[Coco] Gold contacts...

Dave Philipsen dave at davebiz.com
Thu Mar 17 18:58:07 EDT 2016

Thanks for the references, John.  Definitely an interesting read.  I 
would tend to agree with most of what is being said on the mating of 
dissimilar metals...probably not a good idea.  I did take a very close 
peek with a magnifier at my CoCo 3 machines here and they all seem to 
have what appears to be gold plating on the contacts.  Don't know if 
that is the case with all CoCo 3s ever made though.  Interestingly, the 
only part of the contact that has plating is the actual part that wipes 
the contacts on the PCB.  The rest of the contact does not have the gold 
plating.  Regardless, if it is true that the CoCo contacts are 
gold-plated then according to these papers the most logical metal to use 
on the program pak edge connector would also be gold, definitely not 


On 2016-03-17 14:39, John W. Linville wrote:
> Sorry to prolong the thread -- I find the topic interesting!
> On Thu, Mar 17, 2016 at 12:01:42AM -0500, Dave Philipsen wrote:
>> I'm definitely not a chemist or a metallurgist. All I can say is that 
>> I can
>> remember the old game cartridges from long ago having that grey film 
>> on them
>> and how gently rubbing them with a pencil eraser or even just using my
>> fingers would remove some of the junk. And it may just be anecdotal 
>> but I
>> remember a lot of problems with CoCo stuff but nary a problem with 
>> Apple II
>> stuff.  All the Apple II boards I ever saw or used had gold edge 
>> connectors.
>> And if it is a fallacy that the gold connectors improve reliability 
>> then a
>> whole lot of pretty smart people have been duped!  Are most of the 
>> companies
>> who manufacture boards that plug into PC slots now migrating away from 
>> using
>> gold on the edge connectors with this 'new' information coming to 
>> light?
> Definitely anecdotal -- I've got Apple II cards both with and without
> gold connectors.  I've also got an old Apple II friend with more
> stories of cleaning connectors with an eraser than I have ever heard
> at a CoCoFEST! ;-)
> I found some more references to the issue.  The people at AMP probably
> know a few things about connectors:
> 	http://www.te.com/documentation/whitepapers/pdf/sncomrep.pdf
> "Tin-to-gold interfaces are more susceptible to fretting corrosion
> related failures, and lubricants are not nearly as effective at
> stabilizing contact resistance as they are with tin-to-tin interfaces.
> Tin tends to transfer onto the gold surface which can ultimately lead
> to accumulation of tin oxide on the harder gold substrate.  It is more
> difficult to disrupt the tin oxide on the harder gold substrate than
> it is to break through the tin oxide that forms directly over tin."
> Also this:
> 	http://www.tvtechnology.com/audio/0014/connector-contacts-gold-silver-and-tin/218015
> "One caveat: Don’t mate gold with tin as it is subject to fretting
> corrosion. As the connection is made, the tin tends to transfer to
> the gold pins, eventually forming a tin oxide layer on the gold. This
> layer can build up fairly quickly and because of the durable nature
> of the gold, is resistant to cracking and rubbing off."
> Although that quote might have been influence by the previous one --
> tough to say for sure.
> As for 'new' information, I don't think it is new at all.  The AMP
> paper references these sources:
> Krumbein, S. J., Contact Properties of Tin Plates , IEEE Transactions
> on Parts, Hybrids, and Packaging , Vol. PHP-11, No. 2, 1975, p. 155.
> Bock, E. M., The Mateability of Tin to Gold, Palladium, and Silver
> , Proc.  40th Electronic Components and Technol ogy Conference ,
> 1990, pp. 840-844.
> Mottine, J. J. and Reagor, B. T ., The Effect of Lubrication on
> Fretting Corrosion at Dissimilar Metal Interfaces in Socketed IC
> Device Applications , Proc.  Holm Conference on Electric Contacts ,
> 1984, pp.  171-183
> So, definitely not a "new" idea...
> The perceived preference for Gold contacts may simply be a matter
> of prioritizing one thing over another or even a "nobody ever got
> fired for buying IBM" kind of thing.  I also read that some of the
> increased popularity of ENIG finishes comes more from the presence
> of RoHS standards than anything else -- YMMV.
>> Another thing:  If you live in certain areas of this country and do 
>> not have
>> air conditioning you will almost certainly experience condensing 
>> humidity if
>> you leave a window open in the evening.  Just looking at the forecast 
>> for my
>> own location, the temperature is supposed to be at or near the dew 
>> point at
>> least four times in the next week.  This obviously doesn't pose much 
>> of a
>> problem for people who control their indoor climates but...
> Save your program paks -- shut your windows!! :-)
>> Dave
>> On 3/16/2016 4:37 PM, Zippster wrote:
>> >Thanks for that link John.  That was an interesting read.
>> >
>> >I had understood that the possible issue being talked about was galvanic corrosion,
>> >which might cause a problem when using dissimilar metals as electrical contacts
>> >in an electrolyte.  In a “dry” situation like we’ talking about (and this is noted in the paper)
>> >the electrolyte would be humidity in the air condensing on the contacts.
>> >
>> >I’m just not seeing the electrolyte being present unless you’re in a VERY humid environment.
>> >And in the conclusion portion of the paper, their tests for gold on tin contacts showed no
