JPS64342B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a ceramic composition that has a high dielectric constant and can be fired at low temperatures, and a method for manufacturing a multilayer capacitor using the same. Conventionally, materials containing barium titanate as a main component are widely known as dielectric materials having a high dielectric constant. However, the optimal firing temperature for these dielectrics is
It has a high temperature of 1,300°C to 1,400°C, and when used in multilayer capacitors, etc., it has the disadvantage that expensive noble metals mainly composed of platinum, palladium, etc. must be used as internal electrodes. Pb (Fe _1/2 Nb _1/2 ) O ₃ , Pb (Fe _2/3 W _1/3 ) O ₃ and Pb
The three-component ceramic composition containing (Zn _1/3 Nb _2/3 ) O ₃ as the main component solves this drawback, and because it can be sintered densely at temperatures below 950°C, it can be used with nickel or silver as the main component. It is possible to use inexpensive internal electrodes that
57204). Moreover, it is an excellent material with a high dielectric constant, low dielectric loss, and high specific resistance. By the way, in order to make multilayer capacitors smaller and cheaper, it is necessary to make the thickness of the green sheet as thin as possible. For this purpose, it is desirable that the dielectric breakdown voltage be as high as possible. However, in the past, in the manufacturing process, after firing at the highest firing temperature during the firing process, cooling was done at a rate of 100°C or more per hour, or by natural cooling in an electric furnace (the cooling rate was not constant, and the temperature was lower than the highest firing temperature). The average cooling rate until the temperature drops by 300℃ is approximately 150℃ to 200℃/hour)
I've been leaving it to myself. Therefore, even with the above-mentioned three-component ceramic composition, the dielectric breakdown voltage was low. For example, when a sample prepared according to the example described later is fired using the conventional method, the dielectric breakdown voltage is approximately 500~
You can only get something around 700V. The present invention provides a method for producing a ceramic composition that is highly effective in improving the dielectric breakdown voltage of the ceramic composition and improving the reliability of multilayer capacitors using the same. The manufacturing method of the present invention includes the step of firing a sample in which a liquid phase mainly composed of PbO is generated during the firing process at the highest firing temperature during the firing process, and then cooling the sample at a cooling rate of 60°C or less per hour. It is characterized by
Note that cooling at this cooling rate is desirably performed to a temperature of 650°C or less. Pb (Fe _1/2 Nb _1/2 ) O ₃ , Pb (Fe _2/3 W _1/3 ) O ₃ and Pb
(Zn _1/3 Nb _2/3 ) O ₃ ternary system and Pb (Fe _2/3
W _1/3 ) Binary system consisting of O ₃ and PbTiO ₃ or Pb
(Mg _1/2 W _1/2 ) When a binary ceramic composition consisting of O ₃ and PbTiO ₃ is observed using an X-ray microanalyzer, it is found that a substance mainly composed of PbO is present in the grain boundary layer. was confirmed, and its shape revealed that it was in a liquid phase at the maximum firing temperature. Therefore, the present invention reduces the amount of the remaining liquid phase by slowing down the cooling rate after firing, thereby greatly increasing the dielectric breakdown voltage of the ceramic composition. Examples will be explained below. Starting materials include PbO, Fe ₂ O ₃ , Nb ₂ O ₅ ,
ZnO, WO ₃ , MgO, and TiO ₂ were prepared and weighed according to the composition ratios shown in the table. This was wet mixed in a ball mill and calcined at 700°C to 800°C.
This calcined powder was wet-mixed again in a ball mill, filtered, dried, and pulverized, then an organic solvent and an organic binder were added, mixed in a mixer, and formed into a sheet of 40±1 μm using a doctor blade method. This was cut into an appropriate size, and internal electrodes containing silver and palladium were printed on it. For the internal electrodes, a printed pattern with an effective electrode area of about 6 mm ² was used, and sheets were stacked so that the number of effective electrode layers was 15. Firing is shown in the table.
The 10 types of samples were fired at the maximum firing temperatures shown in the same table, and then cooled to 650°C at a cooling rate ranging from 100°C per hour to 10°C per hour. To measure the dielectric breakdown voltage, place the sample in silicone oil at room temperature and increase the applied voltage in 50V increments.
Each voltage was held for 5 seconds. The value was the average value of 10 samples. These values are shown in FIGS. 1 to 3. The numbers assigned to each curve in the figure are the sample numbers shown in the table.

[Table] As is clear from the figure, Pb(Fe _1/2 Nb _1/2 ) O ₃ ,
Ternary system consisting of Pb (Fe _2/3 W _1/3 ) O ₃ and Pb (Zn _1/3 Nb _2/3 ) O ₃ or Pb (Fe _2/3 W _1/3 ) O ₃ and PbTiO ₃
A two-component system consisting of Pb (Mg _1/2 W _1/2 ) O ₃
By applying the manufacturing method of the present invention to materials in which a liquid phase containing PbO as the main component is generated during the firing process, such as a two _- component system consisting of Increased by 1.5 to 2.5 times,
Improves reliability.

[Brief explanation of drawings]

FIG. 1, FIG. 2, and FIG. 3 show the relationship between dielectric breakdown voltage and cooling rate. The numbers in brackets in each figure are the composition numbers shown in the table.

Claims (1)

[Claims] 1. A dielectric material characterized by having a step of firing a sample in which a liquid phase mainly composed of PbO is generated during the firing process at the highest firing temperature during the firing process, and then cooling it at a rate of 60°C or less per hour. A method for producing a porcelain composition.