All of my veroboard-copper-tracks gradually slowly becoming blackish, scratch-like marks, or sometimes brown-black patches.

Here's one from extreme (sorry for bad soldering, it is 7- 8 months old, when I was beginner).

are these copper tarnish

Fig: Black patches, marked with arrow. Are they sort of copper tarnishing?

However all these blackened tracks are yet fully conductive. But would they create problem later-on?

I can prevent it by using a thin layer of solder, but is that okay? (since no-one around me do it on a veroboard).

Is there any other available alternatives in market? (like readymade PCBs use a green paint).

Another older board

This board around same time, 5 or 6 months old.

unused board

A qute-recent un-used board from stock at home, approx. 3 or 4 months old. It was not like this when I bought from shop.

much new Much new board. 1 or 2 month old. (btw it is a repetition of circuit of first one). Only a few little places showing any visible reaction.

a stranded wire

Other than veroboards, here is a piece of stranded copper-wire, maybe approx an years old. It was kept in open air. the inner-portion (which has been split-out today), is normally shiny, but the terminal portions is blackish-brown, almost lustreless, and as brittle as as half-burnt hair.

Whereas those wires were kept inside a tight aluminium-box, are almost like new-one, and exposed-portions are just more deep-coloured and slightly less-shiny.

Once I also once saw, some pieces of stranded wires were kept inside a shaving-box (whose strands were used as fuse), accumulated green waxy rusts in places to places!!! (they were disposed, so could not be photographed)

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    \$\begingroup\$ Use a spray lacquer. \$\endgroup\$ – Andy aka Sep 13 '16 at 7:51
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    \$\begingroup\$ @Andyaka: I just want to know where he lives so I can avoid the place. \$\endgroup\$ – jonk Sep 13 '16 at 7:53
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    \$\begingroup\$ I just don't want to be around a chemical atmosphere that is causing that. I've got lots of veroboard here -- some decades old -- and none of it looks like that. Well, not unless half the parts suddenly exploded because I randomly crossed both hot sides of the 240VAC split phase on the board. Are you keeping these under your sink, next to the sodium hypochlorite crystals container. \$\endgroup\$ – jonk Sep 13 '16 at 8:17
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    \$\begingroup\$ I'm from Kolkata, West bengal, India. yes air-pollution is common here, As well it is a very hot place, and rainy-season is going on. I think that is more important factor I think. \$\endgroup\$ – Always Confused Sep 13 '16 at 8:22
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    \$\begingroup\$ I'm truly sorry to hear that. I just looked it up and there's a wiki page on the atmospheric and drinking water pollution there. So that looks very serious to me. Add heat and humidity to all that and I can see it happening to the boards. I wish I had a solution not just for your boards, but for you. But just oxygenation and moisture will eat copper, I suppose, and I think it does turn black. \$\endgroup\$ – jonk Sep 13 '16 at 8:30

Your photos are useful. Your last photo shows the corrosion spots around the perimeter of the board. The center of the board is relatively free of corrosion. This tells me that some of your corrosion is due to chemical transfer from your fingers to the board.
However, photo #3 is most disturbing - looks like little hand contact. This one suggests an environmental source of corrosion.
Your suggestion to "solder-plate" bare copper is Ok, and allows you to re-work solder connections at a later time. Protecting surfaces with a "paint" makes re-work much harder and more dangerous - heating "paint" with a soldering iron could release dangerous fumes.
Your photos suggest to me that your flux is indeed a rosin type, and I see little corrosion due to active flux. However, be aware that some of these fluxes are "heat-activated" - they clean actively while hot and liquid, then are supposed to de-activate at room temperature when they go crystaline. This appears to be the case in your photos.

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  • \$\begingroup\$ Yes your analysis is very helpful. look at bottom right portion (but not at terminus, but towards middle) of fresh bord ( # 3), there is one blackish fingerprint mark. \$\endgroup\$ – Always Confused Sep 13 '16 at 17:40
  • \$\begingroup\$ Maybe trace of sweat from my finger-tips added some salt as user @rtdsc told, that facilitated the corosion process. \$\endgroup\$ – Always Confused Sep 13 '16 at 17:44
  • \$\begingroup\$ may be the same happens for old copper coins used once upon a time. \$\endgroup\$ – Always Confused Sep 13 '16 at 19:04
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    \$\begingroup\$ @AlwaysConfused - My own copper boards appear as your last photo after a month, and I'd guess that many others have similar experience. Biology and its chemical reactions to Cu are not for this forum. Your photo #3 is exceptional. Since its source is different from others, it may have come to you not properly factory-cleaned of etchant. \$\endgroup\$ – glen_geek Sep 14 '16 at 5:16
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    \$\begingroup\$ @AlwaysConfused - am proposing that you have an air-borne contaminant, carried by water vapour (humidity). If copper-etching chemicals are stored nearby (even if sealed) or if they share air-flow, this could be the source. Your environment of heat and humidity is a very difficult one that makes a small contaminating source very active. \$\endgroup\$ – glen_geek Sep 14 '16 at 7:22

Another option is to "electro-less" (immersion) tin-plate the boards when new. Mix the powder into (distilled) water, dip board, wait a few minutes, remove. Puts a layer of tin onto the copper, which will resist corrosion for awhile. Same can be said for electro-less nickel-immersion-gold (ENIG), although this is more expensive.

