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Electronics => Beginners => Topic started by: dsharp02 on July 21, 2017, 02:23:54 pm

Title: Etching is very slow
Post by: dsharp02 on July 21, 2017, 02:23:54 pm
I purchased some 1oz single-sided copper clad FR1 boards to try my hand at creating a PCB.  I cleaned the boards copper side with a scotch-bright pad and soapy water, degreased them with IPA, and then spray-painted the boards with black spray-paint.  Once the paint was dry, I then used a laser engraver to remove the paint where I wanted the board to etch.

I placed the board into the ferric chloride, and agitated the container until I got tired of standing around shaking it (maybe 10 minutes).  I looked at the board and could see no progress, so I let it sit for an hour.  After an hour, I could just barely start to see spots where the copper had been removed and I could see light through the board.  So I left the board in for another hour.  I could see more clear spots, but it was still mostly opaque.  So I waited another hour, still not complete.  So I left the board in the ferric chloride overnight (7 or 8 hours), and in the morning it appeared to be mostly complete, but there are still a few spots that are still opaque.

12-13 hours seems excessively long to etch a board.  The temperature was roughly 80F/27C in my garage the whole time.  Do I need to warm the etchant?  Could the spray paint I'm using be contaminating the ferric chloride and causing it to not work properly?  Or is this normal?  Do I need to build a rig to agitate the container?

Thanks,
Dave
Title: Re: Etching is very slow
Post by: tautech on July 21, 2017, 02:41:15 pm
I don't use Ferric Chloride but for the etchants I use both heat and agitation speed the process some.
Some use fish tank heaters to keep the solution warm but with more active (faster) etchants the process is over before a preheated solution cools.
For agitation I use a fine air bubbler tube in the bottom of a vertical tank serving two purposes, agitation and removal of bubbles on the copper from the etching process. This bubble removal exposes the copper to faster and more even etching.
Title: Re: Etching is very slow
Post by: sleemanj on July 21, 2017, 03:00:23 pm
Ferric works best hot, and agitation is necessary for any etching method (rocking, bubbling, pumping, sponging, brushing whatever you like, just got to keep etchant moving over all the surface).  When I used Ferric I would boil a jug and fill a pan with the hot water to make a bath, then put the etching container with ferric into that water bath.

(I don't use Ferric any more)
Title: Re: Etching is very slow
Post by: matseng on July 21, 2017, 03:26:14 pm
I've read that people sometimes have problems with the ablated paint re-settling on the board again in a very thin and mostly invisible layer and this causes problems with the etch.

Wiping down the board with IPA after the laser ablation might help to remove the residue.
Title: Re: Etching is very slow
Post by: chickenHeadKnob on July 21, 2017, 04:45:23 pm
I've read that people sometimes have problems with the ablated paint re-settling on the board again in a very thin and mostly invisible layer and this causes problems with the etch.

Wiping down the board with IPA after the laser ablation might help to remove the residue.

My thought as well. To discern if the ferric chloride is weak clean a small test coupon of PCB with no paint or laser ablation steps and see if it etches promptly. Heat the FeCl and sponge the PCB gently every 10 seconds or so.
Title: Re: Etching is very slow
Post by: BurningTantalum on July 21, 2017, 08:45:46 pm
Many years ago I left a nice job where I had access to a spray etch tank. I then had to resort to etching in a plastic tray like the OP. I found that a solution of Ferric had to be as strong as could be mixed, and I used to etch the PCB upside down as I found that it was quicker and I had fewer 'spots' of unetched copper. The etchant had to be discarded when it became too contaminated- it started to take ages to etch.
Those were the days of 'Daler' pens... I should never have left the job!
BT
Title: Re: Etching is very slow
Post by: capt bullshot on July 21, 2017, 09:31:57 pm
The ferric chloride must be heated to at least 40°C to work
Title: Re: Etching is very slow
Post by: BrianHG on July 21, 2017, 09:50:50 pm
At around 70°C, with agitation, it should only take around 4-5 minutes depending on copper thickness, though, there will be some fumes.  At this speed, with some heavy duty rubber gloves, I used to just sit and wave the PCB up and down in the fluid maintaining a consistent flow, checking every minute to verify I wasn't overdoing it.

