Group Assignment on Electronics production

🖨️ Week 8 - Electronics production (Group Work)

In this week's group assignment, our task was to produce a test PCB using our LPKF PCB milling machine and evaluate the quality of the produced PCB.

---

🟢 Gerber file preparation

The task was to manufacture a PCB from a given layout design, which included various PCB trace and isolation widths. The provided file was in PNG format, meaning it needed to be converted to Gerber format to be used with our LPKF PCB milling machine.

We performed this conversion using KiCad:

1. Opened KiCad's Image Converter
2. Imported the PNG file
3. Selected “Negative” (so that the tracks remain as copper and are not drilled)
4. Selected "Footprint" as the output format
5. Clicked Export to Clipboard

Next, we opened the PCB Editor, pasted the converted image, selected the Edge.Cuts layer, and manually drew the board outlines.

We then generated the Gerber files by clicking Plot.

In the Plot settings, we selected F.CU and Edge.Cuts under "Include Layers" and then clicked Plot.

The Gerber output was verified using Gerber Viewer in KiCad before transferring the files onto a USB stick for use with the LPKF PCB milling machine.

🟢 PCB Milling Process

1. Machine and software setup

2. The CircuitPro software was launched on the milling machine's computer.

• The default template was loaded.

• The program prompted us to check if the tool magazine was full and if a bit was inserted.

• Starting the Process Wizard

• We selected "Start Process Wizard" and chose a single-sided PCB (double-sided is possible, but copper through-hole vias are not available).

• The FR-4 board was selected.

• The imported Gerber files were checked for correctness.

1. Tool and Setup Adjustments

2. A 0.2 mm universal cutter was selected for milling.

• Fiducials (positioning holes) can be manually placed at the board edges for alignment if a double-sided PCB is manufactured.

• Holding tabs were placed at the top and bottom to allow easy removal after milling.

1. Preparing the PCB for Milling
2. The PCB was placed on a porous plastic surface, with a vacuum securing it in place.
3. The vacuum (extraction) was turned on via the software.

• For additional stability, the PCB was also taped along the edges.

1. Positioning and Calibration

2. A 35 µm copper thickness was selected.

• The engraver head's x/y position was adjusted so that the depth limiter does not hit the tape when the engraver goes down to touch the PCB surface.

• Reference points (P1 and P2) were marked, with P1 at the lower-left corner and P2 at the upper-right.

• The milling area was positioned at the lower-left edge using the arrows in the program.

• Multiple copies could be selected for production.

• Pressed Continue and Saved the changes.

• Milling and Adjustments

• The board production wizard was started.

• The milling depth was tested using the "Mill a Line" function.

• The bearings warmed up for 2 minutes before starting.

• Evaluating the Milling Process

• Milling width was assessed using a microscope integrated in the machine.

• A V-shaped 0.2 mm mill was used, which makes a deeper cut if it drills deeper.
• The line cut was much too shallow at first, so the knurled rotator was turned in small increments clockwise for a deeper cut:

• Now the milling width was close to the nominal 0.200 mm, so the milling process was started.

• Monitoring the Milling Process

• The machine operation was carefully observed.
• If issues occurred, the milling could be stopped by opening the cover.
• During tool changes, we listened for a "clonk" sound to confirm bit removal.

🔍 Cleaning and PCB Evaluation

1. Finalizing the Milling Process
2. Vacuum and tape were removed to detach the PCB.
3. The sacrificial board was cleaned.
4. The last milling bit was returned to its holder before closing the software:

• The machine head was moved to a safe position before shutdown.

• Inspecting the PCB Quality

• The PCB was cleaned and examined under a microscope.
• The minimum milling width achieved was about 200 µm, and the thinnest trace width is only a few tens of micrometers based on the following camera and microscope measurement:

🖨️ → 📤 Workflow for sending a PCB to a boardhouse

Another task was to document the workflow for sending a PCB to a board house. We started by checking for the cheapest provider on pcbshopper.com. Since our PCB has 50 µm trace/space widths, we selected these parameters on the site. Only one provider matched our criteria: Aisler.

At the Aisler website, we clicked "Get Started," which led us to a window where we simply uploaded our lines.kicad_pcb file.

The file uploaded successfully:

The minimum selectable trace width/space was 125 µm: not quite as thin as our thinnest trace but still very narrow. The delivery time was estimated at two weeks, and the cost was €15.66 for three boards.

🎯 Summary**

• Successfully converted the PNG design to Gerber format using KiCad.
• Configured the LPKF milling machine and completed the milling process.
• Used a microscope to inspect PCB quality and assess the finest trace width.

---