PCB Etching notes

PCB Etching Notes

I did a little research, and found it still took some trial and error to come up with a PCB etching procedure that worked reliably for me.  I also noted that, since I don't etch boards all that often, I kept forgetting how I do it.  So, with that in mind, here are my notes on PCB Etching for my "Note To Self" category.

Materials

• PCB Etchant Solution
• HP Premium Presentation 120g Laser Paper, Glossy, 8.5x11 250 Sheet
• Teenitor Top Quality 20Pcs 100x70x1.5mm Single Sided Copper Clad Laminate PCB Circuit Board
• MG Chemicals Liquid Tin, 125 ml Bottle
• Scotch Thermal Laminator, 2 Roller System, Fast Warm-up, Quick Laminating Speed (TL901C-T )
• Hydrox Alcohol 99% Isopropyl Pint 16 oz Pack 2
• Acetone
• Steel Wool

Circuit design

• I use Diptrace to design my PCBs
• Set the trace width and spacing to 16 mil, if possible.  Thicker traces like this work better for hand etching.  I've succeeded with 10 mil, but the traces were very thin and uneven.  Thicker is better.
• To put letters on the board (copper characters), use "Objects / Place Text".  Hit Enter to complete text entry.  Then right click on the text.  Under "Properties" set the "Type" to "Signal".  That will leave the letters as copper on the board, and leave some space around it.

Saving Gerbers

• Nothing special.  Save the Top layer for use in etching.

Print using Gerbv

• Note, I use Gerbv in Windows.  I don't know how these instructions might work on Linux or Mac systems.
• By default, gerbv will show the layer in color, rather than in a strong black monochrome.  I set the following properties before printing:
• Under "Layer / Change Color"
• Set Opacity slider to 255.
• Set Color name to "#09090e"
• The image will turn black on the screen.  
• Under "Layer / Modify Orientation"
• Set "Mirroring about Y axis"
• This adjusts for the fact that we're putting the paper face down, reversing the image on the copper.
• Do test prints, check that it's very dark, and that the size is right.
• Laser print on the Gloss paper and cut it out.

Copper Clad preparation

• Scrub the copper clad with steel wool to get it shiny.
• Clean it with Isopropyl alcohol.
• Keep fingers away from the surface.

Toner transfer

• Use 1 or 2 pieces of scotch tape to adhere the gloss paper, face down, onto the copper clad.
• Warm up the Laminator on the 5 mil (hotter) setting.
• Run the copper clad, with paper on upper face, through the laminator about a dozen times.  I rotate the copper clad end to end as I do it.  After about 8 passes, as the copper is getting really hot, I rotate the copper clad 90 degrees and run it through sideways a few times.  When I think it's nearly done, I may do a pass or two with the paper side down.
• The copper clad should be unpleasantly hot to handle by the time you're done.
• After about a dozen passes, drop the copper clad into a pan of water.  Keep it submerged for about 5-7 minutes.
• Remove the copper clad from the water, and peel off the paper.  If all goes well, the paper should pull away leaving the toner on the board.
• The toner should be well secured to the board.  Go ahead and rub it with your fingertip to make sure that any glue or paper pulp is removed from the bare copper.  Swish it in the water and make sure the copper looks clean.
• As the toner dries, it's not uncommon for it to turn a bit white.  That's OK.  When it does that, make sure the bare copper spots (to be etched) do NOT have white on them.  If they do, the acid won't etch the copper away.  I usually just keep rubbing with my fingertip until the copper areas remain copper colored when the board is dry.

Etching

• Dry the board off, and then drop it into a pan of the etchant.
• It takes about 10 minutes or so for the copper to come off.  Note, the copper turns pink during one stage of the etching.  That's NOT the fiberglass PCB.  The pink copper is still conductive, and needs to be etched away.  Let is soak longer.
• When it's done, you should see yellow PCB where the etching occurred.
• Remove from the etchant, and rinse with water.
• Note, you can save the etchant and reuse it.
• After etching is done, remove the toner from the board with acetone.  I put some on a few napkins and scrub the board.
• Rinse the board off again, until it's nice and clean. 
• Inspect the copper and traces to make sure it all came out right.

Liquid Tin

• I put liquid tin on the board after etching.  It protects the copper from tarnishing so that soldering will be more effective later.
• Put the PCB in a dish and pour liquid tin on it.  The copper will turn silver immediately.
• Rinse with water.  Save the unused liquid tin.