III. Tin Plated Contacts Need Lubrication.
When it is not possible to achieve absolute mechanical stability–that is, freedom from any motion of the contact interface, protective lubrication is necessary. A thin liquid lubricant film protects contact surfaces from the detrimental effects of disturbance or fretting motions. It does so by:
1.Reducing friction and generation of wear particles due to motion;
2.Protects the surface from atmospheric oxidation, in and around the contact interface; and
3.Prevents fretting corrosion.
As contact forces approach the minimum recommended level of 100 grams, it becomes more important that lubrication be used from the standpoint of protection against fretting and disturbance motions. On the other hand, with higher contact forces lubrication may be necessary to reduce friction and wear during engage/disengage cycling of the connector. In this respect, lubrication will permit higher contact forces than would otherwise be allowed from friction force considerations.
IV. Sliding or Wiping Action haring Contact Engagement is Necessary with Tin Plated Contacts.
Even the zero-entry force type connector should incorporate some wipe. The alternate is to provide sharp points on the contact to break through the tin oxide surface film. This is a less-satisfactory way of breaking through the films from the standpoint of wear life and penetration of the plating to the underlying base metal.
V. Tin Plated Contacts Must Not Be Used to Make or Break Current
Arcing will quickly destroy the tin plating.
VI. Tin Plated Contacts Can Be Used Under Dry Circuit or Low Level Conditions
Under the guidelines set forth above, there are no limits to the voltage and current at which the contacts may be used. This includes microvolt/microampere levels as well as the volts/ampere region.
LOW FORCE CONNECTOR
The name "Low Force" relates to the entry force required to insert a printed circuit board. With a mechanical advantage to help lift the contact over the printed circuit board, some insertion force is required; but part of this force is recovered when the board snaps into place as the contact slips down the other side of the cam. At this time, the back lobe of the contact wipes down on the board with the required normal force. It allows a minimum amount of wiping action to preserve the plating on both board and contact.
This is a "plus" for durability. With tin plated contact and tin-plated covered pads on printed circuit board, samples proved good after 500 cycles of mating and unmating, even with a high normal force of 200 grams. Similar contacts with 1 5>0 grams normal force were cycled 1,000 times, and with lubricated contacts, samples were functional after in excess of 1500 cycles.
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