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Title: Sintered silver nanoparticles for high temperature electronics
Author: Khtatba, Khalid
ISNI:       0000 0004 9351 4085
Awarding Body: King's College London
Current Institution: King's College London (University of London)
Date of Award: 2020
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The stability and reliability of nanoparticle-based die attach materials at high-temperatures is important for a wide range of modern-day applications. With some electronic devices required to operate at temperatures as high as 500°C, traditional solder-based materials are inadequate. This thesis investigates how silver nanoparticle paste based materials can be used for high-temperature environments. Specifically, sintered-silver die attach was explored with regards to the stability of its structure. Despite already being a potential choice for a range of applications, its functionality at high-temperatures beyond 200°C has not been systematically investigated as it has been in this thesis. It was seen that atomic diffusion mechanisms within the die attach change the microstructure significantly above 250°C, while no microstructural evolution was seen below 200°C. A technique is proposed which uses a wire mesh interposer of gold between the substrate and the die which greatly increases the stability at high temperatures. Exposing the sintered silver to the atmosphere prevented the surface diffusion of atoms and also leads to increased stability. A novel steaming technique was demonstrated which built on this discovery, leading to stability of the samples for temperatures of 300°C for 1008 h and temperatures as high as 400°C for 24 h. This is a considerable improvement to samples which were not exposed to the steaming technique, which began to show microstructural changes at only 250°C after 24 h. Interestingly, it was seen that effective barriers can be produced on the silver by simply immersing the sample in water for around 10 minutes before high-temperature exposure. XPS analysis showed that there is indeed an oxide layer present on the sintered silver and it is proposed that the steaming technique changes the surface of the silver from partially to fully oxidised state. Thus, the proposed technique has shown that sintered-silver die attach can be stabilised, for significant amounts of time, for temperatures of 300°C.
Supervisor: Mannan, Samjid Hassan ; Green, Mark Alan Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available