Solder joints are the most fragile parts in electronic package. The properties of joints made of lead-free material are harder and crisper than those of lead-contained material. They tend to break due to dynamic loading by absorbing the impact energy and result in malfunction. Thus, how to improve the reliability of contact joints made of lead-free material in dynamic loading has become an important topic for research. This work is based on JEDEC Standard JESD22 - B111 ¡§Board Level Drop Test Method of Components for Handheld Electronic Products,¡¨ and JESD22 ¡V B110 ¡§Subassembly Mechanical Shock¡¨. The setup of drop test apparatuses was used to conduct dropping tests with the impact of acceleration 1500 G, in order to acquire the reliability of SnAgCu, SnCu, and SnAg alloy, which would be compared with 63Sn37Pb. The specimens would be red-dyed for an analysis under SEM to examine the distribution of the breakage. The results were analyzed by Weibull distribution to predict Mean Time to Failure (MTTF), it is revealed that MTTF of solder joints made of Sn0.7Cu, Sn2.6Ag0.5Cu, and Sn3.0Ag0.5Cu (MTTF=355.32, 295.82, 289.54 cycles respectively) are longer than that made of 63Sn37Pb (MTTF=152.52 cycles). Notably, MTTF of alloy Sn0.7Cu is 2.3 times of solder joints of SnPb. Alloy Sn3.0Ag0.5Cu has the shortest MTTF among the three, which is also 1.89 times of alloy SnPb. That is to say, under impact of 1500G, solder joints made of Sn0.7Cu, Sn2.6Ag0.5Cu, and Sn3.0Ag0.5Cu possess greater resistance to shock than alloy 63Sn37Pb, which is in common by used at present. In addition, the breakage of solder joints mainly generated on Intermetallic Compound (IMC) and around the four corners, distributed from the periphery to the central area. Especially, those on the corners receive greater stresses due to edge effect.

The usage of lead-­free solder joints in electronic packaging is of greatest concern to the electronic industry due to the health and environmental hazards arising with the use of lead. As a consequence, lead is legally prohibited in the European Union and the industry is aiming to produce lead-free products.            The reliability of solder joints is an important issue as the failure could destroy the whole function of a product. SnAgCu is a commonly used alloy for lead-­free solders. Compared to solders containing lead, tin-­rich solders react more rapidly with the copper substrate. The reaction results in formation of brittle intermetallic compounds and in poor mechanical reliability. The formation can be slowed down by the addition of nickel in the under bump metallization.     In this project the objective was to evaluate the mechanical reliability of solder joints in high temperature applications. An alloy of nickel and phosphorus was plated on copper plates by electroless plating. The plates were joined together using SnAgCu solder. The samples were then thermally aged at 180°C for different durations (100, 200, 300, 400 and 500 hours). Tensile tests were performed on the samples. The result from the tensile test showed a decrease in mechanical strength with increasing aging duration. The fracture path shifted from being in the bulk solder to being at the interfaced.

Ball Grid Array (BGA) solder joints are an array of solder alloy spheres sandwiched between package substrate and printed circuit board (PCB). These solder joints provide electrical connections and mechanical integrity to the assembly of package and PCB. Upcoming advanced packaging applications will involve heavier components, higher service temperatures and higher current densities, which will result in additional stresses on BGA joints accelerating their failure. Additionally, mismatch in the coefficient of thermal expansion (CTE) between the substrate, solder balls and PCB results in fracture near the solder-substrate interface posing a reliability risk. Moreover, higher current densities at elevated temperatures, also aggravate electromigration (EM) failure. It is important to mitigate these reliability risks associated with accelerated thermal cycling (ATC) and high current density EM. In this dissertation, various approaches to improve the ATC and EM reliability of packages have been investigated. First, BGA solder alloy composition was modified by doping Bi in the conventionally used Sn-3.0Ag-0.5Cu (SAC305) and Sn-4.0Ag-0.5Cu (SAC405) alloys to improve the mechanical strength of the solder joints. The effect of 1-3% Bi doping on aging induced changes in hardness, creep strength, tensile strength, viscoplasticity and microstructure was studied. Second, a reliability improvement measure (RIM) to mitigate fatigue failure of BGA solder joints was investigated. The microstructures of solder joints subjected to ATC were investigated for fatigue fractures and recrystallization of grains. Third, RIM measures to prevent EM failure of packages caused by high current density were investigated. The ability of novel substrate designs in prolonging time to failure of solder joints in packages along with EM failure mechanisms have been discussed. This dissertation thus provides insights on the efficacy and mechanisms of various reliability improvement measures to mitigate the ATC and EM reliability risks in BGA solder joints to guide future packaging design.

