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During the thermal processing of thin films in which low intensity line heat sources are used, extended processing times are often required to reach steady state (˜15 sec). In addition, the melting of the film may occur some time after processing has begun, and therefore there is no initial melting condition within the film. In such cases, computer simulations may become very time consuming, and the development of an efficient computational method which incorporates the initial formation of the melt during processing is necessary. A general technique was developed to accurately model two‐dimensional heat conduction in a multilayer film structure with one‐dimensional phase change in one of the thin films. These conditions frequently exist in thin film thermal processing when the thermal gradient through the thickness of the melting film can be considered negligible. The method involves an implicit formulation of the modified enthalpy method. The solid/liquid interface energy‐balance equation is taken into account which allows the exact location of the interface to be tracked within a control volume. A comparison is made between the explicit and implicit modified methods to test efficiency and accuracy. The implicit method is then applied to the zone‐melting recrystallization of a silicon thin film in a multilayer structure.

The purpose of this paper is to produce and investigate the interfacial reaction between Sn‐3.0Ag‐0.5Cu (SAC305) thin films and Cu substrates by solder reflow at various temperatures and times.

SAC305 thin films were deposited on copper substrates using a thermal evaporation technique. The as‐deposited SAC305/Cu was then reflowed on a hot plate at temperatures of 230, 240, 250 and 260°C for 30 s. In addition, solder reflow was conducted at a constant temperature of 230°C for 5, 10, 15 and 20 s. The microstructure, phase and thickness of the intermetallic compounds (IMCs) formed were determined after cross‐sectional metallographic preparation.

Cu₆Sn₅ and Cu₃Sn were observed at the as‐reflowed SAC305/Cu interfacial region. The IMC thicknesses increased with the higher reflow temperature and longer reflow times.

Up to now, studies on the thin film characteristics of SAC305 lead‐free solder have been very limited. Thus, this paper presents the deposition of SAC305 thin film by a thermal evaporation technique and its characteristics after solder reflow.

The purpose of this study is to investigate the mechanisms of degradation of aluminum metallization under conditions of thermal shock caused by rectangular current pulses (amplitude j < 8 × 10¹⁰ A/m², duration t < 800 μs).

The results were obtained using oscillography and optical microscopy and through the construction of an empirical model of the thermal degradation of metallization systems.

Initially, for the authors’ studies, they deduced an equation that associated the depth of melting with the parameters of a current pulse.

The authors were able to observe effects only in systems with appropriate adhesion of the thin metal films. For the systems with bad adhesion, the main mechanisms of degradation were associated with the melting of the metal, the formation of melted drops (up to 20 mcm in size) and the movement of these drops along the electrical field due to the electrocapillary effect.

The mechanisms the authors studied could only occur in high-power semiconductor devices.

The principal mechanism of melting of a metallization track is linked to the heat dissipation at the interface of solid and liquid phases under conditions of thermal shock. The authors estimated the mechanical stresses in subsurface layers of silicon in the proximity of a non-stationary thermal source. The authors’ results show that the mechanical stresses that are strong enough to form dislocations emerge with current flow with power measuring approximately 0.7 Pkr.

‘Fluxing and Cleaning in Electronics Soldering’ The Grosvenor Hotel, London, 22 February 1989. ‘To clean or not to clean?’ ‘Aqueous or solvent cleaning?’ ‘What is the future for CFCs and other chlorinated solvents?’ The electronics assembly industry is ringing with such questions that make the cleaning of electronic assemblies the key issue for 1989—an issue that urgently requires answers that have the stamp of authority based on fact rather than speculation. This BABS seminar was therefore very timely and attracted a large audience to listen to eight presentations from speakers representing the cleaning equipment manufacturers, flux manufacturers, MoD quality assurance, and users' experience, as well as background on solvents in the environment.

The purpose of this paper is to examine the corrosion behaviors of SAC305 thin film solder alloy in 6 M KOH solution.

