Safest etchant for home-made PCBs?

[iry100fan]

Hello Everybody,

Just wondering what the general consensus is pertaining to the safest etchant to use in a home.  In the past I had used Ferric Chloride due to the fact that Radio Shack used to sell it.  I'm wanting to etch some PCBs again and wondering if I should stick with Ferric Chloride or move to something else.  What concerns me the most is my safety (skin contact and gassing).  I see lots of posts about homemade mixtures but I have no clue how safe any of them are and thus am hesitant to try them.

Thanks for the info.
-Brian

[CatalinaWOW]

I apologize ahead of time for the Captain Obvious rant.  There is no such thing as a safe etchant.  All will cause problems with enough exposure, all have issues with disposal.  On occasion you will find one that is more compatible with your local safety regulations, but that is more a legal issue than a chemistry issue.  In another jurisdiction the answer is often different. 

The safest way to make PCBs is to buy them.  Board services in China build higher quality product at lower prices than you can achieve at home, so few make their own today.  But for some people it makes sense.  I do on some occasions.

In the small quantities used by a home circuit board maker, and recognizing the extremely small number people who actually do this, the environmental hazard is quite low regardless of the chemistry used.   If you take suitable precautions (apron, gloves, ventilation and so on) and make sure you understand the chemistry of mixing (which order to mix and how to mix, etc. ) any of them are safe enough to use.  So make your decision on what is most easily obtainable and which you are familiar and comfortable with.

[Siwastaja]

Indeed, none is safe. Sodium persulfate is OK, ferric chloride is OK. Both require elevated temperature and bubbling to work properly, IMHO. Both require proper fume extraction (very good open window ventilation at very least if you only do it occasionally). They are not dangerously toxic and not that strong of etchants, so if you get some on your hands, just wash it off and you are good to go. I did a lot of this work without gloves, really, but of course can't recommend that to others.

Safety glasses is the most essential part. The etchants mentioned are not strong enough to do serious permanent damage to your eyes if you flush immediately with a lot of running water and seek for medical help just in case but still... do everything you can to avoid that!

[james_s]

Ferric Chloride is fairly safe to humans but it is nasty stuff that stains everything it touches. It should go without saying that any chemical that etches metal will damage other metal objects it or its vapor comes into contact with. I use HCl + peroxide which is not terrible, HCl is what is in your stomach to digest food, albeit weaker than what you'd use to etch PCBs. Wear gloves and safety glasses and ideally do it outside, I usually etch boards on my deck, after laying out a large plastic trash bag to catch any spills and drips.

[Fred27]

I'm going to jump in ahead of the inevitable "just use hydrochloric acid instead of that nasty ferric chloride". HCl is far nastier. The fumes will rust expensive tools you have in the same room for instance. I've found ferric chloride to be messy but not actually that nasty to work with.

I'll also echo that unless you're enjoying the challenge of home etching or you desperately need it same day, ordering from China is way better in terms of quality, safety, price and time spent. (Just not time elapsed.)

[Fred27]

HCl is what is in your stomach to digest food

Vomit-etching it is then. Readily available and it's organic too. 

[DavidAlfa]

Ferric chloride is way safe. Just dirty as hell, will stain anything, use gloves! It's way slower than HCl, so it's less likely to eat away too much if you miss a minute.
I used it back in the day with 0.5mm-pitch stuff, (tqfp, tssop, qfn, various connectors...) withou any special equipment, just a small tray, wiggling by hand to ensure uniform result.
It's far more important the UV exposure time and the sharpness of the mask. Use at least 1200dpi printer.
For your first tests, make the same patterns in a small pcb, 8-10 times. Exposure 1 minute at a time, then mask one pattern, expose for another minute, repeat until all patterns are done.
The reveal and proceed with the acid.
If your UV source is very powerful, you might have too much difference bertween one minute and another, so repeat, starting at the minutes where it it was slightly underexposed, then masking in 20 seconds steps.
Once you get it perfect, the acid step will be easier. Just remember to take care of the temperature, the results will vary considerably between ex. 25 and 50º.
Also it won't makes bubbles as HCl, sometimes they stick to the pcb and will ruin the work.
If you want it fast: HCl + Hydrogen peroxide 30%. But you must move the solution a lot and ensure you don't overcook it!

