etching pcbs

[MR COFFEE]

Hi Paul,

Why do you recommend a bubbler for a vertical tank? What is it supposed to do? Where do you place it?

I've toyed with the idea of attaching a vibrator to a long stick to jiggle the board in the etchant, but I haven't been frustrated enough yet to get around to it.

Hi Racedriver,

Does persulphate go bad after you have used it to etch a board if you don't keep it hot? Seems like I read that somewhere.

Hey, will it etch *Aluminum* after it has gotten cold?

Now THAT would be cool

[Paul Perry (Frostwave)]

The bubbler goes under the board. As the bubbles rise, it mixes the solution & so the 'used' etchant is continually swept away from the board. Commercial PCB manufacturers have bubbles, why not us?
Persulphate does very slowly decompose after you dissolve it (you can see tiny oxygen bubbles form on the side of the container) but, it is a very slow reaction, I have used it several months after it was dissolved.
I have never tried it, but I believe persulphate will etch aluminum. A standard way of treating waste persulphate etchant is with aluminum scrap, to replace the copper & also reduce the persulphate to sulphate: www.kepro.com/fmc4.htm

[hank reynolds 3rd]

would using filter paper when pouring the ferric chloride solution into a bottle get rid of some of the old crap (prolonging the life of the solution) ??

These tips are great by the way (toothpicks and hairdryers is next for testing!!)

Cheers
Sam

[Mark Hammer]

Etchant is pretty thick even when fresh.  I think you'd need to have filter paper that is pretty porous.

The sludge at the bottom is yet another reason why some etchant tanks are narrow and tall, with the board essentially suspended from the side, pointing downward.  Anything that creates a bigger physical separation of the used stuff at the bottom and the fresher stuff at the top will help.  You could certainly do that with any deep tank and still have a "horizontal" etch but then you'd probably need to have a gallon of etchant hanging around.  Perhaps you wouldn't need to change the etchant very often in that case, but when it comes time to dispose of it, you have a problem on your hands that is perhaps a little bigger than the average home etcher is able to contend with.  A narrow tall container (think spaghetti container) helps to achieve the physical separation with a smaller quantity of etchant involved.

The bubbler is a good idea, and accomplishes - in a manner that doesn't require you to stand there holding something - what the hair-dryer/heat-gun also does.  The bubbling doesn't really need to be frenetic, and I find the gentle breeze from the hot air blower works as well as you need it to.  By applying heat to the surface as well, you induce what I seem to recall from high school physics was called "Brownian movement" - i.e., a local circulation of particles that ends up with fresh and used molecules changing place.

In any event, a suitable bubbler can be provided by using a small air pump intended for an aquarium.  You can buy a bit of plastic tubing from the hardware store to fit over the nozzl on the pump.  Pinch the end off and poke a number of small holes alogn the tube to distribute the air dispersion more broadly.

[MR COFFEE]

Some stimulating ideas here. Thanks guys!

Paul,
Thanks, man! You've got me willing to mix up that old (dry crystals) persulfate I've got sitting out in the garage and put it to use again! I used it a few times years ago when I was doing a big run of boards and just threw it out when I was through. Too gullible, huh?

I've never seen a commercial etch tank with bubbles. What do the commercial tanks use to make the bubble curtain? Is it important that the "bubble curtain" contacts the board? Does evenness matter? Do you have a setup like this you could share a picture of ?

Mark,
I like your heat gun method for doing small stompbox-size boards a few at a time. Thanks for sharing it. It sounds like a great idea with modern PnP. After I thought about it, the overheating problems I had with etchant were with the old KPR negative-acting photoresist, which pinholed on me. And obviously PnP can take a fair amount of heat since you iron it on <doh>.  I'll try it next time I have just a small board to do.

I think I'll dare to warm up the etchant in my tank a bit more, too, and see if it etches a board in 10 minutes like everybody else seems to say it does for them. That'd be nice I think I better put on my helmet first - I can imagine myself slapping myself on the forehead pretty hard over than one 

One thing, though - have you checked you heat gun for corrosion from etchant fumes? I had used an aquarium heater that I *assumed* was sealed (no obvious openings) in an old setup, and the etchant fumes open-circuited it (etched right through the copper wires inside the heater on autopsy) after a couple years of intermittent hobbyist-type use (probably 12 - 4" x 6"  1 oz. copper).   

