Thesis (Ph. D.)--State University of New York at Binghamton, Thomas J. Watson School of Engineering and Applied Science, Department of Mechanical Engineering, 2008. / Includes bibliographical references.

abstract: The mechanical behavior of Pb-free solder alloys is important, since they must maintain mechanical integrity under thermomechanical fatigue, creep, and mechanical shock conditions. Mechanical shock, in particular, has become an increasing concern in the electronics industry, since electronic packages can be subjected to mechanical shock by mishandling during manufacture or by accidental dropping. In this study, the mechanical shock behavior of Sn and Sn-Ag-Cu alloys was systematically analyzed over the strain rate range 10-3 - 30 s-1 in bulk samples, and over 10-3 - 12 s-1 on the single solder joint level. More importantly, the influences of solder microstructure and intermetallic compounds (IMC) on mechanical shock resistance were quantified. A thorough microstructural characterization of Sn-rich alloys was conducted using synchrotron x-ray computed tomography. The three-dimensional morphology and distribution of contiguous phases and precipitates was analyzed. A multiscale approach was utilized to characterize Sn-rich phases on the microscale with x-ray tomography and focused ion beam tomography to characterize nanoscale precipitates. A high strain rate servohydraulic test system was developed in conjunction with a modified tensile specimen geometry and a high speed camera for quantifying deformation. The effect of microstructure and applied strain rate on the local strain and strain rate distributions were quantified using digital image correlation. Necking behavior was analyzed using a novel mirror fixture, and the triaxial stresses associated with necking were corrected using a self-consistent method to obtain the true stress-true strain constitutive behavior. Fracture mechanisms were quantified as a function of strain rate. Finally, the relationship between solder microstructure and intermetallic compound layer thickness with the mechanical shock resistance of Sn-3.8Ag-0.7Cu solder joints was characterized. It was found that at low strain rates the dynamic solder joint strength was controlled by the solder microstructure, while at high strain rates it was controlled by the IMC layer. The influences of solder microstructure and IMC layer thickness were then isolated using extended reflow or isothermal aging treatments. It was found that at large IMC layer thicknesses the trend described above does not hold true. The fracture mechanisms associated with the dynamic solder joint strength regimes were analyzed. / Dissertation/Thesis / Ph.D. Materials Science and Engineering 2012

Depuis l’entrée en vigueur de la directive RoHS (Restriction of Hazardous Substances Directive) interdisant l’utilisation du plomb, les industriels des secteurs aéronautique et militaire se doivent de comprendre le comportement en fatigue des nouveaux alliages sans plomb afin de pouvoir estimer leur durabilité en conditions réelles d’utilisation. En se basant sur les résultats d’essais accélérés et les modélisations éléments-finis associées, les modèles de fatigue mécanique et thermomécanique correspondant aux brasures SAC305 sont développés. Le 1er chapitre traite de la caractérisation mécanique et optique de cet alliage sans plomb. Après une étude bibliographique poussée, les propriétés élastiques et viscoplastiques de l’alliage SAC305 sont établies à partir d’essais d’écrouissage, de traction et de nanoindentation. La courbe d’hystérésis contrainte - déformation en cisaillement est en outre tracée via l’utilisation de jauges de déformation. Des analyses EBSD sont finalement réalisées afin d’identifier les caractéristiques microstructurales des joints de brasure SAC305 après refusion. Le chapitre 2 a pour objectif d’évaluer la durabilité des interconnexions SAC305 soumises à des chargements en vibrations et en chocs. L’hypothèse élastique est retenue et les paramètres matériaux du modèle de Basquin sont déterminés. À partir de l’algorithme de comptage rainflow et de la loi de Miner, une méthode d’évaluation de la durabilité en vibration aléatoire est donnée. La tenue mécanique en chocs des brasures SAC305 est enfin discutée et comparée à l’alliage SnPb63Ag2. Le dernier chapitre porte sur l’étude de la fatigue thermomécanique des joints brasés SAC305. En utilisant le modèle viscoplastique unifié d’Anand, la loi de fatigue énergétique correspondant est développée. Le phénomène de recristallisation caractéristique de l’endommagement thermomécanique des brasures SAC305 est finalement investigué à partir d’analyses EBSD. / Temperature and vibration-induced solder joint fatigue are main reliability concerns for aeronautic and military industries whose electronic equipment used in the field is required to remain functional under harsh loadings. Due to the RoHS directive which eventually will prevent lead from being utilized in electronic systems, there is a need for a better understanding of lead-free solder behavior used in thermal en vibrational environments. This study reports fatigue life prediction methodologies developed to assess the durability of SAC305 solder joints subjected to temperature variations and vibration loadings. Based on accelerated tests and finite element analysis, solder joint fatigue models corresponding to each environment are developed. Chapter 1 discusses SAC305 solder mechanical characterization and its microstructural features. An indepth literature review is conducted and SAC305 solder elastic and viscoplastic properties are determined through tensile, creep and nanoindentation tests. An approach never considered for lead-free solder joints is also applied to plot the SAC305 shear strain - stress hysteresis loop. EBSD analysis is finally performed in order to identify the microstructural “finger print” of asreflowed SAC305 solder joints. Chapter 2 aims to determine the polycyclic fatigue curve corresponding to SAC305 interconnects damage under harmonic vibrations. Considering the rainflow counting algorithm along with the Miner’s linear damage rule, the corresponding Basquin’s model is used as an input data for assessing SAC305 durability under random vibrations. SAC305 endurance under shock loading is finally discussed and compared with SnPb36Ag2 assemblies. The final chapter deals with the thermomechanical fatigue assessment of SAC305 solder joints. An energy-based model is developed using Anand unified viscoplastic law. EBSD analysis is finally conducted to assess the SAC305 microstructure evolution throughout thermal cycling characterized by -Sn grains recrystallization.

