Dissertations / Theses on the topic 'High-temperature electronics packaging'

Currently, wide bandgap semiconductor devices feature increased efficiency, higher current handling capabilities, and higher reverse blocking voltages than silicon devices while recent fabrication advances have them drawing near to the marketplace. However these new semiconductors are in need of new packaging that will allow for their application in several important uses including hybrid electrical vehicles, new and existing energy sources, and increased efficiency in multiple new and existing technologies. Also, current power module designs for silicon devices are rife with problems that must be enhanced to improve reliability. This thesis introduces new packaging that is thermally resilient and has reduced mechanical stress from temperature rise that also provides increased circuit lifetime and greater reliability for continued use to 300°C which is within operation ratings of these new semiconductors. The new module is also without problematic wirebonds that lead to a majority of traditional module failures which also introduce parasitic inductance and increase thermal resistance. Resultantly, the module also features a severely reduced form factor in mass and volume.
M.S.E.E.
School of Electrical Engineering and Computer Science
Engineering and Computer Science
Electrical Engineering MSEE

This study focused on the development and evaluation of die-attach material and substrate technology for high-temperature applications. For the die-attach material, a low-temperature sintering technique enabled by a nanoscale silver paste was developed for attaching large-area (>100 mm2) semiconductor chips. The nanoscale silver paste can be sintered at a much lower temperature (<300 oC) than in the conventional sintering process (>800 oC), and at the same time reached about 80 vol% bulk density. Analyses of the sintered joints by scanning acoustic imaging and electron microscopy showed that the attachment layer had a uniform microstructure with micron-sized porosity with the potential for high reliability under high temperature applications. We also investigated the effects of a large temperature cycling range on the reliability of direct bonded aluminum (DBA) substrate. DBA substrates with different metallization were thermally cycled between -55 oC and 250 oC. Unlike with the DBC substrate, no delamination of aluminum from the aluminum nitride ceramic base-plate was observed for the DBA substrates. However, aluminum surface became roughened during the thermal cycling test. It was believed that in the high-temperature regime, the significant amount of thermomechanical stress and grain-scale deformation would cause recrystallization and grain-boundary sliding in the aluminum layer, which would further lead to the observed increase in surface roughness. The influence of metallization over the aluminum surface on the extent of surface roughness was also characterized. In addition to evaluating the reliability of nanoscale silver paste and DBA substrate individually, this work also conducted experiments that characterize the compatibility of nanoscale silver paste on DBA substrate in terms of reliability in a high-temperature environment. In the large-area attachment, the sintered silver was found to be very compliant with the deformed aluminum. The device-to-silver and silver-to-substrate interfaces remain intact after up to 800 cycles. No large scale delamination and horizontal cracks were observed. However, some vertical crack lines began to show after certain number of cycles. It was believed that these vertical cracks were caused by the thermomechanical stresses in the sintered silver layer. In addition, with regard to the thermal performance, since most of the heat was generated from the semiconductor devices and were transferred vertically through the die-attach material to substrate, these vertical cracks were also considered more advantageous than horizontal cracks.
Ph. D.

The work reported in this dissertation is intended to propose, analyze and demonstrate a technology for a high temperature integrated power electronics module, for high temperature (e.g those over 200oC) applications involving high density and low stress. To achieve this goal, this study has examined some existing packaging approaches, such as wire-bond interconnects and solder die-attach, flip-chip and pressure contacts. Based on the survey, a high temperature, multilayer 3-D packaging technology in the form of an Embedded Chip Module (ECM) is proposed to realize a lower stress distribution in a mechanically balanced structure with double-sided metallization layers and material CTE match in the structure. Thermal and thermo-mechanical analysis on an ECM is then used to demonstrate the benefits on the cooling system, and to study the material and structure for reducing the thermally induced mechanical stress. In the thermal analysis, the high temperature ECM shows the ability to handle a power density up to 284 W/in3 with a heat spreader only 2.1x2.1x0.2cm under forced convection. The study proves that the cooling system can be reduced by 76% by using a high temperature module in a room temperature environment. Furthermore, six proposed structures are compared using thermo-mechanical analysis, in order to obtain an optimal structure with a uniform low stress distribution. Since pure Mo cannot be electroplated, the low CTE metal Cr is proposed as the stress buffering material to be used in the flat metallization layers for a fully symmetrical ECM structure. Therefore, a chip area stress as low as 126MPa is attained. In the fabrication process, the high temperature material glass and a ceramic adhesive are applied as the insulating and sealing layers. Particularly, the Cr stress buffering layer is successfully electroplated in the high temperature ECM by means of the hard chrome plating process. The flat metallization layer is accomplished by using a combined structure with Cr and Cu metallization layers. The experimental evaluations, including the electrical and thermal characteristics of the ECM, have been part of in the study. The forward and reverse characteristics of the ECM are presented up to 250oC, indicating proper device functionality. The study on the reverse characteristics of the ECM indicates that the large leakage current at high temperature is not due to the package surrounding the chip, but chiefly caused by the Schottky junction and the chip passivation layer. Finally, steady-state and transient measurements are conducted in terms of the thermal measurements. The steady-state thermal measurement is used to demonstrate the cooling system reduction. To obtain the thermal parameters of the different layers in the high temperature ECM, the transient thermal measurement is applied to a single chip ECM based on the temperature cooling-down curve measurement.
Ph. D.

