etching pcbs

fergamp · November 23, 2005, 03:59:23 AM

I am trying to etch a circuit board I have made. I have used the blue pnp to print on to the board and that has worked fine, but now I have put it in the tray of ferric chloride deep enougth that the board is just covered but I am not sure it's doing anything will it take 1/2 hour or is it more like 2 hours? I bought a pcb etching kit from maplins and I am using all the parts from that so I assume I am using the right bits. I am just abit concerned that it hasn't done anything yet and it has been in there for 15 mins. any suggestions to what I am doing wrong?
fergamp

fixr1984 · November 23, 2005, 07:32:08 AM

I know when i do mine it takes at least an hour if not two. What does help is to take the pad that they give you in the kit and polish the board up a little bit before etching it. It seems to help speed things up a little bit. At least for me it does. Its funny that the bottle that came in my kit says it takes 20 minutes but after that its only starting to work.

fergamp · November 23, 2005, 07:36:33 AM

I was a bit hasty with my post I was expecting that it would bubble and fizz and etch away at the board furiosly straight away. but after 40 mins it was pretty much done. the pnp method works great other parts that i touched up using a sharpie are not as good but hey it worked.

jrem · November 23, 2005, 08:02:10 AM

next time try to keep the solution warm and agitate it . . . I put the solution in disposable tupperware, and place the tupperware in a sink with a few inches of hot water in it, and rock the tupperware back and forth a bit. It cuts the etching time by two thirds.

fixr1984 · November 23, 2005, 08:34:33 PM

I will keep that in mind...I hate waiting for over an hour.

fixr1984 · November 30, 2005, 10:51:21 PM

Quote from: jrem on November 23, 2005, 08:02:10 AM
next time try to keep the solution warm and agitate it . . .Â Â Â I put the solution in disposable tupperware, and place the tupperware in a sink with a few inches of hot water in it, and rock the tupperware back and forth a bit.Â Â It cuts the etching time by two thirds.

Thanks a bunch..I just did a pcb and it only took half and hour with your hot water method.

WildMountain · December 01, 2005, 05:10:27 PM

When I am etching boards it takes no more then 10-12 minutes. I do use ammoniumpersulfate, so that could make a difference, but I also think it's very important to keep the etching fluid moving. Keep stirring it, or keep moving the board through the fluid (using tweezers of course). As jred said, keep the fluid hot and agitate it.
Good luck.

BILLYL · January 26, 2006, 07:32:12 AM

I made a very simple agitating tank. Using a plastic container and a fish tank heater - for the heat source and fish tank air pump to agitate the etchant. So when I need to etch a board - turn on the heater - warm up the etchant - turn on the air pump and away you go.

Bill

Xlrator · January 29, 2006, 02:40:09 AM

I get a bunch of those little acid brushes and agitate it and smear away some of the black stuff. If you don't have enough, I have found it will slow things down when it starts to get too diluted with copper residue.

hank reynolds 3rd · January 29, 2006, 06:11:00 AM

usually takes me 10 minutes with this method...
using ferric chloride crystals, i add boiling water to the mix (in a tupperware box)...
hold this over a boiling pan of water on the cooker...agitating it by gently shaking it over the pan....
works great and I've not poisoned anyone yet (I scrub the whole cooker top/sideboard down afterwards to make sure)...
neutralise the solution afterwards (i usually do 3 or 4 boards at a time) with sodium bicarb, and that's about it!!

Sam

Paul Perry (Frostwave) · January 29, 2006, 08:13:46 AM

Some people use a big lightbulb close to the etching try to warm things up (think it is more critical to heat up if you are using persulphate).

wui223 · January 29, 2006, 08:24:03 AM

Where to get Sodium Bicarbonate? any easy-to-get replacement which works as good as Sodium Bicarbonate? thanks

hank reynolds 3rd · January 29, 2006, 08:40:38 AM

food stores/Tesco's etc...it's used in cooking, but it will neutralise the ferric chloride so you can chuck it away without poisoning anything..

Sam

Joecool85 · January 29, 2006, 08:45:02 AM

Sodium Bicarbonate = Baking Soda

hank reynolds 3rd · January 29, 2006, 08:53:00 AM

for when you're cooking up a Big Muff Pi!!
waa waa waaaaa

MR COFFEE · January 29, 2006, 09:34:39 PM

Ferric Chloride etch times also vary with the thickness of the copper foil on the laminate. Expect 30 min to much longer if you have over 1 oz. copper.