Saab Microwave Systems, SMW is a supplier of radar systems. The circuit boards that are operating in their radars have components which solder joints contains lead. However, the EU directive RoHs and WEEE are causing SMW to prepare for a transition to lead free solder joints. The objective of this thesis is to gain deeper knowledge of lead free solder joints. Brittle fractures in solder joints is a type of failure that might increase in a transition to lead free solder joints. The brittle fractures are induced by the creation of the intermetallic phases which are formed during soldering. The amount and composition of the intermetallics affects the mechanical strength of the joint. An intermetallic layer is thickened during heat exposure as during soldering, thermal aging and rework. The focus of this thesis was to investigate how rework affect the brittleness of the lead free solder joint and thereby how the intermetallic layers change depending on chemical composition, design and reflow cycles. Two types of components and two types of solder materials (SnPb and SAC305) were studied. To study the mechanical properties of the joint a shear testing device was used. This is a way of measuring the reliability of the joint when subjected to mechanical shock. The intermetallic layers were examined in a Scanning Electron Microscope and the fracture surfaces were studied in a optical microscope, a scanning electron microscope and a stereomicroscope. The heat spread over the board where examined by soldering thermocouples to the board and plotting the values of time and temperature. The results showed that the rework process did not have any significant impact of the intermetallic growth. The adjecent and distant components were not damaged during rework. A lead free rework process can therefor be preformed successfully at SMW. The intermetallic layers formed at the interface between the a lead free solder and a nickel finish grew faster than an intermetallic layer formed between a leaded solder and a nickel finish. The presence of nickel could therefore have a more negative effect on the intermetallic growth rate for the lead free material compared to the leaded.

<p>Saab Microwave Systems, SMW is a supplier of radar systems. The circuit boards that are operating in their radars have components which solder joints contains lead. However, the EU directive RoHs and WEEE are causing SMW to prepare for a transition to lead free solder joints. The objective of this thesis is to gain deeper knowledge of lead free solder joints.</p><p>Brittle fractures in solder joints is a type of failure that might increase in a transition to lead free solder joints. The brittle fractures are induced by the creation of the intermetallic phases which are formed during soldering. The amount and composition of the intermetallics affects the mechanical strength of the joint. An intermetallic layer is thickened during heat exposure as during soldering, thermal aging and rework.</p><p>The focus of this thesis was to investigate how rework affect the brittleness of the lead free solder joint and thereby how the intermetallic layers change depending on chemical composition, design and reflow cycles. Two types of components and two types of solder materials (SnPb and SAC305) were studied.</p><p>To study the mechanical properties of the joint a shear testing device was used. This is a way of measuring the reliability of the joint when subjected to mechanical shock. The intermetallic layers were examined in a Scanning Electron Microscope and the fracture surfaces were studied in a optical microscope, a scanning electron microscope and a stereomicroscope. The heat spread over the board where examined by soldering thermocouples to the board and plotting the values of time and temperature.</p><p>The results showed that the rework process did not have any significant impact of the intermetallic growth. The adjecent and distant components were not damaged during rework. A lead free rework process can therefor be preformed successfully at SMW. The intermetallic layers formed at the interface between the a lead free solder and a nickel finish grew faster than an intermetallic layer formed between a leaded solder and a nickel finish. The presence of nickel could therefore have a more negative effect on the intermetallic growth rate for the lead free material compared to the leaded.</p>

