Due to the introduction of Restriction of Hazardous Substances (RoHS) directive Pb containing solders have been banned from the electronics industry and a reliable replacement for the Sn-Pb solder is being sought for by industry around the globe. Medical and Defense industries are currently exempt from the directive and use Sn-Pb solder in their manufacturing process. The switch to lead-free has led component manufacturers to use different lead-free solders, thus causing mixed solder joints of lead-free components with Sn-Pb paste. In this study, mixed assembly microstructures and mechanical properties were examined. Furthermore, six novel lead-free solders were prepared using SAC105 solder doped with elements: Ti, Ni, Mn, La, Ce and Y. The solidification microstructures, fracture behavior and wetting properties of these solders were evaluated to find a suitable replacement for SAC105 solder.

Essential metals like Ca2+ and Zn2+ play critical roles in biological processes through protein interactions. Conversely, non-essential metals (e.g., Gd3+ and Pb2+) also interact with proteins, often with toxic effects. Molecular metal toxicity is assumed to be due to ionic displacement, and studies have demonstrated that Pb2+ replaces Zn2+, Ca2+ and other essential metals in proteins. The focus of this work was to compare protein Ca2+ and Pb2+ -binding sites and to investigate a mechanism of Pb2+ toxicity in Ca2+-binding proteins, particularly the intracellular trigger protein calmodulin (CaM) which binds four Ca2+ ions and interacts with numerous molecular targets via Ca2+-induced conformational change. A statistical analysis of PDB structural data for Pb2+ and Ca2+-binding (EF-hand and non-EF-hand) proteins revealed fewer binding ligands in Pb2+ sites (4 ± 2), than non-EF-Hand (6 ± 2) and EF-Hand (7 ± 1) Ca2+-binding sites. Pb2+ binds predominantly with sidechain Glu (38.4%), which is less prevalent in both non-EF-Hand (10.4%) and EF-Hand (26.6%) sites. Interestingly, analyses of proteins where Pb2+ replaces Ca2+ (calmodulin) or Zn2+ (5-aminolaevulinic acid dehydratase) revealed structural changes presumably unrelated to ionic displacement. These results suggested that Pb2+ adopts diverse binding geometries and that opportunistic binding outside of known Ca2+-binding sites may play a role in molecular metal toxicity. Ca2+-binding affinities (Kd) using phenylalanine and tyrosine fluorescence were found to be 1.15 ± 0.68 X 10-5 M and 2.04 ± 0.02 X 10-6 M for the N- and C-terminal domains, respectively. The Kd for Pb2+-binding in the N-terminal domain, 1.40 ± 0.30 X 10-6 M, was 8-fold higher than Ca2+. Binding of Pb2+ in the C-terminal domain produced a biphasic response with Kd values 7.34 ± 0.95 X 10-7 M and 1.93 ± 0.32 X 10-6 M, suggesting a single higher affinity Pb2+-binding site in the C-terminal domain with nearly equivalent affinity for the remaining sites. Competitive effects of Pb2+ added to Ca2+-loaded CaM were examined using multiple NMR techniques. Pb2+ was found to displace Ca2+ only in the N-terminal domain, however structural/dynamic changes were observed in the central helix apparently due to Pb2+-binding in secondary sites. These data supported our hypothesis that CaM structure and function is altered by opportunistic Pb2+-binding.

Motivation för ledarskap styrs av värderingar, personlighet och tro på sin förmåga. Forskning har genererat tre motivationskategorier för ledarskap, affektiv-identitet ledarmotivation, icke-kalkylerande ledarmotivation och social-normativ ledarmotivation. Studien undersökte dessa tre motivationskategoriernas inbördes rangordning och skillnader mellan utbildningsinriktning och kön samt samband med generell self-efficacy och personlighetsegenskaper enligt femfaktormodellen.  192 studenter deltog från en mellansvensk högskola, därav 54 män, 90 från socionomprogrammen, 72 från det internationella businessprogrammet och 30 från två ingenjörsprogram.  De besvarade en enkät bestående av Chan och Drasgows Motivation to lead scale, Chen, Gully och Edens General self- efficacy scale och Shafers femfaktormodell Big Five Marker. Resultatet visar att det finns skillnader mellan motivationskategorier och utbildningsinriktning. Det finns samband mellan motivationskategorier och personlighet. Inga skillnader i self-efficacy mellan utbildningsinriktning eller mellan könen. Resultatet diskuteras utifrån behov av ledarskap i samhället, krav i ledarrollen, utveckling av individer i riktning mot ledarskap och utveckling av nya ledarmodeller exemplifierat med delat ledarskap.

