Multilayer capacitor and its mounting substrate

Abstract

To provide a multilayer capacitor having improved bending strength and a mounting board of the same.SOLUTION: The present invention provides a multilayer capacitor and a mounting board of the same. The multilayer capacitor includes: a body which includes a plurality of dielectric layers and first and second internal electrodes alternately disposed with the dielectric layers interposed therebetween, and which further includes an active region where the first and second internal electrodes overlap each other, and upper and lower covers disposed above and below the active region, respectively; and first and second external electrodes disposed on the body to be connected to the first and second internal electrodes, respectively. The upper and lower covers include BT (barium titanate, BaTiO3) and YSZ (Yttria stabilized zirconia).SELECTED DRAWING: Figure 1

Description

Technical Field

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[0001] The present invention relates to a multilayer capacitor and a mounting substrate thereof.

Background Art

[0002] Multilayer capacitors are small in size but can achieve high capacitance, and are used in various electronic devices.

[0003] Recently, with the rapid rise of environmentally friendly automobiles and electric vehicles, the electric drive systems in automobiles have increased, and accordingly, the demand for multilayer capacitors required for automobiles has also increased.

[0004] In order to be used as automotive parts, high levels of thermal reliability, electrical reliability, and mechanical reliability are required, so the performance required for multilayer capacitors is gradually becoming more sophisticated.

[0005] Among such mechanical properties, there is bending strength. If the bending strength is weak, when a multilayer capacitor is mounted on a substrate and pressed, bending cracks in the form of penetrating the multilayer capacitor may occur due to the stress applied to the multilayer capacitor.

[0006] Such bending cracks may cause the internal electrodes to be disconnected, which may cause product defects that reduce the capacitance of the product.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] The object of the present invention is to provide a multilayer capacitor having improved bending strength and a mounting substrate for the same. [Means for solving the problem]

[0009] One aspect of the present invention provides a multilayer capacitor comprising a plurality of dielectric layers, first and second internal electrodes arranged alternately with the dielectric layers in between, a main body including an active region where the first and second internal electrodes overlap, and upper and lower covers arranged above and below the active region, respectively, and first and second external electrodes arranged on the main body so as to be connected to the first and second internal electrodes, respectively, wherein the upper and lower covers include BT (barium titanate, BaTiO3) and YSZ (Yttria stabilized zirconia).

[0010] In one embodiment of the present invention, the YSZ may have a partially tetragonal phase.

[0011] In one embodiment of the present invention, the composition of the active region and the composition of the upper and lower cover regions of the main body may differ.

[0012] In one embodiment of the present invention, the active region may include BT and not include YSZ.

[0013] In one embodiment of the present invention, the upper and lower covers may contain 0.5 to 10 parts by weight of YSZ per 100 parts by weight of BT.

[0014] In one embodiment of the present invention, the YSZ size of the upper and lower covers can be 5 to 25% of the BT size.

[0015] In one embodiment of the present invention, the total thickness of the upper and lower covers can be 10 to 40% of the total thickness of the main body.

[0016] In one embodiment of the present invention, the main body includes a first surface and a second surface facing each other in a first direction, a third surface and a fourth surface facing each other in a second direction perpendicular to the first direction, and a fifth surface and a sixth surface facing each other in a third direction perpendicular to the first direction, the first and second internal electrodes are alternately arranged in the first direction, and the first and second external electrodes can be respectively arranged on the third and fourth surfaces of the main body.

[0017] In one embodiment of the present invention, the first and second external electrodes can each include first and second connection portions respectively arranged on the third and fourth surfaces of the main body, and first and second band portions respectively extending from the first and second connection portions to a part of the first surface of the main body.

[0018] Another aspect of the present invention provides a mounting substrate for a multilayer capacitor, including a substrate having first and second electrode pads on one surface and the multilayer capacitor, and the first and second external electrodes of the multilayer capacitor are mounted so as to be respectively connected to the first and second electrode pads.

Advantages of the Invention

[0019] According to one embodiment of the present invention, a composite material in which BT and YSZ are mixed can be applied to the cover to improve the bending strength of the multilayer capacitor.

