Electronic component and film forming method

Abstract

The invention provides an electronic component and a film forming method. The electronic component includes an element (20), an external electrode covering a portion of an outer surface (21) of the element (20), and a protective film (30) of alumina. The protective film (30) is located between the green body (20) and the external electrode. The thickness of the protective film (30) in the direction perpendicular to the outer surface (21) of the green body (20) is set as the film thickness (TP). The protective film (30) is viewed in a cross-section orthogonal to the outer surface (21) of the element (20) in a cross-section at a location covered by the external electrode. When the average value and the standard deviation of the film thickness (TP) are determined within a range of 1 [mu] m in the direction along the outer surface (21) of the green body (20), the ratio of the standard deviation to the average value is 0.4 or more.

Description

Technical Field

[0001] The present disclosure relates to an electronic component and a film forming method. Background Art

[0002] The electronic component described in Patent Document 1 comprises a body and an external electrode. The body is made of ceramic. The external electrode covers a portion of the outer surface of the body. In addition, the external electrode is formed by applying a conductive paste containing glass powder to the outer surface of the body and firing it. The body has a reaction layer at a location in contact with the external electrode. The glass component contained in the conductive paste reacts with the ceramic component of the body to form a reaction layer. The presence of the reaction layer prevents the body from being corroded by the plating solution and the solder flux.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2000-040635

[0004] In the electronic component described in Patent Document 1, in order to form a reaction layer on the blank, for example, it is necessary to make the conductive paste contain low softening point glass or the like. Therefore, when the conductive paste is fired, the glass component contained in the conductive paste easily flows to the outer surface of the molten conductive paste. As a result, after the conductive paste is fired, the glass component easily precipitates to the outer surface of the external electrode. If a large amount of glass component is precipitated on the outer surface of the external electrode in this way, when a film forming process such as plating is performed on the outer surface of the external electrode, poor film formation is likely to occur. Therefore, in addition to forming a reaction layer on the blank, a technology is required to prevent the blank from being corroded by the plating solution and the solder flux. Summary of the invention

[0005] In order to solve the above-mentioned problems, an electronic component of one embodiment of the present invention comprises a blank, an external electrode covering a portion of the outer surface of the blank, and a protective film of aluminum oxide, wherein the protective film is located between the blank and the external electrode, and the thickness of the protective film in a direction perpendicular to the outer surface of the blank is defined as the film thickness. When the protective film is observed in section at a portion covered by the external electrode in a section perpendicular to the outer surface of the blank, when the average value and standard deviation of the film thickness are calculated within a range of 1 μm in the direction along the outer surface of the blank, the ratio of the standard deviation to the average value is greater than 0.4.

[0006] In addition, in order to solve the above-mentioned problems, a film-forming method of one mode of the present invention is a film-forming method for forming a protective film on the outer surface of a blank, wherein the protective film is a film of aluminum oxide, wherein the film-forming method comprises: a stack preparation step for preparing the blank; a first grinding step for grinding the blank using a first grinding powder, wherein the first grinding powder is a powder of aluminum oxide; and a second grinding step for grinding the blank using a second grinding powder after the first grinding step, wherein the second grinding powder is a powder of aluminum oxide, and when the most frequent value of the particle size in the particle size distribution, i.e., the central particle size, is compared between the first grinding powder and the second grinding powder, the central particle size of the second grinding powder is less than 1 / 10 of the central particle size of the first grinding powder.

[0007] According to the above structure, the coefficient of variation of the film thickness of the protective film is greater than 0.4, so the deviation of the film thickness is relatively large. That is, the protective film has countless bumps on the outer surface. As a result, due to the anchoring effect, the protective film improves the close contact between the glass film and the protective film, and the close contact between the external electrode and the glass film. In this way, if the close contact of each layer stacked on the outer surface of the protective film is high, the plating solution and the solder flux are prevented from infiltrating from the boundary surface of each layer. Therefore, the erosion of the blank by the plating solution and the solder flux can be suppressed.

[0008] In addition, the outer surface of the protective film has countless concave and convex surfaces, so in the curing process, the flow of metal particles in the protective film is suppressed. At this time, the metal particles of the conductive paste are also constrained by the metal particles in the protective film, thus suppressing the fluidity of the metal particles of the conductive paste. Moreover, when the fluidity of the metal particles of the conductive paste is low, the glass component is constrained in the gaps between the metal particles, so the glass component is not easy to flow to the outer surface of the molten conductive paste. Therefore, after the conductive paste is fired, glass is not easy to precipitate to the surface of the external electrode.

[0009] Prevent the blank from being corroded by plating liquid and solder flux. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a three-dimensional diagram of electronic components.

[0011] Figure 2 is a side view of an electronic component.

[0012] Figure 3 It is along Figure 2 Cross-sectional view along line 3-3.

[0013] Figure 4 This is an enlarged cross-sectional view of the protective film and its vicinity.

[0014] Figure 5 This is an enlarged cross-sectional view of the protective film and its vicinity.

