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

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 temperatureresistant 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.

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“…After melting and sintering of the particles, the material behaves like the bulk material (Gibbs-Thomson effect) [31,32]. Thus, high-strength and temperature-resistant joints can be produced at low temperatures, which is of great interest for various joining tasks.…”

“…The strength behavior as a function of the mentioned parameters and other process parameters like heating rate, thickness of paste application, surface pre-treatments of the substrates, a pre--drying process and a subsequent heat treatment are investigated [31]. For joining with nanoparticles, the nanoparticles are suspended in solvents and through the addition of dispersing agents surrounded with an organic shell [31,32]. This shell leads to repulsive forces between the particles, so that agglomerations can be avoided [42,43].…”

“…6. Obraz TEM rozkładu nanocząsteczek i wielkość cząstek w nanopaście Ag [32] A modified hydraulic press was used for the joining experiments. The heating of the samples was carried out in air by means of induction.…”

“…The variation of the process parameters joining pressure and joining temperature shows, that the joining temperature exerts a significantly stronger influence on the achievable strengths in comparison to the joining pressure. A comparison with results for the joining of copper with an Ag nanopaste [31,32], where the pressure has a much greater influence on the strength behavior than the temperature, shows that it is not possible to transfer the results of one material system to another when joining with nanosuspensions. The investigations shown that high tensile shear strengths can already be achieved at temperatures between 650 °C and 850 °C [50].…”

“…A comparison with results for the joining of copper with an Ag nanopaste [31,32], where the pressure has a much greater influence on the strength behavior than the temperature, shows that it is not possible to transfer the results of one material system to another when joining with nanosuspensions. The investigations shown that high tensile shear strengths can already be achieved at temperatures between 650 °C and 850 °C [50]. In comparison to the joints with the substrate DC01, the strengths joints with the austenitic stainless steel are significantly decreased.…”