Thermal-decomposition and crystallization behaviour of coupling agents for silver paste application

摘要

Coupling agents have been widely used to retard the sintering of silver paste and minimize co-firing defects due to densification mismatch between silver and dielectrics. The thermal-decomposition and crystallization behaviour of the coupling agent is a subject of great concern. Formation of the coupling agent layer is achieved by coating an Ag powder surface with Zr, Al or Ti organometallic compounds. Differential thermal analysis (DTA) detected an exothermic peak in Ag powder surfaces coated with Zr, Al or Ti which was absent in the uncoated silver powder. The exothermic peak clearly indicates the presence of the organic coupling agent on the Ag powder surface. The exothermic peak is absent when the sample is analysed in an N_2 atmosphere, which suggests that the exothermic peak is related to oxidation of the coupling agent. To elucidate what is responsible for the oxidation, Ti organometallic compounds were calcined to different temperatures (350, 400, 500, 600 deg C) for 2 h and the crystallization behaviour determined by x-ray diffraction (XRD). This demonstrated the presence of an anatase phase until a temperature of greater than 350 deg C, and the intensity of the crystalline peak of (101) at 2 theta = 25.3 deg increased continuously with the dwel time. Combining the results of DTA and XRD, it was found that formation of nanocrystallized titania accompanied the combustion of organometallic compounds.