Submitted by Irene Nascimento (irene.kessia@ufpe.br) on 2016-09-28T17:50:15Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Tese Edivânia.pdf: 9678189 bytes, checksum: bc6e8c52a38eb49d616a9e268bd0a048 (MD5) / Made available in DSpace on 2016-09-28T17:50:15Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Tese Edivânia.pdf: 9678189 bytes, checksum: bc6e8c52a38eb49d616a9e268bd0a048 (MD5) Previous issue date: 2016-02-26 / PRH / A exploração da energia de petróleo e gás é um campo de importância atual no desenvolvimento da economia mundial a qual tem tomado gradualmente o centro das atenções nos ambientes econômico e científico, elevando a demanda por tecnologias no desenvolvimento de materiais mais resistentes como os aços da classe API. As plataformas de prospecção e produção de petróleo no mar, oleodutos e gasodutos em operação, são fabricados a partir de chapas com diferentes processos de soldagem. Estes equipamentos, quando submersos em água do mar, estão susceptíveis a corrosão por fatores diversos como zona termicamente afetada e salinidade. Esse conjunto de fatores pode enfraquecer o material, principalmente na região da junta de solda podendo ocasionar a nucleação e propagação de trincas em regiões preferenciais. A degradação de materiais metálicos pode tornar-se ainda mais severa quando houver associação do meio corrosivo com micro-organismos os quais se aderem às superfícies e, através do seu metabolismo modificam as condições do meio podendo comprometer alterar a durabilidade e desempenho dos materiais. Neste trabalho foi obtida uma melhor compreensão sobre a ação das bactérias redutoras de sulfato e do Vibrio alginolyticus isoladamente e em consórcio, na corrosão de corpos de prova com juntas de solda do aço API 5L X80 em presença de água do mar. Para tanto, foram expostos corpos de prova do aço X 80 em sistemas contendo água do mar estéril, acrescida dos respectivos micro-organismos, além de um sistema abiótico. Foram feitas quantificações de bactérias sésseis e planctônicas, determinação das taxas de corrosão, ensaio de impacto Charpy e tração, observação das superfícies por microscópio eletrônico de varredura (MEV). Os resultados mostraram que a adesão microbiana e as taxas de corrosão não foram afetadas pela presença da solda e que os micro-organismos provocaram um efeito passivante, na corrosão por perda de massa, porem a observação das superfícies por MEV mostrou ataque por corrosão localizada. Quanto às propriedades mecânicas, os corpos de prova com solda, expostos ao sistema contendo Vibrio alginolyticus apresentara uma queda na absorção de energia, mostrando um enfraquecimento do material nessas condições. / The exploitation of oil and gas energy is a current important field in the development of the world economy which has gradually taken center stage in the economic and scientific environments, increasing the demand for technologies in the development of more resistant materials such as grade steels API. The platforms of oil exploration and production offshore, oil and gas pipelines in operation are made from sheets with different welding processes. These devices, when submerged in seawater, are susceptible to corrosion by several factors such as heat affected zone and salinity. This set of factors can weaken the material, especially in the solder joint in the region may cause the nucleation and propagation of cracks in preferred regions. Deterioration of metallic materials may become even more severe when the corrosive environment associated with micro-organisms which adhere to surfaces and through metabolism modifying the conditions of the environment can compromise alter the durability and performance of the materials. In this work we obtained a better understanding of the action of sulfate-reducing bacteria and Vibrio alginolyticus alone and in consortium, the corrosion test specimens with steel solder joints API 5L X80 in the presence of seawater. For both, it was exposed X 80 steel specimens in water the barren sea, plus the respective micro-organisms, as well as an abiotic system. measurements were made of sessile and planktonic bacteria, determination of corrosion rates, Charpy impact test and pull, observation of surfaces by scanning electron microscope (SEM). The results showed that the microbial adhesion and corrosion rates were not affected by the presence of solder, and that micro-organisms caused a passivating effect on the corrosion weight loss, but the observation of the surface by SEM showed attack by pitting. As for the mechanical properties, the samples with solder, exposed to the system containing Vibrio alginolyticus presented a drop in energy absorption, showing a weakening of the material in these conditions.

This dissertation constitutes two major sections. In the first major section, a kinetic analysis was established to investigate the electromigration (EM), enhanced intermetallic compound (IMC) growth and void formation for Sn-based Pb-free solder joints to Cu under bump metallization (UBM). The model takes into account the interfacial intermetallic reaction, Cu-Sn interdiffusion, and current stressing. A new approach was developed to derive atomic diffusivities and effective charge numbers based on Simulated Annealing (SA) in conjunction with the kinetic model. The finite difference (FD) kinetic model based on this approach accurately predicted the intermetallic compound growth when compared to empirical observation. The ultimate electromigration failure of the solder joints was caused by extensive void formation at the intermetallic interface. The void formation mechanism was analyzed by modeling the vacancy transport under electromigration. The effects of current density and Cu diffusivity in Sn solder were also investigated with the kinetic model. The second major section describes the integration of Step and Flash Imprint Lithography (S-FIL®) into an industry standard Cu/low-k dual damascene process. The yield on a Back End Of the Line (BEOL) test vehicle that contains standard test structures such as via chains with 120 nm vias was established by electrical tests. S-FIL shows promise as a cost effective solution to patterning sub 45 nm features and is capable of simultaneously patterning two levels of interconnect structures, which provides a low cost BEOL process. The critical processing step in the integration is the reactive ion etching (RIE) process that transfers the multilevel patterns to the inter-level dielectrics (ILD). An in-situ, multistep etch process was developed that gives excellent pattern structures in two industry standard Chemical Vapor Deposited (CVD) low-k dielectrics. The etch process showed excellent pattern fidelity and a wide process window. Electrical testing was conducted on the test vehicle to show that this process renders high yield and consistent via resistance. Discussions of the failure behaviors that are characteristic to the use of S-FIL are provided. / text