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

L’accroissement des besoins en énergie électrique pour les systèmes embarqués et leur augmentation de puissance nécessitent de concevoir des systèmes d’électronique de puissance toujours plus performants. Une solution d’avenir concerne la mise en œuvre de composants à base de diamant qui permettent l’augmentation conséquente des tensions et courants mis en jeux, mais aussi de la température maximale de jonction admissible. Le cadre de ces travaux est celui du projet de recherche Diamonix 2, qui concerne l’étude et l’élaboration d’un composant diamant fonctionnant à haute température. L’objectif du travail doctoral présenté ici est l’étude du packaging haute température de ce type de composant diamant. Plusieurs choix de matériaux et de techniques aptes à l’élaboration d’un assemblage de puce diamant sur un substrat métallisé ont été effectués. La caractérisation microstructurale et mécanique de trois types de jonctions ont été réalisées (refusion d’un alliage AuGe, frittage de nano pâtes d’argent et diffusion en phase solide d’indium dans des couches d’argent). Des essais mécaniques de cisaillement de divers assemblages ont permis d’évaluer le comportement thermomécanique des jonctions et des interfaces. Les essais de cisaillement ont servi à l’identification inverse des paramètres interfaciaux d’un modèle de zones cohésives, pour différents types d’interfaces. Des modèles éléments finis d’assemblage, incluant le comportement viscoplastique des jonctions et des lois d’endommagent des interfaces, ont servi à simuler le comportement thermomécanique du packaging d’un composant diamant.

This thesis examines the packaging of high-temperature SiC power electronic devices. Current-voltage measurements were conducted on as-received and packaged SiC power devices. The planar structure was introduced and developed as a substitution for traditional wire-bonding vertical structure. The planar structure was applied to a high temperature (>250oC) SiC power device. Based on the current-voltage (I-V) measurements, the packaging structures were improved, materials were selected, and processes were tightly controlled. This study applies two types of planar structures, the direct bond and the bump bond, to the high-temperature packaging of high-temperature SiC diode. A drop in the reverse breakdown voltage was discovered in the packaging using a direct bond. The root cause for the drop in the breakdown voltage was identified and corrective solutions were evaluated. A few effective methods were suggested for solving the breakdown issue. The forward I-V curve of the planar packaging using direct bond showed excellent results due to the excellent electrical and thermal properties of sintered nanosilver. The packaging using a bump bond as an improved structure was processed and proved to possess desirable forward and reverse I-V behavior. The cross-sections of both planar structures were inspected. High-temperature packaging materials, including nano-silver paste, high-lead solder ball and paste, adhesive epoxy, and encapsulant, were introduced and evaluated. The processes such as stencil printing, low-temperature sintering, solder reflowing, epoxy curing, sputtering deposition, electroplating, and patterning of direct-bond copper (DBC) were tightly controlled to ensure high-quality packaging with improved performance. Finally, the planar packaging of the high temperature power device was evaluated and summarized, and the future work was recommended.
Master of Science

