On 3/5/2019 1:56 PM, Jim Higgins wrote:
Received from Dave at 3/5/2019 05:21 PM UTC:
On 3/5/2019 10:28 AM, Harvey White wrote:
On Tue, 5 Mar 2019 08:26:04 -0600, you wrote:
Thanks. I had found that one earlier today. It has been replace by a more expensive model. After a lot of searching online, it looks as though I just need to look for a suitable container, get a pump, and a heater. The proper shaped glass vase or something. Glass is better.? The etchant tends to eat the seal on rubbermaid containers, but will work.? You could use an air bubbler stone, but that will be attacked by the acid.? At one time, I used an aquarium heater to heat the etchant, from what I remember, I stopped that and just etched on warm days.
Ammonium persulfate (or perchlorate) does not corrode things the way that HCL based etchants do.
Ammonium persulfate solution needs to be heated to etch efficiently and heat causes the solution to decompose. It isn't as efficient at etching copper as other more easily obtained chemicals unless the solution is enhanced via the addition of a trace of mercuric sulfate. That's a really big NO NO for anyone without the ability to manage the waste100% legally. Whether or not heated, the solution can't be rejuvenated and must be disposed of when spent... along with any copper it contains. No problem for those who don't care about proper (legal) disposal... a pain in the butt for those who do. I'd forget ammonium persulfate.
Ammonium perchlorate sounds similar to ammonium persulfate, but it's a completely different thing. It's a super powerful oxidizer with primary uses being in fireworks and as an ingredient in some solid rocket propellants. I can't find any credible references to using ammonium perchlorate for etching PCBs. The chemistry just isn't right.
Use polypropylene or glass and corrosion becomes a non-issue. Note that the material in the soft seal built into the lids of some polypropylene containers isn't polypropylene and could be attacked. That's why I store my solution in a large wide mouth glass jar with a plastic lid left a bit loose to avoid pressure build up.
I follow the law and don't want to contaminate the environment so I will play it safe. I may just be smart and etch outdoors, reclaim my etchant, and figure out what container can actually keep it from seeping out. Or build a small wooden shed just for chemicals (in plastic bottles).
I was just looking at those 8x8 inch square glass blocks as an easy container. The ones that have the rectangular hole already cut in them. May make a good starter bubble tank. So now I already have my first problem. Finding a plastic suitable for my HCL based etchant. :) Or change etchants already... I want to stick with the muriatic and peroxide for now.
When it comes to plastic containers, pretty much any polypropylene container from Walmart will do for etching. No lid needed when etching. The recycling symbol for polypropylene is a recycling triangle with "5" or "05" inside and "PP" below, so it's easy to identify. I etch in a plastic pan and store the solution in a glass container with a plastic lid between uses. I use a large 1-gallon or so wide mouth jar that's about half full... and the bubbler tube comes out thru a small hole in the lid... so when bubbling to rejuvenate my solution any minor splashes from the bubbler stay in the jar. If you just use HCl and peroxide and don't let copper build up appreciably in it, there's nothing to rejuvenate so you can forget the rejuvenation part. (But leave the lid a bit loose because H2O2 decomposes to produce oxygen gas and that can cause pressure to build up.) I actually added a fair bit of copper wire to my initial HCl/H2O2 solution because I wanted to let the cupric chloride that forms plus a bit of HCl do the etching... and I rejuvenate the solution with bubbled air rather than adding H2O2. Using this approach the only thing you add is a bit of water to maintain the volume of the solution and a bit of HCl when the solution won't rejuvenate completely to a nice emerald green. That boils down to adding HCl in the amount needed to make up what gets used when etching... and that's not much unless you etch a heck of a lot of boards. It's adequate to just etch until the solution either won't rejuvenate to a bright emeralds green or if you notice that the etching rate is slowing down. I've never noticed the latter.
Also, a fritted glass bubbler is NOT affected by the etchant. Stone bubblers (as warned above) maybe, depending on the material, but NOT fritted glass. Fritted glass bubblers are a glass tube with a porous glass bubbler on the end. The stone type will almost always have a plastic tube with a bubbler stone glued/epoxied onto it. The smallest (cheap) vibrating aquarium pump will provide enough air for etching and rejuvenating. You don't need a sheet of bubbles flowing vigorously all over the board, you just need the solution moving around enough to continuously remove the brownish reaction products from the surface of the board. The more you agitate the solution the more undercutting you'll get so a large airflow isn't as desirable as one might think.
To it in perspective, you have to etch a heck of a lot of boards to put the slightest strain on a couple of liters of etchant consisting of cupric chloride solution plus HCl.
Jim H
I see people using plastic all the time but thought the square glass block would be interesting. I pretty much understand the rejuvenation part and all that but my main worry is storage and no rusting my stuff in my shop. The info on the fritted glass bubbler is a good tip. I wonder about the plastic tube though that connects it. Will that degrade and if so, how fast? The Radio Electronics article on a bubble tank is something I would like to build and it is only 2 inches wide so I am curious how you would change the hoses out based on the design. I will ask the other Jim about that. And how do you store your etchant safely to avoid rusting any nearby metal/steel? Thanks for all the good info.
