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Please excuse my ignorance. Can someone tell me what a framed solder mask stencil is?? My suspicion is that it is a stencil that fits into some kind of contact frame like screen printing but I have not found an explanation that makes sense to me.? If I am correct then where does one find these contact frames and what are they called?

I asked because I was looking to order some smt boards from one of the Chinese board houses and for $7 I can get a frameless stencil but for $9.20 or so I can get one for a frame.? To me it would be ideal to have a frame since registration would be easier.

Also I have not figured out why all the board houses send a 380mm x 280mm even if the board it is for is small like 32mm x 22mm and that confuses me. Why isn't the stencil a few mm larger than the pc board but not gargantuan like it is?

Again what are the solder mask stencil frames called and where can I get one?? What is a stencil for frames compared to frameless?? Why are the board house stencils so huge compared to the actual size of the pc board the stencil is for?

Thank you.

Jim Pruitt

Hi, I have built a manual pick and place system that gets around my rather unsteady hands (the indignities of age) and have a USB microscope
mounted on it to provide a means of aiming, but I need some sort of cross-hair to help.

I have found PixMicro which works well but only under Windows.

Ideally, I want to use a Raspberry Pi 4 with (ideally) Ubuntu to display the camera output.

Can anyone suggest a Linux webcam viewer that has a cross-hair facility ??

Regards,
Dave

At 5/11/2022 08:52 UTC Morris Odell wrote:

l finally got to etch a board in the more concentrated solution and it works very well. Etching was noticeably faster. the solution started off a lovely emerald green and did get darker as the copper dissolved and the amount of Cu(1) in the solution increased. I wasn't using a very large volume of solution so I had to add some more to keep it going but if finished up very well. I've got it all back in the bottle now with the bubbler going and I expect it to all return to the nice green color.

Excellent! I'm guessing one of two things cause the need to add more solution... either the solution is a bit weak in copper, which would be cured by adding some more copper wire and bubbling... which may also need a bit more HCl. **OR** maybe the volume of the etching tank is a bit small. Either way it works well without any hint that you didn't feel good about it and that's what counts. Good to hear.

When it comes to a possible need for a bit more HCl, maybe test the acidity of the spent etchant in the tank by adding a few drops of it to a bit of dry baking soda (sodium bicarbonate). If it doesn't bubble you need a bit more HCl in the solution before etching next time.

Either way it's working and adding a bit more solution part way thru wasn't a problem.

My interpretation of how this all works is as follows:

The etching process coverts both the green Cu(2) and the solid elemental Cu into black Cu(1) which is then oxidised later back to Cu(2) but at a slower rate than the etch. This means that it's important to start off with enough Cu(2) in the solution to deal with all the copper you need to remove. The solution becomes progressively darker as the etch progresses and this might cause the etch to slow down as the amount of Cu(2) falls unless there is an excess present to begin with. I imagine that commercial operations use high volumes of solution and circulate it between the etch tank and a bubbling tank. Converting the black Cu(1) to green Cu(2) uses oxygen either from the air or from H2O2 and that will gradually make the solution more alkaline so small amounts of HCl need to added to counteract that and provide more Cl- ions to match the Cu dissolved into the solution from the PCB.

Exactly!

I'm retired now but I used to work at a place where there was a chemical lab that employed some every highly educated people with doctorates and years of experience. However the lab was there for other reasons and dealt with entirely different processes and functions than this. Nobody could help with an understanding of CuCl2 etching or even swimming pool chemistry until I found discussions here!

Morris

Ain't the Internet great?!!! Just take some of it with a grain of salt, aka NaCl. ;-)

JimH

l finally got to etch a board in the more concentrated solution and it works very well. Etching was noticeably faster. the solution started off a lovely emerald green and did get darker as the copper dissolved and the amount of Cu(1) in the solution increased. I wasn't using a very large volume of solution so I had to add some more to keep it going but if finished up very well. I've got it all back in the bottle now with the bubbler going and I expect it to all return to the nice green color.

