Sockets contact reliability

[buenos]

I am interested in the topic of card-socket reliability.
Specifically the 90degree PCB edge connectors plugged into sockets.
I would like to know how often it happens that a system with PCI-express-card and DIMM-memory sockets loose contact, in products that are in series production.
Have you heard of cases when you shipped thousands of systems while several of those didn't work initially (at the production test bench) or stopped working in the field because some of the card sockets lost contact?
I am trying to make a case for integrated chip-down design versus multi-card designs.

 

[BradtheRad]

Seeing that it is a long-established connector technology, it apparently is reliable.

Every so often I remove a card and examine the contacts. I can see slight tarnishing where air gets at the copper (brass, bronze, gold). However this is in contrast with the clean appearance of the lines scraped by the slot connector.

Usually I burnish the flat contacts with a pencil eraser, then replace the card. I tell myself I'm doing preventative maintenance.

I am surprised there are not more problems with dirt and tarnish, but if there were, then this type of contact would not have gained industry-wide usage.

 

[buenos]

Any statistics in mass production and RMAs?