Thesis (M.S.)--Ohio University, November, 1987. / Title from PDF t.p.

Thesis (M. Phil.)--University of Hong Kong, 2000. / Includes bibliographical references (leaves 167-171).

The aim of this research is to understand the failure modes and mechanisms of adhesive materials used to flip-chip bond a silicon die onto a polyimide substrate. The bonding material investigated in this research is called Anisotropic Conductive Film (ACF). This is a promising interconnection material and has gained extensive interest in the electronics packaging industry. Both the experimental and finite element analysis (FEA) methods were used in order to investigate the behaviour of the ACF materials when subjected to certain manufacturing and environmental testing conditions. The manufacturing condition investigated was a subsequent solder reflow process on an ACF flip-chip bonded device. The environmental testing condition investigated was the moisture test. For the manufacturing condition, both experimental and modelling results demonstrate the impact of a subsequent reflow process on the behaviour of the ACF joint. Typical failures observed after this process were cracks at the pad/particle interface. This failure mode was more sever with a higher peak reflow temperature. This was also found using FEA where high tensile stresses were predicted in these regions. FEA modelling was also used to help identify the mechanisms leading to these failures. This is primarily due to the Coefficient of Thermal Expansion (CTE) miss-match in the materials and the elastic/plastic deformation behaviour of the conductive particle. Important design variables that can minimise these failures are the Young’s Modulus and CTE of the adhesive and the height of the hump on the die. For the environmental testing condition, an autoclave test at 121°C, 100%RH and pressure of 2atm was used. More than 85% of the ACF joints failed during the first 24 hours of testing. The failure mode observed was cracking along the interface between the adhesive and substrate and pad. A macro-micro modelling approach was used to help identify the mechanisms leading to these failures. It was found that most of the damage is caused by moisture diffusion and associated swelling. Important design variables that will help minimise this mode of failure are: Coefficient of Moisture Expansion (CME) and Young’s Modulus of the adhesive and the height of the bump on the die.

Additive manufacturing (AM) techniques provide engineering design flexibility not available when manufacturing is constrained by the tool-path restrictions of conventional subtractive techniques such as turning, milling and grinding. AM techniques allow the manufacture of complex form, light weight components with optimised geometries and topographies, including internal and re-entrant features. These features may greatly enhance the components functional capability. The design flexibility may allow a reduction in assembly part count, with a corresponding reduction in assembly time. Additionally, the ability to use high performance engineering metals in the AM process, such as 316 stainless steel, titanium Ti6Al4V and cobalt chrome provide the aerospace, medical and automotive industries with a new manufacturing toolbox using familiar raw materials. These quality-driven industries are fully aware of the potential of AM and are actively engaged and invested with the AM industry and research community. The complex features and design freedom providing great potential for these industries also presents challenges for surface measurement and characterisation. Surface measurement is vital to assure compliance with designed sealing, bearing, flow and adhesion properties of the component. Parts manufactured using AM are not exempt from the stringent quality requirements applicable to other manufacturing processes and so surface texture requirements will be incorporated into drawings and design specifications, imposed by customers onto suppliers. There will need to be a common language and approved standards. Compliance verification will be mandatory. If a feature is specified on a drawing then these industries will require verification that the component complies with design requirements. Traditionally, line-of-sight measuring devices were able to follow the tool pathways to access and measure these surfaces. With the advent of additive processes, new techniques will need to be developed. X-ray computed tomography (CT) has been used successfully for dimensional and defect detection as it allows the measurement of internal and re-entrant features. Thus far, there has been little research on the application of CT for the measurement of surface texture. This thesis reports on the development of a novel technique, detailing the first extraction of areal surface texture parameters per a recognised standard (ISO 25178-2) from CT scans of AM components. Industry will require reproducibility of measurements and so an interlaboratory comparison was performed to compare CT measurement results using this technique from four laboratories. The repeatability and accuracy of surface measurements is also vital for industrial applications and so the influence on extracted surface texture parameter values of selected CT measurement and reconstruction factors has been investigated. Extraction of true 3D data from CT requires the generation of new surface characterisation parameters to take full advantage of the technique and a new parameter has been developed to enable the true surface of re-entrant surfaces to be characterised. The additive process itself is complex and verification of consistent additive machine performance is vital for production. A series of small, inexpensive, surfacespecific measurement artefacts has been developed and built to characterise the build chamber and provide production process verification. This series of inter-related experimental investigations were chosen to be industrially relevant, to be linked closely to component function and be used as practical measurement and surface characterisation techniques. This work is intended, as far as possible, to not be machine-specific, but to be applicable to all CT machines and all metal powder bed fusion (PBF) AM machines. As AM and CT machine capability improves, as it inevitably will, the techniques and applications presented here are designed to evolve with these changes.