abstract: Solar photovoltaic (PV) industry is tipped to be one of the front-runners in the renewable industry. Typically, PV module manufacturers provide a linear or step warranty of 80% of original power over 25 years. This power loss during the field exposure is primarily attributed to the development of performance affecting defects in the PV modules. As many as 86 different defects can occur in a PV module. One of the major defects that can cause significant power loss is the interconnect metallization system (IMS) degradation which is the focus of this thesis. The IMS is composed of cell-interconnect (cell-ribbon interconnect) and string-interconnect (ribbon-ribbon interconnect). The cell interconnect is in turn composed of silver metallization (fingers and busbars) and solder bonds between silver busbar and copper ribbon. Weak solder bonding between copper ribbon and busbar of a cell results in increase of series resistance that in turn affects the fill factor causing a power drop. In this thesis work, the results obtained from various non-destructive and destructive experiments performed on modules exposed in three different climates (Arizona - Hot and Dry, Mexico - Warm and Humid, and California - Temperate) are presented. These experiments include light I-V measurements, dark I-V measurements, infrared imaging, extraction of test samples from the modules, peel strength measurements and four-point resistance measurements. The extraction of test samples was performed using a mechanical method and a chemical method. The merits and demerits of these two methods are presented. A drop of 10.33% in fill factor was observed for a 0.05Ω increase in the series resistance of the modules investigated in this work. Different combinations in a cell that can cause series resistance increase were considered and their effect on fill factor were observed using four-point probe experiments. Peel test experiments were conducted to correlate the effect of series resistance on the ribbon peel strength. Finally, climate specific thermal modelling was performed for 4 different sites over 20 years in order to calculate the accumulated thermal fatigue and also to evaluate its correlation, if any, with the increase of series resistance. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2016