L'utilisation du diamant comme composant d'électronique de puissance est une perspective intéressante tant en ce qui concerne les applications hautes température que forte puissance. La problématique principale de ces travaux réalisés dans le cadre du programme Diamonix, réside dans l'étude et l'élaboration d'un packaging permettant la mise en oeuvre d'une puce diamant devant fonctionner à des températures variant entre -50°C et 300°C. Nous nous sommes intéressés au choix des matériaux de connexion de la puce avec son environnement. Suite à l'étude bibliographique, nous proposons différentes solutions de matériaux envisageables pour le substrat métallisé, les brasures et les métallisations. Dans un second temps, les différents éléments ont été réalisés puis caractérisés à partir d'essais de nanoindentation et de nanorayage. Des essais mécaniques ont permis de caractériser le comportement élastoviscoplastique et l'endommagement des brasures. Ces derniers essais ont servi de base expérimentale à l'identification des paramètres d'un modèle de comportement viscoplastique couplé avec l'endommagement et qui a été spécialement élaboré pour cette étude. Le modèle de comportement a été implémenté dans un code de calcul par éléments finis via une sous-routine. Il permet notamment de simuler le processus de dégradation d'un assemblage. Enfin, ce modèle de comportement a été mis en oeuvre dans des modélisations thermomécaniques de différentes configurations de véhicules test. / Use of diamond as constitutive component in power electronics devices is an interesting prospect for the high temperature and high power applications. The main challenge of this research work included in the Diamonix program is the study and the elaboration of a single-crystal diamond substrate with electronic quality and its associated packaging. The designed packaging has to resist to temperatures varying between -50°C and 300°C. We contributed to the choice of the connection materials intended to be used in the final test vehicle and which can handle such temperature gaps. In the first part, we present a state-of-the-art of the various materials solutions for extreme temperatures. Following this study, we propose a set of materials which considered as potential candidates for high temperature packaging. Special focus is given for the most critical elements in power electronic assemblies which are metallizations and solders. Once the materials choice carried out, thin substrate metallizations, solders and DBC coatings are studied using nanoindentation and nanoscratch tests. Mechanical tests were also carried out on solders to study their elastoviscoplastic and damage behavior. The experimental results are used as database for the identification of the parameters of the viscoplastic model coupled with a porous damage law, worked out for the case of solders. The behavior model is implemented as a user subroutine UMAT in a FE code to predict the degradation of a 2D power electronic assembly and various materials configuration for a 3D test vehicle.

Les nouvelles technologies mécatroniques permettent de réduire fortement la consommation d'énergie et les émissions des véhicules individuels, en introduisant des ruptures indispensables pour une chaîne de traction électrifiée complémentaire ou alternative aux moteurs thermiques. Les assemblages en électronique de puissance utilisés dans les systèmes alterno-démarreurs emploient des alliages de brasure dont il s'agit de trouver des substituants, sans plomb, en accord avec les normes internationales. Cette thèse contribue à la caractérisation métallurgique et mécanique de deux joints brasés sans plomb innovants riches en étain. Ces joints sont produits industriellement par un procédé de brasage laser qui leur confère une microstructure de solidification très hétérogène, peu reproductible, multiphasée et qui présente un grand nombre de défauts. L'objectif de cette thèse est d'apporter une meilleure compréhension à la tenue mécanique de ces joints brasés au cours du vieillissement thermomécanique des assemblages. Les sollicitations thermiques engendrent des contraintes et des déformations plastiques à cause de la dilatation différentielle qui existe entre les différentes couches des matériaux brasés. Des lois de comportement isotropes ont été identifiées à partir d'une base expérimentale d'essais de traction sur des matériaux massifs. Ces lois, utilisées dans des simulations aux éléments finis, ont permis d'évaluer l'effet négatif du défaut de porosité inhérent au procédé de brasage. Des essais de vieillissement couplés à des observations de l'évolution de la microstructure ont permis de montrer l'influence de l'orientation des grains d'étain sur l'amorçage de fissure. Nous n'avons pas pu proposer de volume élémentaire représentatif du fait de la complexité de la structure. Une méthode inverse a été mise en oeuvre en parallèle de la conception d'un banc d'essai de flexion in-situ sous profilomètre afin de placer les premières briques permettant la caractérisation mécanique de joints brasés industriels. / The new mechatronic technologies can significantly reduce the energy consumption and gas emissions of personal cars, by introducing rupture innovations in electrified powertrains complementarily or alternatively to combustion engines. The power electronics assemblies used in starter-alternator systems use solder joints which need to be substituted with lead-free solder in agreements with international standards. This thesis contributes to the metallurgical and mechanical characterization of two tin-based lead-free solder joints. These joints are produced industrially with a Die Laser Soldering process which leads to heterogeneous solidification microstructures, poorly reproducible, multiphased, and with defects. The objective of this thesis is to provide a better understanding of the solder joints lifetime during thermomechanical aging. Thermal aging generates stresses and plastic deformation due to the mismatch in the coefficients of thermal expansion between the different layers of the assemblies. Isotropic constitutive laws were identified from an experimental database of tensile tests on bulk specimens. Those constitutive laws were used in finite element simulations in order to assess the negative effect of the solder joint porosity, inherent flaw traced back to the soldering process. Aging tests coupled with observations of the microstructure evolution have shown the influence of tin grains orientation on crack initiation. The heterogeneity of the microstructure prevents us from proposing a representative volume element of the materials. An inverse method has been implemented in parallel with the development of an in situ bending test bench under a profilometer in order to build the first steps for the mechanical characterization of industrial solder joints.

