The microstructure of the Sn-Ag-Cu solder is examined by optical microscopy and scanning electron microscopy (SEM) for various compositions near the ternary eutectic for different cooling rates from the solder melt. Focus is on the size and orientation of Sn grains as indicated by cross-polarized, light optical microscopy, and pole figures from x-ray diffraction. We find that both composition and cooling rate have strong influences on Sn grain size, with Sn grain size increasing an order of magnitude as Cu concentration increases from 0% to 1.1%. Cyclic growth twinning, with twinning angles near 60°, is observed in Sn-Ag-Cu alloys near the composition Sn-3.9Ag-0.6Cu.
How would you……describe the overall significance of this paper? Insight is provided on how to fabricate thermal bondlines so as to maximize thermal conductance, by manipulating filler particles arrangements. Thermal bondlines provide thermal links between heat generating components and heat sinks.…describe this work to a materials science and engineering professional with no experience in your technical specialty? Although it is recognized that the thermal resistance of a thermal bondline is not a material property, little work has been focused on how to vary processing parameters in order to minimize thermal resistance. This works focuses on optimizing such assembly processes for thermal interface bondlines in order to segregate particles into particular regions, and maximize thermal conductance.…describe this work to a layperson? You could fry an egg on the processor of your computer while it is running gaming software for you. Such heat needs to be removed in order to avoid processor malfunction. Bolting on a small radiator does not quite do it; one needs some type of filled, thermal paste between the two in order to fill small gaps and get the heat out. For the most effective solution, the exact speed at which you squeeze such a thermal paste must be controlled.The influence of processing on filledpolymeric bondline microstructure and thermal performance was examined. Cu/thermal interface material/ Cu trilayers were assembled with a viscously applied, adhesive thermal interface material with Ag filler particles. It was found that decreasing the squeeze rate used for bondline formation from 10 to 0.1 µm/s resulted in a change in the microstructure from fairly homogeneous (homogeneous at 50 µm length scales and above) to one with marked segregation of many filler particles into highly compacted structures spanning the bondline thickness. A three-fold increase in effective thermal conductivity was correlated with this microstructure change. Significant changes in microstructure resulted when the compressive force (300N) used to form the bondline was removed before the bondline structure was stabilized by a cure operation and a four fold increase in the thermal resistance of such bondlines was observed.
Thermal properties of niobium-modified PZT95/5(1.8Nb) and PSZT ceramics used for the ferroelectric power supply have been studied from -100 °C to 375°C. Within this temperature range, these materials exhibit ferroelectric-ferroelectric and ferroelectric-paraelectric phase transformations. The thermal expansion coefficient, heat capacity, and thermal diffusivity of different phases were measured. Thermal conductivity and Grüneisen constant were calculated at several selected temperatures between -60°C and 100°C. Results show that thermal properties of these two solid solutions are very similar. Phase transformations in these ceramics possess first order transformation characteristics including thermal hysteresis, transformational strain, and enthalpy change. The thermal strain in the high temperature rhombohedral phase region is extremely anisotropic. The heat capacity for both materials approaches to 3R (or 5.938 cal/(g-mole*K)) near room temperature. The thermal diffusivity and the thermal conductivity are quite low in comparison to common oxide ceramics, and are comparable to amorphous silicate glass. Furthermore, the thermal conductivity of these materials between -60°C and 100°C becomes independent of temperature and is sensitive to the structural phase transformation. These phenomena suggest that the phonon mean free path governing the thermal conductivity in this temperature range is limited by the lattice dimensions, which is in good agreement with calculated values. Effects of small compositional changes and density/porosity variations in these ceramics on their thermal properties are also discussed. The implications of these transformation characteristics and unusual thermal properties are important in guiding processing and handling procedures for these materials.
The microstructure of four types of manufactured lightweight aggregate was studied using scanning electron microscopy and the results were used to provide insight into the dimensional stability of concretes made from these aggregates. Dimensional stability was determined according to the Test Method for Length Change of Hardened Hydraulic-Cement Mortar and Concrete (ASTM C 157) as modified by the procedures covered in the Specification for Lightweight Aggregates for Concrete Masonry Units (ASTM C 331). Aggregate types studied were rotary kiln produced expanded shale, sintered fly ash, palletized cold bonded fly ash and expanded glass. Scanning electron microscopy revealed the nature of the aggregate pore structure and the extent to which the vesicular structure, typical of most lightweight aggregates, is interconnected. When used in concrete, the three aggregates produced at high temperature met the ASTM C 331 shrinkage requirements while the one made by cold-bonding did not. After 100 days of drying the aggregates were immersed in a lime saturated water for an additional 251 days, followed by air drying during which length measurements were taken periodically. The microstructure was shown to have a pronounced effect on the volume stability of the aggregate.
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