Articulating User Needs in Collaborative Design: Towards an Activity-Theoretical Approach

This paper analyses the collaborative design ofa high-technology product, a neuromagnetometerused in the analysis of the activity of thehuman cortex. The producer, Neuromag Company istrying to transform the device from a basicresearch instrument into a means of clinicalpractice. This transition is analyzed as asimultaneous evolution of the product,producer-user network and user activities. Thenetwork is analyzed as a network of activitysystems. Each activity has a historicallyformed object and a motive of its own, as wellas a system of cultural means and expertise. Weuse these to explain and understand theinterests and points of view of the actors inrelation to the product and the contradictionsof the producer-user network. It is suggestedthat the emerging user needs of collectiveactors must be analyzed at three levels. At thefirst level, the use value of the product, itscapacity of solving the vital problems andchallenges of developing user activities, ischaracterized. The second-level analysisconcerns the creation and development of thenecessary complementary tools and services thatmake the implementation and use of the productpossible. This task presupposes collaborationbetween several communities of the innovationnetwork. The third level is the situatedpractical use of the product. In ourexperience, it is advantageous that researcherscontribute with their data to a dialogue inwhich the user needs are articulated.     

Thermal Cycling Reliability of Sn-Ag-Cu Solder Interconnections. Part 1: Effects of Test Parameters

The work presented in part 1 of this study focuses on identifying the effects of thermal cycling test parameters on the lifetime of ball grid array (BGA) component boards. Detailed understanding about the effects of the thermal cycling parameters is essential because it provides means to develop more efficient and meaningful methods of reliability assessment for electronic products. The study was carried out with a single package type (BGA with 144 solder balls), printed wiring board (eight-layer build-up FR4 structure), and solder interconnection composition (Sn-3.1Ag-0.5Cu) to ensure that individual test results would be comparable with each other. The effects of (i) temperature difference (ΔT), (ii) lower dwell temperature and lower dwell time, (iii) mean temperature, (iv) dwell time, and (v) ramp rate were evaluated. Based on the characteristic lifetimes, the thermal cycling profiles were categorized into three lifetime groups: (i) highly accelerated conditions, (ii) moderately accelerated conditions, and (iii) mildly/nonaccelerated conditions. Thus, one might be tempted to use the highly accelerated conditions to produce lifetime statistics as quickly as possible. However, to do this one needs to know that the failure mechanisms do not change from one lifetime group to another and that the failure mechanisms correlate with real-use failures. Therefore, in part 2 the observed differences in component board lifetimes will be explained by studying the failure mechanisms that take place in the three lifetime groups.     

The Reliability of Microalloyed Sn-Ag-Cu Solder Interconnections Under Cyclic Thermal and Mechanical Shock Loading

In this study, the performance of three microalloyed Sn-Ag-Cu solder interconnection compositions (Sn-3.1Ag-0.52Cu, Sn-3.0Ag-0.52Cu-0.24Bi, and Sn-1.1Ag-0.52Cu-0.1Ni) was compared under mechanical shock loading (JESD22-B111 standard) and cyclic thermal loading (40 ± 125°C, 42 min cycle) conditions. In the drop tests, the component boards with the low-silver nickel-containing composition (Sn-Ag-Cu-Ni) showed the highest average number of drops-to-failure, while those with the bismuth-containing alloy (Sn-Ag-Cu-Bi) showed the lowest. Results of the thermal cycling tests showed that boards with Sn-Ag-Cu-Bi interconnections performed the best, while those with Sn-Ag-Cu-Ni performed the worst. Sn-Ag-Cu was placed in the middle in both tests. In this paper, we demonstrate that solder strength is an essential reliability factor and that higher strength can be beneficial for thermal cycling reliability but detrimental to drop reliability. We discuss these findings from the perspective of the microstructures and mechanical properties of the three solder interconnection compositions and, based on a comprehensive literature review, investigate how the differences in the solder compositions influence the mechanical properties of the interconnections and discuss how the differences are reflected in the failure mechanisms under both loading conditions.     

Joining silicon nitride to itself and to metals

This article reviews the progress that has been made in developing and applying joining techniques for Si₃N₄ and discusses our understanding of the influence of process selection on the materials science of the formation and properties of joints. High-performance Si₃N₄ joints can be produced, but it is clear that much work remains to be done before the use of such joints in hot-stressed applications can be disregarded as a problem.     

