PCB etching with less nasty chemicals? - Page 1
Forum section: electronics / projects

author: hlavac
author_rank: Frequent Contributor
timestamp: July 07, 2012, 03:11:32 pm
content: I would be really interested in an etching process that does not produce any chemical waste at all, or one that is not very harmful and/or can be recycled.I've heard that cupric chloride (CuCl2) based etchant can be completely regenerated.Either chemically by adding a bit of HCl to it, converting it back to even more CuCl2, or by removing the Cu from it using electrolysis.Anyone got any experience with that?Also looking for slightly less nasty developer for the photoresist, NaOH is a bit strong for my liking. Wouldn't sodium carbonate (Na2CO3) work as well? I use it as a developer for the solder mask... would be nice if I could use it for both.Guess it's time for some tests...

author: nctnico
author_rank: Super Contributor
timestamp: July 07, 2012, 03:26:07 pm
content: Use FeCl (Ferric Chloride). When etching starts to take longer you can add HCl (Hydrochloric acid). In this way you can use FeCl forever.

author: mianchen
author_rank: Regular Contributor
timestamp: July 07, 2012, 03:44:50 pm
content: Quote from: nctnico on July 07, 2012, 03:26:07 pmthey are both messy and nasty though

author: notsob
author_rank: Frequent Contributor
timestamp: July 07, 2012, 03:48:15 pm
content: a piece for you to read hlavachttp://www.qsl.net/iz7ath/web/02_brew/14_howto/02_clor/index.htm

author: hlavac
author_rank: Frequent Contributor
timestamp: July 07, 2012, 04:53:16 pm
content: Quote from: notsob on July 07, 2012, 03:48:15 pmInteresting. When you etch with Ferric chloride, you get:FeCl3+ Cu --> FeCl2+ CuClFeCl3+ CuCl --> FeCl2+ CuCl2So after etching with ferric chloride you end up with CuCl2etchant solution contaminated with FeCl2.Then you add HCl to it and a bit of hydrogen peroxide and it will start etching again.Funny, this is exactly what you do to regenerate the CuCl2etchant.I bet it works not because of FeCl3has somehow been regenerated, but because CuCl2has been regenerated.This is why it still works for the guy after 4 years.

author: hlavac
author_rank: Frequent Contributor
timestamp: July 07, 2012, 06:05:04 pm
content: Hm, regenerating CuCl2 involves adding Cl to the solution to turn the CuCl- into CuCl2.The stuf with HCl and peroxide oxidizer does just that.This could probably be done with electrolysis:Split the spent etchant solution into two tanks.Electrolyze one of them.Copper will deposit on the cathode.Cl2gas bubbles form on the anode and should go to the other tank to regenerate it...This could make a nice completely closed cycle where the etched copper moves to the anode and nothing leaves the tank...Only problem is, what to make the cathode of? Copper does not look like a good ideaSomething conductive that will not dissolve and can be formed into a fine mesh...

author: SeanB
author_rank: Super Contributor
timestamp: July 07, 2012, 06:37:12 pm
content: Carbon rod?

author: nctnico
author_rank: Super Contributor
timestamp: July 07, 2012, 07:23:54 pm
content: You want to etch boards or (pretend to) be a chemist?

author: hlavac
author_rank: Frequent Contributor
timestamp: July 07, 2012, 07:35:18 pm
content: I want to etch boards and not feel bad about the stuff I send down the drain

author: madires
author_rank: Super Contributor
timestamp: July 07, 2012, 10:43:19 pm
content: Hi!Go milling :-)Cheersmadires

author: 6502nop
author_rank: Regular Contributor
timestamp: July 07, 2012, 11:24:19 pm
content: hlavac, as I've mentioned in another thread, I prefer Quinn's method (I use toner transfer instead of photo-resist, but the same otherwise):http://quinndunki.com/blondihacks/?p=835As for a safe way of doing this? Haven't found one. The H2O2/Vinegar/salt is the safestin storage, but once mixed up, it's very nasty stuff. It has to be.I don't know laws in your area about disposal, but in my neck of the woods, CuCl is used for killing tree roots in sewer drains, and our local treatment plant can handle it without problems. So, I can store safely, mix and etch, then carefully pour it down the drain with lots of running water to dilute it.nop