It had to have been fumes, too, because there was no evidence that even a drop had gotten inside the heater. FWIW. Maybe the positive airflow keeps the fumes out of the gun so it won't be a problem like with my old heater. I'd check though, heat guns aren't cheap.

All,
Has anyone here ever *tried* the jiggler idea?

It *seems* like a good idea in my head when I imagine it - wiggling the board cause turbulence in the etchant right on the board surface where you want it, it would seem to be low precision and I would think fairly low maintenance, etc. Sorta like poor-man's ultrasonic cleaner tech applied to etching.

Anybody see any reason why a board jiggler wouldn't work well to agitate the etchant in general and especially provide some etchant movement right at the board-etchant interface to carry off the sludge on the board surface that slows down the etching?

Thanks again for this great thread.

[Mark Hammer]

One thing, though - have you checked you heat gun for corrosion from etchant fumes? I had used an aquarium heater that I *assumed* was sealed (no obvious openings) in an old setup, and the etchant fumes open-circuited it (etched right through the copper wires inside the heater on autopsy) after a couple years of intermittent hobbyist-type use (probably 12 - 4" x 6"  1 oz. copper).   

Well, I haven't been doing it for years, so I can't offer incontrovertible evidence, but the tip of the heat gun is nice shiny chrome, and hasn't changed its complexion at all.  I might point out that if you want to create a little ripple in the etchant with the air movement, you'll need to hold the heat gun about 8-10" back anyways, so it is unlikely any fumes would affect the heat gun at that distance.

Indeed, that's the thing I like about the heatgun blowing air: it does the warming and the etchant circulation.  The only downside is you need to stand there for a bit holding the gun.  Now, keep in mind I do my etching in my garage, which is several degrees below freezing today.  When I etch in the same spot during the summer, I can point the heat gun for a minute or two, walk away, and it's still warm enough when I come back.

[johngreene]

Just a word of warning on using bubblers. A company I used to work for did a lot of their own boards. It's where I learned to make them. The setup they used when I first joined them was in a spare bathroom in the back of the building. They had the vertical tank with an aquarium heater and bubbler. In about a year of using this for small prototype boards every other week or so, every metal surface in the bathroom was severely rusted/etched. The bubbler was vaporizing some of the etchant into the air which then settled onto every surface in the bathroom.

Mark's idea worked the best for me. But instead of toothpicks I had a little piece of plastic I would put under one corner of the board. Use hot water to mix with the etchant. The black stuff would fall away from the board on it's own and for double sided boards I'd have to flip it over after 10 minutes or so to do the other side. But 20 minutes was tops for etching a board. Took me longer to make the art work and expose the board.

--john

[MR COFFEE]

John,
Are you talking 10 minutes *by the clock* max? Is that Ferric or Persulphate? How hot are you getting the etchant? That's PnP I assume?

Is that for *over* 1 oz foil, i.e., 2 or 3 oz foil like for power amp pcbs?

[twabelljr]

I,d like to get this one from Circuit Specialists, Inc. I think I'm ready to try making my own boards.
It's a vertical tank with agitator and heater for under $40.
http://shop.store.yahoo.com/webtronics/lowcosetsysw.html

[johngreene]

It was for photo resist. We used presensitized boards from GC Electronics, always double sided. We would print the artwork on a laser printer transparency, front side and back side. Cut the top side to be slightly bigger than the board size and line them up and tape them together to form a 'pocket' for the board to slide into. Expose each side in a UV exposure frame, develop, then touch-up with a sharpie. The etching was done in a glass cake pan and we used Ferric Chloride. I always ran the tap water hot and diluted the etchant a little less than 25% with the hot water. I then placed the board in flat with this piece of plastic under the edge to hold it up off the bottom. Give it 10 minutes and the bottom would be fully etched. Flip it over and repeat for the other side. Rinse, clean the resist off with a little acetone, polish with a brillo pad or steel wool, dip it in Kepro tin plating solution and it was time to drill. I liked using double sided because I always had the bottom be a ground plane so I could just drop a via (resistor lead) through the board for all the grounds rather than route them.

