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The effect of the pH value of gold ion plating (PCG) solution on the growth of gold nanoshells with about 100-nm silica cores and 15-nm gold shells was systematically investigated by dynamic light scattering, UV-Vis spectroscopy, scanning electron microscopy, and transmission electron microscopy. The results showed that in PCG solutions, the rapid formation of monomers which intensively influenced by the reducibility of formaldehyde contributed to the growth of gold nanoshells. The reducibility of formaldehyde increased following the increasing pH value from 4.70 to 11.71. Thus at high pH value, it was easy to fabricate the complete gold nanoshells (except of the Cannizzaro reaction of formaldehyde at high pH value). Furthermore, we found that chloride ions also influenced the surface morphology of gold nanoshells by Ostwald ripening process through the Au-Cl complex. [ABSTRACT FROM AUTHOR]

The low-temperature joining of semiconductor chips by sintering of silver paste is emerging as an alternative lead-free solution for power electronics devices and modules working in a high-temperature environment. A promising die-attachment material that would enable the rapid implementation of the sintering process is nanoscale silver paste, which can be sintered at temperatures below 300 ^\circ\C without an external pressure. In this paper, we report our findings on the silver migration in sintered nanosilver electrode-pair patterns on an alumina substrate. The electrode pairs were biased at an electric field ranging from 10 to 100 V/mm and at a temperature between 250 ^\circ\C and 400 ^\circ\C in dry air. The leakage currents across the electrodes were measured as the silver patterns were tested in an oven. Silver dendrites formed across the electrode gap were observed under an optical microscope and analyzed using scanning electron microscopy and energy dispersive spectroscopy (EDS). The silver migration was found in the samples tested at 400 ^\circ\C, 350 ^ \circ\C, 300 ^\circ\C, and 250 ^\circ\C. The measurements on the leakage current versus time were characterized by an initial incubation period, called “lifetime,” followed by a sharp rise as the silver dendrites were shorting the electrodes. A simple phenomenological model was derived to account for the observed dependence of lifetime on the electric field and temperature. The EDS mappings revealed the significant presence of oxygen on the positive electrode but the complete absence on the negative electrode. A mechanism involving the oxidation of silver and the dissociation of silver oxide at the anode was suggested. We suggest that the migration of a sintered nanosilver die attachment can be prevented in high-temperature applications through packaging or encapsulation to reduce the partial pressure of oxygen. [ABSTRACT FROM PUBLISHER]

The low-temperature joining technique of silver sintering is being actively pursued in the power electronics industry as a lead-free die-attach solution for packaging power devices and modules. However, one of the concerns of this technique is the migration of silver at a high temperature. Recently, we have reported our findings of the migration of a low-temperature sintered nanosilver in dry air at a temperature over 250 ^\circ\C. In this paper, we report our results of the effect of oxygen partial pressure on the migration kinetics of the sintered nanosilver at 400 ^\circ\C under an electrical field strength of 50 V/mm. The range of the oxygen partial pressure tested was between <\0.01 and 0.40 atm. The silver migration kinetics were monitored by measuring the leakage current across a metal-finger pattern, which allowed the determination of the “lifetime,” or the onset time for significant leakage current developed across the two electrodes. With decreasing oxygen partial pressure, the lifetime increases exponentially. Our results suggest that the concern for silver migration in a high-temperature application of sintered silver die attach can be effectively remedied through packaging to keep oxygen away from the silver joints. [ABSTRACT FROM PUBLISHER]