From Open Circuits
Chemical etching is one step of some popular PCB fabrication techniques.
In this technique,
- one starts with a copper-clad board.
- one puts a mask over all the copper he want to keep. There are a variety of ways to do this -- see Toner Transfer and Photoetching.
- one removes the parts he don't want to keep, by chemically etching away the copper.
- cleanup: wash off the board in the sink; carefully store or dispose of the acid.
There are a lot of different chemical techniques for doing this, each with its own advantages and drawbacks.
None of these chemicals is incredibly dangerous, but they can all be toxic or caustic, and should be treated with care. Eye protection and gloves are a very good idea. Before you start, make sure you know how dangerous each chemical is, and figure out what you will need to do if you spill it or get it on yourself. Washing with plenty of water is usually a good start. For some chemicals you may want to keep a neutralizing agent handy. An MSDS (Materials Safety Data Sheet) for the chemical will give you some basic information.
 vinegar and salt
- How to get what you want: Salt and Vinegar Etching
- smt pcb with Salt and Vinegar
- The Saltwater etch process
- electro etching a PCB with vinegar, salt, and a 12 V power supply (the copper etched off the PCB is plated on the anode?) -- however, other people claim that "You should not be using any acids (or basic 'acids') with your [electro] etcher at all. No FeCl no vinegar, etc ".
 Ferric Chloride
This is the most common hobbyist etchant. Ferric chloride, FeCl3, is a brownish substance. It's usually sold in a bottle (dissolved in water, perhaps with a little acid or peroxide) or as a powder (which you have to dissolve in water).
The copper clad circuit board is immersed in solution and the solution can be agitated or bubbles can be fed through it to keep the surface exposed to the etchant to decrease etching time. Heating the solution also decreases etching time. Alternatively, gloves and a sponge can be used to continuously wipe the surface of the copper with fresh ferric chloride, which greatly decreases etching time.
When in solution, ferric chloride consists of ferric ions (Fe3+) and a chloride ions (Cl-). The ferric cation undergoes a reduction from ferric cation (Fe3+) to ferrous cation (Fe2+) and copper undergoes an oxidation from metallic copper with a valance of zero (Cu0) to a valance of +1 cuprous cation (Cu1+) and or cupric cation Cu2+. The reaction product (FeCl2) remains with one less chloride ion as ferrous chloride,and the copper enters solution to form cuprous chloride (CuCl) which continues to react to form cupric chloride (CuCl2) using another chloride from another,ferric chloride, FeCl3, molecule.
The reaction products, FeCl2, CuCl2, and CuCl, form a dark sludge which settles to the bottom of the etching tank. When the Ferric Chloride is depleted, the solution needs to be replaced, and the old solution should be disposed of as a hazardous waste.
 Ammonium Persulfate
Expensive & hard to control and optimize the process parameters (such as specific gravity & pH value).
 HydroChloric Acid / Hydrogen Peroxide
Mixing about 1 part HCl (Which can be found at most hardware stores, also known as Muriatic Acid. Ask for concrete cleaner.) into 2 parts Hydrogen peroxide (normally used for cleaning cuts) you can make a fairly powerful etchant. Use gloves and don't breathe the fumes though. This will etch a 3"x5" board in less than 10 minutes. No need to heat it up. I usually like to drill a small hole through the board on a corner and thread a wire or nylon string through to help agitate / remove the board.
When the board is done etching, the etchant will probably look like green kool-aid, from the copper content in it. This stuff is highly corrosive and will burn skin, which is why you should wear gloves. But it is easy to handle, and fairly easy to dispose of. the etchant is easily deactivated with baking soda. Pour enough baking soda into it slowly (to keep it from boiling and overflowing... remember what happens with baking soda/vinegar? ya...) until it is a solid mass, then leave it in the sun to dry. You should contact your local authorities to find out what you should do with it next. Whatever you do, DO NOT dump the stuff down the drain, it will eat through your pipes just like any of the other etchants.
Alternatively, instead of disposing of the etchant, you can re-use it again and again. In fact, after etching a few boards with this solution, you will have successfully made Acid Cupric Chloride (see below). You can also find a detailed tutorial on etching at Muriatic Acid etching tutorial
 Sodium Persulfate
More environmentally friendly than ferric chloride. Can monitor the etching as initially clear new etchant solution turns blue from the copper ions.
 Acid Cupric Chloride
Dead simple etchant made from ordinary, store-bought chemicals (hydrochloric acid and hydrogen peroxide). Has the advantage that it can be regenerated by bubbling oxygen/air through it, or by adding more H2O2. In addition, it doesn't get used up: the etchant bath simply grows with use (kind of like sourdough starter…) The used etchant also makes a great algecide/pH reducer for your pool (and a whole lot cheaper than that stuff they sell at the pool store).
What you need:
- 38% Hydrochloric Acid, HCl (available at finer hardware stores or pool supply stores as Muriatic Acid)
- 3% Hydrogen Peroxide, H2O2 (available from any drug store)
- Plastic or Glass Pans, Jars, and tongs (no metal)
- Mix your HCl and H2O2 1:1 in a non-metalic container, making sure to add the acid slowly to the H2O2. DO NOT ADD THE H2O2 TO THE ACID!!!
- After you've masked your board, dip it in the solution and constantly agitate. You should notice a dark green cloud start to come from the board almost immedately which quickly dissapears or turns lighter as it gets further from the surface of the board.
- Etching should take about 10min depending on the temperature and how well you agitated the etchant. When all of the copper is gone, dip in water to wash off any stray etchant and stop the reaction.
- When done etching, save used etchant in a non-metalic container and mark clearly its contents.
- If your etchant has become a dark, murky green color, add a little bit of H2O2 or bubble air/O2 through the solution to regenerate it back to a light, transparent green color.
See links at bottom for more information on the chemistry and some pictures of the process.
 Disposal procedures
Flushing used etchant down the drain is a bad idea (and usually illegal) because copper ion is toxic. The usual recommended way to dispose of hobbyist amounts of etchant is to convert it to a solid somehow and dispose of the solid in accordance with local laws.
 External Links
- "Sponge + Ferric Chloride Method -- Etch PCBs in One Minute!"
- Ferric Chloride vs. Ammonium Persulfate and other etching chemicals.
- Etching with Air Regenerated Acid Cupric Chloride — an excellent in-depth page on acid cupric chloride etching by Adam Seychell.
- Etching a Copper PCB with HCl and H2O2
- MG ChemicalsA possible source?
- RepRap wiki: Make PCB instructions