abstract: Increasing density of microelectronic packages, results in an increase in thermal and mechanical stresses within the various layers of the package. To accommodate the high-performance demands, the materials used in the electronic package would also require improvement. Specifically, the damage that often occurs in solders that function as die-attachment and thermal interfaces need to be addressed. This work evaluates and characterizes thermo-mechanical damage in two material systems – Electroplated Tin and Sintered Nano-Silver solder. Tin plated electrical contacts are prone to formation of single crystalline tin whiskers which can cause short circuiting. A mechanistic model of their formation, evolution and microstructural influence is still not fully understood. In this work, growth of mechanically induced tin whiskers/hillocks is studied using in situ Nano-indentation and Electron Backscatter Diffraction (EBSD). Electroplated tin was indented and monitored in vacuum to study growth of hillocks without the influence of atmosphere. Thermal aging was done to study the effect of intermetallic compounds. Grain orientation of the hillocks and the plastically deformed region surrounding the indent was studied using Focused Ion Beam (FIB) lift-out technique. In addition, micropillars were milled on the surface of electroplated Sn using FIB to evaluate the yield strength and its relation to Sn grain size. High operating temperature power electronics use wide band-gap semiconductor devices (Silicon Carbide/Gallium Nitride). The operating temperature of these devices can exceed 250oC, preventing use of traditional Sn-solders as Thermal Interface materials (TIM). At high temperature, the thermomechanical stresses can severely degrade the reliability and life of the device. In this light, new non-destructive approach is needed to understand the damage mechanism when subjected to reliability tests such as thermal cycling. In this work, sintered nano-Silver was identified as a promising high temperature TIM. Sintered nano-Silver samples were fabricated and their shear strength was evaluated. Thermal cycling tests were conducted and damage evolution was characterized using a lab scale 3D X-ray system to periodically assess changes in the microstructure such as cracks, voids, and porosity in the TIM layer. The evolution of microstructure and the effect of cycling temperature during thermal cycling are discussed. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2018

Multicomponent metal alloys play an essential role in many technologies and their properties must be optimized by rational selection of the alloy’s components and its fractional composition of each. High-throughput materials synthesis allows us to prepare Composition Spread Alloy Films (CSAFs), sample libraries that contains all possible compositions of a binary or ternary alloy. In our lab, a Rotatable Shadow Mask (RSM) – CSAF deposition tool has been developed for the creation of CSAFs. Such CSAFs can be prepared with composition gradients and/or thickness gradients in arbitrarily controlled directions and on a variety of substrates. Once prepared, the CSAF libraries can be characterized thoroughly using a variety of highthroughput spectroscopic methods. Their bulk composition is mapped across the library using Energy Dispersive X-ray spectroscopy (EDX). The near-surface compositions are mapped across composition space using X-ray Photoemission Spectroscopy (XPS). Finally, the electronic structure can be mapped using UV photoemission spectroscopy (UPS) and valence band XPS. Once characterized, these CSAFs are being used for high-throughput studies of alloy catalysis and thermal properties of the alloys and of alloy-substrate interfaces. First of all, PdzCu1-z CSAF was prepared to show that alloy nanoparticles (aNPs) and thin films can adopt phases that differ from those of the corresponding bulk alloy. The mapping of XPS-derived core level binding energy shifts across PdzCu1-z SCSNaP library shows a promising result that the FCC phase can be dimensionally stabilized over the composition range where B2 phase exists in the bulk. This observation can potentially improve the performance of PdzCu1-z NP catalysts in H2 separation. Secondly, the relationship between catalyst activity-electronic structure-composition has been investigated. A high throughput characterization of electronic structure (valence band energy) of binary PdxAg1-x and ternary PdxCuyAu1-x-y CSAFs were performed by XPS. This XPS-derived valence band center is compared with UPS-derived data across PdxCuyAu1-x-y CSAFs. In addition, H2-D2 exchange reaction was studied on PdxAg1-x CASF. A higher HD formation rate is experimentally observed but cannot be predicted by the Langmuir-Hinshelwood model when the surface coverage is saturated. However, the proposed H2-D2 exchange mechanism (breakthrough model) involved with surface and subsurface hydrogen reaction is investigated to produce a same reaction order as Langmuir-Hinshelwood mechanism, which cannot explain the experimental observation. Furthermore, the thermal interface conductance (G) was studied as a function of metal alloy composition. A high-throughput approach to preparation, characterization, and measurement of G was also demonstrated to study the thermal property of alloyed materials. Our result in studying the G across the AuxY1-x (Y = Pd and Cu) CSAFs-dielectric interfaces has shown a linear relationship with alloy composition, which monotonically increases with decreasing Au (at. %). Lastly, the effect of interdiffusion in metal films on G at metal-dielectric interface was also examined. The XPS depth profiling was designed to experimentally determine the temperature effect on compositional profiles in the Au-Cu system, and how to further influence G. This study provides fundamental understanding of stability of adhesion layer of Cu and the effect of interdiffusion in Cu-Au alloy on the heat dissipation. All in all, the key value to these CSAF libraries is that they enable measurement of important alloy properties across entire binary or ternary alloy composition spaces, without the need to prepare and characterize numerous discrete composition samples.