My interpretation of how this all works is as follows:


The etching process coverts both the green Cu(2) and the solid elemental Cu into black Cu(1) which is then oxidised later back to Cu(2) but at a slower rate than the etch. This means that it's important to start off with enough Cu(2) in the solution to deal with all the copper you need to remove. The solution becomes progressively darker as the etch progresses and this might cause the etch to slow down as the amount of Cu(2) falls unless there is an excess present to begin with. I imagine that commercial operations use high volumes of solution and circulate it between the etch tank and a bubbling tank. Converting the black Cu(1) to green Cu(2) uses oxygen either from the air or from H2O2 and that will gradually make the solution more alkaline so small amounts of HCl need to added to counteract that and provide more Cl- ions to match the Cu dissolved into the solution from the PCB.

I'm retired now but? I used to work at a place where there was a chemical lab that employed some every highly educated people with doctorates and years of experience. However the lab was there for other reasons and dealt with entirely different processes and functions? than this. Nobody could help with an understanding of CuCl2 etching or even swimming pool chemistry until I found discussions here!

Morris

OVERVIEW:

This is a simple procedure for preparing 1 liter of cupric chloride etching solution. The tradeoff for the simplicity is a bit of patience as it may take a while to complete the preparation. The value of this patience is that the resulting solution won't be overburdened with hydrochloric acid and thus won't be as smelly and as corrosive to materials around it as some more quickly prepared solutions may tend to be. It also won't have any residual hydrogen peroxide which will result in a very slightly lower tendency to undercut your PCB traces. That last effect is really quite small, but why not? Also, since we won't be depending on the presence of H2O2 once the etching solution is prepared, we don't have to worry about over diluting our solution by trying to regenerate it with the weak 3% H2O2 commonly available in drugstores. We'll be regenerating with an air bubbler, which can serve double duty to agitate the solution when etching.


MATERIALS:

One large (at least 2 liter/0.5 gallon) glass container with a plastic lid. A 1/2 gallon "iced tea" jar with a plastic lid (plastic lid liner or no lid liner) and a small pop open spout would be ideal because you can open the spout to insert a fritted glass bubbler for use in rejuvenating the solution after use. If you need more than 1 liter (1 qt) of solution, consider using a larger container and increase the amounts of materials below accordingly. I suggest the container be only about half full when done. Only partially full plus a small opening in the lid keeps any spray resulting from regeneration by air bubbling inside the glass container.

One small aquarium pump. The cheap vibrating kind is fine.

One fritted glass bubbler, preferably long enough that it can reach the bottom of the large glass container with at least an inch or more of glass tube sticking out - preferably. If you can't find one that long, then your plastic tubing will extend into the container. I don't like that, but that's just me.

Plastic tubing to connect the pump to the fritted glass bubbler. I like enough tubing that I can place my pump higher then the top of my jar. Not likely the solution will syphon out if the pump is lower, but it's 100% impossible if it's higher.

200 grams (7 oz) of copper wire, copper pipe or other pure copper. I used solid copper wire, but stranded copper will dissolve quite a bit faster. Pennies (even the old type) and some misc plumbing or electrical hardware aren't pure copper and are unsuitable. Tarnish (discoloration) is OK, but it must be clean otherwise. 200 gms of copper is about 14 feet of #10 copper wire... 22 feet of #12... 36 feet of #14... 56 feet of #16.

32% - 37% Hydrochloric Acid - also called Muriatic Acid - free of detergent or other additives. READ THE LABEL! This really needs to be 32% - 37% HCl and free of additives, so READ THE LABEL! You can get concrete driveway cleaner that meets these requirements at Home Depot, Lowes and assorted hardware stores. Look until you find 32% - 37%, Hydrochloric Acid or Muriatic Acid free of additives. You'll be sorry if you don't. It should be easy to find in the USA... might require some looking elsewhere.

3% Hydrogen Peroxide. This is readily available at Walmart, a grocery store or the drugstore. You only need a few ounces so forget about stronger solutions that are harder to find and more expensive. If you think stronger is better and manage to hunt down 35% H2O2, please don't bother to tell me... especially if you hurt yourself... perhaps seriously.


