Thermal Aging Behavior of Fine Pitch Palladium Coated Silver (PCS) Ball Bonds on Al Metallization

The high price of Au has motivated many to look for alternative bonding wire materials in the field of microelectronics packaging. In the present study, the reliability performance of palladium coated silver (PCS) wire in high temperature storage test (HTST) is carried out using 18 μm diameter fine pitch PCS wire. Fine pitch ball bonds are made on Al metallization, with bonded ball diameter (BBD) of 32 ± 0.5 μm and ball height (BH) of 8 ± 0.5 μm. The aging temperature used in HTST is 170 °C and both shear and pull test are used to evaluate the aged ball bonds at regular time intervals. The shear force increases from 9.9 gf at 96 h to 12.5 gf at 192 h, and remains almost constant until 1344 h, and starts dropping gradually until 10.9 gf at 1848 h. The pad lift percentage recorded in pull test gradually drops from 90 % at 96 h to 20 % at 1008 h, and increases to 90 % at 1848 h. The chip side fractography after shear test indicates that the main failure modes are through pad at 96 h, through ball bond at 504 h, and half of both at 168 h, respectively. Cross-sectional images show that the thickness of the intermetallic compound (IMC) layer growth follows parabolic relationship and the rate constant is 0.10 ± 0.02 μm/h½. Gaps are observed along the periphery of the ball bond interface where no IMC is observed. The IMCs are located at the center of the ball bond interface, and the width is 16.0–19.3 μm at 96 h and 17.2–22.7 μm at 1344 h, respectively

The joining development, metallurgical study and characterisation approach of brazed joints between tungsten and fusion related materials for divertor applications

The design of brazed joints between tungsten to other fusion related materials is a significant challenge in developing fusion reactors, largely due to the dissimilar physical metallurgy of the materials to be joined. Under extreme thermal loading and plasma irradiation conditions, selecting suitable materials is very restricted and poses a significant challenge to the design. The candidate brazing filler materials for fusion related materials are often unconventional and lack material data and design experience. The work presented in this thesis focuses on the design and fabrication of dissimilar brazed joints between tungsten and fusion relevant materials with novel gold-based fillers. Vacuum furnace brazed joints of tungsten-tungsten, tungsten-Eurofer 97, tungsten - copper and tungsten-SS316L are successfully joined with a novel gold-based Au80Cu19Fe filler. Metallurgical and interfacial studies have been carried out for each brazed joint to understand their microstructural properties, and nanoindentation testing was performed at the joints to generate mechanical properties of the brazed layers. Optimised brazing procedures for vacuum furnace brazing and induction brazing were developed to limit the defects within the brazed layers with an equivalent Au80Cu20 filler. The brazing developments showed that the gold-based fillers could be used to fabricate qualified brazed joint between tungsten and the dissimilar materials considered. The brazing process design has been used for the proof-of-concept study of divertor mock-up fabrications, and the findings have contributed to the limited test data on fusion relevant materials. Finally, due to the substantial procurement costs of the gold-based filler material and the inability to generate macro scale properties from the braze layer, the use of conventional Cu60Zn40 fillers allowed a casting and brazing process methodology to be developed to correlate the in situ mechanical properties within the brazed layer to the properties generated by macro-level mechanical testing. The findings showed that this methodology could be used for predicting the mechanical properties of the brazed layer by the cast and heat-treated macro-level filler metal specimens, which are applicable to brazed joints in a range of applications.The design of brazed joints between tungsten to other fusion related materials is a significant challenge in developing fusion reactors, largely due to the dissimilar physical metallurgy of the materials to be joined. Under extreme thermal loading and plasma irradiation conditions, selecting suitable materials is very restricted and poses a significant challenge to the design. The candidate brazing filler materials for fusion related materials are often unconventional and lack material data and design experience. The work presented in this thesis focuses on the design and fabrication of dissimilar brazed joints between tungsten and fusion relevant materials with novel gold-based fillers. Vacuum furnace brazed joints of tungsten-tungsten, tungsten-Eurofer 97, tungsten - copper and tungsten-SS316L are successfully joined with a novel gold-based Au80Cu19Fe filler. Metallurgical and interfacial studies have been carried out for each brazed joint to understand their microstructural properties, and nanoindentation testing was performed at the joints to generate mechanical properties of the brazed layers. Optimised brazing procedures for vacuum furnace brazing and induction brazing were developed to limit the defects within the brazed layers with an equivalent Au80Cu20 filler. The brazing developments showed that the gold-based fillers could be used to fabricate qualified brazed joint between tungsten and the dissimilar materials considered. The brazing process design has been used for the proof-of-concept study of divertor mock-up fabrications, and the findings have contributed to the limited test data on fusion relevant materials. Finally, due to the substantial procurement costs of the gold-based filler material and the inability to generate macro scale properties from the braze layer, the use of conventional Cu60Zn40 fillers allowed a casting and brazing process methodology to be developed to correlate the in situ mechanical properties within the brazed layer to the properties generated by macro-level mechanical testing. The findings showed that this methodology could be used for predicting the mechanical properties of the brazed layer by the cast and heat-treated macro-level filler metal specimens, which are applicable to brazed joints in a range of applications

