gerber file is created,  which can be checked in default project folder. Zip this folder to send fabrication.

How to check/View the Gerber file:

1.       In KiCad, we can view the Gerber file by using Gerber view.

2.       Open Gerber view > select Load Gerber file > select any layer > we can see the selected layer.

3.       We can also view Gerber file by using online Gerber viewers. EX:  GerbLook.

4.       Open GerbLook in web browser and load the Zipped Gerber file.  It shows the available errors. If no errors are there, it will show                  Gerber files.

 
Screenshot of Checking the Gerber file on KIcad
 
Fig. 3: Screenshot of Checking the Gerber file on KIcad
 

Filed Under: Tutorials

 

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