New insights for the specification of copper alloy strip metals for connectors

The American Society for Testing and Materials publishes specifications that prescribe the temper of several metals, including copper alloy strip metals. Most of the strip metals used for connectors are included. Manufacturers of these strip metals are obliged to produce them so that they meet ASTM specifications. The mechanical properties in specifications ordained by the Society are published by the manufacturers in promotional materials. Thus, it's not surprising that the specifications most often found in purchasing documents and on engineering drawings coincide with the values published by this Society and the manufacturers. While the effect of this practice on standardization is some what laudable, it often leads to the wrong specification for connector spring metals. At best, mis-specification is discovered in the prototype stage of development, and "merely" causes delay in getting parts on test and into production. At worst, the metal does provide prototype parts that meet initial performance requirements; it is only later, perhaps even after several production shipments, that manufacturing problems develop. Or worse, field failures are reported. It is only then discovered that the strip metal was inadequately specified. ASTM specifications primarily ensure that a particular temper is being obtained, that the metal has a particular breaking strength. Obviously, connector springs are not designed with the breaking strength in mind. Meeting the typical Society specification does not offer assurance that there is enough strength for the required contact force, that the contact force will endure, that there is enough conductivity, that there is a given spring constant, nor even that the part can be stamped without fracture. These problems will be eliminated (or greatly minimized) by using the new insights in this paper for specification.