JP2003309036A - Multilayered electronic parts and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide multilayered electronic parts which have high insulation performance even when a dielectric layer is thin and whose reliability in a high temperature load test is improved, and to provide a manufacturing method thereof. <P>SOLUTION: In the multilayered electronic parts, a pair of external electrodes 3 and internal electrodes 9 alternately connected thereto are formed on the end surfaces of an electronic part main body 1, by alternately laminating a plurality of the dielectric layers 7 containing glass and the internal electrode layers 9. The glass disperses and exists between dielectric crystal particles 21 in a particle state, the relationship of D/t≤0.5 is satisfied when the thickness of the dielectric layer 7 is (t), and the maximum diameter of the glass particles 25 is D. The occupied area by the void 27 on the cross section of the electronic part main body 1 is 1% or less. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated electronic component and a manufacturing method thereof, and more particularly to a laminated electronic component having an extremely thin dielectric layer and a manufacturing method thereof.

[0002]

2. Description of the Related Art In recent years, with the miniaturization and high density of electronic equipment, multilayer electronic parts, for example, monolithic ceramic capacitors, are required to have a small size and a high capacity, which leads to an increase in the number of laminated dielectric layers. The dielectric layer has been made thinner.

As a raw material for forming a dielectric ceramic for such a monolithic ceramic capacitor or the like, for example, one disclosed in Japanese Patent Laid-Open No. 9-35989 is known. In this publication, the particle size of the raw material is D50.
Then, a ceramic green material having a thickness of 0.6 to 1.0 μm is used to form a dielectric green sheet having a thickness of 11 μm, and the firing is performed 1
It is described that by carrying out at a temperature of 270 to 1330 ° C., it is possible to stabilize the capacitance and easily obtain a multilayer ceramic capacitor having excellent reliability.

[0004]

However, in the method of manufacturing a laminated electronic component disclosed in Japanese Patent Laid-Open No. 9-35989, a laminated body formed by using a dielectric green sheet having a thickness of 11 μm as described above. Although excellent characteristics can be obtained in the case of a ceramic capacitor, with the recent increase in the size and capacity of monolithic ceramic capacitors,
When the thickness of the dielectric layer is extremely thin, for example, 3 μm or less, the grain size of the raw material used is D50.
Even if the particle size is adjusted to the range of 6 to 1.0 μm, since many coarse particles are present in the raw material, after firing, BaO—SrO—Li, which is a component of the glass powder, is included.
Glass particles formed of O—SiO ₂ are formed so as to penetrate the dielectric layer, and further, sintering of such coarse glass powder increases the number of voids in the dielectric layer. In the area where glass particles and voids are present, the electric field strength in the thickness direction is reduced, so that the insulation resistance of the dielectric layer is reduced, and in particular, insulation failure is likely to occur in the high temperature load test.

Therefore, it is an object of the present invention to provide a laminated electronic component which has a high insulating property even when the dielectric layer is made thin and which can improve the reliability in a high temperature load test, and a method for producing the same.

[0006]

According to the laminated electronic component of the present invention, the internal electrode layer is formed on the end face of the electronic component main body formed by alternately laminating a plurality of dielectric layers containing glass and internal electrode layers. In a laminated electronic component formed by respectively forming a pair of external electrodes that are alternately connected, the glass is present in the form of particles dispersed among dielectric crystal grains, the thickness of the dielectric layer is t, and the glass is D is the maximum diameter of
The relationship of 0.5 is satisfied, and the area occupancy of voids in the cross section of the electronic component body is 1% or less.

According to this structure, the maximum diameter of the glass, which is considered to have a great influence on the insulating property of the dielectric layer, is D / t ≦ 0.5, which is smaller than the thickness of the dielectric layer. Moreover, by reducing the area occupancy of the voids to 1% or less, the electric field strength in the entire dielectric layer is increased and the deterioration of the insulating property is suppressed, and in particular, the occurrence of insulation failure in the high temperature load test can be suppressed.

In the above laminated electronic component, the glass particles in the dielectric layer are 0.8 with respect to 100 parts by mass of the dielectric crystal particles.
It is desirable that the amount is ˜1.5 parts by mass. By setting the amount of glass in this range, the dielectric layer can be densified, the relative dielectric constant can be increased, and the insulating property of the dielectric layer can be improved.