Lighting technologies have evolved over the years to become higher quality, more efficient sources of light. LEDs are poised to become the market standard for general lighting because they are the most power efficient form of lighting and do not contain hazardous materials. Unfortunately, LEDs pose unique problems because advanced thermal management is required to remove the high heat fluxes generated by such relatively small devices. These problems have already been overcome with complex packaging and exotic materials, but high costs are preventing this technology from displacing current lighting technologies. The purpose of this study is to develop a low-cost LED lighting package capable of successfully managing heat. Several designs were created and analyzed based on cost, thermal performance, ease of manufacturing, and reliability. A unique design was created which meet these requirements. This design was eventually assembled as a prototype and initial testing was conducted. This thesis reviews the design process and eventual results of the LED package design.

As electronic packages and their thermal solutions become more complex the reliability margins in the thermal solutions diminish and become less tolerant to errors in reliability predictions. The current method of thermally stress testing thermal solutions can be over or under predicting end of life thermal performance. Benefits of accurate testing and modeling are improved silicon yield in manufacturing, improved performance, lower cost thermal solutions, and shortened test times. The current method of thermally stress testing is to place the entire unit in an elevated isothermal temperature and periodically measure thermal performance. Isothermally aging is not an accurate representation of how the unit will be used by the customer and does not capture the thermal gradients and mechanical stresses due to different coefficients of thermal expansion of the materials used in the thermal solution. A new testing system, CITRAM which is an acronym for Constant Interface Temperature Reliability Method, has been developed that uses an electronic test board. The approach captures the thermal and mechanical stresses accurately and improves test time by 20-30% as a result of automation. Through this study a difference in the two methods has been identified and the new CITRAM method should be adopted as current practice.

