Managing digital libraries using semantic web technologies

The aim of this work is to improve retrieval and navigation services on bibliographic data held in digital libraries. This paper presents the design and implementation of OntoBib¸ an ontology-based bibliographic database system that adopts ontology-driven search in its retrieval. The presented work exemplifies how a digital library of bibliographic data can be managed using Semantic Web technologies and how utilizing the domain specific knowledge improves both search efficiency and navigation of web information and document retrieval.

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.

Macro-micro modelling of moisture induced stresses in an ACF flip chip assembly

Purpose – This paper discusses the use of modelling techniques to predict the reliability of an anisotropic conductive film (ACF) flip chip in a humid environment. The purpose of this modelling work is to understand the role that moisture plays in the failure of ACF flip chips. Design/methodology/approach – A 3D macro-micro finite element modelling technique was used to determine the moisture diffusion and moisture-induced stresses inside the ACF flip chip. Findings – The results show that the ACF layer in the flip chip can be expected to be fully saturated with moisture after 3?h at 121°C, 100%RH, 2?atm test conditions. The swelling effect of the adhesive due to this moisture absorption causes predominately tensile stress at the interface between the adhesive and the metallization, which could cause a decrease in the contact area, and therefore an increase in the contact resistance. Originality/value – This paper introduces a macro-micro modelling technique which enables more detailed 3D modelling analysis of an ACF flip chip than previously.

Thermo-mechanical modelling of power electronics module structures

Power electronic modules distinguish themselves from other modules by their high power operation. These modules are used extensively in high power application markets such as aerospace, automotive, industrial and traction and drives. This paper discusses typical packaging technologies for power electronics modules. It also discusses the latest results from a UK research project investigating the physics-of-failure approach to reliability analysis and predictions for power modules. An integrated design enviroment for incorporating of affects of uncertainty into the design environment was outlined.

Effects of thermal cycling profiles on the performance of chip-on-flex assembly using anisotropic conductive films

Anisotropic conductive films (ACFs) are widely used in the electronic packaging industries because of their fine pitch potential and the assembly process is simpler compared to the soldering process. However, there are still unsolved issues in the volume productions using ACFs. The main reason is that the effects of many factors on the interconnects are not well understood. This work focuses on the performance of ACF-bonded chip-on-flex assemblies subjected to a range of thermal cycling test conditions. Both experimental and three-dimensional finite element computer modelling methods are used. It has been revealed that greater temperature ranges and longer dwell-times give rise to higher stresses in the ACF interconnects. Higher stresses are concentrated along the edges of the chip-ACF interfaces. In the experiments, the results show that higher temperature ranges and prolonged dwell times increase contact resistance values. Close examination of the microstructures along the bond-line through the scanning electron microscope (SEM) indicates that cyclic thermal loads disjoint the conductive particles from the bump of the chip and/or pad of the substrate and this is thought to be related to the increase of the contact resistance value and the failure of the ACF joints.

Comparative wetting behavior of Sn-0.7Cu and Sn-0.7Cu-0.3Ni solders on Cu and Ni substrates

Electronic packaging industries are now in great challenge to find a suitable lead-free solder as an interconnection material to replace the conventional SnPb solders. Many solders such as SnCu, SnAg, SnAgCu, SnZn, SnBi have already been proposed as the replacement but none of them has reached the physical and metallurgical properties similar to the SnPb solder. However, wetting is one of the basic problems that make the lead-free solder inferior as compared to the SnPb solder. Therefore, alloying with the help of third, fourth or fifth element is the researchers' interest to improve the wetting behavior of lead-free solders. This paper describes the comparative wetting behavior of Sn-0.7Cu and Sn-0.7Cu-0.3Ni solders on Cu and Ni substrates. Wetting balance tests were performed to assess the wetting behaviors. Three different commercial fluxes namely no-clean (NC), non-activated (R) and water soluble organic acid (WS)fluxes were used to assess the wettability for three solder bath temperatures. It was found that Sn0.7Cu-03Ni solder exhibits better wettability on Cu substrate for NC and WS fluxes whereas reverse results were found for R-type flux. In the case of Ni substrate, Sn-0.7Cu-0.3Ni solder showed better wetting behavior compared to the well-known Sn-0.7Cu solder. Among the three fluxes, R-type flux showed the worst performance. Very large contact angles were documented for both solders with this flux. Higher solder bath temperature lowered the contact angles, increased the wetting forces and enhanced the wettability. Computer modeling of wetting balance test revealed that both the wetting force and meniscus height are inversely proportional to the contact angles. Modeling results also reveal that increase in solder bath depths and radiuses do not affect significantly on the wetting behavior.