The corrosion behavior of bare Cu, as-deposited SAC305/Cu and as-reflowed SAC305/Cu thin films at varying temperatures, was investigated by means of potentiodynamic polarization in a 6 M KOH solution. The microstructure, phase and thickness of the intermetallic compounds formed were determined before and after polarization.

Bare Cu was found to possess the best corrosion resistance, whereas the as-deposited SAC305/Cu had the lowest corrosion resistance. As-reflowed SAC305/Cu with an exposed Cu₃Sn layer exhibited better corrosion resistance than did Cu₆Sn₅. The Ag₃Sn phase has the noblest characteristic because it was retained and did not dissolve in the KOH solution. All of the samples contained the corrosion products of oxide. Bare Cu obeys the well-known duplex structure of a Cu₂O/CuO, Cu(OH)₂ layer. For as-reflowed SAC305/Cu, the corroded surface was also mainly composed of SnO and SnO₂.

New analysis on the polarization of thin film characteristics of SAC305 lead-free solder in alkaline solution.

The authors performed FACET (Investigation on Mechanism of Faceted Cellular Array Growth) experiments under long duration microgravity on the International Space Station (ISS) in 2010. The temperature and concentration distributions in the melt during the growth were precisely measured with high spatial resolution. Negative temperature gradient as well as negative concentration gradient ahead of the S/L interface can be expected to be the driving forces of the morphological instability. It is evident that the conventional model based on the frozen temperature approximation is insufficient to explain the growth mechanism of the faceted cellular array.

Material formulation, structuring and modification are key to increasing the unit volume complexity and density of next generation electronic packaging products. Laser processing is finding an increasing number of applications in the fabrication of these advanced microelectronic devices. The purpose of this paper is to discuss the development of new laser‐processing capabilities involving the synthesis and optimization of materials for tunable device applications.

The paper focuses on the application of laser processing to two specific material areas, namely thin films and nanocomposite films. The examples include BaTiO₃‐based thin films and BaTiO₃ polymer‐based nanocomposites.

A variety of new regular and random 3D surface patterns are highlighted. A frequency‐tripled Nd:YAG laser operating at a wavelength of 355 nm is used for the micromachining study. The micromachining is used to make various patterned surface morphologies. Depending on the laser fluence used, one can form a “wavy,” random 3D structure, or an array of regular 3D patterns. Furthermore, the laser was used to generate free‐standing nano and micro particles from thin film surfaces. In the case of BaTiO₃ polymer‐based nanocomposites, micromachining is used to generate arrays of variable‐thickness capacitors. The resultant thickness of the capacitors depends on the number of laser pulses applied. Micromachining is also used to make long, deep, multiple channels in capacitance layers. When these channels are filled with metal, the spacings between two metallized channels acted as individual vertical capacitors, and parallel connection eventually produce vertical multilayer capacitors. For a given volume of capacitor material, theoretical capacitance calculations are made for variable channel widths and spacings. For comparison, calculations are also made for a “normal” capacitor, that is, a horizontal capacitor having a single pair of electrodes.

This technique can be used to prepare capacitors of various thicknesses from the same capacitance layer, and ultimately can produce variable capacitance density, or a library of capacitors. The process is also capable of making vertical 3D multilayer embedded capacitors from a single capacitance layer. The capacitance benefit of the vertical multilayer capacitors is more pronounced for thicker capacitance layers. The application of a laser processing approach can greatly enhance the utility and optimization of new materials and the devices formed from them.

Laser micromaching technology is developed to fabricate several new structures. It is possible to synthesize nano and micro particles from thin film surfaces. Laser micromachining can produce a variety of random, as well as regular, 3D patterns. As the demand grows for complex multifunctional embedded components for advanced organic packaging, laser micromachining will continue to provide unique opportunities.

