I took apart an old remote control and I am realizing that with only one layer of copper the PCB has manages two layers of electrical connectivity. The layer stackup appears to be
fr4 -> copper -> solder mask 1 -> solder mask 2 -> black conductive material
My question is what is the black conductive material that forms the membrane button contacts? It also forms short traces running over copper traces and connects to copper pads.
This method of using conductive black material and two layers of solder mask on one layer achieves two conductive layers with circuit paths crossing each other on only one side of the pcb.
To relate this to the homebrew PCB group, two homebrew methods need to be developed, one to apply solder mask (maybe two layers), and the other to apply the black conductive traces and pads on top of that.
Advantages of a second conductive layer are the same as a second copper layer on the bottom of a normal PCB, but in this application, there are no vias through the board, therefore no drilling.
Please help me understand the layer stackup for this application, and how it is implemented in mass production, and maybe how it can be implemented at home.
I have an example picture here:
http://groups.yahoo.com/group/Homebrew_PCBs/photos/album/1888135896/pic/620635252/viewThanks,
Aaron