Acid Etching Copper & Silver - Before Or After Soldering Pieces ...

I have a question about Acid Etching Copper & Silver that I haven’t seen an answer to in the other Acid Etching Posts:

Goto Boyang to know more.

I’m getting ready to give Acid Etching a try and have read up on it as much as I can, but I haven’t found the answer to these questions yet: Should you Acid Etch Copper and Silver pieces separately, before Soldering them together or Solder the pieces together and then Acid Etch them? I understand that Copper and Silver Acid Etch somewhat differently, but how differently, does one Etch much faster or slower than the other? Also, will Soldering the pieces together after Acid Etching affect the look of the Etched Metal or will it come out fine after Pickling? Lastly, has anyone tried Acid Etching a Copper & Silver object together before and if so, how did it turn out? Thank you so much for any thoughts, experiences or suggestions that you are willing to share!
Jonathan

The main thing is that you need two different acids. Copper will etch with ferric chloride- easy to get at any art store and relatively easy to neutralize. Silver however will require something else- nitric acid is the classic chemical but that’s pretty dangerous to use and I don’t know anyone who’s tried it. You’d need a hazmat disposal lined up. You probably want to electro-etch your silver. I have never done that myself, but there’s a lot of info out there on it.

OK, I apologize, I guess the wording of my questions were not what I should have written…

I do understand that to Etch Silver you need Ferric Nitrate and to Etch Copper you need Ferric Chloride, but what I was actually wanting to know is: Can you Etch a Copper & Silver Object that have been Soldered Together, or do you need to wait and Etch the Copper and or the Silver Pieces Separately and Then Solder them together? In other words, if I wanted to Acid Etch a Silver Disc that has a Copper Rim and Embellishments on it, can I do this Safely or will the Ferric Nitrate React/Eat-Through the Copper (and vise-versa: Copper with Silver Embellishments), even when it’s Covered with a Resist? I guess I’m just curious about How Ferric Nitrate Affects Copper and How Ferric Chloride Affects Silver and How both Acids Affect Solder and if the Metals will React Differently when they’re Soldered Together? Sorry for my confusing wording, though these questions may not be any better… Hopefully someone will understand what I’m asking… Thank you!
Jonathan

Just speculation on my part, the best way to find out is to run a test, but silver chloride is insoluble, so if it formed it would likely form a barrier to further reaction. Copper nitrate is soluble, so if it formed it would dissolve and leave the area to be etched further exposed to additional etching.

I’m going to speculate further, that if you did use an etchant that was effective on both metals the copper, being more reactive, would etch faster, and thus deeper than the silver. So it might be better to etch each metal separately.

Etching is done with a barrier such as lacquer to protect areas from being etched, and neither ferric chloride nor ferric nitrate would penetrate it. So you should be able to etch each metal separately by blocking, then exposing different areas.

Other than the cost of both reagents, there’s nothing to lose by trying each and seeing what happens. Part of the fun of what we do.

Neil A

Neil,
Thank you so much, I really appreciate your responses, that was what I was hoping for! I will do some experimenting, but I wasn’t sure if it was “Safe” to proceed - I didn’t want to produce any Deadly Gases or Explosions or anything - I never took Chemistry in school, I was able to talk my Counselors into letting me take Geology instead (I was preparing to study Architecture in College and then my Uncle talked me into trying out Jewellery Work…)… Anyway, I’m curious to see if the various Etching Acids will leave any Interesting Affects/Textures on the other Metals, other than the ones that they are meant to Etch, that would probably be Affected later by Soldering the pieces together… The fact that Copper would Etch faster than Silver with Ferric Nitrate, might give the piece an interesting multiple-depth design, if I can pull it off, I guess we’ll have to wait and see… Thanks again, I really do appreciate you taking the time to respond!
Jonathan

I do not know about the speed.
But for etching both Silver and Copper one have to avoid any Chloride based etches.
Copper will be etched by Copper or Iron Chloride, but as said, Silver will form Silver Chloride and passify.
Nitric will dissolve/etch both but needs 4 times as much Nitric for Copper than Silver.
The gases emitted by this is NOx and can be dangerous, (You do not want brown fumes)
but in a dilute solution with the amounts needed for this, it should not pose any problems.
Maybe one can use agricultural 3% Nitric for this, impossible to know without testing.
Just keep it in a closed container when not in use.
Ammonium Hydroxide can be used for Copper and maybe Silver too, but the smell is overwhelming.

As everything keeps getting smaller this has become one of the most important steps. A speck of dirt is enough to cause an open circuit on fine lines. The slightest misalignment on artwork top to bottom has the potential to shift dimensions outside the tolerances.

