PCB Etching Tank - Do it yourself

[Tony_Stoynov]

Hi,
the MP is right, the fericloride is saffety. About the ventilation, i has in the pas thank with aeration, and can say taht aeration increase the voapours.

[MP]

Wow!  What were you using for aeration? I have had a pcb lab for more than 20 years and I have always used a low power air line from an air compressor connected to a manifold in the bottom of the tank that allows for even aeration throughout the tank. i.e.- even flow of tiny bubbles. Have never had a problem with fumes by using this method. Believe me, if I needed ventilation, it would not be for me to decide in a business. I would be required to add it by local regulation during inspections.
I think you are talking about etch systems which pressurize the etchant and spray it on the board instead of using the tank method. These systems are much faster than using a tank with simple aeration, but certainly have their added safety precautions. These pressurized systems produce a mist of etchant that is mixed with air. Obviously, this is going to give you an airborne mixture. This is also too dangerous for a hobbyist (in my opinion).

For those interested, the safety data sheet for Ferric Chloride, section 8 states the following:

SECTION 8 EXPOSURE CONTROL/PERSONAL PROTECTION

ENGINEERING CONTROLS/ VENTILATION
NORMAL GOOD ROOM VENTILATION SHOULD BE SUFFICIENT.

RESPIRATORY PROTECTION
N/A

EYE PROTECTION
RECOMMENDED SPLASHPROOF GOGGLES

HAND PROTECTION
RECOMMENDED IMPERVIOUS GLOVES e.g. NITRILE.

SKIN PROTECTION
RECOMMENDED IN FORM OF COVERALLS.

Always read the safety data sheet for any chemical when in doubt.

MP

[Tony_Stoynov]

Hi,
presured air, from compresor, via reducer, in compresor tank the presure is around 6 bar, after reducer valve the presure is below 1 bar. But now i think taht temperature of air can be higir that room temperture becouse the compresion, and this may be is a reson for the voaporation.

[oldgrandpainmi]

Hello All,

Just wanted to put my two cents in on this subject.  I didn't read all of the replys on this tank, so I hope I don't repeat too much!

I built this exact tank (12"x12"x1") 15 years ago with much success.  I used it with Photo Etching and standard copper etching with standard copper etchant.  The only problem is rub off transfers will come off if the heat is too high and bubbles are excessive.  Too low on eather one will cause excessive etching time.  I etched 25-50 hobby pcb's with it before I gave it away.

The artical states that MEK for the glue!  YES!!! but remember to scrape the cut edges of the plexi you plan to glue with a utility knife blade before gluing.  The edges must be as smooth and as close to clear as possibible before applying glue.  For those who don't know, the glue is as thin as water. You have to apply the glue to both edges and let it soften the plexi before mating.  Afterword, the soft glue seems to melt together, giving the appearence of a single piece of plastic.  Mine developed a small leak, so I used a sealant made for aquariums.

I didn't read the articals very well, but don't forget to drill as many holes in the board holder as possibible.  Too few holes will negate the bubbler on the bottom.

Just Food For Thought!

OGPIM

[Fowkc]

I keep meaning to build myself an etch tank, but one thing eludes me:

People use aquarium heaters to heat the etchant, but all the aquarium heaters I've seen have a built-in thermostat that keeps the water at a maximum of about 32C, about 10-15 degrees too cool. How do you get around this, or is there something that I'm missing?

[MP]

The larger aquarium heaters will get hotter than this. I have actually had to watch out for going too hot in my tank. You do not want to heat up the mixture too much. Everything metal in the room will begin to rust....it is also not good to breath this. Your 32C heater is not real hot, but it is still hot enough to make the etching much faster. The other part of the equation is the aeration. The combination of a bubbler and a little heat makes a big difference.

MP
 

[Fowkc]

OK, what sort of wattage heater should I be looking at then? It seems to be the case that a more powerful heater is meant to heat a larger volume of water (i.e. larger fish tank) to the same temperature (about 32C), rather than actually increase the temperature any further and kill your fish.

I can see how a more powerful heater would pump out more heat initially and then pretty quickly turn itself off as the etchant reached temperature, but it would still try and keep the temperature at about 32C.

Obviously I'm mistaken, since lots of people have done it and it works, but I'd like to understand why...

[MP]

All of the ones I have purchased have an adjustment on the top of them. You just set it according to needs. For etching, this is usually near the top of the scale. There is no temperature sensor inside these heaters. It is a metal strip that works like a mechanical thermostat. When the heat expands it enough, it triggers the switch. It is possible that you do not have enough bubbler movement in the tank to allow the heated etchent to move away from the heater and to the other side of the tank well enough. If you have poor circulation, the heat around the heater will turn it off prematurely, causing a lower overall temperature to the etchant. My tank can hold 4-  12" x 12" panels. I use 2 of the longest heaters I could find in the aquarium stores, I do not recall the wattage, but it was quite a jump from the wattage ratings of the smaller ones. I think your problem is with the internal thermostat. If you cannot get the adjustment to go high enough, you could open it up and modify the metal strip of the thermostat to cause it to stay on longer. But check for the circulation problem first. You don't want to cook the etchant near the heater just to get the rest of it warm.
Hope this information is helpful.

