Insertion mount component

Fig. 9.2.8 NeSSI top mount component for use with a Raman ballprobe. The Raman ballprobe inserted into the component, indicating flow channels to probe optic.

The through-hole components (axially leaded parts, pin-grid arrays, solder-tail connectors, etc.) are inserted into their respective PTHs before or after surface-mount component placement. Once the surface-mount components and the solder-tail parts are placed, the pastebearing board is then passed through the SMT reflow oven. During the reflow process, the molten solder coalesces around the through-hole pins wetting between the pin and barrel. Surface tension and capillary action draws the solder down the barrel to complete the solder joint. 

Radio and television uses largely arise from the ability to produce components with a high level of dimensional accuracy coupled with good dielectric properties, high heat distortion temperatures and the availability of selfextinguishing grades. Specific uses include coil formers, picture tube deflection yokes and insert card mountings. 

The rubber stock, once compounded and mixed, must be molded or transformed into the form of one of the final parts of the tire. This consists of several parallel processes by which the sheeted rubber and other raw materials, such as cord and fabric, are made into the following basic tire components tire beads, tire treads, tire cords, and the tire belts (fabric). Tire beads are coated wires inserted in the pneumatic tire at the point where the tire meets the wheel rim (on which it is mounted) they ensure a seal between the rim and the tire. The tire treads are the part of the tire that meets the road surface their design and composition depend on the use of the tire. Tire cords are woven synthetic fabrics (rayon, nylon, polyester) impregnated with rubber they are the body of the tire and supply it with most of its strength. Tire belts stabilize the tires and prevent the lateral scrubbing or wiping action that causes tread wear. 

Finally, when a circuit or component doesn t have to be removed often and it contains a large number of transistors, typically you use a PGA and a ZIP (Figure 1.9). PGA stands for Pin Grid Array, describing the array of pins used to connect the chip to the circuit board. ZIF stands for zero insertion force, which describes how easy it is to place a chip in this kind of socket. It is a type of socket that works with PGA chips to allow them to be mounted on a circuit board. 

In addition, molded holes can be custom designed to aid in insertion of leaded components (entry radii or countersink) or to provide recessed mounting of hardware (counterbore). Furthermore, holes can be oblong, rectangular or parallel to the plane of the molded substrate. Possible hole geometries are illustrated in Figure 1. 

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. 

Figure 16.3. Typical electron-impact source. The source is mounted on a frame and inserted into the flight tube of the mass spectrometer. The voltages in parentheses are typical values for the component parts of a spectrometer operating at 5000 V accelerating potential. Note that the target is at +100 V with respect to the filament, and the filament is at —70 F with respect to the ionization chamber.

Surface-mount technology replaces previous methods of inserting component leads into plated through-holes of PWBs, wave soldering from the back side to flow solder into the holes, and simultaneously forming both mechanical and electrical connections. SMT is highly automated and currently the most widely used production process for the assembly of single-layer, double-sided, and multilayer circuit boards. 

Two types of tapes are discussed carrierless adhesive foils (also called transfer adhesives) used, for example, in mounting or laminating processes, and tapes consisting of an adhesive on a carrier tape, used for contact and distance films in foil keypads, covering tapes in galvanizing and solder processes (Fig. 8), and as component supply in insertion installations (Fig. 9). The tape properties required depend, of course, on the type of application. Therefore, the following properties are important for component supply tapes [12] ... 

Currently, multiple-component, internal gas-assisted and decorative processes are being used more and more frequently in combination with thin-wall techniques. A good example of this is the trend to highly individualized cell phone designs. Decorative processes such as inmold decoration or insertion of preformed, printed foils makes variable coloration of even small run volumes possible. The internal gas-assisted method is used for example to reduce the mass of thick-walled parts and to avoid sink marks minimization of warpage is thus a primary requirement for thin-walled parts. A wide variety of functions can be realized by means of the multiple-component technique, including seals, napped surfaces, improved antishp properties and functional elements, some of which are now still being mounted in complex and expensive additional steps. 

---