Homebrew PCBs

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/view

Thanks,
Aaron

On 25/02/2011 04:09, gpcheshire wrote:
> 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.


It's carbon.

Leon
-- 
Leon Heller
G1HSM

--- In Homebrew_PCBs@yahoogroups.com, "gpcheshire" <cucheshire@...> wrote:
>
> 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
> 

Wasn't there some buzz a while back about printing conductive traces from an inkjet? Here is what I have on it:
http://techref.massmind.org/techref/pcb/direct-inkjet-metal-traces.htm there are links to other inks / methods at the bottom of that page.

I'm thinking after the main copper layer, with power and other high current traces, is etched and done, the pcb goes into an inkjet where regular non-conductive, heat curable ink (like MISPRO or Durabrite) is printed to form the solder mask (perhaps several passes with drying / curing between) then the conductive ink is printed on top of that.

The conductive ink would be used for signal traces only.

Just from memory, I don't think anyone in this group has experimented with these. 

And our friendly list owner will now remind us that inkjet PCB discussion has it's own group:
http://tech.groups.yahoo.com/group/Inkjet_PCB_Construction/