author: nctnico
author_rank: Super Contributor
timestamp: July 07, 2012, 11:39:13 pm
content: Quote from: hlavac on July 07, 2012, 07:35:18 pmThen FeCl and HCl are the way to go. In my previous etching machine I have used the same FeCl for over 15 years. Over here I can take chemical waste to a waste disposal depot.

author: codeboy2k
author_rank: Super Contributor
timestamp: July 08, 2012, 12:19:28 am
content: I like hlavac's desire to electrolyse the copper out of solution. That would be useful too, as you can then use that copper in a future plating process.I am sure the big board houses must do something like this in-house, because they plate copper onto boards and through holes in order to build up the copper layers.

author: IanB
author_rank: Super Contributor
timestamp: July 08, 2012, 12:42:05 am
content: Quote from: 6502nop on July 07, 2012, 11:24:19 pmQuinn didn't mention (or I missed it) the value of printing your layout mirror image on the acetate and placing it face down against the board. This reduces the distance between the ink and the resist and minimizes the tendency for light to creep under the ink during exposure. Of course that doesn't help if you want to double up the layers of acetate as Quinn does.

author: T
author_rank: Newbie
timestamp: July 08, 2012, 02:09:12 am
content: The chemicals involved in etching are just nasty by nature. I use HCL/H2O2 to etch, and it can be regenerated easily by adding a bit more H2O2. Once you get enough copper dissolved into it you end up with CuCl2, which can be regenerated by the regular re-introduction of oxygen, like with using a small air pump and bubbling stone from an fish tank. I believe most PCB houses use CuCl2 because of its regenerative property, so it could be considered the most friendly of the etchants. Also I'd advise anyone not to dump this stuff down the drain, the dissolved copper is highly toxic, but it will also slowly etch away the insides of metal drain pipes each time you dump it.

author: hlavac
author_rank: Frequent Contributor
timestamp: July 08, 2012, 10:59:27 am
content: QuoteYes that's why I'm looking for a way to defuse the mess before dumping it. Either turn it into something harmless or preferably remove the copper from the solution altoghether.If the stuff does not exhaust itself and keeps working forever that's all the better.Funny how all the copper etching chemistries mentioned so far are based on making copper soluble with Cl-ions (H2O2removes H from HCl creating more water with Cl-dissolved in it).Are there any other, different etching chemistries?How about the ammonium persulfate? It needs to work at higher temp (~43 C) and supposedly does not dissolve tin, so it can be used when making thru hole plated boards where stuff that has to remain is covered in tin mask including the hole walls...

author: hlavac
author_rank: Frequent Contributor
timestamp: July 08, 2012, 11:23:42 am
content: As for the "air regeneration" of cupric chloride etchant, I believe it will not work forever as it relies on presence of excess HCl in the solution, and that will get exhausted...You could as well add more peroxide and not borher with the bubbling stuff.

author: Chasm
author_rank: Regular Contributor
timestamp: July 08, 2012, 11:46:31 am
content: Using ammonium persulfate is not a good idea, it ishighlytoxic to aquatic life.Sodium persulfate does not have this particular problem.It is possible to remove the copper from used etchant with fine steel wool. This is a highly exothermic process (=boiling!) and does involve more steps than dumping steel wool in the etchant. So better know WTF you are doing. Before trying.The results can be disposed without problem.I can dispose chemicals for free at the local landfill or at a mobile collection station. Check if there are similar offers in your area.

author: vk6zgo
author_rank: Super Contributor
timestamp: July 09, 2012, 05:28:02 am
content: Collecting & regenerating etchant,or making it safe for disposal may be a new niche market,though you would probably have to team up with a "tame" Chemist so as to have "Geek cred"!

