Building the mainboard as a PCB

Last entry was about designing the mainboard, using Eagle. The result is a layout diagram, which will be the starting point of the next step: building the PCB.

The layout diagram is saved as a postscript file (print into file) to get 1:1 scaled  picture. It’s then lay down on a copper board, using adhesive.

Using something sharp, like a screw, each hole is marked. This is used to localize the holes once the paper is removed (…), and will later help to guide the drill bit.

Once done, the paper is removed. Using a special PCB pen, each hole is marked, according to the layout.

About the pen, it appears other pens also work, though I’ve tested these with details. Particularly, pens used to write on CD-ROM work nice. The thing is to spread a thin layer which will protect the copper from the ferric perchloride.

Start drawing the tracks. This step is very important and delicate. Tracks mustn’t be in contact, the drawing must be regular.
The reproduction of the layout is done. Double-check the tracks. Now it’s time to cut the board.
Use adhesive on both sides of the board. It’ll make the manipulation in the ferric perchloride bath easier.
Put the board into the ferric perchloride bath, and fix it on the sides using adhesive. Be careful, the ferric perchloride is very toxic and dangerous (acid). Use gloves, protect your eyes and your clothes.

Depending on how “new” is your bath and the temperature, the required time to “burn” the board may vary.

About 30min later, the copper starts to disappear. One this step reached, smoothly shake the board into the bath, until all the copper is gone (and the tracks still there…).
About 5 to 10 min later, the board is ready. Get off the bath and rinse with water. The tracks are black due to the pen. It’s time to clean it.
Polish the board to remove the pen layer, with a Dremel or the like. Do not damage the board with the drill. Also watch closely to the tracks to identify potential problems…
… like these ! One track has disappeared, another has several cuts on it. Fortunately, these can be fixed using some wires and an soldering iron.
Start drill the holes. This step is very delicate and could permanently damage your board: while drilling, the drill bit can slide and cut tracks. The best is to use a drill press. Depending on how you’ve marked the holes, things can be easy.

I prefer to drill first with a 0.6mm drill bit, then use a 0.8mm one. Some components required a bigger drill, like the power supply jack, trigger and 7805.

Then solder the components. Start with the straps, as they may be hardly reachable once every components are on the board.
Here’s the final result. Quite nice, even if things could be far better…

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