copy here
 

Sealing
In low current applications the slightest amount of contamination can result in an intermittent signal since the low current cannot penetrate even the smallest amount of contamination.  Consequently lower currents require better sealed and cleaner switches.  As a rule of thumb - HSI recommends hermetically sealed switches with gold contacts for any application with currents under 1 amp.

Contact Material
While Silver provides the best conductive properties for contact material it is also susceptible to the creation of sulfide and oxide films.  For this reason Gold alloy material is used for lower energy circuits.  Platinum base contact material is used for higher energy circuit applications at elevated temperatures.