[0015] Figure 6 This is a flowchart for explaining a method for manufacturing an electronic component.

[0016] Figure 7 This is an explanatory diagram for explaining a method for manufacturing an electronic component.

[0017] Figure 8 This is an explanatory diagram for explaining a method for manufacturing an electronic component.

[0018] Fig. 9 This is an explanatory diagram for explaining a method for manufacturing an electronic component.

[0019] Fig.10 This is an explanatory diagram for explaining a method for manufacturing an electronic component.

[0020] Fig.11 This is an explanatory diagram for explaining a method for manufacturing an electronic component. DETAILED DESCRIPTION

[0021] <One embodiment of electronic component>

[0022] Hereinafter, one embodiment of the electronic component will be described with reference to the accompanying drawings. In addition, the drawings may enlarge the components for easy understanding. The dimensional ratio of the components may be different from the actual dimensional ratio or the dimensional ratio in other drawings.

[0023] (About the overall structure)

[0024] like Figure 1 As shown, the electronic component 10 is, for example, a surface-mounted negative characteristic thermistor component mounted on a circuit board, etc. The negative characteristic thermistor component has a characteristic that the resistance value decreases when the temperature rises.

[0025] The electronic component 10 includes a blank 20. The blank 20 is substantially quadrangular and has a central axis CA. In addition, hereinafter, an axis extending along the central axis CA is set as a first axis X. In addition, an axis orthogonal to the first axis X is set as a second axis Y. In addition, an axis orthogonal to the first axis X and the second axis Y is set as a third axis Z. Furthermore, one of the directions along the first axis X is set as a first positive direction X1, and the direction along the first axis X that is opposite to the first positive direction X1 is set as a first negative direction X2. Furthermore, one of the directions along the second axis Y is set as a second positive direction Y1, and the direction along the second axis Y that is opposite to the second positive direction Y1 is set as a second negative direction Y2. Furthermore, one of the directions along the third axis Z is set as a third positive direction Z1, and the direction along the third axis Z that is opposite to the third positive direction Z1 is set as a third negative direction Z2.

[0026] The outer surface 21 of the blank 20 has six planes 22. In addition, the "face" of the blank 20 mentioned here refers to a face that can be observed as a face when observing the blank 20 as a whole. That is, even if there are tiny bumps and steps that can only be seen by magnifying a part of the blank 20 with a microscope, etc., it is also manifested as a plane or a curved surface. The six planes 22 extend in different directions. The six planes 22 are roughly divided into a first end face 22A facing the first positive direction X1, a second end face 22B facing the first negative direction X2, and four side faces 22C. The four side faces 22C are a face facing the third positive direction Z1, a face facing the third negative direction Z2, a face facing the second positive direction Y1, and a face facing the second negative direction Y2.

[0027] The outer surface 21 of the blank 20 has 12 boundary surfaces 23. The boundary surfaces 23 include curved surfaces existing at the boundaries between adjacent flat surfaces 22. That is, the boundary surfaces 23 include curved surfaces formed by performing R-chamfering processing on the corners formed by adjacent flat surfaces 22, for example.

[0028] In addition, the outer surface 21 of the blank 20 has eight spherical rounded corners 24. The rounded corners 24 are the boundary portions between the three adjacent planes 22. In other words, the rounded corners 24 include the curved surfaces at the intersections of the three boundary surfaces 23. That is, the rounded corners 24 include, for example, the curved surfaces formed by performing R chamfering on the corners formed by the three adjacent planes 22. Figure 1 as well as Figure 2 In the figure, the surface of the glass film 50 described later is regarded as being the same as the outer surface 21 of the base body 20 and is denoted by a reference numeral.

[0029] like Figure 2 As shown, the dimension of the blank 20 along the first axis X is larger than the dimension along the third axis Z. Figure 1 As shown, the dimension of the green body 20 along the first axis X is larger than the dimension along the second axis Y. The green body 20 is made of ceramics obtained by firing a metal oxide containing at least one of Mn, Fe, Ni, Co, Ti, Ba, Al and Zn as a component.

[0030] like Figure 3 As shown, the electronic component 10 includes two first internal electrodes 41 and two second internal electrodes 42 . The first internal electrodes 41 and the second internal electrodes 42 are buried in the base body 20 .

[0031] The material of the first internal electrode 41 is a conductive material. For example, the material of the first internal electrode 41 is palladium. The material of the second internal electrode 42 is the same as that of the first internal electrode 41.

[0032] The first internal electrode 41 is in the shape of a rectangular plate. The main surface of the first internal electrode 41 is perpendicular to the second axis Y. The second internal electrode 42 is in the shape of a rectangular plate like the first internal electrode 41 . The main surface of the second internal electrode 42 is perpendicular to the second axis Y like the first internal electrode 41 .