It has always taken longer to etch my boards than the average DIY article says it takes - and I heat the etchant. Go figure...

DON'T overheat the etchant trying to make it faster - it starts dissolving the resist (voice of experience

)

Taking the board out and rinsing it in clear water every 5-10 minutes isn't a bad idea. It gets the sludge out of the way. Warm water is good. I like vertical PCB etch tanks with something to keep the board bottom end out of the sludge. I rotate the board after every rinse.

You will develop your own way of going at it, which will be consistently reassuring with practice.

RaceDriver205 · January 30, 2006, 04:39:30 AM

I use ammonium persulphate (the 'other' etchant) instead of Ferric Chloride. Cheaper cos its same price per bottle as FeCl, but comes as powder. I can get it 2 etch a board in about 5 minutes, using a bit more powder, and boiling water from a kettle (and swilling the liquid around). Hasnt desolved the PnP resist ever, but goes straight through pen resist.

Paul Perry (Frostwave) · January 30, 2006, 06:11:21 AM

Quote from: MR COFFEE on January 29, 2006, 09:34:39 PM
Taking the board out and rinsing it in clear water every 5-10 minutes isn't a bad idea. It gets the sludge out of the way. Warm water is good. I like vertical PCB etch tanks with something to keep the board bottom end out of the sludge. I rotate the board after every rinse.

Mr Coffee, if you already have a vertical tank, get a fishtank air bubbler. I use a fishtank heater as well, make sure no metal is exposed to the etch (it doesn't quite go as hot as I'd like, but it sure helps with persulphate). An enormous advantage of verticality, is you cn put a desklamp behind it & see thru the PCB, great to check the etching!!

Coriolis · January 30, 2006, 07:29:31 AM

I've had luck with ferric chloride and the tupperware-in-hot-bath method. It takes me about 10 minutes to etch a board, and I've used the same solution for maybe 10 boards now...over several months. IOW, the solution didn't "die" just because I put it aside for a while, so you don't nescessarily need to make a new one everytime you etch, but YMMV. I just keep mine in a plastic bottle. It might soon be so saturated and used up, that I'll have to replace it, but then maybe I mixed it stronger than the stuff you get in a kit...

All in all, it works really well with blue pnp and with a marker for touchups (both a standard waterproof marker, but even better with a real pcb-pen).

Untill I get the space for an uv-lamp and etching tank (with the bubbles!), this will do me fine, and is recommended (and very easy).
Just don't spill the stuff anywhere!

C

Mark Hammer · January 30, 2006, 09:32:44 AM

Etchant that has done the ion-exchange-tango with copper results in a heavier molecule, which sinks to the bottom of the container. This means that the freshest etchant (i.e., the fluid with the largest proportion of otherwise unused molecules) is at the top.

This means that the best and most efficient etches will occur when the board remains as far from the bottom of the container as it can. In some instances the board will easily float if you just plop it, face down, onto the etchant. In other cases, what you can do to assure staying near the surface under any conditions is to drill four little holes, one in each corner of the board, and stick toothpicks in them. This will hold the board up like little table legs. You can snap the toothpicks off to suit the depth of the etchant bath. This method will also let you shake the etchant bath without risking a board sinking to the bottom and getting covered in all that sludge from prior etches. Since one of the enemies of good etchng is air bubbles trapped between the board and etchant, any method which lets you place a board in at a slight angle and assure that all air bubbles escape out the side is a good practice. This would suggest that the "tiny-toothpîck-legs" method has advantages over just dropping it face down. To be fair, though, air bubbles are more likely to be an issue for larger boards like those one-board analog synths. If its a Tonepad board for fitting into a 1590B, air bubbles should not be a problem.

I used to use a table lamp to heat the board from above, and still recommend it if you were going to wander off somewhere and not stay with the board. These days I use a heat gun set for lower heat (a bit warmer than a hair dryer), though a hair dryer will also work nicely. You can point the heat source at the back of the board Assuming that the tank/container has a surface area larger than the board itself, the gentle breeze will agitate the etchant lightly and the floating board will bob around like a raft. The heat accelerates the chemical reaction and action of the etchant, and the gentle movement will increase the likelihood of the board to encounter unused etchant molecules to react with. I find I can do some pretty complex and large boards in 10min with this method, even with etchant that is a few months old and has done plenty of boards.

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etching pcbs