of the solder. In this thesis, a new fabrication process for incorporating NiTi particles (10 vol.% NiTi) into Sn-In solder (80Sn-20In) using liquid phase sintering has been developed. The microstructures of the solders were characterized. The behavior of the solder joints during thermomechanical cycling was also characterized and the results showed that the shear stress induced in the composite solder joint is significantly reduced relative to that in the monolithic solder joint due to the generation of a back-stress associated with the B19Å fÅ *B2 phase transformation of the NiTi particles during the heating part of the cycle. This causes an appreciable reduction of the total inelastic strain range during cycling.

In todayâ s Flip Chip (FC) and Ball Grid Array (BGA) electronic packages solder joints provide both the electrical as well as the mechanical connections between the silicon chip and the substrate. Due to coefficient of thermal expansion (CTE) differences between the chip and substrate the solder joints undergo thermomechanical stresses and strains as an electronic package is heated and cooled with power on/off cycles. Advances in chip designs result in chips that are larger, run hotter and demand improved resistance to creep and low-cycle fatigue in the solder joints. In this study the strengthening of these joints with two different reinforcements is explored: a hard particulate and a shape memory alloy (SMA) single fiber composite (SFC). A baseline is established with a SnAgCu solder that is then compared to test runs on the same solder matrix with Copper particles and then the SMA, Nickel- Titanium wire as reinforcements.

by Yeung Ching Chung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1998. / Includes bibliographical references (leaves 69-71). / Text in English; abstract also in Chinese. / by Yeung Ching Chung. / Table of contents --- p.i / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- General overview --- p.1 / Chapter 1.2 --- The present study --- p.3 / Chapter Chapter 2 --- Sample preparation and characterization / Chapter 2.1 --- Sample preparation / Chapter A. --- General description --- p.5 / Chapter B. --- The thermal pulse furnace --- p.7 / Chapter C. --- The substrates --- p.9 / Chapter D. --- Sample preparation --- p.10 / Chapter 2.2 --- Sample characterization / Chapter A. --- Micro Raman system --- p.11 / Chapter B. --- Rutherford backscattering spectrometry (RBS) --- p.12 / Chapter C. --- X-ray powder diffraction --- p.13 / Chapter D. --- AFM. SEM and Surface Profiler --- p.13 / Chapter Chapter 3 --- Results and discussion / Chapter 3.1 --- The surface morphology / Chapter A. --- General description --- p.15 / Chapter B. --- The as-deposited amorphous film --- p.15 / Chapter C. --- The crystalline Ge film --- p.16 / Chapter D. --- The alloy film --- p.17 / Chapter E. --- The role of a-Si layer --- p.22 / Chapter 3.2 --- The depth profile (RBS) / Chapter A. --- General description --- p.24 / Chapter B. --- Peak temperature dependence --- p.27 / Chapter C. --- Heating rate dependence --- p.30 / Chapter 3.3 --- The near surface composition measured by Raman scattering / Chapter A. --- General description --- p.33 / Chapter B. --- Peak temperature dependence --- p.43 / Chapter C. --- Heating rate dependence --- p.45 / Chapter 3.4 --- Preferred growth direction / Chapter A. --- General description --- p.47 / Chapter B. --- Peak temperature dependence --- p.48 / Chapter C. --- Heating rate dependence --- p.51 / Chapter 3.5 --- Discussion / Chapter A. --- The particle size --- p.55 / Chapter B. --- The participation of Si substrate --- p.58 / Chapter C. --- The alloy formation --- p.58 / Chapter D. --- The abnormally fast interdiffusion --- p.63 / Chapter Chapter 4 --- Conclusion --- p.65 / Appendix --- p.67 / References --- p.69

Aluminum alloys are the subject of increasing interest (in the automotive industry, as well as aircraft industry), aiming to reduce the weight of components and also allowing a profit in term of energy saving. Concerning the assembly, riveting has been widely used in the aircraft industry, whereas welding seems to be promising in the car industry in the case of aluminum alloys. Nevertheless, welding can generate defects, such as porosity or hot cracking, which could limit its development. One of the major problems associated with the welding of aluminum alloys is the formation of gas porosity. Aluminum alloy cleanliness remaining one of the aluminum industry's primary concerns, this project focuses on the formation and distribution of porosity in Al-Si welds. A literature review has been performed, to identify the mechanisms of porosity formation in welds and castings. Porosity distribution in welds has been investigated, based on three different welding techniques: hybrid Laser/MIG welding process, the electron beam welding process, and the MIG dual wire welding process. Porosity distribution results provide information on to the porosity formation mechanisms involved during welding. A complete microstructure, microhardness and EDX analysis have been carried out, to describe and quantify the solidification process within the welds.