author: HardBoot
author_rank: Regular Contributor
timestamp: July 10, 2012, 11:38:12 am
content: Well, you could do away with etching altogether with a small precision C&C... slow and expensive compared to chemicals, but no hazardous waste.Would be a really cool DIY... PCB printer, could make double-sided boards. Only problem is, if you want really high precision for small smt it could only be that accurate if it were extremely expensive or very slow... although could have a coarse and fine gearing.

author: poorchava
author_rank: Super Contributor
timestamp: July 11, 2012, 01:51:03 pm
content: You can check Sodium Persulfate (also known by code B327). It's better than Ferric Chloride because it gives better finish (dunno the actual english word: i mean it doesn't etch copper from under the resist layer near the resist edges).It is nasty, especially in the fact that it will destroy any clothing it drops on, even in low concentrations (once i've got my hands dirty in it, so i washed them very intensively and then touched my t-shirt by accident. effetct: impossible to remove brown-ish stains).Actually i think anything that oxidizes copper fast enough that it can be used as efficient etchant will qualify as "nasty".

author: nctnico
author_rank: Super Contributor
timestamp: July 11, 2012, 05:50:01 pm
content: Quote from: HardBoot on July 10, 2012, 11:38:12 amYou mean CNC milling? That has been tried and has been failing miserably for more than 20 years.

author: HardBoot
author_rank: Regular Contributor
timestamp: July 12, 2012, 12:31:05 am
content: Quote from: nctnico on July 11, 2012, 05:50:01 pmWell I've seen 3-Dimensional objects made of metal ingots CNC'd within a few microns, so a 2D unit with 200 micron accuracy shouldn't be too hard, the board being milled just has to have the copper well attached if you wanted thin traces... or go extremely slow.

author: george graves
author_rank: Super Contributor
timestamp: July 12, 2012, 01:23:17 am
content: Quote from: HardBoot on July 10, 2012, 11:38:12 amWell, except the fiberglass dust particles you get to breath....yea.

author: HardBoot
author_rank: Regular Contributor
timestamp: July 12, 2012, 02:05:35 am
content: Quote from: george graves on July 12, 2012, 01:23:17 amWell often you CNC things under water or oil just to keep things cool and clean, only annoyance is filtering, copper sinks to the bottom, but fibreglass... ugh, not a big problem, just annoying.

author: witek
author_rank: Newbie
timestamp: July 12, 2012, 09:39:14 am
content: Hi,unless you already have CNC chemical way is way cheaper and easier.Forget about FeCl, it is only intermediary to produce CuCl and the CuCl is doing the etching really.You can buy FeCl but not CuCl for few reasons - FeCl is safer (in case somebody eats it - I am serious), it i cheaper to produce (iron is cheaper than copper) and it will make you buy it over and over again (I am serious again).Best ever etchant - CuCl, easy to make, a bit of concrete/patio cleaner + H2O2 in a container and just drop the PCB in it.The peroxide is only to speed things up, it would work without it however you could be waiting days to etch your PCB.It is very easy to regenerate CuCl etchant. Add a little bit of HCl (brick cleaner) nad oxygen. For oxygen you can use more H2O2 or just leave it in open container (covered with some cloth to stop dust getting in) and oxygen from the air will regenerate it without any help. The bigger the surface of the container and shallower it is the better. You can regenerate it in a bottle as well, but you should aerate it (aquarium pump + airstone) if you don't want to wait months for the air oxygen to regenerate it.It last forever, if you do around 200cm2 of PCB a week one litre should last you for around a year before you have to add more HCl and/or H2O2.You will never run out of CuCl ethant, instead you will have more and more of it over time.Over time, as you add HCl and possibly H2O2 and as more copper dissolves of your PCB's the volume of your etchant increases so you have to dispose of some of it.Copper salts are highly toxic to any life, especially aquatic, but you shouldn't worry about your health. As long as you wont drink it or take bath in it you are perfectly safeIn order to make it reasonably safe it is enough to drop some iron/steel or aluminium into your etchant. Both Fe and Al are much less noble then Cu and will replace Cu in solution. As result you will get FeCl3 or AlCl3 and metalic copper in form of sludge or sand like deposit.The solution becomes now much less toxic (still not safe to drink it ! ) and after filtering copper out in most places you could safely dispose it of down the drain (check with you local authorities).

