Week 6: Electronics Production

01 / PCB design

Preparing the board for milling

I modified my Week 5 layout to make it easier to mill.

I increased the clearance to 0.4 mm and used 0.8 mm tracks. Clearance is the gap between copper features; track width is the width of the copper connection itself. I also added a filled copper zone assigned to GND.

In KiCad, I selected a track and pressed U to expand the selection, then E to edit its properties. Pressing B refilled the copper zones. The PCB Editor manual explains these tools in more detail.

Clearance: 0.4 mmTrack width: 0.8 mmCopper zone: GND

KiCad PCB layout with wider tracks and a ground copper zone around the XIAO RP2040 — FIG. 01The revised layout before exporting the milling files.

Exporting Gerber and drill files

In the PCB Editor, I opened File → Plot, selected Gerber, and exported F.Cu and Edge.Cuts. F.Cu contains the front copper trace pattern, and Edge.Cuts defines the board outline. My design also had holes, so I used Generate Drill Files to export the .drl files.

I used gerber2img to convert the fabrication files into PNG images. First I loaded the PTH drill file and the outline Gerber. I selected Black and white, kept the resolution at 1000 DPI, and locked the origin and dimensions. Then I uploaded F.Cu and downloaded the copper image with the same settings. Locking both values keeps successive exports aligned.

gerber2img showing the board outline and holes with origin and dimensions locked — FIG. 02The outline and hole image in gerber2img.

gerber2img showing the front copper image and 1000 DPI export settings — FIG. 03The front copper image for the traces.

02 / CAM and toolpaths

Generating the milling toolpath

The two PNGs became the input for the Carvera milling program in mods.

In mods, I opened machines → Carvera → mill 2D PCB tape. I loaded the copper PNG as the traces image and the outline and hole PNG as the exterior image.

In this setup, the black regions marked the areas to remove. My first attempt had the image inverted, so I got the opposite result, which looked pretty funny.

The Carvera mill 2D PCB tape program in mods with traces and exterior image inputs — FIG. 04The mods program with separate traces and exterior inputs.

Checking the preview

After clicking calculate, I opened the 3D toolpath preview. In my preview, green showed the surface paths and blue showed the cut-through paths. Red showed travel moves between paths.

The software estimated 3 minutes 39 seconds. I saved the toolpath as an .nc file that CarveraController could load.

3D preview of the PCB milling paths in mods — FIG. 05The 3D toolpath preview.

Calculated mods program with the milling paths and time estimate — FIG. 06The calculated job before saving the NC file.

The first milled board with the copper pattern reversed after an image inversion mistake — FIG. 07My first attempt: the copper pattern was reversed.

The first milling mistake

I had removed the copper I wanted to keep. The board made the inversion mistake and I redo it again.

03 / Carvera

Setting up and milling the board

Set up the board.

I connected CarveraController to the machine and uploaded the NC file. I had to use Upload and select. Upload alone was not enough because the controller still needed me to select the job. It took me a while to figure this out.

Once the toolpath appeared, I measured the available copper-clad area with calipers and adjusted the X and Y offsets. I selected auto leveling with a 3×3 grid for this board.

Carvera spindle and laser pointer above the copper-clad stock — FIG. 08The machine is auto-leveling.

CarveraController displaying the PCB toolpath and work area — FIG. 09The toolpath in CarveraController.

Attaching the board and running the job

I attached the FR-1 copper-clad board with tape, pressed out the air bubbles, and trimmed the tape neatly around the edges with scissors. The machine already had two sacrificial layers underneath to protect the bed, so I left them in place.

After that, it started working! When the milling finished, I vacuumed the debris and gently lifted the board off the tape. Holding a light behind it made the traces easier to see, especially on this single-sided board.

The copper-clad board in the Carvera after milling, with debris still on the surface — FIG. 10The board after machining, before cleaning.

The correctly milled board held against light so the trace pattern is visible — FIG. 11The corrected board with the traces visible against the light.

04 / Assembly and debugging

Soldering the components

Soldering this milled board was harder than I expected. It was very easy to make a short.

The goal is to make the joints look shiny and smooth. I used a multimeter to check for shorts as I worked.

I also had to pay attention to the LED polarity before soldering. The green marker on this LED should be the cathode.

The assembled PCB with a XIAO RP2040, button, resistor and LED connected by USB — FIG. 12The board after soldering the components.

Close view of the LED package and green marking — FIG. 13The LED package marking. Click for the uncropped photo.

