On Sunday, June 28, 2020 at 6:15:19 AM UTC-4, 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

The pointer to the tool is interesting to me. It beats keeping an old style pencil eraser around, which tends to dry out over time...speaking of that.....
What is the material in this pen? fiberglass? and does it dry up or change hardness in any way?
Thanks
J