[Benta]

Three options:

1: Ferric Chloride (FeCl₃) 40% solution. Safe, but very messy (impossible-to-remove brown stains if you spill it) and the fumes will cause corrosion in other metal parts in the vicinity. Works well at 20 C. Remains need to be disposed of as chemical waste.
Etch time: 20...30 min.

2: Sodium Persulfate (Na₂S₂O₈), 250 g to 1 litre water. Safe, but needs heating and stirring to work properly (~50 C), which is why you'll see vertical etching baths with heating elements and air pump/bubble tubes. Disposal: chemical waste.
Etch time 10...20 min.

3: WARNING! Only for outdoor use and with a gas mask!!! Chloride gas will be released!!!
H₂O + H₂O₂(35%) + HCl(30%). Mix: 1/4, 1/4, 1/2. Always add HCl last.
Disposal: dilute with water, then as chemical waste.
Etch time: 10...20 seconds.
Process is exotherm, so each PCB you etch will go faster and faster. EXTREMELY HARD TO CONTROL, NOT RECOMMENDED FOR BEGINNERS!!!

[SmallCog]

Depending what you're making the other option is engraving/routing.

There are numerous videos on YouTube of people using small cheap machines (eg the 3018's)

This does away with the chemicals and fumes but you should be aware of the dust hazard and give some consideration to control methods.

This will potentially let you drill though holes and route in isolation slots too.

[iry100fan]

I appreciate everyone's input.  My only experience has been with Ferric Chloride.  I understand that any solution that can eat away metal has a bit of a danger level to it, but it sounds like Ferric Chloride is one of the safer ways to go.  Staining doesn't worry me as I don't have anything near where I do the work that isn't easily replaceable.  And, once a year we have hazardous chemical recycling nearby for me to dispose of the old stuff.

I have a cheap CNC3020 mill and have attempted making boards on it.  That has been a bit of hit and miss for me as some boards turn out okay but most yield poor results.  Maybe I'm expecting too much from such a procedure.

I am a bit leery of home-brew solutions such as muriatic acid and hydrogen peroxide.  Apart both are relatively safe but I have no idea what truly happens when they are combined as I am no chemist.  (No SDS sheet for home-brew recipes.)  However "vomit-etching" seems safe enough.    (That was a good one.)

I do this as a hobby and enjoy the ability to look at a board and say "I made that".  I have only had two boards professionally made and they were not inexpensive to do.  Making boards at home seems to be significantly less expensive but I am lucky that I already have equipment like a CNC mill and a laser printer.  If I factor that into the equation it would be a different story.

Again, thank you to everyone who chimed in here.  Probably goining to stick with Ferric Chloride for now.

-Brian

[emece67]

.

[free_electron]

HCl is what is in your stomach to digest food

Vomit-etching it is then. Readily available and it's organic too. 

if you want it to go faster , hurl harder ... principle of spray etching. i recommend scavenging a meal from the bins behind the local greaseshack...

[sleemanj]

The safest and most convenient etchant in 2022, is the tank of etchant in the Chinese factory, several thousands of kilometers from you, but able to be used with the exchange of a few bucks.

If you really need to DIY there is the old Vinegar, Hydrogen Peroxide and Salt etchant, that's going to be pretty safe.  Bit of a PITA though.  This is a single use mix it as you need it solution.

The persulfate etchants (ammonium, or sodium) are maybe next on the list for safety and cleanliness.  I don't think it can be reused that much, but I havn't used persulfate etchant myself.

Ferric Chloride next probably, it can make a horrible mess if it escapes your etching container, but it's not especially dangerous in and of itself I think.  Can be reused quite a bit.  You can't really see what's going on during etching though which is a downside.