SOLUTION PREPARATION:

Pour 1 liter (4-1/4 cups) of water into your container and clearly mark the level on the outside of the container. Pour out the water. This is the level you will want to maintain later after etching and rejuvenating.

Add the copper to the empty glass container.

Carefully pour 0.6 liters (2.5 cups) of hydrochloric acid into the glass container.

Add 0.1 liter (0.5 cup) of hydrogen peroxide. This should be all the hydrogen peroxide you'll ever need.

The copper wire will begin dissolving as evidenced by a green color forming in the solution and bubbles being generated on the surface of the copper wire.

Place the lid on the container, open the spout and insert the fritted glass bubbler connected to the aquarium pump and begin bubbling to mix the solution.

Here's where patience comes in... continue bubbling until the copper wire is completely dissolved. If the solution becomes a brownish/muddy color, add 1 oz of hydrochloric acid and continue bubbling until the wire is completely dissolved AND the solution is a deep emerald green. You really shouldn't need extra HCl, but if it's weaker than the label says you might. If it's a LOT weaker because you bought the wrong stuff... well... you were warned. When the copper is all dissolved, the color will be fairly dark, so hold the solution up to a bright light, or pour a bit into a smaller container, to gauge the color. If the acid you're using is on the slightly weaker side you may need to repeat the addition of a bit (less than an ounce this time) of hydrochloric acid if several days of bubbling doesn't result in a deep emerald green color with no trace of a brownish or muddy color.

Dilute to 1 liter with water and that's it.

Use it as you'd use any solution to etch PCBs and pour the used solution back into the main glass container when done. Inspect for color of the portion you used for etching each time. (It should be easier to gauge the color in the etching tank because you won't be looking thru as much solution.) As long as it's emerald green or only slightly off color, it's good. No harm in bubbling to rejuvenate after every use, but not necessary until it's no longer a pure emerald green.

The amount of excess HCl in the final solution is designed to be quite low. If a lot of excess HCl is present there's no avoiding some of it being driven off by bubbling, possibly resulting in an odor and the release of corrosive gasses. But at very low concentrations that amount is essentially negligible. For those whom I might consider overly concerned about smell and corrosion... you can have the greater peace of mind you desire by avoiding unnecessary rejuvenation... and when HCl must be added because the solution won't fully rejuvenate, you can add it in smaller increments than I recommend until the solution can be rejuvenated to a pure emerald green. An ounce in excess is enough. And for those who are concerned anyhow, you can always store and rejuvenate someplace well ventilated.

At some point you'll find you can't rejuvenate just by bubbling. When that happens, add 1oz (less if maybe overly concerned about corrosive fumes) of hydrochloric acid and bubble until emerald green. If you add less than an ounce, realize you may need to add several smaller amounts before you can fully rejuvenate. Rejuvenation requires oxygen that you get from the air by bubbling, plus an excess of chloride ions from hydrochloric acid. You don't need a large excess of HCl, but you need some. More isn't better.

Maintain the solution level in the glass container at 1 liter - or whatever your initial volume was - by adding water if it falls lower. If you only add HCl very sparingly, and only when needed, you may find the volume of the solution doesn't increase because some water evaporates when bubbling. If you add H2O2 to regenerate because you're impatient, your solution will continue to increase in volume and may become too dilute.

Over time, depending how much etching you do, copper will build up in the solution. When this occurs you can remove a bit of solution (maybe 0.5 - 1 cup), pour it into a pint jar and set it somewhere to evaporate.

If you accumulate any significant amount of copper chloride crystals in this pint jar, you can scrape it into a small freezer baggie and give it to someone who wants to use it to kick start his own smaller batch of etching solution. DO NOT dispose of excess copper chloride down the drain. It's deadly to pretty much all aquatic life.

That's it.

Jim H

P.S. This was originally: /g/homebrewpcbs/message/36051
Some small changes have been added.

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One of the basics is to use pool acid (hydrochloric/muriatic) and Hydrogen peroxide (drug store variety).

Mix one part of HCL to 6 (IIRC) parts of Hydrogen peroxide.

