Multilayer Inspection

Fig. 17 shows the adsorption isotherms of all (undimerized and dimerized) particles. Except for a very fast increase of adsorption connected with filling of the first adlayer, the adsorption isotherm for the system A3 is quite smooth. The step at p/k T 0.28 corresponds to building up of the multilayer structure. The most significant change in the shape of the adsorption isotherm for the system 10, in comparison with the system A3, is the presence of a jump discontinuity at p/k T = 0.0099. Inspection of the density profiles attributes this jump to the prewetting transition in the... 

Arrangements for chemical feed and control also were limited. In these boilers, 1/2 inch to perhaps 1 inch (12.5-25 mm) of multilayered scale could easily deposit during the period between waterside inspections. It was often assumed that these operating conditions were the norm, that regular acid cleaning was a way of life, and that nothing better could be expected. 

Around 1967, Broekhoff and de Boer [16], following Derjaguin [17], pointed out that the supposition introduced in the derivation of the Kelvin equation, viz. the equality of the thermodynamic potential of the adsorbed multilayer to the thermodynamic potential of the liquified gas (see Eqn. 12.28), cannot be correct. This can be seen immediately from an inspection of the common t curve (Fig. 12.5) at each t value lower than, say, 2 run, the relative equilibrium pressure is lower than 1, the equilibrium pressure of the liquefied gas. 

Inspection of the common normalized isotherm in Figure 9.3 reveals a number of distinctive features. At very low plp°, the isotherm is slightly convex with respect to the p/p° axis and it is evident that the linear, Henry s law region does not extend above p/p° 5x 10-4. Although the isotherm is not truly stepwise (i.e. not a true Type VI isotherm), it does exhibit a characteristic monolayer step. This is followed by a wavy second layer region and then a smooth multilayer curve. Thus, as the multilayer coverage is increased, the isotherm appears to conform to the normal Type II shape. 

A sequence of ATR spectra for a chalcocite (CU2S) electrode in the presence of 10 " M KEX at increasing potentials is shown in Fig. 1.31a [514]. The spectra observed from —0.25 V were attributed to Cu(I)EX (Fig. 7.23). The potential dependence of the VasCOC band, the flotation recovery, and the current are shown in Fig. 1.34b. After correcting for the difference in the EX concentration in the flotation test (a concentration of 1.9 x 10 M implies a cathodic shift of the flotation curve by 0.043 V), the onset of the flotation is seen to coincide with the appearance of the IR signal and the first two peaks in the voltammogram. Thus the spectra suggest that the maximum flotation may be a result of the formation of multilayers of Cu(I)EX, and the current peaks can be attributed to different mechanisms of copper xanthate formation. However, a closer inspection of the spectra shown in Fig. 1.31a reveals a number of differences from the spectrum of bulk Cu(I)EX, which were ignored by the authors. At potentials below -1-0.05 V,... 

A simple inspection of the BET assumptions clearly shows that the BET equation cannot give an adequate physical description of multilayer formation. 

Inspection is an integral part of the screen-printing process, particularly where complex multilayer circuits are involved. A single void, anywhere in any trace or in any layer, can result in the entire structure being scrapped. 

Inspecting printed films in the wet state is somewhat difficult because of the high reflectivity of the film. In the dry or fired state, inspection is easier as there is more of a contrast with the substrate. For laboratory or small manufacturing operations, a microscope with backlighting is an essential tool. It is very easy to see voids or thin areas because alumina and beryllia are translucent to a certain degree. However, for multilayer applications or thicker substrates, this method is inadequate, and one must revert to inspection using top lighting. 

X-ray technology is used to inspect the innerlayers of multilayer PCBs and to verify that the drill pads are located properly. Innerlayer shift is identified easily in an x-ray image, and a simple technique can be used to measure the misalignment accurately. In developing the PCB artwork, a set of stacked pads are located ia the coupon area.These are inspected and a best-fit centering is calculated. 

This method is a good tool to increase yields of complex multilayer panels as well as multilayer flex material. The actual layers are exposed and inspected to determine their position with... 

With complex multilayer product, optical inspection will not be able to identify assem-bly/contamination-induced defects internal to the board in any case, and may still be limited in cases of contaminants or very fine-geometry shorts and opens on external layers. The equipment is somewhat slower than universal grid test systems, particularly when run at very high resolution. For such reasons, it is still not common practice to employ optical inspection (by itself) as a substitute for electrical testing. This may be a method that develops further in the future or that finds acceptance in special circumstances. 

Registration, Layer to Layer, X-Ray Method. The x-ray method provides a nondestructive way to inspect layer-to-layer registration of internal layers of multilayer PCBs. It utilizes an x-ray machine and either Polaroid film or camera sensors to image the internal layers. The multilayer PCB is x-rayed in a horizontal position.The x-ray images are then examined for evidence of hole breakout of the internal lands.The lack of an internal annular ring denotes severe misregistration of layers (see Fig. 51.12). 

EIA-479A Film-Paper, Film Dielectric Capacitors for 50/60 Hz Voltage Doubler Power Supplies EIA-535 Series of Detail Specifications on Fixed Tantalum Capacitors EIA-595 Visual and Mechanical Inspection Multilayer Ceramic Chip Capacitors ElA/IS-35 Two-Pin Dual In-Line Capacitors EIA/IS-36 Chip Capacitors, Multi-Layer (Ceramic Dielectric)... 

In addition to providing information regarding the capacity of the solid surface for the liquid phase adsorbate, the adsorption isotherm can also provide valuable conformational and thermodynamic information. The data of O Fig. 10.14 presents the adsorption isotherms for poly(methylmethacrylate) (PMMA) on oxidized aluminum and silicon surfaces (Watts et al. 2000). O Figure 10.14a shows the behavior at low and medium concentrations, and this follows the expected form for chemisorption. The data at higher concentration, O Tig 10.14b, shows a sharp rise in adsorption that is consistent with multilayer rather than monolayer adsorption. The answer, however, lies in the conformation of the molecules at low concentrations they are in an extended form (illustrated by the schematic inset of Fig. 10.14a), while at higher concentrations they are in a more compact form and pack more efficiently on the surface (shown in the schematic of O Fig. 10.14b). Another usefiil feature that can be established qualitatively from inspection of the isotherms of O Fig. 10.14a is the heat of adsorption. The sharpness of the knee at low concentration provides an indication of this value, thus for the data of PMMA on aluminum and silicon the heat of adsorption for PMMA on aluminum is more exothermic than on silicon. This is as one would expect as the silicon surface will be rich in acidic silanol groups very receptive to the basic PMMA, whilst the aluminum oxide surface is amphoteric and will not react so readily with PMMA. 

Coating thicknesses were measured with a Tooke Inspection Gauge. All of the samples had multilayers of paint (not all lead pigmented), as revealed by scanning electron microscopy, which identified individual layers of paint, and energy dispersive X-ray analysis (EDXRA), which determined the presence of lead in individual layers (see Table 11.4). 

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