Oxidisation of Seagate & WDC PCBs
in [Repair]
|
Prev: Sony KV-32HS500 6 blinks despite MCZ300D(B) chip replacement
Next: Replacement battery cells/packs for an automotive jump-start/air-compressor widget
From: Sergey Kubushyn on 14 Apr 2010 20:00 In sci.electronics.repair Sjouke Burry <burrynulnulfour(a)ppllaanneett.nnll> wrote: > Sergey Kubushyn wrote: >> In sci.electronics.repair Sjouke Burry <burrynulnulfour(a)ppllaanneett.nnll> wrote: >>> Sergey Kubushyn wrote: > cut >>>>> area that looks and feels silver-plated to me, most notably areound >>>>> the screws and on the bottom the contacts to the head assembly. >>>> 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. >>>> >>>> --- >>>> ****************************************************************** >>>> * KSI(a)home KOI8 Net < > The impossible we do immediately. * >>>> * Las Vegas NV, USA < > Miracles require 24-hour notice. * >>>> ****************************************************************** >>> You know of course that the black silver layer is still conductive >>> for low level signals?? >> >> It is not. Look at low level signal relays with stated _MINIMAL_ current >> capacity and think why none of them has silver contacts. > > 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. --- ****************************************************************** * KSI(a)home KOI8 Net < > The impossible we do immediately. * * Las Vegas NV, USA < > Miracles require 24-hour notice. * ******************************************************************
From: 454 on 14 Apr 2010 21:55 Arno wrote: > In comp.sys.ibm.pc.hardware.storage Sjouke Burry > <burrynulnulfour(a)ppllaanneett.nnll> wrote: >> Sergey Kubushyn wrote: >>> In sci.electronics.repair Arno <me(a)privacy.net> wrote: > [...] >>>> 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. >>> >>> 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. > >> You know of course that the black silver layer is still conductive >> for low level signals?? > Silver Silfide is a (bad) conductor? Nope. > 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. The black silver layer conducts that fine.
From: Arno on 15 Apr 2010 06:09 In comp.sys.ibm.pc.hardware.storage Sergey Kubushyn <ksi(a)koi8.net> wrote: > In sci.electronics.repair Arno <me(a)privacy.net> wrote: >> In comp.sys.ibm.pc.hardware.storage Sergey Kubushyn <ksi(a)koi8.net> wrote: >>> In sci.electronics.repair Arno <me(a)privacy.net> wrote: >> [...] >>>>> Those 4 were fine on the top of PCB. Black stuff was underneath, on those >>>>> pads contacting with springy heads pins. >>>> >>>> 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. >> >>> 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. > I agree but it looks like there is a pattern here... >> 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. > 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. 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. >> 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. > 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. That explains it. I have indeed seen it in power relais as well. > 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. 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 -- Arno Wagner, Dr. sc. techn., Dipl. Inform., CISSP -- Email: arno(a)wagner.name GnuPG: ID: 1E25338F FP: 0C30 5782 9D93 F785 E79C 0296 797F 6B50 1E25 338F ---- Cuddly UI's are the manifestation of wishful thinking. -- Dylan Evans
From: Arno on 15 Apr 2010 06:25 In comp.sys.ibm.pc.hardware.storage Sjouke Burry <burrynulnulfour(a)ppllaanneett.nnll> wrote: > Sergey Kubushyn wrote: >> In sci.electronics.repair Sjouke Burry <burrynulnulfour(a)ppllaanneett.nnll> wrote: >>> Sergey Kubushyn wrote: > cut >>>>> area that looks and feels silver-plated to me, most notably areound >>>>> the screws and on the bottom the contacts to the head assembly. >>>> 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. >>>> >>>> --- >>>> ****************************************************************** >>>> * KSI(a)home KOI8 Net < > The impossible we do immediately. * >>>> * Las Vegas NV, USA < > Miracles require 24-hour notice. * >>>> ****************************************************************** >>> You know of course that the black silver layer is still conductive >>> for low level signals?? >> >> It is not. Look at low level signal relays with stated _MINIMAL_ current >> capacity and think why none of them has silver contacts. > I have done brain wave registration, eye movement detection and > skin resistance measurement with silver-chloride electrodes, > and they conducted nicely. 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 -- Arno Wagner, Dr. sc. techn., Dipl. Inform., CISSP -- Email: arno(a)wagner.name GnuPG: ID: 1E25338F FP: 0C30 5782 9D93 F785 E79C 0296 797F 6B50 1E25 338F ---- Cuddly UI's are the manifestation of wishful thinking. -- Dylan Evans
From: 454 on 15 Apr 2010 12:38
Arno wrote: > In comp.sys.ibm.pc.hardware.storage Sergey Kubushyn <ksi(a)koi8.net> > wrote: >> In sci.electronics.repair Arno <me(a)privacy.net> wrote: >>> In comp.sys.ibm.pc.hardware.storage Sergey Kubushyn <ksi(a)koi8.net> >>> wrote: >>>> In sci.electronics.repair Arno <me(a)privacy.net> wrote: >>> [...] >>>>>> Those 4 were fine on the top of PCB. Black stuff was underneath, >>>>>> on those pads contacting with springy heads pins. >>>>> >>>>> 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. >>> >>>> 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. > >> I agree but it looks like there is a pattern here... > >>> 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. > >> 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. > > 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. > >>> 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. > >> 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. > > That explains it. I have indeed seen it in power relais as well. > >> 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. > > 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. 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. |