In the above laminated electronic component, the thickness of the dielectric layer is preferably 3 μm or less. As the thickness of the dielectric layer is reduced to 3 μm or less, the influence of the glass formed in the dielectric layer on the insulating property is increased, and the capacitance can be increased. Therefore, in the present invention, the dielectric layer is used. It is effective to apply to a laminated electronic component having a thickness of 3 μm or less.

The method for producing a laminated electronic component of the present invention is a method for producing a laminated electronic component in which a body of an electronic component body formed by alternately laminating a plurality of dielectric green sheets and internal electrode patterns is fired. , The dielectric green sheet,
It is characterized in that 0.8 to 1.5 parts by mass of glass powder containing Li and / or B and having a particle diameter D50 of 0.4 to 0.7 μm is contained with respect to 100 parts by mass of the dielectric powder.

According to such a manufacturing method, first, by setting the particle diameter of the glass powder within the above range, it is possible to easily form a homogeneous dielectric green sheet without irregularities due to coarse particles.

Further, by setting the glass powder amount relative to the dielectric powder within the above range, segregation of the glass powder can be suppressed even after firing, and formation of coarse glass with respect to the thickness of the dielectric layer can be suppressed. The generation of voids due to the coarsening of glass can be suppressed. That is, since the amount of glass powder relative to the dielectric powder is small, the low resistance phase composed of glass and voids existing between the crystal grains that mainly constitute the dielectric layer is reduced, and the laminated electron with high insulation of the dielectric layer is reduced. Parts can be easily formed.

Further, in the method of manufacturing the laminated electronic component, it is desirable that the thickness of the dielectric green sheet is 4 μm or less. According to the production method of the present invention, since the particle diameter of the glass powder used is controlled to be a fine diameter, even if the thickness of the dielectric green sheet is as thin as 4 μm or less, it is a homogeneous material having no unevenness due to coarse particles. Can be easily formed.

In the method for manufacturing the above-mentioned laminated electronic component, it is desirable that the particle diameter ratio of the glass powder is D50 / D90 ≧ 0.7. In this way, by narrowing the particle size distribution of the glass powder, segregation of the glass formed in the dielectric layer can be further suppressed, so that penetration of the glass due to coarsening of the glass can be prevented and voids can be prevented. Therefore, it is possible to easily form a dielectric layer having a high insulation resistance even with a thinned dielectric layer.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION (Structure) A laminated ceramic capacitor which is a laminated electronic component of the present invention will be described in detail with reference to the schematic sectional view of FIG.

The laminated electronic component of the present invention is constructed by forming external electrodes 3 on both ends of the electronic component body 1.

The external electrode 3 is, for example, Cu or Cu.
And an Ni alloy paste are baked.

The electronic component body 1 has a capacitance portion 11 formed by alternately laminating dielectric layers 7 and internal electrode layers 9, and a capacitance of the same material as that of the dielectric layer 7 around the capacitance portion 11. The non-capacitance portion 13 that does not contribute to

The dielectric layer 7 is a sheet-shaped ceramic sintered body, and is composed of, for example, a dielectric ceramic formed by firing a dielectric green sheet containing BaTiO ₃ as a main component.

Here, the dielectric layer 7 which constitutes the capacitance section 11
The thickness t is preferably 3 μm or less for the purpose of increasing the electrostatic capacity, and in particular, the thickness of the dielectric layer is 1.5 to 10 μm for maintaining the insulating property together with the electrostatic capacity.
More preferably, it is 2.5 μm.

FIG. 2 is an enlarged view of a main part of the dielectric layer 7 sandwiched between the internal electrode layers 9.

As shown in FIG. 2, the dielectric layer 7 is composed of dielectric crystal particles 21 and glass particles 25 as a crystal phase, and these dielectric crystal particles 21 and glass particles 2 are contained.
Voids 27 are unavoidably formed in the grains and / or in the grain boundaries of No. 5. In addition, in the multilayer electronic component of the present invention, the dielectric layer 7 is provided more than the non-capacitance portion 13 side that does not contribute to electrostatic capacitance.
Is sandwiched between the internal electrode layers 9 and contributes to the capacitance.
The 1st side is densified and there are few voids.

