Global Mismatches Research Articles

Global mismatches between threat mapping research effort and the potential of threat abatement actions to reduce extinction risk.

Threat mapping is a necessary tool for identifying and abating direct threats to species in the ongoing extinction crisis. There are known gaps in the threat mapping literature for particular threats and geographic locations, and it remains unclear if the distribution of research effort is appropriately targeted relative to conservation need. We aimed to determine the drivers of threat mapping research effort and to quantify gaps that, if filled, could inform actions with the highest potential to reduce species' extinction risk. We used a negative binomial generalized linear model to analyze research effort as a function of threat abatement potential (quantified as the potential reduction in species extinction risk from abating threats), species richness, land area, and human pressure. The model showed that threat mapping research effort increased by 1.1 to 1.2 times per standardized unit change in threat abatement potential. However, species richness and land area were stronger predictors of research effort overall. The greatest areas of mismatch between research effort and threat abatement potential, receiving disproportionately low research effort, were related to the threats to species of agriculture, aquaculture, and biological resource use across the tropical regions of the Americas, Asia, and Madagascar. Conversely, the threat of linear infrastructure (e.g., roads and rails) across regions, the threat of biological resource use (e.g., hunting or collection) in sub-Saharan Africa, and overall threats in North America and Europe all received disproportionately high research effort. We discuss the range of methodological and sociopolitical factors that may be behind the overall trends and specific areas of mismatch we found. We urge a stronger emphasis on targeting research effort toward those threats and geographic locations where threat abatement activities could make the greatest contribution to reducing global species extinction risk.

Sources of Uncertainty in Regional and Global Terrestrial CO2 Exchange Estimates

The Global Carbon Budget 2018 (GCB2018) estimated by the atmospheric CO growth rate, fossil fuel emissions, and modeled (bottom‐up) land and ocean fluxes cannot be fully closed, leading to a “budget imbalance,” highlighting uncertainties in GCB components. However, no systematic analysis has been performed on which regions or processes contribute to this term. To obtain deeper insight on the sources of uncertainty in global and regional carbon budgets, we analyzed differences in Net Biome Productivity (NBP) for all possible combinations of bottom‐up and top‐down data sets in GCB2018: (i) 16 dynamic global vegetation models (DGVMs), and (ii) 5 atmospheric inversions that match the atmospheric CO growth rate. We find that the global mismatch between the two ensembles matches well the GCB2018 budget imbalance, with Brazil, Southeast Asia, and Oceania as the largest contributors. Differences between DGVMs dominate global mismatches, while at regional scale differences between inversions contribute the most to uncertainty. At both global and regional scales, disagreement on NBP interannual variability between the two approaches explains a large fraction of differences. We attribute this mismatch to distinct responses to El Niño–Southern Oscillation variability between DGVMs and inversions and to uncertainties in land use change emissions, especially in South America and Southeast Asia. We identify key needs to reduce uncertainty in carbon budgets: reducing uncertainty in atmospheric inversions (e.g., through more observations in the tropics) and in land use change fluxes, including more land use processes and evaluating land use transitions (e.g., using high‐resolution remote‐sensing), and, finally, improving tropical hydroecological processes and fire representation within DGVMs.

Calibration of Floating-Gate SoC FPAA System

We present a calibration flow for a large-scale floating-gate (FG) system-on-chip field programmable analog array. We focus on characterizing the FG programming infrastructure and hot-electron injection parameters, MOSFET parameters using the EKV model, and calibrating digital-analog converters and analog-digital converters. In addition, threshold voltage mismatches on FG devices due to their indirect structure are characterized using on-chip measurement techniques. The calibration results in enabling a digital approach, where a design can be programmed without having to deal with the local and global mismatches, on a reconfigurable analog system. This paper shows the results of a compiled nonlinear classifier block comprising a vector-matrix-multiplier and a winner-takes-all on three different calibrated chips.

Special issue on software reuse

Special issue on software reuse

Perils of opportunistically reusing software module

SummaryOpportunistic reuse is a need based sourcing of software modules without a prior reuse plan. It is a common tactical approach in software development. Developers often reuse an external software module opportunistically to improve their productivity. But, studies have shown that this results in extensive refactoring and adds maintenance owes. We assert this problem to the mismatches between the software under development and the reused external module; caused because of their different assumptions and constraints. We highlight the problems of such opportunistic reuse practices with the help of a case study. In our study, we found issues such as unanticipated behavior, violated constraints, conflict in assumption, fragile structure, and software bloat. In this paper, we like to draw attention of the research community to the wide spread opportunistic reuse practices and the lack of methods to pro‐actively identify and resolve the mismatches. We propose the need for supporting developers in reasoning before reuse from the perspective of identifying and fixing both local and global mismatches. Furthermore, we identify other opportunistic software development practices where similar issues can be observed and also suggest the research areas where further investigation can benefit developers in improving their productivity. Copyright © 2016 John Wiley & Sons, Ltd.

