Build Instructions

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• 1

  KiCAD design + export

  When laying out a board in KiCAD, there's few tips to follow:

  • Minimum track width: 0.2mm
  • Minimum track clearance: 0.2mm
  • (optional) Don't do clearance to the board edge (source: https://forum.kicad.info/t/zone-to-board-edge-clearance/45386/4)
  • Place symmetrical align holes, for example a hole in every corner, exactly 3mm from the edge
  • Place board "Grid origin" and "Drill/Place File origin" points in the bottom left corner of the board
  • Take special care of through hole components! This PCB doesn't have plated holes and so the component needs to be soldered from both sides in order to link top and bottom layer. KiCAD will by default link signals or ground planes using a through hole component, in the same way it does with a via. However, some components might cover the top side, making it unavailable for soldering.

  For through-hole component that cover the soldering point on the top layer, it might be a good idea to route a "backup" track on the back layer, just in case it's not possible to solder them from the top, or only route on the back layer where you're sure to get good contact.

  Finally, before exporting, make sure to run design rule check to ensure no silly mistakes spoil the design later (e.g. silk screen placed on top of a copper pad).

  Export

  To export the files, navigate in KiCAD to Files -> Fabrication output -> Gerbers (.gbr) ...
  

  • Set output directory, e.g. "CAM"
  • Include layers: all copper, silk, mask and edge cuts
  • Under "General options", select "Use drill/place file origin"
  • Before export, it's a good idea to run design-rule check. This will provide feedback on any unconnected tracks, overlapping silkscreen etc that should be fixed
  • Finally, press "Plot" to export the files
  • Then, press "Generate Drill Files" to export drill patters and sizes
    • In the new window, make sure "Drill File Format" is "Excellon" and "Drill origin" is "Drill/place file origin"
    • Finally, press "Generate Drill File"
  • Close both dialogs

• 2

  FlatCAM

  Isolation Routing

  To process exported files into a CNC job, we'll use FlatCAM. 

  • Start by importing F.CU layer
  • Double-click the layer and and select "Isolation Routing"
  • In the tools table, we'll set tool diameter to 0.19mm. This has to be lower than the "Minimum track clearance" setting in KiCAD to ensure correct routing. As a side note, I'm using 0.2mm V-bit for isolation routing. So the correct setting here would be 0.24mm instead. So in reality, all the pads and tracks will be 0.05mm undersized. I have tried this step with bit diameter as low as 0.1536mm for a 0.2mm bit, and the results were still satisfying.
  • To generate the CNC object from geometry, set V-Tip diameter 0.15mm for cutting depth of -0.0746mm. Spindle speed 15'000 rpm.

  Settings

  Copper clearing

  Usually, it's enough to just do isolation routing, but sometimes, there's the need for clearing copper areas. FlatCAM has NCC feature for that.

  This can be used to generate geometry and a following CNC job. In this example, I'm using a 0.5mm V-bit for clearing larger areas of copper.

  Back Isolation Routing

  Next, import back copper layer. Before generating geometry and job, the imported gerber object needs to be flipped in either X or Y axis. I prefer flip around Y axis.

  To do so, double-click imported gerber object, and press "Transformations" button from the side menu. From there, press "Flip on Y" from the "Mirror (Flip)" side menu. Using the 4 align/mount holes, confirm alignment between the front and back copper layer.

  Before back layer Y flip

  After back layer Y flip

  From here on, repeat the isolation routing and copper clearing steps in the same way as for the top layer.

  Export cnc jobs

  The above will result in 2 to 4 ".nc" files (isolation and copper clearing per copper layer), CNC job to run on the machine. To make this work with carvera's tool changer, a small tweak in ".nc" files is needed as outlined in the video here.
  

• 3

  Fixture + Cutout

  To work with PCBs, I create a fixture that aligns on carvera bed using pins, and is fastened with 3 screws (file attached here). This fixture has also been milled so that its top face is flat. On the fixture, the bottom-left hole is placed at coordinates (5,5) from the anchor point 1, and it's where I'll have my bottom-left align hole for the PCB.
  

  I always start a PCB project by adding a raw PCB to the fixture, drilling the align holes and cutting the board to the correct size. To create CNC job for that part, I use MakerCAM. Import EdgeCuts and NPTH layers from KiCAD export into MakeraCAM. Select the align holes, and create "Vector Drilling" task for them, end depth of 10mm (to go through the board and create align holes in the fixture for later). Secondly, select the edge cut vector, and create "Vector Contour" job with end depth of 1.6mm. Both the holes and the cutout are made with 1/8" x 12mm single flute bit, in my case set as tool #1. Export both toolpaths together in a joint file, and import to Carvera controller.

  When running the job, set the offset from anchor point in controller such that the bottom left mount hole on the PCB aligns with the bottom left hole in the fixture. I always place that hole on PCB at coordinates (3,3) from origin and since the align hole on fixture is at (5,5), it gives an offset of (2,2).
  

  The PCB is secured to the fixture with double sided tape.

  Once the job is completed, clean up the dust chips from the board and leave it stuck to the fixture. Use the newly made holes and a 1/8" bit to test the alignment on at least 3 holes at the time. The holes might be a bit tight at this point, you can carefully widen them with a 45 deg chamfer bit in a hand drill.

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