[0033] The dimension of the first internal electrode 41 along the direction of the first axis X is smaller than the dimension of the body 20 along the direction of the first axis X. Figure 1 As shown, the dimension of the first inner electrode 41 along the third axis Z is approximately two thirds of the dimension of the body 20 along the third axis Z. The dimensions of the second inner electrode 42 in each direction are the same as those of the first inner electrode 41 .

[0034] like Figure 3 As shown in FIG. 2 , the first internal electrode 41 and the second internal electrode 42 are located at different positions in the direction along the second axis Y. That is, the first internal electrode 41, the second internal electrode 42, the first internal electrode 41, and the second internal electrode 42 are arranged in the order of the side surface 22C facing the second positive direction Y1 toward the second negative direction Y2. In this embodiment, the distances between the internal electrodes in the direction along the second axis Y are equal.

[0035] like Figure 1 As shown, the two first internal electrodes 41 and the two second internal electrodes 42 are both located at the center of the blank 20 along the direction of the third axis Z. Figure 3 As shown, the first internal electrode 41 is located near the first positive direction X1, and the second internal electrode 42 is located near the first negative direction X2.

[0036] Specifically, the end of the first internal electrode 41 on the first positive direction X1 side coincides with the end of the blank 20 on the first positive direction X1 side. The end of the first internal electrode 41 on the first negative direction X2 side is located inside the blank 20 and does not reach the end of the blank 20 on the first negative direction X2 side. On the other hand, the end of the second internal electrode 42 on the first negative direction X2 side coincides with the end of the blank 20 on the first negative direction X2 side. The end of the second internal electrode 42 on the first positive direction X1 side is located inside the blank 20 and does not reach the end of the blank 20 on the first positive direction X1 side.

[0037] like Figure 3 As shown in FIG. 1 , the electronic component 10 includes a protective film 30. The protective film 30 covers the outer surface 21 of the body 20. In the present embodiment, the protective film 30 covers substantially the entire area of ​​the outer surface 21 of the body 20. Figure 4As shown in FIG. 1 , when the outer surface 31 of the protective film 30 is observed under a microscope or the like, there are scattered portions that become perforations in the protective film 30. That is, at these portions, the outer surface 21 of the blank 20 is exposed from the protective film 30. Figure 3 In order to conceptually show that the protective film 30 is located between the body 20 and the glass film 50, the protective film 30 is shown as covering the outer surface 21 of the body 20 with a uniform thickness. The material of the protective film 30 is aluminum oxide, specifically, alumina.

[0038] The electronic component 10 includes a glass film 50. The glass film 50 covers the outer surface 31 of the protective film 30 and the outer surface 21 of the base body 20. Specifically, the glass film 50 covers the entire area of ​​the outer surface 31 of the protective film 30. Moreover, the glass film 50 also covers the portion of the outer surface 21 of the base body 20 that is exposed from the protective film 30. The material of the glass film 50 is insulating glass having silicon dioxide as a main component.

[0039] like Figure 3 As shown, the electronic component 10 includes a first external electrode 61 and a second external electrode 62. The first external electrode 61 includes a first base electrode 61A and a first metal layer 61B. The first base electrode 61A is stacked from above the glass film 50 in a portion of the outer surface 21 of the body 20 including the first end surface 22A. Specifically, the first base electrode 61A is a five-sided electrode covering the first end surface 22A of the body 20 and a portion of the first positive direction X1 side of the four side surfaces 22C. In this embodiment, the material of the first base electrode 61A is a mixture of silver and glass.

[0040] The first metal layer 61B covers the first base electrode 61A from the outside. That is, the first metal layer 61B is stacked on the first base electrode 61A. The first metal layer 61B has a two-layer structure in which nickel plating and tin plating are performed in this order from the base body 20 side.

[0041] The second external electrode 62 includes a second base electrode 62A and a second metal layer 62B. The second base electrode 62A is stacked from above the glass film 50 in a portion of the outer surface 21 of the body 20 including the second end surface 22B. Specifically, the second base electrode 62A is a five-sided electrode that covers the second end surface 22B and a portion of the first negative direction X2 side of the four side surfaces 22C of the body 20. In this embodiment, the material of the second base electrode 62A is the same as that of the first external electrode 61, which is a mixture of silver and glass.

[0042] The second metal layer 62B covers the second base electrode 62A from the outside. That is, the second metal layer 62B is stacked on the second base electrode 62A. The second metal layer 62B has a two-layer structure in which nickel plating and tin plating are performed in this order from the base body 20 side, similarly to the first metal layer 61B.

[0043] The second external electrode 62 does not reach the first external electrode 61 on the side surface 22C, and is arranged separately from the first external electrode 61 in the direction along the first axis X. Moreover, on the side surface 22C of the body 20, the first external electrode 61 and the second external electrode 62 are not stacked in the central portion in the direction along the first axis X, and the glass film 50 is exposed. Figure 1 to Figure 3 In FIG. 6 , the first external electrode 61 and the second external electrode 62 are indicated by double-dashed lines.