HCl+H2O2 (or CuCl2 derived from it) works well, you can see through it to monitor the etching, and doesn't make a mess (but don't use 35% H2O2, or if you do then understand you will need a tiny amount of it in comparison to HCl, literally dribble it in until you see it starting to work, aim for a couple minutes etch time not a few seconds, it's easier to control).  Realistically while the safety precautions are minimal, it's not what I'd call a "safest" etchant.  Been discussed here many times the pros and cons.

[golden_labels]

I know you asked about “safest” not simply “safe”, but let me make some point.

There is no such thing as safe method, because any safe etchant would also be useless. Chemical etching of copper works by turning copper into ions, which then dissolve into water. That happens by copper losing electrons to the etching solution. Which means: it must be an oxidizer. If you don’t want to wait a month for your PCB to be made, it must also be reasonably strong one. And those are not good for you, no matter which you choose.

This leads to an important conclusion. Some substances will be a bit less risky to use, some a bit more. Some may produce dangerous fumes or heat. Some may be cumbersome to store. But you must observe basic safety, because you are dealing with something that is doomed to pose a risk to do its job.

When you accept this, your original question gains a new perspective. If you wear nitrile gloves while working with your etchant, suddenly it becomes of tiny importance if handling the PCB causes irritation to your skin. It shifts towards skipping options that pose risks you can’t easily avoid: like producing fumes, requiring strong acids or giving spontaneous combustion.

The second important thing is: while you may get relatively safe etchants, the waste product of the process is always nasty. That’s because it contains
copper compounds dissolved in it. And copper is toxic. While the amount hobbyists produce is not enough to care about disposal safety, chronic exposure is something you want to avoid. So no eating while etching, cleaning surface you worked on (if that’s your desk or kitchen table), washing hands, no re-use of etching container and tools for food, good rinsing sink with water and cleaning it.

As for recommendations, I only used sodium persulfate. It is widely used here by hobbyist, available as “etchant B-327”. As already noted above it requires elevated temperature to work well, but do not panic: for simpler PCBs you get away without using a heater: hot water (below 70°C) will stay warm enough sufficiently long. Moving the PCB with an old plastic ballpen case. May require a second batch. Proper gear is needed for complex or small pitch boards. Storing it requires reasonable protection against moisture ingress and contact with anything that could react with it. It comes in plastic bags. Keeping that bag sealed and away from pointy items that could puncture the bag is enough.

[tepalia02]

With proper ventilation, you can continue using ferric chloride.

[Siwastaja]

H₂O + H₂O₂(35%) + HCl(30%). Mix: 1/4, 1/4, 1/2. Always add HCl last.
Process is exotherm, so each PCB you etch will go faster and faster. EXTREMELY HARD TO CONTROL, NOT RECOMMENDED FOR BEGINNERS!!!

Indeed, and this includes non-uniform etching (edge effects) during any single PCB, as well. Meaning, lone tracks near larger copper areas get extra heat and agitation out of the reaction nearby and over-etch to the point of 10-mil traces just disappearing while other parts of the PCB are not complete.

It's a crappy process, we did use it at a club for quite some time and getting good PCBs was colossally hard. Some 12/12 mil stuff was barely acceptable. Full ground planes everywhere helped to slow it down.

We transitioned into cupric chloride by basically just starting to collect the waste of the HCL-H2O2 process and reuse it until copper ion concentration goes up and H2O2 can be gradually dropped to zero. This again is much less exothermic and slower process, and easy to control (like ferric chloride). But bubbling is pretty much mandatory, not only to maintain the process itself, but to reduce edge effects and facilitate uniform etching. This is important with every etchant, though.

And by bubbling, I mean a good supply of compressed air, not some tiny aquarium air pump.

Some see the self-agitation of HCl+H2O2 as a positive, but it really isn't because it's a positive feedback which accelerates etching only in certain areas, and that acceleration drives further acceleration there. Instead, using benign etchant and adding controlled agitation keeps the etching rate consistent over the whole board regardless of local patterns.

[magic]

Another vote for sodium persulphate. Widely available (here) and relatively clean. Although, IIRC it may have been persulphate which bleached a few spots on one of my clothes, so watch out for that.

