Conductive paste and method for manufacturing multilayer ceramic capacitor

Abstract

Provided are a conductive paste enabling suppression of occurrence of blisters while allowing a lower sintering temperature, and a method for manufacturing a multilayer ceramic capacitor using the conductive paste. The conductive paste contains: a surface-treated copper powder including a copper powder and a surface treatment agent layer covering the surface of the copper powder; a binder; and a glass powder. The sintering completion temperature T1 of the surface-treated copper powder is 700°C or lower. The difference (T1-T2) between the sintering completion temperature T1 and the temperature T2 at which the surface treatment agent layer degreases is between 100°C and 350°C (both inclusive). The temperature T3 at which the weight reduction rate of the binder is maximized is lower than the temperature T2.

Description

Method for manufacturing conductive paste and multilayer ceramic capacitors

[0001] This disclosure relates to a method for manufacturing conductive paste and multilayer ceramic capacitors.

[0002] As a terminal electrode material for multilayer ceramic capacitors, a conductive paste is applied by dispersing conductive powder such as copper powder or glass powder (glass frit) on a vehicle. After the coating film is dried, the dried film is fired at a high temperature to form terminal electrodes that are electrically connected to the internal electrodes.

[0003] To miniaturize multilayer ceramic capacitors, there is a need to thin the external electrodes. In order to obtain external electrodes that are thin yet highly dense, that is, have few defects and few voids, by baking a conductive paste, it is necessary to finely atomize the copper powder and glass powder contained in the conductive paste.

[0004] Methods for obtaining finely atomized copper powder with a particle size of 1 μm or less include liquid-phase reduction, gas-phase reduction, and atomization. For example, as an example where atomization is preferred, Patent Document 1 describes a conductive paste containing copper powder that is applied to form external electrodes in chip-type ceramic electronic components such as multilayer ceramic capacitors. Patent Document 1 addresses the problem of providing oxidation resistance to copper powder, and proposes incorporating specific amounts of Bi and Mg inside the copper powder particles to solve this problem.

[0005] When copper powder is atomized to less than 1 μm, the sintering start temperature of the copper powder is lowered. While a moderately lower sintering temperature contributes to low-temperature sintering of the external electrode, using ultrafine powder of less than 1 μm can lower the sintering start temperature of the copper powder too much, which can inhibit the degreasing of the binder by heating. If sintering of the copper powder proceeds with inhibited binder degreasing, it can lead to impaired densification of the external electrode or the formation of blisters on the external electrode.

[0006] To delay the sintering of copper powder, flatten the copper powder, ZrO ２ Ya Al２ O ３ Methods for delaying sintering include adding oxides such as [specific example] to the conductive paste as a sintering retarder, or adding dissimilar metals to the conductive paste. However, when sintering is delayed using the above methods, sintering becomes difficult at low temperatures, requiring high-temperature heat treatment for densification.

[0007] Furthermore, with regard to the dried film of conductive paste containing ultrafine powder, the film strength may be significantly reduced due to improved powder packing and an increase in the surface area of ​​the powder, which increases the interface between the powder and the binder. As a result, the dried film of the conductive paste is more prone to peeling during the period from application to drying and firing. To improve the strength of the dried film, it is necessary to increase the amount of binder contained in the conductive paste. On the other hand, increasing the amount of binder makes degreasing the binder even more difficult, and defects such as blistering are more likely to occur.

[0008] Japanese Patent Publication No. 2011-26631

[0009] The object of this disclosure is to provide a conductive paste that can suppress the generation of blisters while lowering the sintering temperature, and a method for manufacturing a multilayer ceramic capacitor using the conductive paste.

[0010] The conductive paste of this disclosure comprises a surface-treated copper powder having copper powder and a surface treatment layer covering the surface of the copper powder, a binder, and glass powder, wherein the sintering completion temperature T1 of the surface-treated copper powder is 700°C or less, the difference (T1-T2) between the sintering completion temperature T1 and the degreasing temperature T2 of the surface treatment layer is 100°C or more and 350°C or less, and the temperature T3 at which the weight reduction rate of the binder is maximum is lower than the temperature T2.

[0011] According to this disclosure, it is possible to provide a conductive paste that can suppress the generation of blisters while lowering the sintering temperature, and a method for manufacturing a multilayer ceramic capacitor using the conductive paste.