That etches well until the excess oxygen is used up, perhaps a month of just sitting around.

From there on, you need to bubble air through the mixture when etching.? Etching for me went from about 7 to 10 minutes with fresh peroxide, to about 20 to 30.? Others will be able to take this further.

Harvey

JimH

I'm a lurker and don't post much.? But I'd love to see a write up on how you make your Cupric Chloride solution.? This has been an interesting thread.

Dave

At 5/6/2022 04:43 UTC Morris Odell wrote:

Thanks Jim,

I added about 3 cm of thick fine-stranded copper wire to my 700 ml of solution and left it overnight with the air pump going. The next morning all the copper had dissolved but the solution was quite dark, indicating that the copper (1) had not been oxidized to copper (2).

To me this means you had some available Cu(2) to dissolve the copper wire, but not enough free HCl to allow 2 Cl ions for each Cu, therefore much of the dissolved copper was in the form of Cu(1)... dark brownish and insoluble.

When it comes to the concentration of copper in the solution, my recipe for making an initial solution calls for about 200 grams (7 ounces) of copper to make a liter of solution. That's about 14 feet of #10 copper wire... 22 feet of #12... 36 feet of #14... 56 feet of #16. That's the generally recommended concentration of copper in the working solution. The 3 cm was a really good test of the problem... no free HCl. Now you need gauge whether you have enough copper. You'll have to do that based on your memory of how much was used to make the solution in the first place.

I added 10 ml of concentrated (pool chemical) HCl and there was some improvement after another night. I added another 10 ml of HCl and now it looks terrific.

Exactly what you needed. Good job!

I tested a tiny sample with a few drops of 6% H2O2 and there was no change, which I think means that oxidation using bubbled air was complete.

Yes. But 10 ml (a bit over 1/3 oz) is a pretty small amount of HCl depending on the total volume of solution... and some of that already went to form CuCl2 so you still don't have much excess... meaning that after not too many etches you might quickly get back to a muddy brown solution you can't rejuvenate just by bubbling. I like to have about a liter (bit over a quart) of solution - although I don't use all of it when etching - and if my solution were acting like you describe I'd add at least one, maybe two, ounces of 37% HCl. That's for a liter of solution. More or less depending on how much solution you have. It shouldn't make for enough excess HCl that you have to worry about fumes.

I'm going to try etching a small piece of board to see whether it can stay oxidized but I won't have time to do that for another couple of days due to other commitments. It does seem that the fix was to make sure there was enough HCl present. I don't have a pH meter but I imagine that one would be quite useful.

The slight excess of HCl was the key in your case.

You don't need a pH meter. Just take a bit of dry baking soda... Arm & Hammer Bicarbonate of Soda is one brand... and add a few drops of solution to it. If it bubbles fairly vigorously you have excess acid (HCl). And if it doesn't have a strong smell you don't have too much HCl.

Yes... please let us know how a trial etch turns out.

JimH

Thanks Jim,

I added about 3 cm of thick fine-stranded copper wire to my 700 ml of solution and left it overnight with the air pump going. The next morning all the copper had dissolved but the solution was quite dark, indicating that the copper (1) had not been oxidized to copper (2). I added 10 ml of concentrated (pool chemical) HCl and there was some improvement after another night. I added another 10 ml of HCl and now it looks terrific. I tested a tiny sample with a few drops of 6% H2O2 and there was no change, which I think means that oxidation using bubbled air was complete. I'm going to try etching a small piece of board to see whether it? can stay oxidized but I won't have time to do that for another couple of days due to other commitments. It does seem that the fix was to make sure there was enough HCl present. I don't have a pH meter but I imagine that one would be quite useful.

Watch this space!

Morris

At 5/4/2022 11:58 UTC Morris Odell wrote:

The 6% will do just fine, BUT... since it appears that your solution may be too dilute already, maybe you need to stop adding peroxide - which further dilutes it - and instead add some copper wire to it and let it bubble, bubble, bubble, adding some HCl to provide the Cl needed to turn that copper into CuCl2. With a stronger solution, with some excess Cl in the form of HCl, you shouldn't need peroxide.