Abstract 4281: Targeted or whole genome sequencing of formalin-fixed tissue samples

Abstract Background: To provide a systematic analysis of formalin fixation artifacts on Illumina sequencing libraries and results, we generated two complementary sequencing libraries (target enrichment sequencing and whole exome sequencing) from 11 pairs of matched formalin-fixed paraffin-embedded (FFPE) and fresh-frozen (FF) tumor samples and two pairs of matched FFPE and FF germline samples. We also generated whole genome sequencing data from a single pair of FF/FFPE tumor samples. Results: The results indicate minimal variations in library fragment size, coverage, and PCR duplicates within FF/FFPE paired samples that are less than 1 year old; whereas, a large variation in these parameters were observed in FF/FFPE pairs in samples that are approximately 2 years old. No significant increase in global mismatch rates and C•G>T•A substitutions were observed in FFPE samples from the former group; whereas, a discernible increase in mismatch rates and C•G>T•A substitutions were observed in FFPE samples from the latter group. However, over 99.7% and 99.5% of concordant calls were observed between matched FF and FFPE pairs at reference and non-reference positions within the targeted regions, respectively. Although an increased rate of global mismatches and C•G>T•A substitutions were observed in some FFPE samples, discordant rates were low (<0.26) in all samples because most of the FFPE artifacts were filtered out using GATK workflow. Consistent with this analysis, C•G>T•A substitutions are comparable in non-reference positions in paired FF and FFPE samples. Conclusions: We developed upfront quality assessment and library preparation method that use low input DNA from FFPE samples to perform next-generation sequencing. The results from our studies indicate the suitability of FFPE samples in sequencing studies. Citation Format: Sarah Munchel, Yen Hoang, Yue Zhao, Joseph Cottrell, Brandy Klotzle, Andrew Godwin, Janelle Noel, Brooke Fridley, Peter Beyerlein, Jian-Bing Fan, Marina Bibikova, Jeremy R. Chien. Targeted or whole genome sequencing of formalin-fixed tissue samples. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4281. doi:10.1158/1538-7445.AM2014-4281

Enhanced thermal fatigue endurance and lifetime prediction of lead‐free LGA joints in LTCC modules

PurposeThe purpose of this paper is to describe the effect of indium alloying on the thermal fatigue endurance of Sn3.8Ag0.7Cu solder in low‐temperature co‐fired ceramic (LTCC) modules with land grid array (LGA) joints and the feasibility of using a recalibrated Engelmaier model to predict the lifetime of LGA joints as determined with a test assembly.Design/methodology/approachTest assemblies were fabricated and exposed to a temperature cycling test over a temperature range of −40‐125°C. Organic printed wiring board (PWB) material with a low coefficient of thermal expansion was used to reduce the global thermal mismatch of the assembly. The characteristic lifetime, θ, of the test assemblies was determined using direct current resistance measurements. The metallurgy and failure mechanisms of the interconnections were verified using scanning acoustic microscopy, an optical microscope with polarized light, and scanning electron microscopy/energy dispersive spectrometry (SEM/EDS) investigations. Lifetime predictions of the test assemblies were calculated using the recalibrated Engelmaier model.FindingsThis work showed that indium alloying increased the characteristic lifetime of LGA joints by 15 percent compared with Sn3.8Ag0.7Cu joints. SEM/EDS analysis showed that alloying changed the composition, size, and distribution of intermetallic compounds within the solder matrix. It was also observed that a solid‐state phase transformation (Cu,Ni)6Sn5(→ (Ni,Cu)3Sn4 occurred at the Ni/(Cu,Ni)6Sn5 interface. Moreover, the results pointed out that individual recalibration curves for ceramic package/PWB assemblies with high (≥ 10 ppm/°C) and low (≈ 3‐4 ppm/°C) global thermal mismatches and different package thicknesses should be determined before the lifetime of LGA‐type assemblies can be predicted accurately using the recalibrated Engelmaier model.Originality/valueThe results proved that indium alloying of LGA joints can be done using In‐containing solder on pre‐tinned pads of an LTCC module, despite the different liquidus temperatures of the In‐containing and Sn3.8Ag0.7Cu solders. The characteristic metallurgical features and enhanced thermal fatigue endurance of the In‐alloyed SnAgCu joints were also determined. Finally, this work demonstrated the problems that exist in predicting the lifetime of ceramic packages with LGA joints using analytical modeling, and proposals for developing the recalibrated Engelmaier model to achieve more accurate results with different ceramic packages/PWB assemblies are given.