Lead is an omnipresent pollutant, and its contamination in natural waters is an issue of current regulatory concern throughout the world including Canada. The free divalent ion of lead (Pb2+) is considered to be the most bioavailable and toxic form of lead. Pb2+ is known to be a calcium antagonist in vertebrates including fish. It is believed that lead causes toxicity to freshwater fish primarily by disrupting ionic homeostasis both during acute and chronic waterborne exposure. Lead can also potentially act as a respiratory toxicant since it is known to impair hemoglobin synthesis in both vertebrates. To date, the mechanistic underpinnings of lead accumulation and toxicity in aquatic invertebrates are not well understood, particularly during acute exposure. Therefore, the main objectives of the present study were in two folds: (i) to investigate the mechanisms of waterborne lead uptake, and (ii) to understand the physiological basis of lead toxicity during acute exposure. I used freshwater crustacean, <i>Daphnia magna</i>, as a model freshwater invertebrate species for my study. <i>Daphnia</i> are known to be quite sensitive to metals and widely used as a model species for toxicity assessments. The results of my study suggest that lead inhibits waterborne Ca2+ uptake in <i>Daphnia</i> in a concentration dependent manner, and this inhibition occurs predominantly through a direct competitive interaction. The entry of waterborne Pb2+ in <i>Daphnia</i> likely occurs via both lanthanum-sensitive and verapamil-sensitive epithelial calcium channels. Moreover, my results also indicate that acute waterborne lead exposure severely disrupts both Ca2+ and Na+ uptake from water, which are concomitant with the increase in the lead body burden in <i>Daphnia</i>. Interestingly however, acute exposure to lead does not affect the rate of oxygen consumption in <i>Daphnia</i>, indicating no acute respiratory toxicity of lead. Overall, it appears that lead acts as an ionoregulatory toxicant to <i>Daphnia</i> during acute waterborne exposure.

Georgia Techs Packaging Research Centers vision of System on Package (SOP) requires that the ball grid array (BGA) package be eliminated and the integrated circuit (IC) directly assembled on the printed wiring board (PWB). Flip-Chip on board (FCOB) emerges as a viable solution which meets the industry requirements of (i) increased I/O, (ii) increased functionality and (iii) improved performance at lower costs. Nevertheless flip-chip on board (FCOB) reliability continues to be an important concern in electronic packaging industry. Moreover transition to Pb-free solder for interconnects and continuously shrinking geometries result in new modeling challenges. In addition, the integrity of the intermetallics (IMCs) at the interfaces of the solder/PWB and solder/die is one of the determinant factors in the reliability and continuity of electrical signals in flip-chip interconnects. Pb-free solder studies for the flip-chip assembly studies are limited and simplified so far, not fully incorporating the effect of intermetallics in the reliability. New modeling challenges involve many details, from geometry to material properties. A brittle IMC will lead to a fracture at the interface. Also IMC thickness can cause the variation in stresses in the underlying layers, causing delamination. Moreover IMC morphology can also depend on the metal finishes on the PWB. In this work, a combined numerical and experimental program has been developed to address the challenges mentioned above. The flip-chip on board assembly is modeled in 3-D for reliability studies, taking into consideration material non linearities and a 104 order of geometric variation to capture the die size in mm to sub-micron intermetallic thickness. The study intends to determine the stresses induced at the critical interfaces under thermo-mechanical loading incorporating the intermetallic material properties. Various failure modes of these assemblies were studied. Experiments were carried out for comparative reliability studies of Pb-free solder with eutectic Pb-based solder. Intermetallic formation and growth are characterized during thermal aging and its effect on reliability is determined. Parameters affecting intermetallic like under-bump Metallurgy (UBM) thicknesses are varied and its effect evaluated. Moreover experiments with three new substrate pad finishes on PWB are carried out to evaluate them as an alternative to Electroless nickel immersion gold (ENIG) for new Pb-free solder. The final aim of this study is to reach a better understanding of the reliability issues in FCOB.

