Currently, there are two major driving forces for considering alternative materials to lead- based products, specifically interconnections, in electronics applications, including the impending legislation or regulations which may tax, restrict, or eliminate the use of lead and the trend toward advanced interconnection technology, which may challenge the limits of present soldering technology. The reliability of solder joints is a concern because fracture failures in solder joints accounts for 70% of failures in electronic components. Lead-free solders are being investigated as replacements for lead solders currently used in electronics. Thermo-mechanical properties describe the stresses accumulated due to thermal fatigue as a result of CTE mismatch within the system. By understanding the failure mechanisms related to lead-free solders, the application of lead- free solders could be more strategically designed for specific applications. The objective of this thesis is to observe microstructural change in large-area solder joints caused by thermal cycling and relate these changes to reliability issues in large-area lead and lead-free solder constructed semiconductor power devices. This study focused on the microstructural changes within the solder alloy of a large-area solder joint under thermal cycling conditions. Two major primary observations were made from this research, they are: 1) due to a combination of testing conditions and material properties, the lead-free solders, Sn/3.5Ag and Sn/Ag/0.7Cu, sustained the most severe damage as compared to Sn/37Pb, and 2) due to elevated stresses at the solder/substrate interface in a simulated power semiconductor device sample damage was found to be most severe. / Master of Science

<div> <div> <div> <p>Transient liquid phase sintering (TLPS) technologies are potential low-temperature solders for sustainable replacements of lead-based solders and high-temperature lead-free solders. Compared to solid-state sintering and lead-free solders, TLPS uses lower temperatures and is, thus, suitable for assembling temperature-sensitive components. TLPS is a non- equilibrium process and determining the kinetics is critical to the estimation of processing times needed for good joining. The tin-indium (Sn-In) system with a eutectic temperature of 119°C is being considered as the basis for a TLPS system when combined with tin. Most models of TLPS include interdiffusion, dissolution, isothermal solidification, and homogenization and are based on simple binary alloys without intermediate phases. The Sn-In system has two intermediate phases and thus the reaction kinetics require additional terms in the modeling. Differential Scanning Calorimetry (DSC) has been used to measure the response of Sn-In alloys during the transient liquid phase reaction. Preparation of tin indium alloys for microstructural analysis is challenging due to their very low hardness. This study uses freeze-fracturing of the tin indium alloys to obtain sections for microstructural analysis. The combination of DSC and microstructure analysis provides information on the reaction kinetics. It was observed that the solid/liquid reaction does not proceed as quickly as desired, that is, substantial liquid remains after annealing even though the overall composition is in the single-phase region in the phase diagram. </p> </div> </div> </div>

Microelectronic systems are subjected to thermal cycling, power cycling, and vibration environments in various applications. These environments, whether applied sequentially or simultaneously, affect the solder joint reliability. Literature is scarce on predicting solder joint fatigue failure under such multiple loading environments. This thesis aims to develop a unified modeling methodology to study the reliability of electronic packages subjected to thermal cycling, power cycling, and vibration loading conditions. Such a modeling methodology is comprised of an enriched material model to accommodate time-, temperature-, and direction-dependent behavior of various materials in the assembly, and at the same time, will have a geometry model that can accommodate thermal- and power-cycling induced low-cycle fatigue damage mechanism as well as vibration-induced high-cycle fatigue damage mechanism. The developed modeling methodology is applied to study the reliability characteristics of ceramic area array electronic packages with lead-based solder interconnections. In particular, this thesis aims to study the reliability of such solder interconnections under thermal, power, and vibration conditions individually, and validate the model against these conditions using appropriate experimental data either from in-house experiments or existing literature. Once validated, this thesis also aims to perform a design of simulations study to understand the effect of various materials, geometry, and thermal parameters on solder joint reliability of ceramic ball grid array and ceramic column grid array packages, and use such a study to develop universal polynomial predictive equations for solder joint reliability. The thesis also aims to employ the unified modeling methodology to develop new understanding of the acceleration factor relationship between power cycling and thermal cycling. Finally, this thesis plans to use the unified modeling methodology to study solder joint reliability under the sequential application of thermal cycling and vibration loading conditions, and to validate the modeling results with first-of-its-kind experimental data. A nonlinear cumulative damage law is developed to account for the nonlinearity and effect of sequence loading under thermal cycling, power cycling, and vibration loading.

