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Take nothing for granted, don’t take chances and never, ever underestimate the power of a CNC machine. |
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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. |
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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).
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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. |
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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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