Here, the size of the glass particles 25 is D / t ≦ 0, where t is the thickness of the dielectric layer 7 and D is the maximum diameter of the glass particles 25 contained in the dielectric layer 7. It is important to satisfy the relationship of 5. In this case, when the D / t ratio is larger than 0.5, the insulation resistance of the dielectric layer 7 decreases due to the low insulating property of the glass particles 25, and
This is because the short-circuit rate after firing increases and the failure rate in the high temperature load test also increases.

In the dielectric layer 7, D / t is 0.2 to 0.4 for the reason that the wettability with the dielectric porcelain is enhanced and the sinterability and the relative dielectric constant of the dielectric layer 7 are enhanced. Is more preferable.

The glass particles 25 are mainly obtained by firing glass powder used in the method for producing a laminated electronic component of the present invention, and include at least one of a crystalline phase and an amorphous phase. However, a mixture of these may be used.

Further, in the present invention, it is important that the area occupancy of the voids 27 in the cross section of the electronic component body 1 constituting the laminated electronic component is 1% or less. When the area occupancy of voids is larger than 1%, the insulating property and the electrostatic capacity of the dielectric layer 7 are lowered. In particular, it is more preferably 0.4% or less for the reason of increasing the insulation resistance of the dielectric layer 7 of the multilayer electronic component and improving the reliability in the high temperature load test.

Further, the average grain size of the dielectric crystal grains 21 constituting the dielectric layer 7 is 1 μm or less for the reason that it has a high insulation resistance, and even if the dielectric layer 7 is 3 μm or less, a high dielectric constant is obtained. The range of 0.1 to 0.4 μm is particularly desirable.

Further, it is desirable that the glass particles 25 contain Li and / or B for the reason of improving the wettability at the interface of the dielectric crystal particles 21, and further, further,
It is more desirable that Li and / or B form a complex oxide with a rare earth element or Si in order to improve the insulating property.

Further, the glass particles 2 in the dielectric layer 7
The content of 5 is 100% in order that the dielectric layer 7 is dense and enhances the electrostatic capacity and the insulating property.
The amount is preferably 0.8 to 1.5 parts by mass, and more preferably 1.2 to 1.4 parts by mass.

On the other hand, the dielectric crystal particles 21 constituting the dielectric ceramic are composed of a perovskite type complex oxide containing Ba, Ti, Mg, and Mn as metal elements, and the capacitance and It is desirable for improving temperature characteristics as well as insulating properties.

The internal electrode layer 9 is made of a metal film obtained by sintering a film of a conductive paste, and its thickness increases the effective area of the internal electrode layer 9 of the multilayer electronic component, for example, a static capacitance of a multilayer ceramic capacitor. 0.5 to 1.5 μm for the reason of increasing the capacitance and suppressing delamination
Is desirable.

Further, the number of laminated layers of the laminated electronic component of the present invention is such that the dielectric layers 7 constituting the laminated electronic component are thinned and multilayered. The number of layers is preferably 100 or more.

(Manufacturing Method) Regarding the manufacturing method of the multilayer electronic component of the present invention, first, a method of preparing the dielectric powder and the glass powder to be the dielectric layer 7 will be described.

BaTiO ₃ powder is preferably used as the main component of the dielectric powder. The synthesis method of the BaTiO ₃ powder is
There are solid-phase method, liquid-phase method (method of passing oxalate, etc.), hydrothermal synthesis method, etc. Among them, hydrothermal synthesis method is preferable because of its narrow particle size distribution and high crystallinity. BaTiO
The specific surface area of the _three powders is preferably 1.7 to 6.6 m ² / g.

The dielectric powder of the present invention is BaTi.
It is prepared by mixing a predetermined amount of magnesium oxide (MgO) and manganese carbonate (MnCO ₃ ) as auxiliary agents with the O ₃ raw material powder.

The average particle diameter and the specific surface area of this dielectric powder promote the thinning and densification of the dielectric layer and improve the capacitance and the temperature characteristics thereof.
0.2-0.5 μm, 1.7-7.5 m ² / g is desirable, and especially the average particle size is 0.3-0.4 μm.
It is more desirable that the specific surface area is ² to 4 m ² / g.