Design, development and validation of iron-based composites for biodegradable implant applications

"Thèse en cotutelle : Doctorat en génie des matériaux et de la métallurgie, Université Laval, Québec, Canada, Philosophiæ doctor (Ph. D.) et Politecnico di Milano, Milano, Italie."Récemment, le Fe et ses alliages ont montré leur potentiel en tant que matériaux dégradables pour des applications biomédicales. Néanmoins, la vitesse de corrosion lente limite leurs performances dans certaines situations. Les matériaux composites à matrice de fer représentent une approche possible, non seulement pour améliorer leurs propriétés mécaniques, mais aussi pour accélérer et ajuster la vitesse de corrosion dans un environnement physiologique. Dans ce travail, des composites à base de Fe renforcés par des particules Mg2Si ont été proposés. Les poudres initiales ont été préparées par différentes combinaisons de procédés de mélange et de broyage, et finalement consolidées par laminage à chaud. L'influence de la microstructure sur les propriétés mécaniques et le comportement à la corrosion de Fe/Mg2Si a été étudiée. Les échantillons contenant des particules Mg2Si plus petites présentaient une distribution plus homogène du renforcement. Le rendement et l’état limite ultime à la traction ont augmenté par rapport à ceux du Fe pur. La présence des particules de renforcement a joué un rôle crucial dans la susceptibilité à l'attaque de corrosion localisée dans les composites à base de Fe. L'initiation de la corrosion et son développement ont été systématiquement suivis pour étudier le mécanisme de corrosion. L'importance des particules de Mg2Si dans le déclenchement des processus de corrosion a été expliquée. Des mesures électrochimiques et des tests d'immersion statique ont indiqué que l'ajout de Mg2Si pourrait augmenter le taux de corrosion du Fe. Il a été constaté que la taille et la distribution des particules de renfort jouaient un rôle crucial à l'uniformité de l'attaque de corrosion. Après, une série de tests d'immersion à différents intervalles d'exposition (20, 50 et 100 jours) à la solution modifiée de Hanks a été réalisée à fin d’évaluer le comportement de dégradation des composites Fe/Mg2Si et Fe pur préparés par différentes techniques de métallurgie des poudres. Les résultats ont révélé l’importance du Mg2Si dans la composition et la stabilité des films protecteurs formés lors des expériences de corrosion statique. Les composites Fe/Mg2Si présentaient des taux de dégradation plus élevés que le Fe pur à toutes les étapes du test d'immersion. Les taux de dégradation à des intervalles d'exposition distincts dépendaient fortement de la composition et de la stabilité des films protecteurs d'oxyde, d'hydroxyde, de carbonate et de phosphate formés sur les surfaces dégradées. La libération d'ions Fe dans la solution aux stades ultérieurs de l'expérience était limitée en raison de l'effet de barrière dû au dépôt insoluble. Cette étude fondamentale a servi de base aux processus de formation de film protecteur dans la solution de Hanks modifiée, permettant une identification détaillée de leurs caractéristiques.Fe-based alloys have shown a potential as a degradable material for biomedical applications. Nevertheless, the slow corrosion rate limits their performance as a biodegradable implant. One approach to control and modify their corrosion properties is the reinforcement addition, to create metal matrix composites in which the second phase is aimed at tuning not only the mechanical properties but also the corrosion mode and rate in a physiological environment. This thesis presents an original and thorough contribution on a very pertinent topic, the design, development, and validation of a new Fe/Mg2Si composites prepared powder metallurgy. The initial powders were prepared by different combinations of mixing and high energy ball milling processes and finally consolidated by hot rolling. Mechanical properties, microstructural features, as well as the corrosion performance, were extensively investigated in relation to the reinforcement size and distribution. The composites made of small size reinforcement particles showed a general increase in tensile strength. For instance, high energy ball milled samples exhibited better tensile performances (YS = 523 MPa, UTS = 630 MPa) while having the lower ductility (around 4%). A