EEVblog #1361 - Dodgy Tactile Switch TEARDOWN

[EEVblog]

By popular demand, Dave tears down the dodgy tactile switch from his aircon, and compared with a couple of others.

[bitter_mike]

Some might describe me as a plating expert. Those dark patches on either side of the snap dome looked like they lined up with the two contacts on either side of the post in the center. I believe those contacts and their respective legs leading out of the body are a single piece and, speculating further, I believe those legs are tin-plated which would mean the two contacts on the inside are also. The black stuff is probably tin oxide as a result of fretting corrosion (its the result of repeated, low amplitude motion between the snap dome and the contacts). I don't think I would say it's bad plating, its just a very cheap way of doing it, both because tin is relatively cheap and because it enables the leg/contact piece to be stamped and plated as a single piece.

Of course I'd have to throw it under the XRF to make sure but the shipping costs....

[jonovid]

use more power microscope,  looks like arcing spots

[floobydust]

Of course these pushbutton switches cannot take a pcb wash, you have to use no clean solder. But that mistake I have seen noobs make.
I'm suspicious the switch didn't get a drop of water inside, as the disc is oxidized black above the contacts only, so electrolysis occurring at those two gaps.

Omron I find the best, I have zero hassles with them but they are expensive. Gold is optional.
E-switch I did not like, just too cheap, they melt easy and plastic cover.