Thermomechanically loaded lead-free LGA joints in LTCC/PWB assemblies

Purpose The purpose of this paper is to investigate the feasibility of using land grid array (LGA) solder joints as a second-level interconnection option in low-temperature co-fired ceramic (LTCC)/printed wiring board (PWB) assemblies for telecommunication applications. The characteristic behaviour of two commercial lead-free solder materials (Sn4Ag0.5Cu and Sn3Ag0.5Cu0.5In0.05Ni) in reflow processes and thermal cycling tests are also evaluated. Design/methodology/approach The effect of the reflow temperature profile on voiding in two lead-free solders in LTCC/PWB assemblies was investigated using X-ray and scanning electron microscopy (SEM) investigations. The test assemblies were fabricated and exposed to a temperature cycling test (TCT) in a 0-100°C or −40 to 125°C temperature range. Organic PWB material with a low coefficient of thermal expansion (CTE) was primarily used. In addition, to compare LGA assemblies with low and high global thermal mismatches, an LTCC module/FR-4 assembly was also fabricated and exposed to a TCT in a 0-100°C temperature range. The characteristic lifetime of the test assemblies was determined using DC resistance measurements. The failure mechanisms of the interconnections were verified using scanning acoustic microscopy, SEM and finite element (FE)-SEM investigations. Findings This work showed that the solderability of AgPt-metallized LTCC modules was poor, resulting in excessive voiding. This problem was avoided by using pre-tinned modules. In the test assemblies, the Sn4Ag0.5Cu joints had a lower void content and a higher characteristic lifetime compared with the Sn3Ag0.5Cu0.5In0.05Ni joints. Furthermore, it was observed that the Sn3Ag0.5Cu0.5In0.05Ni joints were more prone to fail along the interface between the Ag3Sn layer and the solder matrix than were the Sn4Ag0.5Cu joints. It was assumed that the observed difference in the primary failure mechanisms resulted in the decreased lifetime duration of the SnAgCu-InNi/Arlon in both temperature cycling conditions. Originality/value The results proved that the solderability of both solders in AgPt-metallized modules in a typical surface mount technology process was poor; however, the solderability of the test modules can be notably enhanced with pre-tinned pads. This work also demonstrated the effect of the metallization/solder pair on the failure mechanisms and failure rate in LTCC/PWB assemblies with LGA joints; the work also proved in the TCT, over a temperature range of 0-100°C, that using the present LGA joints in LTCC/PWB assemblies with a high global thermal mismatch did not increase the lifetime duration of the joints to the preferred level (3,000 cycles), whereas the performance of these joints was adequate in assemblies with a low global thermal mismatch. Moreover, the results indicated that using the LGA joint configuration enhanced the reliability of the LTCC/PWB assemblies compared with similar assemblies with collapsible ball grid array solder spheres.

Thermal fatigue endurance of collapsible 95.5Sn4Ag0.5Cu spheres in LTCC/PWB assemblies

The behavior of thermomechanically loaded collapsible 95.5Sn4Ag0.5Cu spheres in LTCC/PWB assemblies with high (LTCC/FR-4; ΔCTE ⩾ 10 ppm/°C) and low (LTCC/Arlon; ΔCTE < 10 ppm/°C) global thermal mismatches was studied by exposing the assemblies into two thermal cycling tests. The characteristic lifetimes of the LTCC/FR-4 assemblies, tested over the temperature ranges of 0–100 °C and −40 to 125 °C, were 1475 and 524 cycles, respectively, whereas the corresponding values of the LTCC/Arlon assemblies were 5424 and 1575 cycles. According to the typical requirements for the industrial lifetime duration of solder joints, the former values are inadequate, whereas the latter are at an acceptable level in a few cases. Furthermore, the global thermal mismatch affected the thermal fatigue behavior of the 95.5Sn4Ag0.5Cu spheres in the temperature range of −40 to 125 °C.

An Analytical Elasto-Creep Model of Solder Joints in Leadless Chip Resistors: Part 1—Development and Verification

A novel two-dimensional model is presented for multiaxial thermal stresses, elastic strains, creep strains, and creep energy density at the interfaces of solder joints in leadless chip resistor (LCR) assemblies. The model is applicable to both plane stress and plane strain conditions, and incorporates both global and local expansivity mismatches. Interfacial thermal stresses are approximated using elementary strength of materials theory under arbitrary time-dependent thermal loading. Partial differential equations are linearized through a simple finite difference discretization procedure. The model is mathematically straightforward, and can be extended to include plastic behavior and problems involving external loads and a variety of geometries. The paper presents comparisons with finite element results and considers the mechanics of solder creep accumulation and stress relaxation as predicted by the model.