fundamental understanding of corrosion initiation, protective film formation, and growth on Fe-based materials and leads to a design of smarter and surface responsive biomaterials with modulable degradation rates, at distinct stages of the corrosion process. Here, the corrosion performance of Fe/Mg2Si composites varied with the reinforcement size and distribution. The predominant localized pitting corrosion in Fe/Mg2Si prepared by mixing was replaced by a more uniform pattern found in samples produced by mechanical milling. Further, it was found that Mg2Si plays a significant role in the composition and stability of the protective films formed during the static corrosion experiments. Fe/Mg2Si showed a higher corrosion rate compared to that of pure Fe at all stages of the corrosion experiment (1, 10, 20, 50 and 100 days). Moreover, the final degradation products varied with the substrate chemical composition and microstructure. In case of pure Fe, low solubility (Fe3(PO4)2) covered the entire surface, while Fe/Mg2Si exhibited the presence of carbonates at the latest stages of the test. The details about the degradation behaviour during long-term exposure times to the physiological environment highlighted in this work add a new knowledge on corrosion mechanism of degradable implant materials. In particular, the ability to tune mechanical and corrosion behavior of the composites as a function of reinforcement properties and manufacturing method was experimentally verified, highlighting the microstructure-corrosion property relationship.I biomateriali in ferro puro e in leghe a base di ferro presentano una combinazione interessante di proprietà meccaniche, elettrochimiche e biologiche; per questo motivo, questa classe di materiali metallici possono trovare utilizzo in applicazioni di tipo impiantistico biomedicale. Malgrado ciò, nonostante le sue soddisfacenti proprietà meccaniche, questo elemento impiegato allo stato puro mostra un inconveniente rilevante - un basso tasso di degradazione. L’oggetto di questa tesi è lo studio di un nuovo gruppo di materiali biodegradabili compositi a matrice ferrosa (Fe/Mg2Si), in cui il Fe costituisce la matrice e il Mg2Si è impiegato come rinforzo; questi materiali sono stati sviluppati con tecniche di metallurgia delle polveri, e presentano un, alta resistenza meccanica come caratteristica principale. Le polveri che costituiscono i materiali di partenza sono stati preparati con diverse combinazioni di procedure oltre al semplice mescolamento e/o high energy ball milling (macinatura in mulino a sfere a alta energia). Tutte le formulazioni preparate sono state compattate attraverso laminazione a caldo. Le proprietà meccaniche, le caratteristiche microstrutturali, la composizione delle fasi e le prestazioni in termini di corrosione sono state studiate dettagliatamente, in relazione alla dimensione delle particelle di rinforzo e della loro distribuzione. Lavori precedenti hanno confermato l’efficacia dell’aggiunta di una seconda fase, soprattutto se finemente dispersa, per aumentare il tasso di degradazione di materiali metallici per applicazioni biomedicali a base Fe: gli esperimenti condotti in questo lavoro hanno confermato che i compositi Fe/Mg2Si hanno mostrato, rispetto al Fe puro che compone la matrice, non solo una resistenza meccanica più elevata, ma anche un tasso di degradazione più alto negli esperimenti di laboratorio in vitro. Infine, i materiali ottenuti tramite high energy ball milling, presentano una resistenza alla trazione migliore (carico di snervamento= 523 MPa, resistenza alla trazione = 630 MPa), ma contemporaneamente una ridotta duttilità (circa 4%). Una attenzione particolare è stata posta nello studio degli effetti della presenza di Mg2Si sui meccanismi di corrosione.Tutti i compositi studiati hanno mostrato un tasso di degradazione più elevato rispetto alla matrice fabbricata con la stessa procedura; inoltre, la formazione del film di prodotti di degradazione sulla superficie del materiale cambiava in maniera rilevante in funzione della composizione chimica del substrato e della sua microstruttura. Nel caso del Fe puro, cristalli isolati di vivianite (Fe3(PO4)2) erano presenti su tutta la superficie, mentre carbonati di Fe si formavano principalmente sulla superficie dei compositi, specialmente negli ultimi stadi del processo di degradazione