Brief Description of the Drawings

[0020] [Figure 1] It is a perspective view showing a schematic structure of a multilayer capacitor according to an embodiment of the present invention. [Figure 2] (a) and (b) are plan views respectively showing the structures of the first and second internal electrodes of FIG. 1. [Figure 3] It is a cross-sectional view taken along the line I-I' of FIG. 1. [Figure 4] It is a graph showing the three-point bending strength of a BT-YSZ composite according to the content of YSZ. [Figure 5](a) and (b) are SEM photographs showing the fracture surfaces of the BT ceramic in the active region and the BT-YSZ composite material of the cover, respectively. [Figure 6] It is a graph showing the yield rates according to the pushing depth in a comparative example where the active region and the cover are made of BT and a multilayer capacitor according to an embodiment of the present invention, respectively. [Figure 7] It is a perspective view showing a form in which the multilayer capacitor of FIG. 1 is mounted on a substrate.

Mode for Carrying Out the Invention

[0021] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the embodiments of the present invention can be modified into several other forms, and the scope of the present invention is not limited to the embodiments described below. In addition, the embodiments of the present invention are provided to more fully explain the present invention to those having average knowledge in the technical field. Therefore, the shape and size of elements in the drawings may be enlarged, reduced (or emphasized or simplified) for clearer explanation, and elements denoted by the same reference numerals in the drawings are the same elements.

[0022] Also, throughout the specification, stating that a certain component "includes" means that, unless otherwise stated to the contrary, it does not exclude other components but can further include other components.

[0023] Referring to FIGS. 1 to 3, a multilayer capacitor 100 according to an embodiment of the present invention includes a main body 110 and first and second external electrodes 131 and 132.

[0024] To clearly explain this embodiment, when defining the direction of the main body 110, X, Y, and Z shown on the drawing indicate the length direction, the width direction, and the thickness direction, respectively.

[0025] Here, the thickness direction can be used with the same concept as the stacking direction in which the dielectric layers 111 are stacked.

[0026] Furthermore, the shape of the main body 110 is not particularly limited, and for example, it can have an approximately hexahedral shape.

[0027] In this embodiment, for the sake of explanation, the two opposing surfaces of the main body 110 in the Z direction on which the dielectric layers 111 are stacked are defined as the first and second surfaces 1 and 2, the two opposing surfaces in the X direction connected to the first and second surfaces 1 and 2 are defined as the third and fourth surfaces 3 and 4, and the two opposing surfaces in the Y direction that intersect perpendicularly with these are defined as the fifth and sixth surfaces 5 and 6.

[0028] The main body 110 includes an active region 115 and upper and lower covers 112 and 113 which are margin sections.

[0029] The active region 115 is a part that contributes to the formation of the capacitor's capacitance, and is constructed by stacking multiple dielectric layers 111 and first and second internal electrodes 121 and 122 alternately arranged in the Z direction with the dielectric layers 111 in between.

[0030] The upper cover 112 is a portion formed with a predetermined thickness on the upper surface of the first internal electrode 121, which is located at the top of the active region 115 in the drawing, and the lower cover 113 is a portion formed with a predetermined thickness on the lower surface of the second internal electrode 122, which is located at the bottom of the active region 115.

[0031] In this embodiment, the upper cover 112 and the lower cover 113 can be made of a dielectric having a different composition from the dielectric layer 111 included in the active region 115.

[0032] In this case, the total thickness of the upper and lower covers 112 and 113 can be 10 to 40% of the total thickness of the main body 110.

[0033] The dielectric layer 111 of the active region 115 contains the dielectric powder of the embodiment described above, and in the sintered state, the boundaries between adjacent dielectric layers 111 can be integrated to such an extent that they are difficult to confirm without using a scanning electron microscope (SEM).

[0034] The first and second internal electrodes 121 and 122 are electrodes having opposite polarities, arranged to face each other along the stacking direction of the dielectric layer 111, and can be electrically insulated from each other by the dielectric layer 111 placed in between.

[0035] The first and second internal electrodes 121 and 122 can each have one end exposed through the third and fourth surfaces 3 and 4 of the main body 110.