But it seems to me that something else is at work here. That is an extreme amount of corrosion, and if it hasn't caused electrical problems already, it looks likely to start soon. A tin plate is really only a band-aid solution, as after the tin is consumed, the copper will start corroding. ENIG would be better, but still not impervious. So this may buy you some more usable time from the board, but not solve the problem completely.

As for the corrosion itself, some common chemicals which could be contributing to this are halogen salts. Fluorine, chlorine, bromine, iodine... if any of these are present near the PCB's (even in trace quantities) they will readily destroy them.

But since it looks like most of the corrosion is near solder joints, I strongly suggest you obtain several different fluxes purpose-made for electronics work. Yes, solid rosin can be used as "flux" but there are many newer formulas today (completely different chemicals) which are much better in every way. First and foremost, acid-core solder on PCB's will destroy them. Same with zinc chloride flux. (I don't even like these for soldering copper pipes, they will corrode!)

Try these types of flux (you may need to find a local distributor or import these): Farnell, Mouser, Digikey, etc.

  • "Liquid" is just that, some are very good.
  • "Paste" is fairly thick and goopy, so holds small SMT parts in place.
  • "RA" stands for "Rosin-Activated", meaning it cleans well but is slightly more acidic. Good for "dirty" boards and parts.
  • "RMA" is "Rosin-Mildly-Activated", meaning it cleans ok, and is less acidic. Good for fairly new and clean boards.
  • "R" stands for "Rosin", meaning it is traditional rosin flux, no additives. It is least acidic, but also cleans less. Good for new parts and boards.
  • "No-clean" claims that it does not need cleaning.* May be a synthetic compound, not rosin at all. (ChipQuik smells like sizzling beer!)
  • "Water Soluble" tends to be rather strong and acidic, but can be cleaned with water.
  • "ROHS lead-free" can withstand the higher temperatures of lead-free soldering.
  • Flux Pen - many have tried these and do not like them. Try at your own risk.

Now of these, some fluxes must be removed after soldering. "Water Soluble flux" remains acidic after cooling, so must be removed. WS is also not recommened for fine-pitched parts, as it is difficult to remove all of the product, even if detergent is added to the rinse water. An ultrasonic bath may help.

RMA and RA fluxes may become slightly conductive as they absorb moisture. This is mostly an issue for high-impedance circuits. For low-impedance (simpler) circuits in mild environmental conditions it matters little, but R(M)A should be cleaned for best reliability. Always check the flux manufacturer's datasheets. R(M)A generally won't attack metals like water-soluble flux can.

Here is a video about testing several fluxes. Common Brands to look for:

  • Kester
  • MG Chemicals
  • ChipQuik
  • EdSyn
  • Chemtronics

Note that "no-clean" fluxes are somewhat a misnomer - all fluxes dissolve the oxidization and impurities on the metals, which can remain in the flux and cause problems with conductivity later. Always clean the board (remove all traces of flux) after soldering for best results.

The final step for PCB protection in an environment such as this would be conformal coating. This is essentially encapsulating the PCB in a plastic coating which should block all humidity and corrosive compounds from reaching it. For a one-off design though, a simple dip of the PCB into urethane "clear" would probably work just fine. If any corrosive compounds are present before coating, the coating will not stop this process and the PCB will still corrode.

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  • \$\begingroup\$ What I use is solid resin. (I don't know is it same as rosin). Also in our class, paste and resin any one is used, I'm using resin at home. Did you mean it can cause that? Should I use paste instead resin? \$\endgroup\$ – Always Confused Sep 13 '16 at 14:30
  • \$\begingroup\$ Trace amount of salt can com from hands (my hands sweat a bit), or may come from dust from air or cardboard boxes (previous clothing-packet from my home). \$\endgroup\$ – Always Confused Sep 13 '16 at 14:34
  • \$\begingroup\$ You are correct about the fact "salt", because those-boards' copper-side get fingerprints or finger's touch, become black within few days. While those boards hold strictly only at margin, doesn't turn black so fast. \$\endgroup\$ – Always Confused Sep 13 '16 at 14:53
  • \$\begingroup\$ Veroboards probably come with a very thin layer of resin or lacquer or such, because when my fingers are sweaty, the new boards feel like slight sticky (not like copper-wires), and catch a deep fingerprint. And the moment when the solder is just applied, i.e board is warm, it caught more prominant fingerprints. \$\endgroup\$ – Always Confused Sep 13 '16 at 15:03
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    \$\begingroup\$ BTW, solutions for immersion tin plating are not supposed to go down your sink after use. Especially in India where only God knows where the drinking water comes from. \$\endgroup\$ – Dmitry Grigoryev Sep 13 '16 at 15:07

Applying a layer of solder to your board is going to give you basically the same result as HASL finish. It has much better shelf life than bare copper, but it won't last forever either. With time, two things will happen:

  • tin will oxidize, though slower than copper
  • copper and tin will diffuse into each other, creating bronze

Both processes will result in worse solderability and worse electrical properties of the traces.

Here are a few pointers to prevent the damage in the future:

  • keep your PCBs in a dry place (I keep mines in a plastic food container toghether with some silica gel)
  • buy PCBs with a better finish if you can. HASL is much more durable than bare copper and not too expensive.
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  • \$\begingroup\$ PCBs with green layer never caused any such problems. Veroboards actually give more flexibility to think-out new circuits , and as a student I found it more helpful. Nothing else. \$\endgroup\$ – Always Confused Sep 13 '16 at 14:40

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