In surface mount technology (SMT) electronics assembly, the solder paste is printed onto the PCB's surface through a stencil and the components are later placed over the solder paste deposits. Since 2007, the use of extremely small SMT components for assembly of SMT devices has been widespread, and achieving consistent print deposits for fine pitch (the distance between the leads of the components) components has become a real challenge. The majority of the defects at the printing stage, such as skipping and bridging, were found to be related to the quality of the solder paste. These defects are usually carried over to the reflow process, causing defective final products. Hence, it is important to monitor the quality of the solder paste. Conventional techniques for monitoring the quality of solder pastes during the production and packaging stage are usually based on the viscosity measurements of the solder pastes from the viscometer and rheometer. One of the potential limitations of viscometer- and rheometer-based measurements is that the collection and preparation of the solder paste samples can irreversibly alter the structure and flow behaviour of the sample. Due to the sample preparation process (removal, preshear/ pre-mixing), repeatability issues were often encountered when taking measurements using a viscometer or rheometer. Secondly, rheological measurements and the interpretation of rheological data comprise a very technical and time consuming process, which requires professionally trained research and development (R&D) personnel. Finally, the monitoring/inspection process usually employs random sampling technique from the production batch. Hence, measurement may not represent the actual quality of the whole production batch. This would mean that the conventional solder paste quality control that has been employed in the industry as a benchmark for printability (i.e. checking the viscosity of the paste before being despatched to the customers), would need to be re-evaluated for its feasibility and other possible methods of solder paste quality control would need to be considered. This has brought the ultrasound technique into context as it can offer a non-destructive evaluation of the quality of the solder paste in terms of viscosity. Also, it can be used at different stages of paste production and processing. It is for these reasons that materials suppliers that formulate and produce solder pastes, as well as solder paste consumers (especially contract electronics manufacturers), are keen to see the development of simple, easy-to-use and accurate techniques for the rheological characterisation of solder pastes. This thesis concerns the study of a non-destructive ultrasonic technique for characterising the rheological properties of solder pastes and, specifically, the use of through-mode microsecond ultrasonic pulses for evaluation of viscoelastic properties of solder paste materials. In this study, a wide range of flux systems and solder alloy particle distributions used in the industry are investigated to determine the correlation of the ultrasound attenuation and velocity to the viscosity of the solder paste and their correlation to paste printing performance. The work is part of a bigger study aimed at the development of an on-line quality control technique for paste manufacture based on both conventional rheological tests and ultrasound measurements. Results from the work on the comparative study of standard fluids and both commercial and newly formulated solder pastes and flux vehicle systems have been used to demonstrate the utilisation of the ultrasound technique for on-line, non-destructive measurement of the viscosity of non- Newtonian materials such as solder pastes. The study also found that the viscosity of the solder paste is governed by the intermolecular forces between the solder particles and the flux. The strength of these intermolecular forces depends on the probability of these particles rubbing up against one another while the paste is being sheared. Provided that the right correction factor for a particular shear rate is used, the ultrasound viscosity results obtained were found to be comparable to the rheometer viscosity results or to the viscosity provided by the solder paste manufacturer. The ultrasound technique produced consistent results and was also proven to work at low temperatures. The ultrasound technique may be used to help solder paste manufacturers to add the correct amount of flux or solder particles to their paste in order to reach a desired viscosity. Otherwise, it can be used as a quick go/no-go monitoring tool in the production line for predicting printing quality. Based on the foregoing, it can be concluded that the ultrasound technique is a viable alternative to using a rheometer.