On the other hand, the glass powder is composed of Y ₂ O ₃ powder and SiO _2.
2 powder, further Li ₂ CO ₃ powder and / or B ₂ O ₃ powder are weighed and mixed, and then calcined at a temperature of 900 to 1100 ° C., and then this calcined powder is pulverized by using a ball mill. It is prepared by At this time, it is important that the particle diameter D50 of the glass powder is adjusted to the range of 0.4 to 0.7 μm. When the particle size of the glass powder is smaller than 0.4 μm, the glass powder is likely to aggregate, so that the glass particles 25 having a large maximum diameter are likely to be formed during firing, while the particle size of the glass powder is 0.7 μm. If it is larger than this, coarse glass particles 25 are likely to be formed in the dielectric layer and the number of voids 27 is increased, so that the insulating property of the dielectric layer is deteriorated.

Therefore, the particle size of the glass powder is D50 / D9, because coarse particles are excluded to increase the insulation resistance.
It is desirable that 0 ≧ 0.7.

D50 means a cumulative distribution of 0.5, that is, in this case, 50% by mass based on the total amount of glass powder.
Shows the particle size. D90 indicates a particle size when the cumulative distribution is 0.9, that is, 90% by mass based on the total amount of the glass powder in this case.

Next, a raw material slurry for forming a green sheet is prepared using the above-mentioned dielectric powder and glass powder.

First, glass powder was added to the dielectric powder, and the diameter was 10 mm together with a known dispersant and dispersion medium.
In a ball mill using ZrO ₂ balls, the raw material slurry is prepared by wet pulverizing and mixing until the average particle size becomes about 0.4 to 0.7 μm. It is important that the amount of the glass powder added to 100 parts by mass of the dielectric powder is 0.8 to 1.5 parts by mass, but for the reason that the capacitance and the insulating property of the dielectric layer 7 are kept high, Especially 1.2-1.4
Parts by mass are desirable. In the multilayer electronic component of the present invention, glass particles are formed in an amount corresponding to the amount of glass powder added, as described above. When the amount of the glass powder added is less than 0.8 parts by mass, the sinterability of the dielectric ceramic decreases, so that the number of voids increases, while when it exceeds 1.5 parts by mass, the dielectric material is added. Since the proportion of the glass particles 25 is larger than the proportion of the dielectric crystal particles 21 made of, the electrostatic capacity and the insulating property of the dielectric layer 7 are lowered.

Next, an organic binder is mixed with the mixture of the dielectric powder and the glass powder to obtain a slurry, and a green sheet having a thickness of 1.5 to 4 μm is formed by the doctor blade method. .

Next, an internal electrode paste is applied to the green sheet to form an internal electrode pattern. The internal electrode pattern preferably has a thickness of 0.7 to 2 μm. Here, the average particle size of the base metal particles contained in the conductive paste for forming the internal electrode pattern is preferably 0.1 to 0.5 μm for thinning the internal electrode pattern.

As the base metal powder, at least one metal selected from Cu, Ni and the like is preferably used. Ni is particularly preferable in order to reduce the manufacturing cost by performing simultaneous firing with the dielectric ceramics.

As described above, the thickness of the internal electrode pattern is set to 2 μm.
By setting the particle diameter D50 of the glass powder added as an accessory component to 0.4 to 0.7 μm even if it is m or less, the surface tension of the glass component is lowered and wets the metal powder forming the internal electrode pattern. Since the property is improved, the formation of coarse metal particles can be suppressed, and pressing and penetration of the dielectric layer 7 can be prevented, so that a short circuit between the internal electrode layers 9 can be eliminated.

That is, it is desirable that the particle diameter D50 of the glass powder be less than or equal to twice the particle diameter of the metal powder forming the internal electrode pattern. Further, also for the reason that the formation of coarse metal particles can be suppressed, it is desirable that the particle size of the glass powder is 0.7 or more in terms of D50 / D90.

Next, a plurality of green sheets having the internal electrode patterns are laminated and thermocompression bonded. afterwards,
This laminated body is cut into a lattice shape to obtain a molded body of the electronic component body 1. On both end surfaces of the molded body of the electronic component body 1,
The ends of the internal electrode patterns are exposed alternately.

