Bimodal Sintered Silver Nanoparticle Paste with Ultrahigh Thermal Conductivity and Shear Strength for High Temperature Thermal Interface Material Applications

Abstract

A bimodal silver nanoparticle (AgNP) paste has been synthesized via the simple ultrasonic mixing of two types of unimodal AgNPs (10 and 50 nm in diameter). By sintering this paste at 250 °C for 30 min, we obtained an ultrahigh thermal conductivity of 278.5 W m(-1) K(-1), approximately 65% of the theoretical value for bulk Ag. The shear strength before and after thermal cycling at 50-200 °C for 1000 cycles was approximately 41.80 and 28.75 MPa, respectively. The results show that this excellent performance is attributable to the unique sintered structures inside the bimodal AgNP paste, including its low but stable porosity and the high density coherent twins. In addition, we systematically discuss the sintering behavior of this paste, including the decomposition of the organic layers and the formation of the coherent twins. On the basis of these results, we confirm that our bimodal AgNP paste has excellent potential as a thermal interface material for high temperature power device applications.

Printable Materials for the Realization of High Performance RF Components: Challenges and Opportunities

“…These highly conductive structures are reported to act as bridges across defects and grain boundaries. Similarly, Li et al have recorded thermal conductivity 65% of bulk Ag by utilizing ink with a 2 : 1 ratio of 10 nm Ag NPs to 50 nm Ag NPs to decrease the porosity [73]. Separately, for Au, half of the bulk conductivity has been demonstrated on carefully tailored ligand chemistry and particle sizes at 150°C; however, this was in a thin film ink and not printed [22].…”

On the nature of citrate-derived surface species on Ag nanoparticles: Insights from X-ray photoelectron spectroscopy

“…Citrate ions are widely utilized in the wet chemical synthesis of silver [3][4][5][6][7][8][9][10][11][12][13][14], gold [15][16][17][18][19][20][21], platinum [22] and other nanoparticles, acting as reducing (direct reduction of aqueous Ag + ions by citrate occurs under boiling or hydrothermal conditions [9][10][11][12][13]), complexing, and stabilizing agent, although the precise mechanisms are far from being fully understood. Сitrate is a key reagent for the preparation of silver nanoplates, cubes, disks, etc., as the selective adsorption of citrate on Ag (111) facets impedes their growth and promotes the yield of anisotropic particles [12,[23][24][25].…”

“…Lea [3] as long ago as 1889 is still a rare example of metal colloids stable up to 1 M 4 concentration without high-molecular-weight reagents [4][5][6][7][8][9][10]. It has been reported [5][6][7] that the AgNPs are negatively charged due to adsorption of citrate anions, and their behavior obeys the Derjaguin-Landau-Verwey-Overbeek (DLVO) model, but the studies have been performed for diluted solutions, and the reasons behind stability of the dense sols remain elusive.…”

“…It has been reported [5][6][7] that the AgNPs are negatively charged due to adsorption of citrate anions, and their behavior obeys the Derjaguin-Landau-Verwey-Overbeek (DLVO) model, but the studies have been performed for diluted solutions, and the reasons behind stability of the dense sols remain elusive. Several forms of citrate bonded to the Ag surface through carboxylate groups have been proposed mainly on the base of surface-enhanced Raman scattering (SERS) [8][9][10][11][12]23] and DFT simulation [24,25].…”

“…A hydrogen bond involving alcohol hydroxyl group has been suggested too, while oxidized derivatives of citrate have been observed on the AgNPs only after heating in air [9,10]. In general, however, the results on the surface composition of nanosilver are still scarce and inconclusive, in particular as SERS is not appropriate for quantitative surface analysis.…”