[0036] Furthermore, the ends of the first and second internal electrodes 121 and 122, which are exposed through the third and fourth surfaces 3 and 4 of the main body 110, can be electrically connected to the first and second external electrodes 131 and 132, respectively, via the third and fourth surfaces 3 and 4 of the main body 110.

[0037] When a predetermined voltage is applied to the first and second external electrodes 131 and 132, charge is accumulated between the first and second internal electrodes 121 and 122 that are opposite each other.

[0038] At this time, the capacitance of the multilayer capacitor 100 becomes proportional to the overlapping area of ​​the first and second internal electrodes 121 and 122 that overlap each other in the Z direction in the active region 115.

[0039] The first and second internal electrodes 121 and 122 are formed of a conductive metal, and materials such as nickel (Ni) or nickel (Ni) alloy can be used, but the present invention is not limited thereto.

[0040] Furthermore, the above-mentioned method for printing conductive metals can be screen printing or gravure printing, and the present invention is not limited to these methods.

[0041] The first and second external electrodes 131 and 132 each include first and second connecting portions 131a and 132a, and first and second band portions 131b and 132b, respectively.

[0042] The first and second connecting portions 131a and 132a are located on the third and fourth surfaces 3 and 4 of the main body 110, respectively, and are in contact with and electrically connected to the exposed portions of the first and second internal electrodes 121 and 122, respectively.

[0043] The first and second band sections 131b and 132b are portions that extend from the first and second connecting sections 131a and 132a to a part of the first surface 1 of the main body 110, respectively.

[0044] In this case, in order to improve the bonding strength, the first and second band portions 131b and 132b can be extended from the first and second connecting portions 131a and 132a to a part of the second surface 2 and a part of the fifth and sixth surfaces 5 and 6 of the main body 110, respectively.

[0045] Such first and second external electrodes 131 and 132 can be formed from a conductive paste containing a conductive metal.

[0046] The conductive metal mentioned above may be nickel (Ni), copper (Cu), palladium (Pd), gold (Au), or alloys thereof, and the present invention is not limited thereto.

[0047] On the other hand, the first and second external electrodes 131 and 132 can, if necessary, have a plating layer (not shown) formed on their surface made of nickel (Ni) or tin (Sn).

[0048] One method to improve the bending strength of conventional multilayer capacitors is to stack two multilayer capacitors and connect their external electrodes with a metal frame to create a single element. Another method involves applying a conductive resin layer to the external electrodes.

[0049] However, while the two methods described above alleviate the stress on the multilayer capacitor, if the capacitor is subjected to stress exceeding a certain level, the main body may not be able to withstand it, and bending cracks may occur.

[0050] Furthermore, when using a metal frame, there is the problem that the size of the electronic components themselves increases by the size of the metal frame.

[0051] Furthermore, mechanical strength is a factor that affects the bending strength characteristics of multilayer capacitors.

[0052] When a circuit board on which a multilayer capacitor is mounted is pressed, stress is applied to the chip due to the warping of the board. This stress is greatest at the edges of the band, and small defects in this area can cause cracks to form.

[0053] In other words, one way to minimize crack formation is to increase the mechanical strength near the ends of the band sections in multilayer capacitors, where stress is particularly concentrated.

[0054] For this purpose, in the present invention, a BT-YSZ composite material, in which YSZ (Yttria stabilized zirconia) nanoparticles are mixed with a BT (barium titanate, BaTiO3) matrix, is applied to the upper and lower covers.

[0055] At this time, the upper and lower covers 112 and 113 may contain 0.5 to 10 parts by weight of YSZ per part by weight of BT100.

[0056] Figures 5(a) and (b) are SEM images taken at magnifications of 20,000 to 50,000, showing the microstructure of the fracture surfaces of the BT ceramic in the active region and the BT-YSZ composite material of the cover, respectively. As shown in Figure 5, the YSZ size in the upper and lower covers 112 and 113 can be 5 to 25% of the BT size.

[0057] In this case, the YSZ size is the average value obtained by measuring the YSZ size of images taken at points where the fracture surface, generated parallel to the YZ plane, is divided into three equal parts in the Y direction, after cutting the multilayer capacitor in the center in the X direction.

[0058] BT-YSZ composite materials have a mixture structure in which ZrO2 nanoparticles are dispersed in a BT dielectric matrix.

