The way of multilayer PCB connecting
I do not know how 2 sides are connected, I see on some PCBs there are some circular end points, so it must be going to other side. But how is it connected ?
I've successfully done etched double-sided PCBs using toner transfer paper. This is not easy. Aligning it is a pain, but I recommend that you get some Kapton tape
A method I used before I got some more professional gear was to use a laser printer and clear printable foil. As the laser printer isn't able to print it dark enough on a single foil I used two for every side.
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