what causes the black corrosion /deposit on the pcb?

Hello
I have been battling this issue at my home electronic for quite a while. any electronic after using about a year or so start to show sign of black carbon deposit on any shinny part of the pcb. I thought it was the humidity in the basement that caused the issue but I checked and the humidity is only 35%. anyone have any idea what could cause this issue?

Welcome to ETO!
Are you a smoker?

That is odd. I have never seen it on a board.

You refer to it as a carbon deposit. Do you know that it is carbon? Carbon itself will not dissolve in simple acids, like dilute HCl. Another black compound I would consider is copper (II) oxide (aka "cupric oxide"). That will dissolve in acids. (https://en.wikipedia.org/wiki/Copper(II)_oxide)

If it is copper (II) oxide, left unanswered is how did it get that way. Do you have chemicals in your basement? Some solvents, such as methylene chloride or chloroform may also cause copper to change color, but I have not seen that dense a coloration with those reactions.

I am not a smoker and my house is fairly clean. the only conclusion I can think of is there are some fine particles in my basement and those shinny part attract them. I have had 5 broken hard drives because of this issue and it spread to my router the other day when the router died. still trying to figure out the cause. the air quality in my town is always good. I have no issue with the electronic on the main floor but pretty much all electronic board in the basement suffer this problem after 1 year of use. someone suggested its the furnace causing the black soot but I am running natural gas furnace.

Is it carbon or a copper compound? I think a localized deposit of carbon like that is unlikely.

After looking at an enlargement of your post, I would also consider growth of some microbe -- like a fungus or algae. Despite the anti-fouling nature of copper, some organisms are quite resistant to it. Black streaking on roofs is due to some algae. I do not know of an organism that is dependent on high copper concentrations, but it is an essential trace element.

Can you scrape a little off and look at it under high magnification (microscope at 10x objective should be sufficient).

Wow, never in 30 years have I seen that .... my guess is that it is organic. Try a little bleach or vinegar on a Q-tip to see if it comes off.

I will get a microscope and post some image once I got it. organic material eating copper. that is very interesting. someone suggested it's the black soot from furnace , some say its H2S in the air that acting up with the copper.

The affected equipment is said to be in a basement with a natural gas fired furnace.

My first reaction was to wonder if the copper on the circuit board was reacting with Carbon Monoxide from the furnace.

Can carbon monoxide react with copper to produce copper oxide and carbon? (Both of which are black.)
I don't know, I last studied chemistry 50 years ago.

If this is a reaction with carbon monoxide, the important thing is GET THE FURNACE CHECKED AND SERVICED.

Carbon Monoxide is a KILLER.

JimB

Whether it's furnace gases, black mould or other organic cause, it suggests the basement is inadequately ventilated.
A furnace needs a fresh air supply and proper exhaust extraction. How are they provided?

The fine particles in the air is making the chemical reaction after it comes in contact with humidity whatever it might have in the air in the basement. That is what causing the issue. Why don't you change the room? It will be a better idea.

JimB
I don't think it is carbon monoxide reacting to give copper(II) and carbon. Rather, I would expect copper oxides to be removed by CO and did find some discussions of copper + oxygen + CO to give CO2.

Hydrogen sulfide blackening is a possibility, but certainly the smell woud be a clue. Just FYI, the permissible level of H2S is 20 ppm (lethal is about 600 ppm), yet it can be smelled by most people at 0.0005 ppm (from Wikipedia and elsewhere).

Low levels of H2S can cause darkening of copper, but what is stunning about the OP's image is the density (apparent thickness), uniformity, and dullness of the deposit. He also reports that several pieces of electronic equipment have been ruined. Tarnished copper, as with H2S, or copper oxides (which are non-conductors at room temperature) might be ugly, but wouldn't cause dysfunction per se.

Here is a blow up of a section:


Note the edge on the area on the right. Molds can grow like that before turning black. So far, we have not received any information about whether the coating is strongly adherent or soluble in acid.

The uniformity and density of the blackening makes me wonder whether the PCB's were treated with something, perhaps to clean them, that caused the discoloration. It is also possible, that the OP treated the boards with something like a bluing agent (w/selenium) or other reactive chemical (e.g., tannins and related polyhydroxyphenols). That is NOT an accusation, but merely put forth for completeness.