Thermoelectric devices are useful for a variety of applications due to their ability to either convert heat directly into electricity, or to generate a temperature gradient from an electric current. These devices offer several attractive features including compact size, no moving parts, limited maintenance requirements, and high reliability. Thus thermoelectric devices are used for temperature-control, cooling, or power generation in various industrial systems such as automobiles, avionics, refrigerators, chillers, laser diodes, dehumidifiers, and a variety of sensors. In order to improve the efficiency of thermoelectric devices, many endeavors have been made to design and fabricate materials with a higher dimensionless thermoelectric figure of merit (ZT), as well as to optimize the device structure and packaging to manage heat more effectively. When evaluating candidate thermoelectric materials, one must accurately characterize the electrical conductivity, thermal conductivity, and the Seebeck coefficient over the temperature range of potential use. However, despite considerable research on thermoelectric materials for decades, there is still significant scatter and disagreement in the literature regarding accurate characterization of these properties due to inherent difficulties in the measurements such as requirements for precise control of temperature, simultaneous evaluation of voltage and temperature, etc. Thus, a well-designed and well-calibrated thermoelectric measurement system that can meet the requirements needed for multiple kinds of thermoelectric materials is an essential tool for the development of advanced thermoelectric devices. In this dissertation, I discuss the design, fabrication, and validation of a measurement system that can rapidly and accurately evaluate the Seebeck coefficient and electrical resistivity of thermoelectric materials of various shapes and sizes from room temperature up to 600 K. The methodology for the Seebeck coefficient and electrical resistivity measurements is examined along with the optimization and application of both in the measurement system. The calibration process is completed by a standard thermoelectric material and several other materials, which demonstrates the accuracy and reliability of the system. While a great deal of prior research has focused on low temperature thermoelectric materials for cooling, such as Bi2Te3, high temperature thermoelectric materials are receiving increasing attention for power generation. With the addition of commercial systems for the Seebeck coefficient, electrical resistivity, and thermal conductivity measurements to expand the temperature range for evaluation, a wide range of materials can be studied and characterized. Chapter Two of this dissertation describes the physical properties characterization of a variety of thermoelectric materials, including room temperature materials such as Bi0.5Sb1.5Te3, medium temperature level materials such as skutterudites, and materials for high temperature applications such as half-Heusler alloys. In addition, I discuss the characterization of unique oxide thermoelectric materials, which are Al doped ZnO and Ca-Co-O systems for high temperature applications. Chapter Four of this dissertation addresses the use of GaSn alloys as a thermal interface material (TIM), to improve thermal transport between thermoelectric devices and heat sinks for power generation applications at high temperature. I discuss the mechanical and thermal behavior of GaSn as an interface material between electrically insulating AlN and Inconel heat exchangers at temperatures up to 600 °C. Additionally, a theoretical model for the experimental thermal performances of the GaSn interface layer is also examined. / Ph. D. / Thermoelectric materials can directly convert heat into electricity for power generation, or they can be used for cooling or refrigeration applications when supplied with electric power. This dissertation primarily focuses on the evaluation of materials used in thermoelectric generators (TEGs). Specifically, Chapter Two of this work describes the design, development, and validation of a developed measurement system that can evaluate two important properties, the Seebeck coefficient and electrical resistivity, for a variety of thermoelectric materials. Next, Chapter Three discusses the work using other commercial measurement systems to evaluate several types of thermoelectric materials, including Bi2Te3 based materials, skutterudites, half-Heusler alloys, ZnO, and Ca-Co-O for a TEG module. Finally, I discuss the use of GaSn, a liquid metal alloy, as a thermal interface material to improve heat transport between dissimilar materials for TEGs. The GaSn was applied between a thermoelectric device and a heat exchanger for use in energy harvesting devices. The mechanical robustness and thermal reliability were tested, and the GaSn was shown to improve thermal performances both in experiments and through modeling.

<p>Polymer nanocomposites are a constantly evolving material category due to the ability to engineer the mechanical, thermal, and optical properties to enhance the efficiency of a variety of systems. While a vast amount of research has focused on the physical phenomena of nanoparticles and their contribution to the improvement of such properties, the ability to implement these materials into existing commercial or newly emerging processing methods has been studied much less extensively. The primary characteristic that determines which processing technique is the most viable is the rheology or viscosity of the material. In this work, we investigate the processing methods and properties of nanocomposites for thermal interface and radiative cooling applications. The first polymer nanocomposite examined here is a two-component PDMS with graphene filler for 3D printing via a direct ink writing approach. The composite acts as a thermal interface material which can enhance cooling between a microprocessor and a heat sink by increasing the thermal conductivity of the gap. Direct ink writing requires a shear thinning ink with specific viscoelastic properties that allow for the material to yield through a nozzle as well as retain its shape without a mold following deposition. No predictive models of viscosity for nanocomposites exist; therefore, several prominent models from literature are fit with experimental data to describe the change in viscosity with the addition of filler for several different PDMS ratios. The result is an understanding of the relationship between the PDMS component ratio and graphene filler concentration with respect to viscosity, with the goal of remaining within the acceptable limits for printing via direct ink writing. The second nanocomposite system whose processability is determined is paint consisting of acrylic filled with reflective nanoparticles for radiative cooling paint applications. The paint is tested with both inkjet and screen-printing procedures with the goal of producing a thermally invisible ink. Radiative cooling paint is successfully printed for the first time with solvent modification. This work evaluates the processability of polymer nanocomposites through rheological tailoring. </p><br>

