The Tribology of Contact Finishes for Electronic Connectors Part II: The Effects of Underplate, Topography and Lubrication
This paper is an expanded treatment of the second part of the William Blum Lecture Dr. Antler presented at Sur/Fin 1988 by Dr. Morton Antler. Subjects covered include substrate and lubrication effects on the tribology of contact finishes.
By Dr. Morton Antler
Recipient of the 1987 William Blum AES Scientific Achievement Award
(Originally published as Plating & Surface Finishing, 75 (11), 28-32 (1988).)
The William Blum Lecture presented at SUR/FIN 1988 Los Angeles by Dr. Morton Antler, the 1987 AESF Scientific Achievement Award recipient, was expanded for publication in Plating & Surface Finishing by the author. This second concluding paper covered the effects of substrates and underplates on friction and wear. Part 1 of the 29th William Blum Lecture, entitled "The Tribology of Contact Finishes for Electronic Connectors: Mechanisms of Friction and Wear," was published in the February 2014 NASF Report in Products Finishing. This second paper also contains a summary of the salient points noted in both papers, providing continuity between the two articles published in the February and March 2014. A printable PDF version of this second part is available by clicking HERE.
High hardness and ductility are desirable in contrast to the low-ductility top coating preferred for minimal adhesive wear and friction. Fluids of certain chemical classes, such as the polyphenylethers, are often essential supplementary films that assure low sliding friction and acceptable adhesive and fretting wear. New, low-cost contact finishes under development may be successful in the less critical applications of consumer electronic components. Coatings applied by physical methods such as ion implantation and ion plating are of interest for critical applications.
Hardness - Hard materials are more wear-resistant than soft materials, provided that other characteristics of the metal are the same. This fact originates in the reduction in real area of contact which accompanies increasing hardness. Therefore, with layered materials, increasing substrate and underplate hardness may be beneficial, particularly when the coatings are thin.
Examples of the value of a hard underplate (e.g., nickel, 400 kg/mm2), are given in Fig. 1 for adhesive wear and in Fig. 2 for abrasive wear.1 In Fig. 1, hemispherically-ended solid gold riders with a diameter of 3.2 mm were mated to cobalt-gold plated flats at a series of loads for various numbers of passes on tracks 1 cm long. Adhesive wear of gold was much reduced with the hard underplate. In Fig. 2, a solid rhodium rider with a circular flat contact area 0.5 mm in diameter was mated to a lubricated cobalt-gold plated flat. Equiaxed graded silicon carbide particles were sifted onto the flat. The motion was reciprocating. The figure shows the abrasive-wear-inhibiting ability of the nickel underplate. Hard underplatings have also been found to be effective in reducing the fretting wear of gold electrodeposits.2