Conductive paste and multilayer ceramic electronic component

Abstract

A conductive paste for forming external electrodes for a multilayer ceramic electronic component. The paste contains a glass composition containing (a) BaO, (b) at least one of SrO and CaO, (c) ZnO, (d) B.sub.2O.sub.3, and (e) at least one selected from the group consisting of SiO.sub.2, Al.sub.2O.sub.3, and TiO.sub.2, in which the total content percentage of BaO, SrO, and CaO is 30 mol % or more, the molar ratio represented by B.sub.2O.sub.3/(SiO.sub.2+Al.sub.2O.sub.3+TiO.sub.2) is 0.7 to 1.5, and the content percentage of ZnO is 0 to 5 mol %.

Claims

1. A conductive paste comprising: a conductive component; and a glass composition that contains: (a) BaO; (b) at least one of SrO and CaO; (c) ZnO; (d) B.sub.2O.sub.3; and (e) at least one selected from the group consisting of SiO.sub.2, Al.sub.2O.sub.3, and TiO.sub.2, wherein a total content percentage of BaO, SrO, and CaO is 44.9 mol % or more with respect to a total amount of the glass composition in the conductive paste, a molar ratio represented by B.sub.2O.sub.3/(SiO.sub.2+Al.sub.2O.sub.3+TiO.sub.2) is 0.7 to 1.5, and a content percentage of ZnO is 0 to 5 mol % with respect to the total amount of the glass composition in the conductive paste.

2. The conductive paste according to claim 1, wherein the molar ratio represented by B.sub.2O.sub.3/(SiO.sub.2+Al.sub.2O.sub.3 +TiO.sub.2) is 0.7 to 1.0.

3. The conductive paste according to claim 1, wherein the glass composition contains 20 mol % or more of B.sub.2O.sub.3.

4. The conductive paste according to claim 2, wherein the glass composition contains 20 mol % or more of B.sub.2O.sub.3.

5. The conductive paste according to claim 1, further comprising a total of 1 mol % or less of one or more of Li.sub.2O, Na.sub.2O, K.sub.2O, MgO, MnO, CoO, NiO, CuO, SnO.sub.2, and ZrO.sub.2.

6. The conductive paste according to claim 1, wherein the conductive component has an average particle size of 3 to 4 μm.

7. A multilayer ceramic electronic component comprising: a ceramic body having a plurality of alternately stacked dielectric layers and internal electrode layers; and an external electrode formed from the conductive paste according to claim 1 applied to a surface of the ceramic body.

8. The multilayer ceramic electronic component according to claim 7, further comprising a Ni plating film on the external electrode.

9. The multilayer ceramic electronic component according to claim 8, further comprising an Sn plating film on the Ni plating film.

Description

BRIEF EXPLANATION OF THE DRAWINGS

(1) FIG. 1 is a cross-sectional view illustrating the configuration of a multilayer ceramic capacitor including external electrodes formed with the use of a conductive paste according to the present invention.

(2) FIG. 2 is a cross-sectional view illustrating the configuration of a multilayer ceramic capacitor that is a typical multilayer ceramic electronic component.

DETAILED DESCRIPTION OF THE INVENTION

(3) With reference to an embodiment of the present invention, features of the present invention will be described in detail below.

(4) [Embodiment]

(5) In this embodiment, a case of manufacturing a multilayer ceramic capacitor structured as shown in FIG. 1 will be described as an example.

(6) This multilayer ceramic capacitor is, as shown in FIG. 1, structured to have external electrodes 4 (4a, 4b) provided, so as to be electrically connected to a plurality of internal electrodes 2 (2a, 2b), on both end surfaces 3a, 3b of a ceramic laminate (multilayer ceramic capacitor element) 10 obtained by laminating the internal electrodes 2 (2a, 2b) with ceramic layers 1 as dielectric layers interposed therebetween.

(7) The external electrodes 4 (4a, 4b) have a multi-layer structure including: an external electrode body 11 obtained by baking a conductive paste; a Ni plating film layer 12 formed on the surface of the external electrode body 11; and a Sn plating film layer 13 formed on the surface of the Ni plating film layer 12.

(8) (The external electrode bodies 11 of) the external electrodes 4 mentioned above are formed with the use of a conductive paste prepared in the way described below.

(9) In this embodiment, a copper powder, a glass powder, a binder (resin, solvent), and additives (dispersant, rheology controlling agents, etc.) were blended in proportions as shown in Table 1, and kneaded and dispersed to prepare a conductive paste.

(10) Then, the prepared conductive paste was used to form external electrodes (external electrode bodies) on both of mutually opposed end surfaces of the ceramic laminate (ceramic body) constituting the multilayer ceramic capacitor.

