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Can oxides build up enough to force contacts to disconnect?

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  • \$\begingroup\$ Seems like its possible but I am interested in hearing from the community.. \$\endgroup\$
    – klamb
    Nov 14, 2016 at 18:51
  • \$\begingroup\$ Contrariwise, the mating surfaces can cold weld together. \$\endgroup\$ Nov 14, 2016 at 21:02

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There's no question that pins can oxidize and that the build-up, perhaps combined with minor movements, can lead to an eventual increase in resistance, leading to possible additional heating at the connector, leading to more oxidation, etc. I've seen it happen, on occasion. Faster, when the humidity is high.

If the alloy or metals are dissimilar, in the sense that their anodic indices are different, there will always be a galvanic potential present. In the presence of an electrolyte (tiny amounts of water from the air, for example), this potential can drive ions as well as provide energy for chemical changes.

Each metal is a special case, though. So there is no specific "bright line" that will tell you exactly what happens in every circumstance. Aluminum, for example, oxidizes into what amounts to "transparent aluminum" or sapphire. Abrade any piece of aluminum in the presence of oxygen in air and it will almost immediately form a thin layer on its surface. Given enough time to act, it grows thicker and thicker and it can become strong enough to resist scratching to a degree as well as to insulate. Iron, on the other hand, develops a very soft iron-oxide with entirely different characteristics. (Not that pure iron is ever used in circuit connectors!)

So... It's possible. I've seen it happen with instruments kept untouched in a remotely located electronic shack where it was no more than re-seating of a board or two (to remove some of the accumulation) to get things back running.

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It depends on the connector. So-called gas-tight connectors should remain free from oxidation indefinitely. Turned-pin IC connectors are a typical example.

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  • \$\begingroup\$ I've never heard of one of those gas tight connectors. I'm curious, but a quick google search got me a thousand links to an entirely different kind of gas tight connector. Could you provide a link or a manufacturer name for such connectors? I'd like to get a look at one or two. Thanks. \$\endgroup\$
    – jonk
    Nov 14, 2016 at 19:21
  • \$\begingroup\$ Samtec and Preci-DIP are a couple of manufacturers. \$\endgroup\$ Nov 14, 2016 at 19:56
  • \$\begingroup\$ Hmm. Samtec makes sense -- familiar with other connectors they make. Are you talking about circular connectors with threaded locking rings? Or do they look differently than that? (I'm on digikey right now and just not sure how to get digikey to accept "gas tight" as a search that doesn't result in zero entries. When I select Samtec as the manufacturer, there are lots of choices, but adding gas tight eliminates all of them.) digikey.com/product-search/en/… \$\endgroup\$
    – jonk
    Nov 14, 2016 at 20:22
  • \$\begingroup\$ It's generally accepted that turned-pin connectors are gas-tight. See this: mill-max.com/new_products/detail/158 \$\endgroup\$ Nov 14, 2016 at 20:39
  • \$\begingroup\$ Ah. Thanks. I see now. I didn't associate the terms. Thanks. \$\endgroup\$
    – jonk
    Nov 14, 2016 at 20:43
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Yes. There are several kinds of conditions where mated connectors, even mechanically un-disturbed can develop conditions (not just oxidation) that cause them to become intermittent or even fail completely. Even satellite-grade connectors sometimes fail.

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  • \$\begingroup\$ Can you please comment the names of the failure modes of these, so that I may research? Thanks. \$\endgroup\$
    – klamb
    Nov 14, 2016 at 19:51
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    \$\begingroup\$ Three that come immediately to mind are: (1) Ordinary corrosion. Perhaps exacerbated by harsh environment (like near salt-water). (2) Ill-chosen mating of dissimilar metals or alloys. (3) Simple metal fatigue from badly designed or poorly-selected metal alloys which are depended on to maintain their "spring". There are likely many more. A few quality milliseconds with Google would probably yield enough source material to keep you busy reading for a month. \$\endgroup\$ Nov 14, 2016 at 19:57

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