Board level solder joint reliability modeling and testing of TFBGA packages for telecommunication applications

For thin-profile fine-pitch BGA (TFBGA) packages, board level solder joint reliability during the thermal cycling test is a critical issue. In this paper, both global and local parametric 3D FEA fatigue models are established for TFBGA on board with considerations of detailed pad design, realistic shape of solder joint, and nonlinear material properties. They have the capability to predict the fatigue life of solder joint during the thermal cycling test within ±13% error. The fatigue model applied is based on a modified Darveaux’s approach with nonlinear viscoplastic analysis of solder joints. A solder joint damage model is used to establish a connection between the strain energy density (SED) per cycle obtained from the FEA model and the actual characteristic life during the thermal cycling test. For the test vehicles studied, the maximum SED is observed at the top corner of outermost diagonal solder ball. The modeling predicted fatigue life is first correlated to the thermal cycling test results using modified correlation constants, curve-fitted from in-house BGA thermal cycling test data. Subsequently, design analysis is performed to study the effects of 14 key package dimensions, material properties, and thermal cycling test condition. In general, smaller die size, higher solder ball standoff, smaller maximum solder ball diameter, bigger solder mask opening, thinner board, higher mold compound CTE, smaller thermal cycling temperature range, and depopulated array type of ball layout pattern contribute to longer fatigue life.     

Re-engineering the elective surgical service of a tertiary hospital: a historical controlled trial

In Old World monkeys, intense affiliative interactions between adult males and infants have mostly been observed in the tribe Papionini. Although these male-infant interactions have been reported in most species of the genera Papio, Theropithecus and Cercocebus, they have only erratically been reported in the genus Macaca. In this article I show that the distribution of male-infant interactions within the genus Macaca can be accounted for by the phylogenetic relations among macaque species and by the evolution of the genus Macaca relative to the other Papionini.     

Infection with hepatitis G virus among recipients of plasma products

BACKGROUND: Hepatitis G virus (HGV or GBV-C) is a newly discovered human flavivirus distantly related to hepatitis C virus (HCV). Little information is available on its natural history or routes of transmission, although it can be transmitted parenterally. We investigated the prevalence of persistent infection of HGV and HCV in patients exposed to non-virus-inactivated pooled blood products associated with transmission of HCV. METHODS: RNA was extracted from the plasma of 112 patients with haemophilia and 57 with hypogammaglobulinaemia, as well as from 64 different batches of archived coagulation-factor concentrates and immunoglobulins. RNA was reverse transcribed and amplified with primers from the 5' non-coding region of HCV and HGV by a nested polymerase chain reaction (PCR). Viral RNA was quantified by titration of complementary DNA before amplification. FINDINGS: Among non-renumerated UK blood donors HGV infection (detected by PCR) was more common than HCV infection (four [3.2%] of 125 compared with 137 [0.076%] of 180658 in southeast Scotland). Testing of batches of factor VIII and factor IX concentrates prepared without viral inactivation procedures showed high frequencies of contamination with HGV (16 of 17 factor VIII batches positive; six of six factor IX batches positive), with no difference between renumerated and non-renumerated donors. However, among 95 haemophiliacs who had received non-virus-inactivated concentrates, 13 (14%) were positive for HGV compared with 79 (83%) who were positive for HCV. Two of 37 recipients of long-term immunoglobulin replacement therapy were positive for HGV. Virus inactivation of blood products substantially reduced or eliminated contamination by HGV RNA sequences. INTERPRETATION: Despite the extremely high level of HGV contamination of non-virus-inactivated blood products, their use was not associated with high rates of persistent infection in recipients. The infectivity of HGV in blood products may be lower than that of HCV, or the virus may be less able to establish persistent infection in humans. Whatever the case, the high prevalence of active HGV infection in the general population remains difficult to explain.     

Dopant Effect on Local Dielectric Properties in Barium Titanate Based Electroceramics Determined by Transmission EELS

Local electronic excitations of Nb-doped BaTiO₃ electroceramic were investigated using low-loss electron energy loss (EEL) spectroscopy with a transmission electron microscope. The variations in electronic structure of the BaTiO₃ were monitored as a function of Nb content by using Kramers-Krönig analysis of the low-loss EEL spectra. We found that the valence state of Nb (+5) as compared with that of the Ti (+4) introduces changes in the valence and conduction band states of BaTi_{1− x} Nb _x O₃ samples. The real part of the dielectric function, Re(1/ɛ), displays an increasingly less negative character with higher amounts of dopant and the valence plasmon exhibits "quasi-plasmon" characteristics with the addition of Nb (at 0.0–1.8 at.%). Further, the plasmon energy shifts (by about 0.5 eV) to higher values with Nb additions. Significant changes take place in oscillator strengths of excitations in local (nanometer-scale) regions of the perovskite samples. This investigation demonstrates a method to quantitatively assess electronic properties, at the submicrometer scale, of doped ceramics used in electronic and electrooptical applications.     

The effect of ranitidine on the tuberculin skin test

The previously unreported occurrence of dysbaric osteonecrosis in an amateur sport scuba diver who had no other identified cause of avascular bone necrosis is described.     

Optimization and thermodynamic understanding of conduction-cooled Peltier current leads

Conduction-cooled Peltier current leads (PCLs) are optimized in a superconducting magnetic system. Optimum geometric factors, viz. the ratio of length to cross-sectional area, of both the copper lead and thermoelectric element, are simultaneously found to minimize the heat leak per PCL. A rigorous thermodynamic temperature-entropy (T-s) diagram is constructed. The heat leak as well as the total input power of both PCLs and converntional all-copper leads can be easily identified from the rectangular areas on the simple 2-D T-s plane.     

Additive and interactive effects on response time distributions in visual word recognition.

Across 3 different word recognition tasks, distributional analyses were used to examine the joint effects of stimulus quality and word frequency on underlying response time distributions. Consistent with the extant literature, stimulus quality and word frequency produced additive effects in lexical decision, not only in the means but also in the shape of the response time distributions, supporting an early normalization process that is separate from processes influenced by word frequency. In contrast, speeded pronunciation and semantic classification produced interactive influences of word frequency and stimulus quality, which is a fundamental prediction from interactive activation models of lexical processing. These findings suggest that stimulus normalization is specific to lexical decision and is driven by the task's emphasis on familiarity-based information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Performances of DPSK and FSK CDMA systems with complex signature sequences

This paper investigates the performance of direct‐sequence code‐division multiple‐access (CDMA) communication systems in Gaussian noise channels using binary and M‐ary noncoherent signaling schemes with complex signature sequences. Differential‐phase‐shift‐keyed (DPSK) signaling with differentially coherent demodulation and frequency‐shift‐keyed (FSK) signaling with noncoherent demodulation are considered. Upper and lower bounds are presented for the probability of bit error (p.b.e.) of binary DPSK and binary FSK systems when the number of users is small. Simulation and Gaussian approximation are used to obtained the p.b.e. when the number of users is large. Two types of complex sequences (FZC and 4‐phase sequences) and one type of binary sequences (Gold sequences) are used for evaluating numerical results. Results show that complex sequences outperform binary sequence when the number of users is small. However, as the number of users gets large, all sequences have similar performances. These suggest that complex sequences should be used when the number of users is small, but binary sequences should be used when the number of users is large, as binary sequences are easier to generate. This revised version was published online in June 2006 with corrections to the Cover Date.