Fig-1 Screenshot of the Programming PCB Layout looking down from the Component side.
 Note: Copper (the blue tracks) is on the 'Solder' side.

Gerber Track Isolation Routines

One way to make printed circuit (PCB) boards is to cover the bare copper clad board in an etch resist such as fast dry enamel paint applied from a spray can and then scratch through the resist with a scriber where you want the copper removed by the etch solution. This method while little used is great for prototyping as it is a quick and dirty method which is able to produce a prototype board in a very quick time and at a very low cost! To use this method you need either a working vertical CNC milling machine capable of accepting G-code commands or a plotter capable of accepting  HPGL commands. The software isolation 'Tool' provided with the side4linux package allows you to generate both the G-code isolation command files for the milling machine and the HPGL isolation command files for the plotter. I will now discuss the methodology behind how these files are produced.

The track isolation principle is simple, instead of using an etch resist 'mask' to create areas that are not to be removed we are uncovering areas where copper must be removed. This means that every track must be scratched around so that it's edges are exposed through a film of etch resist. When making a PCB by this process you must check every track with a multimeter after etching to ensure both continuity of signal path and electrical isolation from other tracks not connected. The etch resist can be any spray paint that scratches cleanly and resists the etching fluid, it is applied to the entire surface of the board before scratching the outlines of each track. I should mention that the normal method of creating isolation is to mechanically mill the copper off the board with an engraving cutter but this implies that you have the special equipment needed to do this, if you do then that allows mechanical milling instead of scratching so you can skip the paint and etch processing.

Software must create from the Gerber file a Pixel Map in memory representing the finished PCB tracks for one side of the board. The 'Pixel Map' to be used for this isolation demonstration is shown next ( it has been reversed using the GIMP program to allow you to follow the Demo which shows the tracks from the 'SOLDER' side. Note that the isolation program reverses the X axis if required by a parameter set on entry from the Tools Menue) , The need for reversing is to mirror the Gerber file as Gerber files show only the view from the component side ( sort of Xray viewing!). Note that the origin ( Axis X = 0, Axis Y = 0 ) is always the bottom left hand corner so when simulating this means that the simulation should always appear in the top right hand quadrant of the simulator,  Bmach2d.

Fig-2 Pixel Map of the 'Solder' side of the MC1 Programmer board.

Having read in the Isolation File into a 'Pixel Map' the software must then scan the Pixel Map from the bottom to the top looking for a track to isolate.
The algorithm to do this is shown next,

At the 'Action Box' of this algorithm that says 'Move to a New Location and Mark pixel' there are G-code or HPGL commands written which are then entered into the isolation command file that is created to drive the milling machine/plotter. The end result of all this is the scanned image shown below which is the simulation of the isolation in Bmach2d.

Fig-5 Programmer PCB Isolation simulation pictured in Bmach2d.

Notice the red lines in figure-5 these are fast movement which happens once the cutter ends cutting a track and is raised to travel to the next track. The blue lines are the cutter or drill moving at the machining feed rate as set by the 'F' feedrate command ( we will cover the 'TRACKS.ANC' command file later in this demo). Compare this with the 'Overlay' scanned from Bmach2d below which shows the isolation tool's conversion of the Gerber file of the 'solder side' reversed. Notice in the GCODE isolation above that each track is cut all the way around to isolate it from other tracks on the PCB. Pitfalls of this process are that tracks brought together to form a closed polygon ( such as a box or triangle )  will fail because the isolation automaton can only run around the outside of a track edge and therefore closed polygons should be avoided. Note also that the isolation automaton is not able to do 'backup and retry' maneuvers so if the isolation fails you will need to go back to the pcb layout program and simplify the point of failure. Remember that if the isolation algorithm fails it should fail immediately! Therefore, if there is a failure to complete an isolation look for an uncompleted track in the Bmach2d simulation for the problem.

Fig-6 Programmer PCB Isolation Overlay pictured in Bmach2d.

1. View the Gerber files and identify which one we will use to create the isolation tracks from.
2. Decide on if we are creating a plotter or milling machine command file.
   
3. Decide whether to reverse isolate the tracks  ( used for solder side isolations only! ).
4. Isolate the tracks into a 'TRACK' file ('TRACKS.OVL for the Overlay, 'TRACKS.HGL' for a plotter and 'TRACKS.ANC' for a milling machine)
5. If the 'TRACK' isolation file is for a milling machine then 'COMPILE' it into the machine command file.
6. Simulate it using Bmach2d. ( Practical-2 )
   
7. Actually cut the PCB using the 'milldrive' program or by another means e.g. send it to a plotter.
   

1. Open 'side4linux' and click on Project>Open Project in the Main Menue.
   
2. double click on the 'DEMOS' Product Area,
3. Double click on the 'SIDEdemos' Product,
4. In the file dialog double click the  'PCBS' folder. This takes you to where PCB projects are kept.
5. Double click on 'Mc1_programmer', this opens the 'Mc1_programmer' project folder.
   
6. Double click on 'mc1_programmer.prf'. This opens the 'Mc1_programmer' project file.
7. Notice that the left bottom status bar window says 'Project:Mc1_programmer ' which is the Project Name.
8. Notice that the next window says 'Ptype: PCBS' which is the Project Type.
9. Click on the 'File Explorer' 'Files' tab on the left and view what schematic files are actually in the Project ('power').
10. Click on 'Tools>PCBS>Run PCB, minimise the 'Component Library' window and maximise the main window of the 'pcb' program.
11. Load the layout file 'Mc1_programmer.pcb' from the main menue of 'pcb' ('File>Load Layout').
12. It should look like the graphic below,

Fig-7 Screenshot of the Mc1 Programmer PCB Component Layout ( same as Fig-1 above ).

Now close the pcb' program and open the Gerber file viewer 'gerbv' from the side4linux IDE, 'Tools>PCBS>Gerber Viewer' and click on the 'OFF' button top right.
Try clicking each button below on and off until you see the following graphic which according to the tooltip should be 'Mc1_programmer.group0.grb'.


Fig-8 Screenshot of the Mc1 Programmer PCB, 'Solder' side as seen through from the 'Component' side ( File:: Mc1_programmer.group0.grb ).

  Close the Gerber viewing program and now create the reversed isolation GCODE 'TRACK.ANC' file using the tool provided as follows.

1. Click on 'Tools>PCBS>Isolate GCODE Tracks Reverse'
2. In the file dialog select the file to open 'Mc1_programmer.group0.grb' and click the 'Open' button.

Fig-9 Screenshot of the Isolate GCODE Tracks Reverse File Dialog.