Lead is often relegated to a footnote or sidebar in the study of ancient metals. However, the hundreds of lead ingots discovered in underwater sites over the past half-century have attested to the widespread production and trade of this utilitarian metal. Shipwreck sites allow independent dating evidence not available for many land find. They also provide information about shipment size as well as accompanying cargo which can offer clues about trade patterns and markets for lead in the ancient world. While lead was not particularly rare nor valuable, it represents small- to moderate-scale trade that bridges the gap between luxury trade and the circulation of staple agricultural products. It thus can be viewed as a proxy for the many other perishable materials that supported daily life, such as timber, cloth, cordage, leather and pigments. Due to the abundance of lead ingot finds, published in many different languages with great variation in the details provided, it is difficult to compare all of this material. This thesis, therefore, compiles and presents data on all published lead ingots from Mediterranean and Atlantic shipwrecks through the fourth century C.E., in order to provide a framework to analyze the ancient seaborne lead trade. Sixty-eight sites containing lead ingots, lead ore or lead minerals are included in the analysis, divided into six time periods: Bronze Age, Archaic, Classical, Hellenistic, Roman Republic and Roman Empire. A typology of ingots has been developed to allow for comparison of ingots between wrecks. The uses of lead are reviewed, organized by type of use: domestic, professional, military and infrastructural. This allows insight into both the consumers in need of lead and the volume and regularity of consumption required for each use. An overview of lead production and its economic limitations further informs the discussion of the lead trade. The final analysis considers all of these factors in creating a picture of lead trade for each of the six periods, focusing on the regions of supply, the types of demand, and the dominant forces that drove the mining and production of lead.

Thermal fatigue failure, due to the fracture of solder bumps which was cased by the coefficient of thermal expansion mismatch deformation, is frequently encountered in flip-chip package. Therefore, this thesis attempts to study the effects of geometric parameters variation on lead-free flip-chip package under temperature cycling test. First, we used the finite element method to simulate the thermal loading response of lead-free flip-chip. The accumulated equivalent creep strain and accumulated creep strain energy density of the lead-free solder bumps were calculated, and were used to predict the thermal fatigue life of lead-free flip-chip package. The Taguchi method is applied to obtain the optimal design parameters in order to enhance reliability of the lead-free flip-chip under temperature cycling loading. The analysis of variance (ANOVA) is also used for estimating the influence of the factors quantitatively. The obtained results can be adopted as references for the lead-free flip-chip package design.

­^¤åºK­n¡G In this thesis, a two-step de-embedded techniques was applied to measure the important parameters, ft and fmax , of the heterojunction bipolar transistors(HBTs). The same technique was also used to measure the wide-band S parameters for modeling and evaluating the bump chip carrier(BCC) packages. In the simulation, the Ansoft HFSS simulator was used to calculate the insertion and return losses for some bare and packaged test chips. Comparison between simulated and measured results has been discussed in detail to illustrate the applicability of the HFSS simulator.

This thesis investigates the performance of pulse charging, which is believed to be superior to constant current charging in some respects, such as charging efficiency and charging speed. The investigation is focused upon the extensively used secondary batteries, lead-acid batteries. The consecutive orthogonal arrays method is applied to search for the optimum operating variables of pulse charging, including pulse amplitude, duty ratio and frequency of the charging current. Unfortunately, the experimental results of consecutive orthogonal arrays reveal that charging efficiency is not obviously affected by pulse amplitude, duty ratio or frequency. Instead, charging rate is dominantly influenced by average charging current. These results indicate that pulse charging scheme is not superior to constant current charging. To compare these two charging schemes further, a series of experiments are carried out to discuss the effects of each operating variables. Unfortunately, no evidence from the experimental results can prove the superiority of pulse charging to constant current charging as formerly documented.

Colloid-borne Heavy Metals in the Drainage Gallery of an Abandoned Zn-Pb-Ag Mine (in German). The colloid inventories and the colloid-borne heavy metals in the Rothschönberger Stolln adit, the main drainage gallery of the Freiberg, Germany, mining district, were investigated. This adit runs from Freiberg to the village of Rothschönberg, where it flows into the river Triebisch, a tributary of the river Elbe. The water of the adit is a typical mine water from a flooded ore mine. The main reason for choosing the Rothschönberger Stolln adit for colloid investigations was that ample knowledge concerning the origin of the water and the geology of its catchment area exists. The aim was to characterize the colloids at the mouth of the adit and to elucidate if important contaminants occur in a colloid-borne form. A colloid concentration of about 1 mg/L was found. The particles have a size of 50 to 150 nm. They primarily consist of iron and aluminum oxyhydroxide and carry trace elements such as Pb, As, Cu, Y, La. The contaminants Pb and As are almost entirely colloid-borne. Colloids can have both a retarding and a stimulating influence on the transport of contaminants. The existence of colloids should be taken into account if mine waters flow to the biosphere or if mine waters are to be purified by permeable reactive barriers.