This week focused on transforming a digital PCB design into a functional physical board. Starting from the refinement of my previous design, it was also necessary to prepare the files for fabrication, mill the PCB using the Roland SRM-20, and assemble it through soldering. Finally, the board was programmed to verify its functionality, completing the transition from design to working electronics. For this, I consulted our Group Assignment.
Before fabrication, I reviewed my PCB design from Week 6 to confirm it was ready for production. While the board was already functional, I made a few key adjustments: I enabled additional pins on the Seeed Studio XIAO RP2040 to support future I2C and UART communication, and I repositioned the push button to ensure proper clearance for the USB-C cable, improving both usability and assembly.
The design includes ten LEDs grouped in pairs, each with 220Ω resistors. The previous button was replaced with a Switch Tactile CNK, and a capacitor was added for power stabilization. Power distribution is defined through 3V3 and GND labels with PWR_FLAG symbols. Additionally, pin headers for I2C (SDA, SCL with 4.7kΩ pull-up resistors) and UART (TX/RX) were included for future expansion.
Once the schematic was completed and verified, the design was transferred to the PCB editor in KiCad. Since this board was based on a previous development, the PCB layout was reused and adjusted to the new components.
The layout was also developed following a star-shaped outline, and the outline of the board was defined with a thickness of 2 mm. On the other hand, the routing was carried out using 0.8 mm minimum track width and a 0.7 mm minimum track clearance; ensuring suitable connections for the milling process.
Once the PCB design was completed, the files were prepared for fabrication. For this I exported my files to Gerber, which is used to define each layer of the PCB and its corresponding traces. For this, I went to the option File → Fabrication Outputs → Gerber Files. A configuration window appeared and then click on Plot.
After completing the export process, the program creates a folder containing all the generated Gerber files, which I will be using for the next fabrication steps.
For this step I will be using the gerber2png. I selected all my Gerber Files and uploaded them to the page. Once the files were uploaded, the platform displayed the available layers, such as Top Trace, Top Drill and Top Cut. I clicked on Generate All to produce the corresponding images, then click on “generate PNG”.
For the cutting process I will be using the Roland SM-20 Milling Machine , and to set up its parameters I used modsproject.org, a platform that allows the adjustment of key settings required for the fabrication process.
First, I went to the SRM-20 mill section, and selected the Mill 2D PCB.
Before continuing, it's important to clarify that there are different settings in the Set PCB defaults section:
First, I clicked on Select PNG File Folder to upload my trace and outline files. Then, in Set PCB defaults, I selected the configuration for traces.
I kept most default settings, but in the Roland SRM-20 section I set the speed to 4 and defined the X, Y, and Z origins as 0. Finally, I clicked on/off.
In the mill raster 2D section, I clicked calculate, which generated and downloaded the toolpath file.
The interface also provides a preview of the milling path.
For the outline, I repeated the same process, selecting 1/32 outline and keeping the same settings, except for the speed, which I set to 2.
This was the visualization of the PCB outline.
Although my design does not include perforations, I tested the drill configuration. I uploaded the PNG, selected 1/32 drill, set the speed to 0.2, defined the origin as 0, and activated the process.
This is an example of how the holes for mounting components would look, although they were not used in this design.
Use a copper-clad fiberglass board and fix it onto an MDF sacrificial bed using double-sided tape. Make sure the board is completely flat and well attached to avoid movement during milling.
Secure the sacrificial bed to the machine using screws, ensuring it is firmly fixed and aligned.
Install and open VPanel for SRM-20, then connect the machine via USB. Verify the connection before proceeding.
Use the X, Y, and Z controls in VPanel to position the head. Adjust movement speed in Cursor Setup depending on how precise you need the movement to be.
Choose the correct bits for each process (traces, drills, outline). Always mill in this order: Drills → Traces → Outline, this to avoid misalignment or board movement.
Insert the milling bit and secure it using an Allen key (clockwise). Make sure it is properly tightened to prevent slipping.
Move the head to the lower-left corner of the board (this will be my reference point). Carefully lower the Z axis until the tool just touches the surface (use small step increments like x1 or x0.1 to avoid damaging the bit).
In Set Origin Point, click on X/Y and Z to establish the starting position from which the machine will begin cutting.
Click CUT → ADD → Select the file → OUTPUT to send it to the machine.
The spindle will begin rotating and the machine will execute the cut. Stay close and monitor the process at all times. Keep VPanel open and Pause the job if anything seems incorrect.
After cutting, remove the remaining dust using a vacuum to clearly see the results and avoid complications in the next step.
Move the head if needed, but do not reset X/Y origin . Only reset the Z origin after installing the new bit, since tool length changes.
Click CUT → Delete All → Add the new file → OUTPUT, and repeat for each milling step.
Once all cuts are complete, clean the board using the vacuum, unscrew the sacrificial bed and carefully remove the board.
Organize all SMD components and identify their position on the PCB before starting.
Using tweezers, place the component on its corresponding pads, making sure it is properly aligned.
Heat the soldering iron to around 270 °C and apply flux to improve solder flow and adhesion.
Apply a small amount of solder to one pad while holding the component in place to anchor it.
Heat both the pad and the component lead with the soldering iron, then apply solder until it flows evenly and creates a proper joint.
Continue this process for resistors, LEDs, the microcontroller, button, and pin headers, starting with smaller components and finishing with larger ones.