>> >evidence of galvanic corrosion (presumably in air).  Their final conclusion being that the
>> >gold on tin connectors tested showed no corrosion and were acceptable for
>> >use in consumer electronics.
>> >
>> >If the connectors in the CoCo are indeed gold plated, then gold wold be ideal on the card edge.
>> >If they aren’t, (or are and you use a tin card-edge) then the lack of an electrolyte would still seem
>> >to indicate there wouldn’t be a problem except maybe in super-humid environments.
>> >
>> >It would seem to me all this that normal oxidation on the tin surface (as in storage or just sitting there), which
>> >doesn’t happen with gold (by itself) would probably outweigh any galvanic effects, and even that would take
>> >quite a while to happen.
>> >
>> >The way I look at it is it’s probably just fine either way (at least until normal oxidation affects the tin),
>> >but gold plating is a step up, especially long-term.
>> >
>> >Interesting topic.   :)
>> >
>> >- Ed
>> >
>> >
>> >
>> >>On Mar 16, 2016, at 3:10 PM, John W. Linville <linville at tuxdriver.com> wrote:
>> >>
>> >>There are some papers out there on the topic...
>> >>
>> >>	http://www.jsbtech.com/download/Effects%20of%20Galvanic%20Corrosion%20on%20Au-Sn-Plated%20Contacts.pdf
>> >>
>> >>I'm not much of a chemist, so I'm not prepared to render a verdict.
>> >>
>> >>John
>> >>
>> >>P.S.  I also view "always use gold contacts" with skepticism,
>> >>especially for hobby projects...
>> >>
>> >>On Wed, Mar 16, 2016 at 02:40:39PM -0500, Dave Philipsen wrote:
>> >>>I wholeheartedly agree with you.  It would take a lot of convincing to make
>> >>>me believe that gold edge connectors are going to wear out the cart port
>> >>>more quickly.  And almost all manufacturers of electrical connectors offer
>> >>>gold-plating as a means of making the connection more reliable.  I remember
>> >>>many years ago running my fingers across the contacts of those cheapo
>> >>>cartridges and getting a grey-colored stain on my fingers from the
>> >>>corrosion.  I've worn a gold-alloyed wedding ring for years and never had
>> >>>any kind of stain on my fingers from it.
>> >>>
>> >>>My question to the Facebooksters would be: Why did Intel use gold plating on
>> >>>millions if not billions of their processors that were intended to mate with
>> >>>sockets?  Perhaps they could do a little research on galvanic corrosion and
>> >>>the anodic index of tin https://en.wikipedia.org/wiki/Galvanic_corrosion. An
>> >>>inspection of the edge connectors on three of my CoCo 3s reveals that they
>> >>>all appear to have some amount of gold on the contacts. At least Tandy got
>> >>>that part right.
>> >>>
>> >>>
>> >>>Dave
>> >>>
>> >>>
>> >>>On 3/16/2016 2:15 PM, Zippster wrote:
>> >>>>Gold edge connectors are bad, haven’t you heard?
>> >>>>
>> >>>>Just kidding, but there’s been a small discussion on the Facebook group where it’s being claimed
>> >>>>tin-plated is better and won’t wear out your CoCo’s cart port connector as quickly as gold.  And that
>> >>>>that is why Tandy didn’t use it most of the time, not because of cost.
>> >>>>
>> >>>>Personally I don’t  buy it, I think gold plated edge connectors are the way to go, even though they
>> >>>>cost a bit more.  You can certainly argue it’s not necessary, but worse?  lol.
>> >>>>
>> >>>>- Ed
>> >>>>
>> >>>>
>> >>>>>On Mar 16, 2016, at 1:47 PM, Dave Philipsen <dave at davebiz.com> wrote:
>> >>>>>
>> >>>>>One thing I noticed about the MiniIDE is that there is no gold on the edge connector.  This is a mistake that shouldn't be repeated if someone decides to design a replacement.
>> >>>>>
>> >>>>>Dave
>> >>>>>
>> >>>>>
>> >>>>>On 3/15/2016 6:28 PM, RETRO Innovations wrote:
>> >>>>>>It'd be interesting to see how small one could make the interface. If one used a flash ROM IC and a CPLD, I think one could put an IDE controller with IDE and CF into a 2.2"x2" form factor.  That's be small enough for any use, no?
>> >>>>>>
>> >>>>>>JIm
>> >>>>>>
>> >>>>>>
>> >>>>>>On 3/15/2016 12:51 PM, Tormod Volden wrote:
>> >>>>>>>On Tue, Mar 15, 2016 at 5:29 PM, Bill Pierce wrote:
>> >>>>>>>>Some of the Brazillian Coco guys used the schematic from the Glenside unit and made a more "modern" solution that was smaller wih less parts (and fit the slot better). Maybe we could talk them into letting go of the schematic and get Ed to whip some up :-)
>> >>>>>>>Here are some pictures of both the original Glenside board and the
>> >>>>>>>Brazilian "MiniIDE": http://amxproject.com/?p=2585
>> >>>>>>>Some people would probably prefer the big original with "integrated
>> >>>>>>>MPI" and DIP40 chips, but I'd also be interested in the MiniIDE. Or
>> >>>>>>>even a CPLD-based remake...
>> >>>>>>>
>> >>>>>>>Tormod
>> >>>>>>>
>> >>>>>--
>> >>>>>Coco mailing list
>> >>>>>Coco at maltedmedia.com
>> >>>>>https://pairlist5.pair.net/mailman/listinfo/coco
>> >>>
>> >>>--
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>> >>--
>> >>John W. Linville		Someday the world will need a hero, and you
>> >>linville at tuxdriver.com			might be all we have.  Be ready.
>> >>
>> >>--
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>> >
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> --
> John W. Linville		Someday the world will need a hero, and you
> linville at tuxdriver.com			might be all we have.  Be ready.

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