[0012] Figure 1 is a perspective view showing an example of a multilayer ceramic capacitor manufactured using the conductive paste of the embodiment. Figure 2 is a cross-sectional view taken along line A-A in Figure 1. Figure 3 is a cross-sectional view taken along line B-B in Figure 1. Figure 4 is a cross-sectional view taken along line A-A showing the conductive paste of the embodiment applied to the surface of a ceramic body before forming external electrodes.

[0013] The embodiments will be described in detail below with reference to the drawings.

[0014] As a result of diligent research on conductive pastes, the inventors have discovered that by including surface-treated copper powder having a surface treatment layer, controlling the sintering completion temperature T1 of the surface-treated copper powder within a predetermined range, controlling the difference (T1-T2) between the sintering completion temperature T1 of the surface-treated copper powder and the degreasing temperature T2 of the surface treatment layer within a predetermined range, and controlling the temperature T3 at which the binder weight reduction rate is maximum and temperature T2 to satisfy a predetermined relationship, it is possible to lower the sintering temperature of the conductive paste while suppressing the occurrence of blisters when the conductive paste is applied and sintered. Based on this finding, the inventors have completed this disclosure.

[0015] The conductive paste of the embodiment comprises surface-treated copper powder having copper powder and a surface treatment layer covering the surface of the copper powder, a binder, and glass powder. The sintering completion temperature T1 of the surface-treated copper powder is 700°C or lower, the difference between the sintering completion temperature T1 and the degreasing temperature T2 of the surface treatment layer (T1-T2) is 100°C or more and 350°C or less, and the temperature T3 at which the weight reduction rate of the binder is maximum is lower than temperature T2.

[0016] The conductive paste contains surface-treated copper powder, a binder, and glass powder.

[0017] The surface-treated copper powder contained in the conductive paste comprises copper powder and a surface treatment layer that coats the surface of the copper powder. The coating state of the surface treatment layer provided on the surface of each copper particle constituting the copper powder is not particularly limited as long as the sintering start temperature of the surface-treated copper powder can be delayed, and the surface treatment layer may completely cover the surface of the copper particles or cover only a part of the surface of the copper particles. Furthermore, the copper particles are preferably spherical.

[0018] The sintering completion temperature T1 of the surface-treated copper powder (hereinafter also simply referred to as sintering completion temperature T1) is 700°C or lower, and the difference (T1-T2) between the sintering completion temperature T1 of the surface-treated copper powder and the degreasing temperature T2 of the surface treatment layer (hereinafter also simply referred to as temperature T2) is 100°C or more and 350°C or less. Thus, the sintering completion temperature T1 of the surface-treated copper powder is higher than the degreasing temperature T2 of the surface treatment layer, but is still 700°C or lower. Furthermore, the degreasing temperature T2 of the surface treatment layer is higher than the degreasing temperature of the binder, preferably 350°C or higher. Also, the temperature T3 (hereinafter also simply referred to as temperature T3) at which the weight reduction rate of the binder is maximum is lower than the degreasing temperature T2 of the surface treatment layer. As the heating temperature of the conductive paste increases, degreasing of the binder begins, followed by degreasing of the surface treatment layer, and then sintering of the surface-treated copper powder (copper powder) begins.

[0019] When the sintering completion temperature T1 and the difference (T1-T2) are within the above range, and temperatures T2 and T3 satisfy the above relationship, degreasing of the binder begins as the conductive paste reaches temperature T2, and the rate of weight reduction of the binder reaches its maximum. As the temperature of the conductive paste rises further, when all or most of the binder has been degreased, all or most of the surface treatment layer remains, and all or most of the surface treatment copper powder is unsintered. Then, when the temperature of the conductive paste reaches temperature T2, degreasing of all or most of the surface treatment layer is completed, and sintering of all or most of the surface treatment copper powder begins.

[0020] Furthermore, when the temperature of the conductive paste is below temperature T2, some of the surface-treated copper powder may be sintered, but since the amount of surface-treated copper powder that is sintered is small, good degreasing of the binder and surface treatment layer is maintained.

[0021] Thus, in conductive paste, as the temperature rises, the degreasing of the binder begins, the rate of weight loss of the binder is maximized, the degreasing of the surface treatment layer begins, and the sintering of the surface-treated copper powder begins in stages. If a surface treatment layer is not formed on the surface of the copper powder, the degreasing of the binder and the sintering of the copper powder occur simultaneously during heating, or if the particle size of the copper powder is small, the sintering of the copper powder proceeds at the binder degreasing temperature, resulting in insufficient degreasing of the binder. On the other hand, if a surface treatment layer is formed on the surface of the copper powder, the sintering start temperature of the surface-treated copper powder (copper powder) can be raised, or in other words, the sintering start temperature of the surface-treated copper powder can be delayed, so that the degreasing of the binder can be substantially completed before the sintering of the surface-treated copper powder.