[0044] like Figure 3 As shown, the first external electrode 61 and the end of the first internal electrode 41 on the first positive direction X1 side are connected via a first through portion 71 that penetrates the protective film 30 and the glass film 50. That is, the first through portion 71 is a connection portion that connects the first external electrode 61 and the first internal electrode 41. In addition, although the details will be described later, in the manufacturing process of the electronic component 10, the first through portion 71 is formed by extending the palladium constituting the first internal electrode 41 to the first external electrode 61 side.

[0045] In addition, the second external electrode 62 is connected to the end of the second internal electrode 42 on the first negative direction X2 side via a second through portion 72 that penetrates the protective film 30 and the glass film 50. That is, the second through portion 72 is a connecting portion that connects the second external electrode 62 and the second internal electrode 42. Also in the manufacturing process of the electronic component 10, the second through portion 72 is formed by extending the palladium constituting the second internal electrode 42 toward the second external electrode 62 side. In addition, in Figure 3 In the figure, the first internal electrode 41 and the first through-hole 71 are shown as independent components with a boundary, but in fact there is no clear boundary between the two. The same is true for the second through-hole 72. Figure 1 as well as Figure 2 In the figure, the first through portion 71 and the second through portion 72 are omitted.

[0046] (About protective film)

[0047] The protective film 30 must exist between the edge of the first external electrode 61 and the first through-portion 71, which is the connection portion between the first internal electrode 41 and the first external electrode 61. Figure 5As shown, a vertical line is drawn from any point on the edge of the first external electrode 61 to the outer surface 21 of the body 20. And, a virtual line L connected to any point of the first through-portion 71 along the outer surface 21 of the body 20 is drawn from the foot of the vertical line. Here, as described above, the protective film 30 covers substantially the entire area of ​​the outer surface 21 of the body 20. Therefore, no matter where the above-mentioned point is determined on the edge of the first external electrode 61, and no matter where the above-mentioned point is determined on the first through-portion 71, all the virtual lines L overlap with the area where the protective film 30 is located. The same applies to the second external electrode 62 and the second through-portion 72.

[0048] Here, the film thickness TP of the protective film 30 is defined as the thickness in the direction perpendicular to the outer surface 21 of the body 20. Figure 4 As shown, in the portion where the blank 20 is covered by the first external electrode 61 or the second external electrode 62, a cross-sectional observation is performed in a section orthogonal to the outer surface 21 of the blank 20. Moreover, along the outer surface 21 of the blank 20 within a range of 1 μm, the average value and standard deviation of the film thickness TP of the protective film 30 are obtained. The ratio of the standard deviation to the average value thus obtained is defined as the coefficient of variation. At this time, in the portion covered by the first external electrode 61 or the second external electrode 62, the coefficient of variation of the film thickness TP of the protective film 30 is greater than 0.4. In addition, in the present embodiment, the average value of the film thickness TP of the protective film 30 is less than 100 nm. In addition, the standard deviation of the film thickness TP of the protective film 30 is greater than 10 nm. In this embodiment, the average value of the film thickness TP of the protective film 30 is 27 nm, and the standard deviation is 13 nm. Therefore, the coefficient of variation in this embodiment is approximately 0.48.

[0049] <Method for manufacturing electronic components>

[0050] Next, a method for manufacturing the electronic component 10 and a method for forming the protective film 30 will be described.

[0051] like Figure 6 As shown, the method for manufacturing the electronic component 10 includes a laminate preparation step S11, a first polishing step S12, a second polishing step S13, a solvent introduction step S14, a catalyst introduction step S15, a green body introduction step S16, a polymer introduction step S17, and a metal alkoxide introduction step S18. In addition, the method for manufacturing the electronic component 10 also includes a film forming step S19, a drying step S20, a conductor coating step S21, a curing step S22, and a plating step S23.

[0052] First, when forming the green body 20, in the laminate preparation step S11, the green body 20, that is, the laminate, which does not have the boundary surface 23 and the rounded surface 24 is prepared. That is, the laminate is in a state before R chamfering, and is a rectangular parallelepiped with six planes 22. For example, first, a plurality of ceramic sheets that will become the green body 20 are prepared. The sheet is in the shape of a thin plate. A conductive paste that will become the first internal electrode 41 is stacked on the sheet. A ceramic sheet that will become the green body 20 is stacked on the laminate paste. A conductive paste that will become the second internal electrode 42 is stacked on the sheet. In this way, the ceramic sheet and the conductive paste are stacked. Then, an unfired laminate is formed by cutting into a specified size. Then, the laminate is prepared by firing the unfired laminate at a high temperature.

[0053] Next, the first grinding step S12 is performed. In the first grinding step S12, the boundary surface 23 and the rounded corner surface 24 are formed for the laminated body prepared in the laminated body preparation step S11. Specifically, the corners of the laminated body are R-chamfered by roller grinding, thereby forming the boundary surface 23 with a curved surface and the rounded corner surface 24 with a curved surface. In addition, in the first grinding step S12, the first grinding powder, which is a powder of aluminum oxide, is used for roller grinding. A part of the first grinding powder used in the first grinding step S12 adheres to the outer surface of the laminated body.

