Oxidisation of Seagate & WDC PCBs

I don't think it is something else but everything is possible...

They failed during weekly full backup. One of the files read failed and they entered that infinite loop of restarting themself and retrying. Root filesystem was also on that RAID1 array so there was no other choice than to reboot. And on that reboot all 3 drives failed to start with the same "click of death" syndrome.

Yep, I probably missed it when shoveling through mountains of spam.

I know but I simply didn't think all 3 drives can fail... I thought I have enough redundancy because I put not 2 but 3 drives in that RAID1... And I did have something like a test with regular weekly full backup that reads all the files (not the entire disk media but at least all the files on it) and that was that backup that triggered disk suicide.

Anyway lesson learned and I'm taking additional measures now. It was not a very good experience loosing some of my work...

BTW, I took a look at brand new WDC WD5000YS-01MPB1 drives, right out of the sealed bags with silica gel and all 4 of those had their contacts already oxidized with a lot of black stuff. That makes me very suspicious that conspiracy theory might be not all that crazy--that oxidation seems to be pre-applied by the manufacturer.

In comp.sys.ibm.pc.hardware.storage Sergey Kubushyn wrote: [...]

Yes, I can imagine. I have my critical stuff also on a 3 way RAID1, but with long SMART selftests every 2 weeks and 3 different drives, two from WD and one from Samsung. One additional advantage of the long SMART selftest is that with smartd you will get a warning email on every failing test, i.e. one every two weeks. For additional warning you can also run a daily short test, e.g..

Urgh. These bags are airtight. No way the problem happened on your side then. My two weeks old WD5000AADS-00S9B0 looks fine on the top of the PCB. I think I will have a look underneath later.

Arno

No matter what you do you can not prevent an occasional disaster :( One MUST remember that "backup" in not a noun but a verb in imperative.

Those 4 were fine on the top of PCB. Black stuff was underneath, on those pads contacting with springy heads pins.

Indeed.

Mine is fine on both sides. However there is a quite a bit of contact area that looks and feels silver-plated to me, most notably areound the screws and on the bottom the contacts to the head assembly.

Arno

That makes me wonder why are they silver-plated. It is definitely not the best material longevitywise, especially for such low-level signals. It makes me even more suspicious and adds to the conspiracy theory.

Well, maybe. However I tend to think that "never attribute to malice what can be adequately explained by stupidity" may apply.

These contacts should be gold plated with high quality gold. It is also possible that the HDD vibration (always present with a running HDD) and thermal variation allows the process to creep between the contacts and kill them. Maybe a young, inexperienced engineer was hired to replace an older, experienced (but more expensive one) and that person made a pretty bad judgement call due to inexperience, wanting to save a few cents on the design.

I have to say that the last time I saw silver plating as contact protection was in vaccuum tube equipment. Modern electronics typically uses Gold, or Tin for low insertion cycle contacts.

I also found a statement on Wikipaedia that silver plated copper, once the copper is exposed in a place, will rapidly corrode all over because of some electro-chemical process. No idea whether this is true or not.

Arno

Likely just some fool's reaction to the price of gold.

Nope.

the

You know of course that the black silver layer is still conductive for low level signals??

Silver Silfide is a (bad) conductor? That will help for the R/W signal. However the lines for the moving coil go through the same connector and they need a low resistance path.

Arno

I agree but it looks like there is a pattern here...

They did not save anything on that design. Gold plating is a common procedure, it is everywhere, most of card-edge connectors (e.g. PCI) are gold and they even called "gold fingers" by chinese PCB manufacturers.

Silver, on the other hand, is almost unheard of and I'm pretty sure PCB makers would charge extra for this if they agree to do it at all. And it is NOT that the entire board is silver-plated; there are gold-plated parts on that same board that makes it have at least 2 different platings so it will be more expensive than simple gold all over.

Yep. Silver plating was usually used in microwave equipment, HF coils etc. where skin effect was so profound that current only ran through that silver (that was quite thick, btw.) Silver is also used for HIGH CURRENT relay contacts where the corrosion is removed by mechanical action of closing contacts and burned through with high current.

If you look at low current signal relays with stated minimal current capacity _NONE_ of them have silver contacts. It is usually gold, platinum, rhodium, or a mix thereof.

I am all pro Occam's Razor but all this looks like deliberate effort to make it fail after some time. It is NOT easier or cheaper to put silver there because it is an _ADDITIONAL_ step and not so common one.

for

the

It is not. Look at low level signal relays with stated _MINIMAL_ current capacity and think why none of them has silver contacts.

cut

I have done brain wave registration, eye movement detection and skin resistance measurement with silver-chloride electrodes, and they conducted nicely.

That is totally different application. Yes, silver sulfide is not a perfect dielectric but it is not a good conductor either. And modern HDD heads are magnetoRESISTIVE.

Nope.

The black silver layer conducts that fine.

Good points. An exotic process would be more expensive than a common one and two processes instead of one as well. I also happen to know that putting gold directly on silcer is problematic, but putting it directly on copper is fine. At least that is for galvanics on jewelery and if I remember this correctly.

That explains it. I have indeed seen it in power relais as well.

Well, it only makes the required level of stupidity larger, because (if we have this right) they also need to mess up the economic angle. If we assume they are competent, then indeed this looks very much like a deliberate and rather bad design error.

Arno

Silver cloride and silver sulfide are two different things.

Ok, finally looked it up:

Silver Sulfide (Ag2S) is black and forms when silver is exposed to the atmosphere by a reaction with hydrogen sulfide. As to conducticity, it seems this really messes up contact characteristics, including formiong diode-like effects and the like. I found an abstract of a IEEE article from 1970 online: "Electrical Characteristics of Contacts Contaminated with Silver Sulfide Film" So it seems it does concuct, but not well, uniformly or even in an ohmic fashion. Very bad. THis would explain the HDD failures, I think. If such a noise source is found in the signal path from/to the heads and the moving coil, I think this can cause all sorts of problems.

Silver Chloride (AgCl)is a white crystal used as referecne electrode, becasue it has very stable characteristics, giving you 230mV +/-10mV against a standard hydrogen electrode. I conclude from this that Silver Cloride conducts reasonably well and mostly in an ohmic fashion.

Sorry, but your observation does not aplly to the discussion at hand.

Arno

Or some fool has focussed on the price of gold metal and has lost sight of the fact that more complex pcb manufacturing process negates any advantage by using the cheaper metal.

MUCH more likely than any conspiracy to shaft the user.

Just took a brand spanking new WD5000AAKS drive out of sealed bag with silica gel and all that stuff. The PCB is all _SILVER_ plated, no gold. And that silver is almost totally black right out of the bag.

Not good. Silver really is unsuitable for modern, low voltage, electronics. The last WD disk I bought (a WD5000AADS, 500GB Caviar Green) had mixed gold and silver plating and the silver plating was completely fine, on both sides of the PCB.

Something is fishy here.

Arno