Measurement and modeling of the effective thermal conductivity of sintered silver pastes

Abstract

The effective thermal conductivity of sintered porous pastes of silver is modeled through two theoretical methods and measured by means of three experimental techniques. The first model is based on the differential effective medium theory and provides a simple analytical description considering the air pores like ellipsoidal voids of different sizes, while the second one arises from the analysis of the scanning-electron-microscope images of the paste cross-sections through the finite element method. The predictions of both approaches are consistent with each other and show that the reduction of the thermal conductivity of porous pastes can be minimized with spherical pores and maximized with pancake-shaped ones, which are the most efficient to block the thermal conducting pathways. A thermal conductivity of 151.6 W/m K is numerically determined for a sintered silver sample with 22% of porosity

Microstructure statistics–property relations of silver particle-based interconnects

“…The good agreement between the computational homogenization FEM results, used here as the reference, and the analytical higher-order statistical micromechanics estimates shows that the synthetic models can be used for the prediction of the linear effective material properties of the sintered silver interconnect material in the considered range of volume fractions, thus reducing the material development efforts. Finally, it is remarked that the model predictions are in good agreement with the experimentally measured ranges of thermal and mechanical properties [39], although the experimental data show a significant spread between different publications [40,41,42,13], which can be attributed to large variations in processing conditions (bulk material versus an interconnect), the presence of the defects (e.g. large voids) and the capabilities of measurement techniques to deal with small porous samples.…”

“…-40 • C to 150 • C). For the computation of the effective thermal conductivity, MVEs were subjected to an overall macroscopic temperature gradient, in combination with the periodic boundary conditions, see [31,13] for details. Note, that the use of the periodic boundary conditions results in a non-uniform, but periodic, temperature distribution on the cube faces.…”

“…Although these models can match the experimental values, they usually require some fitting and thus do not establish a direct relation between microstructural variations and the effective properties. Another approach that leads to very good prediction of the effective properties is based on direct numerical (often finite element) simulations of either idealized [10], or actual microstructures obtained from micrographs (2D) [11,12,13], or computer tomography (3D) [14]. This is a very powerful and rather accurate technique, however, demanding from the viewpoint of time and computer resources.…”

The mechanism of pore segregation in the sintered nano Ag for high temperature power electronics applications

“…Miranda [15] measured the thermal conductivity of sintered Ag and found that the reduced porosity were effective in increasing the thermal conductivity. However, the pore segregation will dramatically decrease the thermal conductivity even the total porosity remains the same.…”

Degradation Mechanism of Pressure-Assisted Sintered Silver by Thermal Shock Test

“…Therefore, die attach materials with high thermal conductivity and heat spread within power modules are required. As a die attach material, sintered silver (s-Ag) has attracted many researchers [3][4][5][6]; the thermal conductivity has been reported to exceed 200 W(m/K) in the case of using pressured-assisted s-Ag [7,8], a value that broke the conventional thermal conductivity limit with around 60 W(m/K) of solder material [9][10][11]. As for the heat spreader, copper substrates jointed with a ceramic plate, called direct bonded copper (DBC) substrates, have been frequently used for power modules.…”