SMD components

In Table 4-2, we have the standard SMD component sizes. Note that usually, most pick and place machines cannot mount anything bigger than size 1515. So larger components may need to be hand-soldered. For ceramic capacitors, reliability requirements call for a certain... 

Note that the electronic industry produces smd components called thin-film resistors of the same shape and size of Ru02 thermistors. They are usually made of a thin layer of Ni-Cr. Their resistance is extremely stable with temperature and hence they find application as inexpensive (punctual) heaters (see e.g. Chapter 11). 

The mounting of SMD components onto PCBs or flexible substrates demands a certain amount of interconnection material (solder or conductive adhesive) to form a correct joint. In contrast to wave soldering, where heat and material (molten solder) are provided simultaneously during the soldering... 

For both these concepts to be realized, it is necessary to extend and work on hardware and control software of the PCB basic assembly system. These systems are realized with a widespread standard system at the FAPS Institute. Figure 45 shows the developed MID placement system with the different modules for the handling of SMD components and MID. 

Mounting of resistors is often more expensive than the components themselves. The use of the smallest SMD components is often limited by the difficulty of handling them. The amount of handling and mounting can be reduced by combining a number of resistors with their interconnections to a network on one substrate. This also makes it easier to use smaller resistors. 

Heating-cooling ramps and ensuring that they are within the recommended bounds prescribed in the surface-mount device (SMD) component and solder paste specifications... 

Solder Paste Deposition for Pin-in-Paste Soldering. To prepare a board for pin-in-paste soldering, you deposit generous amounts of solder paste over or adjacent to the circuit board s targeted PTH sites. This is done during solder-paste stenciling in preparation for SMD component placement and reflow (see Fig. 47.15). 

FIGURE 47.15 Solder paste stenciling in preparation for SMD component placement (a) a PWB cross-section prior to solder paste deposition (b) the same PWB after solder paste deposition. Note that SMD pads and PTHs have received solder paste deposits. In the case of (b), paste has been forced into the PTH by the squeegee during solder paste printing. 

Cluster components and provide clearance Group wave-soldered PTH components together. Avoid interspersing nonwave soldered SMD components within PTH fields. Conversely, avoid designs that place an isolated PTH component amid a field of SMD components. Such a placement requires a small wave pallet opening that inhibits solder-wave fluid flow, pre-heating, and wave contact. 

The development of surface-mounted technology (SMT) using surface-mounted devices (SMD) was a major development. SMD are active and passive electronics components without conventional connecting wires. SMD components can be placed on the solder side of the PCB and their metal caps soldered to the copper pads of the PCB. Both layers of the PCB can therefore be used as active areas. The SMT technique opened advantages and new applications through miniaturisation of components and increased reliability. 

This is why there are also different component shapes. Virtually the only components of interest for MID technology are those having metallized pads for connection that can be set directly on to plated lands on the surface of the substrate. These are surface mount devices, SMD for short. Through-hole devices, THD for short, are wired components and are not used for 3D-MID, so they are not discussed in more detail below. The range of SMD components can be subdivided as follows [109] ... 

Dispensing of solder paste placement of SMD components, and soldering... 

SMD-component, lead-free wave soldering is that components experience a solder immersion temperature that exceeds 250°C which may result in component damage. 

Circuits on rigid and multilevel substrates such as FR4 boards or EGAs in combination with SMD components... 

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