PCB etching question

[Schappy]

How long does it normally take to etch a PCB with FeCl?

Ive been etching it for over an hour and there is still alot of copper left. When I say alot I mean there is still a thin sheet of copper over the whole board.

I warmed the solution and agitated every few minutes.

How do you know when its done?

[deadastronaut]

it shouldnt take an hour...takes 10-15 minutes..i'd say..

have you put enough ferric in there....in a little shallow water..just enough to cover your pcb...

colour should be like the colour of bitter beer...ish..

you know when its done ...when there is no copper....not even the little pad dots...

[Schappy]

Are you saying I should dilute the FeCl?

The bottle says not to.

This is weird it doesnt seem like its doing anything.

[fpaul]

you need to heat it up some way.  I place the bottle in a secondary container of very hot water for a while before pouring into the etching container full strength.  My last two boards took maybe 10 to 15 minutes to etch but they were very large(eurocard) boards.  I was also moving the container side to side most of the time.

[Schappy]

I warmed it up in hot water for 10min.

I havent been agitating the whole time but have been every few minutes.

[deadastronaut]

Are you saying I should dilute the FeCl?

The bottle says not to.

This is weird it doesnt seem like its doing anything.

no dont dilute...sorry i mix my own....didnt realise you had the ready mixed stuff..

strange though...should be ok...maybe just leave it in there till its done...but next time warm it a lot more..

good luck.. rob.

[Al Heeley]

Mine take about 20 mins - I continually repleneish a tub of surrounding water with boiling water to keep the heat up, it helps speed up the acid attack a lot

[Mark Hammer]

1) The copper needs to be in contact with viable molecules of FeCl.  That means it can't be sitting at the bottom of the etchant tank, copper side up.  If you leave it in that way, the board is covered with used etchant.  Shaking it will help, but only a bit.  I prefer to etch the board floating on the top of the etchant, copper-side down.  If I have to be away from the board, one trick I use is to drill little holes in all 4 corners and prop the board up by sticking toothpicks in each corner, like little table legs.  That way I know it won't sink to the bottom face down.

2) Finger juice, fingerjuice, finger juice.  Get any of it anywhere on the board and you increase total etch time considerably.  It's like "unofficial toner" the way it resists etching!  I try to handle the board during the final pre-etching stages with a folded up piece of paper or something else that keeps my skin from touching the board.

3)  Counter-intuitive, maybe, but yes adding a bit of warm water to the etchant can sometimes increase its efficiency.  I can go for months at a time without etching anything, and the tupperware bins in the garage can evaporate and get too thick.  Quite possible the water helps by thinning the etchant out and making it more possible for used etchant to sink to the bottom of the tank rather than be suspended.

4) There are plenty of ways to warm up the etchant.   Realistically, you only need to warm up what is in direct contact with the board, so one way to have warm etchant without an entire warm tank is to simply point a study/desk lamp at the back of the board floating on top (i.e., the non-copper side).  The heat is transferred through the board to the etchant directly underneath.  If the etchant is deep enough, any molecules that have undergone the requisite chemical reaction will fall away, and be replaced by fresh available molecules, ready for duty.

[KazooMan]

Yep, warm it up some more.  I switched to the persulfate etching method and that also needs some heat.  I etch my boards in a disposable plastic food container with a snap on lid.  I dissolve the sodium persulfate in hot water, put in the board, and snap on the lid.  I then put about an inch of hot water in my sink tub and float the container in it.  I change the hot water bath as needed.  With the ferric chloride I would warm the bottle well in hot water and do the same hot water bath treatment.  Depending on your container you might be able to heat it with a heat gun or old hair dryer.  The nice things about the plastic food containers is that they are cheap, come in a variety of sizes so you can minimize the amount of etchant needed to cover the board, the snap on lid, and they are clear so you can check your progress without opening it up.  You can keep the etchant in the container after use and use it again if it still has some life left in it.

Rule of thumb in chemistry is that the rate of a reaction doubles for every 10 degree (centigrade) increase in temperature.

[Schappy]

I found my problem I think.

I switched to using Muriatic Acid and peroxide which allows you to see the etch more clearly.

There is a thin film of plastic across the board from my transer.

I used glossy photo paper. Anyway to avoid this or clean it up?

[Brymus]

Sorry I laughed at that,
I read IIRC, John Lyons said it was impossible almost to remove that film.
FWIW an airstone bubbler made my etches way faster than heating the solution in a double boiler on my stove.
I bought a 3$ flat/square airstone and used an old pump from one of my fishtanks and it takes about 10 minutes to etch a normal pedal PCB now.
I also bought a sealable container and used hot glue to glue the airstone to the bottom then I put the lid on and lock it,no muss or fuss.
I found a zip tie around the PCB gives a good handle for positioning and checking the progress.

[Schappy]

If its impossibel to remove the film how do people use glossy photo paper?

[Brymus]

Apperently only certain brands dont leave a plastic film on the copper,I use glossy magazine paper myself.
I havent tried photo paper yet.

[Schappy]

magazine paper worked like a charm!

[studiostud]

http://www.instructables.com/id/Sponge-Ferric-Chloride-Method-Etch-Circuit-Bo/

I've actually tried this method and it works pretty well.  The only thing I would recommend is getting a decent sponge (so not the 10 pack at the dollar store) and get a good set of rubber dishwashing gloves (supermarket or home depot).  After you're finishing etching, make sure you rinse your gloves and sponge.  If a lot of the Ferric Chloride dries on the gloves, it will harden the rubber and crack, especially around the fingertips and then they are useless.