Dos & Don'ts Of Ferric Etching

Ferric chloride is one of the most widely used etchants in the field of chemical etching. It is commonly used to etch steel and stainless steel parts, but it is also capable of etching copper. One of the reasons it is so popular is because of its versatility. With it, you can regenerate the etchant and keep on using the etchant for a while before it expires. It is a great etchant to use for any chemical machining shop, but if you are new to using it there are some things you should make yourself aware of. Here are 6 dos and don’ts you should keep in mind when working with ferric chloride.

1. DO Titrate Regularly

When it comes to running an etch process consistently, it is important to monitor many factors. One of the biggest factors to watch is the free acid content. When it comes to free acid, there are no great ways to monitor it besides having a schedule in place to perform a titration. How often you need to titrate is dependent on how much you are etching each day. If you are using ferric chloride for large-scale production, we recommend titrating as often as once a day.

2. DON'T Introduce Metals Containing Aluminum at High Concentrations

Aluminum and concentrated ferric chloride don’t mix very well. It is possible to etch aluminum-containing metals with it, but it is highly impractical at high concentrations because of the high heat of reaction. According to David Allen’s book, Photochemical Machining and Photoelectroforming, the aluminum etch reaction with regeneration can output ~245 kcal of heat for each gram of aluminum etched -- for comparison, the copper etch reaction with regeneration only outputs ~65 kcal/g. This difference in heat of reaction means that if aluminum is introduced, the temperature of the etchant will rise thus increasing the reaction rate – thus creating a cycle of excessive heat output. Having this much heat output can cause severe damage to your etching equipment and thus require frequent maintenance and replacements. If you wish to etch aluminum, your ferric solution needs to be diluted.

3. DO Quickly Clean Up Spills

If you have ever worked with ferric chloride before, you know how easily it stains whatever it touches. So, to keep your etching shop safe and looking nice, it's best to clean up any spills as soon as you can.

4. DON'T Smut It Up

One of the pesky things about working with ferric chloride is “Smut”. If you do not manage what is etched in your ferric chloride you can get an unpleasant dark coating on your product. This is dark coating is called “Smut”, and it has been known to give many manufacturers headaches because it is nearly impossible to remove once it dries.

Smut can result from a few different factors. The primary way to avoid it is to avoid etching metals that are high in carbon. This also means if you are a manufacturer who will produce copper and steel parts, you cannot etch them in the same etchant. If you are producing copper and steel parts simultaneously, it is best to have two different etchers – one designated for copper and the other for steel. If you do not have to produce them simultaneously, it is also a practice to etch steel panels first then once the etchant gets used enough, that etchant will then be designated for copper etching. Another way to reduce smut is to increase the density of your solution. In David Allen’s book, Photochemical Machining and Photoelectroforming, there is a notable picture showing a significant visual difference between etching at 38 °Bé and °44 Bé.

5. DO Monitor Etchant Conditions

As mentioned before, the key to running a consistent etch process is to monitor the things that factor in on etch rate. This means you will have to maintain the etchant’s density, oxidation-reduction potential (ORP), and temperature. The best way to maintain these properties is to invest in probes that will measure these factors. You can either have a system set up to automatically adjust these factors, or you can manually adjust them when you notice you are starting to get out of range. It is always best to know when your etchant is starting to reduce in quality before it starts producing parts that don’t meet specifications.

6. DON'T Forget About Byproducts

If you are regenerating your ferric chloride to maintain your etchant, it is a good idea to become familiar with the byproducts of the regeneration reaction and to have an idea of how much of the byproduct you are making. One of the most common methods of regeneration is with sodium chlorate. This is because it is one of the most feasible and economic methods of regeneration. One of the downsides of using this form of regeneration is that sodium chloride is a byproduct of the reaction. Thus, over time you will accumulate salt in the etching machines that will need to be removed at some point. If you have other non-typical components added to your etchant, you will also want to consider what reactions and byproducts may result.

We have built and installed many ferric chloride etchers, and we have trained many customers on running a ferric etch process. If you have any more questions or want more details about ferric chloride etching, please feel free to contact us with your questions.