It's apparently not copper areas that are affected. The blackening has spread over what looks like tinned traces/solder-resist/conformal-coating.

here is another photo of my hard drive that suffer the same thing. all solder points are blacken. I have ordered a microscope and will post more photo o nce I scrap the blacken material off.

Cannot tell you what it is but have seen something similar on washing machine boards , but not nearly as bad as what you have.

what i can tell you from my experiences
It is only on one style of board from a single manufacturer.
When i get the board, the unit is erratic.
It only appears at the vias like you hard drive board.
It normally looks like little black lightning strikes radiating out from the via hole. Like tiny arc overs. Sometimes up to three or four lines per via, but sometimes it is all filled in black but not as dense. It's worse when vias are close and they end up bridging over. These little black lightning rods radiating out from the via is not anything i have seen before. First time was probably a couple years ago.
These washing machines are maybe 3-7 years old. Probably did about a dozen or so. I thought it was something to do with the solder or assembly as it's only on one type board and style of machine. Like some sort of weird tin whisker thing and moist environment.
Sometimes it's just in one corner of the board and sometimes it's random over several areas on the board.
Your build up is less than a year, on multiple products, every via on the board and very dense.
I use isopropyl and q tips to wash it away, some need to be rubbed harder and some need extra fluid flooded on the board to clean it up.
I probably don't get down into the vias, but they appear to be plugged with a board coating. Either way, have not 'yet' had some come back saying "it's doing it again". Perhaps it does and they just toss the unit.
The clean up restores the operation.

I do not know if it is the same thing or not. However your hard drive board looked similar but not near as bad, so i gave you my two cents for free.
cheers

Ps. Where is your location? Near salt water?

Thanks pfofit, I will post more update once I received the microscope , perhaps sending a sample of this black stuff to a local chemistry lab to determine what it is.

At this point, I suspect it is microbial. A more productive approach might be to perform a "Scotch" tape prep.* Any clear cellophane tape will work. There are detailed descriptions on the Internet for Class II/III pathogens, but since you have been living with the stuff, I would just do it and take the sample to a microbiology laboratory (i.e., one with lactophenol cotton blue mounting medium), and check for mycelia or spores (more likely the former). It is a very basic test, even high schools may have it. Certainly, university or hospital laboratories will have it too.

You will be looking for any fungus/yeast form/mold/mould (alternative terms and/or spellings). Of particular interest are the dematiaceous fungi. That is not a strictly taxonomic term, but rather a phenotypic term describing a large group of black fungi with melanin in their cell walls. At first, I was a little reluctant to mention that as a prime suspicion, as it didn't explain the propensity for copper areas and vias (I was thinking something that needed or grew well on copper). However, on a little further thought, it occurred to me that those areas were plated with a gold flash. Then the coin dropped. Apparently, that plating involves use of citrate/citric acid and it is not completely removed in the wash (as in "really" completely) and molds can use it as a carbon source (a requirement for all life on Earth). You can search for mold growth on gold plating.

John

*You place the sticky side of the tape on the area, remove it, then place the sticky side down onto a drop the of the stain on a glass slide and examine under a microscope. There will be a very light blue background and dematiaceous fungi will be obvious (look in any textbook) with brownish coloration to the cell walls from melanin.

As a test, I would take a piece of freshly cleaned copper -- like some virgin fr4, or an penny, or some wire, etc -- and leave it near where your electronics are.
The next thing I'd do is test for H2S in the air by bubbling the air through a cupric solution such as copper sulfate (easy to get). If there's any H2S -- whether from combustion, or from microbes -- you'll get a black precipitate. You should, however, be able to smell H2S at any level that would cause any noticeable damage such as yours.
Are you sure nothing liquid has been getting on your boards??
Are there any chemicals or foods stored in your basement?

If this is the area from which the black stuff has been scrapped, it does not look like a copper sulfide, as there is no "raw" copper showing.


I hope the OP will update us.

John

so I take the whole pcb out of the case and as I flipped to the otherside, I see much worse black spot lol. I used the alcohol to clean it and its very hard to come off. I used eraser and the black stuff came off easily and leaving a silver coat on the cupper. I then have to use a utility knife to scrap the silver stuff off to reveal the copper. I am suspecting it is copper dioxide and exact cause is unknown. there is no water damage as it has been sitting on top of the shelf for 3 years.

I am fairly sure it is not copper dioxide (aka copper peroxide). Perhaps you meant cupric oxide (CuO), which is also called copper (II) oxide.

Have you tested solubility in acid as suggests early on?