Heat generation in high power prismatic Li‐ion battery cell with LiMnNiCoO2 cathode material

While in use, battery modules and battery packs generate large amounts of heat, which needs to be accounted for. The main challenge in battery thermal management is the correct estimation of heat generation in the battery cell during charging/discharging. In this paper, a method to calculate accurate heat generation in one individual cell is provided. The heat generation is calculated by measuring the overpotential resistances with four different methods and entropic heat generation in the cell. The effect and contribution of entropic heat generation towards the total heat generation in the cell are also calculated and measured. Finally, calorimeter tests are carried out to compare the calculated and measured heat generation. The results indicate that except for direct current resistance measured by impedance spectroscopy, all the overpotential resistances are very close to each other. Copyright © 2014 John Wiley & Sons, Ltd.     

Hierarchically Designed Bioactive Glassy Nanocoatings for the Growth of Faster and Uniformly Dense Apatite

Crack‐free bioactive nanocoatings embedded with uniformly distributed silica‐rich bioactive spherical aggregates were successfully prepared in situ by controlling the micellization of a SiO₂–CaO–P₂O₅ sol using the tri‐block copolymer P123 followed by dip‐coating onto a bio‐inert glass substrate and calcined. These hierarchically designed nanocoatings embedded with such bioactive glassy nanospheres (BGNS) enabled to induce the deposition of a densely populated, uniform, and well‐developed needlelike crystalline carbonated hydroxyapatite coating reminiscence of the mineral phase of natural bone within a short immersion time in simulated body fluid. The BGNS nanocoatings also supported the growth and attachment of human gingival fibroblasts. The results suggest that these newly designed composite nanocoatings are noncytotoxic, capable of supporting rapid and homogeneous calcium phosphate deposition as well as subsequent crystallization, and likely to be promising candidates for inert glass reinforced bone implants.     

SINR estimation for power control in systems with transmission beamforming

This paper takes a unified approach to the downlink transmission power control, while a transmission beamforming is applied in the base station. The proposed scheme is based on the estimation of signal-to-interference-and-noise-ratios (SINRs) by antenna array measurement and using this estimate in transmission power control. Hence power control algorithms needing SINR-levels can be applied instead of the simple relay power control. The SINR estimation technique does not require any additional measurements compared to a separate adaptive beamforming and power control, since the required measurements are needed for the adaptive beamforming update. The estimation is based on the knowledge of the level of caused interference to the multiple access links in the same cell, and the utilization of relay power control commands in SINR estimation.     

Thermal Cycling Reliability of Sn-Ag-Cu Solder Interconnections—Part 2: Failure Mechanisms

Part 1 of this study focused on identifying the effects of (i) temperature difference (ΔT), (ii) lower dwell temperature and shorter dwell time, (iii) mean temperature, (iv) dwell time, and (v) ramp rate on the lifetime of ball grid array (with 144 solder balls) component boards. Based on the characteristic lifetime, the studied thermal cycling profiles were categorized into three groups: (i) highly accelerated conditions, (ii) moderately accelerated conditions, and (iii) mildly/nonaccelerated conditions. In this work, the observed differences in component board lifetime are explained by studying the failure mechanisms and microstructural changes that take place in the three groups of loading conditions. It was observed that, under the standardized thermal cycling conditions (highly accelerated conditions), the networks of grain boundaries formed by recrystallization provided favorable paths for cracks to propagate intergranularly. It is noteworthy that the coarsening of intermetallic particles was strong in the recrystallized regions (the cellular structure had disappeared completely in the crack region). However, under real-use conditions (mildly/nonaccelerated conditions), recrystallization was not observed in the solder interconnections and cracks had propagated transgranularly in the bulk solder or between the intermetallic compound (IMC) layer and the bulk solder. The real-use conditions showed slight coarsening of the microstructure close to the crack region, but the solder bulk still included finer IMC particles and β-Sn cells characteristic of the as-solidified microstructures. These findings suggest that standardized thermal cycling tests used to assess the solder interconnection reliability of BGA144 component boards create failure mechanisms that differ from those seen in conditions representing real-use operation.