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Requirements and Installation

What and Why

     Printed Circuit Boards (PCBs) are in virtually every piece of modern electronics. They start out as a sheet of fiberglass (or in low-end systems, a cheap plastic called phenolic). Then they are coated on one or both sides with a continuous sheet of copper. Then, in normal manufacturing, a photochemical process is used to remove much of that copper, leaving a desired pattern of traces (i.e. wires) to which electronic components are then soldered to form the desired circuit.

     However, for some applications, particularly very low-volume production, production in home or office environments, and rapid-design cycle R&D environments, the setup costs, environmental hazards, mess, and not least sensitivity of such processes to many variables, suggest that other methods of PCB production be explored.

     Mechanical etch is one major alternate method for PCB production. This process also starts with a copper-clad PCB. However, the unwanted copper is removed mechanically rather than chemically. Most often, a fine-point rotary tool bit is used to create a separation in the copper around the boundary of each trace (middle board in the picture below). The extra copper remaining between the traces is usually left in-place, as it is no longer electrically connected to any trace.

     The obvious thing to do would be to use a very small cutter and just cut around the entire boundary of each trace. In fact, there are a number of commercial systems already available which do just this, for example LPKF's products. But we were are also interested in an alternate method: compute the Voronoi region associated with each trace and cut along the boundaries between such regions.

     What is a Voronoi region? Simple. Imagine that instead of a PCB we are talking about a big flat field of uniform dry grass. Yes a field of grass. Now, simultaneously and uniformly, start little fires where all the traces would be. As each trace's fire spreads, the burned region it leaves is the trace's Voronoi region. You can imagine that the fires from two nearby traces will eventually expand, meet each other, and go out. These meetings of fires occur at the boundaries between the Voronoi regions.

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Acknowledgements

• The raster-to-vector algorithm is heavily inspired by Peter Selinger's potrace and his writeup Potrace: a polygon-based tracing algorithm.
• The voronoi computation is based on the following paper: Kenneth E. Hoff III, Tim Culver, John Keyser, Ming Lin, Dinesh Manocha. Fast Computation of Generalized Voronoi Diagrams Using Graphics Hardware. 1999.
• I learned some undocumented details of the gerber format from the source code for C. Scott Ananian's PCBMill Web Utilities and also the gerbv source code.

Disclaimer

     THIS INFORMATION AND/OR SOFTWARE IS PROVIDED BY THE AUTHOR "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS INFORMATION AND/OR SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.