***Remember, copper flood fill all unused area on your PCB, including the borders and edges, whether it is connected to GND or not is not important.  This will save the life of you ferric chloride chemicals a 5-10 fold (seriously, many PCB just have thin traces and all that extra copper kills the ferric chloride.), this save you money on purchasing more ferric chloride and you also help the environment by not throwing out all of that wasted copper saturated ferric chloride.  I used to use a heavy duty rubber tub with lid for document storage I purchased at office depot and just leave the ferric chloride in there.  Under the tub, I had a weak plug-in radiator heater (I know this is dangerous) which I turned on 1 hour before doing the etch.  The ferric chloride would then be nice and warm and ready to etch multiple boards...
Title: Re: Etching is very slow
Post by: BurningTantalum on July 21, 2017, 10:19:46 pm
The machine that I used in the late 70s/early 80s definitely did not heat the ferric. It consisted of a large plastic welded cabinet with lift up door and two oscillating spray bars. It was large enough to take a PCB of at least 600 x 600 mm.
I never heated my hobby etchant either- I think that heating speeds up the etch time considerably but is not essential for hobby use. The ferric is dangerous enough without having to worry about heating it too!
BT
Title: Re: Etching is very slow
Post by: dsharp02 on July 21, 2017, 10:28:02 pm
Thanks everyone for the advice. I didn't realize that the ferric chloride needed to be heated.  The instructions on the bottle don't mention this.

I will probably place the container on one of my 3d printers, set the heat bed to 45-50C and then "print" a g-code file that moves the bed back and forth to agitate.

Regarding the flood fill.  I did do a copper pour attached to GND so I'm really only removing a tiny bit of the copper.  It also removed the need to route GND connections, so that was nice.





Title: Re: Etching is very slow
Post by: chickenHeadKnob on July 21, 2017, 10:54:33 pm
Agitation helps but what really works is to take a small  disposable foam brush you can buy cheap at any hardware or paint store and daub the surface. That helps remove the converted copper still clinging to the surface and exposes the fresh layer underneath.
Title: Re: Etching is very slow
Post by: uwezi on July 21, 2017, 11:00:57 pm
Ferric chloride does not need to be heated!

It should normally etch 1oz copper layers in less than half an hour, but it is a messy business. Sodium persulfate on the other hand needs to be heated.

Have you tried to etch a tiny piece of blank pcb which you did not expose to the paint/ablation process? The only reason that I can see for your problem is an incomplete ablation.
Title: Re: Etching is very slow
Post by: dsharp02 on July 21, 2017, 11:16:41 pm
I actually ran the laser over the copper twice to remove any paint that had resettled (sadly my Legend 24TT doesn't do bottom up raster engraving), and then I used 90% IPA and gently wiped down the board (was afraid of damaging the paint, so I didn't scrub too hard)>

Title: Re: Etching is very slow
Post by: IanB on July 21, 2017, 11:27:41 pm
Thanks everyone for the advice. I didn't realize that the ferric chloride needed to be heated.  The instructions on the bottle don't mention this.

No, it doesn't need to be heated.