Soldering notes from training

We should start with a clean, tinned iron tip, heat the pad and component terminal together, and feed solder into the joint. A small amount of solder on the tip helps transfer heat. Then wait for the solder to wet the surfaces. Flux helps remove surface oxides so the solder can flow. The joint needs enough heat to form properly, while prolonged heating can damage the part or lift a pad.

I used the multimeter to check for shorts. Inspecting the gaps between pads also helps find shorts. The Adafruit soldering guide has useful examples of bridges, poor wetting, and damaged pads.

A digital multimeter and probes on the workbench — FIG. 14The multimeter I used for continuity and short-circuit checks.

05 / Programming and testing

Testing the board

The physical board worked after the ground connection was fixed.

I uploaded the Arduino sketch for the XIAO RP2040. The button is on D10 and the LED is on D0. With INPUT_PULLUP, the released button reads HIGH. Pressing the button connects the input to ground and makes it LOW.

The program turns the LED on while the button is pressed and off when it is released.

Demo / The assembled board

The button and LED test on the board I milled and soldered. Open video ↗

Program behavior
Button released	Raw input 1 (HIGH), LED commanded off
Button pressed	Raw input 0 (LOW), LED commanded on
Serial output	Raw input, button state, and LED command every 200 ms

View the Arduino sketch

const int BUTTON_PIN = D10;
const int LED_PIN = D0;

void setup() {
  Serial.begin(115200);

  pinMode(BUTTON_PIN, INPUT_PULLUP);
  pinMode(LED_PIN, OUTPUT);
  digitalWrite(LED_PIN, LOW);
}

void loop() {
  int buttonState = digitalRead(BUTTON_PIN);
  bool pressed = (buttonState == LOW);

  digitalWrite(LED_PIN, pressed ? HIGH : LOW);

  Serial.print("BUTTON_RAW = ");
  Serial.print(buttonState);

  Serial.print(" | BUTTON = ");
  Serial.print(pressed ? "PRESSED" : "RELEASED");

  Serial.print(" | LED_COMMAND = ");
  Serial.println(pressed ? "ON" : "OFF");

  delay(200);
}

Download Arduino sketch ↓

Multimeter, oscilloscope, and logic analyzer

We used all three during training. A multimeter measures values such as voltage and resistance, and its continuity mode helps check connections. An oscilloscope shows how voltage changes over time. A logic analyzer captures digital HIGH and LOW states across several channels and can decode communication between devices.

The oscilloscope could also decode serial data. For UART decoding, the baud rate and serial format must match the transmitted data. The logic analyzer was more convenient for reviewing digital communication. Saleae's async serial guide explains those decoder settings.

A Rigol oscilloscope displaying a waveform and decoded serial text — FIG. 15The oscilloscope during training, with waveform and serial decoding.

A logic analyzer connected to a laptop showing captured digital signals — FIG. 16The logic analyzer setup for capturing digital communication.

I am new to electronics, so I chose a simple circuit to get through the whole process first. Now that I have made and tested this board, I can add more functions and keep working on my final project. I still want to try UV laser PCB fabrication later.

06 / Downloads and notes

Files from this build

These are the design, fabrication, and program files from this build. The NC program belongs to this Carvera setup.

Design and fabrication files
File set	Contents	Download
KiCad project	Schematic, PCB layout, and project settings	KiCad ZIP ↓
Milling files	Gerbers, drill files, raster images, and NC program	Milling ZIP ↓
Gerber layers	Front copper and board outline	F.Cu ↓Edge.Cuts ↓
Drill exports	PTH and NPTH drill files from KiCad	PTH ↓NPTH ↓
Raster inputs	Saved outline and copper images	Board.png ↓Traces.png ↓
Carvera job	`20261019_Xiangtao.nc`	NC file ↓
Arduino sketch	D10 button input and D0 LED output	Arduino INO ↓

Terms from this week

PCB production vocabulary
FR-1	A paper and phenolic resin PCB substrate. This was the copper-clad material I used.
mil	One thousandth of an inch. `1 mil = 0.0254 mm`.
Via	A connection between copper on different PCB layers. Board houses commonly use copper-plated hole walls.
Silkscreen	Printed text, component labels, and outlines on a PCB. It is a separate layer from the copper pattern.
Board house	A company that manufactures PCBs from fabrication files. JLCPCB in Shenzhen was one option mentioned in class.
Octopart	A component search engine for finding parts and comparing supplier listings.