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# MSLA PCB Exposure: KiCad → Photon Mono 4
Using an MSLA (Masked Stereolithography Apparatus) resin printer for creating PCBs is a technique known as "Direct UV Exposure." Instead of printing a plastic part, you use the printer's LCD screen as a dynamic digital mask to cure photosensitive materials (etch resist, solder resist and silkscreen) on a copper board.

KiCad PCB layers need to be converted to `.pm4n` files for direct UV exposure on an **Anycubic Photon Mono 4** (9024×5120 px, 17 µm/px, 1494.12 DPI) on the screen size of 153.408 x 87.040 mm.

---

## Preparation

### KiCad: Set your design grid
In KiCad's PCB editor, go to `Preferences → Preferences → PCB Editor → Grids` and add a custom grid of 0.017 mm. This ensures trace edges land on pixel boundaries and avoids the sub-pixel rounding that causes the ±1px size error people see with arbitrary grids.

### Create the `Dummy.pm4n` file

Open **CHITUBOX Basic** slicer (or any other slicer that works for your resin printer), select printer **Anycubic Photon Mono 4**, slice any tiny STL (e.g.: 1×1×0.05 mm box), and save as `Dummy.pm4n`.

This file is reused for every job — it carries the correct LCD resolution metadata.

## Manual processing

`UVtools` has a dedicated `PCB Exposure` tool that converts a Gerber file to a pixel-perfect image given your printer's LCD resolution, specifically for exposing copper traces.

### 1. Install `UVtools`

```bash
sudo apt-get install -y curl
sudo bash -c "$(curl -fsSL https://raw.githubusercontent.com/sn4k3/UVtools/master/Scripts/install-dependencies.sh)"
```

### 2. Run `UVtools`

```bash
cd UVtools
./UVtools
```

### 3. Export `.pm4n` file from Gerber

- You export Gerber from KiCad (not SVG), which natively gives you positive/negative control per layer.
- You open the `Dummy.pm4n` file in `UVtools` (a minimal valid `.pm4n` sliced by `Chitubox` or `Photon Workshop` with any tiny model), then use `Tools → PCB Exposure` to inject your Gerber layer e.g.: `Flow_Controller_Panel-Front.gbr`.
- You control `inversion`, `invert` and the `exposure time` at the bottom of the `PCB exposure` dialog.
- You save it as e.g.: `Flow_Controller_Panel-Front.pm4n` file and print it.

![PCB_Exposure_Dialog_1](images/PCB_Exposure_Dialog_1.png)

![PCB_Exposure_Dialog_2](images/PCB_Exposure_Dialog_2.png)

---

## Automated script

### 1. Install dependencies

```bash
python3 -m venv .venv
source .venv/bin/activate
pip install pygerber Pillow numpy
```

Or activate the `venv` once and put `source .venv/bin/activate` in your shell profile.

### 2. Export multiple layers (e.g. copper + soldermask + silkscreen)

```bash
./export.sh \
    --layers Front,Back,F.Mask,B.Mask,F.SilkS,B.SilkS \
    --invert Front,Back,F.Mask,B.Mask,F.SilkS,B.SilkS \
    --mirror Front,F.Mask,F.SilkS \
    --exposure 60 \
    ../kicad2panel/panel/Flow_Controller_Panel.kicad_pcb
```
It should output:
```bash
Plotted to './output/gerbers/Flow_Controller_Panel-Front.gbr'.
Plotted to './output/gerbers/Flow_Controller_Panel-Back.gbr'.
Plotted to './output/gerbers/Flow_Controller_Panel-F_Silkscreen.gbr'.
Plotted to './output/gerbers/Flow_Controller_Panel-B_Silkscreen.gbr'.
Plotted to './output/gerbers/Flow_Controller_Panel-F_Mask.gbr'.
Plotted to './output/gerbers/Flow_Controller_Panel-B_Mask.gbr'.
output/pm4n/Flow_Controller_Panel-Front.pm4n
output/pm4n/Flow_Controller_Panel-Front.preview.png
output/pm4n/Flow_Controller_Panel-Back.pm4n
output/pm4n/Flow_Controller_Panel-Back.preview.png
output/pm4n/Flow_Controller_Panel-F_Mask.pm4n
output/pm4n/Flow_Controller_Panel-F_Mask.preview.png
output/pm4n/Flow_Controller_Panel-B_Mask.pm4n
output/pm4n/Flow_Controller_Panel-B_Mask.preview.png
output/pm4n/Flow_Controller_Panel-F_Silkscreen.pm4n
output/pm4n/Flow_Controller_Panel-F_Silkscreen.preview.png
output/pm4n/Flow_Controller_Panel-B_Silkscreen.pm4n
output/pm4n/Flow_Controller_Panel-B_Silkscreen.preview.png
```
#### 2.1. Check the layer preview
Check the `output/pm4n/Flow_Controller_Panel-*.preview.png` images — traces should appear black on white background.
- background = UV exposed = resist removed = etched away
- traces = dark = resist kept = copper stays

#### 2.2. Check the printer exposure
Open the `.pm4n` in `Chitubox Basic` slicer to visually verify before printing.

#### 2.3. Adjust exposure
Start with `--exposure 60` and bracket from there — Bungard presensitized at 405nm typically lands between 30–120s depending on board vintage and storage.

### 3. Export single layer (e.g. copper)

Export the front layer as gerber
```bash
kicad-cli pcb export gerbers -o output/gerbers -l F.Cu ../kicad2panel/panel/Flow_Controller_Panel.kicad_pcb
```
It should output
```bash
Plotted to 'output/gerbers/Flow_Controller_Panel-Front.gtl'.
```

Convert the gerber to pm4n and preview
```bash
python3 gerber_to_pm4n.py Dummy.pm4n output/gerbers/Flow_Controller_Panel-Front.gtl \
    --invert --mirror --exposure 120
```
It should output
```bash
output/pm4n/Flow_Controller_Panel-Front.pm4n
output/pm4n/Flow_Controller_Panel-Front.preview.png
```

Open the preview image
```bash
xdg-open output/pm4n/Flow_Controller_Panel-Front.preview.png
```

Open the `output/pm4n/Flow_Controller_Panel-Front.pm4n` in `Chitubox Basic` slicer to visually verify before printing.

---

## Troubleshooting

**`kicad-cli: command not found`** — add KiCad to PATH:
```bash
export PATH="/usr/lib/kicad/bin:$PATH"
```
Or on Flatpak:
```bash
alias kicad-cli='flatpak run --command=kicad-cli org.kicad.KiCad'
```

**Expected Gerber not found** — KiCad's layer→filename mapping:

| Layer | Filename stem |
|---|---|
| `F.Cu` | `Front` |
| `B.Cu` | `Back` |
| `F.Mask` | `F_Mask` |
| `B.Mask` | `B_Mask` |
| `F.SilkS` | `F_Silkscreen` |

---