Does anyone bother watering down Ferric Chloride?

[seb1982]

Hi! 

I'm about to attempt my first etch (toner transfer method) with Ferric Chloride.  I've not etched a PCB since I was at school ... 

On my bottle of 41% ferric chloride, it says to mix it 10 parts FeCl to 3 parts water, but it also says to etch above 35 degrees C.

Since I'll be etching at room temperature, do you think I should bother to dilute it down or just go ahead with it as it is?

Thanks for the advice!

Simon

[komet]

Acids don't work faster by having less water in them, on the contrary. Why don't you water the granules down with warm water from the tap or a kettle?

[seb1982]

Thanks for the reply, Komet

My basic chemistry is lacking, so thanks for putting me right on that!

I *would* use warm water, but I bought it as a liquid rather than granules.  I suppose I could use hot water for the 3 parts water ...

I'm not being terribly bright today, am I! 

[IanB]

Ferric chloride apparently doesn't work if it is too concentrated. I would follow the recommended dilution. No need to dilute it with warm water, cold water will do fine. Only dilute as much as you need, and keep the rest of the concentrated solution in the original bottle.

It will etch faster if you warm it up, but it will also etch fine at room temperature (just takes a little longer, is all).

[sleemanj]

On my bottle of 41% ferric chloride, it says to mix it 10 parts FeCl to 3 parts water, but it also says to etch above 35 degrees C.

I use a hot water bath,  put smaller container with the FeCl into the larger container, pour hot water into the larger container around it (not enough that it floats preferably).  Wait a couple of minutes for it to warm up before putting in the board.

Because I use dry film, I have another smaller container in there warming up next to it, filled with a strong sodium carbonate solution to strip off the resist once the etching is done.

[seb1982]

Woo-hoo!  %-B

Well, that worked better than expected!  I added a touch of water from the kettle, and had it in a larger container filled with hot water, too.

Just verified with my multimeter that I've somehow (through luck, rather than judgement, I suspect!) managed to get decent traces down to 5 mil!

However, despite getting the printer to chuck as much toner as possible at the paper, it seems that there's quite a bit of "graining" (don't know what else to call it) on the traces, so I may well wait until I've got a UV box before doing the board for my power supply.  I'm a bit worried about patchy traces handling 3 Amps of current.

[nanofrog]

However, despite getting the printer to chuck as much toner as possible at the paper, it seems that there's quite a bit of "graining" (don't know what else to call it) on the traces, so I may well wait until I've got a UV box before doing the board for my power supply.  I'm a bit worried about patchy traces handling 3 Amps of current.

You might try touching up your artwork with a black marker (i.e. Sharpie) before etching the board, and see if it improves matters for you.

[c4757p]

However, despite getting the printer to chuck as much toner as possible at the paper, it seems that there's quite a bit of "graining" (don't know what else to call it) on the traces

Try different paper. You want the shittiest paper you can find, that the toner doesn't adhere well to. I use pages torn from a magazine, and it's absolutely wonderful. Thick, dense toner transfer, and delicate enough to do 8mil without effort.

[grumpydoc]

I'm still experimenting with the waxy backing paper used with laser printer labels.

It takes toner well from the printer but releases it readily if a bit of heat is applied - in fact it will release it at quite low temperatures. Running the image through a laminator a couple of times at "ordinary" lamination temperatures will transfer the toner to a PCB, although it's obvious that isn't hot enough to "re-fuse" the toner as it's still pretty easy to scratch off.

I'm just hacking a laminator to increase the temperature, if it works well enough will probably post details but I'm half tempted to try an etch even with the toner not fully fused as it seems fairly well adherent to the board. It will scratch off with a finger nail though so I wouldn't do for a double sided board in a flat tray and might not work with more aggressive etchants such as H₂O₂+HCl.

Slightly changing the topic has anyone tried the "Edinburgh Etch" mixture (ferric chloride solution plus citric acid)?

[seb1982]

Hmmm - perhaps I'll try again with magazine paper before hacking an old scanner into a UV box, then!  Thanks.  I was using 170gsm laser photo paper after reading it recommended somewhere.  It did seem a bit thick at the time!

Never heard of the Edinburgh Etch - it sounds ominous - like a "Glasgow Kiss"! (For those who don't know, a Glasgow Kiss is a headbutt in the North of Britain)

What's the citric acid supposed to achieve?  A lemony fresh fragrance to your hobby room? 

[mikeselectricstuff]

Get some thick (>90gsm) tracing paper. Good toner adhesion & blackness, and fairly cheap.

[grumpydoc]

What's the citric acid supposed to achieve? 

It's supposed to speed up the etch and prevent the build up of sludge with ferric chloride. I haven't found anything on the 'net which properly describes the chemistry though.

[Zapro]

A good tip is heating the ferric chloride for 30 secs to a minute in the microwave. Works wonders!

// Per.