Next, the molded body of the electronic component main body 1 is subjected to binder removal treatment at 200 to 500 ° C. at a temperature rising rate of 5 to 40 ° C./h in the atmosphere, and then 500 in a reducing atmosphere.
The temperature rising rate from ℃ is set to 200 to 500 ℃ / h, 120
Baking at a temperature of 0 to 1300 ° C. for 2 to 5 hours, followed by 20
Cool at a temperature-fall rate of 0 to 400 ° C./h, and in a nitrogen atmosphere,
Reoxidation is performed at 00 to 1100 ° C.

In particular, the glass particles 2 constituting the dielectric layer 7
It is desirable to set the temperature rising rate from 500 ° C. to 200 to 400 ° C./h for the reason that the maximum diameter of 5 can be reduced and the voids 27 can be reduced.

After that, the external electrode paste is applied to both end surfaces of the fired electronic component body 1 and baked in nitrogen to form the external electrodes 3, and further the plated films are formed on the surfaces of the external electrodes 3. .

[0051]

Example A monolithic ceramic capacitor, which is one of multi-layer electronic components, was manufactured as follows.

First, as a glass powder, Y ₂ O ₃ was used in a molar ratio.
40% powder, ₂ Li ₂ CO ₃ powder or ₂ B ₂ O ₃ powder
0%, SiO ₂ powder was weighed and mixed so as to have a ratio of 40%, calcined at a temperature of 1000 ° C., and thereafter,
The calcined powder is crushed to obtain particle sizes D50 and D50 / D9.
Glass powder was prepared by finely pulverizing 0 into the particle size shown in Table 1.

Next, BaTiO ₃ raw material powder having an average particle size of 0.4 μm and a specific surface area of 3.2 m ² / g was used.
For 100 parts by weight of TiO ₃ , magnesium oxide (M
gO) 0.15 parts by mass, manganese carbonate (MnCO ₃ ).
And 0.15 parts by weight, Y ₂ O ₃ powder and SiO ₂ powder, further Li ₂ CO ₃ powder or B ₂ O ₃ powder of the above glass powder prepared by mixing a predetermined ratio shown in Table 1 So that the diameter is 10 mm together with a known dispersant and dispersion medium.
Crushed and mixed in a ball mill using ZrO ₂ balls of
A raw material slurry was prepared. After mixing this ceramic powder and an organic binder to obtain a slurry, a dielectric green sheet having a desired thickness was prepared by a doctor blade method.

Next, screen printing was performed on this green sheet using an internal electrode paste composed of Ni powder having an average particle size of 0.3 μm, ethyl cellulose and terpineol. At that time, the effective area of the internal electrode pattern is 4.
It was set to 5 mm ² . Next, 100 green sheets on which the internal electrode pattern is formed are laminated, and 20 green sheets on which the internal electrode paste is not printed are laminated on the upper and lower surfaces thereof, respectively, and hot pressed to integrate them into a predetermined size. It cut | disconnected and the electronic component main body molded object was produced.

Then, the molded body of the electronic component main body was subjected to binder removal treatment at 400 ° C. in the atmosphere, and thereafter at a temperature rising rate of 200, 300, 400 ° C. and a maximum temperature of 1270 ° C. (oxygen partial pressure of 10 ⁻⁶ Pa). It was fired for 2 hours, and then reoxidized at 1000 ° C. in an air atmosphere to produce an electronic component body.

Next, after barrel-polishing the electronic component body, external electrode paste containing Cu powder is applied to both ends of the electronic component body and baked in nitrogen at 850 ° C. to form the external electrode 3. A Ni plating layer and a Sn plating layer were sequentially applied on the electrodes.

First, each of the manufactured monolithic ceramic capacitors was subjected to cross-section polishing by five pieces, and then observed using an electron microscope, and the area occupancy of voids was calculated from the cross-section photograph.

Next, the initial capacitance (C) and insulation resistance (R) of each of these 100 monolithic ceramic capacitors were measured. The measurement is performed at a reference temperature of 25 ° C., the capacitance is 1.0 kHz, and the input signal level is 0.5.
It was measured under the condition of Vrms. Further, the short-circuit rate was calculated from the number of laminated ceramic capacitors that were short-circuited during the measurement. In addition, the insulation resistance was calculated as an average value excluding the short-circuited sample.

