Measurements of electrical resistivity and Raman scattering from conductive die attach adhesives

It is well known that the development of electrical conductivity in silver (Ag)-filled conductive polymer adhesives is dependent on the thermal profile of the curing process. Over the past decade, studies of polymer adhesive systems have identified various chemical reactions at the interface of the micron-sized Ag filler, which determine the subsequent performance of the conductive system. In this investigation, we have performed simultaneous electrical resistivity and surface enhanced Raman scattering (SERS) measurements on a commercial conductive adhesive to correlate the behavior of electrical conductivity with the chemical nature of the particle interface. Results show that at room temperature in the low conductance state (~10^-9 ohms^-1 ), the SERS spectrum from the uncured adhesive displayed peaks that were identified with a molecular species bound to Ag surface via the carboxylate functionality of the adsorbate. During thermal cure, the SERS signature showed a partial decomposition of the carboxylate species and the formation of an amorphous carbon layer at the Ag surface. Comparison of the electrical resistance and SERS data showed a strong correlation between the development of high conductance (~1 ohm^-1 ) in the adhesive and the formation of the amorphous carbon layer