Week 8, Electronics Production¶

Assignment¶

Group Assignment¶

Characterize the design rules for your in-house PCB production process: document feeds, speeds, plunge rate, depth of cut (traces and outline) and tooling.
Document the workflow for sending a PCB to a boardhouse
Document your work to the group work page and reflect on your individual page what you learned

Individual Assignment¶

Make and test a microcontroller development board that you designed

Checklist¶

from Nueval

Linked to the group assignment page
Documented how you made the toolpath
Documented how you made (milled, stuffed, soldered) the board
Documented that your board is functional
Explained any problems and you fixed them
Uploaded your source code
Included a ‘hero shot’ of your board

Individual Work¶

For an electronics production project, I built from the same design used for Electronics Design (week 6). Since this will milled on our Roland Modela MX-20 3d mill. In the lab, while an MX-20 can be used in multiple processes (including small 3d milling and scanning) we have a MX-20 which is dedicated for milling copper circuit boads.

Desiging with KiCad, my circuit will utilize an RP-2040, a button switch, and an LED paired with a resistor. I added these itesm to KiCad. Rather than attach the RP-2040 directly to the board, I will use a socket profile, which will allow the microprocessor to be removable for use on other boards. I made the connections with wires. Labels would be better, particularly for more complicated boards, but this is my starting point.

While I detail specifications of the MX-20 further on, a critical part of board milling is ensuring that the copper traces are broad enough, while also having sufficient separation. To ensure this, the board design rules are important to ensure this happens. I therefore set the minimum clearance and widths to 0.45mm, which are not the defaults in KiCad.

In the PCB design tool, I made paths for the circuits, also placing the items for the board.

Then, to prepare for milling, the board outlines need to be converted to a PNG. This is a multistep process, which leverages Inkscape. To begin, using the “Plot” command in KiCad, the front copper layer is exported as an SVG.

The SVG is imported into Inkscape. This came in as black on white background, while the MX-20 needs the reverse. Therefore, I drew a box around the traces, turned the traces to white, and make the background box black. The box borders will become the edge trace for the board. With this created, the image is exported as an 1000 DPI PNG.

Now we have the necessary input for the MX-20, we can review the specifications for the machine. While the MX-20 can be used for other milling, ours is dedicated to copper board milling.

Item	Value
Working Area	220 mm (X) x 160 mm (Y)
Max Part Size	203.2mm[X] x 152.4mm[Y] x 60.5mm[Z]
Spindle Motor	10W DC motor
Feed Rate	0.1~15 mm/sec
Max Load	1kg
Resolution	0.025 mm/step
Spindle Speed	6500 rpm
Acceptable Materials	Wood, Plaster, Resin, Machinable wax, Styreform, Chemical wood, Copper

Specifications of the MX-20

Our machine is on our local network, and the HTTP server to control is on port 12345. While the IP address is dynamic, the current address is used. With that, I used my personal computer to browse to the server controlling the MX-20. With that, I load the PNG image for the board, then define my output time (Rolland mill, [.rml]), and then come to the process tab, which is set to cut paths.

Then the PNG needs to be changed to the cut paths. With the loaded image then do the “calculate” button. It is important to make sure that the “server” is set to the same IP address as the web address, and also to make sure that the machine is set to “MX-20”.

The bit on the MX-20 is changed to the v-cut bit for making the traces, and the X,Y are zeroed to be just inside the area to be cut. Those positions are manipualted via the server interface. See the X0, YO positions in the previous image. To move the X,Y change those positions and use the xy0 jog command. The bit height is set by lowering the Z axis (with buttons on the MX-20) until the bit is just above the board. Then, gently loosen the bit and let it touch the board. Tighten the bit while holding it at the position and then this is ready to cut paths. Use the “send” command on the computer, and the paths will be cut.

After the board traces are cut, the edge PNG is uploaded. The process is repeated with some small changes. The process is now the edge cut, and the bit is changed to the wider one that cuts edges.

Then the components are soldered onto the board. As seen, I used two rows of seven pin connectors for the socket. My LED proved to be a dud, and was removed. I soldered on a new LED after this immage.

Based on sample code from the Fab Academy course page, I used the following to program the board. I used VS Code with this code, which was connected to the board via USB-C. As seen in the code, this is in MicroPython.

from machine import Pin

# For the RP2040, use the micropython pins
button_pin = 27
led_pin = 26

# Variable for the button
button = Pin(button_pin,Pin.IN,Pin.PULL_UP)
# To track the button state
button_up = True

# Define the LED
led = Pin(led_pin,Pin.OUT)

# Overall state: Button up, LED off
#                Button down, LED on

# Button down is detected as 0

while True:
  # If button pushed, and the button state is 'up'
  # Then turn on the led
  if ((button.value() == 0) and button_up):
    led.value(1)
    print('LED on')
    button_up = False
  # If button is up, and the state is not up
  # Then turn off the led
  elif ((button.value() == 1) and (not button_up)):
    led.value(0)
    print('LED off')
    button_up = True

The board was programmed so that the button turns on the LED.

Hero video of working board

The design files for this work have also been used for the week 6 work. A zip archive with design files.

Ordering board¶

I also wanted to evaluate ordering a board via a PCB house. To start, I used the same PCB board design, but cleaned up the labels for the front silkscreen.

For ordering, the board is exported in Gerber format. This requires export of the copper layers, silkscreen, masks, and the edge cuts.

The exported files were combined in a single .Zip archive, and uploaded to a PCB fabrication house. For my test, I tried JLCPCB. I uploaded the files, and made a mock order. This order costs $2, though another $17.50 for shipping.

This was a simple process, and could be very useful in the future.