Modeling the effect of lead-free soldering on flexible substrates

Flexible Circuit Boards (FPCs) are now being widely used in the electronic industries especially in the areas of electronic packages. Due to European lead-free legislation which has been implemented since July 2006, electronic packaging industries have to switch to use in the lead-free soldering technology. This change has posed a number of challenges in terms of development of lead-free solders and compatible substrates. An increase of at least 20-50 degrees in the reflow temperature is a concern and substantial research is required to investigate a sustainable design of flexible circuit boards as carrier substrates. This paper investigates a number of design variables such as copper conductor width, type of substrate materials, effect of insulating materials, etc. Computer modeling has been used to investigate thermo-mechanical behavior, and reliability, of flexible substrates after they have been subjected to a lead- free solder processing. Results will show particular designs that behave better for a particular rise in peak reflow temperature. Also presented will be the types of failures that can occur in these substrates and what particular materials are more reliable.

Predicting the behaviour of micro-electronic displays using computational mechanics

Micro-electronic displays are indispensible devices used in high performance applications such as aerospace, medical, marine and industrial sectors.These devices provide an interface to real time mission critical devices and therefore require good optical visual performance and high reliability, all this within varied and challenging environments.

Thermo-mechanical analysis of the packaging process for micro-electronic displays

Micro-electronic displays are sensitive devices and its performance is easily affected by external environmental factors. To enable the display to perform in extreme conditions, the device must be structurally strengthened, the effects of this packaging process was investigated. A thermo-mechanical finite element analysis was used to discover potential problems in the packaging process and to improve the overall design of the device. The main concern from the analysis predicted that displacement of the borosilicate glass and the Y stress of the adhesive are important. Using this information a design which reduced the variation of displacement and kept the stress to a minimum was suggested

Constitutive modeling of kinematic-hardening and damage in solder joints

Solder constitutive models are important as they are widely used in FEA simulations to predict the lifetime of soldered assemblies. This paper briefly reviews some common constitutive laws to capture creep in solder and presents work on laws capturing both kinematic hardening and damage. Inverse analysis is used to determine constants for the kinematic hardening law which match experimental creep curves. The mesh dependence of the damage law is overcome by using volume averaging and is applied to predict the crack path in a thermal cycled resistor component

Thermal-mechanical analysis of flexible substrates during lead-free solder reflow

This paper presents modeling results about the performance of flexible substrates when subjected to higher lead-free reflow temperatures. Both adhesiveless and adhesive types of polyimide substrates were studied. Finite element (FE) models of flex substrates were built, two copper tracks located in the centre of the substrate was considered. The thermal induced shear stress in the flex substrate during the lead-free reflow process was studied and the effect of the design changes including the track thickness, flex thickness, and copper width were studied. For both types of flexes, the one of most important variables for minimizing damage to the substrate is the height of the copper tracks. The height of flex and the width of copper track show less impact. Beside of the geometry effects, the increase in reflow peak temperature can also result in a significant increase in the interfacial stress between the copper track and flex. Higher stresses were identified within the adhesive flex due to the big CTE mismatch between the copper and adhesive/dielectric

Computer modeling of a micro-manufactured one-turn inductor

The results of a finite element computer modelling analysis of a micro-manufactured one-turn magnetic inductor using the software package ANSYS 10.0 are presented. The inductor is designed for a DC-DC converter used in microelectronic devices. It consists of a copper conductor with a rectangular cross-section plated with an insulation layer and a layer of magnetic core. The analysis has focused on the effects of the frequency and the air gaps on the on the inductance values and the Joule losses in the core and conductor. It has been found that an inductor with small multiple air gaps has lower losses than an inductor with a single larger gap

Assessment of microInductors for DC-DC converters

There are increasing demands on the power density and efficiency of DC-DC power converters due to the soaring functionality and operational longevity required for today's electronic products. In addition, DC-DC converters are required to operate at new elevated frequencies in the MHz frequency regime. Typical ferrite cores, whose useable flux density falls drastically at these frequencies, have to be replaced and a method of producing compact component windings developed. In this study, two types of microinductors, pot-core and solenoid, for DC-DC converter applications have been analyzed for their performance in the MHz frequency range. The inductors were manufactured using an adapted UV-LIGA process and included electrodeposited nickel-iron and the commercial alloy Vitrovac 6025 as core materials. Using a vibrating sample magnetometer (VSM) and a Hewlett Packard 4192A LF- impedance analyzer, the inductor characteristics such as power density, efficiency, inductance and Q-factor were recorded. Experimental, finite element and analytical results were used to assess the suitability of the magnetic materials and component geometries for low MHz operation.

An analysis of a microfabricated solenoid inductor

A microscale solenoid inductor is manufactured using electrodeposition method. The inductor is designed for switching mode DC-DC converters operating at switching frequencies in the mega-Hertz range. Two magnetic core materials, electroformed permalloy Ni80 Fe20 film and Vitrovac 6025 which is a commercial magnetic film, have been analyzed using experimental and computer modeling techniques