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I recently had occasion to make a very simple circuit board intended to modify the program sequence and timing of an existing industrial controller. The board makes use of the PIC programmable microprocessor and as size is of no concern it is of the legacy type with drilled holes, components mounted on one side and the through leads soldered on the other. I had not tried the ‘isolation routing’ method for making pcb’s before so everything was a learning experience. As it turned out the process is very simple and easy to do so I decided to share my experience.

Once the circuit had been designed the next stage was to produce a layout of the circuit tracks and pads and there are many excellent programs with free (limited) versions available to do this and some will even export the GCode straight to file.

 

If you are serious about wanting to make circuit boards and are prepared to learn how to use the software then ‘Target 3001 Discover’ can be downloaded from the Majosoft website or ‘Eagle’ from Cadsoft together with ‘PCB_GCODE’ by John Johnson makes an excellent combination to draw, outline the tracks and create the GCODE all within the one package. See related links page for download details.

 

My layout here is a raster or bitmap image, the tracks and pads have been deliberately thickened up ready to be outlined or traced into a vector image. The vector image was then saved or exported into an HPGL plot file which was in turn converted to GCode (setting the safe Z and Z depth) using Martin’s excellent little program ‘Target2GCode’. When converting images from one program or format to another there is a possibility that the correct scale may be lost therefore some known reference point on the image should be used to finally set the scale before routing begins (I used the DRO Scale function in Mach3 to make a small correction).

 

These pictures show the completed routing, made with a standard engraving bit in one pass. There are a few burrs produced but, for this circuit, these can easily be removed by sanding with fine emery over the entire surface. Although a standard engraving cutter works a purpose made cutter would, I think, have made a much better job. Copper is a soft metal and positive rake cutters are usually used for this material.

 

As mentioned earlier this is a very simple circuit but it serves to illustrate the principle. By using finer pointed cutters and reducing the depth of cut to the minimum necessary (with fine work multi-pass is essential to avoid creating burrs and/or damaging the traces), extremely complex, double-sided boards perhaps incorporating surface mount IC’s with 1mm pin spacing's can reasonably be expected to be achieved by this method.

 

It should be stressed that the dust produced by the routing of glass fibre is toxic and care must be taken not to inhale the dust.

Another simple circuit board, this time it is for a two position bipolar stepper motor driver.

 

It took less than 3 hours from drawing the circuit, producing the layout, routing the tracks, assembling, soldering and testing the finished board. Not bad for a mornings work.

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A small panel, made to mount four LED’s as part of my laser project. This is a short video clip of the pcb being isolation routed.

 

As it was held on a vacuum table the through holes have just been centred ready for drilling manually as another operation.

Another, perhaps interesting, way of producing more complex printed circuit boards is to clean and then spray the copper clad board with ‘rattle can’ car spray paint which is resistant to ferric chloride pcb etchant. When dry the unwanted paint is etched away using the laser then the board is placed into ferric chloride to etch away the unwanted copper. The holes are drilled then the remaining paint removed with solvent ready for soldering the components.

 

Here I used the Mach3 Impact/Laser Engraving plugin to create the board from the original image (for a low power VHF pll Transmitter) which was in .png format.

 

This is a very fast process but it is best suited to ‘surface mount’ technology rather than ‘thro hole’. This is because there is no specific X-Y coordinate GCode file and as a result a drilling file cannot easily be produced and drilling all these holes manually would be extremely tedious, especially when there is a CNC machine sitting idle.

A couple of small PCB’s, isolation routed and profile cut, made for my low profile tool height setter.

 

The PCB on the right has also had the rear surface machined giving an overall thickness, including the switches, of just 2mm.