Le silicium a atteint sa limite d’utilisation dans de nombreux domaines tels que l’aéronautique. Un verrou concerne la conception de composants de puissance pouvant fonctionner en haute température et/ou en haute tension. Le recours à des matériaux à large bande interdite tels que le carbure de Silicium (SiC) apporte en partie une solution pour répondre à ces besoins. Le packaging doit être adapté à ces nouveaux types de composants et nouveaux environnements de fonctionnement. Or, il s’avère que l’intégration planaire (2D), composé de fils de câblage et de report de composants par brasure, ne peut plus répondre à ces attentes. Cette thèse a pour objectif de développer un module de puissance tridimensionnel pour la haute température de type bras d’onduleur destiné à l’aéronautique. Une nouvelle structure 3D originale constituée de deux puces en carbure de silicium, d’attaches par frittage d’argent et d’une encapsulation par du parylène HT a été mise au point. Ses différents éléments constitutifs, les raisons de leur choix, ainsi que la réalisation pratique de la structure sont présentés dans ce manuscrit. Nous nous intéressons ensuite à un mode de défaillance particulier aux attaches d’argent fritté : La migration d’argent. Une étude expérimentale permet de définir les conditions de déclenchement de cette défaillance. Elle est prolongée et analysée par des simulations numériques
Silicon has reached its usage limit in many areas such as aeronautics. One of the challenges is the design of power components operable in high temperature and/or high voltage. The use of wide bandgap materials such as silicon carbide (SiC) provides in part a solution to meet these requirements. The packaging must be adapted to these new types of components and new operating environnement. However, it appears that the planar integration (2D), consisting of wire-bonding and soldered components-attach, can not meet these expectations. This thesis aims to develop a three dimensional power module for the high temperature aeronautics applications. A new original 3D structure made of two silicon carbide dies, silver-sintered die-attaches and an encapsulation by parylene HT has been developed. Its various constituting elements, the reason for their choice, and the pratical realization of the structure are presented in this manuscript. Then, we focus on a failure mode specific to silver-sintered attaches : The silver migration. An experimental study allows to define the triggering conditions of this failure. It is extended and analyzed by numerical simulations

Le développement de composants de puissance à base de carbure de silicium (SiC) permet la réalisation d’interrupteurs pouvant fonctionner au-delà de 200°C. Le silicium présente plus de limitations au niveau physique du matériau qu’au niveau des technologies d’assemblages. Le SiC est un matériau semi-conducteur grand gap ce qui permet d’obtenir des courants de fuite inverse qui restent faibles à haute température ; d’où un fort intérêt pour des applications haute température. Mise à part son utilisation à des températures pouvant dépasser les 300°C, c’est un matériau qui permet aussi d’augmenter les fréquences de commutation ainsi que la densité de puissance par rapport à des composants à technologie silicium. Ceci en fait un candidat idéal pour des applications forte puissance dans le domaine de la traction, des protections de réseaux électriques ou de la transmission et de la distribution d’énergie. L’utilisation du SiC pour une application haute température pose le problème de son packaging, des choix de matériaux et de sa configuration. Cette thèse a pour but d’effectuer une étude de fiabilité et de durée de vie des briques technologiques d’assemblage et de connexions nécessaires à la réalisation d’un cœur de puissance haute température à base de JFET SiC. Une étude des différentes technologies d’assemblages de convertisseurs de puissance haute température est effectuée afin de définir différentes briques technologiques constitutives de ces systèmes. Cette première étude nous permet de procéder à une sélection de certaines technologies d’assemblages comme le frittage de pâtes d’argent pour la technologie de report de puces. Ces briques technologiques feront l’objet d’études plus approfondies allant de la réalisation de véhicules tests jusqu’à la mise au point des essais de cyclages associés aux techniques d’analyse nécessaires à l’étude de leur défaillance.Les études expérimentales concernent des essais de cyclage passif et de stockage thermique, l’apparition de délaminages en cours de cyclage thermique (scan acoustique, RX), le report par frittage de pâtes d’argent nano et microscopiques et la caractérisation électrique et thermique (Rth, I[V])
The development of power components based on silicon carbide (SiC) allows for the design of power converter operating at high temperature (above 200 or 300°C). SiC is a semiconductor material with a large band gap that not only can operate in temperatures exceeding 300°C but also offers fast switching speed, high voltage blocking capability and higher thermal conductivity compared to silicon technology components. The classical die attach technology uses high temperature solder alloys which melt at around 300°C. However, even a soldered die attach with such high melting point can only operate up to a much lower temperature. Alternative die attach solutions have recently been proposed: Transient Liquid Phase Bonding, soldering with higher melting point alloys such as ZnSn, or silver sintering.Silver sintering is a very interesting technology, as silver offers very good thermal conductivity (429W/m.K, better than copper), relatively inexpensive (compared to alternative solutions which often use gold), and has a very high melting point (961°C).The implementation of two silver-sintering processes is made: one based on micrometer-scale silver particles, and one on nano-meter-scale particles. Two substrate technologies are investigated: Al2O3 DBC and Si3N4 AMB. After the process optimization, tests vehicles are assembled using nano and micro silver particles paste and a more classical high-temperature die attach technology: AuGe soldering. Multiple analyses are performed, such as thermal resistance measurement, shear tests and micro-sections to follow the evolution of the joint during thermal cycling and high-temperature storage ageing