Ferric chloride should etch a board in minutes at room temperature, but you do have to agitate it. Where etching is happening you should see darker colored liquid floating away from the etched surface. If etching is too slow, make sure the ferric chloride is the proper strength. Be sure to read the instructions if you are buying the dry crystals and making it up yourself.
Title: Re: Etching is very slow
Post by: alanb on July 22, 2017, 12:24:10 am
I would try etching a small sample of cleaned, de-greased board before you have added the paint. It should then be possible to see if the issue is with the etchant or the rest of the process.
Title: Re: Etching is very slow
Post by: rdl on July 22, 2017, 12:41:24 am
Just a few words of caution. I would not allow ferric chloride anywhere near valuable equipment such as 3D printers or anything with exposed metal you value. Be very careful when agitation is used, particularly airstone/bubbler types. The small aerosol particles formed can travel long distances and will corrode everything in sight.
Title: Re: Etching is very slow
Post by: BrianHG on July 22, 2017, 02:26:12 am
@rdl +1, I corroded the outside of my lead plumbing in my room a few decades ago...
Title: Re: Etching is very slow
Post by: IanB on July 22, 2017, 03:24:00 am
By agitation I only mean gentle stirring with a plastic implement, or rolling the liquid around the etching tray. There is no need for anything vigorous like shaking or bubbling.
Title: Re: Etching is very slow
Post by: rdl on July 22, 2017, 04:33:38 am
As I said, just words of caution. The stuff is damned insidious. In my personal experience the finish on one bathtub faucet was ruined and another kitchen sink fixture nearly so, using nothing but gentle rocking of the tray for agitation. The damage was not immediately obvious and I was surprised it happened because I thought I was being careful. I stopped using it indoors after that, and eventually decided to quit using it completely.
Title: Re: Etching is very slow
Post by: jpanhalt on July 22, 2017, 04:38:49 am
Re. etch speed:   Etching is an oxidative reaction in which the metallic copper is oxidized.  Thus in spray etching, the ferric chloride can be considered saturated with air/oxygen and works faster at lower temperature than bath etching in which not only may the etchant not be saturated with air, but there is a laminar layer on the copper surface.   Gentle rocking helps, but so does heat.   As a rule of thumb, reaction rate doubles for every increase in temperature of 10°C.   I etch in a bath at 40° to 60°C.   It generally take about 15 minutes.   There is an "edge" effect, which means the edges will etch faster than the center of the board, and fine details (remember viscosity and laminar layer) will etch slower.   On occasion, I will use a soft sponge with the etchant to carefully rub over those areas.

Re. your resist:  What wavelength is your laser?  Presumably near IR?  I would consider a dye that absorbed that wavelength in preference to a pigment.   I would also try to find materials that ablated without leaving an ash.  Some "paints" will be worse than others.  Acrylics and cellulose-like lacquers (e.g, clear model dope) are probably better than enamels.  I would not use water-based latex paints.

After ablating, the etchant should wet the areas to be etched and tend to bead up on the painted areas.   If you don't see the wetting, you probably have some residual resist.   The initial etching reaction is very fast.   I use a photoresist.  Sometimes, after development, I may doubt whether more development is necessary.   I very quick dip in or drop of ferric chloride will turn clean copper a salmon color.  If I don't see wetting or the color, I develop a little longer.  As you get your system standardized, that will rarely be an issue, but when starting out, it is a good test and a lot quicker than waiting for hours to find almost no etching.

John
Title: Re: Etching is very slow
Post by: Brumby on July 22, 2017, 11:43:45 am
Thanks everyone for the advice. I didn't realize that the ferric chloride needed to be heated.  The instructions on the bottle don't mention this.

No, it doesn't need to be heated.

Ferric chloride should etch a board in minutes at room temperature, but you do have to agitate it. Where etching is happening you should see darker colored liquid floating away from the etched surface. If etching is too slow, make sure the ferric chloride is the proper strength. Be sure to read the instructions if you are buying the dry crystals and making it up yourself.

^^^ This has been my experience.

I would suggest you don't need things like bubble tanks and heating for ferric chloride.  Those are necessary for ammonium persulphate etching, but ferric chloride is nasty effective enough without them.

If you have fresh solution made up at the right strength, then at the temperature you are talking about, with some simple agitation - the only impediment I can think of is surface contamination.  12-13 hours should be long enough to etch through a copper pipe.

To test this, I would suggest you take a small piece of PCB and simply do the scrub and clean.  No paint, masking or laser stuff - just a piece of plain board.  Then just drop it into your solution and, with a little bit of agitation, see how long it takes to etch.

If that takes anywhere near 12-13 hours, then your process would seem exonerated - but your ferric chloride would be highly suspect.
Title: Re: Etching is very slow
Post by: dsharp02 on July 23, 2017, 01:13:27 pm
Quote
Re. etch speed:   Etching is an oxidative reaction in which the metallic copper is oxidized.  Thus in spray etching, the ferric chloride can be considered saturated with air/oxygen and works faster at lower temperature than bath etching in which not only may the etchant not be saturated with air, but there is a laminar layer on the copper surface.   Gentle rocking helps, but so does heat.   As a rule of thumb, reaction rate doubles for every increase in temperature of 10°C.   I etch in a bath at 40° to 60°C.   It generally take about 15 minutes.   There is an "edge" effect, which means the edges will etch faster than the center of the board, and fine details (remember viscosity and laminar layer) will etch slower.   On occasion, I will use a soft sponge with the etchant to carefully rub over those areas.

