OK been making some PCBs lately, and at first I was using Sodium Persulphate to do the job. Worked nicely but I hadnt read much aboutt it and seemed every store I went to only sold Iron Chloride (Ferric Chloride) or Hydrogen peroxide.
So… running out of persulphate I got myself some ferric chloride and did an etch last night. 80x80mm board in 500ml of water with 300ml of III… took 3 hours to etch, and was they pitted and poor in comparison with persulphate.
The Na2S2O8 persulphate took 50 minutes to etch, the chloride took 3 hours by which time the resist had started to get that saturated it was been eaten as well (hence the pitting).
Both mixtures were kept at 40 degrees to start with then room temperature after about 30 mins.
I guess my question is what do you guys use and find best, and do you have any tips on etching? I am thinking of getting a small fish tank and heater and fitting some PC fans to act as water circulation, and make myself a little temperature controlled etching bath.
Ferric chloride etches my PCBs in about 5 minutes. I put the etchant dish (a plastic food container) in a washing up bowl with about 1" of very hot water in it, and rock it continuously. Just leaving boards in the etchant doesn’t work.
Using photo-etch I can use 8 mil tracks (I’ve even done 5 mil on a test board), but I usually use 10-12 mil.
Although I now have a “proper” bubble etch tank I managed for many years with kit procured from the local pet shop.
Go to your local glazier and get him to cut you some 6mm glass for an open top (“fish”) tank. Mine was approx 13"x13"x1.5". Stick it together with some proper glazing silicone (use sticky tape to hold it while the silicone dries).
For a heater I used a fish tank heater. It looks like a large glass test tube with a heating element inside.
For the bubbles I used a fish tank airation pump and a porus fish tank tube. Put the porus tube in the bottom of your tank with some weights to hold it at the bottom. Connect it to the little air pump unit with some plastic tube. I think mine all came as kit with pump, porus tube and weights.
You will need a means of get the board in and out of the tank without putting your fingers in. I had a plastic pcb frame that clamped to pcb edges but a simple bag made from some plastic garden netting would do. (Don’t use anything made of metal !)
With the tank running at about 50degc you should be able to etch a board in new soloution within 4-6 mins. If the solution is becoming weak it will start to take long, perhaps 10-20 minutes.
However you can get “pitted” boards that a long time to etch and usually turn out tob scrap with the following issue.
If the PCB is not fully developed in the developing tank you may not fully remove protection film from the UV exposed parts of the circuit. So when you try to etch it looks like something is happening but it is just not etching every where it should.
You can check the board is developed properly by washing your board in fresh water after its been in the developer and dip it briefly in some etchant and wash the board off again in clean water. All the UV exposed parts should turn from a shiny copper finish to a matt russet colour. If not the developing was not complete. You can try putting the board back into the developer for bit long to finish it properly.
Also I nearly always use a fresh mix of developing solution every time I do a batch of boards, if you keep it a few days it never seems to work the same.
Thanks for the advice. Sounds like ferric should do the job. Must admit I didnt do much moving about for the board but even so 3 hours was a bit crazy!
Will make a new batch up tonight and give it another go with another board now I know it shouldnt take more than 15-20 mins hopefully.
Failing that I’ll make a heated tank up as suggested.
I have heard of people just putting the board in a zip lok plastic bag along with your etchant and keep sloshing it around between the your hands until done. The heat from your hands would help but perhaps doing it in bowl full of hot water would be more affective.
heat is definitely important as you’ve heard. Agitation is much more important than you might think. If you don’t agitate, you get areas of depleted etchant as the copper gets converted to CuCl or what ever. This slows the etching process, especially if the PCB is held horizontally.
I have a vertical acrylic etch tank I built - 2" X 10" X 10". Most of the aquarium cement gets attacked by etchant (don’t ask how I know…) so I used an acrylic glue that basically fuses the plastic together. I use a hacked aquarium heater - they usually have a 100F thermo switch. I just twisted the one in mine to short the leads. I don’t know the final temp but think 50C sounds about right. I also use an aquarium bubbler but the ammonium persulphate I use attacked the plastic bubble “stone”. I drilled 30 mil holes in some plastic tubing (PET, I think) to make a bubbler. Works OK. I get 5-10 min etching times - depending on the thickness of the copper layer.
I’ve used a number of etchants and greatly prefer Ammonium Persulphate which is very similar to Sodium Persulphate. Our local Frys carries it - about $18 for 1 Kg. It really is so much nicer than FeCl - you can see though it and thus inspect the progress of the etch with out lifting it out (in a vertical etch tank). Also, it doesn’t stain. For disposal, I precipitate out the CuCl and take it to the semi-annual disposal events that take batteries, TV, paints, etc.
Just to let you know did some etching over the weekend with ferric chloride on a sponge and rubbed the board. Etched fantastically within minutes before my eyes. No mess, no hassle, no wait. Rinsed sponge, cleaned board and I was done in time for dinner, was brilliant!
Will try to get my hands on some amonnium persulphate next week to give that go also.