Circuit boards surface mount technology

The electronic unit of the LAPS device can be created on a double-sided printed circuit board with the help of surface-mounted technology to bring it as close as possible to the sensor chip. The integrated electronic unit enables an easy access to the different measurement spots and provides an amplified, filtered and easily measurable (converted) voltage signal (several V) with respect to the sensor signal (several pA). The electronic unit contains different blocks, which are described in Fig. 6.2. 

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. 

In order to miniaturize products and to improve productivity in the electronics industry, a method of soldering resinous electronic parts has been developed for affixing parts, such as connectors, switches, relays and coil bobbins to printed circuit board (PCB). This method is addressed as surface-mount technology. 

Microfluidic Boards Microfluidic board interconnection technologies seek to mimic the electronic printed circuit board for ease of use, reliability, and versatility. In microfluidic board technologies, the substrate contains the passive microfluidic channels and reservoirs, with active components (e.g., sensors, valves) mounted on top (e.g.. Ref. [2]) (see Fig. 1) similarly to electronic components mounted on a printed circuit board (PCB) or multichip modules (MCM) in surface-mount technologies (SMT). Electronic coimections between components are provided on top of the board, while fluidic interconnection is usually provided in the board material itself. Microfluidic circuit boards can be made from a variety of materials, including silicon, glass, and polymers, e.g., polydimethylsiloxane (PDMS), epoxy, or polymethyl methacrylate (PMMA). Microfluidic boards can be as simple... 

Bono, D., The Assessment of the Corrosivity of Soldering Flux Residues Using Printed Copper Circuit Board Tracks, Solder Surface Mount Technology, No. 2, June 1989, pp. 22-29. 

FIGURE 40.10 Surface-mount technology circuit boards showing the range of passive and active device sizes and geometries. (Courtesy of Sandia National Laboratories and American... 

The trend in surface-mount technology is to use smaller passive devices such as capacitors, resistors, and inductors. Also, there is the use of embedded passive devices, that is, resistors and capacitors that are located within the circuit board laminate. Embedded passive devices free up additional surface area for larger, active components. 

Dispensing. In surface-mount technology, three classes of materials must be dispensed on to the circuit board adhesives, fluxes, and solder pastes. Each of these three categories, which utilize very similar equipment options for the actual dispensing action, is discussed in the following subsections. 

With the growing use of surface mount technology and related techniques such as chip-on-board, printed circuit board manufacturers are continually seeking new processes to enable production of boards with increased circuit densification and decreased circuit feature sizes. Consequently, line widths are now approaching those of early semiconductor devices, and this has in turn placed new demands on the resolution capabilities of the inner-layer and outer-layer photoresists used in the industry. 

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