Recent advances in isotropic conductive adhesives for electronics packaging applications

Isotropic conductive adhesives (ICAs) have recently received a lot of focus and attention from the researchers in electronics industry as a potential substitute to lead-bearing solders. Numerous studies have shown that ICAs possess many advantages over conventional soldering such as environmental friendliness, finer pitch printing, lower temperature processing and more flexible and simpler processing. However, complete replacement of soldering by ICAs is yet not possible owing to several limitations of ICAs which are mainly related to reliability aspects like limited impact resistance, unstable contact resistance, low adhesion and conductivity etc. Continued efforts for last 15 years have resulted in development of ICAs with improved properties. This review article is aimed at providing a better understanding of ICAs, their principles, performance and significant research and development work addressing the technological utility of ICAs.     

Effect of process parameters on impact strength of Al-7% Si alloy castings produced by VAEPC process

The castings produced by the evaporative pattern casting (EPC) process have blow holes. The blow holes in EPC castings are because of the non-escape of the gas produced as a result of burning of polystyrene pattern in the sand mold. To overcome the problem of blow holes, the EPC process is combined with the vacuum (V)- process. The vacuum applied to EPC mold draws the decomposed gases and improves the casting quality produced by the EPC process. The developed hybrid process has been termed as the vacuum assisted evaporative pattern casting (VAEPC) process. The objective of this paper to investigates the effect of process parameters, i.e, degree of vacuum, pouring temperature, grainfineness number, amplitude of vibration and time of vibration on the impact strength of Al-7% Si alloy castings in VAEPC process. In order to evaluate the effect of selected process parameters, the response surface methodology (RSM) is used to formulate a mathematical model which correlates the independent process parameters with the desired impact strength. The central composite rotatable design has been used to conduct the experiments. The results indicate that the impact strength decreases with increases in the grainfineness number and pouring temperature. Whereas, it has an inverse relationship with amplitude of vibration, time of vibration and degree of vacuum. The best value of impact strength (2.34 N/mm²) has been obtained at 400 mm Hg degree of vacuum imposed, 650°C as pouring temperature, 60 as sand grainfineness number, 460 μm as amplitude of vibration, and 70 s as time of vibration.     

Lean philosophy: implementation in a forging company

This research addresses the implementation of lean philosophy in a forging company with a focus on radial forging production flow lines. Here, the prime motive is to evolve and test several strategies to eliminate waste on the shop floor. In this research, a systematic approach is suggested for the implementation of lean principles. This paper describes an application of value stream mapping (VSM). Consequently, the present and future states of value stream maps are constructed to improve the production process by identifying waste and its sources. Furthermore, Taguchi’s method of design of experiments is pursued here to minimize the forging defects produced due to imperfect operating conditions. A noticeable reduction in set-up time and work-in-process (WIP) inventory level is substantiated. Finally, we conclude with a discussion of managerial implications and the future scope of research.     

Sintering studies of nano-crystalline zinc oxide

Sintering and grain growth of nano-crystalline undoped ZnO has been studied in detail over a wide range of temperature and holding time. Below 800 °C, sintering of over 70% theoretical density is not observed, irrespective of particle size. At 900 °C for 6 h, the nano-crystalline sample sinters to 99% of theoretical density whereas the density for as received sample is 93% of theoretical density. However, at 1300 °C or higher, the densification is found to be much faster and after a few hours becomes independent of holding time. Grain growth studies reveal a similar feature of attaining saturation over holding time. The average saturated grain size is found to be ∼1.5 and ∼2.2 μm at 800 and 900 °C, respectively, while at 1300 °C or higher, it is in between 12 and 13 μm.     

Modeling and sensitivity analysis of fire emissions in southern Africa during SAFARI 2000

This paper uses three recently generated southern African satellite burned area products for the month of September 2000 in a sensitivity study of regional biomass burning emissions for a number of trace gases and particulates. Differences in the extent and location of areas burned among products generated from Moderate Resolution Imaging Spectroradiometer (MODIS), Systeme Pour l'Observation de la Terre (SPOT-VEGETATION), and Along Track Scanning Radiometer (ATSR-2) data are significant and result in different emissions estimates for woodland and grassland land cover types. Due to the different emission profiles in woodlands and grasslands, favoring relatively more products of incomplete combustion in woodlands compared with products of complete combustion in grasslands in the late dry season, these changes are not proportional to the differences in the burned area amounts. The importance of accurate burned area information not just in terms of the total area but also in terms of its spatial distribution becomes apparent from our modeling results. This paper highlights the urgent need for satellite data producers to provide accuracy assessments associated with satellite-derived products. Preferably, these accuracy data will be spatially explicit, or defined in a way that can be applied in a spatially explicit modeling context, to enable emissions uncertainties to be defined with respect to different landscape units in support of greenhouse gas emissions reporting.     

A family of lower- and higher-order transversal linearization techniques in non-linear stochastic engineering dynamics

Sample pathwise numerical integration of noise-driven engineering dynamical systems cannot generally be performed beyond a limited level of accuracy, especially when the noise processes are modelled using (filtered) white noises. Recently, a locally transversal linearization (LTL) strategy has been proposed by the author (Proc Roy Soc London A 2001; 457 :539–566) for direct integration of deterministic and stochastic non-linear dynamical systems. The present effort is focussed on a host of extensions along with detailed theoretical error analyses of the linearization approach, especially as applied to problems in non-linear stochastic engineering dynamics. Thus, to begin with, estimates of local and global error orders in the basic LTL scheme are obtained separately for the displacement and velocity vectors when the system is driven either by a set of additive noises or by an arbitrary combination of (independently evolving) additive and multiplicative noises. Following this, a new family of higher-order LTL schemes is proposed in order to improve upon the basic LTL method and the associated error orders are established. A stepwise implementation of the lower- and higher-order versions of the LTL method, along with certain computational aspects, is also outlined. The proposed schemes are numerically illustrated, to a limited extent, for a single degree-of-freedom (SDOF) and a two degree-of-freedom (TDOF) non-linear engineering systems under additive and/or multiplicative white noise excitations. Copyright © 2004 John Wiley & Sons, Ltd.     

A dynamic programming method for building free algebras

We are interested in deciding if a given nonassociative polynomial h is an identity for a variety of nonassociative algebras. We present an algorithm for constructing a certain homomorphic image of a free nonassociative algebra which is sufficient to answer the question. The algorithm resembles dynamic programming in that the algebra is built by constructing a sequence of subspaces; the basis of each subspace is determined by the basis of previous subspaces. The number of arithmetic operations required to construct the algebra is bounded by a polynomial in the degree of h and the dimension of the resulting algebra.     

Mechanism of the skeletal isomerisation of linear butenes over ferrierite: analysis of side reactions

An investigation of the effect of reaction conditions on product distribution in the skeletal isomerisation reaction of linear butenes has been carried out. The main reaction routes over ferrierite have been identified. Beside the main product isobutene, major by-product formation occurs. The unwanted reactions include dimerisation of butene to form octenes, hydrogen transfer yielding small amounts of saturated C₃ and C₄ hydrocarbons and disproportionation producing propene and pentenes. The most abundant by-products were pentene and propene, though these were not formed in equimolar amounts as could be expected. Oligomerisation experiments of propene over ferrierite produced large amounts of butene and pentene, revealing the presence of adsorbed nonene. The cracking of this surface species to hexene and propene is the most likely reaction route for the excess propene formation. This additional path to propene formation operates mainly at temperatures above 623 K.