Jul 18, 2015
Increase Contact Performance by Pre-Stressing
In this short discourse we discuss the consequences of residual stress that had developed in a contact beam that had been subjected to stresses beyond the materials elastic limit. We intend to show that residual stress may be beneficial, or if not properly configured, may actually be very harmful to a contact spring..
May 12, 2015
Silver – A Superior Finish for High Current Applications
Connector designers have available a wide selection of finishes to consider for high current applications, both noble as well as non-noble metals. The choice would consider performance as well as cost aspects. Failures of high current contacts are somewhat distinct from those of signal contacts, which in that case are primarily associated with loss of information. In contrast, the failure of a high current contact could involve something as catastrophic as the initiation of a fire, with its associated risks.
In this short discourse, we will focus on silver and discuss a number of attributes that characterize it as a finish for high current applications. Silver has the highest value of electrical conductivity of any material – this is clearly a significant factor when considering the ability of a contact to carry current. Silver is “semi-noble”, in that although oxide formation is mitigated, it is susceptible to the formation of tarnish films. As with noble metals, silver will not degrade as a consequence of fretting corrosion. For electrical contacts, by utilizing the recommended normal forces and plating thicknesses, successful performance (in spite of tarnish formation) can be expected.
May 12, 2015
Contact Design Considerations For Long-Term Reliability
For those critical electrical contact applications where the consequences of failure are severe and long-term reliability is paramount, reliance is customarily placed on noble metal finishes. Gold is by far the noble metal finish of choice. Gold, of the proper thickness and with an appropriate underplate, will form little or no tarnish film. This note will discuss reliability with respect to the ability of a contact system to operate successfully in spite of external contamination factors – the presence of/ entrapment of non-conducting material at the contact interface.
Mar 20, 2015
Why Even Minor Increases in Contact Resistance Matter
When a contact is mated, only a relatively small area is actually touching.All of the current must flow through this small area – the actual contact interface.Because the current is constricted to flow through this zone of contact, the resistance associated with this current constriction is called “constriction resistance”.Connector designers understand that many variables impact contact area (normal force, materials, surface finish, environment, etc.), and how important this issue is for the contacts to adequately do their job.