Formation of Cu Nanodots on Diamond Surface to Improve Heat Transfer in Cu/D Composites

Diamond‐dispersed copper matrix (Cu/D) composite materials with different interfacial configurations are fabricated through powder metallurgy and their thermal performances are evaluated. An innovative solution to chemically bond copper (Cu) to diamond (D) has been investigated and compared to the traditional Cu/D bonding process involving carbide‐forming additives such as boron (B) or chromium (Cr). The proposed solution consists of coating diamond reinforcements with Cu particles through a gas–solid nucleation and growth process. The Cu particle‐coating acts as a chemical bonding agent at the Cu–D interface during hot pressing, leading to cohesive and thermally conductive Cu/D composites with no carbide‐forming additives. Investigation of the microstructure of the Cu/D materials through scanning electron microscopy, transmission electron microscopy, and atomic force microscopy analyses is coupled with thermal performance evaluations through thermal diffusivity, dilatometry, and thermal cycling. Cu/D composites fabricated with 40 vol% of Cu‐coated diamonds exhibit a thermal conductivity of 475 W m^?1 K^?1 and a thermal expansion coefficient of 12 × 10^?6 °C^?1. These promising thermal performances are superior to that of B‐carbide‐bonded Cu/D composites and similar to that of Cr‐carbide‐bonded Cu/D composites fabricated in this study. Moreover, the Cu/D composites fabricated with Cu‐coated diamonds exhibit higher thermal cycling resistance than carbide‐bonded materials, which are affected by the brittleness of the carbide interphase upon repeated heating and cooling cycles. The as‐developed materials can be applicable as heat spreaders for thermal management of power electronic packages. The copper‐carbon chemical bonding solution proposed in this article may also be found interesting to other areas of electronic packaging, such as brazing solders, direct bonded copper substrates, and polymer coatings.

     

Architectural optimization for microelectronic packaging

The aim of this paper is to provide a methodical approach for architectural optimization of power microelectronic devices. Because critical parameters of electronic devices are linked with reliability, architectural optimization, selection of the geometrical parameters of device and optimization of these parameters by iteration method associated by numerical analysis of reliability have to be achieved. In this way, this paper discusses about a methodical and numerical approach for the optimization of reliability in electronic devices, in particular the influence of geometrical parameters on the device reliability.     

Interface analysis in Al and Al alloys/Ni/carbon composites

Nature of fibre/matrix interfaces existing in Al/C composites were investigated depending on the presence of a nickel interlayer deposited on carbon fibres and on the composition of the aluminium matrix. Auger and electron microprobe analyses were used. The role of the nickel layer on the chemical evolution of the system after a 96 h heat treatment at 600°C is discussed. The presence of this nickel layer limits the diffusion of carbon into aluminium, and thereby, eliminates the formation of a carbide interphase, Al₃C₄, which is known to lower the mechanical properties of Al/C composites. The mechanisms differ according to the composition of the matrix. In the case of pure aluminium, an Al-Ni intermetallic is formed after thermal annealing. It does not react with the carbon fibre and so inhibits the growth of Al₃C₄. In the case of the alloyed matrix (AS7G0.6), the dissolution of the Ni sacrificial layer, after annealing, does not lead to the same Al-Ni intermetallic but a thin nickel layer remain in contact with the carbon fibre avoiding formation and growth of Al₃C₄ carbide. This difference of behaviour is tentatively ascribed to the presence of silicon that segregates at the fibre/matrix interface.     

Thermal conductivity improvement of copper–carbon fiber composite by addition of an insulator: calcium hydroxide

The effects of adding calcium hydroxide (Ca(OH)₂) to a copper–CF (30 %) composite (Cu–CF(30 %)) were studied. After sintering at 700 °C, precipitates of calcium oxide (CaO) were included in the copper matrix. When less than 10 % of Ca(OH)₂ was added, the thermal conductivity was similar to or higher than the reference composite Cu–CF(30 %). A thermal conductivity of 322 W m^?1 K^?1 was measured for the Cu–Ca(OH)₂(3 %)–CF(30 %) composite. The effects of heat treatment (400, 600, and 1000 °C during 24 h) on the composite Cu–Ca(OH)₂(3 %)–CF(30 %) were studied. At the lower annealing temperature, CaO inside the matrix migrated to the interface of the copper matrix and the CF. At 1000 °C, the formation of the interphase calcium carbide (CaC₂) at the interface of the copper and CFs was highlighted by TEM observations. Carbide formation at the interface led to a decrease in both thermal conductivity (around 270 W m^?1 K^?1) and the coefficient of thermal expansion (CTE (10.1 × 10^?6 K^?1)).     