(11) To explain the conductive paste in more detail, a powder of 3 to 4 μm in average particle size (D.sub.50) was used as a conductive component constituting the conductive paste in this embodiment.

(12) In addition, as the glass powder, BaCO.sub.3, SrCO.sub.3, CaCO.sub.3, H.sub.3BO.sub.3, SiO.sub.2, Al.sub.2O.sub.3, TiO.sub.2, ZnO, and Na.sub.2CO.sub.3 as glass raw materials were blended to provide intended compositions in terms of oxide after vitrification.

(13) Then, the blended raw materials were mixed in a crucible, and then melted by heating to 1200 to 1400° C., and the melt was rapidly cooled with a double roll mill. Thereafter, grinding with a ball mill was carried out with zirconia as a grinding medium to prepare a glass powder of 2 μm in average particle size.

(14) As the binder, an acrylic resin based binder with dihydroterpineol as a solvent was used.

(15) In order to provide the conductive paste with printability, a fatty acid amide based thixotropy imparting agent was added as an additive.

(16) Then, the copper powder, the glass powder, the binder, and the additive were mixed in respective proportions: 67 wt %; 10 wt %; 22 wt %; and 1 wt %, and dispersed with a triple roll mill to make paste form, thereby preparing the conductive paste (external electrode paste).

(17) Then, a mother laminate was prepared by stacking green sheets with electrodes, obtained by forming an internal electrode pattern in such a way that an internal electrode paste containing nickel (Ni) as a conductive component was applied to ceramic green sheets containing barium titanate (BaTiO.sub.3) as their main constituent.

(18) Then, the mother laminate was cut in predetermined positions to be divided into individual elements (unfired ceramic laminates), and subjected to firing to obtain fired ceramic laminates (ceramic bodies), that is, laminated structures structured to have a plurality of internal electrodes laminated with dielectric ceramic layers interposed therebetween.

(19) The conductive paste prepared in the way described above was applied by a method such as dip coating to both of mutually opposed end surfaces of the thus prepared ceramic laminates (ceramic bodies), dried, and then subjected to firing in a reducing atmosphere to form external electrodes (external electrode bodies).

(20) Then, Ni plating film layers were formed on the surfaces of the external electrode bodies, and Sn plating film layers were further formed on the Ni plating film layers, thereby preparing multilayer ceramic capacitors according to this embodiment (samples according to Examples 1 to 6 in Table 1), structured as shown in FIG. 1. The Ni plating film layers and the Sn plating film layers were sequentially formed by an electroplating method.

(21) For each of the samples (multilayer ceramic capacitors) prepared in the way described above, the following properties, that is, “Glass Flotation” at the external electrodes, “Presence or Absence of Void Generated” at corner parts of the external electrodes, and “Flexure Strength” of the multilayer ceramic capacitors were examined respectively by the following methods.

(22) In addition, the plating resistance of the external electrodes were examined by the method described below.

(23) (1) Glass Flotation

(24) After the conductive paste applied was subjected to firing to form the external electrodes, central parts of the end surfaces of the samples (multilayer ceramic capacitors) with the external electrodes formed were observed at 500-fold or more magnification with the use of a scanning electron microscope. Then, in view of the contrasts of the images of the external electrode surfaces observed, the sample with a glass floatation part of 10 μm or more in incircle diameter (shortest) was regarded as defective (x), whereas the sample with a glass floatation part of less than 10 μm therein was regarded as non-defective (o).

(25) (2) Void Generation (Generated or Not)

(26) After the conductive paste applied was subjected to firing to form the external electrodes, at cut surfaces exposed by cutting the samples (multilayer ceramic capacitors) in a direction perpendicular to the end surfaces with the external electrodes formed, the cut surfaces of the external electrodes formed at four corners (corner parts) of the samples were observed at 500-fold or more magnification with the use of a scanning electron microscope. The sample without any void generation found was regarded as non-defective (O), whereas the sample with void generation found was regarded as defective (x).

(27) (3) Flexure Strength (Rate of Flexural Crack Generation)

(28) In accordance with the test method JIS C 60068-2-21 for the flexural capacity of printed boards, the samples (multilayer ceramic capacitors) were warped up to 1.5 mm, and the crack generation after the test was checked. Then, the proportion of cracked samples to the samples subjected to the test (Rate of Flexural Crack Generation) was figured out.

(29) (4) Plating Resistance

(30) In order to examine the plating resistance of the external electrodes, the glass of each composition shown in Table 1 and an acrylic resin binder were mixed at a ratio of 1:1, and dispersed with a triple roll mill to prepare a glass paste. Then, this glass paste was printed by a doctor blade method onto an alumina substrate so that the applied thickness was 20 μm or more, and subjected to firing in a reducing atmosphere.

