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Please don't dump your solvent down the drain like every Silicon Valley fab did back in the day, poisoning the entire region for decades to come. Just look up how many EPA Superfund sites are in the South Bay due to trichloroethylene, TCE contamination. Dispose of it properly and safely.

I ran a small fab on the peninsula back in the day, and we certainly didn't dump any trico down the drain. We did put a small amount of propanol (used to switch from a water rinse to trico drying) down, but that's pretty harmless. The trico was taken away by a reprocessing company. It was still essentially pure - some of it contained a bit of dissolved photoresist or beeswax.

I read through the OP - he's making good choices and doing it much as we did fifty years ago. I would have killed to get that maskless photolith setup, though.

For a small fab (three furnace tubes, two fume hoods), the main issue is acids from photoresist ashing, wafer cleaning, tube etch cleaning, and metal etching. These are easily neutralized with a vat of marble chips built into the plumbing under the fume hoods.

If you are doing this, avoid epitaxy, which involves arsine and phosphine. I would say never attempt those! You can buy epi wafers. Either use spin-on dopants like he did, or use oxidized boron nitride wafers and small amounts of phosphorous oxychloride like we did.

The effluent from a plating facility or a dry cleaning establishment would be far more concerning.

Our furnace and photolith operation fit in a 20 x 30 ft room. It was one of the leading operations of its kind in the world at that time.

> Please don't dump your solvent down the drain like every Silicon Valley fab did back in the day, poisoning the entire region for decades to come.


Please develop a workable waste disposal strategy BEFORE thinking about cool disruptive home brew nanofab MEMS/circuit hacks.

There are a few things I don't want disrupted, and my endocrine system is one of them.

Speaking of which, does anyone know where (in the US) I can safely dispose of ferric chloride, sulfuric acid, and hydrochloric acid? I used to etch my own boards years ago. And ever since then the spent stuff just sits in glass jars in a double plastic box in my garage. I don't etch anything anymore, and it's taking up space.

> safely dispose of ferric chloride, sulfuric acid, and hydrochloric acid

The first step is easy: neutralize them with any base, such as baking soda. You don't need precision, just add a lot of it, and make sure the pH is close to 7 (or beyond, baking soda is not corrosive) at the end. After this step, the solution is no longer acidic or corrosive and much safer to handle.

Unfortunately, the next step is tricky. The solution is safe, but it still contains a lot of Cu+ ions, which is a heavy metal pollutant and poisonous.

On the other hand, if your sulfuric or hydrochloric acid is unused for etching anything (clean without those nasty ions), you are good to go, just dump them in the sink after you've neutralized them (test with pH paper) it's perfectly safe.

Is this what people actually do? I mean I'm aware I could neutralize them, but Cu is still going to be in there and I still can't pour this stuff down the drain. Then there's ferric chloride which is just nasty stuff that will likely stain everything it comes in contact with. I just want to get rid of it in a fully environmentally safe way.

I'm not sure it is economical, but I had some Sodium Persulfate etchant that was full of copper and accidentally dropped a piece of steel in it. The copper plated onto the steel almost instantly. You could probably use iron filings (or some metal that won't dissolve in your acid) to pull most of the copper out of the acid, and then neutralize. I'm not sure what you would do with the solid copper after that. It might take some effort to get a system that was reliable and economical, but the basic idea of precipitating out the copper before neutralization should work.

I don't think it's hard. My high school chemistry teacher did this, reusing the same copper every year. (I dont remember the details though)

Don't ask me, I don't know, as I'm asking the same question. I'm waiting for some answers to my question: https://news.ycombinator.com/item?id=20659004

There are usually reactions you can do to make them safe to dispose of in a regular manner, you should be able to find them with a decent amount of googling.

pretty easy really. Add acid to water, then add baking soda to the acidic water until it's neutralized. (no more bubbling), then pour it down the sink with more water. Use appropriate precautions, gloves, goggles, well-ventilated area, etc. Once the acid is neutral, it won't hurt anything in the pipes.

But is it acceptable to dump wastewater with Cu+/Cl- ions inside? I've read that according to some regulations in some areas, they are considered pollutants and should not be dumped directly to the drainage.

