Disabling of Nanoparticle Effects at Increased Temperature in Nanocomposite Solders

Omid Mokhtari,Michael P Clode,Roya Ashayer,Ali Roshanghias,Farzad Khomamizadeh,Mark Miodownik,Samjid H Mannan,Amir H Kokabi,Hiren R Kotadia

doi:10.1007/s11664-012-1976-y

Omid Mokhtari, Michael P Clode + Show 7 more

Open Access

https://doi.org/10.1007/s11664-012-1976-y

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Abstract

The use of nanoparticles to control grain size and mechanical properties of solder alloys at high homologous temperature is explored. It is found that silica nanoparticles in the 100 nm range coated with 2 nm to 3 nm of gold can be dispersed within solders during the normal reflow soldering process, and that these particles are effective in hardening the solder and restricting dynamic grain growth during compression testing at low homologous temperature. As the homologous temperature increases towards 0.75, the effects of the nanoparticles on both mechanical properties and dynamical grain growth reduce, and by homologous temperatures of 0.86 the effects have completely disappeared. This behavior is explained by introducing the concept of an effective volume fraction of pinning nanoparticles, and the practical implications for using nanoparticles to control solder properties via Zener pinning at high homologous temperatures are discussed.

Highlights

As a response to environmental concerns, the previous two decades have seen the gradual replacement of traditional eutectic tin-lead solders with ‘‘Pb-free’’ solders
The grain diameter increases up to 100°C due to dynamic grain growth during compression,[19] resulting from failure of the pinning particles (Cu6Sn5 and Ag3Sn intermetallic particles in the SAC case, and below 150°C, the silica nanoparticles in the nanoparticle-enhanced SAC case) to resist grain boundary movement due to the applied compressive stress
The results show that gold coating allowed nanoparticles to be captured within the solder during the solder reflow process

Summary

INTRODUCTION

As a response to environmental concerns, the previous two decades have seen the gradual replacement of traditional eutectic tin-lead solders with ‘‘Pb-free’’ solders. While traditionally the dispersed particles are in the micron size range, theoretically the maximum benefit is obtained with the smallest particles These should be uniformly sized and homogeneously distributed within the solder in order to impede grain boundary sliding and dislocation movement.[6,7,8] The mechanism of grain growth limitation by second-phase particles is termed Zener pinning, and Mokhtari, Roshanghias, Ashayer, Kotadia, Khomamizadeh, Kokabi, Clode, Miodownik, and Mannan the original treatment predicts the relationship between limiting grain size, R, particle size, r, and the particle volume fraction, f,9 as r. The nanoparticles chosen for this study are initially composed of a silica core and thin Au metallic shell to ensure solder wettability.[13,14] Silica was chosen as it is thermodynamically and chemically stable under the experimental conditions

EXPERIMENTAL PROCEDURES

RESULTS AND DISCUSSION

CONCLUSIONS