Multilayer chip capacitor

Electricity storage Specific dielectric properties Monolithic and multilayer chip capacitors... 

FIGURE 9.5 A large continuous furnace used in industry to produce traditional ceramic products and advanced ceramics such as multilayer chip capacitors. 

Sintering HA powders, or a mixture of suitable reactant powders, uses naphthalene particles that volatilize during heating to create an interconnected porous network. Similar approaches have been used to produce foam glass (Section 26.9) and in the fugitive electrode method of producing multilayer chip capacitors (MLCCs) (Section 31.7). 

Figure 9.5 shows an example of a large industrial continuous furnace. The classic use is for firing bricks, pottery, tiles, and whitewares. Similar furnaces are used in the production of advanced ceramics such as multilayer ceramic chip capacitors. 

The ceramics industry, like many others, can establish production facilities in which labor costs are lower. For example, KEMET Corporation based in Greenville, SC, a manufacturer of tantalum electrolytic and multilayer ceramic chip capacitors, is relocating all manufacturing to lower-cost facilities in Mexico and China. 

Equipment is now available to produce the thin tapes (less than 3 pm). There is also equipment available to screen-print and laminate these very thin tapes. Multilayered capacitors with 5-pm layers that are 300 layers thick are currently being manufactured. Maher states that there is a practical limitation where the dielectric constant of the material itself reaches its peak value as a function of the sintered grain size. If the grain size is in the range of 0.8 to 1.1 pm then there is a limitation on the minimum tape thickness at about 4 to 5 pm in order to maintain the dielectric breakdown properties of the chip capacitor. Maher also contends that a minimum of about 5 grains in series is desirable for reliability. It is generally believed that the 3-pm limitation on tape thickness will be the norm in the future. 

Chip-type capacitors are the main products due to their superior frequency performance and volumetric efficiency, which meet the requirements from the advanced electronics devices. A schematic diagram of the multilayer ceramic capacitor (MLC) is shown in Figure 5.1.1. The capacitor is composed of many thin plate capacitors in parallel connection. Thinning the dielectric layer, and stacking them maximum number into the limited thickness achieve maximum capacitance. The capacitance of the MLC of electrode area S, dielectric thickness t and number of dielectric layers n is given by... 

Demand for microwave dielectric ceramics used in telecommunications, as well as in cable communications using optical fibers, is increasing rapidly. Whereas, in the past microwave communications were used primarily for military purposes such as radar, weapon guidance systems and satellite communications, more recently microwaves have been utilized extensively in communications devices such as mobile radios and phones, and in satellite broadcasting (see Chapter 8). The market volumes for ceramic dielectric materials for chip capacitors and multilayer capacitors (MLCCs) were estimated in a study by Paumanok Publications Inc. (2006). 

Chip capacitors are constructed from a special oxide-based ceramic that is built up of alternating layers of ceramics and thin film layers that provide the device capacitance value. This capacitor is the multilayer thin film (MLTF) type. The second capacitor type has electrodes on the top and bottom surfaces of a homogenous block of ceramic. The ceramics used to make... 

Ceramic and ferrite components such as multilayer ceramic capacitors, chip resistors, and chip inductors are generally terminated with a fired-on silver or silver palladium paste. Because silver dissolves easily into molten Sn-Pb solder, a Ni/Sn or Ni/Au overplate is recommended. 

EIA-479A Film-Paper, Film Dielectric Capacitors for 50/60 Hz Voltage Doubler Power Supplies EIA-535 Series of Detail Specifications on Fixed Tantalum Capacitors EIA-595 Visual and Mechanical Inspection Multilayer Ceramic Chip Capacitors ElA/IS-35 Two-Pin Dual In-Line Capacitors EIA/IS-36 Chip Capacitors, Multi-Layer (Ceramic Dielectric)... 

EIA/IS-37 Multiple Layer High Voltage Capacitors (Radial Lead Chip Capacitors) EIA/IS-717 Surface Mount Tantalum Capacitor Qualification Specification IEC-384-3 Sectional Specification,Tantalum Chip Capacitors IEC-384-10 Sectional Specification, Fixed Multilayer Ceramic Chip Capacitors lECQ Draft Blank Detail Specification, Fixed Multilayer Ceramic Chip Capacitors IECQ-PQC-31 Sectional Specification, Fixed Tantalum Chip Capacitors with Solid Electrolyte... 

EIA-CB-11 Guidelines for the Surface Moimtiiig of Multilayer Ceramic Chip Capacitors IPC-CM-770D Guidehnes for Printed Board Component Mounting IPC-SM-780 Electronic Component Packaging and Interconnection with Emphasis on Surface Mounting... 

The final applications discussed here are electrodes and metallizations for fine ceramics. This includes ohmic contact pastes for varistors and thermistors as well as materials for complex multilayer components. Figure 8.105 illustrates a cross-sectional view of a ceramic chip capacitor. The internal electrode can be Pt, Pd, or Ag-Pd depending on the type of ceramic formulation and its respective firing temperature. The end termination may be Ag or Ag-Pd and is typically required to be platable. The technical requirements of these materials are extremely challenging. 

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). 

---