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richie00boy 19th July 2004 06:43 PM

PCB Etch Probs
 
I am trying to etch a board that developed beautifully (as always). The board is at least a year old. I'm using sodium persulphate etch (the clean stuff) following the instructions exactly. My tank bubbles a bit, thanks to the fishtank pump tube.

Basically it's not etching. It's attacked the edges slightly and the copper has barely gone pink. It's got a kind of grid pattern across the copper if you look carefully. This is after about an hour in the tank. According to the instructions it should take about 10 mins in a bubble tank, 30-45 mins in a plain tank. At 45 degrees C.

Are my problems due to the solution not being hot enough or is it because the board is old? I thought it was only the developing that was affected by age. The solution was warm, but has obviously cooled down over the hour.

Devil_H@ck 19th July 2004 08:14 PM

I think it's because it's too cold. I once left a board in the etchant for over 2 hours and not a bit of copper was etched away.

Now I just put the etchant in the microwave for 20-30 seconds and etch. Every 5-10 minutes or so I put it in the microwave again (don't forget to take out the PCB, I don't think the copper will like being in the microwave).

SteveA 19th July 2004 08:52 PM

I've used ammonium persulfate with good success. It requires heating to about 45-50C (110-120F) to oxidize at a reasonable rate. I agree with the Devil who must have warmer temperatures at his location.

SteveA

richie00boy 19th July 2004 09:52 PM

Hmmm, after I had written that post I filled the sink up with hot water to keep the tank warm. Still no more progress after another 30 minutes. The solution was 40 degrees C when I put the board in and I reckon got no colder than 20 degrees C. It must have been at least 30 degrees C even after 15 minutes which, with the bubbles should have at least attacked a bit, according to the instructions. Do I really need to keep it above 40?

Isn't ammonium persulphate different to sodium persulphate?

Is it possible that the protective coating was not totally removed during developing due to being old board? It looked fine to me.

:bawling: :dead: :bawling:

Brian Donaldson 20th July 2004 02:34 AM

If it turned the copper pink, then it is exposed. The bubbler may be cooling the etch faster than you think. Get the good stuf....ferric cloride at room temp.

richie00boy 20th July 2004 09:32 AM

The copper did not go pink at all. However, I believe that when using persulphates it isn't supposed to, it's supposed to go greenish.

Good stuff? FeCl @ room temp? I've been doing that for years now and am sick of mess and stains, and it's still crap at room temp anyway.

Centauri 20th July 2004 10:11 AM

The copper should dull off pretty quick. I would suspect that the development process did not fully remove the coating - it can be sometimes hard to tell. Scrub away a little of the exposed copper area with steel wool and compare the brightness of the copper - you may be surprised. A very thin layer of the coating can still remain even though it looks clear.

Cheers

richie00boy 20th July 2004 10:20 AM

This is what I am beginning to suspect. I first suspected there may be somethign wrong with the development as when I withdrew the board from the etchant the first time, the solution ran off it, almost like a polished car.

Also, there are a couple of spots on the board where the copper has been removed completely, and these look like they may have been where small scratches occurred during the many removals of the board from the etchant.

So I guess the problem is old board and the resist not being fully removed? Also, this time I exposed for just over a minute rather than my usual 2:30.

Has anybody had much success with board over 1 year old?

GUILHERME 20th July 2004 10:25 AM

Quote:

Good stuff? FeCl @ room temp? I've been doing that for years now and am sick of mess and stains, and it's still crap at room temp anyway.
Indeed.

Bellow is a formula for a clean and dirt-cheap etchant that I've used for many years. I'm not the first to make it public and in fact it is printed in the instruction paper that comes with Kontact's Positiv 20 photoresist spray. But first read this warnings from start to finish:

:att'n: :att'n: :att'n: MAKE SURE YOU READ THIS WARNINGS BEFORE DOING ANYTHING :att'n: :att'n: :att'n:
Prepare, use and dispose of the mixture in a well ventilated area and while using goggles and a pair of rubber gloves. Don't store the used mixture for latter use and NEVER put it in a closed recipient. Buy the oxygenated water at 10% volume, which is what is usualy available for medical care anyway. Even if you have access to higher concentrations, don't use them - the mixture will became very aggressive and will eat both exposed and unexposed parts before you can say "big mistake".
Once you've finished using it, dispose of it by very slowly adding baking soda. Don't fall on the temptation of just dumping it in the sink or it will corrode your pipes all the way back to the main sewer.

The formula:
At room temperature, put one part of muriatic acid (aka hydrochloric acid - very cheap, easly accessible, it is used for cleaning toillets). Add one part of oxygenated water (aka hydrogen peroxide - even more cheap, can be bought in any local pharmacy). Thats it.

As you put the PCB in, it should go brown in the copper areas, if it doesn't add a bit more ox. water.

J.Guilherme

jmateus 20th July 2004 02:35 PM

pcb etching
 
Senhor Guilherme

How long does it take to get a regular PCB etched with your
solution?

I've seen a guy doing PCB in Portugal (coincidence) who used
pure "acido cloridrico", imagine! It took 10 seconds....

Of course this is not the case I suppoe...
Jmateus


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