There are 3 "conventionally" used chemicals for etching copper:
• Ferric Chloride - a corrosive, called "FeCl"
• Ammonium Persulphate - an oxidizer, called "AP"
• Sodium Persulphate - an oxidizer, called "SP"
What's the difference?
Corrosives (powder or liquid) work MUCH faster than oxidizers and have unlimited "shelf life". Of course both are absorbing copper ions as the working solution is etching the copper so there is a ramping down of efficiency the more it is used.
Oxidizers (always a powder) work much slower than corrosives and have a short shelf life once activated by water which is normally about a month and that's it - it's dead! The ratio for normal working strength is 1 pound to 1 gallon but can be higher if preferred.
The 4 "main players" who sell FERRIC CHLORIDE:
If using our "ContactEtch" technique (see Tech Support > No Etching Tank), there is little need to buy a gallon since just a quart size will last you quite some time! Here are your 4 main sources...
1. Radio Shack:
They normally carry the pint sized bottle for $9.95 (276-1535) however, not all stores carry it. Click their link here then look for the "Find It Near You" link (under Model/Catalog numbers on the right) to see what stores near you have it in stock.
2. MG Chemicals:
Even though they are a Canadian-based company, they do have a very aggressive marketing campaign in the USA, Canada and Internationally. Generally their prices are higher than most for Persulphates but very competitive for Ferric Chloride. To find a store that carries this brand, click here for their store listing by State, Province or Country then call the local store nearest you for availability. In the USA, Ferric Chloride (FeCl) is about $15 for a quart which is bit better than Radio Shack's $9.95 for a pint. Make the drive to your local Radio Shack to satisfy our lust for "instant gratification"!
3. GC Electronics (GC/Waldom):
You will have to locate dealers for this brand as they don't sell direct. Their part number for the quart size is 22-238 and the gallon size is 22-239. Many resellers of GC also sell the Phillmore brand quart size, part number 12-2038. Prices are pretty competitive. Do a simple Google search for "PCB etchant [part number]".
This company sells direct. They sell a pint for $6, a quart for $10 and a gallon for $35. Again, if using our "ContactEtch", it might be a bit dumb to buy that much etchant when you use so little per etch.
What Are The Advantages & Disadvantages of All 3 Popular Etchants:
The main reason so many people don't like FeCl is that it stinks, it stains clothes permanently (or anything it comes in contact with for that matter) and if a large quantity (quart or more) is left exposed (like sitting in an open tray, it produces a highly corrosive atmosphere! We tested this years ago by placing a 1" diameter chromed rod 12" away from a photographic tray with a pint of Ferric Chloride sitting in it uncovered, undisturbed for a week in the high desert of California with humidity near single digit. It was completely, 100% RUSTED! Ok, that was a good confirmation test to what we've heard over the years so it's true!
In your travels to other retails, you will no doubt run across bags of "anhydrous" Ferric Chloride (a dry powder). Stay away from this like the plague! It's nasty and messy. Difficult to mix and you must be very careful to add it to water - not to add water to it or you'll have a isothermal reaction of sorts. Just leave it sit on the store shelf where it belongs unless you're the adventurous type!
PERSULPHATES (Amonium & Sodium):
Yes, persulfates are clear when they are mixed with water and take on a very pretty light blue tint when copper ions are released during the etching process. And if you get some working solution splashed on your clothes it doesn't stain! Rather, it'll eats holes in your right into your shirt which you'll discover after about a week! Is this a good trade off? In contrast to Ferric Chloride, persulfates are almost completely odorless when a fresh batch is made, however, when the working solution nears the end of it's life it takes on a "rotten egg" smell which really lets you know the condition of the mixture. Phew! This is not pleasant!
We said "working solution" above because you must mix water with the powder. Remember it's an oxidizer, and water is the catalyst. It starts breaking down from minute one! Even if you never used a new batch, it'll be useless in about 30 days. It's a slow progression of death. At 2 weeks, it'll take twice as long to etch as it did when mixed fresh. This is not the ideal etchant for our situation when board fabrication is a few here, a few there. Having an etchant that won't last long stretches between boards is kind of dumb and can get pretty expensive with the "store bought" variety of this etchant.
Here's something to consider... MG Chemical's price for their 1Kg (2.2lb) bottle is about $20 on average. Since you use 1lb/gallon of water, you've got a mixture that cost you $10 and as slow as it acts, it will take twice as long in 2 short weeks and dead in 2 more weeks. Yes, you can refrigerate it to make it last longer. Do we really want to do that? Remember, it's a poison so no food in the refrigerator! There is, however, an alternative if you're hard over on using AP or SP. Open the Yellow Pages under "Chemical Supply" houses. You can buy from them as a customer off the street, a 50 pound bag of either etchant for about $60... that's now only $1.25/gallon mixture... vs $10 for MG! We have found that "imported" chemical is cheaper, but we've always preferred the performance of the USA's "FMC" brand to a better crystal and it doesn't "lump".
More Info On Etchants...
Click this link here for a very good website that explains the in's and out's of using these and other chemical etchants including proper disposal. One etchant can even be made using two common chemicals from any swimming pool supply store and any drug store! Disposal is also an important issue because after etching, the resulting chemical, even though it's "spent" is a "heavy metal" and should NEVER be put down a septic tank! Even though city sewar systems treat for heavy metals we should be conscientious about proper disposal. For more info on the do-it-yourself etchant, use the search term "muriatic acid hydrogen peroxide etching". Remember the golden rule when mixing chemicals... always pour the stronger into the weaker. The acid is added to the peroxide NOT the other way around. Also keep in mind that this inexpensive etchant can be a bit dangerous in the wrong hands (eg. children around) and this is a much slower acting etchant because it's an oxidizer not a corrosive so it falls into the category of the "persulfates" mentioned above.
"The Good, The Bad & The Ugly"
Down to the "brass tacks". Most etching tanks hold about a gallon of chemistry. The GC Electronics and the MG Chemicals tanks hold 1.25 gallons (4 liters). Which chemical do you want to fill your tank with? One that will be dead in a month but you can more easily see your board as it etches? Or one that has a corrosive atmosphere but at least it doesn't die on you?
The answer is neither! You don't want the etching tank to begin with and you don't need it anymore! They are all very inefficient and a waste of money. We developed a very simple trick to prove we've been etching boards the wrong way for the past 70 something years.
Back in 2005 we stumbled across a very simple, cost effective and most important of all, FAST method of etching that does not require an etching tank and uses only a few ounces (yes, ounces) of Ferric Chloride... just enough to do the job with no waste! One small pint of Ferric Chloride will last you through dozens of boards! Read about how simple this technique is. We don't make a dime off it because we're here to share information to help you work more efficiently with our techniques and products. It's a revolution in how to make PCB's better, faster and less costly. This simple technique is found under the "TECH SUPPORT" Section. Click on the "No Etching Tank?" button.