Thanks for the tip, I'll do just that!

Realizing it may take some time... please try to remember to let us know the result. It might help a few others who may have strength/peroxide/whatever issues.

I'll hunt down and repost my recipe for making Cupric Chloride solution involving copper wire (or other source of pure copper), hydrochloric acid, peroxide, bubbling with air and patience. If anyone tries it and leaves out the patience, they're on their own. ;-) I'd rather not have to try to figure out how to adjust the result if my recipe isn't followed.

Once made, peroxide won't be required to produce good results when etching PCBs.

JimH

> The 6% will do just fine, BUT... since it appears that your solution may be too dilute already, maybe you need to stop adding peroxide - which further dilutes it - and instead add some copper wire to it and let it bubble, bubble, bubble, adding
> some HCl to provide the Cl needed to turn that copper into CuCl2. With a stronger solution, with some excess Cl in the form of HCl, you shouldn't need peroxide.

Thanks for the tip, I'll do just that!

Morris

At 5/3/2022 06:23 UTC Morris Odell wrote:

I do regenerate the solution by bubbling air through it from an aquarium pump but when I'm etching a board the solution gets darker faster than it can regenerate so I give it a little dose of H2O2 which brightens it up instantly. The dark color is due to the Cu(1) reaction product. Once it goes dark I leave the bubbling going overnight and it's as good as new in the morning. Maybe my solution is too dilute but If I use a lot of it it's hard to see how the etch is progressing.

If the solution goes dark due to Cu(1) during etching you either have a solution that is too dilute or you're using an insufficient volume of solution. I'd guess too dilute.

I'm in Australia where "safety" restrictions on chemical sales are inconsistent to put it mildly. You can buy big containers of concentrated HCl from pool shops but at hardware outlets it's kept under lock and key - go figure. You can get all sorts of inflammable solvents, poisonous pesticides and other chemicals from them with no problems. However the laboratory supply stores that were a fun part of my youth have all disappeared.

And the lab supply stores whose customers are commercial labs are reluctant to sell anything remotely dangerous to a home user, or else their prices are too high.

Anyway I might pass on the 35% H2O2 just because it's quite a nasty substance it it encounters something that will decompose it. The potential silver chloride problem is something I didn't know about either and I wouldn't relish having to clean it up. I guess the small bottles of 6% will have to do for my hobby purposes.

The 6% will do just fine, BUT... since it appears that your solution may be too dilute already, maybe you need to stop adding peroxide - which further dilutes it - and instead add some copper wire to it and let it bubble, bubble, bubble, adding some HCl to provide the Cl needed to turn that copper into CuCl2. With a stronger solution, with some excess Cl in the form of HCl, you shouldn't need peroxide.

JimH

On 3/5/22 4:23 pm, Morris Odell wrote:

Thanks to everyone who replied!
I do regenerate the solution by bubbling air through it from an aquarium pump but when I'm etching a board the solution gets darker faster than it can regenerate so I give it a little dose of H2O2 which brightens it up instantly. The dark color is due to the Cu(1) reaction product. Once it goes dark I leave the bubbling going overnight and it's as good as new in the morning.? Maybe my solution is too dilute but If I use a lot of it it's hard to see how the etch is progressing.
I'm in Australia where "safety" restrictions on chemical sales are inconsistent to put it mildly. You can buy big containers of concentrated HCl from pool shops but at hardware outlets it's kept under lock and key - go figure. You can get all sorts of inflammable solvents, poisonous pesticides and other chemicals from them with no problems. However the laboratory supply stores that were a fun part of my youth have all disappeared.
Anyway I might pass on the 35% H2O2 just because it's quite a nasty substance it it encounters something that will decompose it. The potential silver chloride problem is something I didn't know about either and I wouldn't relish having to clean it up. I guess the small bottles of 6% will have to do for my hobby purposes.

If it's a bit viscous, dilution with 1:1 water will speed things up.

HCl already has water in it, so that helps too.

Because of the success of air-ation, i've still got a 20L bottle of FeCl i got 20 yrs ago (i'm in australia).