Shine-through Halloween PCB Pins

Introduction

Happy Halloween!

For this year's halloween project I decided to go a bit simple and experimented with creating shine-through PCB pins using KICAD. I had to set up some constraints from the get go as not to go over budget and wanted to create a small batch of pins to give away to friends! The LED's are attached upside down which makes them a bit harder to solder, but it creates this beautiful diffused glow when done properly.

Supplies

📝NOTE
You can keep track of the components with this interactive guide

Electronics

Per PCB:

• LED Amber Clear 1206 SMD x 5
• 200 OHM 0805 SMD Resistors x 5
• Battery retainer coin 20mm SMD
• Micro Switch Slide SPDT 0.3A 5V
• 20mm Silver Craft Pins

Tools

• Soldering Iron
• Tweezers
• SAC305 Lead free solder

PCB Gerbers

Find the latest gerbers in the project repo.

Inspiration

Using the PCB substrate as a diffuser

Cross section diagram of a single layer PCB: The lower and upper soldermask layers are removed from the PCB to take advantage of the fiberglass semitransparent PCB core also widely known as FR-4 which naturally diffuses the light

The industry standart PCB core FR-4 is a glass-reinforced epoxy laminate material composed of woven fiberglass binded with epoxy resin, which makes it a semi-trasnparent frosty material great at diffusing light.

Some makers take advantage of these properties by soldering SMD LEDs upside down and shine the light directly into the PCB core to create a diffused glow as seen on these pins found on Tindie.

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I wanted to explore this technique as well to experiment with light diffusion using only the PCB core!

Design

Drawing

My initial idea was to create a simple jack-o lantern pin, but the CR2032 battery was taking too much space, so I had to adjust the design to make room for the battery.

That’s how I ended up with this final drawing: a ghost wearing a pumpkin on its head.

PCB

The first step was creating the schematic for the LEDs. For this project, I used five LEDs in parallel, each paired with its own resistor, powered by a CR2032 coin cell battery.

I imported my artwork layer by layer to the PCB Layout with File --> Import --> Graphics. The key detail here is that the part where you want the light to shine through must be imported as F.Mask. which is used to create a custom solder mask opening.

After finalizing the layout, I sent the board out for manufacturing. I chose a black solder mask with a gold ENIG finish on the pads to get as close as I can to the pumpkin+ghost theme.

Cards

I made these pins as Halloween gifts for my friends, so I thought it would be fun to attach them to custom “Happy Halloween” cards.

I designed the cards in Figma and left a small space under the text to write each friend’s name.

Assembly

Soldering

For the the components, I've ordered 1206 Orange color LED's along with 0805 200 ohm resistors, a micro switch and a coin cell battery clip.

Soldering the components was a bit challenging because the LEDs had to be mounted upside down.

The method that worked best for me was to first place a small blob of solder on the tip of the soldering iron and use it to attach one side of the LED.

After that, I soldered the other side by carefully applying solder from both the top and bottom to ensure proper electrical contact.

Once both sides were secure, I went back to the first joint to reflow and smooth it out.

After the LEDs were in place, soldering the remaining components was relatively straightforward.

And with that, the Halloween pins were complete!