(31) Then, this substrate was immersed in a Ni plating solution and a Sn plating solution, and the amounts of change in weight between before and after the immersion were figured out as the amounts of dissolution. In addition, the amounts of change in weight were divided by the glass density and printed area for each substrate to be converted to the thicknesses dissolved per unit time.

(32) It is to be noted that when the obtained values are regarded as dissolution rates in the plating solutions, the dissolution rates in the plating solutions are desirably 0.1 μm/h or less in the Ni plating solution, and desirably 1.0 μm/h or less in the Sn plating solution.

(33) In addition, the dissolution rate in the Sn plating solution is more desirably 0.5 μm/h or less.

(34) For the samples (Table 1) according to Examples 1 to 6 in Table 1, which meet the requirements of the present invention, Table 1 shows together evaluation results or measurement results for “Glass flotation” at the external electrodes, “Presence or Absence of Void Generated” at the corner parts of the external electrodes, “Rate of Flexural Crack Generation” for the multilayer ceramic capacitors, and “Plating Resistance” of the external electrodes, which were examined by the methods described above.

(35) Furthermore, for comparison, comparative conductive pastes for failing to meet the requirements of the present invention were prepared in such a way that a copper powder, a glass powder, a binder, and an additive were blended, and kneaded and dispersed under the same conditions as in the case of the samples according to the examples described above, except for the use of glass powders of compositions as shown in Table 2, and the conductive pastes were used to prepare samples as comparative examples (samples according to Comparative Examples 1 to 7) (Table 2) in the same way as in the case of the samples 1 to 6 according to the examples. Then, for the samples according to Comparative Examples 1 to 7, the “Glass Flotation” at the external electrodes, “Presence or Absence of Void Generated” at the corner parts of the external electrodes, “Rate of Flexural Crack Generation” for the multilayer ceramic capacitors, and “Plating Resistance” were examined in the same way as in the case of the samples according to Examples 1 to 6.

(36) The measurement results are shown together in Table 2.

(37) TABLE-US-00001 TABLE 1 Example Example Example Example Example Example 1 2 3 4 5 6 BaO + [SrO + CaO] 48.8 47.1 44.9 47.6 51.3 48.7 B.sub.2O.sub.3/(SiO.sub.2 + Al.sub.2O.sub.3 + TiO.sub.2) Molar Ratio 1.00 0.88 0.75 0.83 1.23 1.24 ZnO 0.0 0.0 0.0 0.0 0.0 5.0 Characterization Glass Flotation ∘ ∘ ∘ ∘ ∘ ∘ Data Presence or Absence ∘ ∘ ∘ ∘ ∘ ∘ of Void Generated Plating Ni Plating 0.1 0.1 0.1 0.1 0.1 0.1 Resistance Solution (μm/h) Sn Plating 0.3 0.2 0.1 0.2 0.8 0.9 Solution Rate of Flexural 0/10 0/10 0/10 0/10 0/10 0/10 Crack Generation Composition of Na.sub.2O — — — — — — Glass CaO 9.8 9.4 9.0 9.5 10.3 9.7 Composition SrO — — — — — — [mol %] BaO 39.0 37.7 35.9 38.1 41.0 39.0 B.sub.2O.sub.3 25.6 24.7 23.6 23.8 26.9 25.6 SiO.sub.2 12.2 11.8 11.2 20.3 12.8 12.2 Al.sub.2O.sub.3 13.4 12.9 12.4 8.3 9.0 8.5 ZnO — — — — — 5.0 TiO.sub.2 — 3.5 7.9 — — — Total 100.0 100.0 100.0 100.0 100.0 100.0

(38) TABLE-US-00002 TABLE 2 Comparative Comparative Comparative Comparative Comparative Comparative Comparative Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 BaO + [SrO + CaO] 45.0 40.1 36.8 54.0 30.0 43.0 44.4 B.sub.2O.sub.3/(SiO.sub.2 + Al.sub.2O.sub.3 + TiO.sub.2) Molar Ratio 1.28 1.28 1.89 1.61 0.33 0.66 0.61 ZnO 12.1 21.6 26.5 0.0 5.0 0.0 0.0 Characterization Glass Flotation ∘ ∘ ∘ ∘ x ∘ ∘ Data Presence or Absence ∘ ∘ ∘ ∘ x x x of Void Generated Plating Ni 0.2 0.3 0.6 0.1 0.1 0.0 0.0 Resistance Plating (μm/h) Solution Sn 1.7 2.5 4.1 2.0 0.0 0.1 0.1 Plating Solution Rate of Flexural 1/10 1/10 5/10 2/10 0/10 0/10 0/10 Crack Generation Composition of Na.sub.2O — — — — 5.0 — — Glass CaO 8.9 7.9 6.5 10.8 — 8.6 8.9 Composition SrO 0.3 0.3 0.3 — — — — [mol %] BaO 35.8 31.9 30.0 43.2 30.0 34.4 35.5 B.sub.2O.sub.3 24.1 21.5 24.0 28.4 15.0 22.6 21.1 SiO.sub.2 11.3 10.1 8.5 13.5 40.0 10.8 26.7 Al.sub.2O.sub.3 7.5 6.7 4.2 4.1 5.0 11.8 7.8 ZnO 12.1 21.6 26.5 — 5.0 — — TiO.sub.2 — — — — — 11.8 — Total 100.0 100.0 100.0 100.0 100.0 100.0 100.0