Due to the power requirements for today\'s microprocessors, point of load converter packaging is becoming an important issue.   Traditional thermal management techniques involved in removing heat from a printed circuit board are being tested as today\'s technologies require small footprint and volume from all electrical systems.  While heat sinks are traditionally used to spread heat, ceramic substrates are gaining in popularity for their superior thermal qualities which can dissipate heat without the use of a heat sink.  3D integration techniques are needed to realize a solution that incorporates the active and components together.  The objective of this research is to explore the packaging of a high current, high power density, high frequency DC/DC converter using ceramic substrates to create a low profile converter to meet the needs of current technologies.
    One issue with current converters is the large volume of the passive components.  Increasing the switching frequency to the megahertz range is one way to reduce to volume of these components.  The other way is to fundamentally change the way these inductors are designed.  This work will explore the use of low temperature co-fired ceramic (LTCC) tapes in the magnetic design to allow a low profile planar inductor to be used as a substrate.  LTCC tapes have excellent properties in the 1-10 MHz range that allow for a high permeability, low loss solution.  These tapes are co-fired with a silver paste as the conductor.  This paper looks at ways to reduce dc resistance in the inductor design through packaging methods which in turn allow for higher current operation and better heavy load efficiency.  Fundamental limits for LTCC technologies are pushed past their limits during this work.  This work also explores fabrication of LTCC inductors using two theoretical ideas: vertical flux and lateral flux.  Issues are presented and methods are conceived for both types of designs.  The lateral flux inductor gives much better inductance density which results in a much thinner design.
    It is found that the active devices must be shielded from the magnetic substrate interference so active layer designs are discussed.  Alumina and Aluminum Nitride substrates are used to form a complete 3D integration scheme that gives excellent thermal management even in natural convection.  This work discusses the use of a stacked power technique which embeds the devices in the substrate to give double sided cooling capabilities.  This fabrication goes away from traditional photoresist and solder-masking techniques and simplifies the entire process so that it can be transferred to industry.  Time consuming sputtering and electroplating processes are removed and replaced by a direct bonded copper substrate which can have up to 8 mil thick copper layers allowing for even greater thermal capability in the substrate.  The result is small footprint and volume with a power density 3X greater than any commercial product with comparable output currents.  A two phase coupled inductor version using stacked power is also presented to achieve even higher power density.
    As better device technologies come to the marketplace, higher power density designs can be achieved.  This paper will introduce a 3D integration design that includes the use of Gallium Nitride devices.  Gallium Nitride is rapidly becoming the popular device for high frequency designs due to its high electron mobility properties compared to silicon.  This allows for lower switching losses and thus better thermal characteristics at high frequency.  The knowledge learned from the stacked power processes gives insight into creating a small footprint, high current ceramic substrate design.  A 3D integrated design is presented using GaN devices along with a lateral flux inductor.  Shielded and Non-Shielded power loop designs are compared to show the effect on overall converter efficiency.  Thermal designs and comparisons to PCB are made using thermal imaging.  The result is a footprint reduction of 40% from previous designs and power densities reaching close to 900W/in3.