[0054] Next, the second grinding step S13 is performed. In the second grinding step S13, the laminated body ground in the first grinding step S12 is further ground. In the second grinding step S13, the second grinding powder, which is a powder of aluminum oxide, is used for drum grinding. Here, when the mode value of the particle size in the particle size distribution, that is, the central particle size, is compared between the first grinding powder and the second grinding powder, the central particle size of the second grinding powder is less than one tenth of the central particle size of the first grinding powder. In the second grinding step S13, the first grinding powder attached to the laminated body in the first grinding step S12 is crushed. In addition, a part of the second grinding powder used in the second grinding step S13 is attached to the outer surface of the laminated body. As a result, aluminum oxide powders of various particle sizes are attached to the outer surface 21 of the blank 20. In addition, the aluminum oxide powder attached to the outer surface 21 of the blank 20 penetrates or is buried in the outer surface 21 of the blank 20. In addition, a part of the surface of the aluminum oxide powder is fused to the outer surface 21 of the blank 20. Therefore, the aluminum oxide powder is not easy to fall off from the outer surface 21 of the blank 20. Thus, the protective film 30 is formed on the outer surface 21 of the body 20 .

[0055] Next, the solvent adding step S14 is performed. Figure 7 As shown, in the solvent adding step S14 , 2-propanol is added as the solvent 82 into the reaction container 81 .

[0056] Next, if Figure 6 As shown, the catalyst feeding step S15 is performed. Figure 8 As shown, in the catalyst introduction step S15, first, stirring of the solvent 82 in the reaction container 81 is started. Then, ammonia water is introduced into the reaction container 81 as an aqueous solution 83 containing a catalyst. The catalyst in this embodiment is a hydroxide ion, and functions as a catalyst for promoting the hydrolysis of a metal alkoxide 85 described later.

[0057] Next, if Figure 6 As shown, the blank feeding step S16 is performed. Fig. 9 As shown, in the green body loading step S16 , a plurality of green bodies 20 formed in advance in the second grinding step S13 as described above are loaded into the reaction container 81 .

[0058] Next, if Figure 6 As shown, the polymer feeding step S17 is performed. Fig.10 As shown, in the polymer introduction step S17 , polyvinyl pyrrolidone is introduced into the reaction container 81 as the polymer 84 . Thus, the polymer 84 introduced into the reaction container 81 is adsorbed on the outer surface 21 of the blank 20 .

[0059] Next, if Figure 6 As shown, the metal alkoxide is added into the process S18. Fig.11 As shown, in the metal alkoxide feeding step S18, liquid tetraethyl orthosilicate is fed into the reaction vessel 81 as the metal alkoxide 85. In addition, tetraethyl orthosilicate is sometimes referred to as tetraethoxysilane. In the present embodiment, the amount of the metal alkoxide 85 fed in the metal alkoxide feeding step S18 is calculated based on the area of ​​the outer surface 21 of the blank 20 fed in the blank feeding step S16. Specifically, the amount of the metal alkoxide 85 per blank 20 required to form the glass film 50 covering the outer surface 21 of the blank 20 is multiplied by the number of the blanks 20 to calculate.

[0060] Next, if Figure 6 In the film forming step S19, after the metal alkoxide 85 is introduced into the reaction container 81 in the metal alkoxide introducing step S18, the stirring of the solvent 82 started in the above-mentioned solvent introducing step S14 is continued for a predetermined time.

[0061] In the film forming step S19 , the glass film 50 is formed by a liquid phase reaction in the reaction container 81 .

[0062] Next, a drying step S20 is performed. In the drying step S20, after stirring is continued for a predetermined time in the film forming step S19, the base body 20 is taken out from the reaction container 81 and dried. Thus, the sol-like glass film 50 is dried to become a gel-like glass film 50.

[0063] Next, the conductor coating step S21 is performed. In the conductor coating step S21, the conductor paste is coated on two parts of the surface of the glass film 50, including a part of the portion covering the first end face 22A of the blank 20 and a part of the portion covering the second end face 22B of the blank 20. Specifically, the conductor paste is coated so as to cover the entire area of ​​the first end face 22A and a part of the four side faces 22C of the glass film 50. In addition, the conductor paste is coated so as to cover the entire area of ​​the second end face 22B and a part of the four side faces 22C of the glass film 50.

[0064] Next, the curing step S22 is performed. Specifically, the curing step S22 heats the base body 20 coated with the glass film 50 and the conductive paste. Thus, the protective film 30 formed on the outer surface 21 of the base body 20 is fired. In addition, water and the polymer 84 are vaporized from the gel-like glass film 50, so that Figure 3 As shown, the glass film 50 covering the protective film 30 is fired and cured. In the curing step S22, the conductor paste applied in the conductor application step S21 is fired to form the first base electrode 61A and the second base electrode 62A.

