Resources

1. Issue No 41 - May 2012 - The Effects of Arcing

   Arcing generates electromagnetic interference that must be suppressed by shielding and filtering.  Arcing will usually, but not always, result in transfer of metal from the anode to the cathode.  In AC circuits, the net transfer will be close to zero.  During a closing operation, the current inrush or arcing can melt the contact materials, welding the two halves of the interface together.  Silver metal oxides and silver carbon composites are more resistant to welding than other contact materials.  Mechanical wear and fatigue of the contact surface is a concern as well.  Build-up of carbon deposits and other corrosion products can activate the surface (make it more likely to arc.)  Bounce of the contact upon closing is highly damaging, so bouncing must be minimized by using small, stiff contacts.  Arc duration should be minimized by increasing the separation velocity.

2. Issue No 40 - April 2012 - Introduction to Arcing Contacts

   Arcing is a phenomenon where electrical current crosses the gap between two contact surfaces upon opening or closing of the interface. The arc will burn as long as the current exceeds the minimum arc current and the voltage exceeds the minimum arc voltage.  Showering arcs occur when the arc repeatedly extinguishes and reignites.

3. Issue No 39 - March 2012 - Silver As A Contact Material

   Silver has the highest electrical conductivity of the contact materials.  It does not tend to oxidize, although it will form sulfide and chloride films.  Silver is often alloyed with small amounts of copper, platinum, or palladium in an effort to improve corrosion resistance.  Composites of silver and molybdenum, carbon, nickel, or various metal oxides are used as contact materials where arcing is likely to occur.

4. Issue No 38 - February 2012 - The Platinum Group Metals As Contact Materials

   Palladium (and to a lesser extent, platinum) is used as a contact interface material.  It is harder and slightly less conductive than gold.  It is usually combined with silver for use in arcing contacts, or combined with nickel or gold for non-arcing contacts.  It is susceptible to the formation of frictional powder, due to its tendency to adsorb and catalyze the reaction of organic contaminants in the surrounding atmosphere.

5. Issue No 37 - January 2012 - Gold As A Contact Material

   Gold has a number of advantages that make it an ideal material for electrical interfaces, including good conductivity, excellent corrosion resistance, and low normal force requirements.  Hard gold is used for extra durability.  Gold is usually used in low current, low voltage connectors.  Due to its high price, it is usually spot plated or applied as a very thin flash coating.  Porosity is a problem with gold, so it requires a nickel underplate.

6. Issue No 36 - December 2011 - Nickel As An Undercoating

   The use of a nickel underplate can improve corrosion resistance by functioning as a diffusion barrier.  It can passivate pores by forming a protective nickel oxide layer that does not grow.  It will also reduce the number of pores that extend to the base metal.  It can also impede the migration of corrosion products from bare edges.

7. Issue No 35 - November 2011 - Creep Corrosion And Pore Corrosion

   Nickel forms a passive (self-limiting) oxide layer.  Copper base metals will usually form active corrosion layers, in which the corrosion product continually grows and spreads.  If there are pores in the plating, corrosion products can spread from across the surface from these pores.  If the contact has bare (unplated) edges, corrosion products can originate at the edges and then spread across the surface

8. Issue No 34 - October 2011 - Nickel As A Coating Material

   Nickel coatings have outstanding hardness, wear resistance, and corrosion resistance.  If used alone as a contact material, high contact force or high voltages are required.  The high hardness, low ductility, and residual tensile stress in these coatings may limit formability and fatigue life.

9. Issue No 33 - September 2011 - Fretting Corrosion

   Tin coatings form a hard, brittle oxide film that must be disrupted upon mating for good electrical contact, using a wiping action and sufficient normal force.  This oxide film can also cause fretting corrosion if the contact moves or oscillates on a microscopic scale.  Lubrication can alleviate the problem.

10. Issue No 32 - August 2011 - Tin As A Coating Material

    Tin is a low cost, easily applied, solderable coating.  However, it does have limitations.  A copper-tin intermetallic layer formed during the coating process may grow over time and limit performance.  Electroplated tin is subject to whiskering, which can be controlled by reflowing or alloying with lead.  Tin is also subject to fretting corrosion.