L’augmentation de la puissance électrique consommée à bord des avions a récemment conduit à introduire des convertisseurs électroniques de puissance à base d'interrupteurs à IGBT dans de nombreuses applications aéronautiques. L'utilisation de ces interrupteurs diffère de leurs emplois traditionnels dans les domaines du ferroviaire ou de l'automobile. En effet, les sollicitations environnementales ainsi que les cycles de commandes électriques sont différents de ceux rencontrés jusqu’alors, ce qui amène à remettre en cause les résultats actuels au sujet de la durée de vie et de la fiabilité de ces interrupteurs. Face à ces interrogations, les sociétés THALES et Hispano-Suiza se sont associées au sein du programme de l’avion plus électrique MODERNE (MODular ElectRical NEtwork) initié par Airbus, en vue de développer des solutions à haut niveau de fiabilité pour des applications aéronautiques sévères. C’est dans ce contexte que prennent place les présents travaux, dont les objectifs sont dans un premier temps de proposer de nouvelles architectures de modules susceptibles de présenter de meilleures performances d’intégration, et dans un second temps d’en étudier la fiabilité. Pour répondre à ces questions, un état de l'art des technologies utilisables a été mené. La confrontation de ses technologies aux contraintes et recommandations aéronautiques a conduit au choix de deux approches d'assemblage, proposées avec un jeu de matériaux sélectionnés pour leurs propriétés physiques et en conformité avec les réglementations sur l’utilisation de matériaux polluants. À l'issue d'une analyse de défaillances, différents développements ont été conduits afin de modéliser et caractériser le comportement thermique, mécanique puis à défaillance des modules. Des modèles Éléments Finis de structures représentatives des solutions proposées ont alors été mis au point et exploités pour l'élaboration de règles de conception, sur la base de plans d'expériences couplés à de la simulation numériques. Les informations générées ont servi à la conception de trois prototypes destinés à des applications différentes. Les performances de ces prototypes ont été évaluées, notamment leurs fiabilités obtenues par des calculs mécano-fiabilistes ayant permis l'optimisation de la conception des différents modules. / Within the framework of the electric plane programs, the aircraft industry is facing higher demands of electric power, fact which involves an increasing use of IGBT modules in aeronautical power converters. Although such modules have been well studied and known in railway and the automotive domains, they will be subjected to stresses and operational cycles specific to the aeronautical environment. Consequently, this requires manufacturers to answer some questions about their lifetime and reliability issues. Faced with these questions, THALES and Hispano-Suiza have associated in the more electric aircraft project launched by Airbus (MODERNE - MODular ElectRical NEtwork), with the aim of developing high reliability solutions for harsh aeronautic applications. This work takes place in this context, with the objectives of proposing power modules architectures likely to exhibit better performances and integration level, and then study the reliability of different prototypes. To answer these questions, technological studies of the possible packaging and connecting solutions, faced with aeronautical stresses and requirements led to the choice of two basic assembling approaches. A set of materials selected for their physical properties and their compliance with polluting materials regulations was also proposed. The potential failure modes of these solutions were pointed out and taken into account within experimental and numerical developments, to model and characterize the thermal, mechanical and failure behaviour of the modules. Then, different Finite Element models representative of the proposed technologies structures were developed and investigated for defining design rules on the basis of Designs of Experiments. The whole knowledge generated by the simulations was used to design three prototypes of IGBT module for different applications. The performance of these prototypes have been evaluated and compared to the requirements, including their reliability obtained by mechanical calculations coupled with probabilistic methods which led to their optimization.