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When you are all done and the ink is dry (a few minutes) it's time to etch. The proper etchant is ferric chloride, which you should purchase already in liquid form. (It's also available dry, but can release toxic gasses while dissolving it into a water-based etching solution.)
There are other etching solutions and methods you may read about on the Web. While these may be fine for laser toner resist, many of them tend to dissolve the felt-tip marker resist used for the direct-draw method. Also, some use dangerous acids or release toxic fumes. Ferric chloride is toxic, but it is probably one of the safest etchants. Stick with ferric chloride for best results and safety.
Use a glass or plastic tray for etching (NOT metal!), and dedicate it for this purpose alone... ferric chloride is not only toxic, it also stains many things permanently. Old darkroom trays work well. You will never get your tray really clean afterward, so don't even think about borrowing kitchen utensils here!
Ferric chloride works best if it is warmed to about 100 degrees F or so, but this is not critical. You can set the tray on an old heating pad if you are working in a cool area. Be sure to remove any fabric cover from the heating pad first, and since you will certainly slop some etchant onto it you will probably want to dedicate the pad for etching only, just like the tray.
Store your etchant in the bottle it comes in, and fill the tray about a half inch deep or so for each etching session. The circuit board will float on the surface if you set it down carefully... copper side toward the etchant, of course! To avoid having to touch the etchant with your hands, use a strip of masking tape wider than the tray, and affix it to the board. Then just hold the ends of the tape and lower the board into the etchant. Immerse one end first and tilt to immerse the other, squeezing out any trapped air bubbles.
Slosh the board back and forth gently to dislodge any residual bubbles, then stick the ends of the tape to the outside edges of the tray. Check the board every 10 or 15 minutes to monitor the etching process: Simply peel back the tape ends and tilt the board enough to see if the unmarked copper is gone yet. This typically takes 20 to 40 minutes. It's OK if you leave it in a little longer, but since eventually the marker lines will dissolve, you don't want to just go away and forget it.
Here's an important tip about an amazing etchant phenomenon: New etchant is typically packaged at a higher concentration than ideal. While this does mean you are getting a "good deal" for your money, it will actually etch slower than the proper dilution... sometimes ridiculously slower! So you should be prepared to adjust the concentration as needed. Also, as the etchant ages and some evaporation takes place, you may need to adjust it again. (That's why you should store it in its airtight bottle instead of just putting a lid over the tray.)
The proper concentration is a specific gravity of 1.30, or 30% more dense than water. You can measure this with a device called a hydrometer, but this is not something most people have lying around the house. If you have access to a good balance, you can determine the weight of a known volume of etchant and add water accordingly. Water has a specific gravity of 1.00 by definition, which means 100 ml of water should weigh 100 grams, hence 100 ml of etchant should weigh 130 grams.
But if you want to avoid having etchant in contact with your measuring vessels, you can use the trial-and-error method with fair results: If the etch time exceeds 40 minutes, add about 5% water before you use it again.
NOTE: Eventually, after many boards, your etchant will become exhausted and dilution won't help. Put it back in its bottle and take it to the hazardous waste disposal center in your community. Please do NOT pour it down the drain... it's now full of copper, which is toxic to fish and to most other living organisms, including those that break down ordinary waste.
When the board is done etching, rinse thoroughly in tap water. Remove the marker ink with the same scouring pad used to clean the surface earlier, following this as before with a drop of detergent and a water rinse before drying.
See also Printed Circuit Construction
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