Solid-state dewetting of magnetic binary alloy thin films and application as nanowire and nanotube growth catalysts.

Ph.DDOCTOR OF PHILOSOPH

Sulfur tolerance of Pd/Au alloy membranes for hydrogen separation from coal gas

This work provides a detailed characterization study on H2S poisoning of Pd and Pd/Au alloy composite membranes to obtain fundamental understandings of sulfur poisoning phenomena and preparation of sulfur tolerant membranes. The enhancement of the sulfur tolerance by alloying Pd with Au has been confirmed by both permeation test and microstructure analysis (SEM and XRD). While pure Pd membranes exhibited the permeance decline in the presence of H2S due to both sulfur adsorption and bulk Pd4S formation, Pd/Au alloy membranes showed the permeance loss merely resulted from the surface sulfur adsorption without bulk sulfide formation up to 55 ppm H2S. The XPS study confirmed that the H2S adsorption on the Pd/Au alloy surfaces was dissociative, and both surface Au and Pd sulfides were formed with the preferential Au-S bonding. The adsorption type of sulfur on the Pd/Au alloy surfaces was monolayer with a limited coverage, which increased with decreasing temperature. The permeance loss of Pd/Au membranes was essentially fully recoverable in H2, and the integrity of the membranes remained unaltered after the poisoning/recovery tests. Increasing Au composition in the Pd/Au membranes increased the sulfur tolerance. A Pd/Au alloy membrane of 16.7 wt% Au exhibited a permeance over 50% of its original value in the presence of 5 ppm H2S at 400°C, while a Pd membrane showed 85% permeance loss. The Pd/Au alloy membranes were fabricated by the Au displacement deposition, which had an empirical reaction order of 3.2 determined by the AAS. The HT-XRD study verified that the formed Pd/Au alloy layers were thermally stable up to 500°C

Pd based Inorganic Hollow Fibre Membranes for H2 Permeation and Methylcyclohexane Dehydrogenation

The availability of inorganic membranes which can withstand high temperatures and harsh chemical environments has resulted in a wide range of opportunities for the application of membranes in chemical reactions and separations. In particular, the combination of membrane separation and catalytic reaction into a single operating unit is an attractive way to increase conversions, improve yields and more efficient use of natural resources in many reactions. In this study, asymmetric alumina hollow fibres with different macrostructures consisting of finger-like macrovoids and a sponge-like packed pore structure in varying ratios have been prepared by a combined phase inversion/sintering technique. The asymmetric membranes in hollow fibre geometry possess superior surface area to volume ratios with less gas permeation resistance in comparison to commercial symmetric membranes in tubular and disk configurations. Such asymmetric hollow fibres are used as substrates onto which a Pd membrane is directly deposited by an electroless plating (ELP) technique without any pre-treatment of the substrate surface. A systematic study of the electroless plating of Pd and Ag onto an asymmetric alumina hollow fibre substrate has been carried out by direct measurement of one of the gaseous products, i.e. N2, using gas chromatography (GC). In addition, the influences of the substrate macrostructure on hydrogen permeation through the Pd/Al2O3 composite membranes have been investigated both experimentally and theoretically. Furthermore, a multifunctional Pd/alumina hollow fibre membrane reactor (HFMR) has been developed and employed for the catalytic dehydrogenation of methylcyclohexane (MCH) to toluene (TOL). The developed HFMR consists of a thin and defect-free Pd membrane coated directly onto the outer surface of an asymmetric alumina hollow fibre substrate. 50 wt% Ni/Al2O3 nano-sized catalysts were directly impregnated into the substrate. The performance of HFMR has also been compared with several different reactor configurations

