Modeling and Simulation - The Effects of Grain Coarsening on Local Stresses and Strains in Solder Microstructure

A critical issue in the long-term reliability of solder connections used in electronic packages is the joint failure during thermal cycling. Presently in most finite element analysis to predict the solder joint fatigue failures, solder is assumed as a homogeneous single-phase metal. However in the last decade, several metallurgical studies have shown that solder microstructure may have a role in early solder joint failures (ref 1). Investigators have observed (ref 1) that solder microstructure coarsens in local bands during aging and during thermal cycle fatigue. In a failed solder joint, the fatigue cracks are found in these bands of coarse grains. It is speculated that the grain coarsening increases the local strains within the microstructure, thereby increasing the likelihood for a crack to initiate. The objective of this study is to model and simulate the effect of grain coarsening on local stresses and strains. During solidification of eutectic Pb/Sn solder, two types of microstructure form, namely lamellar and equiaxed. In this study, I have developed a computer code to generate both types of microstructures of varying grain coarseness. This code is incorporated into the finite element (FE) code that analyzes the local stresses and strains within the computer-generated microstructure. The FE code, specifically developed for this study, uses an algorithm involving the sparse matrix and iterative solver. This code on a typical single-processor machine will allow the analyst to use over 1 million degrees of freedom. For higher number of degrees of freedom, we have also developed a code to run on a parallel machine using message passing interface. The data reported in this paper were obtained using the single-processor code. The solder microstructure, if assumed to be homogeneous single phase, has gradual variation in local stresses and strains. In 2-phase solder, von mises stresses and strains are heterogeneously distributed. In general, the maximum von mises stress in 2-phase solder case are higher than in 1-phase solder. In lamellar microstructure of 2-phase solder, the maximum von mises stress in the microstructure gradually increases with grain coarseness. In equiaxed microstructure of 2-phase solder, the maximum von mises stress does not follow a general trend, increasing or decreasing, with increasing grain coarseness

Elevated potential for intraspecific competition in territorial carnivores occupying fragmented landscapes

The distribution of mammals is determined by a suite of endogenous and exogenous factors. In territorial, polygynous species like tigers (Panthera tigris), males often center their space-use around female territories, repelling competitors from these areas. Competition among males for females leads to increased mortality of both sexes and infanticide of unrelated cubs, which can lead to population declines. We hypothesized that increased territorial overlap among adult male tigers and elevated levels of inter and intra-sex competition would be manifest in populations with male-biased adult sex ratios (ASR). We also assessed whether inter-sex variation in adult survival or degree of habitat connectivity resulted in skewed ASR. We evaluated these hypotheses using camera trap data from three tiger populations occupying habitat patches with varying levels of connectivity and ASRs. Data were analyzed using multi-state occupancy models, where states were defined as habitat use by one or more male tigers in sites with and without female use. As predicted, in populations with male-biased or even ASR we found evidence for increased spatial overlap between male tigers, particularly pronounced in areas adjacent to female territories. Given parity in adult survival, habitat fragmentation likely caused male-biased ASR. Our results suggest that the persistence of small tiger populations in habitat patches with male-biased ASR may be significantly compromised by behavior-mediated endogenous demographic processes that are often overlooked. In habitat fragments with pronounced male biased ASR, population recovery of territorial carnivores may require timely supplementation of individuals to compensate for population losses from intraspecific competition

Mini ball grid array (mBGA) assembly on MCM-L boards

Sandia National Laboratories has developed a chip scale packaging technology called mini Ball Grid Array (mBGA). The mBGA is a flip chip die, obtained by redistributing peripheral pads in existing dies to an area array of pads 10 mils or larger in diameter with a minimum pitch of 20 mils. The peripheral pads are redistributed to area array pads using two polyimide dielectric and two metal conductor layers. mBGA can be closely tiled together on a substrate to yield a very high circuit density. In an earlier report, the authors presented the results on the reliability and thermal performance of mBGA on silicon and ceramic substrates. In this report, they present an mBGA cost analysis, improvements in the mBGA bump adhesion, and reliability and thermal performance of mBGA assemblies on FR-4 boards

Demostración de resultado económico: percepción del comando da aeronáutica de Brasil