導熱介面材料(Thermal Interface Materials, TIM)是所有電子相關產品不可或缺的組成元素之一，沒有了它，市面上就不會有電腦、遊戲機、智慧型手機，也不會有電視機、LED燈，更不會有油電混合車；既然如此不可或缺，但它卻又不造就了是電子產業慣例定義中的關鍵零組件。如此特殊的屬性與定位，導熱介面材料的不凡與平凡。 台灣廠商高柏科技過去十年，趁著消費性電子產品的興起，投入導熱介面材料的生產與銷售，並且堅持自行研發產品，十年間已見規模。但是由於小廠迅速冒出，削價競爭，殺戮慘烈，平凡的低階產品市場已成紅海。有鑑於全球總體的大趨勢，節能減碳需求與日俱增，導熱、散熱等熱管理產業已然成為下一波的主流市場，高柏科技是否可再一次順應潮流，再創另一個豐收的十年，全球競爭力的提高將是成敗關鍵。 高柏科技於是亟思運用既有核心競爭優勢，輔以積極開闢海外市場，希望以全球佈局的高度，以敏銳的市場洞察力，察覺導熱介面材料下一個世代的產品應用之星，找到一片屬於導熱介面材料的不凡的深湛藍海。 / Thermal Interface Materials (TIM) is one of key components in many electronics applications. TIM generally works to solve thermal issues in these electronic products. T-Global Technology Co., one of the top 15 leading companies in the global TIM industry, has been building its own brand by manufacturing and marketing it own products since 10 years ago. The company faces much higher competitions from producers of emerging markets who focus on the low-cost or entry-lever productions. This study considers and investigates how to develop sustainable growth strategies in the current situation. A thorough analysis suggests that strategies of deeper penetrating and expanding into global markets by leveraging the company's core competence may well serve the purpose.

Since most of the energy input is converted to thermal energy in laser applications, the proper thermal management of laser systems is an important issue. Maintaining the laser diode and crystal temperature distributions in a narrow range during the operation is the most crucial requirement for the cooling of a laser system. In the present study, thermoelectric cooling (TEC) of a 1064 nm wavelength diode pumped laser source is investigated both experimentally and numerically. During the heat removal process, the thermal resistance through and between the materials, the proper integration of the TEC assembly, and the heat sink efficiency become important. For the aim of evaluating and further improving the system performance, various assembly configurations, highly conductive components, efficient interface materials and heat sink alternatives are considered. Several experiments are conducted during the system development stage, and parallel numerical simulations are performed both for comparison and also for providing valuable input for the system design. Results of the experiments and the simulations agree well with each other. As the laser device works in the transient regime, the experiments and the simulations are also implemented in this regime. In the final part of the study, the experiments are performed under the actual device working conditions. It is proved that with the designed TEC module and the copper heat sink system, the laser device can operate longer than the required operational time successfully.

No description available.