Statistical Techniques and Non-Destructive Testing Methods for Copper Wire Bond Reliability Investigation

Microelectronic devices require packaging for mechanical protection and electrical interconnections. Reliability challenges in microelectronics packaging are becoming more severe, as applications demand smaller package sizes and operation in harsher environments, such as in automotive applications. At the same time, manufacturers are seeking to reduce production costs by using new materials, for example in wire bonding by replacing costly gold wire with more economical copper. Because microelectronic devices are expected to function reliably for years or even decades, depending on the application, reliability testing is commonly accelerated, e.g. by using elevated temperature and/or humidity. Even so, testing is often time consuming, requiring weeks or months for product qualification. Furthermore, although standard test conditions exist, little guidance is available in the literature to indicate how long products passing these tests will survive in operation. Non-destructive testing methods provide a great deal of information regarding product degradation and reliability. With proper statistical analysis, strong conclusions can be made about device reliability with relatively short test durations, since testing need not continue until all samples fail. However, data analysis techniques used in the electronics packaging literature are often limited, with statistical analyses and confidence bounds rarely presented. Analysis of incomplete or censored data requires specialized techniques from the field of survival analysis. The contributions of this thesis can be divided in two topics. The first topic is the equipment and techniques used to obtain new reliability results, including a method for temperature calibration of the miniature ovens used, a modification of those ovens for use as environmental chambers with humidity control, and procedures for optimization of wire bonding processes. Second, statistical techniques for analysis of reliability data are demonstrated, using accelerated failure time models to analyze resistance data from copper wire bonds in high temperature storage testing. In doing so, new information was provided to answer an important open question in the field of copper wire bonding, namely, the maximum temperature at which one can expect copper wire bonds on aluminum metallization to perform reliably. In particular, ball bonds made from 25 µm diameter palladium-coated copper wire are estimated to be highly reliable up to at least 167 °C in a clean environment without encapsulation, with failure rate of only 1 ppm after 12000 h. PCC wires were more reliable than bare Cu wires when unencapsulated or when encapsulated in silicone. Conversely, bare Cu was more reliable than PCC when encapsulated in epoxy. The best-performing encapsulated bonds tested were bare Cu wire with a highly heat tolerant epoxy, which are estimated to survive 12000 h with 1 ppm failure probability at 159 °C. Effects of several other factors on bond reliability were also investigated, namely the cleaning process, Al bond pad thickness, and the bonded ball size. Sample and environmental cleanliness were found to be critical to good reliability. Bond pad thickness and bonded ball size had only minor effects on reliability, suggesting that these factors can be safely chosen to satisfy other requirements such as bond pad pitch or current-carrying requirements

Development of Lead-Free Electroless Nickel Plating systems and Metal Thin Films on Silicone and Nafion membranes

Ph.DDOCTOR OF PHILOSOPH

Design and Assembly of Nanostructured Complex Metal Oxide Materials for the Construction of Batteries and Thermoelectric Devices

