Placement of components

Once the interconnection medium has been applied, the next step is to place the electronic components. Current advances in MID technology and the growing number of series-production applications have given the market a variety of production systems for automated 3D-MID assembly and placement. In terms of implementing 3D assembly, they all satisfy the primary requirement the component s joining direction must be normal to the process surface. The systems achieve this by integrating additional degrees of freedom and drives in various kinematic variants (Fig. 4.12). Broad distinctions between these kinematic variants can be drawn as follows  

Throughout the entire placement process, the circuit carrier is held immobile and the components are rotated, positioned, and placed. 

Or the interconnect device is rotated and positioned and the components are placed. 

FIGURE 4.12 Kinematic variants with immobiie or mobiie circuit carriers 

By way of example. Fig. 4.13 shows how components are placed in the kinematic variant with a moved circuit carrier. The process surface is brought to the position at which the components can be placed vertically on the process surface. Once all of the components have been placed on one process surface, the MID is repositioned and the components are placed on the next process surface. 

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When using isotropically conductive adhesives, placement of components is performed by the same equipment as used for nonadhesive attachment techniques. Die bonders are similar to those used for eutectic bonding except for the type of adhesive dispenser. Surface-mounted placement machines developed for solder paste assembly can also be... 

Fortunately, advanced robotic equipment has been developed and is commercially available for accurate, high-speed placement of components. Entry-level automated placement machines canplace 3,000-5,000 parts per hour while mid-range equipment, that can hold more feeders, can place 8,000-10,000 parts per hour. On the high-end, placement speeds of30,000... 

Fig. 2. A typical installation of an automatic machine for placement of components on to printed circuit boards. In the centre can be seen the mounted syringe for automatic application of the adhesive...

Of course, various levels of automation may be considered, depending on production volumes and capital expenditure costs. However, with continued miniaturization of surface-mount products as well as the strict requirements for the repeatable placement of specific solder paste volumes and accurate placement of components, will be a foregone necessity to assemble surface-mount technology with a fuUy automated assembly process. 

Placement of components with the incorrect surface finish—Pb-Sn (high-reliability electronics) versus 100 percent Sn (consmner electronics)... 

Coplanarity is very important in the placement of SMT components with leads. Occasionally, lead preparation to form the leads of SMT components is necessary to achieve the proper coplanarity for mannal or automatic placement of components on the PCB. Most times, however, the components are purchased packaged with leads prepared and ready to be automatically placed by pick-and-place equipment. Another critical parameter for all surface-mounted components is the accuracy of placement of the components onto the pads of the PCB. 

Placement of components that are hkely to be operated frequently, or to require maintenance or removal, at a convenient height for working. 

For reliability, surface area of pressure boundaries should be minimized. This is to include the recuperator and gas cooler. Arrangement and orientation may help protect the system against external impacts, such as from micrometeoroids. (See Section 7 Reliability) As arrangement efforts progressed, one consideration for placement of components would have been shielding of the more vulnerable components by more robust elements and orientation of components so that the more vulnerable surfaces face away from higher particle flux directions. 

Where possible, consideration should be given to placement of components in a manner which provides extra shielding for local components (e.g., alternator) or for the space vehicle bus For example, aligning the axis of the Brayton with the axis of the space ship and placing the turbine and compressor closer to the shield than the alternator may provide added shielding for the alternator. Also, placement of equipment of substantial mass closest to the back side of the shield with respect to the rest of the plant components provides additional gamma shielding for plant o>mponent. ... 

The melt delivery system can be optimized for minimal transmission of flow oscillations from the extmder to the die. This involves proper sizing of piping and placement of components. 

An imponant component of the complex metallizations for both semiconductor devices and magnetic media is the diffusion barrier, which is included to prevent interdiffiision between layers or diffusion from overlyii layers into the substrate. A good example is placement of a TiN barrier under an Al metallization. Figure 7a illustrates the results of an SNMSd high-resolution depth profile measurement of a TiN diffusion barrier inserted between the Al metallization and the Si substrate. The profile clearly exhibits an uneven distribution of Si in the Al metallization and has provided a clear, accurate measurement of the composition of the underlying TiN layer. Both measurements are difficult to accomplish by other means and dem-... 

The rig selection will dictate the basic layout of the pad. Based on the necessary area needed to support its functions, ancillary equipment may be added in space conservative measures. In addition to the placement of various stationary rig site components, other operations such as logging, trucking and subsequent completion operations must be provided for. The most environmentally sensitive design will impact the least amount of area, and in that it will be the most economic. Potential pad sites and access routes should be laid out on a topographic map prior to the actual survey. At this time, construction costs can be estimated and compared. Figure 4484 shows such a layout. The cost of building a location includes the cost of reclamation such as any remediation. 

Radiographic Inclusions, voids, materials variations, placement of internal components... 

Two important terms used to describe additives in polymeric mixtures are distribution and "dispersion . When mixing polymers with additives, we want to create a system in which the additive is both well distributed and dispersed. Distribution refers to the even placement of the additive throughout the polymer. For example, a well made batch of chocolate chip cookies has good distribution of the chips if every bite has a chocolate chip in it. A poorly distributed cookie would have all its chips on one side. Dispersion, on the other hand, refers to the separation of the individual components of a solid additive into its smallest parts. Figure 10.6 illustrates both good and bad distribution and dispersion. 

Plate 8.1 (a) Key to placement of tablet matrix and pure component reference samples for high-throughput... 

Source plates may be prepared in advance and stored frozen, depending upon fhe probe ink stability. In any case, source plates should be brought to ambient temperature to assure that all components have redissolved. We recommend that source plates be centrifuged to remove any entrapped air bubbles from fhe bottoms of the wells. While manual preparation of source plafes is possible, the use of a robotic dispensing sysfem is highly recommended in order to avoid mistakes in placement of fhe probe inks in fhe wells and to avoid cross-contamination. The use of such a device will also allow more xmiform preparation of subsequent source plates. 

K), Fe-S cluster assembly (nIfM) and the biosynthesis of the iron molybdenum cofactor, FeMo-co (nifN, B, E, Q, V, H)(5a). It is the last two functions, involving the placement of unusual transition metal sulfide clusters into the nitrogenase proteins, that cause nitrogenase and its components to be appropriately included in this symposium. 

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