Comparison of different flex materials in high density flip chip on flex applications

This paper presents the results from the evaluation of different types of flexible substrates for high-density flip chip application. In this work four different flexible substrates were used. The flex substrates were Espanex, Upilex and epoxy glass with 80 μm pitch and Upilex with 54 μm pitch. Two different test IC’s were used for both pitches. In test IC1 (80 μm pitch) and IC3 (54 μm pitch) the bumps were in one row and test IC2 (80 μm pitch) and IC4 (54 μm pitch) in two rows. The total amount of contacts in test IC1 was 190, in test IC2 173, in test IC3 293 and in test IC4 270. The anisotropically conductive adhesive that was used in the tests was epoxy based thermosetting adhesive film with conductive particles. The conductive particles in the adhesives were isolated soft metal-coated polymer particles. The contact resistance was measured using Kelvin four-point method and the continuity and series resistance using daisy chain structure. The reliability of the flip chip interconnections was tested in temperature cycling test and environmental test. Cross section samples were made to analyse the possible reason for failures. The results presented in this paper are from FLEXIL development project that is part of European Union IST research program.     

Mechanical properties of additive manufactured titanium (Ti–6Al–4V) blocks deposited by a solid-state laser and wire

In this paper, the mechanical properties and chemical composition of additive manufactured Ti–6Al–4V blocks are investigated and compared to plate material and aerospace specifications. Blocks (seven beads wide, seven layers high, 165 mm long) were deposited using a 3.5 kW Nd:YAG laser and Ti–6Al–4V wire. Two different sets of process parameters are used and three different conditions (as-built, 600 °C/4 h, 1200 °C/2 h) of the deposit are investigated. The particular impurity levels of the blocks are considerably below those tolerated according to aerospace material specifications (AMS 4911L). Static tensile samples are extracted from the blocks in the deposition direction and punch samples are extracted in the building direction. The experiments show that as-deposited Ti–6Al–4V can achieve strength and ductility properties that fulfill aerospace specifications of the wrought Ti–6Al–4V material (AMS 4928). The 600 °C/4 h heat treatment leads to a significantly higher strength in the deposition direction, but can also decrease ductility. The 1200 °C/2 h treatment tends to decrease the alloy’s strength.     

Optimization of picosecond laser structuring for the monolithic serial interconnection of CIS solar cells

We report on the optimization of selective picosecond laser structuring for the monolithic serial interconnection of (Cu(In,Ga)(S,Se)₂) CIS thin film solar cells. We introduce a quantitative value to compare the energy efficiency of the different investigated laser processes, the specific ablation energy, which indicates the required energy to remove a certain volume of the specific material. We have examined the structuring efficiencies for induced laser ablation processes for a modification of the beam profile (elliptical and flat‐top beam shaping) and for the application of different laser wavelengths (1064 and 532 nm). Application of induced laser processes (often referred as “lift‐off”) decreases the specific ablation energy dramatically by nearly one order of magnitude. Modifications of the beam profile such as elliptical and flat‐top beam shaping are nearly halving the energy per ablated volume relative to a circular beam. The application of a laser wavelength 532 nm decreases the specific ablation energy compared with 1064 nm significantly for processes involving the CIS layer. We finally demonstrate that with a picosecond laser power of only 2 W, the molybdenum back contact (P1, glass side) and the ZnO front contact (P3, ZnO on CIS) can be structured with a process speed of up to 4 m/s. About 2 µm thick CIS layer (P2) is structured by standard direct laser ablation at higher energy densities with 200 mm/s. Copyright © 2012 John Wiley & Sons, Ltd.     

Leaching losses from Kenyan maize cropland receiving different rates of nitrogen fertilizer

Meeting food security requirements in sub-Saharan Africa (SSA) will require increasing fertilizer use to improve crop yields, however excess fertilization can cause environmental and public health problems in surface and groundwater. Determining the threshold of reasonable fertilizer application in SSA requires an understanding of flow dynamics and nutrient transport in under-studied, tropical soils experiencing seasonal rainfall. We estimated leaching flux in Yala, Kenya on a maize field that received from 0 to 200 kg ha^?1 of nitrogen (N) fertilizer. Soil pore water concentration measurements during two growing seasons were coupled with results from a numerical fluid flow model to calculate the daily flux of nitrate-nitrogen (NO₃ ^?-N). Modeled NO₃ ^?-N losses to below 200 cm for 1 year ranged from 40 kg N ha^?1 year^?1 in the 75 kg N ha^?1 year^?1 treatment to 81 kg N ha^?1 year^?1 in the 200 kg N ha^?1 treatment. The highest soil pore water NO₃ ^?-N concentrations and NO₃ ^?-N leaching fluxes occurred on the highest N application plots, however there was a poor correlation between N application rate and NO₃ ^?-N leaching for the remaining N application rates. The drought in the second study year resulted in higher pore water NO₃ ^?-N concentrations, while NO₃ ^?-N leaching was disproportionately smaller than the decrease in precipitation. The lack of a strong correlation between NO₃ ^?-N leaching and N application rate, and a large decrease in flux between 120 and 200 cm suggest processes that influence NO₃ ^?-N retention in soils below 200 cm will ultimately control NO₃ ^?-N leaching at the watershed scale.     

