Particle tolerance

Soft errors in microelectronic packages are a difficult, troublesome problem to address. Eliminating them is virtually impossible. Soft error rate effects can be reduced in a number of ways, including the use of shielding, software correction methods (although this reduces performance), alpha particle-tolerant structures (e.g., SOI), and utilization of low-alpha-emitting materials. Let us now focus on the reduction of alpha particle-induced SER from traditional lead-based solders. 

Specialty Aluminas. Process control (qv) teclmiques permit production of calcined specialty aluminas ha nng controlled median particle sizes differentiated by about 0.5 ]lm. Tliis broad selection enables closer shrinkage control of high tech ceramic parts. Production of pure 99.99% -AI2O2 powder from alkoxide precursors (see Alkoxides, metal), apparently in spherical form, offers the potential of satisfying the most advanced appUcations for calcined aluminas requiring tolerances of 0.1% shrinkage. 

Another time-of-flight instmment, the Aerodynamic particle sizer (APS), is manufactured by TSI Incorporated (St. Paul, Minnesota). This system operates at subsonic flow conditions and cannot tolerate as high a flux of particles as the AeroSizer. As of 1996, the development of time-of-flight instmments is ongoing. 

Ceramic matrix composites are candidate materials for high temperature stmctural appHcations. Ceramic matrices with properties of high strength, hardness, and thermal and chemical stabiUty coupled with low density are reinforced with ceramic second phases that impart the high toughness and damage tolerance which is required of such stmctural materials. The varieties of reinforcements include particles, platelets, whiskers and continuous fibers. Placement of reinforcements within the matrix determines the isotropy of the composite properties. 

As a general nile, the direct-heat units are the simplest and most economical in construction and are emploved when direct contact between the solids and flue gases or air can be tolerated. Because the total heat load must be introduced or removed in the gas stream, large gas volumes and high gas velocities are usually required. The latter will be rarely less than 0.5 m/s in an economical design. Therefore, employment of direct rotating equipment with solids containing extremely fine particles is likely to result in excessive entrainment losses in the exit-gas stream. 

Sieving Methods and Classification Sieving is probably the most frequently used and abused method of analysis because the equipment, an ytical procedure, and basic concepts are deceptively simple. In sieving, the particles are presented to equal-size apertures that constitute a series of go-no-go gauges. Sieve analysis presents three major difficulties (1) with woven-wire sieves, the weaving process produces three-dimensional apertures with considerable tolerances, particularly for fine-woven mesh (2) the mesh is easily damaged in use (3) the particles must be efficiently presented to the sieve apertures. 

Figure 3.6.1 (Berty 1979) is a Sankey (1898) diagram, used in power engineering, where the bandwidth is proportional (here qualitatively only) to the flowing masses. This illustrates the calculation results for a rather extreme case of an NOx reduction problem. The case is extreme because the catalyst particle has a dp=0.2mm, i.e., 200 microns. Flow resistance is very high, therefore an L=1 mm deep bend is used only. Per pass concentration drop is still high, Ci-C=1.2ppm, or Dai=0.11. This was tolerated in this case, since it is between 11.2 and 10.00 ppm concentration, and nothing better could have been achieved.

The effect of sample volume on peak width has been considered and treated theoretically in Chapter 6 however, it is of interest to determine the maximum sample volume that can be tolerated with modern columns packed with small particles. The maximum sample volume is defined by the following equation,... 

In a packed column the HETP depends on the particle diameter and is not related to the column radius. As a result, an expression for the optimum particle diameter is independently derived, and then the column radius determined from the extracolumn dispersion. This is not true for the open tubular column, as the HETP is determined by the column radius. It follows that a converse procedure must be employed. Firstly the optimum column radius is determined and then the maximum extra-column dispersion that the column can tolerate calculated. Thus, with open tubular columns, the chromatographic system, in particular the detector dispersion and the maximum sample volume, is dictated by the column design which, in turn, is governed by the nature of the separation. 

Similarly, for the analysis of polymers using high-temperature solvents, the important concern is column stability and durability. Eor this reason, 10-/am particles are the best column choice. Waters Styragel HT columns are designed for this kind of application. Similarly, these columns are also more tolerant to eluent changes. Therefore, these columns are also recommended... 

PL aquagel-OH consists of macroporous, hydrophilic particles that exhibit a polyhydroxyl functionality. The columns exhibit extremely good stability during operation they will tolerate an operating pressure up to 140 bar and an eluent composition containing organic modifier up to 50% by volume and eluent pH in the range of 2-10. 

It is impossible to generalize about types of filter to be used. Selection depends on the system, the rate of contamination build-up and the space available. However, a common arrangement is to have a full-flow filter unit before the pump with a bypass filter at some other convenient part of the system. Many industrial systems working below 2000psi can tolerate particles in the order of 25-50 microns with no serious effects on either valves or pumps. 

Moderate tolerance of dirt particles, depending on hardness of bearing... 

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