Low temperature joining of copper by Ag nanopaste: correlation of mechanical properties and process parameters

S Hausner,G Wagner,S Weis,B Wielage

doi:10.1007/s40194-016-0381-1

Abstract

Nanoparticles exhibit a decrease in sintering and melting temperature with decreasing particle size in comparison to the corresponding bulk material. After melting or sintering of the nanoparticles, the material behaves like the bulk material. Therefore, high-strength and temperature-resistant joints can be produced at low temperatures, which is of big interest for various joining tasks. Joints (substrate: Cu) were prepared with an Ag nanoparticle-containing paste. The influence of the adjustable process parameters joining pressure, joining temperature, holding time, heating rate, thickness of paste application, surface treatment, pre-drying process, and subsequent heat treatment on the strength behavior of the joints was investigated. It is shown that in particular, the joining pressure exerts an essential influence on the achievable strengths. In addition, temperature, holding time, and thickness of paste application have a significant effect on strength behavior. In contrast, the pre-drying process, heating rate, surface pre-treatment, and subsequent heat treatment possess hardly any influence on joint strength.

Highlights

Due to the large specific surface area, nanoparticles exhibit a decrease in sintering and melting temperature with decreasing particle size, Fig. 1
The thermal behavior of the Ag nanopaste was investigated by simultaneous thermal analysis (STA)
The investigations prove that the nanopaste offers a great potential for joining at low temperatures

Summary

Introduction

Due to the large specific surface area (high surface-tovolume ratio), nanoparticles exhibit a decrease in sintering and melting temperature with decreasing particle size, Fig. 1 This effect, which had been theoretically predicted already in 1909 by Pawlow [4, 5] and experimentally verified since the 1950s [6,7,8], was technically implemented only a few years ago and is the subject of intense research. Structural damages of the substrates, e.g., abnormal grain growth or undesirable phase transformation, can be avoided. The utilization of this effect would be of great interest for the joining of materials with different coefficients of thermal expansion such as carbide-metal joints and ceramic-metal joints, to reduce the often critical thermally induced residual stresses of the joints. There is an increasing demand for novel hybrid compound joints, for example, between fiber-

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Conclusion