PCB CNC

Introduction

CNCs can facilitate in the creation of PCBS:

• Manual etching and then using CNC to drill automatically.
• Cutting out the board , to have round PCBs, or similar.
• Automated isolation routing: From a PCB some surface parts are milled away, so that the connection copper area are left isolated.

Currently, all three steps are working on the Geilomat.

A rather badly isloated and drilled PCB done on the Geilomat. One can get much better results. Short-Circuiting Copper flakes are visible on the center left.

For the isolation, there is the normal approach, where all contours of copper areas are milled.

A normal milled PCB, using pcb-gcode eagle plugin

However much faster results can be obtained by milling the minimal path necessary to create the PCB-topology.

A voronoi milled PCB (left), a normally milled PCB, and a traditional PCB. Source

Some results are given in the soup of the Geilomat

Time Consumption

For a complete, dense EuroPCB, expect about one hour of total time:

• 10 minutes for preperation, mounting and setup.
• 15 minutes for drilling/cutting.
• 20 minutes for the isolation of the bottom layer.
• 5 minutes for flipping/remounting/aligning
• 20 minutes for the top isolation
• 2 minutes for manual overworking the board.

For an arduino shield, expect about 30 minutes:

• 10 minutes for preperation, mounting and setup.
• 5 minutes for drilling/cutting.
• 5 minutes for the isolation of the bottom layer.
• 5 minutes for flipping/remounting/aligning
• 5 minutes for the top isolation
• 1 minutes for manual overworking the board.

Pros/Cons

Pros:

• Quite Faster than manual UV-exposing, etching and drilling.
• Cool
• No chemicals
• Good for high currents, as wired are wide.
• Cheaper PCB material. (Same area approx 50% the price)
• PCBs of up to 30x20 cm. However, flatness is problematic.

Cons:

• If the board is not mounted completely flat, the isolation might be not deep enough, and hence there are short circuits.
• Sometimes, flakes of copper short circuit neighboring copper areas. Usually at corners. A knife helps.
• Dust.
• Loud.
• Capacity between adjacent copper areas.
• Hotter soldering is required, as there are no thermal pads.

Metaboard*.sh

Metaboard are some bash shell scripts, that will automatically create cnc-paths in the form of gcode files. The starting point is the eagle .brd file. Download of the files: Here

Usage: metaboard3.sh <options> filename filename: eagle brd file to process

-double: create a double sided gcode
-0.8:    use a 0.8mm mill head instead of a 0.6
-tight:  only offset by a distance of 0.3 mm
-filled: the eagle board file has a filed dimension area instead of lines

It calls a couple of external programs:

• Eagle: to output the gerber files of the top and bottom layer
• eagle: to call an ulp-program "drillbernhard.ulp" that outputs the drilling and cutting paths.
• Eagle: to output the excellon drill files.
• Visolate: To create the isolation paths. We use an unreleased version, that is scriptable.
• Meanwhile, pcb2gcode was adopted and is used.
• grecode To mirror the board for second side. (Grecode was created especially for metaboard.sh by --Bkubicek 09:55, 26. Jul. 2010 (CEST))

While these are called, a couple of windows will pop up and hopefully disappear again. only shell output will be produced. you will get some debug images also in the current directory.

Usage

The workflow splits into the following points:

• Preperation: create an eagle brd file, copy it
• Metaboard*.sh: create the gcode files for the geilomat
  • For the most current worflow use metaboard3.sh . It will require a 0.6 mm mill head, which is the best, as small IC holes are possible, and the tool length is so small that little sidewards forces are created. Hence, mill speed is larger than for 0.8mm tools.
• Setup:
  • mount the board in the geilomat using double sided sticky tape.
  • On the flat milled wood area.
  • Which should be de-dusted first.
  • Double sided tape should not overlap, as this creates 0.1mm height difference.
  • Insert a suitable tool. Either a sharp Gravierstichel .

• EMC-setup: home the machine "home all", "touch off"/set coordinate system so milling will be on the actual board

Bottom layer:

• • Isolation-milling: use the *back.ngc file created by metaboard3.sh
  • drilling: use the *drill*.ngc file created by metaboard3.sh
  • and cutting: use the *outline*.ngc file created by metaboard3.sh.

For single sided boards, the process stops here. Double sided boards are more sophisticated:

• Flipp the board, mounting it in any usefull position.
• Top layer:
• note down two drill hole coordinates from the drill file, in mm units.
• navigate using the joypad to the holes location on the flipped mounted PCB. Write down the coordinates of the special holes.
• call "grecode -align x1 y1 x2 y2 X1 Y1 X2 Y2 *front*.ngc > tmp.ngc" to rotate and shift. Maybe you have to change the signs of the x1 and x2, depending of the pcb2gcode version you use.
• Loading the tmp.ngc file just created
• check if the gcode is now aligned with the pcb.
• Isolate the top.

Removing the boards works best by using a twist motion around the z-axis. A brush should be nearby to clean the grooves.

Links

PCB milling

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