author: nctnico
author_rank: Super Contributor
timestamp: July 12, 2012, 09:50:15 am
content: Quote from: HardBoot on July 12, 2012, 12:31:05 amThis forum has several threads on milling PCBs and all end with the conclusion that it just doesn't work. The CNC machine you are talking about cost more than $100000. Now count how many PCBs you can have made for that amount of money. I think a lot even if you choose for one day service.Once you have the setup (UV phototransfer and etching machine) its pretty easy to etch boards at home.

author: HardBoot
author_rank: Regular Contributor
timestamp: July 12, 2012, 01:25:11 pm
content: Quote from: nctnico on July 12, 2012, 09:50:15 amI don't see why'd you would blow $100k on a general purpose CNC when you could diy it for $2000, optical positioning on the rails is easy and cheap compared to mechanical precision, if you only concentrate on accuracy and not speed, screw rods with very high thread count let you be within 100-200 microns off the bat, then have a fine adjust.

author: witek
author_rank: Newbie
timestamp: July 12, 2012, 02:50:17 pm
content: If yourONLYgoal is to make PCB's I really don't see the point of spending $2000 and lots of time and effort building the CNC if for $20 you could have etchant which will last you a lifetime.On the other hand building CNC would be fun in itself

author: nctnico
author_rank: Super Contributor
timestamp: July 12, 2012, 04:33:44 pm
content: Quote from: HardBoot on July 12, 2012, 01:25:11 pm200um is useless. When I etch a PCB myself I use 250um traces and 200um clearance (minimum values). I actually need to set my laserprinter to the best resolution it can do to print the layouts on opaque paper.

author: HardBoot
author_rank: Regular Contributor
timestamp: July 12, 2012, 06:54:53 pm
content: Quote from: nctnico on July 12, 2012, 04:33:44 pmResolution vs accuracy; precision confidence.The CNC used at the T&D I use is 100um but I've never seen it off more than 10um.250um traces and 200um clearance isn't too hard on a slow 2D CNC, my spare plotter steppers with the stock gears (down 10x) give me 0.75 degree accuracy, on a high turn count screw rod that's pretty damn accurate. That along with optical position checking... could even mill bga stuff.Only concern is how well the copper is stuck to the board.

author: hlavac
author_rank: Frequent Contributor
timestamp: July 12, 2012, 07:07:54 pm
content: I was looking into the DIY CnC the other day, if I used M8 threaded rod (thinnest I would be comfortable with rotating due to flexing) with a stepper motor that has 200 steps per revoltion the resolution would be 6,25um. It would be slow as hell to move, but more than enough resolution for PCB milling.Getting thin enough cut (200um?) would be the real problem. 0,2mm milling tool would need extremely fast rotation speed and would probably be expensive and not last long.I was thinking about some sort of small cutting disk but that would require positioning along the line of cut and turns would be tricky... maybe two disks at right angle could do but that means 2 tools/z axes...

author: HardBoot
author_rank: Regular Contributor
timestamp: July 12, 2012, 07:56:21 pm
content: 2 tools is annoying, although it'd be pretty quick with a saw and drill bit, saw would also last a long time.Both tools could use the same Z control, just have the one not in use pulled back.Saw would be centred for rotation.XYZR... 4 steppers, 3 screw rods, and a gear rod... mechanically an easy project, hard part is controlling the thing, I'd find programming a $3 micro harder than making the CNC lol.Would probably just buy two dremels for the saw and drill... could made prototype out of wood or plastic, but you'd have to go steel for the stability needed to keep the saw/drill steady.