Sorry, I didn't understand you well. Google-translated word "lightly" as "gentle", so I don't know where to be gentleJoe g said:i just clean it very lightly ( i use bar keepers cleaner before i etch it, to remove any toner residue and to double check traces are correct before etching). just go lightly
w/ the cleaning.
It depends what do you mean under "pitting"; for me where is pitting there is no copper and you can see small hole through copper, especially if you're working with FR4 and inspect PCB toward source of light. BUT, in my case, I can "ferret out" that dot with a needle and then orange/yellow copper appear! So I concluded it is CuO, not a toner. But OK, we can call that "pitting".duffy said:So it IS pitting. Pitting is often caused by leaving it in the etchant too long. Are you heating the solution and agitating?
Hi to everyone!
Long story short: In last dozen of attempts(I'm using toner-transfer method) everything seems fine until I remove toner after apparently successful etching - I got black stuborn dots and marks all over the copper (regardless whether it is a larger copper filling or trace/pad) - please see picture. It is, as I know, black copper-oxide - I can't remove it by any means! It is not "standard" pitting, as someone could conclude from picture - copper is not etched totally in "dot-areas" - it looks like somebody imprinted black particles into healthy copper surface! I tried different plates (from different batch), every sort of papers (including TRF-Green!) but with no avail. Note: after laminating (toner sticks to PCB very well), if I remove toner (without etching) I just get clean copper surface!
View attachment 62790
I'm using muriatic acid (20%) and hydrogen-peroxide (12%) without adding water.
Any opinion appreciated! Especially if somebody had the same problem!
TIA!
I totally agree with you!PCBWING said:Chemical reaction is always very complicated. Side reaction or toner stripping is possible.
I will, although it is messy. I can't buy it in my town, and I must have certain PCB "yesterday"...PCBWING said:Try Ferric chloride [FeCl3]
As first, thank you for clarification about term "pitting". I said before that is not pitting, but after your "definition" I can say -YES it IS pitting (also as Duffy suggested)! And, yes, it is clearly the same thing as in your picture (although it doesn't look "so black" like on my PCB)!John said:"Pitting" does not mean the etch went through the entire copper layer. In this image you can see a similar pitting from a defective mask...
It is not copper oxide on the surface of copper before laminating! I cleaned the copper thoroughly with: fine sand-paper, some dishwasher-detergent and "Scotch-brite" sponge, and finally with acetone - it is very clean and shiny (actually it was pretty clean even before cleaning).John said:I doubt it is a copper oxide on the surface, because both copper oxides are soluble in HCl, which you had an excess of. Of course, in the crevice of a pit, there could be some copper oxide.
I will try! Did you mean real paint or "permanent-marker" pen (like "Sharpie" or "Edding") because in my experience "Sharpie" or similar has no chance in HCl+H2O2 ?John said:To prove it is pitting, make your regular toner transfer. Then use a paint marker over some areas. After etching, I will bet the areas with paint to not have the black spots.
You could also try one of those papers that is supposed to be ironed one over the resist to fill defects.
I agree! I think peroxide is more problematic! I know for many "recipes" how to mix HCl and H2O2, and I always wondered why, for example, for 1 liter of solution you have to add about 700ml of (preferably distilled water) - not counting the water contained in, say, 20% HCl solution! Why so much water? It seems that "pure water" plays bigger role than bare concentrations of HCl&H2O2! Currently, I'm using HCl(20%) and pharmacy grade 12% peroxide WITHOUT adding any water! One more thing: there are not any little bubbles (as I seen (long time) before, when I used to add extra water)! The solution turns light green immediatelly after putting the board in, but etching took over an hour!John said:Peroxide/HCl etchant is quite aggressive in my experience. I use the photoresist method. You could actually see it attacking that resist. So, I would second the suggestion to try ferric chloride.
John, I can "smear" visible pores on the toner with Edding permanent marker instead of whiteboard marker. Anyway, I think I got some clue! I just found on the (plastic) bottle with my HCl that it is produced 1997 (!) and shelf life is 3 years! If so, my HCl is expired for more than 11 years!? Did you know that muriatic acid has shelf-life? I didn't! I will now try to measure pH of it, and tell you (all) result. So, I still think that black spots are CuO, a mineral also known as tenorite (Wiki Tenorite). If I really have too weak acid, I can't get CuO dissolved! So I must repeat soaking PCB in fresh HCl, to see if it is really tenorite!
The question is: what causes forming of tenorite? Some time ago I put blank piece of PCB into pure peroxide, and copper just turns brown (as it should). So, peroxide alone is not strong enough oxidiser to make "higher grade" oxide of copper, i.e. CuO.
Another thing (maybe you can figure something out): during one of my attempts to make PCB (with this weak (as I think) HCl) I put some HCl into container and added very little peroxide (no additional water); I put PCB in that solution and color of a liquid almost instantly turned to light green BUT copper didn't change color to brown (as usual)! I waited some 10 min. without any reaction. So I concluded there must be too little peroxide; I added a bigger "splash" of peroxide (and a little HCl) - the whole PCB changed color to BLACK!? I realised that PCB is already ruined enough so I remove half etched board from solution and saw that all remained copper is BLACK!? Under running water almost complete toner together with protective layer, simply detached from board in large "patches". Maybe deteriorated HCl "enriched" solution with additional oxygen that, in combination with peroxide, caused such a strong oxidation? I don't know, I am not a chemist.
I found this chemical equation, and I hope it would be useful to you.
View attachment 62815
which of the several other known reactions is the predominant reaction under the conditions of light
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