I got a foam brush instead of a sponge, and that seems to help a bit.  The etchant is 42 baume, whatever that means. I finished one board, but I there were some broken tracks (from undercutting during the long bath overnight?).

Quote
Re. your resist:  What wavelength is your laser?  Presumably near IR?  I would consider a dye that absorbed that wavelength in preference to a pigment.   I would also try to find materials that ablated without leaving an ash.  Some "paints" will be worse than others.  Acrylics and cellulose-like lacquers (e.g, clear model dope) are probably better than enamels.  I would not use water-based latex paints.

I think it's 10600 nm.  It's a CO2 laser.

Quote
After ablating, the etchant should wet the areas to be etched and tend to bead up on the painted areas.   If you don't see the wetting, you probably have some residual resist.   The initial etching reaction is very fast.   I use a photoresist.  Sometimes, after development, I may doubt whether more development is necessary.   I very quick dip in or drop of ferric chloride will turn clean copper a salmon color.  If I don't see wetting or the color, I develop a little longer.  As you get your system standardized, that will rarely be an issue, but when starting out, it is a good test and a lot quicker than waiting for hours to find almost no etching.

Thanks for your help.  I may try the photoresist method at some point.

Dave
Title: Re: Etching is very slow
Post by: tronde on July 23, 2017, 02:09:58 pm
Have you got ferric (III) chloride (brownish-yellowish) or ferric (II) chloride (greenish)?

Ferric (III) chloride does not need much heat or agitation. I remember from very long time ago I got ferric (II) chloride. Was extremely slow. Don't remember if it ever managed to finish the etching.
Title: Re: Etching is very slow
Post by: IanB on July 23, 2017, 02:13:05 pm
The etchant is 42 baume, whatever that means.

I think it means you bought the product ready mixed as a solution in a bottle. Is that correct? Also, we presume the product was sold specifically for etching copper?
Title: Re: Etching is very slow
Post by: orin on July 23, 2017, 02:25:28 pm
Many years ago I left a nice job where I had access to a spray etch tank. I then had to resort to etching in a plastic tray like the OP. I found that a solution of Ferric had to be as strong as could be mixed, and I used to etch the PCB upside down as I found that it was quicker and I had fewer 'spots' of unetched copper. The etchant had to be discarded when it became too contaminated- it started to take ages to etch.
Those were the days of 'Daler' pens... I should never have left the job!
BT


I use the pre-mixed Ferric Chloride solution from MG Chemicals in a photographic tray, float the tray in a sink of hot water and rock it back and forth.  Takes 15 to 20 minutes.  When it's done, I pour as much as possible of the FeCl back in the bottle.

(To prepare the boards, I use the MG Chemicals positive resist boards, laser or inkjet printer on transparencies and a single UV tube about 6 inches over the board for their recommended exposure time, then their developer diluted as recommended.)

If the etching (or developing come to that) gets slow, it's time to replace the solutions.

So, if etching is taking longer than 30 minutes at room temperature, there is something really wrong...
Title: Re: Etching is very slow
Post by: IanB on July 23, 2017, 05:00:56 pm
It really should not be necessary to do anything special to make ferric chloride work. Here's an illustration of the process from Big Clive. In his words, the etching takes "several minutes":

https://youtu.be/W_oDBp_wgJQ?t=10m
Title: Re: Etching is very slow
Post by: ion on July 24, 2017, 02:14:24 am
Warm Ferric Chloride does etch faster, but don't heat it much past 50°C - as you approach 60°C it will start releasing HCl fumes.

