Etching

[RTurner]

I first discovered this at the gyraf.dk website (the DIY section has tons of great stuff including some nice tutorials).

I always seem to have bad luck etching with ferric chloride, and it seems like I’m always out- which means I either have to order it (and wait a week), or go to radio shack and pay $$$$ for their brand.

But there is another way, it’s cheap, easy, does a good job, and the chemicals are readily available…

Instead of using ferric chloride, I started using hydrochloric acid (approx 50% solution) and hydrogen peroxide (3%, the same stuff at the drug store).

Hydrochloric acid is sold as muriatic acid in hardware stores as a cleaner, and I bought two gallons for four dollars and change. 

Procedure: as opposed to the procedure on the Gyraf Audio website (which is good, but requires a form of hydrogen peroxide that is hard to find, and depending on where you live- illegal to transport), I used a 1:1 ratio of HCL and H2O2, this seemed to work well. 

What you need:

HCL 50% (or close to 50%, sold as Muriatic acid)

H2O2 3% (sold as antiseptic)

WATER! (Enough for the rinse, and a jug on hand… Just in case, see below)

2 PYREX measuring cups (one for each chemical)

2 PYREX pans (one for etch, one for rinse)

SAFETY GOGGLES

DISPOSABLE GLOVES

First of all, you absolutely have to do this outside.  The procudure can develop chlorine gas.  I’d recommend even having a portable fan on hand to blow away the fumes.  You Absolutely must wear safety goggles.  This stuff will F-you up if you get it in your eyes.  You must wear disposable gloves.  I say disposable, because there is a good chance that some of the acid will find its way down into them, this is not a huge problem, you will know that this is the case way before you have a serious burn, but it’s easier to mitigate this risk by having plenty of disposable gloves.  The etching reaction is exothermic- this means that it produces heat, though it’s unlikely, there is a chance that the etching solution could get hot enough to actually boil- you’ll know that it’s about to do this if it starts fuming a lot.  If this begins to happen, slow down the reaction by CAREFULLY pouring water into the etching solution. 

I used a 13"x8" dish as my etch, and one significantly larger as my rinse. 

Into the etching dish I measured, then poured 1.5 cups of H2O2, and then did the same for the HCl.  ALWAYS (except in the above exothermic-doomsday scenario) pour acids into water, not the other way around.  This minimizes the risk of splashing yourself with a very very corrosive substance.

The actual amount etchant isn’t that important, what is important is that it’s about a 1:1 ratio, and that it only filled the dish up about half-way.

CAREFULLY slide the PCB into the solution (it’d be a good idea to have the first edge to go under- towards you, as to minimize the risk of splashing). 

Immediately, the un-masked copper will turn a dull yellow-orange color, and bubbles should soon start to form.  I’d recommend manipulating the etch as little as possible (no sponges, no rubbing, and definitely no toothbrushes- all of these things will ensure that the edges of your traces will start to dissolve).  The rate at which it etches seems to be dependent on the temperature, the first time I tried it, the etch took about 5 minutes, though it has cooled off a lot since then, and the last etch I performed (at about 45 degrees farenheit) took closer to 30.  If it is etching really slow, it seems to help to gently rock the solution back and forth over the board. 

Cleanup:  HCl and H2O2 are both relatively safe to the environment.  There will be a little bit of copper dissolved in the solution- which isn’t the best for the environment, but, at the very least this stuff can be thrown down the sink without too much of guilty conscience.  If you wanted to be extra safe, you could try to neutralize the HCl with NaOH (which you probably have as your pcb photo-developer), this should form salt water- which is of course, safe to flush.

Anyways, I feel liberated with this method.  The chemicals are easy to get, and cheap, the quality of the etching I’ve performed with it has improved dramatically.  It’s safer for the environment, and on-average seems faster too.

[Jidis]

I believe this is the post I was looking for the other day.

• Thanks!

(saved to disk)

[Jidis]

Robin (if you’re in here)-

Any idea what the “shelf life” is on this concoction? I didn’t feel like neutralizing/disposing of my last batch, so I bottled it, but I don’t want to ruin my next board if it isn’t 100% reusable.

Thanks!

George

PS- One of the reasons I didn’t pursue the sodium persulfate etching I got into was that the mixture didn’t seem to work the same after I let it sit for a period. That stuff supposedly doesn’t work well immediately after it’s mixed either… go figure. :-\

[RTurner]

Hey George,

  The HCl + H2O2 etchant, just like ferric chloride, will lose it’s ability to dissolve copper (or any metal) as it reacts to form cupric chloride.

