Films Before Thermal Processing

If the amount of deflection at the center of the sample is small ( 10%) compared with the thickness of the substrate, if the effective Youngs modulus of the film and the substrate are approximately equal, = [. y/(l — f) l[EJ — V )] 1, and if the film is much thinner than the substrate, the magnitude of the stress, a, is related to the radius of curvature of the substrate, R, by the relation  

The curvature of the substrate can be determined by a variety of techniques. For all of these techniques, to increase the sensitivity of the curvature measurement, a thin substrate, or the order of 100 [tm thick, may be used, keeping in mind that 

Characterization of Thick Fiims During Thermai Processing 

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In order to determine whether the new nanotubule electrode shows improved performance, a control electrode composed of the same material but prepared via a more conventional method is required. This control LiMn204 electrode was prepared by applying the precursor solutions described above directly onto a 1 cm Pt plate and thermally processing as before. Scanning electron micrographs showed that these films consisted of LiMn204 particles with diameters of —500 nm [124]. Spectrophotomet-ric assay showed that this control electrode also contained 0.75 mg of LiMn204 per cml A polypyrrole coat identical to that applied to the tubular electrode (0.065 mg) was also applied to this control electrode. 

The heat supplied by the barrel heaters has to be conducted through the entire thickness of the barrel and through the entire thickness of the melt film before it can reach the solid bed. Problems with this energy transport are considerable heat losses by conduction, convection, and radiation. Another, probably more severe, problem is the low thermal conductivity of the polymer. The heat has to be transferred across the entire melt film thickness. Therefore, the conductive heat flux will be small, particularly when the melt film thickness is large. Increasing the barrel temperature can accelerate the heating process however, this temperature is limited by the possibility of degradation of the polymer. 

The advent of the Durham route developed by teams at Durham University and BP Research introduced higher-quality material and an important concept in the preparation of conjugated polymers [98]. The Durham route involves the preparation of trans-FA via a soluble precursor polymer, which can be cast and the resultant films then stretch-aligned before thermal conversion (Fig. 4.17). The use of the precursor route allows processing and alignment to be achieved on what is otherwise an intractable material. Other methods that will be discussed later are the prerequisite to any real application of these materials. 

The second method is based on the use of polyimides with lower glass transition temperatures that can be melt-processed. For example, intrinsically photosensitive preimidized polymers formed by reacting 3,3 4,4 -benzopheno-netetracarboxylic acid dianhydride (BTDA) with methyl-substituted 4,4 -methylenebisbenzeneamine (MDA), blended to epoxy resins, give high strength laminate with copper. Poly(isoimides), which exhibit good melt-flow properties before thermal isomerization to imides, are also used to make flexible circuits. In the last process copper is electroless plated on polyimide film such as Kapton 200H. 

Spray pyrolysis involves the spraying of a solution, usually aqueous, containing soluble salts of the constituent atoms of the desired compounds, onto heated substrates. A typical example of the spray pyrolysis process is deposition of tin oxide films by thermal dissociation of an alcoholic solution of SnCl Whether or not the process can be classified as CVD depends on whether the liquid droplets vaporize before reaching the substrate or react on it after splashing. Several workers have used preheating... 

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