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.
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.
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).
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).
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.
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.
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
Cheers
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?
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?
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:
MAKE SURE YOU READ THIS WARNINGS BEFORE DOING ANYTHING 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
richie00boy said:
Hi,
You should at least develop the PCB in the alkaline solution for 5 minutes. An underexposed PCB does not develop well, no matter how long and how hot you try to etch it. Make sure you have the right exposure time. This is rather critical. Old material requires somewhat longer exposre. My PCB material darkens the areas where the copper has to remain in the developer.
Hope this helps.
Hello JMateus.
It depends on how much copper area there is to etch. Last one I did (some 25x15 cm.) took about 20~30 minutes. If you've got the patience to stir the solution as it etches it will go noticeably faster.
If time of etching is important (which in diy I don't think it is), raising the oxygenated water volume percentage will dramatically accelerate the process. It will also generate more heat and fumes in the process. Again, I DO NOT RECOMEND THIS.
J.Guilherme
It depends on how much copper area there is to etch. Last one I did (some 25x15 cm.) took about 20~30 minutes. If you've got the patience to stir the solution as it etches it will go noticeably faster.
If time of etching is important (which in diy I don't think it is), raising the oxygenated water volume percentage will dramatically accelerate the process. It will also generate more heat and fumes in the process. Again, I DO NOT RECOMEND THIS.
J.Guilherme
IT is definitely too cold.
I put a stainless steel tank on a small burner on my stove set to medium. In the SS dish I put some boiled water, I then put a smaller glass dish into the SS dish floating on the water, I put my etchant into the glass dish and wait for it to come up to temperature (usually about 5 minutes or less) and this keeps the whole thing heated nicely while I am etching a board.
I put a stainless steel tank on a small burner on my stove set to medium. In the SS dish I put some boiled water, I then put a smaller glass dish into the SS dish floating on the water, I put my etchant into the glass dish and wait for it to come up to temperature (usually about 5 minutes or less) and this keeps the whole thing heated nicely while I am etching a board.
It is not too cold I have rubbed a small part of the board with wire wool and put back into the tank. Wthin 10 minutes (the recommended time) the rubbed part was perfectly etched.
Elso, I appreciate what you say but my board also develops so you can see the tracks, too. What is puzzling me is that the developer appeared to clean away the unwanted areas perfectly. Even under close scrutiny I cannot see any tint to the copper.
I will cut some more board and expose for much longer and see what happens.
Many thanks to all who answered.
I have rubbed a small part of the board with wire wool and put back into the tank. Wthin 10 minutes (the recommended time) the rubbed part was perfectly etched.Elso, I appreciate what you say but my board also develops so you can see the tracks, too. What is puzzling me is that the developer appeared to clean away the unwanted areas perfectly. Even under close scrutiny I cannot see any tint to the copper.
I will cut some more board and expose for much longer and see what happens.
Many thanks to all who answered.
A few comments that may help from http://www.atmsite.org/contrib/Webb/pcb/
I suspect your old board has a passive surface layer, a thin but tight film that's developed over the storage period that resists corrosion. Several minutes dipped in Coke (dilute phosphoric acid) would probably shift it and allow normal etching to proceed.
I had actually read that article you quoted when I was Googling to try and see if there were any reported problems with etching with Sodium Persulphate. One thing that concerned me about it was on the tub of crystals I got, it says under no circumstances allow to go above 50 degrees C or it will render the solution less effective and also massively reduce the storage life.
Thanks for the tip on the coke. I will definitely try it as I have about 4 other boards that are awaiting etching and I don't want to waste them and have the hassle of cutting and developing another lot.
Won't the coke also take off some of the resist though? And if persulphate is an acid, how come that doesn't get rid of the unwanted film? Or is the persulphate just an oxidiser and I need an acid to shift the film?
Thanks for the tip on the coke. I will definitely try it as I have about 4 other boards that are awaiting etching and I don't want to waste them and have the hassle of cutting and developing another lot.
Won't the coke also take off some of the resist though? And if persulphate is an acid, how come that doesn't get rid of the unwanted film? Or is the persulphate just an oxidiser and I need an acid to shift the film?
That does indeed happen, the hot solution gradually breaks down to sodium sulphate and sulphuric acid, with oxygen bubbles coming off.richie00boy said:
2Na2S2O8 + 2H2O --> 2Na2So4 +2H2SO4 + O2
If you're making up small quantities & discarding after use that wouldn't be a problem.
Vinegar is acetic acid and, according to the link, "Acetic acid, CH3CO2H, also dissolves copper, but unfortunately is also a very good organic solvent, dissolving ink from virtually any source. "
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