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Title:Sintering behavior of Ag-Sn alloys prepared via cryogenic high-energy ball milling
Author(s):Hestroffer, Jonathan Michael
Advisor(s):Bellon, Pascal
Contributor(s):Averback, Robert
Department / Program:Materials Science & Engineerng
Discipline:Materials Science & Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Severe Plastic Deformation
Ball Milling
Ag nanopaste
Die-attach materials
Abstract:In the pursuit of improved power density and efficiency of power-electronics, there is a need to develop high temperature die-attach materials that are mechanically stable at operating temperatures of 300◦C and provide excellent thermal conductivity between die and substrate materials. There are no obvious choices for all applications, however, low temperature sintering silver nanopastes show great promise given their inherent high melting point, and corrosion resistance. One challenge these materials face is recrystallization at operating temperatures. Recrystallization and grain growth reduce the sinterability of these materials, by removing the paths of diffusion grain boundaries provide, and lower the mechanical strength of the sintered joints. One possible approach to overcome these problems is to employ alloying to stabilize the grain boundaries by segregation or precipitation at grain boundaries, provided that the alloying element does not interfere with the sinterability at low temperatures. One such candidate system is Ag-Sn. This research investigates the microstructural evolution of Ag-Sn alloys, prepared via cryogenic high-energy ball milling, as well as their sinterability. Multiple Sn compositions were studied ranging from 6-15at%Sn. Cryomilling is shown to extend the solid solubility of Sn in Ag from 8 to 15.4at% at room temperature, as well as produce anomalous Bragg peak shifting attributed to the presence of stacking faults and dislocation loops. These alloys prove to sinter better and achieve higher densification than pure Ag. The 15at%Sn alloy achieves a density of 65% when compacted at 350◦C for 1hr under 7 MPa applied load, compared to 54% for pure Ag under similar conditions, even though the average particle size is an order of magnitude smaller than that of the Ag-Sn alloy.
Issue Date:2016-04-29
Rights Information:Copyright 2016 Jonathan Hestroffer
Date Available in IDEALS:2016-07-07
Date Deposited:2016-05

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