Around 50°C and occasionaly rocking the etching bath, most of my boards are etched in about 10 minutes.  While room temperature Ferric Chloride will work, if you have fine traces a faster etch will probably give a better result.
Title: Re: Etching is very slow
Post by: dsharp02 on July 24, 2017, 02:42:52 am
Quote
I use the pre-mixed Ferric Chloride solution from MG Chemicals in a photographic tray, float the tray in a sink of hot water and rock it back and forth.  Takes 15 to 20 minutes.  When it's done, I pour as much as possible of the FeCl back in the bottle.
I'm also using MG Chemicals Ferric Chloride.  I'm afraid of putting the used etchant back into the bottle.  I worry that bits of the paint I used as resist will contaminate the solution.  For now I'm just keeping the used etchant in a separate container.

Quote
(To prepare the boards, I use the MG Chemicals positive resist boards, laser or inkjet printer on transparencies and a single UV tube about 6 inches over the board for their recommended exposure time, then their developer diluted as recommended.)

If the etching (or developing come to that) gets slow, it's time to replace the solutions.

So, if etching is taking longer than 30 minutes at room temperature, there is something really wrong...

Hrm... I really don't know what's causing the issue.  It take more than 20 minutes just to get the etch started to the point where there are areas starting to show through.

Dave

Edit:  I've added a picture of my board.  The upper middle seems to be mostly clear, but the long traces on the left side and the traces for the H-bridge in the bottom center are not completely etched.
Title: Re: Etching is very slow
Post by: KL27x on July 24, 2017, 10:53:02 am
Quote
I'm also using MG Chemicals Ferric Chloride.  I'm afraid of putting the used etchant back into the bottle.  I worry that bits of the paint I used as resist will contaminate the solution.  For now I'm just keeping the used etchant in a separate container.
FYI, I wouldn't worry about that, at all. I read somewhere that aside from contamination with solvents, there's not much you can do to screw up ferric chloride etchant. I would add soap to the list, if you use a bubbler. And w/e is in Kemtech 15% muriatic acid.

Flecks of paint, leaves, twigs, dust, don't really matter. I keep a lid on my tank, but it is outdoors. I get some occasional debris. I pick or strain it out when the moon is blue.

I suspect OP had issues with paint re-adhering to the board, as others have pointed out. But if you have tried clean copper and it's still slow, a couple thing I'm gonna do. Check the thickness of your copper. If you're using 2+ oz pour, there's nothing necessarily wrong. The etching will be slow and uneven.

If you're using 1oz or lower, and/or you feel like the ferric is just too slow, add some hydrochloric acid. The ferric needs a little bit of excess HCl. If it doesn't have any (and pure lab grade ferric won't have any), it will etch fine for the first tiny bit, but it will quickly slow down. If you are using only a little part of your etchant, and keeping the rest in the bottle, you are setting yourself up for that problem. Some peeps seem to prefer this method, seeing it as less wasteful. I've seen where some people are putting a little Ferric on a sponge and wiping the board till its done. Then tossing it. And thinking they found the best way to use it without "wasting" any. This is obviously retarded AFAIC. This is just a dude who happened to use a half oz board and thought he discovered magic.

If you don't want to waste it, just use the whole 1L* bottle of it. And pour it back in a bottle or next time. Trying to use a little of it at a time and then disposing of it is more wasteful, in the long run.

*Or w/e volume will reasonably fill your container without fear of spilling. You can try the whole, put the pcb in a bag and a few mL or ferric, but this is not creating less mess or using less ferric. This is just dumb. 
Title: Re: Etching is very slow
Post by: M4trix on July 24, 2017, 11:20:42 am
@dsharp02,

I don't wanna sound like a smartass but do yourself a favor... ditch the ferric-chloride etchant and use 'modern' etchants like sodium persulfate or HCL+ hydrogen peroxide. The second one doesn't even need to be heated. The downsides of ferric-chloride are already mentioned in this thread so I'll skip that part. If you want to use HCL+HP then this is my recipe which always work:

For 1L etchant -->

700ml - destilled water
250ml -  35% HCL
50ml - 30% hydrogen peroxide

The only downside of this etchant is a nasty odor like vomit.  ;D         
Title: Re: Etching is very slow
Post by: KL27x on July 24, 2017, 11:31:20 am
If you have 30% peroxide, this is a good etchant. But I wouldn't mix up a liter at a time, unless I were going to do a big stack of boards. With HCl and peroxide, you really don't want to mix up more than you need and try to save it for next time. Use just enough to do your boards, so it saturates with cupric chloride. And you will have to use less of your 30% peroxide to restore it for continued use.