Clear solution, no fumes. The products are sodium sulphate and blue copper sulphate. Both crystallize out if the solution is left to dry, so little waste product is generated if you don't want to dump Cu₂₊ down the drain.

Small boards can work without heating - start with hot water and wait a bit longer.

[rdl]

I would highly recommend not to use ferric chloride indoors. Sloshing and bubbling creates aerosol particles that can travel far and are nearly invisible until they start etching all the exposed metal in your house. It will also eat holes in your clothing. Nasty stuff in my opinion. You could try to use a contained system but that's probably more trouble than it's worth. Really, getting your boards made by professionals is the best choice if that's possible.

[tkamiya]

With reasonable care, Ferric Chloride is safe to use.  Use gloves to handle it and use it in well ventilated area.  I used to use an old Tupperware in another Tupperware, then put that whole thing outside.  Ferric Chloride is very staining.  If you get it on your clothing, it will not wash out. 

Ferric Chloride is really not something to be freaking out about.  Just respect it as chemical and take a reasonable care.  Really, that's all it takes.

[Siwastaja]

Indeed, much much more dangerous chemicals are sold to general public. You can get 100% NaOH or KOH granules, which will dissolve your eyes and skin and splash around in boiling exothermic reaction when mixed with water, that's some crazy shit compared to mild etchants like ferric chloride.

[tepalia02]

Here is an interesting article. It's about the commonly used etchants.
https://www.pcbway.com/blog/News/Testing_The_Efficiency_Of_PCB_Etchants.html
They have tested the Efficiencies Of PCB Etchants.

[westfw]

Quote

HCl is what is in your stomach to digest food

Vomit-etching it is then. Readily available and it's organic too.

Plain HCl is not going to etch copper in any reasonable timeframe.  You need to add the peroxide, making it significantly more dangerous (probably.)  (also: NOT "organic.")

The "fumes will corrode any nearby metal" is probably true of any etchant.  The amount that an etchant will fume is variable, though.  Ferric Chloride is pretty dense stuff, and is not supposed to produce gasses while etching (though apparently it CAN when initially dissolving the FeCl3 in water.)    HCl fumes a lot (with or without peroxide)(I mean, it's a GAS dissolved in water, essentialy.)
Anything that "needs" aeration or heating is going to be worse than things that work at or near room temperature.
Especially aeration - micro-droplets are going to get scattered all over (and breathed) without some sort of enclosure.

[free_electron]

the safest and easiest etchant is the one in a chinese pcb factory.
- it's far away where it can not splash , spill or creates fumes for you
- it's cheap. way cheaper than what you would pay per kg and it comes with a free doublesided board, soldermask , silkscreen and all.

drawback
it takes roughly 5 to 8 days to "etch" the board... but you can use that time to do something else.

[AndyBeez]

the safest and easiest etchant is the one in a chinese pcb factory.
- it's far away where it can not splash , spill or creates fumes for you
- it's cheap. way cheaper than what you would pay per kg and it comes with a free doublesided board, soldermask , silkscreen and all.

drawback
it takes roughly 5 to 8 days to "etch" the board... but you can use that time to do something else.

Seconded. Thirded even.

The board also etches both sides in perfect register, gets a solder mask in any color, plates through holes and vias, tins pads, then finishes with silk printing - often on both sides. Then the holes all drill, mill and rout themselves, in any size.

I made a couple of PCBs years ago, from stick on pads, etch resist pen, ferric chloride crystals, a crude bubble tank and a hobby drill. Just sending gerbers and drill files to a fab house then waiting a week is the smart 21st Century to do. So unless you're on a desert island with no UPS, a fab house is cheaper. It's the fab house's problem to dispose of their hazmats.

[BlackICE]

Many decades ago I ran out of Radioshack's ferric choride. I had some 6M nitric acid I got from Chem class and used that. Nasty N02 gas is emitted. Not the safest is use but what I had on hand. It worked better than ferric choride in speed.

I agree the safest is to get them made in China where the pollution is 1000s of miles away. Downside is the turnaround time.