Electronic Circuits and Projects Forum

Originally Posted by spyghost

hi,

can another chemical be added to ferric chloride so that it can etch much faster? when etching, i use near boiling water with ferric chloride to etch my boards, but i still find it quite slow. i am too anxious to try out acid etching (due to the fumes).

what chemical, or whatever compound is there available that i can add to ferric chloride to make it etch faster?

I havn't heard of any chemical catalyst to speed it up. I would imagine it would be popular if such a thing existed (that was safe). I have heard of agitating the fluid however. That should speed it up by some.

:shock:
You must have 30-40% concentation of ferric chloride in water for have a fast eatching. And the solution optimum temperature is around 40C, NOT BOILING!! The board must be with eatched face down(very important).

what happens if the solution is too concentrated?

and what if the temp is too high?

well, its kinda weird in my place... there are two kinds of ferric chloride sold, pellets and mixed.

the pellets are real cheap. converted into usd one bag costs 0.45 cents which must be mixed with 1 liter of water. on the other hand, a 100ml of premixed ferric chloride costs 0.30 to 0.50 cents. big difference right?

what i was wondering is that those premixed solutions really etch much much faster than the pellet form. so i have thought, those premixed ferric chlorides might have some catalyst added in them, thats why etching is faster...

before i forget... the premixed solutions are near black in color, while the pellet form (when mixed with water) is just brown in color.

I find that "agitating" the board by hand works well for speeding things up a bit.

I put on two pairs of latex gloves, and hold the PCB by its edges. Then I gently lift the board in and out of the solution, letting most of the Ferric Chloride run off of the board. The resulting "washing" process seems to remove the copper more quickly.

As Johnson says, Agitation will speed up the etching process. As the etchant "eats" the copper away from the surface of your PCB it becomes less effective (the etchant becomes saturated "locally"), by agitating the board/etchant you move circulate the locally saturated etchant away from the copper and allow fresh etchant at it.

This can be done in two ways either by moving the the board in the solution, or by moving the solution round the board (eg, gently passing air through the solution, used by many commercially available etchant tanks).

For best results when etching, it is often advisable to use a combination of aggitation, heating etc. But remember that etchant solution is an acid so care needs to be taken.

some recent observations in my latest etch:

if temp is raised too high, etching would be slower... i have a rough estimate of the same rate as that of an etchant at room temp. the temp of the solution must be "optimal." i don't have a thermometer for an quantitative representation, but here is the setup i had - an aluminum pan with water that is kept at a temp wherein vapor comes out but not boiling. i have plastic pan containing ferric chloride mixture on top of that hot water. the level of water outside the plastic container is the same as that of the etchant.

undercutting is minimized if the "sideways" agitation is "not performed." i simply did the etching w/o agitation. i just let the board float over the etchant. after around 2 4-minute songs... 8) the board is completely etched. well, the thinest trace that i had was 12mils and its located near the edge of the board. the board size is 6"x4". there are no copper pours on the board, only traces... i even had text printed on the board which is a lot thinner than the 12-mill trace. it was clear and readable...

in this method of no agitation, if the board is left over a long period of time, undercutting would be seen - very visible even w/o magnifying glass. also, if the mixture is too strong, undercutting would be seen...

lastly, although it is obvious... the ferric chloride mixture must be well mixed...