Hi,

recently came across an SMD board with lots of chip resistors (0805) and similar size ceramic caps. There was mild surface corrosion on the ends of each resistor - enough to prevent a DMM from reading the value until cleaned with a "fibre pen". For the puzzled, it's an essential servicing tool.

https://www.ebay.com.au/itm/Fibregla...-/310094191492

The item itself looked new, but was in fact 9 years old.
Eventually I found 3 open resistors, all with values like 1Mohm.

Googling tells me this is a known hazard not shared with through hole parts - has to do with the use of silver plating on top surface of the resistor being subject to sulphiding and similar air borne contaminants.

Any insights?


..... Phil