Thick-film circuit

There are three basic classes of thick-film material (conductors, resistors, and dielectrics) and all have at least one component that is a ceramic. They are supplied in the form of a paste or ink, which contains the following  

At a pH of 5.9 the mobility is zero this point is referred to as the isoelectric point (lEP). At the lEP the potential is zero. Table 27.4 shows lEPs for several different oxides. Acidic oxides such as Si02 have low lEPs and basic oxides such as MgO have high lEPs. 

Thick-film materials are deposited onto flat substrates by screen printing. The origins of screen printing date back more than 3000 years when the Chinese used silk screen printing to deposit multilayered colored patterns onto fabrics. A similar process is still used today to print designs and logos onto T-shirts. 

Soda-lime silica glass NajO-O.SS CaO-3,70 SiOj 2-3 

FIGURE 27.14 A typical thick film circuit used in a personal computer showing the different components. 

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Alumina ceramics are widely used for thick-film circuit substrates and for integrated circuit packaging. This aspect is discussed in Section 5.5.5. 

Another important low-permittivity, low-loss ceramic is alumina. Alumina has such an excellent combination of good mechanical properties, high thermal conductivity, and ease of metallization that it is widely used today for thick-film circuit substrates and integrated electronic packaging. 

Riemer DE. Material selection and design guidelines for migration-resistant thick-film circuits with silver-hearing conductors. In Proc. 31st Electron. Comp. Conf 1981. Licari JJ, Enlow LR. Hybrid Microcircuit Tech. Handbook. 2nd ed. Noyes PubUcations 1998 137-142. 

In addition to describing some of the methods used to apply thick ceramic films to a substrate, we also describe the tape casting process. Films produced by tape casting are not used as coatings but as self-supporting ceramic sheets (down to 25 pm thick) that are widely used in the production of thick-film circuits. 

Thick-film circuits are single or multilayer structures produced by depositing a layer, or layers, of a specially formulated paste or ink onto a suitable substrate. Thick-film technology began in the early 1960s when DuPont introduced a thick-film resistor system for application in miniaturized circuits. IBM used thick-film materials in then-family of IBM/360 computers. Currently the worldwide market for thick-film circuits and devices is around 14 billion. Most thick-film circuits are still used in electronic applications such as in computers (Figure 27.14). 

FIGURE 27.15 The screen printing process for depositing thick film circuits. The ink is forced through the screen, which then snaps away leaving a film on the substrate. 

Substrates for thick-film circuits generally have to satisfy the following requirements ... 

FIGURE 27.16 Typical thick film circuit tiring profile. 

In this chapter we described tape casting. This process is used to make fiat sheets. Although this is a means of shaping and could have been described in the shaping chapter we described it here because it shares a common feature with the other thick film coating methods it uses a slurry. It also is the process most often used to make ceramic substrates for thick-film circuits. Ceramics are a major component of thick-film circuits. Even in thick-film conductors, ceramics are important in ensuring adhesion between the metal layer and the substrate (which is invariably also a ceramic). 

Figure 27.14 shows a thick-film circuit, (a) What is the role of the sealing glass (b) Why is it green (c) What properties are important for the sealing glass ... 

Riemer, D. E., Material Selection and Design Guidelines for Migration-Resistant Thick-Film Circuits with Silver-Bearing Conductors, Proc. 3P Elect. Components Conf. (1981)... 

Processing Thick-Film Circuits Screen Printing... 

Figure 11.9 illustrates two typical thick-film circuits. 

The fimction of the substrate is to provide the base onto which thin-film circuits and/or thick-film circuits, which make up the electrical circuits, are fabricated and various multilayer films are deposited. In addition, the substrate provides the necessary mechanical support and rigidity needed to produce a reliable functional circuit. It must have adequate thermal management ability to ensure proper temperature operation, and it must possess a proper electrical insulation to withstand circuit voltages without breakdown. One can think of the substrate as the foimdation on which the circuit traces and components are mounted and supported. Ceramic materials are often used for thin- and thick-film applications, because ceramics have high thermal conductivity, good chemical stability, and are also resistant to thermal and mechanical shock [4]. 

Frmctions of a thick-film conductor include conductor interconnections, soldered lead and device attachment, thick-film resistor terminations, crossover connections, capacitor electrodes, chip and die bonding, wire bonding, low-value resistors, and packaging of thick-film circuits. The factors considered in... 

Standard prefired ceramic substrates have been used to fabricate complex hybrid microelectronic circuits for many years. Figure 4.15 and Figure 4.16 show examples of thick- and thin-film circuits. Figure 4.15 is a digital logic circuit fabricated on a three-layer thick-film circuit, whereas Figure 4.16 is a... 

Patterns on a thick film circuit formed by screen printing. 

Stencils are seldom used for printing complex geometries, such as thick-film circuits, because it is difficult to prevent sharp comers and angles in the stencil from bending. Also, all openings must be siuroimded by the metal foil to maintain continuity of the stencil, further limiting complexity of the pattern [20]. 

Muller, J., Thust, H., and Driie, K.-H., Laser structuring and trimming of RF-elements in multilayer thick film circuits. Proceedings of the International Conference on Electronics Technologies, Windsor, June 1994. 

LC Polyesters can be used for making flexible circuit. Etched copper or printed polymer thick film circuit pattern can be printed over a polymer film base, which forms a flexible circuit... 

Cadmium Cd 0.01 Platings, ink pigments, paint pigments, batteries, detectors, and thick film circuits... 

There are several different constrnctions for keypads on flexible circuits. Thick-film circuits on polyester film called membrane switch could be a low-cost solution with many millions of reliable contacts. The basic mechanism of the switching is illustrated in Fig. 64.25. Generally, the membrane switches are connected through FFC connectors to the main circuit board. Polyimide-based circuits are necessary with soldering of components. 

A thick-film circuit is a type of additive manufacturing process. If an organic resin matrix is used, the conductor can be flexible, and this process has been applied in flexible circuits. 

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