No ano de 2010, uma alteração no quadro normativo brasileiro introduziu a Demonstração do Resultado Econômico (DRE) para o setor público, que busca comparar custos internos de produção com valores de mercado, segundo o conceito de custo de oportunidade. Este estudo procura analisar as possíveis respostas estratégicas dos gestores , buscando perceber se a cultura contábil existente no País permite a aceitação do novo instrumento. Por meio das percepções dos agentes públicos do Comando da Aeronáutica (Comaer), no Brasil, conclui-se que a resposta estratégica dos entrevistados tende para a atitude de aceitação da nova rotina, demonstrando traços de menor conservadorismo e maior interesse pela evidenciação de resultados.In 2010, a change in the Brazilian accounting regulatory framework introduced the Demonstração do Resultado Econômico (DRE) [Economic Income Statement] for the public sector, which seeks to compare the internal costs of production to market values, according to the concept of opportunity cost. This study aims to analyse the possible strategic responses of managers and tries to understand if the existing accounting culture in Brazil facilitates the introduction of the new statement. By means of perceptions of officials of the Aeronautical Command (Comaer), in Brazil, it is possible to conclude that the strategic response of respondents is closer to acceptance of the new routine, showing traces of less conservatism and greater interest for displaying results.En el año 2010, una modificación del cuadro normativo brasileño introdujo la Demostración del Resultado Económico (DRE) para el sector público, que busca comparar los costos internos de producción con los valores del mercado, según el concepto de costo de oportunidad. Este estudio tiene como objetivo analizar las posibles respuestas estratégicas de los gestores, con el fin de percibir si la cultura contable existente en el país permite la aceptación del nuevo instrumento. Por medio de las percepciones de los agentes públicos del Comando da Aeronáutica (Comaer), en Brasil, se concluyó que la respuesta estratégica de los entrevistados tiende a aceptar la nueva rutina, mostrando rasgos de menos conservadurismo y más interés por la manifestación de resultados.Fundação para a Ciência e a Tecnologia (FCT

A male infant with Xq22.2q22.3 duplication containing PLP1 and MID2

Abstract Background The Xq22.2 q23 is a complex genomic region which includes the genes MID2 and PLP1 associated with FG syndrome 5 and Pelizaeus–Merzbacher disease, respectively. There is limited information regarding the clinical outcomes observed in patients with deletions within this region. Methods We report on a male infant with intrauterine growth retardation (IUGR) who developed head titubation and spasticity during his postnatal hospital course. Results Chromosome microarray revealed a 6.7 Mb interstitial duplication of Xq22.2q22.3. Fluorescence in situ hybridization showed that the patient's mother also possessed the identical duplication in the Xq22.3q22.3 region. Among the 34 OMIM genes in this interval, the duplication of the PLP1 (OMIM# 300401) and MID2 (OMIM# 300204) appears to be the most significant contributors to the patient's clinical features. Mutations and duplications of PLP1 are associated with X‐linked recessive Pelizaeus–Merzbacher disease (PMD). A single case of a Xq22.3 duplication including the MID2 has been reported in boy with features of FG syndrome. However, our patient's clinical features are not consistent with the FG syndrome phenotype. Conclusion Our patient's clinical features appear to be influenced by the PLP1 duplication but the clinical effect of other dosage sensitive genes influencing brain development cannot be ruled out

High-G Accelerometer for Earth-Penetrator Weapons Applications LDRD Final Report

Micromachining technologies, or Micro-Electro-Mechanical Systems (MEMS), enable the development of low-cost devices capable of sensing motion in a reliable and accurate manner. Sandia has developed a MEMS fabrication process for integrating both the micromechanical structures and microelectronics circuitry of surface micromachined sensors, such as silicon accelerometers, on the same chip. Integration of the micromechanical sensor elements with microelectronics provides substantial performance and reliability advantages for MEMS accelerometers. A design team at Sandia was assembled to develop a micromachined silicon accelerometer capable of surviving and measuring very high accelerations (up to 50,000 times the acceleration due to gravity) 1 . 4 The Sandia integrated surface micromachining process was selected for fabrication of the sensor due to the extreme measurement sensitivity potential associated with integrated microelectronics. Very fine measurement sensitivity was required ..