Master of Science

Conventional microelectronic and power electronic packages based on Si devices usually work below 150°C. The emergence of wide-bandgap devices, which potentially operate above a junction temperature of 250°C, results in growing research interest in high-density and high-temperature packaging. There are high-temperature materials such as encapsulants on the market that are claimed for capability of continuous operation at or above 250°C. With an objective of identifying encapsulants suitable for packaging wide-bandgap devices, some of commercial high-temperature encapsulants were obtained and evaluated at the beginning of this study. The evaluation revealed that silicone elastomers are processable for various types of package structure and exhibit excellent dielectric performance in a wide temperature range (25 - 250°C) but are insufficiently stable against long-term aging (used by some manufacturers, e.g., P²SI, to evaluate polymer stability) at 250°C. These materials cracked during aging, causing their dielectric strength to decrease quickly (as soon as 3 days) and significantly (60 - 70%) to approximately 5 kV/mm, which is below the value required by semiconductor packaging. The results of this evaluation clearly suggested that silicone needs higher thermal stability to reliably encapsulate wide-bandgap devices. Literature survey then investigated possible methods to improve silicone stability. Adding fillers is reported to be effective possibly due to the interaction between filler surface and polymer chains. However, the interaction mechanism is not clearly documented. In this study, the effect of Al₂O₃ filler on thermal stability was first investigated by comparing the performance of unfilled and Al₂O₃-filled silicones in weight-loss measurements and dielectric characterization. All test results on composites filed with Al₂O₃ micro-rods indicated that thermal stability increased with increasing filler loading. Thermogravimetric analysis (TGA) test demonstrated that the temperature of degradation onset increased from 330 to 379°C with a 30 wt% loading of Al₂O₃ rods. In isothermal soak test, unfilled and 30-wt%-filled silicones lost 10% of polymer weight in 700 and 1800 hours, respectively. The dielectric characterization found that both Weibull parameters, characteristic dielectric strength (E₀, representing the electric field at which 62.3% of samples are electrically broken down) and shape parameter (β, representing the spread of data. The larger the β, the narrower the distribution) can reflect the thermal stability of polymers. Both of them were influenced by microstructure evolution, to which β was found to be more sensitive than E₀. The characteristic dielectric strength of unfilled silicone decreased significantly after 240 hours of aging at 250°C, whereas that of Al₂O₃/silicone composites exhibited no significant change within 560 hours. The shape parameter of Al₂O₃-filled silicone decreased slower than that of unfilled silicone, also indicating the positive effect of Al₂O₃ micro-rods on thermal stability. Improved thermal stability can be explained by restrained chain mobility caused by interfacial hydrogen bonds, which are formed between hydroxyl groups on Al₂O₃ surface and silicone backbone. In this study, the effect of hydrogen bonds was investigated by dehydrating Al₂O₃ micro-rods at high temperature in N₂ to partially destroy the bonds. Removal of hydrogen bonds impaired thermal stability by increasing the initial weight-loss rate from 0.025 to 0.036 wt%/hour. The results explained the importance of interfacial hydrogen bond, which effectively reduced the average chain mobility, hindered the formation of degradation products, and led to higher thermal stability. The main discoveries of this study are listed below: 1. Al₂O₃ micro-rods were found to efficiently improve the thermal stability of silicone elastomer used for high-temperature encapsulation. 2. Characteristic dielectric strength and shape parameter obtained from Weibull distribution reflected the change of material microstructure caused by thermal aging. The shape parameter was found to be more sensitive to microscale defects, which were responsible for dielectric breakdown at low electric field. 3. Hydrogen bonds existing at filler/matrix interface were proven to be responsible for the improvement of thermal stability because they effectively restrained the average chain mobility of the silicone matrix.
Ph. D.

L'objectif d'un avion plus électrique conduit à l'utilisation croissante de systèmes d'électronique y compris dans des zones de haute température. Les modules de puissance classiques doivent être adaptés à cet environnement: les composants en SiC sont commercialement disponibles mais l'environnement de la puce est à modifier. Cette thèse s'intéresse aux techniques d'attaches de puces basses température que sont le frittage d'argent et la brasure en phase liquide transitoire (TLPB) or-étain. Dans une première partie, les enjeux de l'électronique de puissance et plus particulièrement des applications haute température est donnée. Les mécanismes physique (mouillage, diffusion)qui régissent le frittage et le TLPB (Transient liquid Phase Bonding) sont ensuite décrits avec précision. La deuxième partie de cette thèse s'intéresse à la mise en oeuvre d'un protocole fiable d'attache de puce par frittage d'une nanopoudre d'argent commerciale. Une fois établie, la méthode a ensuite été optimisée pour différentes tailles de composants. La caractérisation de l'attache a été réalisée en shear-test et par des images en microscopie optique. La troisième et dernière partie de ce travail a pour objet la réalisation d'attaches de puces par TLPB or-étain. Ce chapitre traite de la mise en oeuvre expérimentale de la technique, depuis la métallisation des wafers jusqu'à la caractérisation des attaches en microscopie (optique et MEB). Ce travail de thèse est très expérimental car même si un protocole de mise en oeuvre existe (pour le frittage), il est indispensable de l'adapter aux conditions expérimentales pour l'optimiser. Ce travail a aussi mis en évidence certaines difficultés techniques de préparation des surfaces.