(39) As shown in Table 1, in the case of the samples according to Examples 1 to 6, which meet the requirements of the present invention, it has been confirmed that favorable results are achieved for all of the glass flotation, void generation, and flexure strength.

(40) In addition, it has been confirmed that the plating resistance is not particularly problematic for any of the samples according to Examples 1 to 6, due to the fact that the dissolution rate in the Ni plating solution is favorably 0.1 μm/h or less, whereas the dissolution rate in the Sn plating solution is also favorably 1.0 μm/h or less.

(41) As for the flexure strength, it has been confirmed that favorable results are achieved, due to the fact that the frequencies of crack generation are all 0/10 (no cracked sample among ten samples) in the test performed by keeping the samples warped up to 1.5 mm in accordance with the above-described test method JIS C 60068-2-21 for the flexural capacity of printed boards.

(42) In contrast, in the case of the samples according to the comparative example, it has been confirmed that the plating resistance (the resistance in the Ni plating solution and the Sn plating solution) is defective in the case of the samples according to Comparative Examples 1 and 2 using the conductive pastes blended with the glass compositions with the ZnO content beyond the scope of the present invention, and the sample according to Comparative Example 3 using the conductive paste blended with the glass composition with the values of the ZnO content and molar ratio of B.sub.2O.sub.2/(SiO.sub.2+Al.sub.2O.sub.2+TiO.sub.2) both beyond the scope of the present invention. Moreover, in the case of the samples according to Comparative Examples 2 and 3, flexural crack generation was confirmed.

(43) In the case of the sample according to Comparative Example 4 using the conductive paste blended with the glass composition with the value of the molar ratio of B.sub.2O.sub.2/(SiO.sub.2+Al.sub.2O.sub.2+TiO.sub.2) beyond the scope of the present invention, the resistance to the Ni plating solution was favorable, whereas the resistance to the Sn plating solution was defective, and flexural crack generation was confirmed.

(44) In the case of the sample according to Comparative Example 5 using the conductive paste blended with the glass composition with the value of the molar ratio of B.sub.2O.sub.2/(SiO.sub.2+Al.sub.2O.sub.2+TiO.sub.2) below the scope of the present invention, glass flotation and void generation found were confirmed to be unfavorable.

(45) In the case of the samples according to Comparative Examples 6 and 7 using the conductive pastes blended with the glass compositions with the values of the molar ratios of B.sub.2O.sub.2/(SiO.sub.2+Al.sub.2O.sub.2+TiO.sub.2) below the scope of the present invention, void generation found was confirmed to be unfavorable.

(46) From the foregoing results, it has been confirmed that the use of the conductive paste containing the glass composition which meets the requirements of the present invention makes it possible to form external electrodes which have excellent plating resistance without glass flotation or voids, and multilayer ceramic capacitors which have excellent flexure strength are achieved by including external electrodes formed with the use of the conductive paste which meets the requirements of the present invention.

(47) It is to be noted that while a case of manufacturing a multilayer ceramic capacitor with the use of the conductive paste according to the present invention has been described as an example in the embodiment, the conductive paste according to the present invention is able to be applied to various multilayer ceramic electronic components including electrodes within ceramic laminates, such as not only multilayer ceramic capacitors but also, for example, multilayer LC composite components and multilayer varistors.

(48) The present invention is moreover not to be considered limited to the embodiment described above even in other respects, but various applications and modifications can be made within the scope of the invention.

DESCRIPTION OF REFERENCE SYMBOLS

(49) 1 ceramic layer

(50) 2 (2a, 2b) internal electrode

(51) 3a, 3b end surface of ceramic laminate (ceramic body)

(52) 4 (4a, 4b) external electrode

(53) 10 ceramic laminate (ceramic body)

(54) 11 external electrode body

(55) 12 Ni plating film layer

(56) 13 Sn plating film layer