I'm trying to make a hole partially through a PCB in Eagle to allow a reverse mount led to shine through to the other side. I got this idea when I saw a torch shine through a pcb where there was no ground plane on either side as shown below.
I have some 1206 SMD leds and want to figure out how to design a hole in Eagle that only cuts through about 1/2 of the pcb or layers 1-15. I did some googling and couldn't find anything relating to this.
This is something which is usually not covered by the functionality of common EDA-Tools like EAGLE.
Here's why: This is done by milling after processing all other production steps of the PCB. It can't be done by just omitting something in the prepregs used, as they can contain only drills for vias. And the latter is only done when buried vias are needed.
Milling through some of the layers is rarely needed, so there is no standard in handling those special requests. It can't be defined in gerber or drill files. There is no need to describe it in an EDA tool, as this doesn't make any sense, when no CAM file can't be generated to describe the necessary milling actions.
There is a milling layer in EAGLE, but it it's only purpose are millings through all layers of the PCB.
You might need some luck to find a PCB manufacturer who is even able to do such millings.
I recommend to add a new layer for each milling depth you want to have on your PCB and export it as DXF along with the alignment marks. Then explain your demands to your favourite PCB manufacturer and see what happens.
Edit: There are further arguments, why EAGLE doesn't provide mechanism to describe intricate millings. Most layers describe electrical features and the copper layers can hold information only on the distinction where to remove copper and where not. There are no layers describing the prepregs and where they should have gaps or not.
If your going to do this, you might be able to create an additional mechanical layer and supply that to the manufacturer. It's been a while since I have used eagle, and it's my understanding that you can't create additional layers. One way to get around this would be to use a gerber editor (like viewmate) and create the mechanical layer in viewmate.
Either way an additional file would need to be used. Contact the manufacturer and ask them if they could create a hole in the layers that you want. This will create additional cost for you (and it might be a lot of additional cost), as the manufacturer will have more steps in their process. Realize that some manufacturers might reject this, but you should be able to find one that will do something like this.
Another "much less coolness factor" option would be to use two through holes around the LED as shown below (or one directly below the LED if it is large enough):
Other options include: - Not using a cutaway and removing all copper in the PCB - Using a light pipe with a complete cutaway