The peroxide starts to spontaneously bubble off into the atmosphere as soon as you mix it with HCl. Next time you use it, you add more peroxide, and it works, again. I suppose it is practical if you have easy access to cheap 30% peroxide.

If you mix up just enough to get by, you will increase the copper concentration in the solution. (It will get greener). And next time you add peroxide, some of it will instantly be transferred to the copper I in the solution, turning it to copper II. And this etches copper. And it doesn't spontaneously release that O2 to the air.
Title: Re: Etching is very slow
Post by: M4trix on July 24, 2017, 12:27:51 pm
if you have easy access to cheap 30% peroxide.

Unfortunately, here in Croatia you can find 30% hydrogen peroxide only on the black market or if you have a friend who works in a hair salon. The drugstores sell only 3%. Well, there were times when you could buy 30% peroxide in drugstores but the lady behind the desk asks for your ID and asks for what purpose you're buying peroxide. Sometimes they give it without questions but that's rare.  :palm:   
Title: Re: Etching is very slow
Post by: IanB on July 24, 2017, 12:47:56 pm
Unfortunately, here in Croatia you can find 30% hydrogen peroxide only on the black market or if you have a friend who works in a hair salon. The drugstores sell only 3%. Well, there were times when you could buy 30% peroxide in drugstores but the lady behind the desk asks for your ID and asks for what purpose you're buying peroxide. Sometimes they give it without questions but that's rare.  :palm:

Ah, but that's not really a problem. 50 ml of 30% peroxide contains 15 ml of peroxide (approximately). However, 500 ml of 3% peroxide also contains 15 ml of peroxide. So you just adjust the proportions in the above recipe:

250 ml - distilled water
250 ml - 35% hydrochloric acid
500 ml - 3% hydrogen peroxide solution

Next problem: is 35% hydrochloric acid available where you are? Here in the USA hardware stores sell it, but in Europe, I'm not so sure. Probably the best bet is pool supply stores, since HCl can be used for pH control in pools.

To me, this all starts to sound a bit complicated given that ferric chloride etching solution is so readily available.

Title: Re: Etching is very slow
Post by: sleemanj on July 24, 2017, 01:00:54 pm

Next problem: is 35% hydrochloric acid available where you are?


Way too strong if you ask me, that will be fuming.

I use 15%, which should be pretty easy to come by in most places, hardware stores, pool supplies, paint supplies, concrete driveway people...  Peroxide is typically harder to get in quantity.

By the same token as H2O2, exchange water for less concentrated HCl in the first place, all the water is doing is diluting.

You don't need to be precise about this stuff.  Take HCl, dilute until not fuming if it is, put PCB in HCl, add peroxide a little dribble at a time and watch the reaction.

Yeah I know, one should really "do like you ought'a, add acid to water", but in this case it's not practical, just don't go dumping a pile of H2O2 in at once, especially if it's 30% (excitement for sure!), a little dribble, mix, observe, repeat until the reaction is working at a rate you are comfortable with.  It shouldn't be giving off clouds of fumes and foaming up like an angry sea covering your bench in corrosive juices, it should just sit there quietly with some little bubbles forming on the surface of the PCB.

As above, save the etchant, use it again next time, following the same add-H2O2 and observe procedure, you probably won't need much.

Title: Re: Etching is very slow
Post by: M4trix on July 24, 2017, 01:21:31 pm
Well, that's why I stashed on time some 40-50 liters of 35% HCL and 6 liters of 30% peroxide. Just in case if bad time comes.  ;)
Title: Re: Etching is very slow
Post by: orin on July 24, 2017, 01:45:53 pm
Quote
I'm also using MG Chemicals Ferric Chloride.  I'm afraid of putting the used etchant back into the bottle.  I worry that bits of the paint I used as resist will contaminate the solution.  For now I'm just keeping the used etchant in a separate container.
FYI, I wouldn't worry about that, at all. I read somewhere that aside from contamination with solvents, there's not much you can do to screw up ferric chloride etchant. I would add soap to the list, if you use a bubbler. And w/e is in Kemtech 15% muriatic acid.