[0022] Therefore, it is possible to suppress the simultaneous occurrence of binder degreasing and surface-treated copper powder sintering during heating, and even if the particle size of the surface-treated copper powder (copper powder) is small, it is possible to suppress the progression of sintering of the surface-treated copper powder at the binder degreasing temperature. Furthermore, the sintering completion temperature T1 of such surface-treated copper powder is 700°C or lower, which is in the low temperature range. As a result, the conductive paste can lower the sintering temperature, suppress the generation of blisters due to insufficient degreasing during the sintering of the conductive paste, and furthermore, densify the surface-treated copper powder (copper powder).

[0023] Thus, although the sintering completion temperature T1 of the surface-treated copper powder is relatively low, if the difference (T1-T2) is within the above range and temperatures T2 and T3 satisfy the above relationship, at the sintering completion temperature T1, the binder disappears or most of the binder disappears, and the surface treatment layer disappears or most of the surface treatment layer disappears. Therefore, the binder and surface treatment layer do not hinder the densification of the copper powder.

[0024] Furthermore, due to the strong interaction between the surface treatment layer of the surface-treated copper powder and the binder, the surface-treated copper powder is firmly bonded to the binder at the interface between the surface treatment layer and the binder, resulting in a strong dry film of the conductive paste. Therefore, peeling of the dry film of the conductive paste can be suppressed without increasing the amount of binder contained in the conductive paste.

[0025] Furthermore, the surface treatment layer, which allows the surface-treated copper powder to bond more firmly to the binder at the interface between the surface treatment layer and the binder, thereby further suppressing the peeling of the dried film of the conductive paste, has at least one of the following characteristics: it is nonpolar, it has many unsaturated bonds (π electrons), and it has a small excluded volume due to steric repulsion. In other words, if the surface treatment layer has at least one of the above characteristics, the interaction between the surface-treated copper powder and the binder becomes stronger, and the peeling of the dried film of the conductive paste can be further suppressed. From this viewpoint, the surface treatment layer is preferably composed of a nitrogen-containing heteroaromatic compound, a linear saturated or unsaturated aliphatic organic acid, or a linear saturated or unsaturated aliphatic organic acid salt, and more preferably composed of a nitrogen-containing heteroaromatic compound. An example of a nitrogen-containing heteroaromatic compound is benzotriazole (BTA). An example of a linear saturated or unsaturated aliphatic organic acid is lauric acid.

[0026] One example of a method for preparing surface-treated copper powder is to coat the surface of copper powder with a surface treatment agent to obtain surface-treated copper powder.

[0027] The sintering completion temperature T1 of the surface-treated copper powder is obtained from thermomechanical analysis (TMA). First, the surface-treated copper powder is filled into a cylindrical body, and a punch is pressed in from the top of the housing, and the surface-treated copper powder is pressurized with 10 kg for 1 minute to obtain a cylindrical compact of surface-treated copper powder with a diameter of 4 mm and a height of 3 mm. Subsequently, the obtained compact is analyzed using a thermomechanical analyzer. ２ O ３The compacted material is sandwiched between two plates and positioned so that its long axis is vertical, and then TMA measurement is performed. The TMA measurement is performed under conditions where a load of 98.0 mN is applied to the compacted material in the direction of its long axis, a nitrogen gas flow rate of 20 cc / min is maintained, and the temperature is raised from room temperature to the top temperature at a rate of 20°C / min under a nitrogen atmosphere. In this TMA measurement, the top temperature is set to 500°C, 550°C, 600°C, 650°C, 700°C, and 750°C, and the compacted material is removed after the temperature is raised to the top temperature. The obtained compacted material is embedded in resin and cut, and the cut surface is polished to obtain the cross-section of the compacted material. The cross-section of the compacted material is then observed with a scanning electron microscope (SEM). The obtained SEM image is binarized using image analysis software, and the porosity is measured. The temperature at which the porosity is 5% or less is defined as T1.

