New coating resists sliding wear

By: 
December 07, 1998

Harrisburg, PA--Wear resistance is a major preoccupation of any engineer involved in designing surfaces that are in sliding contact. That's certainly the case with electronic connectors, where, for example, some switches in automobile applications must survive 50,000 to 100,000 mating/unmating cycles.

After several years in development, AMP (Harrisburg, PA) is introducing a palladium cobalt (PdCo) alloy plating for connector contacts that exhibits superior sliding wear performance at a potentially lower price than traditional coating materials. Electroplating Chemicals & Services (EC&S; Murray Hill, NJ), a venture of Lucent Technologies, worked with AMP to develop the electroplating processes used to deposit the material.

"We're always looking for new coating materials with good performance characteristics," says Dr. James Sykes, director, AMP Global Technology. What engineers strive to achieve, he adds, is a plating surface that ensures constant low contact resistance across the interface and no reduction or distortion of the signal or power.

AMP and EC&S appear to have hit a home run with the new PdCo alloy, which contains 20% cobalt by weight. With a hardness of between 590-640 KHN(sub 25) PdCo outperforms the palladium nickel (PdNi) alloy (450-550 KHN(sub 25)) it replaces. Hardness is a measure of a material's wear resistance, as supported by data from both sliding wear and fretting tests.

Although PdCo and PdNi are roughly comparable in price, AMP believes that the PdCo may be less expensive from an overall cost standpoint. That's because of a quality control issue associated with the plating of PdNi, says Joe Abys, president of EC&S.

In typical connector design, a thin layer of nickel is deposited on the copper contacts in order to prevent diffusion of the copper into the interface. But this nickel layer poses a challenge in trying to control the thickness of the PdNi which is deposited on top of it.

"The trick is how do you measure just the thickness of the PdNi?" says Abys. "With x-ray fluorescence, the signals pick up not only the nickel in the coating, but also the nickel in the base."

Being able to accurately measure and control the thickness of the plating, which varies between 25-75 (mu)-inches, is a major advantage, particularly when you consider that palladium costs approximately $280 per Troy oz.

Several companies have already expressed interest in the new coating material. AMP is currently developing connectors using PdCo with some customers and plans to offer the coating on some of its higher volume products. "One of the first products we're looking at is the 50 centerline connector," says Sykes.

As for future developments, AMP and Lucent are looking at making the connector materials more lubricious on the surface.

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