Coupling monolayers for protection of microelectronic circuits

Two polymeric coatings, a silicone gel (Dow Corning 6646) and an epoxy resin (Dexter FP 4402), were glob-top coated onto representative microelectronic circuits, AT&T Triple Track Testers (TTTs), and subjected to the Pressure Cooker Test (PCT). Coupling monolayers were self- assembled on the TTTs prior to encapsulation to improve the moisture protection capabilities of the coatings. Leakage current measurements were made to evaluate the effect of applied monolayers on the moisture protection capability. The moisture protection capability was assessed in short-term and long-term leakage current measurements. MHDA (16-mercaptohexadecanoic acid) and APS (gamma-aminopropyltriethoxysilane) monolayers, in combination with silicone gel and epoxy resin respectively, exhibited very good moisture protection performance.     

Use of microwaves for the synthesis and processing of materials

An overview of the synthesis of materials under microwave irradiation has been presented based on the work performed recently. A variety of reactions such as direct combination, carbothermal reduction, carbidation and nitridation have been described. Examples of microwave preparation of glasses are also presented. Great advantages of fast, clean and reduced reaction temperature of microwave methods are emphasized. The example of ZrO₂-CeO₂ ceramics has been used to show the extraordinarily fast and effective sintering which occurs in microwave irradiation.     

Morphology–property relationship in oriented PET films: Microstructural reorganization during heat treatment

Morphology–property relationships for simultaneously biaxially stretched films and heatset with fixed dimensions in the temperature range of 100–240°C have been studied. The observed transition in various properties at 180°C can be explained on the basis of microstructural changes caused by competition among several processes, such as crystallization, solid-state thickening, melting, and molecular relaxation as well as by melting and recrystallization. The resulting structures and, thereby, the properties are different in temperature Regime-II (T_g to T_max) and Regime-III (T_max to T_m). In Regime-II, the high rate of crystallization compared to the rate of molecular relaxation develops a constrained amorphous phase, whereas the predominant melting and recrystallization process in Regime-III generates the relaxed amorphous phase. The structural reorganization during heat treatment is almost the same for uniaxially oriented film, fibers, and biaxially oriented films prepared under similar processing conditions. © 1994 John Wiley & Sons, Inc.     

Thermogravimetric studies of Y1Ba2Cu3O7−x superconductors

The synthesis conditions and oxygen stoichiometry were determined using a thermogravimetric analyser. The kinetics of oxygenation at different temperatures and at different atmospheres were studied. The oxygenation kinetics were found to be sensitive to porosity of the material. The appropriate oxygenation temperature was found to be 400 °C. For oxygenation temperatures below 400 °C, the oxygenation occurs by a nucleation and growth process, whereas for higher temperatures it is diffusion limited.     

Ordering and structural transformations in Ni3Al alloys

X-ray diffraction profile studies on the filings of stoichiometric and off-stoichiometric compositions of Ni₃Al alloys, with and without boron additions, were conducted to clarify some of the significant anomalies noticed in the literature. The long-range order parameter was estimated as a function of temperature in all the four alloys from (1 0 0)/(2 0 0) and (1 1 0)/(2 2 0) pairs of reflections. The L1₂ structure appears to attain a maximum stability at about 600 °C, around which temperature its order parameter was close to the theoretical value. Above 600 °C, this structure becomes less stable and there appears to be formation of an additional structure of a lower symmetry. Also in the Materials Science Section, Faculty of Mechanical Engineering, University of Twente, Enschede, The Netherlands.     

151Eu Mössbauer studies on Zn-doped EuBa2Cu3O7−y

¹⁵¹Eu Mössbauer studies have been performed on the compounds EuBa₂(Cu_1?x Zn _x )₃O_7?y withx=0·0, 0·025, 0·05, 0·075 and 0·1. The parent compound, EuBa₂Cu₃O_7?y is superconducting with a transition temperature (T _c ) of 88 K.T _c is depressed as Zn is substituted for Cu in this system and the compounds withx>0·05 do not show superconductivity down to 12 K.¹⁵¹Eu Mössbauer studies at 295 K show a single Mössbauer line in all the compounds (whether superconducting or not) with isomer shift value typical of Eu^{3 +} ion. Further, the isomer shift values are nearly independent ofx and the temperatures down to 10 K. These observations imply that the Cu-O network responsible for superconductivity is very weakly coupled to the Eu sublattice.     

Nickel–Alumina Functionally Graded Materials by Electrophoretic Deposition

Electrophoretic deposition has been used to synthesize nickel–alumina, functionally graded materials from NiO and alumina suspensions in ethanol. Suspension stability and the kinetics of deposition were studied to determine optimum conditions. Deposition starts with an alumina suspension into which a stream of NiO suspension is injected at various flow rates to obtain the desired profiles. The latter were controlled by varying the deposition current density and component flow rate. The green bodies obtained were sintered in Ar/H₂ atmosphere to reduce the NiO to nickel. Various gradation profiles were obtained illustrating the facility of EPD to synthesize continuously graded materials. NiO was used as the precursor for nickel to alleviate settling and rough columnar deposit problems.