The work discussed in this thesis is aimed at examining the formation of freeze layers and refractory wear on water-cooling elements within direct smelting processes through the use of computational modelling techniques. The motivation of performing this work is to examine the cooling of regions of the Smelt Reduction Vessel of the HIsmelt process closer to the molten bath material. HIsmelt is a novel process for the production of pig iron which has been under development by Rio Tinto and is now being ommercialised. The previous work performed in this are has been reviewed with particular focus on the refractory wear mechanisms as the solidification algorithms have been thoroughly implemented within the Computational Fluid Dynamics (CFD) framework PHYSCIA used within this work. The governing equations along with the Finite Volume discretisations of these equations are set out within this thesis. Some comment is made about the solution methods used, and how boundary conditions are implemented. The Free-surface flow and Solidification governing relationships are also described as these are important for investigating the formation of freeze layers. The implementation of the refractory wear mechanisms are discussed in some detail. The three mechanisms implemented are for the penetration of slag into the refractory, the corrosion of the refractory by this penetrated slag; and the erosion of the refractory by the bulk flow of slag within the furnace. To be able to reasonably predict refractory wear, it is necessary to make the properties of the materials within the system temperature dependent. During the pilot plant trials at the HIsmelt® Research and Development facility, located in Kwinana Western Australia, accretions formed on the end of the solids injection lances. These accretions have been termed Elephant's Trunks. With the imminent construction of the Development Plant which injects the iron bearing feeds at an elevated temperature rather than at ambient temperatures used on the pilot plant, the formation of these pipe-like accretions under both the cold and hot injection conditions have been examined. This work provides confidence that the freeze layers predicted from the model will reflect those formed within the furnace. To evaluate the effectiveness of the refractory wear mechanisms, data from experimental and the HIsmelt pilot plant have been modelled. Sections of refractory samples from an induction furnace test and a rotary slag test have been modelled. The results are in agreement with the profile and affected regions of the sectioned refractory test pieces. A part of the HIsmelt pilot plant Smelt Reduction Vessel (SRV) has been modelled for the period of campaign 8-1 & 8-2 (just over 20 days). The predicted wear is in agreement with the measurements taken after the vessel had been cooled. To bring together freeze layer formation with the refractory wear mechanisms, a water-cooled element was modelled for the sloping slag section. The results show the growth of a small freeze layer that is consistent with the small freeze layer seen on the upper cooling panels of the pilot plant SRV. This model is an ideal tool to evaluate different water-cooling strategies for HIsmelt and other similar direct smelting processes. This work has developed models that predict the formation of freeze layers and refractory wear within direct smelting processes. The models have focused on slag-refractory interactions and further work would be needed to extend the refractory wear models to account for metal-refractory interactions. To examine spalling, stress calculations could be performed to determine when this may occur.

Environmental concerns have brought attention to the requirement for more efficient and renewable processes for chemicals production. Lignin is the second most abundant natural polymer, and might serve as a sustainable resource for manufacturing fuels and aromatic derivatives for the chemicals industry after being depolymerised. In this work, two main approaches were investigated with the aim of treatment of lignin with a mediator, 2,2’-azinobis(3-ethylbenthiazoline-6-sulfonic acid) diammonium salt (ABTS), in 1-ethyl-3-methylimidazolium ethyl sulfate, ([C2mim][C2SO4]). In the first approach, laccase from Trametes versicolor (LTV) was used to treat organosolv lignin, using [C2mim][C2SO4] as a co-solvent in the presence of ABTS. LTV was shown to possess catalytic activity for the degradation of organolsov lignin in systems containing ionic liquid and syringaldehyde was found to be a major product obtained from the process. ABTS alone has been evaluated for its reaction with lignin by means of cyclic voltammetry (CV). Here, the non-phenolic lignin model compound veratryl alcohol and three types of lignin (organosolv, Kraft and lignosulfonate) were specifically examined. The presence of either veratryl alcohol or organosolv lignin increased the second oxidation peak of ABTS under select conditions, indicating the ABTS-mediated oxidation of these molecules at high potentials in [C2mim][C2SO4]. Furthermore, CV was applied as a quick and efficient way to explore the impact of water in the ABTS-mediated oxidation of both organosolv and lignosulfonate lignin. Higher catalytic efficiencies of ABTS were observed for lignosulfonate solutions either in sodium acetate buffer, or when [C2mim][C2SO4] (15% v/v) was present in an aqueous solution, whilst there was no change found in the catalytic efficiency of ABTS in neat [C2mim][C2SO4]-lignosulfonate mixtures relative to ABTS alone. In contrast, organosolv showed an initial increase in oxidation, followed by a significant decrease on increasing the water content of a [C2mim][C2SO4] solution. Despite enhanced lignin solubility in ionic liquids, the yields of small molecules attributed to depolymerisation in ionic liquids are often quite low. Since depolymerisation approaches examined herein are thought to proceed via free-radical mediated mechanisms, two different stable radicals 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ABTS were assessed for the rapid monitoring of radical activity of lignin-related compounds in ionic liquid systems. While these assays are successful in aqueous and organic solvent systems, the presence of the ionic liquids complicates the assay procedure, requiring further developmental work.

