I want to preface this log entry, and probably every other entry in this project, that I am very new to PCB design. I designed my first PCB about 4 months ago so I would take any information in this post with a pinch of salt and healthy dose of scepticism .
I decided to use this project to try out a few PCB techniques that I've seen in other projects that I thought were really cool.
First up was the reverse mounted LEDs as seen in lots of badges. It's where the LED is mounted so that its illuminating through the PCB. For example the Fat Pika SAO
This is achieved by not having any solder mask (the colour of a PCB, often green, purple for Oshpark, yellow above on Pika) or any copper so the LED can shine through and be diffused.
As mentioned earlier, I am far from an expert on the subject, and to be honest I find it hard to find much information on how exactly to do it, or even what its called! But I decided to give it a go in EasyEDA (I can hear the suggestions of "KiCad" from here by the way :) )
The first thing I needed to do was add the Top & Bottom Solder Mask layer to the shown views, you do this by clicking on the cog on the layers window and adding the layers.
Almost counter intuitively, adding designs on these layers is the instruction to not add Solder mask to that area. For the LEDs I added a square to the bottom Solder Mask layer (the same side the LED is mounted), so there would be no solder mask between the pads of the LED and added a larger circle on the Front Solder Mask Layer. I guessed the size of the larger circle in terms of how much the LED will diffuse (it's about 0.7cm in diameter).
Now that we have a footprint that might work it was time to move onto the LEDs
You can buy specific reverse mount LEDs but I normally buy all the components for my projects from China and reverse mount LEDs don't seem to be too easy to come by. But I was speaking to Dave Darko and he was telling me he just used regular 0603 LEDs upside down in his word clock project.
They seemed to work out pretty well for him so I said I would just go with them.
Soldering them upside down is not too bad actually, the hardest part is actually keeping it flat to the board. For soldering, just put a bit more solder on the first pad than you would normally and place the LED carefully down with a tweezers.
I was really happy with the result of my first effort at reverse mounting the LEDs, if thats even what its called!