Interfacial thermal stresses in solder joints of leadless chip resistors

A novel two-dimensional analytical model has been developed for the interfacial thermal stresses in the solder joints of a leadless chip resistor (LCR) assembly under both plane stress and plane strain conditions. Both global and local expansivity mismatches are incorporated into the model. Interfacial thermal stresses are approximated using elementary strength of materials theory. Governing differential equations are linearized through a finite difference discretization procedure. The conditions of zero shear stress at the free edges and self-equilibrated peel stresses are met. The model is more accurate than existing ones, is mathematically straightforward, and can be extended to include inelastic behavior. The results are compared with available data in the literature and finite element analysis, and a geometry optimization is performed for a sample LCR as an example of the use of the model.

Optimal through-thickness temperature gradients for control of interlaminar stresses in composites

Analytical solutions are sought for optimal temperature distributions to control the interlaminar stresses near the free edges of composite laminates subjected to uniaxial loading. Optimal through-thickness temperature gradients are obtained by minimizing appropriate performance indices that are functions of the far-field properties, with respect to the through-thickness temperature differences. Through the application of these temperatures, effects of local mismatches as well as global mismatches in two of the elastic properties, the Poisson's ratio and coefficient of mutual influence, are minimized. Numerical examples are given for several lay-ups made of graphite epoxy. It is shown that for a cross- or angle-ply laminate a uniform temperature rise or drop can completely eliminate all of the interlaminar stresses, whereas for other laminates nonuniform temperature distributions must be applied to minimize the stresses.

Alloy 42 — A Material to be Avoided for Surface Mount Component Leads and Lead Frames

Alloy 42 and, similarly, Kovar were developed to provide metallic feed‐throughs from the interior of ceramic components to the exterior. The low coefficient of thermal expansion (CTE) of ceramic needs to be almost matched by the feed‐through metal to allow reliable hermetically sealed connections. For this purpose these alloys have served very well. However, because of its wide‐spread use for military applications, for which component hermeticity has been required, as well as because of the easier attachment of low‐CTE die to low‐CTE lead frames, Alloy 42 has found its way into plastic components with often disastrous results. When surface mount solder joints connect materials with different CTEs, global thermal expansion mismatches result. Also, if the materials to which the solder bonds have CTEs that differ from the CTE of solder, local thermal expansion mismatches result. These thermal expansion mismatches are the cause of most SM solder joint failures. Alloy 42 and Kovar not only cause significant global and local thermal expansion mismatches, but are inherently more difficult to solder because of the low solubility of nickel and iron, the main constituents of these alloys, in tin. Pull tests of solder joints show that under the best of circumstances a solder joint that includes an Alloy 42 or Kovar surface is only half as strong as one made to copper surfaces.

Analysis of edge stresses in composite laminates under combined thermo-mechanical loading, using a complementary energy approach

An approximate method is presented to investigate the interlaminar stresses near the free edges of composite laminate plates that are subjected to a combined thermo-mechanical loading. The method is based upon admissible function representations of stresses which account for the effects of both the global mismatches and the local mismatches in two of the elastic properties, the Poisson's ratio and the coefficient of mutual influence. For this purpose, new thermo-mechanical mismatch terms are defined to reflect an effective deformation under the combined thermo-mechanical loading. Closed form solutions of all the stress components are sought by minimizing the complementary energy with respect to the unknown functions, in the stress representations, of the width coordinate. These unknown functions are determined by solving five ordinary differential equations along with a set of free edge boundary conditions, which allow complex as well as real roots for their exponential decaying rates. The resulting solutions satisfy the stress equilibrium and all of the boundary conditions exactly, but compatibility is met in a weak form. Numerical examples are given for several typical laminates, and are compared with previous results obtained by finite element and other approximate methods. It is found that the present approximate method yields interlaminar stress results in an efficient, fast and yet reliable way. It is also concluded that unlike some previous approximate methods, the current method is numerically robust and stable.

Attachment reliability evaluation and failure analysis of thin small outline packages (TSOP's) with Alloy 42 leadframes

A series of studies designed to evaluate the long term surface mount reliability of Alloy 42 leaded thin small outline packages (TSOPs) using thermal cycling as an acceleration method is described. Visual inspections, pull strength, and scanning electron microscopy were used to characterize the solder joints. In addition, the solder plating, lead wetting, and aging characteristics were evaluated. Failure during thermal cycling was primarily caused by the coefficient of thermal expansion (CTE) mismatch between the package and the printed wiring board. By using acceleration factors based on solder joint strain energies induced by global and local mismatches during thermal cycling, the experimental results are extrapolated to various use conditions and life expectancies. The TSOP solder joint reliability depends on environmental conditions (cyclic temperature range, temperature maximum, and dwell time), board thickness and materials, product intended service life, and expected hazard rate limits. >