On Sun, 28 Jun 2020 03:15:16 -0700 (PDT), Phil Allison
wrote:



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

As formation of sulphides is a surface phenomenon, I doubt
it plays a role in properly reflow-soldered junctions.

Mechanical stress can.

Needle-pointed probes are quicker, though possibly painfull
when left lying around. Detachable ones make sense, if they
don't get lost.

RL