Spark plasma sintering behavior of pure aluminum depending on various sintering temperatures

We have successfully fabricated high-density pure aluminum (Al) bulk by means of a spark-plasma-sintering (SPS) process. The relative density of Al was enhanced as the sintering temperature of the SPS process increased. During the SPS process for pure Al power, the Al oxide layer on the surface of the Al particle was partially broken by the microplasma and applied pressure. The microstructures of the spark-plasma-sintered compacts obtained at various temperatures were observed by optical microscopy, field-emission scanning electron microscopy, and high-resolution transmission electron microscopy. We believe that the pinning effect, rapid heating cycle, and applied pressure played an important role in restraining the particle growth despite the increase in sintering temperature. It is feasible that the employed SPS process could be very useful to achieve fully densified Al compact.     

Stress and phase purity analyses of diamond films deposited through laser-assisted combustion synthesis

Diamond films were deposited on silicon and tungsten carbide substrates in open air through laser-assisted combustion synthesis. Laser-induced resonant excitation of ethylene molecules was achieved in the combustion process to promote diamond growth rate. In addition to microstructure study by scanning electron microscopy, Raman spectroscopy was used to analyze the phase purity and residual stress of the diamond films. High-purity diamond films were obtained through laser-assisted combustion synthesis. The levels of residual stress were in agreement with corresponding thermal expansion coefficients of diamond, silicon, and tungsten carbide. Diamond-film purity increases while residual stress decreases with an increasing film thickness. Diamond films deposited on silicon substrates exhibit higher purity and lower residual stress than those deposited on tungsten carbide substrates.     

Microstructure and chemical analysis of C/Cu/Al interfacial zones

The fibre–matrix interface in carbon–aluminium composites has been examined. Composites were prepared using uncoated carbon preforms and carbon preforms coated with copper. Auger and transmission electron microprobe microscopy were used to study the interface. The role of the copper layer on the microstructural and chemical evolution of the system after a 96 h heat treatment at 600 °C is discussed.     

PET Treatment in Different Solvents: Influence on the Adhesion After Metallization

In order to correlate the adhesion of Al/PET laminates with the number of nucleation sites, gold replicates have been observed by TEM on PET immersed in various solvents before metallization. The question of the relationship between the morphology of the aluminum films evaporated onto these treated polymers is also addressed. Treatments in water, acetone, ethanol, and methanol result in a decrease of the number of nucleation sites and of the adhesion of the subsequently-evaporated aluminum films. Chloroform behaves differently and produces the reverse effect. The special behavior of CHCl₃ is tentatively attributed to the substitution of some surface hydrogen atoms by chlorine atoms, giving rise to new active centers on the PET surface. The decrease of the adhesion in all the other cases may be determined by the decohesion of the PET skin resulting from the diffusion of solvents.     

Variability in Pheromone Communication Among Different Haplotype Populations of <Emphasis Type="Italic">Busseola fusca</Emphasis>

The relationship between pheromone composition and mitochondrial haplotype clades was investigated by coupling DNA analyses with pheromone identification and male mate searching behavior among different geographic populations of Busseola fusca. The within-population variations in pheromone blend were as great as those observed between geographic populations, suggesting that the female sex pheromone blend was not the basis of reproductive isolation between the geographic clades. Furthermore, while data from wind tunnel experiments demonstrated that most of the tested males were sensitive to small variations in pheromone mixture, there was considerable within-population variability in the observed response. The study identified a new pheromone component, (Z)-11-hexadecen-1-yl acetate, which when added to the currently used three-component synthetic blend resulted in significantly higher traps catches. The new recommended blend for monitoring flight phenology and for timing control measures for optimal efficacy of B. fusca is (Z)-11-tetradecen-1-yl acetate (62%), (E)-11-tetradecen-1-yl acetate (15%), (Z)-9-tetradecen-1-yl acetate (13%), and (Z)-11-hexadecen-1-yl acetate (10%).     

Influence of the interface structure on the thermo-mechanical properties of Cu–X (X = Cr or B)/carbon fiber composites

This study focuses on the fabrication, for power electronics applications, of adaptive heat sink material using copper alloys/carbon fibers (CF) composites. In order to obtain composite material with good thermal conductivity and a coefficient of thermal expansion close to the ceramic substrate, it is necessary to have a strong matrix/reinforcement bond. Since there is no reaction between copper and carbon, a carbide element (chromium or boron) is added to the copper matrix to create a strong chemical bond. Composite materials (Cu–B/CF and Cu–Cr/CF) have been produced by a powder metallurgy process followed by an annealing treatment in order to create the carbide at the interphase. Chemical (Electron Probe Micro-Analysis, Auger Electron Spectroscopy) and microstructural (Scanning and Transmission Electron Microscopies) techniques were used to study the location of the alloying element and the carbide formation before and after diffusion. Finally, the thermo-mechanical properties have been measured and a promising composite material with a coefficient of thermal expansion 25% lower than a classic copper/carbon heat sink has been obtained.