Microstructural Evolution and Arrest in a Silver Nanoparticle Based Die Attach Material for Extreme Environments

Student thesis: Doctoral ThesisDoctor of Philosophy


Utilisation of silver nanoparticle paste as high temperature die attach has been investigated. The examinations of high temperature behaviour of sintered silver have indicated massive grain growth and microstructural evolution at 250 °C. The rate of evolution of the microstructure has been found to increase substantially above 350 °C. This high temperature behaviour can undermine the reliability of sintered silver nanoparticles at high operating temperatures if no modifications are applied to the pure form of this material. In addition to the microstructural evolution of the silver in isolation, silver atoms inside the die attach undergo massive migration towards any gold interfaces contacting the die attach. This behaviour can result in reduction of the mechanical performance of the die attach and undermine the thermal reliability as well. Here two new techniques are introduced addressing these two concerns, both of which produce joint structures with improved thermal stabilities. In one technique oxidation of sintered silver’s internal surfaces has been able to stop microstructural evolution of sintered silver up to 400 °C, increasing the thermal stability of sintered silver from 200 °C to this new limit. The other technique has combined sintered silver with a gold mesh interposer to use the mass migration of silver and gold atoms to obtain extreme thermal stability. The samples produced with this technique could withstand testing at 600 °C. Furthermore, a review of literature on this field has uncovered the result that while applying sintering pressure on the die results in improved mechanical strength, without this pressure the higher porosity allows better thermal cycling resistance of sintered silver. This indicates another important advantage of the second thermal stabilization technique, namely that using a mesh interposer allows control over the amount of porosity, helping to achieve the desired properties.
Date of Award2017
Original languageEnglish
Awarding Institution
  • King's College London
SupervisorChris Lorenz (Supervisor) & Samjid Mannan (Supervisor)

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