Or is it something you can just ignore, because at the end of the day everything goes to a wastewater treatment plant, and your volume/concentration is too low to be considered hazardous, and actually not more harmful than the wastewater of commercial chemical cleaners, and well within the wastewater processing capabilities for small volumes?

Can anyone give an authoritative answer to this question?

The official advice is to keep neutralising it, collect the sludge and pour the waste water away.


> The solution must not be put down the drain because of residual copper ions left in it. To make it safe for disposal, you can add sodium carbonate (washing soda) or sodium hydroxide to it to neutralize it, until the pH value goes up to between 7.0 and 8.0, testing it with indicator paper. Copper will be deposited as a sludge. Allow the sludge to settle, pour off the liquid, further dilute it with water and then it can be poured down the drain. Collect the sludge in plastic bags and dispose of it as required by your local waste authority.

Cl's in toilet cleaner. Dilute is not a problem.

Cu though is an aquatic herbicide (used to rid decorative ponds of all plant life including algae) and can mess up things.

> at the end of the day everything goes to a wastewater treatment plant

Some of these things, especially the photosensitive chemicals in particular ammonium dichromate will annihilate the wastewater treatment plant. Experienced this problem in an industrial context once, resulting in tens of millions of dollars in damages to taxpayers and a giant fiasco. As a result our privileges to use the municipal sewage system were withdrawn and we had to spend tens of millions in evaporation towers since no water could leave our facility ever again.

Cl ions are fine; dissolved table salt consists of them, plus some cations. The copper is more of a problem, and I don't know the official answer. I'd think that if you could oxidize it to copper monosulfide (covellite), cupric oxide (tenorite), or even fully hydrated copper carbonate (malachite) if you don't have acid rain, that would adequately protect it from weathering and thus allow you to dispose of it safely. But it might be more practical, as well as legally safer, to electrolytically reduce it back to copper and sell it for recycling. Copper, as a semi-precious and semi-noble metal, is recycled actively everywhere the humans live.

I think the biggest problems for chip fabrication waste (not circuit board etching) are HF and nonpolar organic solvents. I'd think neutralizing HF with chalk would yield fluorspar, which is resistant to weathering even over geological timescales. But again I don't know what the official answer is. Maybe dumping fluorspar in your yard will get you arrested.

First warning with neutralizing acids: You're going to release a lot of heat, make sure you have a large thermal mass to absorb it. Someone else mentioned mixing your ingredients with water first. This is why.

From what I understand the last thing you want to experience is an explosion of hydrofluoric acid.

The internet seems to suggest lime (->fluorspar) or soda lye (->NaF, used for fluoridating water) to neutralize HF, but that's two other substances you wouldn't want raining on your head... be careful out there.

Yeah if you just dump a base into these strong acids things go foom! and you end up with dead makers.

Don't mix this stuff in dilution in an enclosed space either as the H2 gas can create another explosion hazard.

HF is technically a weak acid, but I wouldn't venture to neutralize it quickly; it's very reactive even if it doesn't fully dissociate in water.

As for hydrogen, neutralizing acids with bases doesn't generally produce it, but ventilation is still a good idea.

Why wouldn't you want fluorspar raining on your head? Just because it's heavy and hard?

I suggested fluorspar rather than NaF because a backyard full of fluorspar is a pretty rock garden, while a backyard full of NaF is a toxic waste dump.

The concern probably isn't the acidity, but the heavy metals and other toxins in the solutions. Pouring tpxins down the drain isn't a good idea.

Yeah it's being talked around in this thread but I think most of the participants seem to get it.

The solvents can be broken down to things that are compatible with the sewer system.

The hard part to deal with is the material you dissolved with the solvent.

> Dispose of it properly and safely.

I see a lot of people say this, but I rarely see any actionable advice.

How does your average residential person find and dispose of chemicals like this? Seems like most people end up pouring them down the drain simply because they don't know how to actually find a better means of disposing them.

A person doesn't get a pass on things like this because other people didn't spoon-feed them the info. Read the law, call the EPA, google it.

