Preventing corrosion of PCBs in storage

[Lomax]

I recently got a bunch of blank PCBs, which will likely take me a year or two to get through - what is the best way to store these to prevent the exposed copper from oxidising? These are uncoated boards btw - I will be isolation milling them.

[Ian.M]

Are you equipped to store them in a dry inert atmosphere?
If not, its probably better to simply clean to bright copper immediately before use.

[nicknails]

Maybe vacuum seal in a bag with a silica gel packet?

[helius]

CorTec has a line of VpCI products that can be used to prevent corrosion in storage (films, papers, and satchets) but I don't know whether there is a distributor in the UK.

[Lomax]

An airtight container with desiccant sachets inside might be the best option. I was thinking maybe I could spray them with something which is easy enough to clean off when it's time to use them.

[Ian.M]

No. I wouldn't recommend vacuum sealing. I read some articles that plasticizer migration from the bag was a major issue.  Apparently a desiccant didn't help.  What did help was a foil bag with an oxygen adsorber or purged with dry nitrogen. 

OSP treatment was also recommended but if the O.P.'s going to be isolation milling them then a coating that gunks up the cutter is undesirable.  I suspect that a mix of white rosin and paraffin wax in Naptha applied as a thin film with a spray gun would be a fairly effective preservative coating/flux, but if anything needs to be glued to the board that will make it more difficult.

[helius]

You could wipe them with a high-grade motor oil (like Royal Purple) and clean it off with thinner when you are ready to use them. There are specialty products that may be easier to handle like Cortec VpCI-377 and -239, which may not require cleaning as the film they leave is not oily.
Then there's the option of storing them with pieces of camphor. I'm not sure how well it works compared to commercial inhibitors, but it's better than nothing.

[elecman14]

I would recommend doing nothing to the PCB when you store it. Prior to use, grab a high grit sand paper and give it a quick sand. In fact you may find that it does not matter. I have some copper clad that has been stored in a fairly damp environment (basement) for around 10 years. It is still solder-able and does not show a large amount of copper oxide.

[Ian.M]

If yoiu are trying to avoid cleaning the copper before use, I would suggest wrapping with acid free tissue paper then with Aluminum foil then store in an airtight container with an oxygen adsorbing sachet.   No Oxygen = no Copper Oxide buildup. However the copper needs to be fingerprint free to start with to prevent other corrosion buildup.

Cleaning is probably more cost-effective: you don't have to invest time or money till you need the board, and can be certain the surface is clean bright copper.

[bji900]

I would suggest picking up a large tuperware container and placing your PCB's inside of it. Get a small damp rid container and then place the entire container in a large plastic bag in a cool area. That will minimize the primary oxidation source of moisture.

[djnz]

Edit: nvm forgot that these were blanks.

[BrianHG]

If you never touch the boards, ie no fingerprints, use cheap latex gloves when handling, and you have a clean tupperware type container, and a source of steam distilled water, you can keep the PCBs in the water.  As long as the water is pure and there are no other oxidizing elements on the PCB, keep the tupperware container sealed when storing, the copper should not oxidize at all.  However, it only take a little contamination to mess this up.
Ohh, and if the water freezes, you may damage the PCBs.

[Spuddevans]

Another option would be if you know someone who has a TIG welder. Use the ubiquitous air-tight box, pop the PCB's in the box, take the lot to the TIG welder friend, get him/her to fill the box with pure Argon (being heavier than air will displace all the oxygen in the box allowing you to pop the lid back on without losing all the inert gas) Pop the lid on tightly, and store upright.

If you are careful, you may be able to, gently, remove some PCB's without losing all the Argon.