[0028] The temperature T2 at which the surface treatment layer degreases is obtained from thermomechanical analysis. First, surface-treated copper powder is filled into a cylindrical body, and a punch is pressed in from the top of the housing, and the surface-treated copper powder is pressurized with 10 kg for 1 minute to obtain a cylindrical compact of surface-treated copper powder with a diameter of 4 mm and a height of 3 mm. Subsequently, the obtained compact is analyzed using a thermomechanical analyzer. ２ O ３ The compacted material is sandwiched between two plates and positioned so that its long axis is vertical, and then TMA measurement is performed. In the TMA measurement, a load of 98.0 mN is applied to the compacted material in the direction of its long axis, while the nitrogen gas flow rate is 20 cc / min. The temperature is raised from room temperature to 900°C at a rate of 20°C / min under a nitrogen atmosphere, and the temperature at which the change rate of the sample length in the resulting TMA chart becomes 5% is defined as T2.

[0029] Furthermore, the particle size of the surface-treated copper powder is preferably 1 μm or less, more preferably 500 nm or less, and even more preferably 300 nm or less. When the particle size of the surface-treated copper powder is 1 μm or less, the sintering completion temperature T1 of the surface-treated copper powder can be sufficiently lowered while maintaining the sintering start temperature of the surface-treated copper powder, that is, while having a sintering delay effect on the surface-treated copper powder, thus allowing the sintering temperature of the conductive paste to be lowered. Also, for example, from the viewpoint of ease of manufacturing the surface-treated copper powder, the particle size of the surface-treated copper powder is preferably 50 nm or more.

[0030] The binder contained in the conductive paste is preferably composed of an acrylic resin (AC), an ethylcellulose resin (EC), or a resin containing both an acrylic resin and an ethylcellulose resin.

[0031] Furthermore, it is preferable that the temperature difference between T2 and T3 (T2-T3) is 50°C or more. When the difference (T2-T3) is 50°C or more, the amount of binder residue decreases further or the binder is completely degreased when the temperature of the conductive paste reaches temperature T2. As a result, the occurrence of blisters can be further suppressed and the surface-treated copper powder can be further densified.

[0032] The temperature T3 at which the binder weight loss rate is maximum is obtained from thermogravimetric differential thermal analysis (TG-DTA). A thermogravimetric differential thermal analyzer is used, with 1.5 mg of binder, a nitrogen gas flow rate of 300 ml / min, under a nitrogen atmosphere, and a heating rate of 10°C / min. The temperature of the largest peak obtained from the differential of the weight loss curve (DTG curve) is defined as T3.

[0033] The glass powder contained in the conductive paste is preferably B-Si glass, Ba-B-Si glass, Sr-B-Si glass, or Ba-Sr-B-Si glass.

[0034] Furthermore, from the viewpoint of lowering the melting point of the glass powder and thus lowering the sintering temperature of the conductive paste, it is preferable that the particle size of the glass powder be 1 μm or less. Also, from the viewpoint of ease of manufacturing the glass powder, for example, it is preferable that the particle size of the glass powder be 50 nm or more.

[0035] The solvent included in the conductive paste is not particularly limited as long as it can suppress blister formation while lowering the sintering temperature of the conductive paste; for example, conventional solvents found in conductive pastes, such as terpineol, can be used.

[0036] Furthermore, if the sintering temperature of the conductive paste can be lowered while suppressing the occurrence of blisters, the conductive paste may contain various additives, such as coating properties improvers, in addition to the surface-treated copper powder, binder, glass powder, and solvent mentioned above.

[0037] Since the conductive paste can suppress the generation of blisters while reducing the sintering temperature as described above, it is suitably used as a paste for forming an external electrode of a multilayer ceramic capacitor.

[0038] Next, a method for manufacturing a multilayer ceramic capacitor according to an embodiment will be described.

[0039] FIG. 1 is a perspective view showing an example of a multilayer ceramic capacitor manufactured using the conductive paste of the embodiment. FIG. 2 is a cross-sectional view taken along the line A-A of FIG. 1. FIG. 3 is a cross-sectional view taken along the line B-B of FIG. 1. FIG. 4 is a cross-sectional view taken along the line A-A in which the conductive paste of the embodiment is applied to the surface of the ceramic element before forming the external electrode.

[0040] Here, as shown in FIGS. 1 to 2, the direction in which the first external electrode 2a and the second external electrode 2b, which are the external electrodes 2, face each other is defined as the length direction L of the multilayer ceramic capacitor 1. Further, as shown in FIGS. 1 to 4, the direction in which the plurality of internal electrodes 31 and the plurality of dielectric ceramic layers 32 are laminated is defined as the lamination direction T of the multilayer ceramic capacitor 1. Also, as shown in FIGS. 1 and 3, the direction orthogonal to both the length direction L and the lamination direction T is defined as the width direction W of the multilayer ceramic capacitor 1.