Thermoelectric devices and lithium-ion batteries are among the fastest growing energy technologies. Thermoelectric devices generate energy from waste heat, whereas lithium-ion batteries store energy for use in commercial applications. Two different topics are bound with a common thread in this thesis - nanotechnology! In fact, nanostructuring is a more preferred term for the approach I have taken herein. Another commonality between these two topics is the material system I have used to prove my hypotheses - complex metal oxides. Complex metal oxides can be used for both energy generation and storage as they are stable at high temperatures, are benign and inexpensive, and are chemically stable. . Nevertheless, complex metal oxide-based materials have drawbacks when they are used in thermoelectric devices. Since they have high thermal conductivities and low power factors, they have lower thermoelectric figures of merit (ZT). This affects their performance as thermoelectric materials. Nanostructuring can solve this critical problem as thermal conductivity, electrical conductivity and Seebeck coefficient become quasi-independent of each other under these conditions. However, oxide-based materials have proven to be greatly recalcitrant to forming nanostructures when traditional synthetic methods such as solid-state reactions have been employed. Solid-state reactions usually proceed at extremely high temperatures that are not particularly conducive to forming nanostructures. The first part of this thesis presents novel solution-based synthetic methods that were developed in order to produce novel nanostructured complex metal oxides. Typical structures include nanowires. The second part of this thesis extends this methodology to study the effect of nanostructuring on the thermal conductivity of strontium titanate (SrTiO3), a promising high temperature thermoelectric material. Ultrathin nanowires of SrTiO3 were synthesized using a novel hydrothermal reaction. These ultrathin nanowires were compressed into a `nanostructured\u27 bulk pellet through spark plasma sintering. The thermal conductivity measured on the nanostructured bulk pellet showed a drastic decrease compared to bulk SrTiO3. Through theoretical modeling it was realized that drastic decrease in thermal conductivity was due to scattering of phonons, which contribute to the lattice thermal conductivity, at the interface of the nanowires. Another aspect of the thermoelectric research presented herein includes the development of a new phase of misfit layered oxide, calcium cobalt oxide (Ca9Co12O28), for high temperature applications. This phase had hardly been researched in literature because of its high thermal conductivity, thus limiting its use in thermoelectric devices. Through a unique single source precursor-based technique, porous nanowire structures of Ca9Co12O28 were prepared at much lower temperatures than conventional solid-state techniques. Significantly improved ZT were observed in our nanowire system up to 700K due to reduced thermal conductivity and enhanced Seebeck coefficient. The synthetic approach was also applied to prepare different nanostructures (porous nanowires and nanoparticles) of lithium cobalt oxide (LiCoO2) by tuning individual reaction parameters. The importance of reaction temperature and the role of nanostructures on the final electrochemical performance of LiCoO2 was also deduced. Saliently, the nanostructured electrodes so prepared can withstand high cycling rates and achieve capacities that are close to the theoretical capacity of LiCoO2 at 0.1C

Application of Immobilized Palladium Monolithic Catalysts in Suzuki-Miyaura and Tsuji-Wacker Redox Reactions

Herein, a wholistic analysis of the viability of monolithic catalysts for redox reactions is presented. The interdisciplinary approach taken in this systematic study included preparation and investigation on Pd-on-carbon monoliths as catalysts in a flow and electrochemical settings. The Suzuki-Miyaura reaction-focused study led to rational design, preparation, and successful application of Pd0-on-graphene oxide (GO) monolithic catalysts in flow conditions. In this study a combination of chemical reduction, freeze-casting, and vapor-phase reduction processes was applied to Pd-GO structures leading to the preparation of these monoliths. The Suzuki flow synthesis reactions revealed that the monolithic structure led to significantly improved catalytic longevity compared to 2D solid-supported catalysts. Nonetheless, the turnover frequency and product metal contamination (leaching-off) analysis indicated superior performance for monolithic catalysts. Electrochemical Wacker-type oxidations are among the most common reactions in the industry. However, in order to prepare a rationally designed monolithic catalyst for this reaction, further catalyst studies were required. Therefore, a comprehensive study on 2-dimensional Pd-on-graphene nanoplatelets was conducted, leading to a proposed industrial design space for oxidation catalyst manufacturing. Afterwards, as a proof of concept viability of PdII-on glassy carbon (GC) monoliths were used as catalytic electrodes for Wacker-type oxidation in the electrochemical setting. Via this approach, a comprehensive investigation and validation of monolithic catalyst preparation and applications in industrially feasible synthetic processes, including catalytically different redox reactions in flow and electrochemical settings, were successfully attained