Surface mount disadvantages

Pad array carrier (PAD), a surface mount equivalent of the PGA package. This package extends surface mount silicon efficiency from 15 to 40%. A disadvantage of this package is that the solder joints cannot be visually inspected, although X-ray inspection can be used to verify the integrity of the bKnd solder connections (and to check for solder balls and bridging). Individual solder joints, however, cannot be repaired. 

The main disadvantages of surface-mount components stem from the fact that there are no leads to easily grip with instrumentation probes and that there may not be access to the leads... 

Yet another disadvantage of surface-mount parts stems from their small size. It is more difficult to remove heat from SMT packages than it is for their through-hole equivalent. In some cases, such as high-performance processors, the heat generated by the IC is too high to permit proper operation in an SMT package. 

Owing to the widespread application of solar hot water systems, a great number of variations of fluid collectors have been developed and commercialized circulation. It is mostly the 1-2 m surface-mounted units that are available commercially these, joined in an appropriate number, form a full collector system. The advantage of commercially available collector surfaces is the quick and simple replacement of the elements and guaranteed thermal efficiency. A disadvantage is the usually high investment cost and the long payback time. For indirect solar dryers, lower cost is involved with panel-type collectors, if the costs... 

These disadvantages are overcome by the so-called dance-floor principle which is supposed to become the major beamline construction principle of the future. Figure 4.11 shows a dance floor during the construction of the beamline hall at the ANSTO neutron-scattering facility at Lucas Heights near Sydney, Australia. The dance floor is featuring an extremely plane and hard floor surface from granite. Optical components, detectors and sample chambers are mounted on supports with a flat lower surface. While compressed air is blown into the gap between the dance floor and the area of support, components are easily moved and adjusted in the optical beam path. 

These difficulties are obviated to some extent by arranging the screens in the form of concentric cylinders, with the coarsest in the centre. The disadvantage of all screens of this type is that only a small fraction of the screening area is in use at any one time. The speed of rotation of the trommel should not be so high that the material is carried completely round in contact with the screening surface. The lowest speed at which this occurs is known as the critical speed and is analogous to the critical speed of the ball mill, discussed in Chapter 2. Speeds of between one-third and a half of the critical speed are usually recommended. In a modified form of the trommel, the screen surfaces are in the form of truncated cones. Such screens are mounted with their axes horizontal and the material always flows away from the apex of the cone. 

With anodic oxidation very controlled and narrow pore size distributions can be obtained. These membranes mounted in a small module may be suitable for ultrafiltration, gas separation with Knudsen diffusion and in biological applications. At present one of the main disadvantages is that the layer has to be supported by a separate layer to produce the complete membrane/support structure. Thus, presently applications are limited to laboratory-scale separations since large surface area modules of such membranes are unavailable. 

The resulting relief-patterned metal surface serves to reflect incident light into a reconstructed image of the hologram. A disadvantage of this approach is the requirement to conduct such metal deposition in a vacuum environment and to mask areas where metal deposition is not desired, especially if the hologram is mounted on a document. 

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