BUT, as far as just sitting on a shelf…  I would think that the shelf life of the stuff would be on the order of a few months.  The hydrogen peroxide will decompose into water and hydrogen with time, even if there’s nothing to react with. 

I don’t think it’d be possible to actually ruin a board by using “expired” etchant..  It would just sit there…  and not much would happen.

On the other hand, it’s been years since I took a chemistry class- and half the point of using this method is that the etchant is dirt cheap and disposable…

Good luck,

and tell me how it’s working out with your pcbs

Robin

[Jidis]

Good luck,

and tell me how it’s working out with your pcbs

Robin,

Thanks, and great (so far as the etching goes :)). I have to do it outside and I’m really careful with it, but the speed is awesome, as is the cost obviously.

No, it won’t likely be sitting anywhere near that long. Right now the stuff I last used is bottled up tight, in a thick plastic Hydrogen Peroxide bottle in the shed. I’m sure I’ll be doing something with it over the next week or so. If it slows down any or does something weird, I can always mix more. It was mainly just a matter of avoiding disposal for a bit. BTW- By “ruin” I just meant having it react poorly with the board and having to let the board sit in it for too long to get everything etched. When I’ve had that happen with other chemicals, I’ve always ended up with an inconsistent etch, where thin traces started getting eaten away while there were still some disappearing “islands” of copper in other areas.

Thanks Again,

George

PS- Here’s the latest from it-

Of course, having it actually work might be nice too. :'(  (  http://www.midibox.org/forum/index.php?topic=7895.0  )

[RTurner]

George,

  First, your board looks great!  Lately it seems like I’ve become the high-priest of hydrochloric acid on here, maybe I should direct people to your image…

  I’ve found that with about three cups of etchant I can etch 2-3 4"x6" boards before it starts to slow down too much.  But then I just make a new batch :)  Even if the etch is going kinda slow, with HCl it still etches pretty much uniformly.  Unlike with FeCl where one side of the board will be completely gone before the other is done etching.

  The bad part is that the temperature has been dancing around freezing lately, and this seems to s-l-o-w the etch process down quite a bit…  I have to do it outside as well.  Maybe I can install a hood as a business expense…  In the meantime the cold etch just gives me more opportunity to catch up on the important things in life, drinking and smoking.

Robin

[Jidis]

Yeah, I hadn’t considered the outside temp changes. It was a bit chilly on the last one. Come to think of it, it may have actually taken a bit longer, but it seemed to do OK anyhow. That was one of the things I liked most about it when I first tried it. It not only didn’t require any additional heat source, but it also sort of fizzled away at the board on it’s own. I periodically wash it around with a plastic knife, but little more than that. Everything I used in the past was dramatically different with higher temperature and mechanical agitation.

Not to underestimate the dangers. I’m definitely afraid of it, but the extra bit of caution is worth the results and convenience.

Take Care

[RTurner]

George-

  Ok, apparently you must not store mixed etchant, it gasses- even when bottled up- enough to possibly break the bottle it is in.  If I were you, I’d find a careful way of disposing of that bottle you have around…  Sorry, I just happened upon this information.

Hey- what method did you use for masking your board??  We’re revising our method, and I’m researching every technique under the sun.

Typically we’ve been using boards that have a pre-sensitized positive photo resist on it, but…

advantages:

-Easy, and at least the exposure & developing are pretty consistent.

disadvantages:

-boards seem to only be available in 1oz 1/16", and not available in large sheets.

-quality of the boards seem to vary wildly from manufacturer to manufacturer- the tell-tale sign of a crap board is when grooves following the top-grain of the fiber-glass etch out several minutes before the rest.  But also the handling of the board from the manufacturer until the time of development seems to be important- and partially beyond our control, often times if the boards were roughly-handled in the mail scratches will show up during development.

-boards are costly

-we’re not really sure if it’s because of the thickness of the copper, the thickness of the etch-resist, or that we use a flourescent bulb instead of a point-source, but it rarely produces really crisp edges, at least on the entire board, which makes it unsuitable for SMD work.

-time consuming (9 minutes for exposure, 10-ish minutes to develop.

We’ve recently tried toner-transfer..  using both specialty decal paper and plain paper, also with and without foil.

Advantages:

-Consistently produces edges that are as crisp as your artwork.

-Plain paper is about as cheap of a way to do this as I can envision there being. 

-plain clad board can be bought in nearly any size, thickness, and copper-weight that exists.

-plain clad board is also cheaper for the above reason (we have a small, as in miniscule, business- and having things that are cheap and readily available is the name of the game)

Disadvantages:

-The decal paper hates our laser printer, when set to maximum toner-density (little flecks of toner get taken off the image and end up down the page).