Aluminum - Silicon alloys are recognized as appropriate materials for high performance cast components used in transportation powertrain applications. A combination of excellent wear resistance, good thermal conductivity and low density make these materials good candidates for engine bore applications. It is well accepted that the tribological properties of these alloys are dictated by the presence of hard eutectic silicon particles and their distribution in the soft aluminum matrix. Three near-eutectic aluminum-silicon engine bore alloys manufactured by different processing routes such as sand casting, chill casting and spray compaction were investigated to determine the influence of solidification on evolution of microstructure of these alloys and to establish correlation of microstructure with tribological properties. The spatial distribution of the silicon particles in aluminum matrix is analyzed using various image analysis techniques and contact distribution studies. The chill cast alloy shows large columnar primary aluminum dendrites interspersed with coarse silicon particles. The sand cast and spray compacted alloys show better spatial distribution of refined silicon particles. Microstructures generated under different solidification modes are found to have varying morphologies. The crystallographic orientations of the dendritic and eutectic aluminum as well as that of the eutectic silicon were studied using electron backscatter diffraction (EBSD). The eutectic silicon nucleating in chill cast alloy is found to exhibit strong orientation relationship with the aluminum matrix. The crystallographic orientation relationship shows that the solidification modes of the eutectics in these three alloys are different, from alloy to alloy, due to their different solidification rates and due to the addition of grain refiners and modifiers. The hardness values of the aluminum matrix and silicon particles of these alloys were found using nanoindentation and micro indentation tests. Preliminary wear studies were carried out on etched and unetched test alloys in dry reciprocating sliding. The results show that of the three test alloys, the alloy in which eutectic regions nucleate heterogeneously from the primary aluminum dendrites gives the best wear resistance and the highest hardness. The very low friction coefficient recorded for the etched alloys is accounted for by the insitu formation of a thin sheet of tribofilm on the protruding silicon particles. The physical and chemical natures of this protective film are being investigated.

No description available.

Cast Al-Si and Al-Si-Mg alloys containing up to 12.6 wt. pct. silicon and 1.0 wt. pct. magnesium were prepared. The changes in electrical conductivity/resistivity of these alloys due to strontium additions have been investigated and explained in terms of variations in microstructure. The conductivity behaviour of strontium-containing and strontium-free alloys was found to exhibit marked differences, depending on the silicon and magnesium contents and the rate of solidification. The electrical conductivity of single phase alloys containing less than 1.60 wt. pct. Si decreased with increasing silicon and magnesium levels. However, strontium had no effect on the conductivity of these solid solution alloys since it does not dissolve appreciably in the aluminum matrix or change the solid solubility of silicon and magnesium in aluminum. Silicon precipitation processes in the supersaturated solid solution alloys of Al-Si and Al-Si-Sr have been examined using the Johnson-Mehl-Avrami equation and found to be isokinetic. Strontium, however, retarded the growth rate of silicon precipitates. Strontium did not affect the kinetics of G.P. zone formation in Al-Si-Mg alloys but it suppressed the formation of stable Mg$ sb2$Si precipitates during subsequent aging at 175$ sp circ$C. Unlike the single phase alloys, two phase Al-Si and Al-Si-Sr alloys, in the range of 2.0 to 12.6 wt. pct. Si, exhibited different electrical conductivity behaviour. The strontium-containing alloys showed a higher conductivity than alloys with no strontium, and this conductivity difference increased as the silicon and magnesium contents were increased and the solidification rate was decreased. It has been demonstrated this difference is due to changes in the silicon morphology. Electron scattering at the interface between the aluminum matrix and the eutectic silicon phase contributes significantly more to the resistivity of unmodified alloys than that of modified alloys. In addition, the resistivity of

Thesis (M.S.) in Electrical Engineering--University of Maine, 2007. / Includes vita. Includes bibliographical references (leaf 44).

Thèse (M.Eng.) -- Université du Québec à Chicoutimi, 2005. / Bibliogr.: f. [247]-254. Document électronique également accessible en format PDF. CaQCU

Thèse (M.Eng.) -- Université du Québec à Chicoutimi, 2005. / Bibliogr.: f. [188]-199. Document électronique également accessible en format PDF. CaQCU