It was always 1 oz. copper. I did mostly low power circuits but I did a couple of AC30 clones and just made the traces really wide for the output section.

--john

[MartyB]

     I've posted this one a few times before, (because I like it really well)  but I'd like to add my two-cents FWIF.  My etching setup is very simple and easy.  I use ferric chloride from Fry's Electronics or Radio Shack.  I place up to three pcbs in a snack-size ziploc bag and add about 10cc of etchant per board (wearing gloves) then seal the bag after evacuating as much air as possible neatly.  I immerse it into a small tupperware tray (I've also used a child's plastic pencil/crayon box) about 1/2 - 2/3 full of the hottest water that will come out of my tap.  Still wearing the gloves I 'slosh' the baggie in the hot water tray by either waving it through the water or rocking the tray with two hands.  I do this outside, or in the garage.  If the water gets alittle cool before etching is complete, I drain some of the cold off and add more hot.  Etching rarely takes more than 20 minutes for me. Usually it's done in 10.  I keep the spent etchant in glass bottles with screw lids until I have a safe way of disposing them.  After the etching is done I drain off the etchant into a bottle and add some cold water promptly to the bag. This all-but ceases the etching and after a rinse or two with more tapwater I dry the board.  I don't reuse the baggies.  Tinning with Tinnit used to come next,  but now I pretty-much use them as they are, or tin with a thin smear of protecting solder added while populating.  If I had to reuse etchant or had large numbers of pcbs to etch, and couldn't afford the time to do them all by hand, it would make sense to use a specially-made immersion tank with an agitator.  But I can press'n'peel two or three pcbs, etch, drill, populate, wire, and test at least one of them in an afternoon off.  Its at least worked well for me the past  3+ years.

HTH,
MartyB

[Apehouse]

     I've posted this one a few times before, (because I like it really well)  but I'd like to add my two-cents FWIF.  My etching setup is very simple and easy.  I use ferric chloride from Fry's Electronics or Radio Shack.  I place up to three pcbs in a snack-size ziploc bag and add about 10cc of etchant per board (wearing gloves) then seal the bag after evacuating as much air as possible neatly.  I immerse it into a small tupperware tray (I've also used a child's plastic pencil/crayon box) about 1/2 - 2/3 full of the hottest water that will come out of my tap.  Still wearing the gloves I 'slosh' the baggie in the hot water tray by either waving it through the water or rocking the tray with two hands.  I do this outside, or in the garage.  If the water gets alittle cool before etching is complete, I drain some of the cold off and add more hot.  Etching rarely takes more than 20 minutes for me. Usually it's done in 10.  I keep the spent etchant in glass bottles with screw lids until I have a safe way of disposing them.  After the etching is done I drain off the etchant into a bottle and add some cold water promptly to the bag. This all-but ceases the etching and after a rinse or two with more tapwater I dry the board.  I don't reuse the baggies.  Tinning with Tinnit used to come next,  but now I pretty-much use them as they are, or tin with a thin smear of protecting solder added while populating.  If I had to reuse etchant or had large numbers of pcbs to etch, and couldn't afford the time to do them all by hand, it would make sense to use a specially-made immersion tank with an agitator.  But I can press'n'peel two or three pcbs, etch, drill, populate, wire, and test at least one of them in an afternoon off.  Its at least worked well for me the past  3+ years.

HTH,
MartyB

I have to also say this method has worked far better than any of the others i've tried.I've only done single boards in a bag myself but it works great.  I'm not even sure my boards take ten minutes. Usually when i look at the board thru the baggie, if its not exactly perfect i just rub the board(thru the bag) and the last little bit comes right off. Quick and definitely the cleanest method i've done so far (also seems to use a lot less etchant than the other methods i tried).
-greg

[Paul Perry (Frostwave)]

Johngreene, was the etchant that ate the bathroom ferric chloride? There doesn't seem to be as much fume problem with persulphate. Not that one should put ANY chemicals up ones nose, of course.