Ultimately if you want to use chemicals that have the potential to poison our shared environment you need to be willing to do the legwork to be confident that you are doing things responsibly.

We don't give people cars without a test. Perhaps such chemicals shouldn't be dispensed without training.

I don't know, but if I were doing this, I'd find out. Call your residential waste management company and ask them who handles commercial hazmat in the area, if you can't think of any other way to start.

If you're planning out your own home fab, you're researching a bunch of other things and giving serious thought to a lot of nontrivial problems. Choosing to ignore waste disposal is irresponsible, and you deserve any legal hassle you run in to.

> I see a lot of people say this, but I rarely see any actionable advice.

If you have industrial quantities of chemicals (more than a gallon or so), you need to call the relevant entities.

If you are lucky enough to have a hazardous waste disposal locally, obviously use that.

If you have stuff that doesn't break down well in water (cooking grease, for example), pouring that down the drain is always a recipe for trouble. You're simply going to clog your pipes. You need to dispose of that properly. There is a reason why restaurants have grease traps. Normally, residential quantities of this stuff can be placed in normal trash.

You can try to dispose of motor oil at gas stations, service stations, etc., but a lot of places won't take oil from end consumers anymore as it may be contaminated and their recycler will charge them. I actually had a very difficult time disposing of motor oil about 15 years ago. (I don't do my own oil changes anymore for this reason). I got told by the local enforcement "At the end of the day, dishwashing liquid and pour it down the toilet and the sewage treatment plant will chew it up the rest of the way." Obviously if everybody does this, it's a problem, but if it's really a one-off, it's okay-ish.

If, however, your stuff is soluble in water and you have a relatively small amount of it and your waste goes to a sewage treatment plant, pouring it down the drain while diluting it with a lot of water is often your only choice (be careful--solvents and acids can produce fairly noxious vapors even when diluted heavily) Quite often industrial disposal sites simply will not take small quantities of waste from individuals as there are liability issues involved.

Now, you may not like what even a dilute solution does to your plumbing, but that's a different issue. If your sewage doesn't go to a sewage treatment plant, but instead goes to something like a septic system, then you probably don't want to do this.

DO NOT POUR STUFF DOWN STORM DRAINS. Those normally do NOT go to sewage treatment plants (there are exceptions--but they are rare) and, as such, are a really quick way to contaminate the environment.

PSA: here in the SF bay, auto parts stores all have oil recycling receptacles. Check with them before you go and put it down the drain, surfactant or not. For other substances, there are also hazmat acceptance sites around, although they seem to keep annoying hours.

I rarely see any actionable advice.

How's this? If you don't know how to safely dispose of the toxic chemicals used in chip fabrication don't fabricate chips at home.

Just google hazardous waste disposal and give it your location. My experience is in the US, and here many counties have something like this:


If you're in MA the link is: https://www.mass.gov/info-details/safely-manage-hazardous-ho...

Other states probably have similar things?

Very much worth researching before you get into a hobby where you start accumulating hazmats!

Your average residential person doesn't have a homemade semiconductor manufacturing facility in their garage either, I'm sure getting into contact with local waste disposal agencies is a far easier task than building all this stuff.

> How does your average residential person find and dispose of chemicals like this?

How do you dispose electronics? Batteries? Oil? Tires? Cars? Furniture? construction materials? ...

You go to the webpage of your local garbage disposal authority, and read their FAQ, which typically contains where all their disposal centers are, their addresses, opening hours, etc. and what can you dispose on each one.

If what you want to dispose is not listed anywhere, you call them and ask them.

In my country if you want to buy these types of chemicals, you need to ask a company for a price, and the company will ask: who are you? what do you want them for? what's your process for the chemicals? Etc. If you fail to answer any of the questions, they are obligated to report that a "sketchy" party tried to buy some chemicals from them. That might get you a visit from the police, asking even more questions.

That's balancing your freedom to do whatever you want with chemicals with my freedom to enjoy a world that hasn't been polluted by idiots that didn't know what they were doing.

Your local rubbish service will point you in the right direction.

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