No description available.

This dissertation investigated the effects of price and various forms of discounts on buyers' subjective evaluations of products. The role that price plays in product evaluations was examined from both the economic and behavioral perspectives, and a conceptualization derived from these two perspectives was reviewed. This original price-perceived quality conceptualization was extended using transaction utility theory. Based on the extended price-perceived quality model, hypotheses were developed to posit the relationships that the extrinsic cues of price and forms of discounts have with the constructs of perceived quality, perceived sacrifice, perceived value, willingness to buy, acquisition value, transaction value, and redemption effort. Also, the relationship among these constructs as posited by the extended conceptualization was examined. The research was conducted in three phases. The first phase determined the product and price levels to be used in the final stage of the research; the second phase checked the reliability of the indicators to be used in the final stage of the research; and, in the final phase, a 4 x 4 between subjects design was used to test the research hypotheses. PACKAGE was used to test the reliability of the indicators for each construct in both the pretest and fmla data collection stages. The analysis for the experiment incorporated ANOVA, Duncan's multiple comparisons, trend analysis, and LISREL to test the significance of the proposed relationships. In general, the analysis provided good support for the hypothesized effects. The principal exceptions being the posited relationships of perceived quality and perceived value with the independent variable forms of discounts. Also, the relationships of several of the dependent variables with transaction value were weak leading to speculation of the role that transaction value has in buyers' subjective product evaluations. Finally, the major findings of the research were discussed with respect to the theoretical, methodological, and managerial significance. Limitations and directions for future research were also discussed. / Ph. D.

Woven engineering fabrics generally serve as advanced composite preforms and are an important class of engineering material. This thesis focuses on improving the accuracy of Computer Aided Engineering (CAE) tools for simulating the deformation of such materials during the press-forming manufacture process. Specifically, this has involved better understanding: (i) the material behaviour during deformation and (ii) the extent and influence of material variability on forming behaviour. To this end, the use of a novel fabric shear test, the BBE test, capable of characterising the shear-tension coupling of engineering fabrics has been used for the first time in an extensive characterisation program, involving three different woven engineering fabrics. Results show a strong dependence of shear compliance on in-plane tension. Wrinkling behaviour during shear has also been characterised using two new analysis methods, a transmitted backlighting technique and a tracer line analysis technique. The onset of wrinkling is clearly shown to be an increasing function of the in-plane tension applied to the deforming fabric. Variability of fibre orientation, otherwise known as ‘tow meander’ can degrade the final mechanical properties of a textile composite part and can also influence measurements of the fabric’s shear compliance. Accordingly, variability of tow orientation in a pre-consolidated textile composite and three engineering fabrics has been characterised using two different image processing methods: a simple manual method and a semi-automated method. The latter has been found to be a promising tool in terms of increasing accuracy and in reducing manual effort during the characterisation process. Modelling tow meander has also been conducted using a numerical code, VarifabGA, that has been developed during the course of this work. The code has allowed the effects of tow meander on shear compliance to be investigated in numerical simulations using a technique of assigning an initial fibre orientation to each element in a Finite Element (FE) mesh before conducting shear test simulations. The experimentally measured shear-tension coupling has also been modelled by enhancing a pre-existing Non-Orthogonal Constitutive Model (NOCM). A comparison between model predictions and experimental results of the sensitivity of this shear-tension coupling has shown that the model provides good results. Finally, a novel geometrically complex 3D forming tool of a kart wheel has been designed and manufactured for use in experimental and numerical forming studies. The part provides a challenging modelling problem with which to demonstrate the use of the new computational tools developed during the course of this work.