The 6502

Building the 6502 SBC


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Helpful information on the WWW

http://en.wikipedia.org/wiki/Photomask
http://en.wikipedia.org/wiki/Ferric_chloride
http://en.wikipedia.org/wiki/Sodium_hydroxide
http://en.wikipedia.org/wiki/Printed_circuit_board

Bill of materials
  • Eisen-III-Chlorid 60% FeC13 6H2O - Mix 0.25/0.50:1.00 with water
  • Natriumhydroxid - NaOH - 10gr to 1 ltr. of water
  • Basismaterial epoxyd zweiseitig 536199 - Epoxy plate with copper clad on each side and photosensitive coating.
  • UV Exposure Unit LV 202E (MEGA Electronics Ltd.
  • Clear protective lacquer
  • Steel wool
  • Photomask - The circuit layout printed on a transparent film
  • Rubber gloves


Etching and construction

6502 SBC Schematic Clockwise: FeCl3, copper clad epoxy plate with photo-sensitive coating, transparent photomask of the layout, natriumhydroxid(NaOH) for developing


6502 SBC Schematic The photomask is placed on the UV exposure unit and on top we place the epoxy plate with the protective removed facing down

It is recommended to warm up the UV unit by leaving the light on for several minutes for consistent exposure. When exposing the epoxy, I find the best results are achieved by 2.5 minutes exposure when using 8 watt tube.

Pouring NaCl developing solution photo-developed epoxy plate is placed in a solution of NaOH mixed 1:10 to water

Depending on the strength of the solution the time to develop the circuit may vary. If the solution is to strong we face the risk of removing all of the photosensitive layer, leaving us with an empty copper plate.

Photo devolped print on copper We now have a copper epoxy plate with the desired traces printed on too

The traces will protect the copper underlying while the exposed copper will be etched away.

Photo devolped print on copper Warming up the FeCl3 solution

For faster and better etching results, we heat the FeCl3 solution to approximately 40°C.

FeCl Etching the copper away For a single sided PCB we would have the copper side facing down, for a double sided PCB we must regularly revolve the plate

While the board is immersed in the FeCl3 solution, we must agitate it continuously to achieve as much uniform reaction to the solution as possible. This as well speeds up the etching process.

Resulting PCB The resulting PCB, we are only using the half of the plate, the other half is still intact with the protective seal

After washing the etched PCB with water we clean the copper traces with steel wool to remove the photo-sensitive material. Shortly after, within 5 minutes, the copper will begin oxidation which will make the soldering process harder. We therefore must apply protective lacquer coat to the plate.

Finished TOP view All parts in place (top view)

Finished BOTTOM view Bottom view


As mentioned before the address and data lines were not routed to sockets 1 and 2 and therefore must be connected directly by wires.