-The Kinkos down the street uses a toner composition that refuses to adhere to the copper.  I watched in horror as the resist for the traces simply lifted up and floated away half-way through an etch.

-The toner is semi-porous, so what at first may look like a perfect etch, when given the through-light test reveals a starscape of pinholes.  This simply is unacceptable for any board that will be leaving the workshop.

[Jidis]

Hey again Robin,

Thanks for the info on the used stuff. I’ll try to get rid of it tomorrow. I bought more Hydrogen Peroxide a few days back, so I should have plenty to do many more batches. I had way more of the acid at first, due to the quantity they make you buy.

• I’m guessing this gas thing isn’t something where you could slowly relieve the pressure every so often right?

My masking is more low tech than you may guess. It’s just many many trials and refinements to the toner technique (most of what’s described on Tom Gootee’s page). I’m currently using that last grade of paper he recommended by Staples, and am running an HP LaserJet 6L, with what I believe to be the original toner cart. You sound like you have access to proper equipment. I just figured I was sort of stuck with that, and managed to get pretty good with it. 

I’m using an iron with an eighth inch plate of aluminum “JB Welded” to the base:

I’ll keep an eye on the pinholes and stuff. I probably get them but don’t notice it. I’m wondering if that green TRF coating would fill that sort of thing in??

Take care and thanks again for all the info,

George 

PS- I’ve thought many times that I’d gladly trade my skill (or luck) with the toner transfers for some better assembler or electronics knowhow :-.

[Mr_modnaR]

don’t look now jidis, but i think there’s a baby godzilla in your house!!

[RTurner]

Heheh, imagine my predicament, I ended up in a small electronics company (tube pre-amps mostly), and my training was in architecture.  The whole electronics thing is coming slowly.  As for now I’d happily trade my knowledge of building codes for a better way of etch-masking PCBs.

Ok, so the problems we’ve been having with toner transfer are probably related to the toner we’re using, or the paper.  Hmmmm.  Guess it’s time to go shopping.

But looking at your… umm… PCB manufacturing setup proves that we should experiment with toner transfer until we get it to a consistently high quality level.

Otherwise I think we’ll try putting photo-mask film onto bare copper board- so that we can have more control over the process. 

I’ve even considered putting in an order for a moderately sized medium-duty CNC machine to mechanically etch PCBs (and front panels)- but that’ll cost us several thousands of dollars, which means it’ll be that much harder to get a pay check.

Speaking of panels, I’m not sure if you’d be interested in this, but- you can use HCl to etch aluminum.  What you can do, is carefully apply a negative mask to an aluminum panel, use masking tape to mask-off the edges and back of the panel and to touch-up mistakes, and give it a dip for a few minutes.  BE CAREFUL.  The reaction that dissolves copper is nothing compared to dissolving aluminum, where (especially if you’re etching a large surface area) the reaction can become violent as 3HCl + Al = 3H + AlCl3.  In other words… No smoking.  The solution will actually appear to boil as Hydrogen is released.  But the results are pretty nice looking.

robin

[Jidis]

I’m not sure if you’d be interested in this, but- you can use HCl to etch aluminum.

Yes, very much so ;).

I coincidentally tried that a week or so back after reading that link here for the guitar pedal etching:

I wish I had read it earlier. I just did an EQ controller module with black on aluminum, and would much rather have etched the labels (I just did toner with a protective clear coat). That text in the picture is on a strip of metal that’s only about an inch and a half tall. It doesn’t look all that bad considering, plus it was ragged to begin with, and I wasn’t happy with the “blackening” part of the process, so I kept sanding it down and retrying. I ultimately ended up spraying a coat of semi-gloss black on it, and burning it back down on a sharpening stone, but I don’t like the shine, and it’s inconsistent. The process on the pedal site just used the sludge left from the toner, but that had sort of a flat gray look, which didn’t provide enough contrast. The other trouble was the large masked areas you have to deal with. Sort of wasteful and messy on toner. Next time I may try a light hatch pattern or something on the print, and then just paint mask over it like they did on the pedals. I also want to try different colors and types of filler, but I’m not sure what to expect.

BTW- I didn’t mess with the HCl on that. I used regular FeCl, like on the site (didn’t know I could use HCl). It does leave a bubbly “goo” as it etches, which makes it sort of hard to see the progress. I think I wiped that off a couple times with a toothbrush or something, and it helped, but I wouldn’t want to risk smearing off any toner.

Thanks Again,

George

[Jidis]

i think there’s a baby godzilla in your house!!

