Point Alloy Research Articles

Point Defects and Alloy Incorporation in Ultrawide Bandgap β-(AlxGa1-x)2O3 Films

Point Defects and Alloy Incorporation in Ultrawide Bandgap <i>β</i>-(Al_xGa_1-x)₂O₃ Films

Metamorphic barcodes based on lithographically defined microdots incorporating nanoparticles of phase change materials

Printed barcode lacks distributability as each barcode associated with sample cannot be divided when multiple copies of the same barcode are needed for forensic analysis. This article reports a metamorphic barcode with desired distributability to label objects (liquids or solids) in a covert and high-fidelity manner using polymer microdots containing a panel of phase change nanoparticles (low melting point metal or alloy). The microdots can be made with photolithography at large quantity or serial laser fabrication and have unique serialization numbers based on the melting characteristics of nanoparticles. The microdots can be distributed evenly in liquid or attached on various location of an object and decoded with differential scanning calorimeter. Incorporation of magnetic nanoparticles allows facile collection of polymer microdots with a magnet. The microdots are non-toxic and stable over one year without losing coding information and have higher large labeling capacity than other covert barcode systems.

Posture Following Fixture Method in Large Components Flexible Assembly

How to keep and fasten reliably the adjusted posture is always a key problem in large components assembly such as airplane. Based on the phase-change principle of low-melting-point alloy,a new posture following fixture method of large components and a posture following fixture are presented,and it is proved feasible and reliable by a series of experiments and calculations. The method is described as follows:heat and melt the low-melting-point alloy in the cylindrical metal,insert the mandrel rigidly jointed with the large component into the melted alloy,and cool the metal to keep and fasten reliably the mandrel without posture change,and lock the inner core rigidly connected with the cylindrical metal,reheat and remelt the low-melting- point alloy again to release the mandrel and to resume the adjustable posture of the large component.

Electrically Conductive Adhesives for Electronic Packaging and Assembly Applications

Some recent advances in materials, structures and properties that affect the mechanical and electrical characteristics and reliability performance of electrically conductive adhesives (ECAs) are discussed. This is done in the context of electronic packaging and assembly applications. Micro-silver-filled epoxy ECAs (with an average silver particle size of 5 μm) modified by addition of a conducting polymer, low melting point (LMP) alloys, or nanoparticles (average particle size of 80 nm) are described and compared with respect to volume resistivity, tensile strength and adhesion to copper. To understand the conduction and sintering behaviors of the various ECA formulations, SEM, optical microscopy and X-ray photoelectron spectroscopy (XPS) are used to investigate the micro-structure and chemical nature of the cured ECAs. Volume resistivity of the specially formulated adhesives is in the range of 10–4 to 10–6 Ohm cm. Adhesives formulated with a conducting polymer exhibit the greatest tensile strength with copper when compared to the other formulations investigated. The conducting polymer-modified ECA exhibited electrical conductivity on the order of that achieved with conventional ECAs. Hence, good electrical performance is achieved concurrent with superior mechanical properties. It was found that with increasing curing temperature, the volume resistivity of all ECAs decreased. This is attributed to sintering of metal particles at higher temperatures. Incorporation of nanoparticles reduces sintering temperature. Sintering of ECAs with micrometer-scale silver particles was further evaluated using high temperature/pressure lamination. A continuous metallic network resulted when the lamination temperature was greater than 300°C. Electrical stability of ECA joints with aluminum was evaluated by stress testing in an environment of elevated temperature and humidity. A thin layer of silane-based coupling agent on the aluminum surfaces retards the degradation of the electrical properties of the joint. In general, proper preparation of the metal surface to which an ECA is mated is critical for maintaining both electrical and mechanical performances.

Development of conductive adhesive materials for via fill applications

As mobile computing and telecommunication electronics are spreading fast, a demand for microelectronics packaging schemes for high density, fine pitch, high performance and low cost becomes even more severe. Specifically, the conventional printed circuit board (PCB) with plated-through-hole (PTH) vias is difficult to justify its manufacturing cost as well as the packaging density requirement. To meet this challenge, several new manufacturing schemes of high density and high performance PCB have been recently introduced such as surface laminar circuit (SLC), any layer inner via hole (ALIVH) and others. This new PCB fabrication process is categorized as sequential build-up (SBU) or build-up multilayer (BUM) using laminate-based substrates, where via holes are filled with a conductive paste material to make reliable vertical or Z-interconnects. In this paper, a new electrically conducting paste material to be used for via filling is introduced. The new conducting material consists of a conducting filler powder coated with a low melting point metal or alloy, a mixture of several thermoset resins, and other minor organic additives. By varying the filler content and resin chemistry, several formulations have been produced to fill via holes with a high aspect ratio. Via fill experiments have been performed to demonstrate void-free microstructure with good electrical continuity. Various bulk properties such as thermal, electrical and mechanical have also been characterized to understand the material behavior during via filling as well as the field service.

Characterization of electroplated bismuth-tin alloys for electrically conducting materials

Electrically conducting adhesive materials are promising alternatives for lead (Pb)-containing solders in microelectronic applications. However, most common silver-filled epoxy materials have various limitations to meet the requirements of the solder joints yet. To overcome these limitations, several new formulations have been developed recently. Among them, a new high conductivity Pb-free, conducting adhesive developed for low temperature applications has been previously reported. This conducting adhesive contains a conducting copper filler powder coated with a low melting point metal or alloy, such as Sn or BiSn alloys. The low melting point layer serves as a joining material among the filler particles as well as to the substrate. In this paper, characterization of electroplated BiSn alloys on a Cu substrate is reported for their microstructure, electrical properties, oxidation behavior, and others. The experimental results have provided a better understanding of the joining mechanism of the newly developed Pb-free conductive adhesive materials.

A model for the formation of the Earth's core

The recent discovery of a phase transformation in Fe0.94O by Jeanloz and Ahrens has allowed a more detailed development of a model for core formation involving oxygen as the principal light alloying element in the core. It is predicted, based on calculations, that an increasing pressure in the system FeO‐MgO will result in a gradual exsolution of an almost pure high‐pressure phase FeO(hpp), leaving an iron‐depleted (Fe, Mg)O rocksalt (B1) phase. We also predict that FeO(hpp) will form a low‐melting point alloy with Fe at high temperature and high pressure. On the basis of our interpretations, we have constructed a model for core segregation. Assuming the earth to have accreted from the primordial solar nebula as a relatively homogeneous mixture of metallic iron and silicate‐oxide phases, core segregation involving oxygen would commence at a depth where pressure is sufficiently high to cause exsolution of FeO(hpp) from the rocksalt phase, and temperature is sufficiently high to allow formation of an Fe‐FeO(hpp) melt. A gravitational instability arises, leading to vertical differentiation of the earth as molten blobs of the metal sink downwards to form the core and the residual depleted silicate material coalesces to form large bodies which rise diapirically upwards to form the mantle.

Improvements i.o.r.t. the melting and casting of high melting point metals or alloys

Improvements i.o.r.t. the melting and casting of high melting point metals or alloys