Soap, bubbler?  Is this from experience?

Quote
If you don't want to waste it, just use the whole 1L* bottle of it. And pour it back in a bottle or next time. Trying to use a little of it at a time and then disposing of it is more wasteful, in the long run.

*Or w/e volume will reasonably fill your container without fear of spilling. You can try the whole, put the pcb in a bag and a few mL or ferric, but this is not creating less mess or using less ferric. This is just dumb.


There's a bit of a tradeoff for me - the more FeCl in the photographic tray, the less floating the tray in hot water warms it up... but with less FeCl there, it might weaken faster...  For the size of boards I do, it's a non-issue - and flood fill ground planes mean there's not much Cu to etch anyway!

Orin.
Title: Re: Etching is very slow
Post by: lowimpedance on July 24, 2017, 01:46:57 pm
Well, that's why I stashed on time some 40-50 liters of 35% HCL and 6 liters of 30% peroxide. Just in case if bad time comes.  ;)
Watch the shelf life of your peroxide !, it will slowly decompose when sealed, much faster after being opened.
Title: Re: Etching is very slow
Post by: KL27x on July 24, 2017, 02:37:43 pm
Quote
Soap, bubbler?  Is this from experience?
I scrub my boards with a drop of dishsoap and coarse stainless steel wool. And I use a very thin vertical tank (slightly less than 3/4" thick, about half a liter of cupric chloride) hooked up to an air compressor to give a lot of aeration. Depending on the airflow/pressure I give it, I can get 2 or 3" of head WITHOUT neglecting to carefully rinse all the dishsoap. And you only make that mistake once.

If I'm doing a tall board and there's not quite enough etchant, I can just turn up the air. There's a good inch or so of height added just from the density of bubbles swirling in it, not even including the foamy head (which appears to etch at least as fast as the liquid fraction).

This vertical tank has better throughput than a large tank I had once made using an igloo cooler running off fish tank bubblers and holding half a gallon of etchant.


Quote
Ah, but that's not really a problem. 50 ml of 30% peroxide contains 15 ml of peroxide (approximately). However, 500 ml of 3% peroxide also contains 15 ml of peroxide. So you just adjust the proportions in the above recipe:

250 ml - distilled water
250 ml - 35% hydrochloric acid
500 ml - 3% hydrogen peroxide solution
But if you have only 3% peroxide, you really want to take care to not mix up too much of this stuff. If you mix up a liter to etch a single 2"x3" board, you might as well throw it out when you're done. Next time you use it, a month or two later, it will just be diluted HCl. You won't be able to revive it, easily. The more peroxide you add, the more you dilute what you mixed up in the first place. FWIW, BP of peroxide is around 150C. So it is possible to boil 3% peroxide to make a higher concentration. But that would be a wee bit of extra work. This was the point I was trying to make. W/e you mix up, if you etch as much copper as you can into it, it will work better (albeit much slower) the next time around. Because it will have a higher concentration of cupric chloride in it. If you build a bubbler tank, you won't ever use peroxide and HCl, again. It's a pain due to the concentration of corrosive fumes, and it is a very innaccurate etchant, relatively speaking.

Quote
Watch the shelf life of your peroxide !, it will slowly decompose when sealed, much faster after being opened.
Even the lower % stuff has buffers added to keep it stable. The higher purity stuff, yes, take extreme care. Any foreign debris that gets in there will catalyze the decomposition. Think Mentos and Diet Coke.
Title: Re: Etching is very slow
Post by: dsharp02 on July 24, 2017, 10:13:11 pm
I think I'm going to use my vacuum sealer to create a sealed bag like in Clive's video.  A couple of dowels, and 3D-printed clips and I think I'll have the messiness bit sorted.

I'm going to try etching piece of a bare pcb and see if that works any faster.

I tried to use sharpie ink as a resist, but the laser does not seem to ablate it very well.