There are many different exposure units on the market now. Most do a very good job, but there are a few things that are important to have to make sure you can etch fine features.

Those features are collimated light (or LDI) and features that help create near perfect alignment. You will also need a yellow room. Keeping the yellow room and material clean will help you significantly.

The last tip we have is to hold the panel for 30 minutes after exposing it so the resist can lock into the metal more before developing it.

Approximate Cost = $200,000

The developer is used to dissolve the photoresist that was not exposed to the UV light in the above step. Removing the unpolymerized resist exposes the metal you would like to etch away. This provides you with the design you want to etch into your material.  

Developing is normally looked at as less critical than etching. This is true, BUT it doesn’t mean you can overlook the developing step. The photoresist can be underdeveloped or overdeveloped.

Underdeveloped means all the unpolymerized resist was not completely removed. So, you did not fully expose the metal that you want to etch away. This results in smaller holes or no breakthrough for chemical milling and shorts for circuits.

Overdeveloping will cause the developer solution to start undercutting the resist. This can cause your resist to lift while etching and reduce your etch quality. With resist lifting, you may not meet the specifications you need or you may receive open circuits.

Approximate Cost = $92,000

The etcher is where the metal removal happens and is the most critical piece of wet processing equipment. Like photoresists, the chemistry used in the etcher needs to be matched with the metal you want to etch.

What is so critical about the etcher?

The etch uniformity is first and foremost. To have great etch uniformity you need to have the solution moving. If the solution sits on one spot for too long the solution becomes less or non-reactive.

If you want to learn more, please visit our website Cu Etching Liquid.

Additional resources:
Hydrogen Peroxide Solution - FDA

This causes poor etch uniformity. This is known as the puddle effect.

Secondly, transport is important. Most material thickness has no issue in the developer because all the metal is there, and the photoresist adds to the thickness. However, during etching, the metal is being removed.

That means the panel is becoming less rigid and prone to wrapping around a roller. (Most transportation issues only apply to thin material processing)

Buying an etcher that has great etch uniformity and transportation is key to building a successful etching shop.

Approximate Cost = $97,000

Stripping the photoresist from the metal is the next step. As a whole stripping is less technical than the other wet processes. Basically, the resist needs to be in the chemistry long enough to strip.

There are a couple of important factors to consider if you want an efficient stripping line.

First, you will need to check with your chemical and photoresist supplier to ensure that they are compatible with each other. If they are not compatible you will see your resist stripping off in sheets, as goo, as large pieces, or very fine pieces. All of which can create problems for your equipment and process.

You want your resist to strip in small chips. The reason you want small chips is that strippers are designed to filter out small chips. If you are getting any other size or goo, this means your resist and chemistry are a mismatch, and the stripper will have a hard time filtering out particles.

This will result in plugged nozzles.

Secondly, you will want to decide what design is best for your shop. Are you running high volume or just a couple of boards a day? This will help you determine how the filtering is set up.

You will also want to understand how the filtering works. If the machine you select does not filter the resist well, you will experience lots of downtime due to nozzle clogging.

No one wants down time, so make sure your stripper has an adequate filtering system.

Approximate Cost = $103,000

Many etching shops put all three of these processes in one line. This allows shops to use less operators because the panel will go through all three processes before it needs to be unloaded.

There are some negatives to putting all three together. The line is much larger, so you need a large room.

The processes do not run at the same speed so some chambers may need to be larger than a stand-alone machine. If you move forward with opening a shop a Chemcut employee can help you through this decision process.

Approximate Cost = $360,000  

There are multiple options for wastewater treatment, but the most popular is a batch wastewater treatment. A batch wastewater treatment system will consist of a collection tank, a treatment tank, filter press, clear well tank, ion exchange, and final tank.

The collection tank will collect all the runoff from your wet processing equipment. All your machines will have some liquid leaving the system. Mostly from your rinses.

The wastewater that is collected can be transferred to the treatment tank (precipitation tank). The wastewater will be treated here, and all the metals will precipitate to the bottom of the tank.

The clear water can be decanted into the clear well tank and if all the metals are removed the water can be transferred to the final tank. From the final tank, the water can be pH corrected and sent down the drain.

The metals (sludge) that settles at the bottom of the treatment tank will be pumped through the filter press. The filter press will remove all the sludge and this sludge can then be shipped off your facility as toxic waste.

The last piece of equipment you will need is a scrubber for the fumes that are being pulled out of your wet processing line.

Approximate Cost = $350,000

For more Photoresist Thinnerinformation, please contact us. We will provide professional answers.