[0065] In the present embodiment, during heating in the curing step S22, palladium contained in the first internal electrode 41 side is attracted to the first underlying electrode 61A side containing silver due to the Kirkendall effect caused by the difference in diffusion speed between the first internal electrode 41 and the first underlying electrode 61A. As a result, the first internal electrode 41 is connected to the first underlying electrode 61A by the first through portion 71 extending from the first internal electrode 41 toward the first underlying electrode 61A through the protective film 30 and the glass film 50. The same is true for the second through portion 72 connecting the second internal electrode 42 to the second underlying electrode 62A.

[0066] Next, a plating step S23 is performed. Electroplating is performed on the first base electrode 61A and the second base electrode 62A. Thus, a first metal layer 61B is formed on the surface of the first base electrode 61A. In addition, a second metal layer 62B is formed on the surface of the second base electrode 62A. Although not shown in the figure, the first metal layer 61B and the second metal layer 62B are electroplated with nickel and tin to form a two-layer structure. In this way, the electronic component 10 is formed.

[0067] (Effects of the present embodiment)

[0068] (1) According to the above embodiment, the coefficient of variation of the film thickness TP of the protective film 30 is 0.4 or more, so the deviation of the film thickness TP is relatively large. That is, the protective film 30 has countless concave and convex portions on the outer surface 31. As a result, due to the anchoring effect, the adhesion between the glass film 50 and the protective film 30, and the adhesion between the first external electrode 61 and the second external electrode 62 and the glass film 50 become high. In this way, if the adhesion of the layers stacked on the outer surface 31 of the protective film 30 is high, the plating solution and the solder flux are prevented from penetrating from the boundary surfaces of the layers. Therefore, the erosion of the blank 20 by the plating solution and the solder flux can be suppressed.

[0069] In addition, the outer surface 31 of the protective film 30 has numerous concavoconvexities, so in the curing step S22, the flow of the metal particles in the protective film 30 is suppressed. At this time, the metal particles of the conductive paste are also constrained by the metal particles in the protective film 30, so the fluidity of the metal particles of the conductive paste is suppressed. Moreover, when the fluidity of the metal particles of the conductive paste is low, the glass component is constrained in the gaps between the metal particles, so the glass component is not easy to flow to the outer surface of the molten conductive paste. Therefore, after the conductive paste is fired, glass is not easy to precipitate on the surface of the external electrode.

[0070] (2) According to the above embodiment, the average value of the film thickness TP of the protective film 30 is 100 nm or less. In this way, the protective film 30 is formed thin, so it is not easy to hinder the formation of the first through-portion 71 and the second through-portion 72 based on the Kirkendall effect. That is, the connectivity between the first internal electrode 41 and the first external electrode 61 and the connectivity between the second internal electrode 42 and the second external electrode 62 can be ensured.

[0071] (3) In the above embodiment, the standard deviation of the film thickness TP of the protective film 30 is 10 nm or more. If the film thickness TP of the protective film 30 varies greatly in this way, the outer surface of the glass film 50 stacked on the outer surface 31 of the protective film 30 also varies greatly following the shape of the protective film 30. Therefore, the anchoring effect of the first external electrode 61 and the second external electrode 62 with respect to the glass film 50 is easily obtained.

[0072] (4) According to the above embodiment, the protective film 30 is always present between the edge of the first external electrode 61 and the first internal electrode 41, that is, the first through-portion 71, which is the connection portion between the first external electrode 61 and the first internal electrode 41. As a result, the intrusion path of the plating solution, flux, etc. that intrudes from the edge of the first external electrode 61 to the above connection portion is blocked. Therefore, poor connection between the first external electrode 61 and the first internal electrode 41 is prevented. The same applies to the second external electrode 62, the second internal electrode 42, and the second through-portion 72.

[0073] (5) According to the above embodiment, the glass film 50 is sandwiched between the protective film 30 and the first external electrode 61 and the second external electrode 62. Therefore, it is possible to obtain the protective effect of the protective film 30 on the base body 20, and also obtain the protective effect of the glass film 50 on the base body 20. In addition, the glass component contained in the conductive paste diffuses into the glass film 50 and integrates with it, thereby improving the bonding strength between the glass film 50 and the first external electrode 61 and the second external electrode 62. Therefore, each external electrode is not easily peeled off from the base body 20.

[0074] (6) According to the above embodiment, the center particle size of the second abrasive powder is significantly smaller than that of the first abrasive powder. Thus, by using two abrasive powders having different center particle sizes, a protective film 30 having a large deviation in film thickness TP can be formed on the outer surface 21 of the blank 20 without adding a special process for surface roughening.

[0075] <Change Example>

[0076] The above-described embodiment and the following modified examples can be implemented in combination with each other within the scope of no technical contradiction.

[0077] In the above embodiment, the electronic component 10 is not limited to a negative characteristic thermistor component. For example, as long as some wiring is provided inside the base body 20, it may be a thermistor component other than a negative characteristic component, or may be a laminated capacitor component or an inductor component.