Tim

[Ian.M]

I think the best bet for inert atmosphere on the cheap would be a mylar foil ziplock bag and an Oxygen absorber.  See http://www.fresherpack.co.uk/products/12/55/oxygen_absorbers_-_300cc/

[Lomax]

Wow, so many suggestions here, from doing nothing to using exotic gases I had hoped someone knew of a spray protection which can be soldered through - would be easy enough to lay out the boards side by side, give them a good coating (repeating on the reverse for double sided boards) and just chuck them in a box. Something like ElectroLube CPL200H perhaps? Ideally such a coating could be left on throughout the process, but if I had to wipe the boards with a solvent before use then that's no biggie - the important thing is that they haven't oxidised, and that whatever was done to keep them pristine doesn't interfere with solderability, or affect the substrate negatively. I think storing them in distilled water is not such a good idea: the copper might be fine, but the FR4 substrate is sure to absorb some water over time. Argon and other protective gases is too much hassle. Oxygen absorbers sound good, but would need to be renewed (I'm assuming this means replaced). What I've done, for now, is to wipe the boards clean with alcohol (they already had some finger prints on them, from the supplier ), put them back in their respective bags (too keep the different copper thicknesses from getting mixed up), and put all this in an airtight Tupperware style container, together with 3x25g of fresh dessicant.

[anishkgt]

Or maybe wipe with Wd40. Just a thought not sure how well it work.


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[Lomax]

Or maybe wipe with Wd40. Just a thought not sure how well it work.

WD-40 is good for some things, I use it for cleaning handtools and loosening rusted bolts, and its capabilities as a lubricant when milling aluminium are widely acknowledged - but it's terrible for most other uses and provides little, if any, long term corrosion protection. Typical mistakes I've seen includes lubricating bicycle chains, and "fixing" scratchy pots, both truly terrible uses for "Water Displacer 40", which was originally designed for the protection of stainless steel tanks in missiles. I basically hate the stuff, though that may be partly a consequence of its ubiquity. Rule of thumb: if you think WD-40 might be good for X, it probably isn't.

[anishkgt]

Well that is something new to learn. Thought it had that oily base which would protect the layer of copper.


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[Lomax]

Well that is something new to learn. Thought it had that oily base which would protect the layer of copper.

I didn't say it won't work - only that based on personal experience of "alternative uses for WD-40" it probably isn't that great. Because WD-40 isn't that great.

[CatalinaWOW]

I am going to second those who say do nothing.

I have blank PCB that I have owned over 20 years (purchased as scrap/second hand) that still solders fine in spite of a noticeable oxide layer.  Flux is wonderful stuff.  Since the OP is not etching his boards none of the other reasons for keeping boards shiny bright apply.

Just normal relatively clean storage.  Mine is in plastic storage bins, and over the years has been in various garage and basement locations, so no meaningful environmental control is required.  If you want it bright and shiny for use (either for aesthetic reasons or if you are doing fine pitch reflow soldering) then any of the abrasive cleaning methods is fine.  I use (off brand version) Scotch Brite pads, but lots of things will work.  Just follow up with washing to eliminate the debris.

[CraigHB]

I have a stack of blanks I keep in a drawer stored in a zip-lock bag.  No issue and the stock is quite old now.  Of course I live in a dry climate and that helps a lot.  I find WD40 does do a good job of keeping my tools and metal items from corroding, but just regular oil will do a better job.  The advantage of WD40 is it's easy to remove with just about any kind of solvent.  The formula for WD40 is mostly mineral oil and mineral spirits.  Mineral oil is considered one of the best for preserving and cleaning hand tools.

[Ian.M]

WD40 has a bad rep for oxidising to form hard to remove gums and varnishes.

[Rudane]

The two obvious answers are:

1. ENIG finish. Basically, tin the board with a small amount of nickel and a thin layer of gold. This would be done by the manufacturer; if it's not done now it would be too costly to do it. For future reference you should know that if you are going to store your boards unpopulated, look into an ENIG finish.
2. Invest in the parts to populate all the boards now, then store them.

As for storing blank PCBs: it's a slight risk. Using copper or steel wool to buff the board before soldering works well, but remember that you are removing a thin layer of the copper on the board.

