February 26, 2013 1

Fretting Corrosion… Is It What We Have?

● Email from Molex sales engineer, February 20, in response to my question about the increase of contact voltage drop from the expected <40mV to 100..200mV:

- You should never mate gold with tin. The results of your measurements are on the low end of what could happen if left untreated. It's called Fretting Corrosion. Please switch out one of the parts as soon as possible

and what to do about it:

- If one side is damaged it would be the tin side, as that is where the corrosion would build generally. Secondly the female side is generally the side that it builds on the design of the male terminal is to "wipe" the corrosion off upon mating and unmating. I would suggest replacing both parts if possible and choosing the same the plating. If the tin one is the one that needs replaced, please use a gold plated version.

February 26, 2013 2

Fretting Corrosion

● Fretting Corrosion (FC) is caused by a relative movement of mated contact surfaces in (micro-milli)meter range due to mechanical vibration, shock etc. ● In case of a noble contact finish the base metal can be exposed due to relative movement, with subsequent FC and contact resistance increase

● Lubricant might help to some extent to reduce the friction and wear as well as shield surface from air

February 26, 2013 3

CRB Board

● [At Rice] CRB connector: Molex gold finish receptacle Peripheral backplane: Molex tin finish pins

● The CRB is attached to a backplane with 4 screws on the edges. Then the connectors in the middle are presumably more susceptible to FC than the ones on the edges… Do we have any evidence of that?

2 mounting screws 2 mounting screws