Silver Migration and the Reliability of Pd/Ag Conductors in Thick-Film Dielectric Crossover Structures
ABSTRACT The relative performance characteristics of thick-film Pd/Ag conductors (0-34% Pd) for dielectric crossover structures in hybrid microelectronic circuits are described. The materials were supplied from Du Pont and Engelhard. The experiments involved waterdrop (WD) tests and temperature-humidity-bias (THB) tests at 90°C, 90% RH, and a dc bias of 5-50 V applied between the conductor electrodes for periods up to 1000 h. WD tests showed that the rate of Ag migration decreased by approximately 100 times as the Pd content in the conductor was increased from 10%-19%. However, the results of these tests were considerably scattered for electrodes of high Pd content. In addition, no conclusive results could be reached on the effect of the substrate or various encapsulants on the rate of migration. The rate of migration under THB conditions was considerably lower (10-4times) than that under the water-drop tests. Surface migration was found to be the dominant mode of failure in dielectric crossover structures. The rate of migration increased with the increasing voltage gradient. When the voltage was increased it caused an abrupt change in the capacitance and isolation resistance. The migration was more pronounced on the surface of bare alumina substrates than on substrates covered with a dielectric layer. Finally, a Du Pont 9137 glass encapsulant was found to be effective in preventing silver migration under THB conditions while an ESL 240 SB encapsulant enhanced the rate of migration.
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ABSTRACT: Diffusion of silver inner-electrode occurred during sintering of commercial low temperature co-fired glass ceramic substrate made the dielectric surface become light yellow. The samples added with silicon oxide (SiO2) powder, however, maintained white color. Silicon-oxide powder was used to modified the sintering behavior and inhibit the silver ions diffusion for the LTCC ceramics. The alumina particles in the LTCC substrates could be regarded as the diffusion barrier of silver ions. The activation energy for silver ions diffusion in the LTCC substrates was 101kJ/mol. When 5wt% SiO2 powder was added into the LTCC substrate, the diffusion activation energy of silver ions became 145kJ/mol. At sintering temperature of 1180K, the diffusion coefficient of silver ion in the LTCC ceramic substrates with and without additional SiO2 were 8.88×10−13cm2/s and 1.08×10−12cm2/s, respectively.Journal of Materials Science 04/2012; 46(13):4695-4700. · 2.16 Impact Factor
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ABSTRACT: 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°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°C and 400°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°C, 350°C, 300°C, and 250°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.IEEE Transactions on Device and Materials Reliability 07/2011; · 1.52 Impact Factor
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ABSTRACT: 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°1C. In this paper, we report our results of the effect of oxygen partial pressure on the migration kinetics of the sintered nanosilver at 400°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.IEEE Transactions on Device and Materials Reliability 07/2011; · 1.52 Impact Factor