Effect Of Zn Addition On Microstructure, Intermetallic Compound Formation And Mechanical Properties Of Sn-0.7cu Solder On Cu Substrate

Solder joints serve as both electronic and mechanical connections between components as well as substrates in electronic devices. Concern over the toxicity of lead sparked intense focus on finding alternative lead-free solders to replace the traditional Sn-Pb solder. An attractive candidate is Sn-Cu alloy as it is cheaper than Ag-containing solders. However, Sn-0.7Cu has been reported to have lower strength than the other lead-free solders. There is potential to further improve the performance of Sn-0.7Cu and increase solder joint reliability especially for high-powered solder joints. In this study Sn-0.7Cu, Sn-0.7Cu -0.5Zn and Sn-0.7Cu -1.0Zn bulk solder alloys were developed. The addition of Zn potentially refines solder microstructure and results in secondary particles that could strengthen the solder. Alloying of Zn also has been reported to decrease thickness of Cu-Sn IMC layer in Sn-based solder alloys. Characterization of the solder alloys focused on the bulk solder microstructure and IMC evaluation. Melting point of solder was determined using Differential Scanning Calometry (DSC) while elemental composition of solders were analysed using X-ray fluorescence (XRF). Aging was done for 100, 200 and 500 hours at 150 °C and 180 °C. Microstructure of bulk solder and the IMC formed at interface between solder and Cu substrate were observed using SEM equipped with EDX. Addition of Zn slightly decreased the wettability compared to Sn-Pb, but still having good wettability because all the wetting angle are in range of 34°to 38°. Results showed that wettability reduced with increasing amount of Zn but the hardness was increased. The addition of Zn also showed increased shear strength up to 40% higher than that of the Sn-Cu solder alloys

Development of Advanced Nanocomposite for Micro/Nanosystems Packaging

Ph.DDOCTOR OF PHILOSOPH

Potential dopant in photocatalysis process for wastewater treatment-a review

Nowadays, too much pollution has happened around us, and one of them is water pollution, which each day has become more severe and worse. One of the sources of water pollution comes from the industry that has used dyes either excessively or not. In case of that, the wastewater needs to be treated before released to the river or environment. In this paper, a review of the wastewater treatment using dopants such as nitrogen and magnesium, will be discussed

Active Solders and Active Soldering

Due to the relatively high stability of ceramic surfaces, ceramics, graphite, and alloys that easily form an oxide passivation layer by natural oxidation, such as aluminum alloys, titanium alloys, and magnesium alloys, are not wetted by common solders and brazing fillers. Moreover, in most applications, the brazing temperature is so high that it causes hot cracking or functional degradation of the difficult-to-wet materials. Active filler metals containing active elements have been developed, which can successfully join the nonwetting materials at low temperatures (<250°C) in air. The active elements, such as titanium, magnesium, and rare earth elements, in active solders play an important role in wettability and reactivity between filler metals and difficult-to-wet materials. Solders with active element content have been shown to provide excellent wettability. Hence, direct active soldering has been developed to simplify the manufacturing of difficult-to-wet material joints. A practical understanding of the design and characterization of low melting point active solders and active soldering processes is elaborated in this chapter. The effects of active elements, active solder characteristics, mechanism of active soldering, active soldering techniques, and specific applications are introduced. The influence of the thermal and mechanical activation on the interfacial reactions between filler metals and difficult-to-wet materials during the active soldering process is also discussed

MICROSTRUCTURAL CHARACTERIZATION AND THERMAL CYCLING RELIABILITY OF SOLDERS UNDER ISOTHERMAL AGING AND ELECTRICAL CURRENT