Title: Re: Etching is very slow
Post by: oldway on July 25, 2017, 06:13:56 am
@dsharp02,

I don't wanna sound like a smartass but do yourself a favor... ditch the ferric-chloride etchant and use 'modern' etchants like sodium persulphate or HCL+ hydrogen peroxide. The second one doesn't even need to be heated. The downsides of ferric-chloride are already mentioned in this thread so I'll skip that part. If you want to use HCL+HP then this is my recipe which always work:

For 1L etchant -->

700ml - destilled water
250ml -  35% HCL
50ml - 30% hydrogen peroxide

The only downside of this etchant is a nasty odor like vomit.  ;D       
The solution can be used again dozens of times, just add a little peroxide each time.
I noticed that the rapidity of the reaction depends mainly on the amount of peroxide added and little on the acid concentration.
But whenever peroxide is added, the solution is further diluted.
It is therefore advantageous:
-to use concentrated peroxide
- not to dilute too much the solution at the first use.
Title: Re: Etching is very slow
Post by: M4trix on July 27, 2017, 08:48:07 am
just don't go dumping a pile of H2O2 in at once, especially if it's 30% (excitement for sure!)

http://www.youtube.com/watch?v=OTGZcY7WyYI (http://www.youtube.com/watch?v=OTGZcY7WyYI)

 :palm:  ;D
Title: Re: Etching is very slow
Post by: cdev on July 27, 2017, 10:29:32 am
Try:

Toner transfer

Vinegar
Hydrogen peroxide
Salt. Add more salt to get more etching.

nail polish remover for cleaning off the board at the end.

Then treat it as you would with any other just etched PCB
Title: Re: Etching is very slow
Post by: IanB on July 27, 2017, 01:06:00 pm
I still haven't found out what is being given off in that video. It obviously isn't Chlorine gas or we'd have heard about it. I'm thinking it must be water vapor as steam. I think if it was me I'd be using less concentrated peroxide just to slow things down a few notches.

It's oxygen, from the peroxide. Basically, it is wasting the peroxide solution since the oxygen is bubbling off instead of helping to dissolve the copper. It suggests to me that a more dilute peroxide solution would be satisfactory.

Note: a common high school chemistry experiment is to add a drop of blood to some hydrogen peroxide. The blood catalyzes the decomposition of the peroxide solution and causes a similar reaction.
Title: Re: Etching is very slow
Post by: uwezi on July 28, 2017, 08:11:04 am
Try:

Vinegar
Hydrogen peroxide
Salt. Add more salt to get more etching.


Don't think that you are environmentally friendly or safer just because you use vinegar instead of "chemicals" such as hydrochloric acid, ferric chloride or sodium persulfate. Especially the copper salts formed in any of these etching methods are environmental hazards and need to be taken care off properly.

Also in Europe - at least Sweden and Germany - it is much easier to buy ferric chloride (if you want to stain yourself, your clothes, everything) or sodium persulfate than hydrogen peroxide.
Title: Re: Etching is very slow
Post by: cdev on July 28, 2017, 01:47:40 pm
I have a plastic bottle I pour the liquid into when I am done and then it just evaporates leaving some solids on the bottom. All the PCBs Ive ever done's (maybe a few dozen ;) etchant's remnants are in the bottom of this bottle and its still not that deep.. Unless you did it commercially, even if the boards you made were much much larger than the tiny ones I usually make I bet a single plastic bottle would probably hold a whole lifetime's worth of leavings.


Quote from: uwezi on Today at 16:11:04 (http://www.eevblog.com/forum/index.php?topic=92190.msg1266755#msg1266755)>Quote from: cdev on Yesterday at 18:29:32 (http://www.eevblog.com/forum/index.php?topic=92190.msg1265971#msg1265971)
Try:

Vinegar
Hydrogen peroxide
Salt. Add more salt to get more etching.


Don't think that you are environmentally friendly or safer just because you use vinegar instead of "chemicals" such as hydrochloric acid, ferric chloride or sodium persulfate. Especially the copper salts formed in any of these etching methods are environmental hazards and need to be taken care off properly.

Also in Europe - at least Sweden and Germany - it is much easier to buy ferric chloride (if you want to stain yourself, your clothes, everything) or sodium persulfate than hydrogen peroxide.