[0078] The outer surface 21 of the blank 20 only needs to be formed with the protective film 30, and may not have the boundary surface 23 and the rounded surface 24. For example, when the boundary between adjacent planes 22 in the outer surface 21 of the blank 20 is not a chamfered shape, there is no curved surface at the boundary. Therefore, in such a case, the boundary surface 23 and the rounded surface 24 may not exist.

[0079] The shapes of the first internal electrode 41 and the second internal electrode 42 can be any shapes as long as they can ensure electrical conduction with the corresponding first external electrode 61 and the second external electrode 62. The number of the first internal electrode 41 and the second internal electrode 42 is not limited, and the number of internal electrodes can be one or three or more.

[0080] The structure of the first external electrode 61 is not limited to the above-described embodiment. For example, the first external electrode 61 may be composed of only the first base electrode 61A, and the first metal layer 61B may not be a two-layer structure. The same applies to the second external electrode 62 .

[0081] The combination of materials of the first internal electrode 41 and the first base electrode 61A is not limited to the combination of palladium and silver. For example, it may be a combination of copper and nickel, copper and silver, silver and gold, nickel and cobalt, or nickel and gold. In addition, for example, it may be a combination of silver on one side and silver and palladium on the other side. In addition, for example, it may be a combination of palladium on one side and silver and palladium on the other side, or it may be a combination of copper on one side and silver and palladium on the other side. In addition, for example, it may be a combination of gold on one side and silver and palladium on the other side.

[0082] · In addition, depending on the combination of the first internal electrode 41 and the first base electrode 61A, the Cockendall effect may not be obtained. In this case, it is sufficient to perform processing so that the first internal electrode 41 is exposed before the external electrode forming step. For example, it is sufficient to physically remove a portion of the protective film 30 and the glass film 50 by grinding the first end face 22A side of the blank 20. Then, by performing the base electrode forming step, the first internal electrode 41 can be connected to the first base electrode 61A. In this case, the surface of the first internal electrode 41 exposed from the outer surface 21 of the blank 20 is the connecting portion. This also applies to the combination of the materials of the second internal electrode 42 and the second base electrode 62A.

[0083] The arrangement position of the first external electrode 61 is not limited to the example of the above embodiment. For example, the first external electrode 61 may be arranged only on the first end surface 22A and one side surface 22C. The same applies to the second external electrode 62 .

[0084] The conductive metals contained in the first foundation electrode 61A and the second foundation electrode 62A may be different. For example, the first foundation electrode 61A may contain Ag, and the second foundation electrode 62A may contain Cu.

[0085] The protective film 30 may not cover the entire outer surface 21 of the body 20. For example, the protective film 30 may cover only the portion of the outer surface 21 of the body 20 covered by the first outer electrode 61 and the second outer electrode 62, and may not cover the rest of the outer surface 21 of the body 20. In addition, for example, only the connection portion between the first inner electrode 41 and the first outer electrode 61 or the connection portion between the second inner electrode 42 and the second outer electrode 62 may be covered by the protective film 30 on the outer surface 21 of the body 20.

[0086] The average value of the film thickness TP of the protection film 30 may be greater than 100 nm. For example, if the first internal electrode 41 and the first external electrode 61 are not connected via the first through-hole 71 formed by the Kirkendall effect, even if the average value of the film thickness TP is greater than 100 nm, there is little disadvantage.

[0087] The standard deviation of the film thickness TP of the protective film 30 may be less than 10 nm. Even if the standard deviation of the film thickness TP is 10 nm or more, as long as the coefficient of variation is 0.4 or more, the adhesion between the glass film 50 and each external electrode and the protective film 30 can be ensured.

[0088] The protective film 30 may not necessarily exist between the edge of the first external electrode 61 and the first internal electrode 41 and the first external electrode 61, that is, the first through-portion 71. That is, when a virtual line L is drawn along the outer surface 21 of the body 20, which connects the foot of a vertical line drawn from an arbitrary point on the edge of the first external electrode 61 to the outer surface 21 of the body 20 and an arbitrary point on the first through-portion 71, a part of the virtual line L may not overlap with the area where the protective film 30 is located. The same applies to the relationship between the second external electrode 62 and the second through-portion 72.

[0089] The glass film 50 does not have to cover the entire area of ​​the outer surface 31 of the protective film 30. The range covered by the glass film 50 may be appropriately changed in accordance with the shape of the base body 20, the positions of the first external electrode 61 and the second external electrode 62, and the like.

[0090] Regarding the portion of the glass film 50 covered by the first underlying electrode 61A, the glass in the glass film 50 may diffuse into the glass in the first underlying electrode 61A, and the two may be integrated.

[0091] The glass film 50 may be omitted. In addition, another film formed to follow the shape of the outer surface 31 of the protective film 30 may be formed instead of the glass film 50. That is, high adhesion due to the anchoring effect or suppression of glass precipitation may be obtained by having unevenness on the outer surface of the film. In addition, the first base electrode 61A and the second base electrode 62A may be stacked on the outer surface 31 of the protective film 30.