Interconnects in power module result in thermal interfaces. The thermal interfaces degrade under thermal cycling, or chemical loading. Moreover, the reliability of thermal interfaces can be especially problematic when the interconnecting area is large, which increases its predisposition to generate defects (voids, delamination, or nonuniform quality) during processing. In order to improve the quality of the bonding process, as well as to be able to accurately assess interface reliability, it would be desirable to have a simple, reliable, and nondestructive measurement technique that would produce a 2-d map of the interface thermal resistance across a large bonded area. Based on the transient thermal method of JEDEC standard 51-14, we developed a measurement technique that involves moving a thermal sensor discretely across a large-area bonded substrate and acquiring the interface thermal resistance at each location. As detailed herein, the sensor was fabricated by packaging an IGBT bare die. An analytical thermal model was built to investigate the effects of thermal sensor packaging materials and structural parameters on the sensitivity of the measurement technique. Based on this model, we increased the detection sensitivity of the sensor by modifying the size of the sensor substrate, the material of the sensor substrate, the size of the IGBT bare die, the size of the heat sink, and the thermal resistance between sample and the heat sink. The prototype of the thermal sensor was fabricated by mounting Si IGBT on copper substrate, after which the Al wires were ultrasonic bonded to connect the terminals to the electrodes. The sensor was also well protected with a 3-d printed fixture. Then the edge effect was investigated, indicating the application of the thermal sensor is suitable for samples thinner than the value in TABLE 2 3. The working principle of the movable thermal sensor – Zth measurement and its structure function analysis – was then evaluated by sequence. The Zth measurement was evaluated by measuring the Zth change of devices induced by degradation in sintered silver die-attach layer during temperature cycling. At the end of the temperature cycling, failure modes of the sintered silver layer were investigated by scanning electron microscope (SEM) and X-ray scanning, to construct a thermal model for FEA simulation. The simulation results showed good agreement with the measured Zth result, which verified the accuracy of the test setup. The sensitivity of structure function analysis was then evaluated by measuring thermal resistance (Rth) of interface layers with different thermal properties. The structure function analysis approach successfully detected the Rth change in the thermal interface layer. The movable thermal sensor was then applied for 2d-mapping of the interface Rth of a large-area bonded substrate. Examining the test coupons bonded by sintered silver showed good and uniform bonding quality. The standard deviation of Rth is about 0.005 K/W, indicating the 95% confidence interval is about 0.01 K/W, which is commonly chosen as the error of measurement. The sensitivity of the movable thermal sensor was evaluated by detecting defects/heat channels of differing sizes. The 2-d mapping confirmed that the thermal sensor was able to detect defect/heat channel sizes larger than 1x1 mm2. The accuracy of the sensitivity was verified by FEA simulation. Moreover, the simulated results were consistent with the measured results, which indicates that the movable sensor is accurate for assessing interface thermal resistance. In summary, based on structure function analysis of the transient thermal impedance, the concept of a movable thermal sensor was proposed for two-dimensional mapping of interface thermal resistance. (1) Preliminary evaluation of this method indicated both transient thermal impedance and structure function analysis were sensitive enough to detect the thermal resistance change of thermal interface layers. With the help of transient thermal impedance measurement, we non-destructively tested the reliability of sintered silver die-attach layer bonded on either Si3N4 AMB or AlN DBA substrates. (2) An analytical thermal model was constructed to evaluate the design parameters on the sensitivity and resolution of the movable thermal sensor. A detailed design flow chart was provided in this thesis. To avoid edge effect, requirements on thickness and materials of test coupon also existed. Test coupon with smaller thermal conductivity and larger thickness had a more severe edge effect. (3) The application of the movable sensor was demonstrated by measuring the 2-d thermal resistance map of interface layers. The results indicated for bonded copper plates (k = 400 W/mK) with thickness of 2 mm, the sensor was able to detect defect/heat channel with size larger than 1x1 mm2. / Doctor of Philosophy / Interconnects in power module result in thermal interfaces. The thermal interfaces degrade during operation and their reliability can be especially problematic when the interconnecting area is large. In order to improve the quality of the bonding process, as well as to be able to accurately assess interface reliability, it would be desirable to have a simple, reliable, and nondestructive measurement technique that would produce a 2-d map of the interface thermal resistance across a large bonded area. Based on the transient thermal method of JEDEC standard 51-14, we developed a measurement technique that involves moving a thermal sensor discretely across a large-area bonded substrate and acquiring the interface thermal resistance at each location. As detailed herein, the sensor was fabricated by packaging an IGBT bare die, which allowed us to get a 2-d map of the interface thermal resistance. A thermal model was also constructed to guide the design of the sensor, to increase its performance. Moreover, the preliminary test of the test setup was conducted to prove its feasibility for the sensor. Eventually, the sensor’s performance and application was demonstrated by measuring the 2-d thermal resistance map of the bonded interfaces.