Archive for January 30th, 2009

Making PCBs: Etching and Plating

PCB Etched and Plated - Front

PCB Etched and Plated - Front

Continuing the saga from there, this is the etched and plated board.

I mask around the edges with ordinary masking tape and cover the back surface with duct tape. Basically, the less copper you remove, the better and faster the job.

I use ferric chloride etchant, formerly available in nearby Radio Shack stores. These days it’s getting harder to find, so I picked up a few kilos of dry powder on eBay. Most likely that supply will vanish, too.

The usual directions call for heating the etchant, submerging the board, bubbling or agitating, and so forth and so on. The folks at Pulsar suggest simply rubbing the etchant on the board with a sponge and, perhaps not surprisingly, that works perfectly with boards sealed using their green film.

I hold the board horizontally in my left hand, pour a dollop of etchant on it, then rub it with a small sponge in my right hand. The etchant gradually turns into a gel as it removes copper from the board; when the gel becomes too stiff, I just wipe it off with the sponge.

I do this over a small glass tray and scrape the accumulated gunk off the sponge into the tray. Pulsar recommends diluting the residue in a gallon of water, but I’d just as soon not have that much spent solution sitting around.

PCB Etched and Plated - Rear

PCB Etched and Plated - Rear

Wear latex gloves, an apron, and eye protection. Expect that everything within a radius of two meters will accrue small spots of ferric chloride that will instantly produce a vivid, permanent yellow stain. Repeat: everything within two meters will sprout yellow spots.

You have been warned!

Even if you pay attention to the board’s edges and corners, those will still be the last areas to finish etching. You’ll also learn to not run fine lines parallel to the edges right next to the masking tape, as the tape protects adjacent areas from the sponge: no contact, no etching!

Spent ferric chloride (most likely, it’s now copper chloride or some such) disposal occurs on our town’s Household Hazmat collection days, but direct etching leaves very little bulk waste. Although it’s not particularly hazardous, the rituals should be observed.

After eching, rinse the board, remove all the tape, and rinse the board again.

Acetone and paper towels remove the green sealant film and the laser toner from the board, an operation best done outdoors. I have yet to find protective gloves that don’t disintegrate in acetone, so I simply try to not soak my hands in the stuff. Remember: leave the mask on the back side of the board to help protect it from the etchant when you do the front side.

Then I silver-plate the copper with Cool-Amp Silver Plating Powder, which makes the board look and solder better. Looks are important, as the boards sometimes wind up in my Circuit Cellar columns.

That hasn’t stopped me from hand-soldering SMD parts: the bigger the blob, the better the job.

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