髋关节置换术后股骨应力的三维有限元分析及与骨密度变化的相关研究

目的应用三维有限元分析假体周围的应力情况,同时连续测定骨密度,探讨二者之间的相关性。方法选择自2008-2009年在南昌大学第二附属医院进行全髋关节置换术的患者共20例,分别在术后1、3、6个月,1、2、3年应用三维有限元方法分析股骨假体周围应力变化,同时应用双能X线骨密度仪测量股骨假体周围骨密度,股骨柄假体区,采用Gruen方法分7个测量兴趣区,即ROI①、②、③、④、⑤、⑥和⑦区。并将其与同一患者未置换部位进行比较,应用SPSS 15.0分析软件对收集到的数据进行处理,用t检验进行组间显著性测定。结果 20例患者均进入结果分析。ROI⑦区应力遮挡最明显,ROI③应力遮挡最少,各区在术后1、3、6个月的应力遮挡无统计学意义（P〉0.05）,术后1、2、3年的应力遮挡较1、3、6个月明显减少（P〈0.05）。股骨假体周围骨密度在术后1个月时无明显下降（P〉0.05）,术后3个月开始明显下降（P〈0.01）,且以ROI⑦区最明显,术后1、2、3年骨密度无明显下降并趋于平稳。结论髋关节置换术后假体周围骨密度变化与其应力遮挡存在明显的相关性,并随时间的变化也是一致的。     

Influence of solution composition on sprayed ZnO nanorods properties and formation process: Thermoanalytical study of the precursors

ZnO is an important inorganic material for numerous applications. Different physical and chemical methods have been applied to deposit ZnO. Spray pyrolysis method being simple, rapid and low-cost is amongst the many options and has been chosen for this study. Fabrication of ZnO nanorods crystals by chemical spray pyrolysis was performed using an acidic solution of ZnCl₂1 or a basic ammonia-containing solution of ZnCl₂2. All layers were studied using X-ray diffractometry and Scanning Electron Microscopy. The formation of ZnO nanorods from 2 appeared at 450?°C, whereas spraying acidic solution 1 yielded ZnO nanorods like morphology at 550?°C.Thermal decomposition of precursors for ZnO layers prepared by de-watering of acidic aqueous solution of ZnCl₂ with pH =?3 (1) and basic solution of ZnCl₂ and NH₄OH with pH =?10 (2) was monitored by simultaneous thermogravimetric and differential thermal analysis (TG/DTA) in air coupled online with evolved gas analyses by Fourier transformed infrared spectroscopy (FTIR).The precursor (1) is ZnCl₂ *nH₂O; the precursor (2) is a mixture of (NH₄)₃(ZnCl₄)Cl, Zn(NH₃)₂Cl₂, NH₄Cl(NH₃)₃ and Zn(OH)₂ phases. The thermal decomposition of (1) and (2) in the temperature range of 30–700?°C consists of two steps with total mass losses of 86.2% and 93.8%, respectively. The main evolved gases from (1) are H₂O and HCl, whereas the main evolved gases from (2) are H₂O, NO_x and NH₃. Degradation of (1) and (2) is completed by 670 and 620?°C, respectively. The final decomposition product of (1) and (2) at 700?°C is ZnO.This study shows that the use of basic solutions enables to decrease the temperature of ZnO formation and the deposition temperature of ZnO nanorods layers.     

Nature‐Inspired Boiling Enhancement by Novel Nanostructured Macroporous Surfaces

World energy crisis has triggered more attention to energy saving and energy conversion systems. Enhanced surfaces for boiling are among the applications of great interest since they can improve the energy efficiency of heat pumping equipment (i.e., air conditioners, heat pumps, refrigeration machines). Methods that are used to make the state‐of‐the‐art enhanced surfaces are often based on complicated mechanical machine tools, are quite material‐consuming and give limited enhancement of the boiling heat transfer. Here, we present a new approach to fabricate enhanced surfaces by using a simple electrodeposition method with in‐situ grown dynamic gas bubble templates. As a result, a well‐ordered 3D macro‐porous metallic surface layer with nanostructured porosity is obtained. Since the structure is built based on the dynamic bubbles, it is perfect for the bubble generation applications such as nucleate boiling. At heat flux of 1 W cm^‐2, the heat transfer coefficient is enhanced over 17 times compared to a plain reference surface. It's estimated that such an effective boiling surface would improve the energy efficiency of many heat pumping machines with 10–30%. The extraordinary boiling performance is explained based on the structure characteristics.     

Classification of bioacoustic time series based on the combination of global and local decisions

Automated classification of cricket songs from Thailand and Ecuador is the topic of this study. For this, the locations of pulses are determined and different features in the time and the frequency domain are extracted automatically from the time series. For the categorization of the sound patterns these features are combined through data fusion, temporal fusion and decision fusion. Local features and global features are distinguished. For the classification a fuzzy-k-nearest-neighbour classifier was used. Classification results for a data set containing songs of 28 different species are presented.     

Iron‐Rich Iron‐Aluminium‐Molybdenum Alloys with Strengthening Intermetallic μ phase and R phase Precipitates

Single‐phase and two‐phase ternary Fe‐Al‐Mo alloys with Al contents of usually 10 ‐16 at.% and Mo contents up to 42 at.% have been studied with respect to hardness at room temperature, yield stress and fracture strain at room temperature and higher temperatures up to 1000 °C and oxidation at temperatures of 400 ‐ 1000 °C. Thse alloys are strengthened by precipitation of the metastable R phase and/or the stable m phase depending on composition and heat treatment; both are hard and brittle intermetallic phases. The yield stress as well as the brittle‐to‐ductile transition temperature increases with increasing Mo content to reach yield stresses above 1400 MPa with, however, fracture strains below 1 % at temperatures below 800 °C. The observed short‐term oxidation is similar to that of other Fe‐Al alloys.