[0059] The inserted ZrO2 particles are oxide particles with a size of several tens of nanometers that contain 3 mol% Y2O3 and are partially stabilized as a tetragonal phase.

[0060] While BT dielectric ceramics have a bending strength of approximately 30-80 MPa, depending on the additives and sintering temperature, ZrO2 particles, when sintered, have a high bending strength of 1,200 MPa.

[0061] Therefore, as shown in Figure 4, in the case of a composite material in which ZrO2 particles are inserted into BT, the bending strength increases to 125 MPa depending on the YSZ content, and it is expected that the bending strength characteristics will be higher than those of dielectric ceramic materials formed only from BT when fabricating multilayer capacitors.

[0062] Furthermore, in the case of YSZ, the sintering temperature is higher than that of BT, at over 1,300°C. Therefore, when BT and YSZ are mixed and sintered, most of the compound remains in the secondary phase. As a result, the mechanical properties of the BT-YSZ mixed material, such as elastic modulus, Young's modulus, and flexural strength, increase according to the rule of mixture.

[0063] Therefore, in the case of the multilayer capacitor of this embodiment in which BT-YSZ composite material is applied to the upper and lower covers, the bending strength of the multilayer capacitor can be improved compared to existing multilayer capacitors in which the upper and lower covers are made only of BT, thereby significantly reducing or preventing the occurrence of bending cracks.

[0064] On the other hand, when sintering BT-YSZ composite materials at temperatures above 1,200 degrees Celsius, a portion of the ZrO2, which is partially in the tetragonal phase, diffuses into the BT crystal grains, thus achieving the effect of doping the BT dielectric with Zr.

[0065] When the effect of doping the BT dielectric with the Zr element appears in this way, changes in the dielectric properties may be induced in the active region. To prevent this, in this embodiment, it is preferable to apply the BT-YSZ structure only to the upper and lower covers, and to realize the active region with BT only, without including YSZ.

[0066] Figure 6 shows a comparison of the bending deformation test results of a multilayer capacitor having the structure of an embodiment of the present invention and a conventional multilayer capacitor.

[0067] Here, Comparative Example (#1) is a structure in which the active region and the cover are made of the same BT, while Example (#2) is a multilayer capacitor having a structure in which the upper and lower covers are made of BT-YSZ composite material.

[0068] In this case, the multilayer capacitors used in each sample had a length of 1.6 mm in the X direction, a length of 0.8 mm in the Y direction, and an electrical characteristic of 2.2 μF.

[0069] In this embodiment, 3 parts by weight of YSZ were added to the upper and lower covers per 100 parts by weight of BT.

[0070] These multilayer capacitors were each mounted on a PCB, and the occurrence of cracks in the multilayer capacitors was observed while increasing the indentation depth of the PCB by 1 mm increments, as shown in Figure 6.

[0071] Referring to Figure 6, in the comparative example, cracks began to appear when the pressing depth was 5 mm, the good product rate approached 0% when the pressing depth exceeded 10 mm, and the good product rate was 0% when the pressing depth exceeded 11 mm. The good product rate can be determined as follows: When an MLCC is mounted on a PCB board and the board is pressed using a customized circular chip, the board bends and the capacitance of the MLCC changes. At a certain pressing depth, the capacitance decreases rapidly due to crack formation. In this case, the MLCC is short-circuited, which means it is dead. The good product rate is the percentage of surviving MLCCs (MLCCs that are not defective) out of all MLCCs tested. In #1 of Figure 6, the total number of MLCCs tested is 20. At a pressing depth of 4 mm, there are no cracks in any of the MLCCs, but at 5 mm, one is defective, so the good product rate at 5 mm is 95% (1 / 20 dead). Furthermore, with an insertion depth of 6mm, the yield rate is 80% (4 / 20 dead).

[0072] In contrast, in the example, the yield rate was 99% or higher up to an indentation depth of 9 mm, and even when the indentation length was 10 mm, the yield rate was 95%. Furthermore, the phenomenon of a sharp decrease in the yield rate, as seen in the comparative example, did not occur even when the indentation depth exceeded 11 mm.

