Page:Gametronics Proceedings.djvu/100

 Since conformance to the basic design requirements has been demonstrated, we will now review the contact materials and technology used in this connector system. The p.c. board mating interface will be described in detail first, with supporting test data, and then the flat cable connections will be discussed briefly.

The choice of a contact material was based on the need for high reliability for introduction of the first second generation game, and the potential use of dry circuit voltages. Considerable concern for the use of nickel in this application was present to preclude its use, based on prior research conducted at Burndy. In a 1972 report entitled "Contact Properties of Nickel Containing Alloys", nickel was mated with a gold probe at various force levels after exposure to several environments. The results in Figure 6 indicate that the long term effect of sulfur dioxide and humidity type exposures is to produce very high contact resistances. A gold system was therefore recommended for the contact surface.

The specific alloy selected for the contact spring mating surface contains 94% gold and 6% nickel. As an inlay, it has a hardness of 200 KHN minimum before forming, as compared to the 130 to 200 KHN hardness of electroplated hard gold found in most connector applications. The alloying of nickel and gold reduces the tendency of the gold to smear to stick and forms an excellent contact material where increased resistance to wear is required. A thickness of 50 microinches minimum was specified.

To evaluate the integrity of the 94 Au/6 Ni inlay after forming, microscopic examinations and porosity tests were conducted. Examination of cross sections through the contact spring showed excellent adhesion of the gold alloy to the nickel underlay carrier, and of the nickel to the phosphor bronze spring. (See Figure 7). Nitric acid vapor exposure for one hour exhibited acceptable pore densities when compared with standard electroplated gold contacts.

In designing for minimum wear, contact normal forces were kept low. To determine spring performance, normal force and permanent set vs. deflection characteristics of the contacts were measured with equipment having a very sensitive force transducer and micrometer stage. The results in Figure 8 show that within a design range of .020 to .050 inches tolerance range for spring deflection, 90 to 210 grams normal contact force is initially obtained. The permanent set that occurs at high deflection levels serves to reduce maximum forces at tolerance extremes. By comparison, standard gold system edge connectors work in a range of 50 grams minimum in stationary applications, and 100 grams minimum where vibration and mechanical shock is anticipated, to maximum forces of 300 to 350 grams. This connector, therefore, utilizes springs with appropriate minimum forces and substantially lower maximum forces, which aids in reducing wear and increasing the number of permissible mating cycles.