Standard crystalline silicon photovoltaic (PV) modules are designed to continuously convert solar energy into electricity for 25 years. However, the continual generation of electricity by the PV modules throughout their designed service life has been a concern. The key challenge has been the untimely fatigue failure of solder interconnections of solar cells in the modules due to accelerated thermo-mechanical degradation. The goal of this research is to provide adequate information for proper design of solar cell solder joint against fatigue failure through the study of cyclic thermo-mechanical stresses and strains in the joint. This is carried-out through finite element analysis (FEA) using ANSYS software to develop the solar cell assembly geometric models followed by simulations. Appropriate material constitutive model for solder alloy is employed to predict number of cycles to failure of solder joint, hence predicting its fatigue life. The results obtained from this study indicate that intermetallic compound thickness (TIMC); solder joint thickness (TSJ) and width (WSJ) have significant impacts on fatigue life of solder joint. The impacts of TIMC and TSJ are such that as the thicknesses increases solder joint fatigue life decreases. Conversely, as solder joint width (WSJ) increases, fatigue life increases. Furthermore, optimization of the joint is carried-out towards thermo-mechanical reliability improvement. Analysis of results shows the design with optimal parameter setting to be: TIMC -2.5μm, TSJ -20μm and WSJ -1000μm. In addition, the optimized model has 16,264 cycles to failure which is 18.82% more than the expected 13,688 cycles to failure of a PV module designed to last for 25 years.

This thesis focuses on soldering technology in microelectronics. It describes in detail the basic ways of soldering and repairs in electronics. This piece of work shows the principles of technological equipment for bulk soldering and used repairing devices. In the theoretical part of this work there are also briefly described the packages for integrated circuits that were used in the practical part of the thesis. The practical part of the thesis deals with setting of the heat profiles for hot air repair station Fritsch Mikroplacer for LQFP64, SOIC16, TSSOP14, QFN16 and DSBGA5 packages. The heat profiles for assembly and disassembly of the particular types of the packages on designed and manufactured test printed circuit board were set and tested. The resulting heat profiles are compared with the recommended heat profile of an ordinary solder paste SnAg3Cu0,5 which was used for the test. This thesis can serve as an aid for the further settings of heat profiles in other types of packages not only on Fritsch Mikroplacer devices, but also on other repairing devices of this type.

This thesis deals with novel trends in solder paste technology. It focuses on nanoparticle applications used as a tool for improving a state of the art lead free solder alloys. The recently published results about the impact of different types of nanoparticles on properties of newly-emerged nanocomposite solders are discussed and summarized in the thesis. Preparation, practical application and testing of new solder paste based on low temperature SnBi alloy with an admixture of titanium dioxide are also discussed. Finally, properties of solder joints using these solder pastes are investigated and the results are evaluated.

published_or_final_version / abstract / Electrical and Electronic Engineering / Master / Master of Philosophy

Lead-tin solder has been widely used as interconnection material in electronics packaging for a long time. In response to environmental legislation, the lead-tin alloys are being replaced with lead-free alloys and electrically conductive adhesives in consumer electronics. Lead-free solder usually require higher reflow temperatures than the traditional lead-tin alloys, which can cause die crack and board warpage in assembly process, thereby impacting the assembly yields. The high tin content in lead-free solder forms tin whiskers, which has the potential to cause short circuits failure. Conductive adhesives are an alternative to solder reflow processing, however, conductive adhesives require up to 80 wt% metal filler to ensure electrical and thermal conductivity. The high loading content degrades the mechanical properties of the polymer matrix and reduces the reliability and assembly yields when compared to soldered assemblies. Carbon nanotubes (CNTs) have ultra high aspect ratio as well as many novel properties. The high aspect ratio of CNTs makes them easy to form percolation at low loading and together with other novel properties make it possible to provide electrical and thermal conductivity for the polymer matrix while maintaining or even reinforcing the mechanical properties. Replacing the metal particles with CNTs in conductive adhesive compositions has the potential benefits of being lead free, low process temperature, corrosion resistant, electrically/thermally conductive, high mechanical strength and lightweight. In this paper, multiwall nanotubes (MWNTs) with different dimensions are mixed with epoxy. The relationships among MWNTs dimension, volume resistivity and thermal conductivity of the composite are characterized. Different loadings of CNTs, additives and mixing methods were used to achieve satisfying electrical and mechanical properties and pot life. Different assembly technologies such as pressure dispensing, screen and stencil printing are used to simplify the processing method and raise the assembly yields. Contact resistance, volume resistivity, high frequency performance, thermal conductivity and mechanical properties were measured and compared with metal filled conductive adhesive and traditional solder paste.

