Can oxides build up enough to force contacts to disconnect?
Electrical – Can connector pins oxidize while mated and lose contact
connectorcorrosionsignal
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The goal of plating is to protect copper or other metals from oxidation (which increases contact resistance). Since gold doesn't oxidize contacting surfaces need a sufficient amount. I can tell you from personal experience that a gold flash <1um doesn't do much.
Here is some info from a manufacturer:
KAT Electroless Nickel/ Immersion Gold (ENIG) KAT ENIG is the industry standard for producing uniform mid-phos EN deposits with a thin topcoat of immersion gold, over copper substrates. This PCB finish is highly resistant to corrosion, and is both solderable and aluminum wire bondable. It is an ideal contacting surface.
Electroless Nickel, Electroless Palladium, Immersion Gold (ENEPIG) ENEPIG is formed by the deposition of electroless nickel, followed by electroless palladium, with an immersion gold flash. ENEPIG has exceptionally wide application: it is suitable for soldering, gold wire bonding, aluminum wire bonding, and contact resistance. KAT UF (ENEPIG) Universal Finish This unique Ni/Pd/Au surface finish is solderable, aluminum and gold wire bondable, and a superb contact surface. The recommended thickness is 3 – 5 microns (120 – 200 µins) of electroless nickel, 0.16 micron (4 – 6 µins) of electroless palladium, and 0.02 to 0.04 micron (1 – 2 µins) of immersion gold.
The thicker the gold the better, how long will it last? There isn't much information on that. From Viasystems surface finishes
If your really worried about it and this is essential for your product, I think I'd do some mechanical testing while measuring the contact resistance (Here as an example) Otherwise, stay away from the really thin flashes and the thicker the better. Remember that thicknesses and some definitions vary from manufacturer to manufacturer (such as the definition of hard and soft gold) so make sure you know what your getting.
From this article on contact resistance:
Golden Rule No.3: Gold Coatings Can Be Used For High Durability
Coating a contact with pure (i.e. soft) gold generally results in a connector with low durability and high insertion forces (i.e., high coefficient of friction), especially when the thickness is greater than 0.13 microns (5 microinches). In practice, gold coatings are usually hardened by adding small amounts cobalt or nickel to the gold. Such coatings are defined as ‘hard gold’ and produce coatings with a low coefficient of friction and excellent durability characteristics. Hard gold coated contacts can generally withstand hundreds to thousands of durability cycles without failing. The durability of hard gold coatings can be enhanced by using an underlayer having a hardness value that is greater than that of gold and which will provide mechanical support. Nickel is generally recommended as an underlayer for this purpose. Lubricants are also effective at increasing the durability of gold coatings. Generally, lubrication can increase the durability of a gold contact by an order of magnitude.
The design you show is done with pogos. Springs could also be used but pogos are cheap and typically have better industrial design appearance. These are widely used in medical and consumer industries.
The contact can be quite good if both sides are gold and kept clean by the end user. Datasheets tend to be ~50-100 mOhm and in practice I've seen closer to ~10-30 mOhm nominal connection. This does depend on your contact and spring force tho, so your mileage might vary. Various designs also exist that may conduct through the spring or through the shell of the pogo. Custom designs are possible to meet impedance requirements or current requirements.
Pogos are robust in axial loading as long as you stay within their working range. Pogos do terribly under lateral loads, usually worse than springs. A side force on them tends to fracture the solder quite easily or break the pogo. There are through-hole pogos but they are still not really designed for lateral forces. Usually the mechanical design requires that they are somehow protected (such as being placed in a pocket which ensures no side loading). The pogo side of the mate typically goes on the charger. The other side is typically just a puck and can be super robust as it can have no moving parts. It's better to put this side on the product (assuming you'd rather replace a charging cable instead of the whole product if misuse breaks the pogos). Pogos with a roller bearing at the top do exists and perform better under lateral loads to the tip but are more expensive and more limited in mechanical design freedom.
Best Answer
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.