Silver is not going to last for a year without oxidizing - unless it is 
sealed in something that can act as an oxygen barrier.  The black silver 
oxide layer that will form has low electrical conductivity, and will resist 
soldering unless the solder fluxes can carry it away in sufficient quantity.

Gold is more resistant to atmospheric oxidation than silver, and the oxide 
layers tend to be thinner when they do form.  We have soldered components 
on large gold/nickel plated boards more than five years after the boards 
were made.  The only prep that was done was a wipe-down with anhydrous 
alcohol to clean surface dirt away.

Normally, silver plating would be used in an area on a PCB where enhanced 
thermal conductivity was required between mechanically fastened components 
(i.e. heatsink bolted to PCB, etc.).  Another application would be high 
current mechanical contact pads.  Silver is not used as a means of 
inhibiting exposed PCB conductor oxidation because it oxidizes as readily 
as the copper it would be trying to protect.


At 01:50 PM 4/23/02 +1200, you wrote:
>Sorry this is a little off topic but you guys are the ones who will know.
>
>I have 3 issues,
>
>1) I require a smooth finish, hence gold or silver plating/ flashing
>2) I need the PCB's to last in stores for a period of time, for arguements
>sake call it 1 year without oxidising
>3) I need to have some pads hand soldered and require a good wetting effect
>(spreading of the solder when applied)
>
>I would appreciate it if anyone out there has tried both and could indicate
>which may be the better finishing material to use.
>
>
>thanks
>
>Wayne Bickers
>Electronics Engineer
>Tru-Test Ltd
snip

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