Solder joints on printed circuit boards provide electrical and mechanical connections between electronic devices and metallized patterns on boards. These solder joints are often the cause of failure in electronic packages. Solders age under storage and operational life conditions, which can include temperature, mechanical loads, and electrical current. Aging occurring at a constant temperature is called isothermal aging. Isothermal aging leads to coarsening of the bulk microstructure and increased interfacial intermetallic compounds at the solder-pad interface. The coarsening of the solder bulk degrades the creep properties of solders, whereas the voiding and brittleness of interfacial intermetallic compounds leads to mechanical weakness of the solder joint. Industry guidelines on solder interconnect reliability test methods recommend preconditioning the solder assemblies by isothermal aging before conducting reliability tests. The guidelines assume that isothermal aging simulates a "reasonable use period," but do not relate the isothermal aging levels with specific use conditions. Studies on the effect of isothermal aging on the thermal cycling reliability of tin-lead and tin-silver-copper solders are limited in scope, and results have been contradictory. The effect of electrical current on solder joints has been has mostly focused on current densities above 104A/cm2 with high ambient temperature (&#8805;100oC), where electromigration, thermomigration, and Joule heating are the dominant failure mechanisms. The effect of current density below 104A/cm2 on temperature cycling fatigue of solders has not been established. This research provides the relation between isothermal aging and the thermal cycling reliability of select Sn-based solders. The Sn-based solders with 3%, 1%, and 0% silver content that have replaced tin-lead are studied and compared against tin-lead solder. The activation energy and growth exponents of the Arrhenius model for the intermetallic growth in the solders are provided. An aging metric to quantify the aging of solder joints, in terms of phase size in the solder bulk and interfacial intermetallic compound thickness at the solder-pad interface, is established. Based on the findings of thermal cycling tests on aged solder assemblies, recommendations are made for isothermal aging of solders before thermal cycling tests. Additionally, the effect of active electrical current at 103 A/cm2 on thermal cycling reliability is reported

Pulse Electrodeposition of Lead-Free Tin-Based Composites for Microelectronic Packaging

This chapter provides a detailed overview of the various Sn-based composites solders reinforced with ceramic nanoparticles. These solders are lead free in nature and are produced by various process like powder metallurgy, ball milling, casting as well as simple and economic pulse co-electrodeposition technique. In this chapter, various electrodeposited composite solders, their synthesis, characterization, and evaluation of various properties for microelectronic packaging applications, such as microstructure, microhardness, density and porosity, wear and friction, electrochemical corrosion, melting point, electrical resistivity, and residual stress of the monolithic Sn-based and (nano)composite solders have been presented and discussed. This chapter is divided into the following sections: such as introduction to microelectronic packaging, synthesis routes for solders and composites, various nanoreinforcement, and the mechanism of incorporation in solder matrix, the pulse co-electrodeposition technique, the various factors affecting composite deposition, and the improved properties of composite solders over monolithic solders for microelectronic packaging applications are also summarized here

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

Microstructures and properties of new Sn-Ag-Cu lead-free solder reinforced with Ni-coated graphene nanosheets

© 2015 Elsevier B.V. All rights reserved. This paper deals with microstructures and properties of SAC305 lead-free solder reinforced with graphene nanosheets (GNS) decorated with Ni nanoparticles (Ni-GNS). These Ni-coated GNS nanosheets were synthesized by an in-situ chemical reduction method. After morphological and chemical characterization, Ni-GNS were successfully integrated into SAC305 lead-free solder alloy with different weight fractions (0, 0.05, 0.1 and 0.2 wt.%) through a powder metallurgy route. The obtained composite solders were then studied extensively with regard to their microstructures, wettability, thermal, electrical and mechanical properties. After addition of Ni-GNSs, cauliflower-like (Cu,Ni)6 Sn5 intermetallic compounds (IMCs) were formed at the interface between composite solder joint and copper substrate. Additionally, blocky Ni-Sn-Cu IMC/GNS hybrids were also observed homogenously distributed in the composite solder matrices. Composite solder alloys incorporating Ni-decorated GNSs nanosheets showed slightly reduced electrical resistivity compared to the unreinforced SAC305 solder alloy. With an increase in the amount of Ni-GNS, the composite solders showed an improvement in wettability with an insignificant change in their melting temperature. Mechanical tests demonstrated that addition of 0.2 wt.% Ni-GNS would result in 19.7% and 16.9% improvements in microhardness and shear strength, respectively, in comparison to the unreinforced solders. Finally, the added Ni-GNS reinforcements in the solder matrix were assessed with energy-dispersive X-ray spectroscopy, scanning electron microscopy and Raman spectroscopy