This study aims to review the recent advancements in high entropy alloys (HEAs) called high entropy materials, including high entropy superalloys which are current potential alternatives to nickel superalloys for gas turbine applications. Understandings of the laser surface modification techniques of the HEA are discussed whilst future recommendations and remedies to manufacturing challenges via laser are outlined.

Materials used for high-pressure gas turbine engine applications must be able to withstand severe environmentally induced degradation, mechanical, thermal loads and general extreme conditions caused by hot corrosive gases, high-temperature oxidation and stress. Over the years, Nickel-based superalloys with elevated temperature rupture and creep resistance, excellent lifetime expectancy and solution strengthening L12 and γ´ precipitate used for turbine engine applications. However, the superalloy’s density, low creep strength, poor thermal conductivity, difficulty in machining and low fatigue resistance demands the innovation of new advanced materials.

HEAs is one of the most frequently investigated advanced materials, attributed to their configurational complexity and properties reported to exceed conventional materials. Thus, owing to their characteristic feature of the high entropy effect, several other materials have emerged to become potential solutions for several functional and structural applications in the aerospace industry. In a previous study, research contributions show that defects are associated with conventional manufacturing processes of HEAs; therefore, this study investigates new advances in the laser-based manufacturing and surface modification techniques of HEA.

The AlxCoCrCuFeNi HEA system, particularly the Al0.5CoCrCuFeNi HEA has been extensively studied, attributed to its mechanical and physical properties exceeding that of pure metals for aerospace turbine engine applications and the advances in the fabrication and surface modification processes of the alloy was outlined to show the latest developments focusing only on laser-based manufacturing processing due to its many advantages.

It is evident that high entropy materials are a potential innovative alternative to conventional superalloys for turbine engine applications via laser additive manufacturing.

An overview has been presented on the topic of alternative surface finishes for package I/Os and circuit board features. Aspects of processability and solder joint reliability were described for the following coatings: baseline hot‐dipped, plated, and plated‐and‐fused 100Sn and Sn‐Pb coatings; Ni/Au; Pd, Ni/Pd, and Ni/Pd/Au finishes; and the recently marketed immersion Ag coatings. The Ni/Au coatings appear to provide the all‐around best options in terms of solderability protection and wire bondability. Nickel/Pd finishes offer a slightly reduced level of performance in these areas which is most likely due to variable Pd surface conditions. It is necessary to minimize dissolved Au or Pd contents in the solder material to prevent solder joint embrittlement. Ancillary aspects that include thickness measurement techniques; the importance of finish compatibility with conformal coatings and conductive adhesives; and the need for alternative finishes for the processing of non‐Pb bearing solders are discussed.

This paper aims to demonstrate low-temperature bonding for piezoelectric materials at temperatures well below the relevant Curie temperatures so as to avoid depolarization of the piezoelectric material during bonding.

Au-coated test samples of lead zirconate titanate (PZT) are bonded to a WC-based resonant backing layer with In–Bi eutectic material in which the In–Bi metal system is a preform or thin, evaporated layers. The bonded samples are characterized using electrical impedance spectroscopy and cross-section microscopy. The first technique verifies the integrity of polarization and reveals the quality of the bondline in a non-destructive manner, particularly looking for voids and delaminations. The latter technique is destructive but gives more precise information and an overview of the structure.

Successful low-temperature (115°C) bonding with intact PZT polarization was demonstrated. The bondlines show a layered structure of Au/Au–In intermetallic compounds (with Bi inclusions)/Au, capable of withstanding temperatures as high as 271°C before remelting occurs. For bonded samples using In–Bi preform, repeatable bonds of high quality (very little voiding) were obtained, but the bonding time is long (1 h or more). For bonded samples using evaporated thin films of In–Bi, bonding can be performed in 30 min, but the process needs further optimization to be repeatable.

Low-temperature solid-liquid interdiffusion (SLID) bonding is a novel technique, merging the fields of low-temperature solder bonding with the SLID/transient liquid phase (TLP) approach, which is normally used for much higher temperatures.