Publications Details
The Effect of Atmosphere on the Interdiffusion of Silver and Palladium
Conductor inks containing silver and palladium, used in ceramic co-fired circuits, sometimes undergo an anomalously large expansion during heating in the temperature range where interdiffusion occurs. Therefore, the interdiffusion of silver and palladium was studied during heating in both air and argon using both powder and foil samples. Measurements on a powder compact made of a mixture of Ag and Pd (80% Ag) particles indicated that a very rapid expansion occurred between 375 and 400 C when heated in air but only a slight expansion occurred in Ar. A pre-alloyed powder with the same composition did not expand during heating. In situ high temperature x-ray diffraction studies indicated that both powders oxidized during heating in air, with the mixture oxidizing more and that interdiffusion occurred between 300 and 500 C. Microstructural examination indicated that larger particles with internal pores had formed in the mixture heated in air to 375 C due to rearrangement during interdiffusion. A porous region much thicker than the original silver film formed on a palladium foil sample when it was heated in air, whereas in inert atmosphere pores formed only in the silver film, indicating a Kirkendall effect occurs in both cases. Based on these results, it was concluded that the expansion of the Ag-Pd powder mixture was due to interdiffusion in the presence of oxygen, not solely to the oxidation of the Pd.