[IconicPCB]

I do exactly what you wish to do.
And I do nothing with respect to the copper surfaces.
I do not handle the blank material unnecessarily, I keep it in original packing until i need it.
I do use a buffing ( scouring ) pad  to clean the copper surfaces prior to machining.
More specifically i use a scourer not unlike a kitchen scourer  with the difference that the plastic fibers are loaded with grit.
Superior to sandpaper, finer grit than sand paper resulting in less virgin material removal,
I purchase these scourer pads from the local automotive paint and supplies shop.
They come in a number of grit sizes and loads.
White pad has no grit content. A brownish purplish pad is the most aggressive and just right to polish up the copper.
These pads are intended to be used in automotive painting shops so they are not likely to damage copper.

[Ian.M]

Actually, silver plating them would be better than ENIG.  You can do silver plate at home, either buying the individual chemicals or with a Caswell plating kit.

Silver:
http://www.pcbdesignschool.com/2009/08/01/immersion-silver/ and http://www.pcbdesignschool.com/2009/08/02/immersion-silver-storage-and-handling/

N.B. Note the recommendation to avoid dessicant sachets and other sources of sulphur compounds.  That's less of a problem with bare copper but still something to be aware of.

v.s ENIG
http://www.pcbdesignschool.com/2012/11/25/when-enig-doesnt-solder/

Personally I'd look again at Oxygen absorbers - if you use an over-size one it will still be effective after a fair number of brief bag openings.   Split your stock up into several separate bags, each with a selection of thicknesses, and don't open the next until the previous bag's run out of one or more thicknesses, then consolidate into the next bag.

[Gregg]

Search for no-ox-id. 
https://www.amazon.com/NO-OX-ID-Compound-Electrically-Conductive-Grease/dp/B00HSW341A
It is used extensively in the high amperage DC world like telephone and wet cell lead acid battery connections.  It is like an industry standard.
It has a grease like consistency and only needs to be applied in a very thin layer.  I have seen 30 year old copper bus bars that look like new that were coated with it and were in a terrible environment of a battery room with tons of vented lead acid batteries.  It can easily be removed with acetone or 99+ IPA.   

[tautech]

I have a stack of blanks I keep in a drawer stored in a zip-lock bag.  No issue and the stock is quite old now. 

+1
I've got blanks that are at least 5 yrs old now in the plastic bags they were supplied in and laid flat and stacked in a drawer. Still look perfect. Considering one would likely do a pre-etch or a a light abrasive scrub before use there won't be any problems.
I've still got a small bit of paxolin PCB bought when I was a kid some 40 yrs ago and although it's quite oxidised (dark brown) from years of sitting on a shelf with a bit of elbow grease it cleans up OK and etches fine

[KL27x]

They come from the factory sealed in plastic. So, yeah, that would be pretty ideal. If they have corroded, already, I'd do same as I do for my toner transfer boards. Wipe on a coating of rosin flux with a paper towel. This dissolves and wipes away the oxidation. When the residual flux dries out, it seals the surface of the board fairly well against further oxidation and humidity. When the flux is thoroughly dry, it is no longer tacky. But if it isn't broke, yet, don't fix it. Seal it up and forget about it.

[MakeMonthly]

If you wanted to coat them in something that is easily removable, acrylic enamel spray paint would work.

I spray all my bare boards because I use my laser cutter to cut the traces out in the paint and then etch the board. The paint comes off just as easily as say toner transfer with a bit of acetone.

It's effort though, I'd just scrub up the boards before use. 

[SeanB]

WD40 and copper is not a good idea, it will result in a lot of green crud with time. It is noted in the data sheets not to use on brass, as it will damage it long term. wWorks fine on steel, keeping it reasonably free of corrosion in a semi controlled atmosphere.

Best is sealed in a non permeable laminated vapour proof bag, with a sachet of desiccant in there, and wrapped with each sheet of PCB in acid free kraft paper, all with a overpack inside of plastic lined wax paper. That will, provided it is not opened, or is resealed very fast after a careful open ( make a long end so you can do a number of seals before needing a new bag) and quick removal of the needed quantity, last for decades.