Approved for public release; distribution is unlimited / Solder joints provide both electrical and mechanical interconnections between a silicon chip and the packaging substrate in an electronic application. The thermomechanical cycling (TMC) in the solder due to the mismatch of the coefficient of thermal expansion (CTE) between the silicon chip and the substrate causes numerous reliability challenges. This situation is aggravated by the ongoing transition to lead-free solders worldwide, and the trend towards larger, hotter-running chips. Therefore, improved solder joints, with higher resistance to creep and low-cycle fatigue, are necessary for future generations of microelectronics. This study reports in the development a process to fabricate solder joints with a fine distribution of shape memory alloys (SMA) NiTi particulates. The microstructure and interface zone of the as-reflowed solder-SMA composite has been characterized. / Lieutenant, United States Navy

by Chow Yeung Ming = 化學鍍鎳層的表面性質與焊接能力之關係 / 周洋明. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (leaves 62-65). / Text in English; abstracts in English and Chinese. / by Chow Yeung Ming = Hua xue du nie ceng de biao mian xing zhi yu han jie neng li zhi guan xi / Zhou Yangming. / Abstract --- p.i / 論文摘要 --- p.ii / Acknowledgements --- p.iii / Table of Contents --- p.v / List of Figures --- p.viii / List of Tables --- p.ix / Abbreviations --- p.x / Chapter Chapter 1 --- INTRODUCTION / Chapter 1.1 --- Electroless Plating (Autocatalytic Deposition) --- p.1 / Chapter 1.2 --- Electroless Nickel (EN) Plating --- p.2 / Chapter 1.3 --- Types of Electroless Nickel Deposits --- p.2 / Chapter 1.4 --- Properties of Electroless Nickel --- p.5 / Chapter 1.5 --- Applications of Electroless Nickel in Electronic Packaging Industry --- p.7 / Chapter 1.6 --- Importance of Solderability --- p.8 / Chapter 1.7 --- Literature Review of Solderability Studies of Electroless Nickel --- p.9 / Chapter 1.8 --- Motivations & Aims of Studies --- p.10 / Chapter Chapter 2 --- EXPERIMENTAL & INSTRUMENTATION / Chapter 2.1 --- Electroless Nickel Plating --- p.11 / Chapter 2.2 --- Solderability Measurements / Chapter 2.2.1 --- Soldering --- p.13 / Chapter 2.2.2 --- Various test methods for solderability --- p.13 / Chapter 2.2.3 --- Wetting balance method --- p.15 / Chapter 2.2.4 --- Solderability measurements of electroless nickel deposits --- p.17 / Chapter 2.2.5 --- Assessment of wetting curves --- p.19 / Chapter 2.3 --- Surface Oxidation Studies / Chapter 2.3.1 --- Use of X-ray photoelectron spectroscopy (XPS) in surface characterization --- p.19 / Chapter 2.3.2 --- XPS system --- p.22 / Chapter 2.3.3 --- Surface composition of electroless nickel deposits --- p.22 / Chapter 2.3.4 --- Oxide thickness characterization by angle-resolved XPS --- p.25 / Chapter 2.3.5 --- Oxide thickness characterization by XPS depth profiling with low-energy-ion sputtering --- p.28 / Chapter 2.4 --- Surface Morphology Studies / Chapter 2.4.1 --- Surface morphology studies by scanning Auger electron microscopy (SAM) & atomic force microscopy (AFM) --- p.28 / Chapter 2.4.2 --- SAM studies of electroless nickel surfaces --- p.29 / Chapter 2.4.3 --- AFM studies of electroless nickel surfaces --- p.29 / Chapter 2.5 --- Oxide Quality Studies --- p.31 / Chapter Chapter 3 --- RESULTS & DISCUSSIONS / Chapter 3.1 --- Solderability Measurements by the Wetting Balance Method --- p.33 / Chapter 3.2 --- Surface Oxidation Studies / Chapter 3.2.1 --- Surface composition of electroless nickel deposits --- p.36 / Chapter 3.2.2 --- Oxide thickness characterization by angle-resolved XPS --- p.38 / Chapter 3.2.3 --- Oxide thickness characterization by XPS depth profiling with low-energy-ion sputtering --- p.44 / Chapter 3.2.4 --- Conclusion --- p.47 / Chapter 3.3 --- Surface Morphology Studies / Chapter 3.3.1 --- SAM studies of electroless nickel surfaces --- p.49 / Chapter 3.3.2 --- AFM studies of electroless nickel surface --- p.49 / Chapter 3.3.3 --- Conclusion --- p.53 / Chapter 3.4 --- Interpretation of Wetting Kinetics of Electroless Nickel --- p.54 / Chapter Chapter 4 --- CONCLUSIONS & FURTHER STUDIES / Chapter 4.1 --- Conclusions --- p.59 / Chapter 4.2 --- Further Studies --- p.60 / Appendix --- p.61 / References --- p.62