I finally got around to making some acid cupric chloride (CuCl2) etchant today. Everything went well, following the numerous sources online made things very straight forward.
Here’s how I did it in case anyone would like to know.
I mixed one part [~31.5% by weight] hydrochloric acid (HCl) into two parts [3% by weight] hydrogen peroxide (H2O2)
Next, I added about two feet of ~22 AWG stranded copper to the mixture. I let this sit until the wire was completely dissolved.
This made about a half liter of etchant, and was a nice neon green in color.
Initially, I stored the solution in a polycarbonate (PC) jug; a re-purposed Arizona Green Tea gallon jug. After reading online that PC and HCl don’t play very well together, I decided to switch to something better. I found an high-density polyethylene (HDPE) container to use instead; a re-purposed body wash container. However, after closing the container and letting it sit for an hour or so, the container visibly bulges, and bubbles are visible on the interior. I fear that this means I have done something wrong with creating my solution, because when I place the acid in a polypropylene (PP) dish for etching, bubbles form on the plastic as well. If I brush away the bubbles from the HDPE or PP, they reappear (nearly instantly in the case of PP, lots of tiny bubbles that slowly grow).
Have I messed up creating the solution, or is the bubbling normal? Is there a better storage solution than plastic? I realize glass is a sure fire approach, but I don’t have an sealable glass container (an excuse to buy some more alcohol, :P), and I’d rather not have to worry about the fragility of the container.
Also, any other tips or suggestions about the use of cupric chloride as an etchant would be welcome.
I would use an old container of hydrochloric acid.
I found no matter how well sealed a container of hydrochloric acid might be, metal around it rusted over the years. And that was the original container.
I always use old plastic milk bottles (rinsed of course) for my etchant and developer. I keep them in an old washing-up bowl, in case they spring a leak. I use ferric chloride, but I didn’t have any problems when I was trying cupric chloride, with HCl and H2O2 in the container, and I have regenerated ferric chloride with H2O2 and HCl, and stored it in the same containers for a year or more, without problems.
The solution will off gas as the H2O2 decomposes and O2 is slowly released from solution. A loose fitting top may prevent a bottle burst and ruining of one’s underwear… I use 1 HCl to 2 H2O2 as etchant directly. It is very fast, and slightly heated, will etch the average board in a minute or so. I am confused why the copper is added to the solution, as this should weaken the etching action. Unless it is to slow it slightly?
The copper is added to produce cupric chloride, which is a good etchant in its own right. As boards are made, one gets more etchant, but some is needed to start things off.
Acid cupric chloride regenerates itself as it etches copper. This means one doesn’t need to continually purchase fresh HCl and H2O2, or ferric chloride. A very good [writeup is available here. It covers the reactions taking place, and actually goes into quite a bit of experimenting and detail. The references used in the article are also worth reading if you’re wanting to get serious about things.
Well, the plastic doesn’t appear to be dissolving or damaged, I can’t see any noticeable difference between the portion of the tub that held the acid, and the portion that was exposed, and there is no line between the two either. Also, the pressure appears to have subsided after letting it sit and having released the initial pressure. Bubbles still form on the plastic, however. I’m not sure if this is a chemical reaction with the plastic, or if it’s a process similar to nucleation of carbon dioxide in carbonated beverages due to the texture of the plastic (it appears smooth, but I’m sure a microscope would claim otherwise).
Leon, any particular reason for the switch [back] to ferric chloride?
I was actually regenerating ferric chloride by adding H2O2 and HCl. Gradually the ferric ions would have been washed out, and I’d have ended up with mostly cupric chloride. It worked OK, but it was noticeably slower than ferric chloride, so I went back to that. I’m impatient!
So, I’ve nearly finished my etch tank, and I decided I would start whipping up the final amount of etchant. I made about two and a half liters, starting with the small batch I made prior.
In order to not dilute the solution, I figured I ought to be able to use the existing cupric chloride as the oxidizer for fresh copper metal. I added some fresh HCl, and about 150 grams of copper metal, and turned on the aeration. I let this run overnight, and upon inspection in the morning, the solution had turned a dark green; I couldn’t see through it (about 3.5 inches worth; clear acrylic walls). There was still metal copper visible at the bottom of the container, however.
I then added about a third cup (~100ml I’m guessing) of hydrogen peroxide to the solution, and the solution immediately cleared up; I could see through to the other side. I’m wondering if adding the hydrogen peroxide is necessary or not. It’s my understanding that aerating with oxygen will work just fine, but takes longer than use the very strong oxidizing hydrogen peroxide. I was expecting that overnight ought to be enough, given what I had gathered from the various online sources. Perhaps the overnight refers to the much smaller cuprous amounts given from a single board etch?
Thanks for the thoughts! I’ll be posting a writeup or such shortly, hopefully.
I’ve tried three types of magazine paper, the Staples® Photo Plus Paper gloss inkjet paper, but I still can’t get a transfer that is good enough to use. I’ve tried different temperature and pressure combinations as well, mostly with the magazine paper. The gloss photo paper doesn’t work well at all, it actually left parts of the gloss on the PCB, and soaking it in water didn’t do much of any good, I still had to peel away the paper (the plastic kept the water from soaking between the paper and the board).
I’ve also got issues with the traces deforming; they “smush” outward on some of the traces as can be seem in the pictures. I’m not sure if this is too much heat, or too much pressure, or both, but it makes the transfers unusable. The design I’m trying to transfer is a 10 mil trace/space layout for a 0.5 mm 32 pin QFN.
My buddy insists that the Dextrin coated paper and laminator offered by pulsar will work excellent without a hitch. I’m a bit hesitant to spring for a laminator, as the information form the first hand users isn’t conclusive, and seems to vary just as much as that of folks using an iron. The only research touting it as the holy grail are the folks who will directly profit from my purchase, and my friend.
How is everyone else doing toner transfer, and are my results the norm, or do I just need to keep experimenting?
Could also be your printer - I have a laminator + the high end transfer paper and I still get crap results. I looked at the printed output under my inspection scope and its really all over the place; a test print on another [read more expensive] printer worked fine.
I’ve had the best success with low heat (basically as low as the iron can go) and my whole body weight for pressure. After I realized how cheap you can outsource boards these days I don’t bother messing around with homemade boards anymore though.
If your in Canada, Alberta printed circuits offers some amazing deals for hobby work, plus you can have your boards in 3 - 5 days.
Yeah, I use APC for a lot of stuff. Its mostly things like breakouts that I need ASAP, and don’t want to wait for. RE: Storing the acid - I just use the jug the HCL came in, and some old plastic yogurt containers.