[johngreene]

Yes, it was Ferric Chloride. And it corroded 'everything' in that bathroom. The window latches, the drainpipes, the faucet handles, the coat hanger.....

--john

[Mark Hammer]

This is why I prefer methods that result in less physical disturbance of the etchant bath and risk of splashing or spattering.  Etchant is an absolute bugger to get out of things.  It is the HIV of clothing, and will leap from t-shirt to washing machine wall to white shirt in a blink.

[MR COFFEE]

Hi twabelljr,

I think I'd reconsider that setup in favor of Mark Hammer's approach or Marty B's. You read the whole thread, right?

Hi Paul,
A cover cap kept the fumes from going all over when I used a bubbler, but the cutout for the aquarium heater didn't keep the fumes in well-enough to keep it from getting eaten up. And it was pretty tight (less than 1/16th inch gap).

Hi John,
So I take it you don't know the exact temperature?    I guess if it's etched in 10 minutes you won't get pinholes - at least with the GC photo stuff. That was a long time ago for me.

Hi Marty,
Neat idea guy!! I guess I missed it before. Thanks for taking the time to share it again!!

Hi All,
Nobody's tried the jiggler idea then?

Although I guess I don't need my *big* (relatively speaking, that is)vertical tank for single boards, now, do I?  Oh well... 

This is such a good thread y'all.

[MR COFFEE]

<bump>
"Such a fine line I hate to see it go" - Rev. Gary Davis

[R.G.]

If you do tray etching, get yourself some plastic clips, like those they put on men's slacks in clothing stores, and trim them down so you can put one on each corner. Then put the PCB in the tray copper side down. Now the iron-oxide/chloride complexes fall to the bottom away from the copper. Gravity helps.

Before you start, fill a sink with hot water from the hot water heater (generally 120-130F) and stand the plastic bottle of FeCl in that for 20 minutes or so, rewarming the water periodically. I use a Pyrex baking tray that's never used for baking as an etching tray, and I soak that in hot water, too.

Also, put a heat lamp fixture above and pointing at the tray to keep it hot. Don't get it so hot that trails of yellowish vapor come off the FeCl - that stuff is intensely irritating to lungs.

Put a small string or cord under and across the tray in the middle so you can rock the tray and get end-to-end agitation without spilling.

Use a funnel to pour etchant back into the original bottle. A bottle will etch X square inches of PCB surface depending on the depth. Depth is usually 0.014" for one-ounce copper. If you don't especially try to get heavier copper, you'll get one ounce or half-ounce copper. Mark the bottle with how many square inches you etched this time. When you get to noticeable slowing even with heat, the etchant is approaching exhaustion. Add up the square inches, and now you know how many PCB square inches the next bottle will do.

Neutralizing with baking soda is good, but messy. It foams. A lot.

[Dean Hazelwanter]

Here's another option. Pour some etchant (ferric chloride) onto a sponge, then rub the PCB on the sponge. http://www.pulsar.gs/PCB/a_Pages/5_Support/4b_Tips_Tricks/Tips_Tricks.html I've never tried it myself, I just read about it last week.

I still prefer ammonium persulfate. It never takes me more than 5-6 minutes to etch.

[Mark Hammer]

Neutralizing with baking soda is good, but messy. It foams. A lot.

Yep.  Hell, buy yourself a case of beer, invite some friends over, and watch it foam.  A heap of fun.....as harmless but quirky chemical reactions go.  Actually, no. Make THEM buy the beer, before they come over to watch.   Just make sure you have a REALLY big container for when you turn etchant into foam.  It expands at least 10 times in volume.  If you don't have something big to catch the "foamover" in, you'll be scrubbing that crap out of things for days, and cursing with every hand motion.

You will want to keep loading up with baking soda until it is dry and crumbly.  If you have a thick spaghetti-sauce-like sludge, you're still not done.  Mixing it around with a plastic utensil will get the soda and etchant mixing and reacting.  Once it is deactivated, you can scrape up all that rusty-looking crumbly stuff, throw it in a garbage bag and set it out by the curb on garbage day.  The container can then be rinsed and refilled with fresh etchant.

But it really IS a hoot to watch that stuff just grow real fast, like outer space slime!