Making Printed Circuit Boards with the Fab Lab

Marc Boon, Feb 2008

Step 4: Milling and drilling the pcb

For making a PCB, we use standard single-sided copper-clad board of 1.6 mm thickness. The base material is FR-4 glass-reinforced epoxy (or FR-2 pertinax, if you can find it), with a copper layer of 35 micron (0.035 mm) thickness. We have to place the material on the bed of the milling machine using a proper fixture, which will allow drilling through the material. The fixture should therefore be made of a material which is easily drilled, but of sufficient rigidity to keep the board in place. A suitable material for the fixture is MDF. It is beyond the scope of this how-to to describe a way to build a proper fixture. In the most simple case it consists of a piece of MDF, on which you fix the PCB material using double-sided tape.

Once the PCB material is mounted, we are ready to set the Z-position or datum. The Roland Modela milling machine does not do this automatically, so we have to set the milling head to the proper vertical position before we start sending any files. The easiest way to do this is to lower the drill to just above the surface of the PCB, then loosen the screw which holds the tool, until it drops on the material, and then tighten it again.

We will first mill the contours of the traces, and after that drill the holes.
To send the file microtv.mill to the machine, assuming the machine is connected to a serial port either directly or through a USB-to-Serial adapter, use the appropriate method for your platform:

Open a command prompt by Clicking on the Start button, selecting Run.. and typing 'cmd',
then go to your Eagle project directory using the 'cd' command,
then send the milling file to the machine by typing 'type microtv.mill >com1'.

Mac and Linux:
Open a Terminal window, go to your project folder using the 'cd' command,
send the milling file to the machine by typing 'cat microtv.mill >/dev/ttyUSB0'

The exact name of the serial port may be different on your system. Substitute the right port name for com1 or /dev/ttyUSB0. If nothing happened, you probably didn't specify the right serial port.

After milling is completed, we will send the file for drilling the holes (and optionally milling them to the right diameter). Just repeat the above commands while substituting the .mill file with the .drill file.

Here's an image of the PCB after milling, but before drilling:Micro TV milling

Finally Step 5: Soldering and testing!

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