The high temperature load test was conducted for 100 samples under the conditions of a temperature of 85 ° C. and a voltage of 9.5 V for 1000 hours to evaluate the insulation resistance. The insulation resistance (R) was measured by applying a DC voltage of 10 V for 1 minute.

On the other hand, as a comparative example, a sample was prepared in which the raw material particle diameter of the dielectric powder and the glass powder was 0.8 μm at D50, and the same evaluation as in the present invention was performed.

[0061]

[Table 1]

As is clear from the results in Table 1, the D50 of the glass powder was 0.4 to 0.7 μm, the particle size D50 / D90 of the glass powder was 0.4 to 0.9, and after firing. When the thickness of the dielectric layer is t and the maximum diameter of the glass particles constituting the dielectric layer is D, Sample No. No. D / t set to 0.5 or less. In 2 to 15, although there is a difference in capacitance depending on the amount of glass powder added, the insulation resistance is 330 MΩ
As described above, the short-circuit rate was 9% or less, and the number of defects was as small as 9/100 or less in the high temperature load test.

Particularly, the particle size of the glass powder is set to D50 / D90.
N of 0.7 or more and D / t of 0.3 or less
o. 8-10, the void area occupation ratio is 0.3-0.
It was as low as 4%, the short-circuit rate after firing was as low as 3% or less, and there were no defects in the high temperature load test.

On the other hand, in Sample 1 in which the D50 of the dielectric powder and the glass powder was 0.8 μm, the particle size D50 / D90 ratio of the glass powder was not controlled and the number of coarse particles increased, so that the dielectric layer D / t of the glass particles inside is 0.8
As a result, the insulation resistance of the laminated ceramic capacitor after firing decreased to 140 MΩ or less, the short-circuit rate increased to 18% or more, and the failure in the high temperature load test was 2
There were many as 5/100.

[0065]

As described above in detail, in the present invention, when the thickness of the dielectric layer is t and the maximum diameter of the glass particles contained in the dielectric layer is D, D / t ≦ 0.5. In addition, the area occupancy rate of voids in the cross section of the electronic component body is 1% or less, so that even the thinned dielectric layer has improved insulation properties, and in particular, insulation failure occurs in a high temperature load test. Can be prevented.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a multilayer electronic component of the present invention.

FIG. 2 is an enlarged view of a main part of a dielectric layer sandwiched between internal electrode layers of FIG.

[Explanation of symbols]

1 Electronic component body 3 external electrodes 7 Dielectric layer 9 Internal electrode layer 21 Dielectric crystal particles 25 glass particles 27 void

Claims (6)

[Claims] 1. A pair of external electrodes, to which the internal electrode layers are alternately connected, are formed on an end face of an electronic component body formed by alternately laminating a plurality of glass-containing dielectric layers and internal electrode layers. In the laminated electronic component, the glass is present in a state of being dispersed between the dielectric crystal particles in a particle shape, and when the thickness of the dielectric layer is t and the maximum diameter of the glass particles is D, D / A multilayer electronic component satisfying the relationship of t ≦ 0.5 and having an area occupation rate of voids of 1% or less in the cross section of the electronic component body. 2. The multilayer electronic component according to claim 1, wherein the glass particles in the dielectric layer are 0.8 to 1.5 parts by mass with respect to 100 parts by mass of the dielectric crystal particles. 3. The laminated electronic component according to claim 1, wherein the thickness of the dielectric layer is 3 μm or less. 4. A method for producing a laminated electronic component, comprising firing an electronic component main body formed by alternately laminating a plurality of dielectric green sheets and internal electrode patterns, wherein the dielectric green sheets are dielectric layers. With respect to 100 parts by mass of body powder,
It contains Li and / or B and has a particle size D50 of 0.4 to 0.
A method for producing a laminated electronic component, comprising 0.8 to 1.5 parts by mass of glass powder having a size of 7 μm. 5. The method for producing a laminated electronic component according to claim 4, wherein the thickness of the dielectric green sheet is 4 μm or less. 6. The particle size ratio of the glass powder is D50 / D90 ≧
It is 0.7, The manufacturing method of the laminated electronic component of Claim 4 or 5 characterized by the above-mentioned.