The basics of capacitors are explained in this technical column.
The topic dealt with in this part describes the structure of multilayer ceramic capacitors and the processes involved in the production of these capacitors.
[Lesson 3: How multilayer ceramic capacitors are made]
<Basic structure of multilayer ceramic capacitors>
The most basic structure used by capacitors to store electrical charge consists of a pair of electrodes separated by a dielectric, as is shown in Fig. 1 below.
One of the indicators used to express the performance of a capacitor is how much electrical charge it can store. And in the case of a multilayer ceramic capacitor, by repeating the same structure shown in Fig. 1 level after level, the amount of charge it can store is increased. Fig. 2 shows the basic structure that results.
<How multilayer ceramic capacitors are made>
After the raw materials of the dielectric are completed, they are mixed with various solvents and other substances and pulverized to form a slurry-type paste. This paste is then formed into thin sheets and, after passing through the eight fabrication processes described below, the materials are turned into finished multilayer ceramic capacitor chips.
<Fabrication processes of multilayer ceramic capacitor chips>
Process <1>: Printing of internal electrodes onto dielectric sheets
The dielectric sheets, which have been made into rolls, are coated with a metal paste that will become the internal electrodes. In recent years, nickel has been the principal metal used for the internal electrodes of multilayer ceramic capacitors, and in the case of such capacitors, the dielectric sheets are coated with a nickel paste.
Process <2>: Stacking of dielectric sheets in layers
After the dielectric sheets have been coated with the internal electrode paste, the sheets are stacked in layers, one on top of the other.
Process <3>: Pressing
Pressure is applied to the stacked layers of the dielectric sheets to crimp and form them. As a rule, the processes so far are undertaken in a clean room to keep the materials free from foreign matter.
Process <4>: Cutting
The blocks of the stacked dielectric are cut to dimensions of 1.0 mm × 0.5 mm, 1.6 mm × 0.8 mm or any other specific chip size.
Process <5>: Firing
The cut chips are fired at a temperature in the range of 1000 to 1300 degrees Celsius. The ceramic and internal electrodes are made into an integrated whole as a result.
Process <6>: Coating of external electrodes and baking
The two ends of the fired chips are coated with a metal paste that will become the external electrodes. If nickel is used for the internal electrodes, a copper paste is applied, and the chips are baked at a temperature of around 800 degrees Celsius.
Process <7>: Plating
After the external electrodes have been baked, one layer of nickel and one layer of tin are plated onto their surfaces. Electrolytic plating is normally used: Nickel plating is for improving reliability and tin plating is for facilitating solder mounting. With this process, the chips are now complete.
Process <8>: Measurements and packing (supplementary processes)
Finally, the completed chips are checked to verify that they have the prescribed electrical characteristics, after which they are taped or packed in some other forms, and shipped.
In recent years, multilayer ceramic capacitors have become increasingly smaller and their capacitance has increased while their fabrication processes have been improved; for instance, the dielectric layers have become thinner and the precision with which the layers are stacked has been enhanced.
Person in charge: Murata Manufacturing Co., Ltd. Y.G