Modelling methodology for thermal analysis of hot solder dip process

The shift of electronics industry towards the use of lead-free solders in components manufacturing brought also the challenge of addressing the problem of tin whiskers. Manufacturers of high reliability and safety critical equipment in sectors such as defence and aerospace rely increasingly on the use of commercial-of-the-shelf (COTS) electronic components for their products and systems. The use of COTS components with lead-free solder plated terminations comes with the risks for their long term reliability associated with tin whisker growth related failures. In the case of leaded type electronic components such as Quad Flat Package (QFP) and Small Outline Package (SOP), one of the promising solutions to this problem is to “re-finish” the package terminations by replacing the lead-free solder coatings on the leads with conventional tin–lead solder. This involves subjecting the electronic components to a post-manufacturing process known as Hot Solder Dip (HSD). One of the main concerns for adopting HSD (refinishing) as a strategy to the tin whisker problem is the potential risk for thermally induced damage in the components when subjected to this process.     

用可编程逻辑创建专用微控制器

微控制器是最原始的芯片系统（SoC)器件，在最近几年，FPGA和PLD厂商提出了“可编程芯片系统”（SOPC）的概念，用可编程逻辑来设计专用硬件如微控制器。创建专用微控制器的要素包括全功能的32位RISC微处理器、现成的外设以及可选的专用外设、IP的各种开发工具。这些要素都是现在的，再结合低成本的可编程器件（PLD），设计者就可以为现有的微控制器增加各种功能。本文讨论设计者在PLD设计专用微控制器时的问题，列举的设计实例包括用户定义的硬件加速专用指令和外设。     

Perceptually lossless medical image coding

A novel perceptually lossless coder is presented for the compression of medical images. Built on the JPEG 2000 coding framework, the heart of the proposed coder is a visual pruning function, embedded with an advanced human vision model to identify and to remove visually insignificant/irrelevant information. The proposed coder offers the advantages of simplicity and modularity with bit-stream compliance. Current results have shown superior compression ratio gains over that of its information lossless counterparts without any visible distortion. In addition, a case study consisting of 31 medical experts has shown that no perceivable difference of statistical significance exists between the original images and the images compressed by the proposed coder.     

Assessing the performance of crack detection tests for solder joints

This paper presents both modelling and experimental test data to characterise the performance of four non-destructive tests. The focus is on determining the presence and rough magnitude of thermal fatigue cracks within the solder joints for a surface mount resistor on a strip of FR4 PCB. The tests all operate by applying mechanical loads to the PCB and monitoring the strain response at the top of the resistor. The modelling results show that of the four tests investigated, three are sensitive to the presence of a crack in the joint and its magnitude. Hence these tests show promise in being able to detect cracking caused by accelerated testing. The experimental data supports these results although more validation is required.     

Single‐Step Deposition of Au‐ and Pt‐Nanoparticle‐Functionalized Tungsten Oxide Nanoneedles Synthesized Via Aerosol‐Assisted CVD,and Used for Fabrication of Selective Gas Microsensor Arrays

Tungsten oxide nanostructures functionalized with gold or platinum NPs are synthesized and integrated, using a single‐step method via aerosol‐assisted chemical vapour deposition, onto micro‐electromechanical system (MEMS)‐based gas‐sensor platforms. This co‐deposition method is demonstrated to be an effective route to incorporate metal nanoparticles (NP) or combinations of metal NPs into nanostructured materials, resulting in an attractive way of tuning functionality in metal oxides (MOX). The results show variations in electronic and sensing properties of tungsten oxide according to the metal NPs introduced, which are used to discriminate effectively analytes (C₂H₅OH, H₂, and CO) that are present in proton‐exchange fuel cells. Improved sensing characteristics, in particular to H₂, are observed at 250 °C with Pt‐functionalized tungsten oxide films, whereas non‐functionalized tungsten oxide films show responses to low concentrations of CO at low temperatures. Differences in the sensing characteristics of these films are attributed to the different reactivities of metal NPs (Au and Pt), and to the degree of electronic interaction at the MOX/metal NP interface. The method presented in this work has advantages over other methods of integrating nanomaterials and devices, of having fewer processing steps, relatively low processing temperature, and no requirement for substrate pre‐treatment.     

Ultra-Low-Power Interface Chip for Autonomous Capacitive Sensor Systems

Traditionally, most of the sensor interfaces must be tailored towards a specific application. This approach results in a high recurrent design cost and time to market. On the other hand, generic sensor interface design reduces the costs and offers a handy solution for multisensor applications. This paper presents a generic sensor interface chip (GSIC), which can read out a broad range of capacitive sensors. It contains capacitance-to-voltage converters, a switched-capacitor amplifier, an analog-to-digital converter, oscillators, clock generation circuits and a reference circuit. The system combines a very low-power design with a smart energy management, which adapts the current consumption according to the accuracy and speed requirements of the application. The GSIC is used in a pressure and an acceleration monitoring system. The pressure monitoring system achieves a current drain of 2.3 muA for a 10-Hz sample frequency and an 8-bit accuracy. In the acceleration monitoring system, we measured a current of 3.3 muA for a sample frequency of 10 Hz and an accuracy of 9 bits     

Integration of analytical techniques in stochastic optimization of microsystem reliability