Orientador: Antonio Jorge Abdalla / Coorientador: Marcelo dos Santos Pereira / Banca: Tomaz Manabu Hashimoto / Banca: Fernando de Azevedo Silva / Banca: Carlos Antonio Reis Pereira Baptista / Banca: Danieli Aparecida Pereira Reis / Resumo: Os aços Maraging são aços de ultra-alta-resistência, tem composição à base de ferro ligado com cerca de 18% de níquel, com limite de esoamento entre 1.400 a 2.500 MPa. Possuem propriedades superiores, tais como a alta ductilidade, boa soldabilidade, tratamento térmico simples sem deformações, boa usinabilidade, alta resistência e resistência ao desgaste. A sua boa tenacidade permiti que suporte tensões repetidas de fadiga por maior tempo, comparado com outros aços de alta resistência. Para o presente trabalho, a partir de diversos testes de solda a laser, aplicação de tratamentos térmicos e tratamento superficial de nitretação a plasma, foram estudadas as propriedades mecânicas através de ensaios de tração, fadiga, impacto, dureza e rugosidade. Foram também analisadas, com auxílio do Microscópio Óptico, as características microstuturais da zona de fusão (ZF), zona térmica afetada (ZTA) pelo calor da solda e camada nitretada. Com o auxílio de um Microscópio Eletrônico de Varredura (MEV) analisou-se o mecanismo da fratura e foram realizadas análises por E.D.S. (Energia Dispersiva de Raios X). Foram realizados vários teste com tempos e temperaturas para se definir a melhor condição de envelhecimento, obteve-se a temperatura de 480°C por 3 horas como satisfatoria. A solda a laser mostrou-se eficaz para a união das chapas, com perda de resistência inferior a 10%, quando comparada com a resistência do aço maraging sem solda. As análises da superfície fraturada mostram que a ruptura dos corpos de prova soldados ocorrereu na região da zona fundida, e possui natureza dúctil, com a formação de dimples, para todas as condições de tratamento térmico, o processo de soldagem e nitretação a plasma não alteraram o tipo de fratura típica dos aços maraging. A vida em fadiga não foi prejudicada ...( Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Maraging Steels are ultra-high-strength, that have their composition based on iron alloyed with approximately 18% Nickel, with yield strength between 1.400 to 2.400 MPa. They have superior properties, such as high ductility, good weldability, simple heat treatment without deformation, good machinability, high strength and wear resistance. Their hardness and resistance allow them to supports repeated stress of longer fatigue in comparison with other high strength steels. The maraging steel has a significant cost advantage due to the good workability, predictable and uniform retraction during heat treatment, making this steel be promising. For this work, from various laser welding tests, heat treatment and surface treatment of plasma nitriding, The mechanical properties were studied by means of testing: traction; fatigue; impact; hardness; and roughness. We also analyze, with the aid of optical microscope, the microstructural characteristics of the fusion zone (FZ), the heat affected zone (HAZ) due the welding and by nitrided layer. With the aid of SEM (Scanning Electron Microscope) and EDS (Energy Dispersive Scanning), we analyzed the fractured mechanisms. Several tests were carried out with times and temperatures to determine the best aging condition and the chosen temperature was 480°C for 3 hours. The application of laser welding seems to be effective for joining the plates with loss in the yield strength or tensile strength less than 10%, compared with the strength of maraging steel without welding. The analyses of the fractured surface showed that the rupture of the welded samples occurred in the fused zone region and has ductile nature, with formation of dimples for all heat treatment conditions. The welding and plasma nitriding process have not modified the type of typical fracture of the maraging steel. The life in ... (Complete abstract click electronic access below) / Doutor

abstract: With increasing concerns of the intrinsic toxicity of lead (Pb) in electronics, a series of tin (Sn) based alloys involving silver (Ag) and copper (Cu) have been proposed as replacements for Pb-Sn solder and widely accepted by industry. However, they have a higher melting point and often exhibit poorer damage tolerance than Pb-Sn alloys. Recently, a new class of alloys with trace amount of rare-earth (RE) elements has been discovered and investigated. In previous work from Prof. Chawla's group, it has been shown that cerium (Ce)-based Pb-free solder are less prone to oxidation and Sn whiskering, and exhibit desirable attributes of microstructural refinement and enhanced ductility relative to lanthanum (La)-based Sn-3.9Ag-0.7Cu (SAC) alloy. Although the formation of RESn3 was believed to be directly responsible for the enhanced ductility in RE-containing SAC solder by allowing microscopic voids to nucleate throughout the solder volume, this cavitation-based mechanism needs to be validated experimentally and numerically. Additionally, since the previous study has exhibited the realistic feasibility of Ce-based SAC lead-free solder alloy as a replacement to conventional SAC alloys, in this study, the proposed objective focuses on the in in-depth understanding of mechanism of enhanced ductility in Ce-based SAC alloy and possible issues associated with integration of this new class of solder into electronic industry, including: (a) study of long-term thermal and mechanical stability on industrial metallization, (b) examine the role of solder volume and wetting behavior of the new solder, relative to Sn-3.9Ag-0.7Cu alloys, (c) conduct experiments of new solder alloys in the form of mechanical shock and electromigration. The research of this new class alloys will be conducted in industrially relevant conditions, and the results would serve as the first step toward integration of these new, next generation solders into the industry. / Dissertation/Thesis / Ph.D. Materials Science and Engineering 2012

