Effect of Addition of Al to Sn-Zn Solder Alloys

Conventional solders consist of Lead, that was found to be toxic and carcinogenic. Hence, restrictions were put on its use by the industrially developed nations. To counter the use of Lead, active research was pursued into the development of Lead-free solders. In our project, we fabricated alloys of composition 3:15:82, 7:43:50 and 10:80:10 (in terms of Aluminium, Zinc and Tin respectively), under furnace cooled and air-cooled conditions. The use of Aluminium was made so as to increase the resistance of the solder to atmospheric corrosion, and also to improve the wettability of the samples. Optical micrographs were obtained for each sample so as to analyze their microstructures. For a deeper understanding, SEM images of each sample were obtained, and EDX analysis was performed side-by-side so as to understand the elemental composition of different phases present in the sample. DSC and TG tests were conducted to determine the melting point of the solder alloy, and the weight gain in the alloy on oxidation respectively. The wettability of each sample was also analyzed. We recorded and plotted down the trends in each case. We then tried to evaluate the most effective solder composition on the basis of the above tests. The near-eutectic composition was considered so as to avoid the formation of a pasty phase that will cause disruption in electrical work

Effect of aluminum content on structure, transport and mechanical properties of Sn-Zn eutectic lead free solder alloy rapidly solidified from melt.

The greatest advantage of Sn-Zn eutectic is its low melting point (198 oC) which is close to the melting point. of Sn-Pb eutectic solder (183 oC), as well as its low price per mass unit compared with Sn-Ag and Sn-Ag-Cu solders. In this paper, the effect of 0.0, 1.0, 2.0, 3.0, 4.0, and 5.0 wt. % Al as ternary additions on melting temperature, microstructure, microhardness and mechanical properties of the Sn-9Zn lead-free solders were investigated. It is shown that the alloying additions of Al at 4 wt. % to the Sn-Zn binary system lead to lower of the melting point to 195.72 ?C. From x-ray diffraction analysis, an aluminium phase, designated ?-Al is detected for 4 and 5 wt. % Al compositions. The formation of an aluminium phase causes a pronounced increase in the electrical resistivity and microhardness. The ternary Sn-9Zn-2 wt.%Al exhibits micro hardness superior to Sn-9Zn binary alloy. The better Vickers hardness and melting points of the ternary alloy is attributed to solid solution effect, grain size refinement and precipitation of Al and Zn in the Sn matrix. The Sn-9%Zn-4%Al alloy is a lead-free solder designed for possible drop-in replacement of Pb-Sn solders

Technology of Welding and Joining

In this book, you will find information on new materials and new welding technologies. Problems related to the welding of difficult-to-weld materials are considered and solved. The latest welding technologies and processes are presented. This book provides an opportunity to learn about the latest trends and developments in the welding industry. Enjoy reading

Thermomechanical behavior of monolithic Sn-Ag-Cu solder and copper fiber reinforced solders

Solder joints provide both electrical and mechanical interconnections between a silicon chip and the packaging substrate in an electronic application. The thermomechanical cycling in the solder causes numerous reliability challenges, mostly because of the mismatch of the coefficient of thermal expansion between the silicon chip and the substrate. The actual transition to lead-free solders and the trend towards hotter-running, miniaturized and higher current density chips aggravate this situation. Therefore, improved solder joints, with higher resistance to creep and low cycle fatigue, are necessary for future generations of microelectronics. This study focuses on a thermomechanical behavior comparison between monolithic Sn-Ag-Cu, copper fiber and copper ribbon cylindrical reinforced solders. The composite solders were found to reduce the inelastic strain range of the joint relative to monolithic solder, but at the expense of increased stress range.http://archive.org/details/thermomechanical109452062Approved for public release; distribution is unlimited

Corrosion Resistance

The book has covered the state-of-the-art technologies, development, and research progress of corrosion studies in a wide range of research and application fields. The authors have contributed their chapters on corrosion characterization and corrosion resistance. The applications of corrosion resistance materials will also bring great values to reader's work at different fields. In addition to traditional corrosion study, the book also contains chapters dealing with energy, fuel cell, daily life materials, corrosion study in green materials, and in semiconductor industry

Soldering by the Active Lead-Free Tin and Bismuth-Based Solders

The chapter deals with Sn and Bi-In-based lead-free solders. The term “active solders” is used for the solders which contain one or more elements with enhanced affinity to some element contained in the substrate material. Mainly, Ti, In, lanthanides, etc. belong amongst the active metals. The role of an active element is to ensure a good wetting by a reactive decomposition of the surface layer of substrate. The perspective solders for joining the combined materials, as ceramics/metal, are mainly the tin-based, lead-free solders, which are enriched with titanium (usually up to 4 wt. %). The advantage consists in the fact that they offers a sufficient plasticity reserve, by what they are capable to compensate undesired residual stresses formed in the joint. Titanium also reacts with carbon, nitrogen or oxygen of the ceramic material, eventually it forms the intermetallic phases, which increase the strength of joint interface. The Sn-Ti, Sn-Ag-Ti and Bi-In-Sn solders were selected for the experiments. These solders were applied for fabrication of Al2O3 ceramics/Cu joints. The phase composition and microstructure of solders and soldered joints was analysed. Interactions in the interface of ceramic/solder and Cu substrate/solder were determined. The shear strength of soldered joints was measure

Soldering interconnects through self-propagating reaction process

This thesis presents a research into the solder interconnects made through the reactive bonding process based on the self-propagating reaction. A numerical study of soldering conditions in the heat affected zone (HAZ) during bonding was initially carried out in order to understand the self-propagating reactive bonding and the related influencing factors. This was subsequently followed by an extensive experimental work to evaluate the feasibility and reliability of the reactive bonding process to enable the optimisation of processing parameters, which had provided a detailed understanding in terms of interfacial characteristics and bonding strengths. In addition, by focusing on the microstructure of the bonds resulted from the self-propagating reactions, the interfacial reactions and microstructural evolution of the bonded structures and effects of high-temperature aging were studied in details and discussed accordingly. To study the soldering conditions, a 3D time-dependent model is established to describe the temperature and stress field induced during self-propagating reactions. The transient temperature and stress distribution at the critical locations are identified. This thus allows the prediction of the melting status of solder alloys and the stress concentration points (weak points) in the bond under certain soldering conditions, e.g. ambient temperature, pressure, dimension and type of solder materials. Experimentally, the characterisation of interconnects bonded using various materials under different technical conditions is carried out. This ultimately assists the understanding of the feasibility, reliability and failure modes of reactive bonding technique, as well as the criteria and optimisation to form robust joints. The formation of phases such as intermetallic compounds (IMCs) and mechanism of interfacial reactions during reactive bonding and subsequent aging are elaborated. The composition, dimension, distribution of phases have been examined through cross-sectional observations. The underlying temperature and stress profile determining the diffusion, crystallization and growth of phases are defined by numerical predictions. XXI Through the comparative analysis of the experimental and numerical results, the unique phases developed in the self-propagating joints are attributed to the solid-liquid-convective diffusion, directional solidification and non-equilibrium crystallization. The recrystallization and growth of phases during aging are revealed to be resulted from the solid-state diffusion and equilibration induced by the high-temperature heating. In conclusion, the interfacial reactions and microstructural evolution of interconnect developed through self-propagating reactive bonding are studied and correlated with the related influencing factors that has been obtained from these predictions and experiments. The results and findings enable the extensive uses of self-propagating reactive bonding technology for new design and assembly capable of various applications in electronic packaging. It also greatly contributes to the fundamentals of the crystallization and soldering mechanism of materials under the non-equilibrium conditions