This paper presents an integrative application of several numerical analytical techniques and associated analysis tools for design optimization and damage prediction in electronics packages and microsystems. This design-for-reliability approach is based on four different types of numerical techniques that allow (1) high-fidelity modelling, (2) reduced order modelling, (3) numerical optimization and (4) uncertainty analysis. The capabilities and the characteristics of the methods that underpin these four types of modelling and analysis tools are firstly investigated. The integration of the methods and tools is then examined and a methodology for coupling the tools in an optimization process is proposed. This numerical methodology involves the following steps: (1) Define sampling points for the design of interest by design of experiments (DOE) and calculate the design response at each DOE point using high-fidelity analysis; (2) construct reduced order models (ROM) for fast analysis using the obtained response values at the DOE points; (3) Undertake deterministic optimization in the defined design space by ROM; and (4) Probabilistic optimization by including variation and uncertainty of the design in the optimization task. This approach is suitable to address design-for-reliability requirements at early design stages in a wide range of application areas. The application of this approach is demonstrated in a case for minimizing the thermal fatigue damage of flip-chip solder interconnects. Design modifications show that this approach can provide improved reliability of the package and in the same time satisfy a number of design requirements.     

薄膜无源技术和无源微电路抬头射频技术掀起革命风暴

无线电技术的不断推陈出新已成为微电子技术领域发展的强大动力,无论是在客户应用中还是关键业务应用中,都要求解决方案的体型更小、功能更强、可靠性更高、信号清晰度更好,并且始终保持更低的能耗.这无疑对新技术提出了更高的要求,而射频电路的设计无疑是所有设计中极为关键的设计之一,本文通过介绍下一代薄膜无源技术和无源微电路来揭示如何迎接射频技术挑战.     

Nonequilibrium Operation of Arsenic Diffused Long-Wavelength Infrared HgCdTe Photodiodes

We demonstrated a device with a unique planar architecture using a novel approach for obtaining low arsenic doping concentrations in long-wavelength (LW) HgCdTe on CdZnTe substrates. HgCdTe materials were grown by molecular beam epitaxy (MBE). We fabricated a p-on-n structure that we term P ⁺/π/N ⁺ where the symbol “π” is to indicate a drastically reduced extrinsic p-type carrier concentration (on the order of mid 10¹⁵ cm⁻³); P ⁺ and N ⁺ denote a higher doping density, as well as a higher energy gap, than the photosensitive base π-region. Fabricated devices indicated that Auger suppression is seen in the P ⁺/π/N ⁺ architecture at temperatures above 130 K and we obtained a saturation current on the order of 3 mA on 250-μm-diameter devices at 300 K with Auger suppression. Data shows that about a 50% reduction in dark current is achieved at 300 K due to Auger suppression. The onset of Auger suppression voltage is 450 mV at 300 K and 100 mV at 130 K. Results indicate that a reduction of the series resistance could reduce this further. A principal challenge was to obtain low p-type doping levels in the π-region. This issue was overcome using a novel deep diffusion process, thereby demonstrating successfully low-doped p-type HgCdTe in MBE-grown material. Near-classical spectral responses were obtained at 250 K and at 100 K with cut-off wavelengths of 7.4 μm and 10.4 μm, respectively. At 100 K, the measured non-antireflection-coated quantum efficiency was 0.57 at 0.1 V under backside illumination. Received November 7, 2007; accepted March 19, 2008     

Diindenoperylene derivatives: A model to investigate the path from molecular structure via morphology to solar cell performance

Efficient organic electronic devices require a detailed understanding of the relation between molecular structure, thin film growth, and device performance, which is only partially understood at present. Here, we show that small changes in molecular structure of a donor absorber material lead to significant changes in the intermolecular arrangement within organic solar cells. For this purpose, phenyl rings and propyl side chains are fused to the diindenoperylene (DIP) molecule. Grazing incidence X-ray diffraction and variable angle spectroscopic ellipsometry turned out to be a powerful combination to gain detailed information about the thin film growth. Planar and bulk heterojunction solar cells with C60 as acceptor and the DIP derivatives as donor are fabricated to investigate the influence of film morphology on the device performance. Due to its planar structure, DIP is found to be highly crystalline in pristine and DIP:C60 blend films while its derivatives grow liquid-like crystalline. This indicates that the molecular arrangement is strongly disturbed by the steric hindrance induced by the phenyl rings. The high fill factor (FF) of more than 75% in planar heterojunction solar cells of the DIP derivatives indicates excellent charge transport in the pristine liquid-like crystalline absorber layers. However, bulk heterojunctions of these materials surprisingly result in a low FF of only 54% caused by a weak phase separation and thus poor charge carrier percolation paths due to the lower ordered thin film growth. In contrast, crystalline DIP:C60 heterojunctions lead to high FF of up to 65% as the crystalline growth induces better percolation for the charge carriers. However, the major drawback of this crystalline growth mode is the nearly upright standing orientation of the DIP molecules in both pristine and blend films. This arrangement results in low absorption and thus a photocurrent which is significantly lower than in the DIP derivative devices, where the liquid-like crystalline growth leads to a more horizontal molecular alignment. Our results underline the complexity of the molecular structure-device performance relation in organic semiconductor devices.