Hermetically sealed assemblies

Hermetically sealed assemblies were not as compatible and, as expected, did not tolerate the pressure of the cleaning process. A motor stater, composed of wire windings potted in place with an unfilled epoxy was also found to be incompatible with the cleaning process. In this case, the carbon dioxide would fill voids in the epoxy and then during depressurization cause fi cturing at these voids. Later this problem was alleviated by cleaning at a lower pressure and decreasing the decompression rate. 

These pumps incorporate an electric motor whose rotary assembly is hermetically sealed inside a stainless steel or exotic alloy can. The motor, pump shaft and bearings all operate wet inside the pumped liquid as show ii in Figure 6-12. 

The only single-phase item involved is the solution heat exchanger, which is intensified by the use of laminar flow in a matrix of fine channels. A sketch of the single-effect Rotex (13) design is shown in Figure 15, where it can be seen that a hermetically sealed rotating disc assembly fulfills the four functions listed. The working fluid consists of a water solution of either mixed alkali metal hydroxides or lithium bromide. 

In high-frequency induction sealing a metallic component is located at the point of joining in such a manner as not to inhibit the flow of molten material the inset is designed to ensure a flow of material sufficient to give a seal of the strength required. The method is used mainly for the assembly of moulded components, or for the sealing of plastic bottles in instances where a tamper-evident hermetic seal is needed. 

In the case of in-use stiction, it is hypothesized that moisture from the environment (relative humidity) comes in contact with the MEMS structural surfaces. If, during operation, these structures come in contact, the moisture can cause a temporary bond that, like release stiction, can then become permanent with time. To reduce in-use stiction, three basic techniques have been attempted. The first is to use a hermetic seal around the microstructure to eliminate the possibility of moisture encountering the structure. Secondly, the use of techniques to minimize the work of adhesion has been employed. Specifically, Houston et al. have used ammonium fluoride to reduce the work of adhesion on surface micromachined structures [59, 60]. Lastly, various coatings and/or surface treatments have been used on the microstructure to eliminate the chance of contact between two surfaces that have the prevalence to stick (e.g., polysilicon and silicon, each material with a native oxide). The University of California, Berkeley has pioneered techniques of using self-assembled layer monolayer coatings to minimize in-use stiction [18, 25, 59, 61]. Also, other researchers have used fluorocarbon coatings to minimize the in-use stiction [62-64]. 

The principle of all aerosols is that a liquefied gas in a pressurised container will provide a constant pressure while the container is being emptied. The essential components of an aerosol beside the container itself are the product, propellant, and valve assembly. The valve is designed to dispense the product in the required manner while maintaining both the product and propellant hermetically sealed until the product is expended. The fact that the product is sealed in the container and protected from air and other outside contaminants has obvious advantages in the field of pharmaceuticals. The intimate mixture of propellant and product in a true aerosol results in a rapid expansion of the propellant as it leaves the valve orifice. This breaks up the product into small particles giving a fine mist, coarse spray, foam, or dust according to the nature and relative quantity of the product and the propellant and the type of valve. 

A wet sample was hermetically sealed in a sample pan. The empty sample pan and the sealed pan were weighed. The sealed pan was quickly frozen Inside the DSC chamber to -40 C and several minutes were allowed for the system to come to equilibrium. The sample holder assembly was then heated at a rate of 5 C/mln. A scanning speed of 5 C/mln was found to give the optimum values of peak height and peak spread. This minimized the errors In experimental measurements. After the DSC measurement, the pan was punctured... 

With respect to the present state of battery development, it can be simply stated that most of the current work is being carried out at the laboratory level and that it is concentrated towards acquiring the necessary technology for the design and construction of practical cells and battery systems. However, there have been several successful attempts to build hermetically sealed cells and to assemble a large number of these cells into batteries. Four notable examples are discussed below. 

Adhesives are also tailored to meet specific requirements of the packaging or assembly technology used (Table 5.9). Thus, the requirements for single-chip packaging in hermetically sealed ceramic packages such as CERDIPs will be somewhat different from those of plastic dual-in-line packages (PDIPs) and plastic-encapsulated microcircuits (PEMs). 

The first specifications for adhesives were generated by the staff of NASA and the DoD who were prompted by the high reliability that was required of microcircuits used in aerospace programs. These specifications covered primarily die and substrate attachments for hermetically sealed integrated circuits, hybrid microcircuits, and multichip modules. Subsequently, with the increased use of surface-mount adhesives in the assembly of commercial printed-wiring boards and underfills for flip-chip devices, industry associations took the lead in generating the requirements and test methods. 

Fungus-resistance tests are used to determine the reaction of adhesives to several species of fungi under high humidity and a warm environment in the presence of inorganic salts. Testing for fungus resistance is more appropriate for exposed adhesives as in printed-wiring assemblies than for hermetically sealed devices or modules. One test method specified as Method 4.5.14 in IPC-SM-817 references Method 2.6.1 of IPC-TM-650, Test Methods Manual... 

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