Les environnements ont tendance à être plus sévères (plus chauds et quelquefois plus froids). À ce titre, l'électronique de puissance haute température est un enjeu majeur pour le futur. Concernant les technologies d'assemblage à haute température, les brasures haute température comme l'alliage 88Au/12Ge, 97Au/3Si et 5Sn/95Pb pourraient supporter ces niveaux de contraintes thermiques, qui sont actuellement développées pour répondre à ces exigences. Nous avons effectué les caractérisations électriques, mécaniques et thermomécaniques des matériaux d'assemblage. Une étude thermique a réalisée par des méthodes expérimentales et des simulations numériques, l'étude numérique est réalisée sous ANSYS dans le but d'estimer les influences des différents paramètres sur la performance thermique de l'assemblage. En plus, les cyclages thermiques passif de grande amplitude sont effectués pour analyser la fiabilité des modules de puissance dans ces conditions d'utilisation.

碩士
國立臺灣科技大學
材料科學與工程系
99
In this study, the multi-layer structure (In/Ni/Cu/Ni/In) and Sn/Cu substrate reflowing at 200, 240 and 300oC for 2 h, then aging at 100oC for 50-100 h. Hoping to use this structure to replace the high-temperature Sn-Pb solders and achieve both reliability and environmental protection requirements. The results showed the all systems were formed the (Cu,Ni)6(Sn,In)5 phase and Cu2In3Sn phase at interface. In the 200oC system, it formed a planar layer (Ni,Cu)3(Sn,In)4 near Ni layer; In the 300oC system, it formed a planar layer Cu3(Sn,In) near Cu substrate, and most of them were (Cu,Ni)6(Sn,In)5 and Cu3(Sn,In) two phases. All systems formed IMCs don’t change with increasing aging time. But in the systems which were reflowed at 200 and 240oC, Cu2In3Sn and (Cu,Ni)6(Sn,In)5 phases of the occupied area ratio were increased; In the system which was reflowed at 300oC, Cu3(Sn,In) phase was growth with increasing aging time, and the growth mechanism is controlled by diffusion. In the mechanical strength testing, the reflowed at 300oC system is the most excellent. From all the results, this study finds that under the reflowed at 300oC system, this multi-layer structure is most suitable choice to replace high-temperature Sn-Pb solder.

All power electronics consist of solid state devices that generate heat. Managing the temperature of these devices is critical to their performance and reliability. Traditional methods involving liquid-cooling systems are expensive and require additional equipment for operation. Air-cooling systems are less expensive but are typically less effective at cooling the electronic devices. The cooling system that is used depends on the specific application. Until recently, silicon based devices have been used for the solid-state devices in power electronics. Newly developed silicon-carbide based wide band gap devices operate at maximum temperatures higher than traditional silicon devices. Due to the permissible increase in operating temperatures, it has been proposed to develop an air-cooling system for an inverter consisting of silicon carbide devices. This thesis presents recent research efforts to develop the proposed air-cooling system. The thermal performance of the each design iteration was determined by numerical simulations via the finite element method in both steady state and transient mode using COMSOL Multi-physics software version 3.5a. For all simulations presented in this thesis, the heat dissipated in the MOSFETS and diodes are specified as functions of current, voltage, switching frequency, and junction temperature. For both the steady state and transient simulations, the junction temperature was determined iteratively. Additionally in the transient simulations, the current distribution is a function of time and was deduced from the EPA US06 drive cycle. After several design iterations, a thermally feasible design has been reached. This design is presented in detail in this thesis. Under transient simulations of the final design, the maximum junction temperatures were determined to be below 146 ºC for air flow rates of 30 and 60 CFM, which is substantially lower than the 250 ºC maximum allowable junction temperature of Si-C devices. However for steady state simulations, junction temperatures were found to be much higher than the transient simulations. It was determined that a minimum flow rate of 50 CFM is required to meet the temperature requirements of the Si-C devices under steady state operating conditions. The power density of this air-cooled final design is 11.75 kW/L, and it is competitive with liquid-cooled systems.