[0073] Therefore, as in the embodiment of the present invention, it can be confirmed that applying BT-YSZ composite material to the upper and lower covers improves the bending strength characteristics of the multilayer capacitor.

[0074] Figure 7 is a perspective view showing the multilayer capacitor from Figure 1 mounted on a substrate.

[0075] Referring to Figure 7, the mounting substrate for the multilayer capacitor according to this embodiment includes a substrate 210 on which the multilayer capacitor 100 is mounted, and first and second electrode pads 221 and 222 formed on the upper surface of the substrate 210 so as to be spaced apart from each other.

[0076] The multilayer capacitor 100 can be electrically connected to the substrate 210 by solder 231, 232, with the first and second external electrodes 131, 132 positioned to contact the first and second electrode pads 221, 222, respectively.

[0077] In this case, in order to achieve the effect of improving the bending strength of the multilayer capacitor 100, it is preferable that the first and second internal electrodes 121 and 122 are arranged horizontally with respect to the substrate 210, as in this embodiment.

[0078] Here, the multilayer ceramic capacitor 100 is a multilayer ceramic capacitor according to the embodiment of the present invention described above, and a detailed explanation will be omitted below to avoid redundancy.

[0079] Although embodiments of the present invention have been described in detail above, it will be clear to those with ordinary skill in the art that the scope of the present invention is not limited thereto, and that various modifications and variations are possible without departing from the technical idea of ​​the present invention as described in the claims. [Explanation of Symbols]

[0080] 100 Multilayer Capacitors 110 Main Unit 111 Dielectric layer 112, 113 Upper and lower covers 115 Active region 121, 122 First and second internal electrodes 131, 132 First and second external electrodes 210 circuit boards 221, 222 First and second electrode pads

Claims

1. A body comprising a plurality of dielectric layers including a first surface and a second surface facing each other in a first direction, a third surface and a fourth surface facing each other in a second direction perpendicular to the first direction, and a fifth surface and a sixth surface facing each other in a third direction perpendicular to the first direction, and a first internal electrode and a second internal electrode arranged alternately in the first direction with the dielectric layers in between, an active region where the first internal electrode and the second internal electrode overlap, and an upper cover and a lower cover arranged above and below the active region, respectively. The body includes a first external electrode and a second external electrode, which are arranged on the third and fourth surfaces of the body, respectively, so as to be connected to the first internal electrode and the second internal electrode, respectively. The upper cover and the lower cover are made of BT (barium titanate, BaTiO ３ ) and YSZ (Yttria stabilized zirconia), The upper cover and the lower cover contain 0.5 to 10 parts by weight of YSZ per 100 parts by weight of BT. YSZ is distributed throughout the entire upper cover and the lower cover. Multilayer capacitor.

2. The multilayer capacitor according to claim 1, wherein the YSZ has a partially tetragonal phase.

3. The multilayer capacitor according to claim 1 or 2, wherein the composition of the active region and the composition of the upper cover and lower cover regions are different for the main body.

4. The multilayer capacitor according to claim 3, wherein the active region includes BT and does not include YSZ.

5. The multilayer capacitor according to any one of claims 1 to 4, wherein the YSZ size in the upper cover and the lower cover is 5 to 25% of the BT size.

6. The multilayer capacitor according to any one of claims 1 to 5, wherein the total thickness of the upper cover and the lower cover is 10 to 40% of the total thickness of the main body.

7. In the upper cover and the lower cover, the YSZ size is 5 to 25% of the BT size. The multilayer capacitor according to any one of claims 1 to 6, wherein the total thickness of the upper cover and the lower cover is 10 to 40% of the total thickness of the main body.

8. The multilayer capacitor according to any one of claims 1 to 7, wherein the first external electrode and the second external electrode each include a first connecting portion and a second connecting portion disposed on the third and fourth surfaces of the main body, and a first band portion and a second band portion extending from the first connecting portion and the second connecting portion to a part of the first surface of the main body, respectively.

9. A substrate having a first electrode pad and a second electrode pad on one side, A multilayer capacitor according to any one of claims 1 to 8, A mounting substrate for a multilayer capacitor, wherein the first external electrode and the second external electrode of the multilayer capacitor are mounted such that they are connected to the first electrode pad and the second electrode pad, respectively.

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