Interdiffusion between connector contact materials and nickel diffusion barriers during precipitation hardening of high performance spring materials

Due to miniaturization, pre-striped material is gaining favor over post-plated parts in certain connector applications. Closed box designs often shield the contact area preventing adequate deposition during post plating. Large total surface areas combined with small contact areas increase costs. High strength spring materials are required because of small beam sections. Selected spring materials develop strength from precipitation hardening. Formability demands may preclude the use of mill hardened strip. Therefore, the parts may be thermally processed after forming in order to develop the requisite strength level. The precipitation hardening treatment is accomplished at temperatures between 290°C and 510°C for times ranging from hours at low temperatures to minutes at high temperatures. Published diffusivity data for gold-nickel planar couples indicate that significant interdiffusion between gold and nickel will occur after hours at low temperature or minutes at high temperature. The coating technology, the base metal and the resulting precipitation hardening process time-temperature parameters all influence the degree of interdiffusion. This study investigates the influence of coating technology and constitution on the degree of interdiffusion between the contact material and the nickel interliner. Both electroplated and metallurgically processed coatings were evaluated. The spring material was C17200, 1/4 H. The precipitation hardening treatment was 315°C for 2 hours. It was found that significant gold-nickel interdiffusion occurred in the electroplated material, whereas inconsequential interdiffusion was detected in the metallurgically processed material. The difference between the electroplated and the metallurgically processed material was related to both the seating technology and constitution.