Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@y..., "Austin Franklin" 
<darkroom@i...> wrote:
> Hi Jim,
> 
> > the contacts on the (what? power transistor I think?) sockets to 
be
> > gold plated, so as to give better connection. This being my field
> > (electrical connectors) at which I worked for real $$ at the time, 
I
> > knew this to be pure nonsense. In this application, tin or even 
nickel
> > would have worked maybe even better.
> 
> I thought tin oxidized over time, and gold didn't...therefore, for
> longevity, gold (or now paladium is it?) were preferred?  That is my
> understanding as to why edge connectors use gold plated fingers, 
isn't it?
> 
> Regards,
>

No, because, given enough contact force, after insertion, an airtight 
connection is usually acheived. Tin, being soft, can look oxidized, 
but wipe a contact across it that digs in, and that layer is broken. 
Nickel is a little tougher.

More than this, if voltages signifigant enough for power transistors 
are coursing through a point of contact, I don't care what is 
seperating them- oxidation,  minor rust, etc...it will arc through.

Paladium is many times a wise alternative for gold when low signals 
are being passed. It still can form an oxidation layer, so it must be 
used with discretion to replace a gold connector.

Gold is used when: low level signals are being transmitted; the mating 
connectors have ultra-low insertion forces because of say, you're 
plugging in a pc board connector with hundreds of fingers (imagine a 
sort of super super long ISA/ PCI  or DIMM slot- lots of force to get 
it in, so each contact must have lower insertion force); there just 
isn't a lot of wiping travel going on from start of contact to end. SO 
gold is still what should be used on a 'puter finger edge connector.

And yes, in high humidity or excessive environmental specs gold IS 
considered when high reliability is needed as in the military. But so 
is Paladium. If I remember the copy from all those years ago, a power 
transistor socket, if that is what it was in Fred's box, just really 
doesn't need it. 

Gold is many times a detriment because it is VERY soft and after some 
number of insertions, wears through to the base below it. Instead, 
using tin, one can plate a much heavier thickness and it isn't as 
soft. And as such, tin is less sensitive to variations in contact 
force which can occur due to manufacturing tolerances.

Yada yada yada.<g>. My heads starting to hurt...
Jim H. 

> Austin