[0041] The method for manufacturing a multilayer ceramic capacitor includes a film forming step and a sintering step.

[0042] In the film forming step, as shown in FIG. 4, a coating film formed by applying the conductive paste of the above embodiment to the surface of the ceramic element 3 where the internal electrode 31 is exposed is dried to obtain a dry film 20 of the conductive paste.

[0043] In the sintering process, which follows the film formation process, the dried film 20 is heated and sintered. The heating temperature of the dried film 20 in the sintering process is equal to or higher than the sintering completion temperature T1 of the surface-treated copper powder. By sintering the dried film 20, external electrodes 2 covering the surface of the ceramic body 3 are formed, as shown in Figures 1 to 3. The thickness of the external electrodes 2 is, for example, 30 μm to 60 μm. In this way, a multilayer ceramic capacitor 1 can be manufactured. In the manufacturing of the multilayer ceramic capacitor, because the above-mentioned conductive paste is used, the sintering temperature is lowered while suppressing the occurrence of blisters on the external electrodes 2.

[0044] According to the embodiments described above, the conductive paste contains surface-treated copper powder having a surface treatment layer, the sintering completion temperature T1 of the surface-treated copper powder is controlled within a predetermined range, the difference (T1-T2) between the sintering completion temperature T1 of the surface-treated copper powder and the degreasing temperature T2 of the surface treatment layer is controlled within a predetermined range, and the temperature T3 at which the weight reduction rate of the binder is maximum and temperature T2 are controlled to satisfy a predetermined relationship, thereby lowering the sintering temperature of the conductive paste while suppressing the occurrence of blisters when the conductive paste is applied and sintered.

[0045] Although embodiments have been described above, the present invention is not limited to the embodiments described above, and includes all aspects included in the concepts and claims of this disclosure, and can be modified in various ways within the scope of this disclosure.

[0046] Examples and comparative examples will be described next, but this disclosure is not limited to these examples.

[0047] (Examples 1-18) Surface-treated copper powder, having the particle size shown in Tables 1-2, was obtained by kneading the surface-treated copper powder, the binder shown in Tables 1-2, glass powder (Ba-B-Si glass), and solvent (terpineol) to obtain a conductive paste having the sintering completion temperature T1 of the surface-treated copper powder, the degreasing temperature T2 of the surface-treated layer, and the temperature T3 at which the weight reduction rate of the binder is maximum, as shown in Tables 1-2. The monomer species of the acrylic resin (AC) used in the binder was isobutyl methacrylate.

[0048] Subsequently, a coating film formed by applying the obtained conductive paste by the dipping method to the surface of the ceramic green body where the internal electrodes were exposed was dried to form a dry film of the conductive paste. Subsequently, the dry film was heated and sintered at 720 °C to form an external electrode with a thickness of 30 μm. Thus, a multilayer ceramic capacitor was obtained.

[0049] [Measurement and Evaluation] The following measurements and evaluations were performed on the conductive pastes and multilayer ceramic capacitors obtained in the above Examples and Comparative Examples. The results are shown in Tables 1 to 2.

[0050] [1] Particle size of the surface-treated copper powder The surface-treated copper powder used in the conductive paste was photographed with a SEM, and the average value D50 of 500 particle sizes was obtained using image analysis software, and this value was taken as the particle size of the surface-treated copper powder.

[0051] [2] Sintering completion temperature T1 of the surface-treated copper powder The surface-treated copper powder was filled into a cylindrical cylinder, a punch was pushed in from the upper part of the housing, and the surface-treated copper powder was pressurized at 10 kg for 1 minute to obtain a compression molded product of the surface-treated copper powder in a cylindrical shape with a diameter of 4 mm and a height of 3 mm. Subsequently, using a thermomechanical analyzer (manufactured by Rigaku Corporation), the obtained compression molded product was sandwiched between Al ２ O ３ single plates, arranged so that the long axis of the compression molded product was in the vertical direction, and TMA measurement was performed. The TMA measurement was carried out under the conditions that a load of 98.0 mN was applied to the compression molded product in the long axis direction, the nitrogen gas flow rate was 20 cc / min, and the temperature was raised from room temperature to the top temperature at 20 °C / min in a nitrogen atmosphere. In this TMA measurement, the top temperatures were set to 500 °C, 550 °C, 600 °C, 650 °C, 700 °C, and 750 °C, and the molded product was taken out after being heated to the top temperature. The obtained molded product was embedded in resin and cut, the cut surface was polished to expose the cross section of the molded product, and then the cross section of the molded product was observed with a scanning electron microscope (SEM). Regarding the SEM image obtained by the observation, it was binarized with image analysis software (A-Image-kun) and the porosity was measured. The temperature at which the porosity became 5% or less was taken as T1.