Another method is to dip the clean boards in hot paraffin wax, and then into a waxed paper cover, and then place the whole lot in more waxed paper and then finally in a vapour proof bag. Nuts , bolts and complete delicate assemblies preserved that way come out looking like new after a quick boiling in solvent to get the wax off.

[Rudane]

Yes, silver is good too! However, I've noticed not all manufacturers have the option for silver.

[Lomax]

Search for no-ox-id. It is used extensively in the high amperage DC world like telephone and wet cell lead acid battery connections.  It is like an industry standard. It has a grease like consistency and only needs to be applied in a very thin layer.  I have seen 30 year old copper bus bars that look like new that were coated with it and were in a terrible environment of a battery room with tons of vented lead acid batteries.  It can easily be removed with acetone or 99+ IPA.

Vaseline. You're talking about vaseline.

[helius]

It's actually the product formerly known as Cosmoline, which consists of petrolatum with fumed silica and other agents.

[Lomax]

WD40 and copper is not a good idea, it will result in a lot of green crud with time. It is noted in the data sheets not to use on brass, as it will damage it long term. Works fine on steel, keeping it reasonably free of corrosion in a semi controlled atmosphere.

Thank you. Inappropriate uses of WD-40, and its derivatives, is a pet peeve of mine - not least since I once spent an entire weekend clearing out gummed up (what I assumed to be) WD-40 from the (Alps) faders and pots on a 32 channel mixing desk with dual swept mids, four sends, and eight subs. My fingers hurt just thinking about the amount of knob-twiddling that involved. Some of the pots in particular, had gummed up so hard it was impossible to turn them until they'd been soaked for an hour. I used up a whole tray of alcohol spray bottles, and had to remove each of the channel strip PCBs from its front panel - that's something like 14 pots and one fader per channel, times 32, plus the subgroups and masters - all of them with their own fiddly lock-screw and fixing nut. I still have nightmares about it, but the exercise was a success in that the console became fully functional.

Best is sealed in a non permeable laminated vapour proof bag, with a sachet of desiccant in there, and wrapped with each sheet of PCB in acid free kraft paper, all with a overpack inside of plastic lined wax paper. That will, provided it is not opened, or is resealed very fast after a careful open ( make a long end so you can do a number of seals before needing a new bag) and quick removal of the needed quantity, last for decades.

Another method is to dip the clean boards in hot paraffin wax, and then into a waxed paper cover, and then place the whole lot in more waxed paper and then finally in a vapour proof bag. Nuts , bolts and complete delicate assemblies preserved that way come out looking like new after a quick boiling in solvent to get the wax off.

It was exactly some kind of spray on wax I was imagining would be the right thing; (relatively) easy to remove, solid enough not to smear onto everything around, and (probably) solderable through, in case you haven't cleaned it off 100%.

[Lomax]

Full disclosure: I live on a boat. Or at least I will be, once the shipyard tires of pillaging my bank account.

[Ian.M]

You are FUBARed - your *ONLY* long term chance would be the foiled mylar bags and an Oxygen Adsorber.   Every copper surface on a boat eventually goes black, green or crumbles away!

Assuming you are on salt water, SeanB's suggestion may work if you can go inland a few miles to get away from the salt in the air to initially clean the boards and pack the bag, but if you open it on board, chlorides will get in for certain, and you'll also get sulphur compounds and salty oily particulates from traces of your own or nearby diesel exhaust that have blown into the cabin recently.

[KNSSoftware]

all these modern techniques - just ask your grandma; bury them in rice!

[mmagin]

CorTec has a line of VpCI products that can be used to prevent corrosion in storage (films, papers, and satchets) but I don't know whether there is a distributor in the UK.

This is probably the best answer, as far as something that's actually effective and that you won't have to clean off afterwards.  There are various brands of vapor-phase corrosion prevention products, some may be specifically for steel, but many of them are sold for multi-metal use.