A monolithic multilayer ceramic (MLC) capacitor, as shown in cutaway view Fig. 1-14, is a multilayer ceramic chip capacitor that offers high volumetric efficiency because a large capacitor area is compressed into a small block. Preformed metallized layers are stacked and fired to form MLCs in a wide range of sizes and values with different properties. Originally developed for hybrid circuits, MLCs are widely used in surface mounting because they can substitute for larger capacitors with comparable capacitance values. They offer low residual inductance values and low resistance, a wide range of capacitance values in a given size, and a wide selection of temperature coefficients. They also exhibit lower inductance and resistance values than tantalum capacitors with comparable ratings. MLCs are used for timing and frequency selection.
MLCs are made as sandwiches of “green” (unfired) barium-titanate ceramic strips 0.8 mils (20 μm) thick that have been imprinted with silver-palladium ink to form plates. Up to 40 layers of the soft doughlike strips are stacked, compressed, diced, and furnace fired to form the monolithic chips.
End terminals for solder bonding MLCs to a circuit board or attaching leads are made by plating successive layers of silver-palladium, nickel, and tin or lead-tin on the ends of the chips. The process used depends on whether the chip is to be leaded and coated with insulation or is to remain bare for bonding directly to a circuit board.
Bare MLCs are used on hybrid microcircuits and in surface-mount assembly. They will withstand the 232°C reflow-soldering temperatures and the 282°C wave-soldering temperatures. Bare MLC chip sizes are standardized. Examples include 0.08 × 0.05 in (2.0 × 1.3 mm), designated 0805; 0.125 × 0.063 in (3.2 × 1.6 mm), designated 1206; and 0.225 × 0.05 in (5.7 × 1.3 mm), designated 2225. Standard MLCs have capacitance values of 10 pF to 3.5 μF, capacitance tolerances of +- 1 to 20 percent, and maximum voltages of 50 V.