Orientador: Paulo Roberto Mei, Antonio José Ramírez Londoño / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-22T11:54:34Z (GMT). No. of bitstreams: 1 Theodoro_MariaClaudia_M.pdf: 33501237 bytes, checksum: 62a29876bfd5fdbffed02fa45d21d938 (MD5) Previous issue date: 2013 / Resumo: A Soldagem por Atrito com Pino Não-Consumível (SAPNC) ou Friction Stir Welding (FSW) é uma técnica que proporciona a união de materiais no estado sólido. Traz como vantagens em relação à soldagem onde ocorre a fusão dos materiais, a redução de macro e micro defeitos, ausência trincas e porosidades causadas pela fusão e solidificação do material, redução da segregação de solidificação, excelentes propriedades mecânicas da junta soldada e boa reprodutibilidade. A técnica também não necessita de metal de adição nem gás de proteção e não produz gases nocivos ao homem ou meio ambiente. Diversos tipos de soldagem dissimilar por SAPNC já foram obtidos com bons resultados em alumínio-alumínio, cobre-alumínio, magnésio alumínio, alumínio-aço e aço-aço. Os principais interessados nas juntas dissimilares são a indústria petroquímica, automobilística, naval e aeronáutica. Apesar de terem sido registrados soldagens dissimilares de diversos tipos de materiais, não há dados na literatura sobre soldagem dissimilar de aços inoxidáveis austeníticos UNS S31603 e duplex UNS S32750 pela técnica de SAPNC. Sendo assim, o presente trabalho se torna inédito por ser o primeiro registro de soldagem por atrito com pino não consumível desses dois aços. Placas de aços inoxidável austenítico (UNS S31603) e superduplex (UNS 32750) com 6 mm de espessura soldadas por atrito com pino não consumível utilizando um passe de ferramenta de PCBN-WRe com penetração entre 90 e 92 % da espessura da chapas, apresentaram bons resultados em duas condições: 1) velocidade de rotação de 150 rpm, avanço de 100 mm/min e com controle de força axial de 57 kN; 2) velocidade de rotação de 200 rpm, avanço de 100 mm/min e com controle de posição. A análise metalográfica das juntas soldadas não indicou a presença de defeitos internos ou superficiais. Não foram detectadas por microscopia óptica e difração de raios-X outras fases além de ferrita e austenita na região de solda. O ensaio de dobramento indicou que não houve penetração total em ambas as juntas, sugerindo um segundo passe de xvii soldagem ou a utilização de uma ferramenta com comprimento de pino maior, que permita penetração superior a 92% da espessura da chapa / Abstract: The Friction Stir Welding (FSW) is a solid-state joining process that has, as advantages, reduction or absence of superficial and internal flaws, absence of cracks and porosities caused by material fusion and solidification and good repeatability. The joints also present excellent mechanical properties. Many aluminum-aluminum, cooper-aluminum, magnesium-aluminum, aluminum-steel and steel-steel FSW dissimilar welds presented good results. Petrochemical, automotive, naval and aeronautics industries are the most interested in dissimilar joints. In spite of many diferent dissimilar joints registred, no dissimilar joints of UNS S31603 and UNS S32750 have been performed by FSW. This project seems to be inedited for being the first dissimilar friction stir welded joint of this both materials. Austenitic (UNS S31603) and superduplex (UNS 32750) stainless steel 6 mm thick plates one pass friction stir welded with a PCBN-WRe tool and thick plate penetration between 90 and 92% presented good results in two conditions: 1) tool rotation speed of 150 rpm, traverse speed of 100 mm/min and axial force control of 57 kN; 2) tool rotation speed of 200 rpm, traverse speed of 100 mm/min and tool position control. These welded joints showed adequate bead width, absence of galling and good appearance. Metallographic analysis presented no internal defects. Optical microscopy and X-ray diffraction showed no other phase on the joint except ferrite and austenite. The bendind tests indicate lack of penetration in both joints, suggesting two weld passes or tool penetration greater than 92% of the material thickness to perform total penetration joints / Mestrado / Materiais e Processos de Fabricação / Mestra em Engenharia Mecânica

Abstract Low-temperature co-fired ceramic (LTCC) based system-in-package (SiP) is an emerging multilayer module technology for wireless communication applications, mainly due to its excellent high-frequency material properties. LTCC-SiP modules are typically soldered onto an organic motherboard, but the lifetime of the 2nd-level solder joints is often poor due to the high stress level of the joints in test/field conditions. Moreover, using lead-free solders in the interconnections of LTCC modules raised new questions about the feasibility and reliability of the solder joints in LTCC applications. Therefore, the characteristic features of the 2nd-level solder joint configuration were determined in this thesis work. It was proved that collapsible Sn4Ag0.5Cu spheres are not a feasible option in LTCC/PWB assemblies with a large global thermal mismatch; a non-collapsible ball grid array (BGA) joint with a plastic core solder balls (PCSBs) was required to attain an adequate lifetime for such assemblies. To enhance the thermal fatigue endurance of the non-collapsible lead-free joints, a novel BGA joint consisting of Sn7In4.1Ag0.5Cu solder and PCSBs was developed. Moreover, this work proved that there is a relationship between the primary failure mechanisms of various Sn-based lead-free solders and thermomechanically induced stress level in the present non-collapsible BGA joint configuration. The effect of the plating material of the solder lands on the failure mechanism of the BGA joints in the LTCC/PWB assemblies was studied. The results showed that the adverse phenomena related to the sintered Ag-based metallization materials can be avoided using electroless nickel with immersion gold (ENIG) as a deposit material. On the other hand, this study also demonstrated that the inadequate adhesion strength of the commercial base metallization in the ENIG-plated modules resulted in the disadvantageous failure mechanism of the test assemblies. Therefore, the criteria for material selection and the design aspects of reliable 2nd-level interconnections are discussed thoroughly in this thesis.

