Solderability Characteristics of Palladium , Palladium Nickel , Hard and Soft
Palladium and palladium alloys are the only serious ahematives to gold as an "electronic finish". In the past, the major impetus for such a substitution has been economic; however, today palladium's technological advantages are generally recognized. This is especially true in the connector markets where the material properties (e.g. hardness, ductility, thermal stability, etc.) of palladium are in many instances superior to hard gold. Recent advances in plating technologies coupled with a m r e thorough understanding of the materials properties have expanded the use of electroplated palladium and palladium alloys in the PCB, semiconductor and optoelectronic packaging markets. To assess the suitability for such applications, the wire bondability and solderability of these finishes need to be investigated.
Contact resistance characteristics of noble metal alloys for connector contacts
Contact resistance characteristics, corrosion characteristics, and the degradation mechanism for several binary and ternary alloys are investigated to evaluate the applicability of lower-cost noble metal alloys to connector contacts. These alloys include Pd, Ag, low-content Au, and Ni. The test connector contacts are clad inlays mated with each other, clad inlays mated with hard gold plating, and clad inlays with hard gold flash mated with inlays of the same material. The atmospheric conditions are air mixed with one or more of the following gases: SO/sub 2/. NO/sub 2/, Cl/sub 2/, or H/sub 2/S. The following alloys, used in inlays of the same alloy that are mated with each other, are listed in order of increasing contact resistance: Au-Ag, Ag-Pd, Au-Ag-Pd, Au-Pd, and Pd-Ni. The contact resistance characteristics of inlays mated with hard gold plating and those of inlays with hard gold flash mated with inlays of the same material are as stable as those of hard gold plating mated with hard gold plating The dominant degradation mechanism affecting the inlay contacts of these alloys is the formation of a corrosion product on the surface area of the contact material. The dominant corrosion products causing an increase in contact resistance are the chlorides in Pd alloys. >
Sliding Wear of Inlay Clad Metals and Electrodeposited Cobalt-Gold
Clacl noble metals are of interest for the contacts of electronic connectors,because they are often less expensive to fabricate than electroplates. A wear study was conducted with a number of inlay claddings of pure metals and alloys of palladium, gold, and silver. Hemispherically ended riders of solid gold and coated with electrodeposited cobalt-gold (0.2 percent Co) were mated to fiats in reciprocation. Coupons plated with cobalt-gold were used as controls. The solid gold riders and the clad metals were found to be significantly more prone to transfer and wear than electroplated cobalt-gold. The relative hardnesses of the metals on the members determined the direction of transfer, with the softer moving initially to the harder, although prows sometimes formed on the rider which reversed the direction of net metal movement. The sliding performance of combinations of contact materials can be ranked as follows: electrodeposited cobalt-gold versus itself (best), electrodeposited cobaltgold versus claddings, and solid gold versus claddings. The harder clad materials such as DG 60Pd40Ag (also called DG R156)---an alloy of gold, palladium, and silver with a graded composition, from a gold-rich (55-85 percent) surface to 60Pd40Ag in the body of the metai--60Pd40Ag, and 40Au36Pd24Ag were superior to those which were softer, like 70Au30Ag and 69Au25Ag6Pt. Clad palladium was also relatively poor. A polyphenyl ether fluid lubricant improved sliding significantly, with electroplated cobalt-gold against itself still the best material combination. The clad metals of this study may be satisfactory replacements for electrodeposited cobalt-gold in connector contacts provided the opposing member has a plated cobalt-gold finish and a good boundary lubricant is used.