Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@y..., "Len" <len@m...> wrote:
> Hi Austin:
> 
> No, tin doesn't oxidize.  That's why it's used to make pewter--and 
line "tin" cans.  But it's very soft (malleable), which may be why it 
won't be used for electrical connectors.  Also, it may not be very 
conductive, like gold and silver.
> 
> Len

HHmmm...well, not being a metalurgist just a contact tester, tin may 
not oxidize. But it puzzles me because I was able to get all kinds of 
white growth when torture testing tin plated connectors. Strange thing 
is, you can just plug and unplug a tin connector a few times after 
this and contact reestablishes through the tin-IF the contact force is 
high. You rely on it's softness to re-establish connection. And on 
it's thickness of plating, since it's so cheap you can make it thick.

I always found gold to be softer than tin, but it is true that there 
are different hardnesses of gold connector, as called out by the 
military, unless they dropped the spec since I've been away. There is 
'soft gold' and 'hard gold', and I believe their was even a 'medium 
hard gold'. This is really scraping my memory but I believe that 
Nickel was added to the gold to make it "harder". Most applications 
ten years ago called out for hard gold, at the risk of some minor 
oxidation seeping through the porosity of the gold mixed in with the 
small amount of nickel (not an alloy of course- a mixture). Hard gold 
worked best on pc board fingers, since repeated insertions were 
expected, but soft gold made the best contact under low contact 
forces/wiping travel.

So if you have inserted a gold plated finger too many times and the 
gold has worn, it is more unreliable than a tin connector. But tin is 
impractical for other reasons that I have already stated in my last 
post (low insertion force, travel, low level signal transmisssion).

So yes gold has better conductivity, but not always, for pragmatic 
reasons.

Ugh! I retired years ago. Ask me about Fred Picker or 
something...<GGG>
JIm H.