Electronics Production

Hero Shot

This is the finished ESP32-S3 board I made this week: milled, stuffed, soldered, and tested working.

Introduction

During Electronics Production week I brought the ESP32-S3 board I designed in Electronics Design Week into the real world. This week was all hands on. I used CNC milling software, a milling machine, and steady hands to go from a digital PCB file to a real, assembled board.

I split the work into two main stages: preparing and milling the PCB, then assembling components onto the finished board. Each stage needed care, from setting up the tool path in Mods to probing the CNC bed and mounting small SMD components.

Assignments

Tools Used

The production workflow relied on a small, focused set of tools. Each one handled a specific stage, from file preparation through physical milling and assembly.

Production Workflow

The full process split cleanly into two phases. Phase 1 covers everything needed to go from KiCad file to a freshly milled copper board. Phase 2 covers component assembly and testing.

Step 01

Export PCB Design as SVG

I opened the completed ESP32-S3 board in KiCad's PCB Editor. I used File then Plot to export the front copper layer as an SVG file. This vector format keeps the trace geometry exact and is the input format Mods Project needs.

KiCad PCB EditorSVG ExportFront Copper Layer

Step 02

Prepare the Tool Path in Mods

I went to modsproject.org and opened the PCB milling workflow. I uploaded the exported SVG file, then set three key parameters before calculating the tool path:

• 01 Invert the PCB. This flips the image so the milling paths remove copper around the traces instead of the traces themselves.
• 02 Set tool size. I entered the diameter of the milling bit so Mods calculates accurate clearances around each trace.
• 03 Calculate. Mods generates the isolation routing paths from the SVG geometry and the tool size, then I exported the G-code.

modsproject.orgInvert PCBTool SizeToolpath Calculation

Why invert? The SVG from KiCad shows copper as filled areas. Mods needs to know what to remove, so inverting the image tells the milling bit to cut around the traces and leave them standing on the board.

Step 03

Set Up Candle CNC — Import, Probe & Height Map

I installed and launched Candle CNC, imported the G-code from Mods, and checked the tool path preview matched the board layout before touching the machine.

Then I used Candle's built-in probing routine to set the X, Y, and Z origin, and ran an automatic height probing scan across the full board surface. Candle uses this height map to raise and lower the Z axis during milling, so the trace depth stays even even if the FR4 blank has any warp. This step is what separates a clean board from one where half the traces barely cut through.

Candle CNCG-code ImportZ ProbingHeight MapSurface Compensation

Why height map? FR4 blanks are rarely perfectly flat. Without probing, a warped blank causes the bit to cut too deep on one side and barely scratch the other. The height map fixes this automatically.

Step 04

Milling the PCB

I started the milling job in Candle. The CNC machine ran the isolation routing passes, removing copper between the traces to reveal the board layout. I watched the whole process closely for any trouble, like a broken bit, material lift, or the tool path drifting, and I was ready to pause the moment something looked wrong.

Isolation RoutingCopper RemovalCNC MillingProcess Monitoring

Step 05

Component Placement & Soldering

I placed all the components following the KiCad layout. I started with the smallest SMD passives, the resistors and capacitors, then the voltage regulator, and finally the ESP32-S3 module. I added plenty of flux before soldering each part, and used a fine tip iron at a controlled temperature to avoid lifting a pad or making a cold joint.

SMD SolderingESP32-S3FluxFine Tip Iron

Step 06

Testing the Board is Functional

With the board fully assembled I connected it to a computer over USB and opened the Arduino IDE. I selected the ESP32-S3 board target and the correct COM port, then uploaded a basic blink sketch to check the microcontroller was alive, the power regulation was stable, and the UART programming interface worked.

• 01 Hold BOOT. I pressed and held the BOOT button to put the ESP32-S3 into programming mode.
• 02 Upload sketch. I clicked Upload in the Arduino IDE, which compiles and flashes the firmware over UART.
• 03 Press EN. I tapped the EN reset button to leave programming mode and run the new firmware.
• 04 Verify output. I confirmed the LED blinks at the expected interval and watched the Serial Monitor for the boot messages.

Arduino IDEESP32-S3 TargetBlink SketchSerial MonitorBOOT + EN Buttons

This is the exact test sketch I uploaded to check the board was alive. You can copy it and try it on yours.

board_test.inocopy

int ledPin = 2;

void setup() {
  Serial.begin(115200);
  pinMode(ledPin, OUTPUT);
  Serial.println("Board is alive");
}

void loop() {
  digitalWrite(ledPin, HIGH);
  delay(500);
  digitalWrite(ledPin, LOW);
  delay(500);
  Serial.println("blink");
}

Result: The board accepted the firmware upload, the LED blinked as expected, and the Serial Monitor printed clean boot output. That confirmed the power section, the MCU, and the programming interface all work. The board is functional.

Problems and Fixes

Nothing went perfectly the first time. Here are the real problems I hit and exactly how I solved each one.

Outcome

By the end of the week the custom ESP32-S3 board was milled, fully stuffed, and tested. It accepted firmware, blinked its LED, and printed over Serial, so the board is functional.

Conclusion

Downloadable files