[0092] In the first polishing step S12 and the second polishing step S13, the first polishing powder and the second polishing powder are preferably alumina, but their compositions are not limited as long as they are alumina powders with different center particle diameters. In addition, the first polishing powder and the second polishing powder may be alumina of different compositions.

[0093] <Note>

[0094] The following is a summary of technical ideas that can be grasped from the above-mentioned embodiments and modifications. [1]

[0096] An electronic component, wherein

[0097] A green body, an external electrode covering a portion of the outer surface of the green body, and an aluminum oxide protective film.

[0098] The protective film is located between the green body and the external electrode.

[0099] The thickness of the protective film in a direction perpendicular to the outer surface of the body is defined as the film thickness.

[0100] When the protective film is observed in a cross section perpendicular to the outer surface of the body at a portion covered by the external electrode, the average value and standard deviation of the film thickness are obtained within a range of 1 μm in the direction along the outer surface of the body.

[0101] The ratio of the standard deviation to the average value is 0.4 or more. [2]

[0103] An electronic component according to [1], wherein:

[0104] The above average value of the above film thickness is 100 nm or less. [3]

[0106] The electronic component according to [1] or [2], wherein:

[0107] The standard deviation of the film thickness is 10 nm or more. [4]

[0109] The electronic component according to any one of [1] to [3], wherein:

[0110] It also includes an internal electrode located inside the green body, and a connecting portion connecting the external electrode and the internal electrode.

[0111] When a perpendicular line is drawn from any point on the edge of the external electrode to the outer surface of the body, and a virtual line is drawn along the outer surface of the body connecting the foot of the perpendicular line to any point on the connecting portion,

[0112] All of the virtual lines overlap with the region where the protective film is located. [5]

[0114] The electronic component according to any one of [1] to [4], wherein:

[0115] A glass film is further provided between the protective film and the external electrode. [6]

[0117] A film forming method is a film forming method for forming a protective film on the outer surface of a green body, wherein the protective film is an aluminum oxide film, wherein the film forming method comprises:

[0118] A laminate preparation step of preparing the above-mentioned green body;

[0119] a first grinding step of grinding the green body using a first grinding powder, wherein the first grinding powder is a powder of aluminum oxide; and

[0120] A second grinding step, after the first grinding step, grinding the green body with a second grinding powder, wherein the second grinding powder is a powder of aluminum oxide,

[0121] When the mode value of the particle size distribution, that is, the center particle size, is compared between the first ground powder and the second ground powder,

[0122] The center particle diameter of the second abrasive powder is 1 / 10 or less of the center particle diameter of the first abrasive powder.

[0123] Explanation of reference numerals: 10...electronic component; 20...blank; 30...protective film; 31...external surface; 50...glass film; 61...first external electrode; 62...second external electrode; 71...first through portion; 72...second through portion; S12...first grinding step; S13...second grinding step; TP...film thickness.

Claims

1. An electronic component, in, A green body, an external electrode covering a portion of an outer surface of the green body, and a protective film of aluminum oxide, The protective film is located between the green body and the external electrode. The thickness of the protective film in a direction perpendicular to the outer surface of the green body is defined as the film thickness. When the protective film is observed in a cross section perpendicular to the outer surface of the body at a portion covered by the external electrode, the average value and standard deviation of the film thickness are obtained within a range of 1 μm in the direction along the outer surface of the body. The ratio of the standard deviation to the average value is 0.4 or more.

2. The electronic component according to claim 1, in, The average value of the film thickness is 100 nm or less.

3. The electronic component according to claim 1 or 2, in, The standard deviation of the film thickness is 10 nm or more.

4. The electronic component according to any one of claims 1 to 3, in, It also includes an internal electrode located inside the green body, and a connecting portion connecting the external electrode and the internal electrode. When a vertical line is drawn from any point on the edge of the external electrode to the outer surface of the body, and a virtual line is drawn along the outer surface of the body connecting the foot of the vertical line to any point on the connecting portion, All of the virtual lines overlap with the area where the protective film is located.

5. The electronic component according to any one of claims 1 to 4, in, A glass film is further provided between the protective film and the external electrode.

6. A film forming method, which is a film forming method for forming a protective film on the outer surface of a green body, wherein the protective film is an aluminum oxide film. in, The film forming method comprises: A laminate preparation step of preparing the green body; A first grinding step, grinding the green body with a first grinding powder, wherein the first grinding powder is a powder of aluminum oxide; as well as A second grinding step, after the first grinding step, grinding the green body with a second grinding powder, wherein the second grinding powder is a powder of aluminum oxide, When the mode value of the particle size distribution, that is, the center particle size, is compared between the first ground powder and the second ground powder, The central particle size of the second abrasive powder is less than 1 / 10 of the central particle size of the first abrasive powder.

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