The factors determining the quality of surface mount technology (SMT) solder joints are numerous, and complex. The exploration of these factors, and how they may affect the reliability and quality of the joints can only be achieved through continuous research. In this project, essential areas of SMT joints were selected for study and analysis, with the intention of providing additional design and process guidelines for the production of quality SMT joints. In the infrared reflow process, one of the common defect phenomena is the occurrence of tombstoning; that is after soldering only one end of the component is soldered while the other is lifted up, assuming a position like a tombstone. The initiation of tombstoning during reflow was analysed based on the forces acting on the component. A model was developed to predict the initiation of this phenomenon. The model shows that, under vibration-free conditions, the surface tension of the molten solder is the source of the force causing the initiation of tombstoning. The contact angle, which varies with the length of the printed circuit board solder land, has a significant effect on the value of the surface tension acting as a force pulling upward on the component. The model further shows that tombstoning initiation is due to the combined effects of the surface tension; the weight of the component; the dimensions of the component; the length of the solder underneath the component; and the length of the solder protruding from the end of the component. Selected components were used as examples for predicting the conditions of initiation, and these conditions were further substantiated by a series of experiments. Another area of study was a method which directly pulled the components off printed circuit boards and this was used as a means for testing the bond quality of surface mount technology leadless chip solder joints. Components D7243, CC1206, RC1206, RC121O, and CC1 812 were selected for this study. It was found that the ultimate tensile force which breaks a component off the printed circuit board has the potential to be used as a parameter for measuring the quality of the solder joint. The effect of solder thickness on the strength of a joint has also been investigated. The shape of joints soldered by two methods, wave soldering and infrared reflow, were compared. Joints at the two ends of a component produced by infrared reflow were found more uniform than the ones produced by wave soldering. A recommendation is made here for the wave soldering approach in achieving uniform solder joints. The effects of solder shape on the joint strength were further investigated by finite element analysis. A convex joint was found marginally more robust than a concave joint. Two aspects of the internal structure of SMT solder joints were investigated, void content and copper/tin intermetallic compounds. The voiding conditions of wave-soldered and infrared reflow joints were compared. No voids were found in all specimens that were produced by wave soldering. However, there were always voids inside joints produced by infrared reflow. Microhardness tests indicated that the hardness of compounds at the copper/solder interface of infrared reflowed joints is lower than that in the wave-soldered joints. It is considered that the lower hardness of the interfacial region of the infrared reflowed joints is due to the presence of voids. Scanning electron microscopy was used to study the formation of copper/tin intermetallic compounds for joints produced by infrared reflow. The results show that Cu 6 Sn5 was the only compound with a detectable thickness. Other compounds such as Cu3 Sn, were virtually not found at all. Aging of the joints at 100°C, shows that both the Cu 6Sn5 and the overall interfacial thickness grew with time. One of the important areas which had been overlooked previously and was studied in some details was the effects of solder paste exposure on the quality of solder paste. The characteristic changes of solder paste due to exposure were investigated in three areas, weight loss, tackiness, and rheology. The evaporation of low boiling point solvents was considered as the main contribution to the loss in the weight of the solder paste. The weight loss against exposure time was found to follow an exponential behaviour. A method was designed to evaluate the tackiness changes of solder paste due to exposure. It was found that the decay of tackiness against exposure time can be expressed by a power law. It is recommended that solder paste manufacturers should provide the necessary characteristic constants so as to enable the characteristics to be calculated after a specific exposure. The rheological changes of the solder paste as a result of exposure were also investigated. The implication on the printability of the solder paste due to these changes was studied and discussed.

This diploma thesis deals with the soldering process in manufacturing instrument transformers. It summarizes the knowledge of soldering process, lead-free alloys and test methods selected solder joint. In the practical part is the analysis the manufacturing process in terms of soldering operations, testing of selected lead-free alloys, which are considered as a replacement for lead-based alloy - now used in the manufacturing process. The conclusion is optimized manufacturing process to reduce operating costs and improve quality.