Roya Ashayer

Nanoparticle Enhanced Solders for High Temperature Environments

Nanoparticle enhanced solders have been reported to have superior creep and reliability properties compared to simple alloyed materials. The nanoparticles, typically added at 1-2 wt% concentrations into the solder serve to harden the solder, stabilize the microstructure and improve reliability in high temperature environments. The nanoparticles may be added to the solder before production of solder particles, or added as a separate ingredient of the solder paste. This paper explores the latter approach. For this investigation, nanoparticles composed of a silica dielectric core and Au metallic shell were used, and the efficacy of different synthesis routes compared. In particular, it was found that poly diallyldimethyl ammonium chloride (PDADMAC), served as a better linker molecule than 3-aminopropyltrimethoxysilane (APTMS) for attaching the shell to the core. However, even with solder wettable shells, it was found that the majority of the particles were expelled from the SAC solder during reflow in air, and the causes were examined with the aid of computational fluid dynamics to model the reflow process.

Nanoparticle synthesis and formation of composite solder for harsh environments

The demand for electronics capable of operating at high ambient temperatures above 150degC is increasing in the oil/gas drilling and automotive industries in particular. These demands have accelerated the progress of materials development and processing technology. Nanoparticle enhanced solders have been reported to have superior creep and reliability properties compared to simple alloyed materials. The nanoparticles, typically added at 1-2 vol% concentrations into the solder serve to harden the solder, stabilize the microstructure and improve reliability in high temperature environments. The nanoparticles may be added to the solder before production of solder particles, or added as a separate ingredient of the solder paste. This paper explores the latter approach.

Pressure free sintering of silver nanoparticles to silver substrate using weakly binding ligands

The use of a weakly binding ligand to facilitate sintering between particles and a planar substrate in the absence of pressure and at low homologous temperature has been explored. Ag nanoparticles in the 5-15 nm range suspended in water and stabilized by a BH4 complex were dropped onto a polished Ag substrate heated to 333 K. The Ag particles sintered to each other and to the substrate to form a largely pore free system. A molecular dynamics simulation is used to understand the theoretical limits of pressure free sintering and practical implications for adhesive systems based on Ag nanoparticle suspensions are discussed.

Evaluation of the Morphological, Electrical, and Mechanical Properties of Silver Nanopastes

This study investigated the sintering behavior of silver nanopastes at 150°C, 180°C, and 210°C. The synthesized silver nanoparticles were dispersed to form ink pastes with 70 wt. % and 80 wt. % silver. The morphology of the sintered silver nanopastes was studied via transmission electron microscopy (TEM), scanning electron microscopy, and x-ray diffraction analyses. Electrical characterization, thermal/humidity aging, and mechanical testing were also performed. Silver nanoparticles were prepared via a chemical reduction method. TEM images revealed particle sizes ranging from 10 nm to 20 nm. Results showed that electrical conductivity could be achieved at 150°C. When the sintered silver nanoparticles were subjected to 1000 h of 85°C/85 % relative humidity testing, a stable resistivity was achieved at a sintering temperature no lower than 210°C. These results showed that a stable network of sintered silver nanoparticles with good mechanical properties could be achieved at 210°C.