Low temperature sintering of Ag nanoparticles for flexible electronics packaging

Abstract

We achieve robust bonding of Cu wires to Cu pads on polyimide with silver nanopaste cured at 373 K. The paste is prepared by simply condensing Ag nanoparticle (NP) solution via centrifuging. The bonding is formed by solid state sintering of Ag NPs through neck growth and direct metallic bonding between clean Ag–Cu interfaces. Both experiment and Monte Carlo simulation confirm that the melting point of joint clusters increases during sintering. This creates improved bonds for use at an elevated operating temperature using Ag NPs.

Effects of Joining Conditions on Joint Strength of Cu/Cu Joint Using Cu Nanoparticle Paste

“…Furthermore, the sintering behavior of metallic nanoparticles has been exploited to write electronic circuits and join components to substrate [15][16][17][18][19][20]. For example, Ide et al [16] reported achieving Cu-to-Cu joining using Ag metallo-organic nanoparticles at a low bonding temperature (573 K) and a bonding pressure of 1 or 5 MPa; the shear strength of the resulting joints was 25-40 MPa.…”

“…Bonding was believed to occur because of the large surface energy contributed by the nanoparticles. As the latest work for low temperature bonding using Ag nanoparticles, Hu et al [19] reported that robust bonding of Cu wire to Cu pads on polyimide was achieved at 373 K through solid state sintering of Ag nanoparticle and metallic bonding of Ag to Cu substrates. Using the sintering behavior of Cu nanoparticles, Jang et al [20] reported using Cu nanoparticles as ink to print a conductive Cu pattern directly on flexible polyimide substrate using their own functional materials and printing system.…”

Are Sintered Silver Joints Ready for Use as Interconnect Material in Microelectronic Packaging?

“…However, a minimum pressure-the ''threshold stress''-must be exceeded to form a reliable sintered Ag joint. It should be noted here that it is not necessary to completely remove the capping agent for bonding to be effective, 28,32,33 but leaving the organic residues in the sintered Ag joint will pose a risk to long-term reliability.…”

“…27 In another study, regarding the neck size and particle size of Ag nanoparticles, the neck size was found to grow rapidly until it reached 50 % of the particle size before slowing down. 28 In the case of micron-sized Ag particles, other endothermically decomposable silver compounds, such as Ag-oxide or Ag-oxalate compounds, provide the bonding phases between adjacent silver particles when they reduce to reactive and pure Ag at temperatures above $200°C (i.e., 220°C for Ag oxide). The application of pressure aids in the diffusion of Ag atoms to densify the Ag joints during sintering.…”

Silver Recovery from Acidic Solutions by Formation of Nanoparticles and Submicroparticles of Ag on Microfiltration Membranes

“…The size and shape of the nanoparticles depends on different parameters such as, silver, nitric and ascorbic acids concentrations and the stirring rate of the solutions. Considering the extensive applications of nano and submicrometer Ag particles as catalysts, conductive adhesives, display devices, passive components, inkjet printing, photon emission, and higher order multiples resonances substrates (Dai et al, 2011;Hu et al, 2010;Xu et al 2008;Sung et al, 2010;Gloskowskii et al, 2008), this methodology could be used in a wide range of industrial applications.…”