MP

[Fowkc]

I haven't actually bought anything yet, I'm collecting information.

I'll only be etching one-off boards, so I won't have a lot of etchant to heat.

I'm still not sure about this, you say:

All of the ones I have purchased have an adjustment on the top of them. You just set it according to needs. For etching, this is usually near the top of the scale.

Well "top-of-the-scale" for the aquarium heaters I've seen is about 32C. Presumably you get your etchant hotter than that, so how do you do it? Do your heaters go higher than that temperature, or is it a result of heating much less liquid that they were actually designed to heat?

[gogo2520]

hello Fowkc

    Hey guy if you just want to see how it works you don't need all this stuff. To etch one board, first is the transfer of the image to the board, once you have that any tank that the board will fit into will do. Hot water from a kitchen sink and a plastic bowl will work. Ferric Chloride dose good at 32C% or 100F%(same I think).
     When I did my first one  I bought a kit for about 14.00 dallors U.S. I got all the stuff ready and put on some plastic gloves and went to work. First thing I did is prewarm the Ferric Chloride in a double bath (plastic bowl inside a plastic bowl) hot water from the sink.
    Then the board went in, one hand on the inside bowl and rocked it back it back and forth, I could see the stuff work but I though it would happen faster. No it took 15 minutes, but it worked and I didn't need to buy all that stuff. It was my first board and it looks good.
   Oh I use press_on transfers that came with the kit.
         I now have a tank set up with the heater and air pump, works much faster, and use a laser iron-on
transfer. (office gloss paper).
         After of about two months of reading and another month of planning  I tryed this, I could do it, and now I make my own double sided boards. COOL.
                                           Have fun
                                            gogo

[MP]

Well "top-of-the-scale" for the aquarium heaters I've seen is about 32C. Presumably you get your etchant hotter than that, so how do you do it? Do your heaters go higher than that temperature, or is it a result of heating much less liquid that they were actually designed to heat?

It is actually a combination of smaller tank and more circulation from the bubbler. The smaller tank causes more efficiency of a small heater (more wattage per mass to heat up). Then you have the bubbler action which aerates and moves the water more than you would with an aquarium. Again small mass of water, more circulation. This will pull the heat away from the heater more efficiently so that the internal thermostat does not turn it off prematurely. Thus, the entire body gets more overall heat than what you would see in an aquarium with it's larger mass of water and poor circulation.

My larger etch tank holds approximately 17 to 18 liters of etchant. For this, I use two heaters. One on each side. Not that two heaters are required fo the temperature, but to keep things even from one side to the other. I also have a very aggressive bubbler system.
However, I have had one of the small hobbyist tanks in the past, like what you see at www.circuitspecialists.com and they are just as efficient with their small tank, fish aquarium heater and fish aquarium bubbler. It is all the same principal.

BTW: Gogo is correct. 32C will help the etch process considerably over cold etch. It is around 90F, but you don't want to get ferric too hot or it will vaporize and you will breath it.

MP

[Pete9]

Hi guys I have been reading with interest the various methods of etching a board,I have tried most of them over the years and my final equipment is a plastic bucket that I put the board in etching face up ,pour in about 10mm of ferichloride stand it in some warm water and agitate,a swirling action is the best,I find the board will be etched in about 3-4 minutes. Total equipment cost 2$. Another tip if you are making a UV exposure box,use the UV tubes that are sold for Insect sappers,also sold for killing mosquitos, and seen in most butcher shops, these tubes are a fraction of the price,you can also get them in a U shape which will give a bigger area of light.If you are not conversant with wiring these tubes get an electrician to do it for you,or run them from a home made inverter.I do all my artwork with cad drawing,or in the case of good quality art work that is published copy and print on a inkjet printer ,5 minutes on my uv light box with presenstised board gives good results,with most  presensitised boards they supply a developer that is quite expensive ,try using sodium hydroxide 20 grams to 1 litre,very cheap,use at about 20degrees centigrade .  I printed the artwork for the 0-30volt power supply and had it etched and drilled in 4 hours.Hope this has been useful.         

[Fowkc]

I already etch lots of one off boards, current process is printing onto tracing paper, UV exposure, develop and etch in a plastic tray. This would be fine if I didn't share a house with four other guys. If it could go a bit quicker and be a bit more "self-contained", I'd get in the way less.

Thanks for all the help, sorry I was a bit insistent. I was sure it would work, I just like to understand why.

[Omni]

1. Slightly oversize a pyrex glass tray to the copper clad board.
2. Pour some common Ferric Chloride in the tray and place your board in the latter solution.
3. Every 20 min using your hand lift one side and allow the ferric to wave over the board.
4. After 1 hour your board should be complete (depending on size).
5. Using tongs remove board and flush with water, clean resist from PCB.
6. Pour the Ferric back into its bottle and use on the next project!
7. Clean tray with water and allow the faucet to run for 45 sec - min (flush pipes).

The above process has been used since the dawn of time, why try to reinvent the wheel.
Furthermore, when making a PCB at home remember it is an enjoyable hobby, time is not a big concern...