Components surface-mounting

A selection of components surface-mounted to carrier plates is shown in Figure 4.34. The carrier plates support the internal fluidic pipes and can also be equipped with electrical heaters to permit trace heating of the fluid. The surface-mounted components of this system are compatible with the backbone concept introduced in the following. 

Fig. 10.19 Examples of surface-mount instrument interfaces. (A) A simple gas chromatograph helium gas metering system, showing the traditional assembly made from tubing and fittings, a four-component surface-mount replacement, and the surface-mount layout and flow diagram at the top. (B) A simple two-component surface-mount interface for...

In the least complicated format, only an operator places the odd-form components on the circuit board. The soldering process is automated in that the operator picks components from bulk bins and repeatedly positions them onto the circuit board as it is carried along the conveyor Une. For paste-in-hole assembly, the solder paste and other components (surface-mount or through-hole) may already be on the board, being held in place only by the tackiness of the paste. Therefore, the operator must not inadvertently displace other components off of then-sites during handling. 

The need to provide smaUer, hghter-weight products with ever-increasing functionality has led to optimization of several areas. One is to make efficient use of printed circuit board areas by utihzing both sides of boards to mount components. Surface-mount technology (SMT) lends itself particularly weU to this approach. 

PCT may be used for the production of electronic and automotive components such as circuit board components, connectors, switches and relays, and alternator armatures and pressure sensors. The main application has been in the fabrication of surface-mount connectors that can withstand infrared reflow soldering operations. 

We should not think that heat is lost only from the copper side. The usual laminate (board material) used for SMT (surface mount technology) applications is epoxy-glass FR4, which is a fairly good conductor of heat. So some of the heat from the side on which the device is mounted does get across to the other side, where it contacts the air and helps reduce the thermal resistance. Therefore, just putting a copper plane on the other side also helps, but only by about 10 to 20%. Note that this opposite copper plane need not even be electrically the same point it could for example just be the usual ground plane. A much greater reduction of thermal resistance (by about 50 to 70%) can be produced if a cluster of small vias (thermal vias) are employed to conduct the heat from the component side to the opposite side of the PCB. 

Ru02 resistors are commercial small-power (volume of few mm3) electronic components. They belong to the group of smd (surface mount device) thick-film resistors and are... 

Surface-mount devices, surface-mount interconnection devices, PCMCIA card frames... High-performance motor components... 

Figure 4.34 Surface-mounted components such as valves, gauges and pressure regulators of the NeSSI consortium [23] (by courtesy of CPAC).

A process scheme (Figure 4.87) consists of standardized surface-mount components and can be arranged on the screen to a customized system. The software also delivers a summary considering necessary seals and pipe fittings which can be used for ordering directly (Figure 4.88). 

Multilayer technology is exploited just as for multilayer capacitors (see Section 5.4.3) to EIA size specifications, and inductor chips can be bandoliered ready for surface mounting, typical inductance values lying in the range 1 nH to about 20 /rH. They find important applications as EMI suppressors as well as for a wide range of applications as a lumped circuit component in equipment of all types -communications, entertainment , computers, etc. (see Fig. 9.17). 

Note that the sort of oscillator circuit shown in Rgure 6.13(b) can be constructed by the interconnection of line-powered modular instnnnentaticm [30], by the use of printed-circuit board-mounted, DC-powered components [31], by the use of surface-mount devices on a suitably metallized substrate, or even on a sin-... 

Other workers have published improved procedures for inspecting both reinforced concrete and prestressed concrete structures with regard to determination of the embedded steel components [110]. A prototype ultrasonic procedure was developed to determine the condition of prestressed and pretensioned tendons in concrete. The application of electrochemical surface-mounted systems for estimating the rate of corrosion of reinforcing steel and other embedded steel components in large concrete structures was described using this technique. 

Figure 2. Multilayer circuit board with surface mounted components.

SMT has been used in the hybrid industry since the late 1950s. Nowadays, however, SMT implies the assembly of surface mountable components onto organic substrates such as glass epoxy and phenolic paper. Surface mounting makes more efficient use of substrate area through the use of smaller components and the elimination of large PTH s, because only smaller via holes will be required. As the IC complexity, customization and pin count increase there will be no alternative interconnection technology that can cope. 

By taking this value engineering approach to its extreme with the total replacement of all through-hole components by their surface mounting equivalents, reductions in PCB sizes of between 60% and 70% can be achieved. However, the performance improvements are limited and, although a great many of the current SMT implementations have taken this approach, many have found SMT a less than satisfactory alternative to insertion. 

Generally, some improvement in Tg will be required, partly because this will help retain the mechanical properties over a wider temperature range, and partly because the soldering of surface mounting components often puts a large heat load on the entire board and not just on one surface. 

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