Low Temperature Bonding of Cu Metal through Sintering of Ag Nanoparticles for High Temperature Electronic Application

Abstract

Lead-based solders bring pollution to the environment and result in health threat to humans. The preparation and application of metallic nanoparticles provide a potential method to develop Pb-free bonding materials. In this article, bonding of Ag-coated Cu bulks was realized through low temperature sintering by directly using the chemically-reduced Ag nanoparticle paste and baked nanoparticle powders at 60 o C, respectively. The results indicate that the capillary flow of paste caused a ring-like deposit on substrate coating, while this phenomenon disappeared when using the powders. Increasing bonding temperature facilitated the sintering, and shear strengths of 20 MPa and 84 MPa was obtained at bonding temperature of 250 o C for 30 min under 20 MPa when using the Ag paste and powders, respectively. High joint strength value of bonded region using paste is due to the high effective bonding pressure and small effective bonded area. Finally, for the extensive application in packaging industry especially for high temperature electronics, challenges such as the improvement of screen and stencil printing ability of paste, avoiding bonding pressure and lowering the cost were pointed out based on our and other researcher's achievements. Cu nanoparticle or Cu-containing nanoparticle mixture pastes are promising but the problems of oxidation and bonding stability must be resolved urgently.

Time-Efficient Sintering Processes to Attach Power Devices Using Nanosilver Dry Film

“…The present average shear strengths in the range of 26.1MPa to 46.6MPa are also comparable with those of the sintered silver joints using wet silver pastes which took longer processing time [16,17]. For example, the shear strengths were 15.7 to 80 MPa for those sintered joints prepared at sintering temperatures of 220 to 300°C, pressures of 1 to 20 MPa and sintering times of 60s to 1800s [11,[17][18][19]. From the above comparisons, it can be seen that the dry nanosilver film with lower amount of organics could indeed have impacts on the microstructures and properties of the sintered joints.…”

Shear strength of copper joints prepared by low temperature sintering of silver nanoparticles

“…[2,9,11,12] The starting temperature of nanoparticle sintering is controlled by solvent evaporation and organic component burnout. The vaporization of the liquid phase and organic shell decomposition have been reported to occur at temperatures close to 150°C.…”

“…The vaporization of the liquid phase and organic shell decomposition have been reported to occur at temperatures close to 150°C. [11,12] The sintering of silver nanoparticles takes place at temperatures above 170°C and is practically finished at 210°C. [9] Higher temperatures favor the sintering process.…”

Fracture analysis of Ag nanobrazing of NiTi to Ti alloy

“…Ti-Ag binary phase diagram [16] shape were tested for laser brazing NiTi to Ti6Al4V in lap joints configurations. This brazing alloy had already been used in other applications successfully [11,12]. Ag has a high melting point (960 ºC), however, it was seen that the bulk Ag has a higher melting temperature than individual nanoparticles in a paste [15], so the heat necessary to melt the brazing alloy is lower.…”

“…Silver nanoparticle paste has been successfully used in bonding micrometric copper wires of 50 micron diameter [11,12] and research work has been done to understand the interfacial bonding mechanisms of these nanoparticle pastes to bulk materials [13,14]. No information exists on the use of Ag nanopaste to bond parts in the 1 mm range, thus the relevance of analyzing its applicability.…”