I thought that thing looked familiar. ;D

[Jidis]

Robin (if you’re around)-

Just got stuck doing an HCl etch outside in some really nasty weather and it still did OK. Weather site says 41 degrees(F) and “feels like 33”. Also raining of course. ;D

I see what you’re saying on the differences in board stock. I’m starting to notice that my extra thick double sided stuff doesn’t usually give me as clean of an etch as the single sided I’ve got. I’m not sure if it’s the overall quality, or just the thickness of the copper though. I think the double is heavier there (on each side). The other thing that sucks is that the substrate itself is so thick that most stuff has to be forced down tight, just for the pins to get good surface area through for soldering on the bottom. Then, some of the parts need to sit up just a little, to get decent access for any “top soldering”. I really need to get hold of some of those conductive “rivet” insert things, but some better layout skills probably wouldn’t kill me.

Take Care,

George

[Jidis]

FWIW, I just dunked a scrap of aluminum flashing into a container of the acid mix and it had no effect whatsoever.???

I figured maybe they’ve coated it with something (it does have sort of a “greasy” feel to it), so I lightly rubbed a spot on another piece with fine sandpaper. That one bubbled a bit, and now has some dark speckled scratches in the center of the rubbed area, but the stuff is already so thin, I’m not sure that’s a solution. Maybe try acetone or something next.

I’d like to see if it could actually take a deep enough etch to make for readable labels. It’s flexibility would lend to some interesting corner options for panels. Worst case, I guess straight toner would work (no etch). I’ve also tried it on plastic laminate and gotten a good print (that stuff can also wrap around a corner to some degree).

Take Care,

George

[RTurner]

Most aluminum sheeting that ends up not being sold as straight-up sheet metal will have an enamel coating on it, since aluminum is decently reactive.  Also, if I remember correctly, aluminum used for casting has silicon added- which makes it easier to cast for one reason or another- but also makes it unsuitable for etching.  My guess, without looking into it, is that you could possibly remove the enamel with some sort of non-polar solvent.  Try using goof-off or one of the scarier non-polars that usually are used in industrial applications…  Have you tried Comet BTW???

If you’re looking for sheet metal, and you don’t mind waiting for shipping- Mcmaster-carr (www.mcmaster.com) has all sorts of materials.  Usually metal being sold as sheet metal (as opposed to flashing, which would be coated to protect it from the elements) doesn’t have any treatment.

Plus Mcmaster has some pretty cool stuff.  Everything from 2" thick sheets of hard felt (the sort of stuff the beaters for bass-drum pedals and timpani mallets are made of), sheets of silicone, perforated brass sheeting (like the tops on a bunch of vintage hi-fi tube amplifiers), woven metal cloth (microphones), all manners of metal cylinders (custom-lathed knobs?).  The list goes on and on.  Lets you select materials by ASTM numbers.  It’s a very cool place, and has everything you need for fabrication that you can’t get from digikey/mouser.

[Jidis]

Robin,

No, haven’t tried Comet yet. I got to thinking on the metal and there may be a way I can mix flashing with regular aluminum plate for the panel part, which might be better for the panel anyway. The flashing would’ve gone on a substrate. I’d still like to see what flashing looks like etched anyway (if that’s possible). If removing the coating kills the look, it probably wouldn’t be worth messing with though.

I’ll let you know if it turns out anything decent.

Thanks for that McMaster link too. That main home page full of links is insane. They probably do have lots of stuff I need from time to time. Do they actually stock all that stuff or are they like that electronics house where the parts get shipped directly from manufacturers all over the place? (that’s a heck of a lot of stuff)

Take Care,

George

[Jidis]

Just realized the “mist” from that acid seems to have put an orange/brown film on a whole box of router bits and a dovetail saw which were sitting near where I used it the other night. I had it a couple feet inside my shed with the doors open. I guess “outside” means completely outside from now on. :-[

[Tibia]

Jidis…

McMaster-Carr is one of those very unusual distributors.  They actually do stock most all things from their catalog.    For one job I needed a tool from their catalog.    Was in the area of their Los Angeles branch.  Drove over and picked it right up.  No other company had one in stock within 100 miles.  Its very unusual when they  don’t have an item in stock at one of their facilities.

Tibs

[Jidis]

Must be nice.

I found a chemical supply house on eBay a few months back, which turned out to be about 20 minutes from here. They’re sort of like McMaster-Carr for weird chemicals, and have just about anything. Got my sodium persulfate from them. They said if I needed anything to regenerate it, or the FeCl, they’d probably have it, and if not, tell them what it was and they’d get it in stock. Our electronics suppliers in this part of VA suck however. AFAIK, we’re left now with nothing but Radio Shacks, and they can’t talk to you unless you’re buying a phone or a radio controlled car.  >:(

George