How to make 4 layer flexible circuit
The process will take an hour and some luck when you master it.
flexible LED matrix ring
copper foil circuit can be quite robust if all connection pins are well designed. And most importantly, with more epoxy cover layers, the chance of shorting is lower.
break down steps here
the reason why I did this
single side boards are easy to make, but when there are a lot components, it's quite easy to short somewhere. Sadly, the below board didn't work. I was using a heat bed and it luckily didn't take long. So I decided to revise Neil's double layer board a little bit and make it more robust and flexible.
too hard to figure out where went wrong. So the 4 layer flexible circuit journey started
added a cover epoxy film layer 4 to prevent thin copper line from bending
vinyl cut layer 1 copper foil on top of a base epoxy film, adjust strenth to make sure it only cut throught copper (cameo studio setting 1 depth 8 speed 20 pressure,it can be different depends on the knife's condition). peel off useless copper
vinyl cut layer 2 epoxy foil, stick it on top of layer 1
vinyl cut layer 3 copper foil, take the foil off its back film and stick it on the transfer film's back film to vinylcut. Save the transfer film itself for later use
when finishing cutting, put the transfer film on top of layer 3 copper foil. And then pull the three layer sandwich out of the cutting mat of Cameo. The transfer film prevent the circuit torn apart while peeling off from the mat.
pull the transfer film's back film off the copper foil. Apply force parallel to the surface.
apply the copper foil layer 3 on top of the layer 2 epoxy film. Peel off the transfer film using parallel force to the surface.
Peel off useless part of layer 2
vinyl cut layer 4 epoxy foil and apply it on top of everything else. voir là!
Btw, a good way to clean up useless part of epoxy film layer is sticking it on the back of your hand and take it off.
Failure is the mother of success. Above is the knowlege gain from this mess. Hope it can help someone. You just need this and some luck to make it work.
led array ring
too bulky though
I forgot to mention. Make sure you check if there is any obvious shortage/break before putting on that surface layer epoxy film.
stuffed, changed ISP to wire to reduce torn on the circuit.