[0052] [3] Temperature T2 at which the surface treatment layer degreases Surface-treated copper powder is filled into a cylindrical body, a punch is pressed in from the top of the housing, and the surface-treated copper powder is pressurized with 10 kg for 1 minute to obtain a cylindrical compact of surface-treated copper powder with a diameter of 4 mm and a height of 3 mm. Subsequently, a thermomechanical analyzer (manufactured by Rigaku Corporation) is used to analyze the obtained compact, which is then analyzed using Al ２ O ３ The compacted powder material was sandwiched between two plates and positioned so that its long axis was vertical, and TMA measurements were performed. During the TMA measurement, a load of 98.0 mN was applied to the compacted powder material in the direction of its long axis, while the nitrogen gas flow rate was 20 cc / min. The temperature was increased from room temperature to 900°C at a rate of 20°C / min under a nitrogen atmosphere, and the temperature at which the change rate of the sample length in the resulting TMA chart became 5% was defined as T2.

[0053] [4] Temperature T3 at which the binder weight loss rate is maximum A thermogravimetric differential thermal analyzer (manufactured by Rigaku Corporation) was used to measure the temperature with 1.5 mg of binder, a nitrogen gas flow rate of 300 ml / min, under a nitrogen atmosphere, and a heating rate of 10°C / min. The temperature of the largest peak obtained from the differential curve of the weight loss curve (DTG curve) was defined as T3.

[0054] [5] Blister evaluation 100 multilayer ceramic capacitors manufactured by forming external electrodes on a ceramic substrate with planar dimensions of 1.0 mm × 0.5 mm were visually observed using an optical microscope to check for the presence or absence of blistering on the external electrodes. If no blistering was observed in any of the 100 multilayer ceramic capacitors, it was judged as excellent (○). If blistering was observed in one multilayer ceramic capacitor, it was judged as good (△). If blistering was observed in two or more multilayer ceramic capacitors, it was judged as poor (×).

[0055] [6] Humidity resistance reliability evaluation Ni plating and Sn plating were applied to the manufactured multilayer ceramic capacitors. Humidity resistance reliability was measured for each of the 18 obtained multilayer ceramic capacitors as follows. First, a voltage of 4V was applied to the multilayer ceramic capacitor and the current was measured to calculate the initial resistance value. Next, a voltage of 4V was applied to the multilayer ceramic capacitors that had been left standing for 200 hours in an environment of 85°C and 85% RH and the current was measured to calculate the resistance value after 200 hours. For all 18 multilayer ceramic capacitors, if the resistance value after 200 hours decreased to less than one order of magnitude from the initial resistance value, it was judged as excellent (○). For all 18 multilayer ceramic capacitors, if the resistance value after 200 hours decreased to between one and two orders of magnitude from the initial resistance value, it was judged as good (△). For one or more multilayer ceramic capacitors, if the resistance value after 200 hours decreased to two orders of magnitude or more from the initial resistance value, it was judged as poor (×).

[0056] [7] Evaluation of Adhesion Strength of Dry Film A coating film was formed by applying conductive paste to a ceramic substrate with planar dimensions of 3.2 mm × 2.5 mm using the dip method, and then drying the coating film at 100°C for 15 minutes to form a dry film. Using a vibrating parts alignment machine (MRV-MINI-M, manufactured by Westec), a simulated vibration test was performed on 100 multilayer ceramic capacitors on which the dry film had been formed. In the vibration test, the machine was vibrated 10 times back and forth at a frequency of 50 Hz. The dry film after the vibration test was observed with an optical microscope, and the number of multilayer ceramic capacitors with defects in the dry film out of the 100 capacitors was counted. If the number of defects was less than 10, it was classified as excellent (○), if the number of defects was 10 or more but 20 or less, it was classified as good (△), and if the number of defects was 21 or more, it was classified as poor (×).

[0057] [8] Overall Evaluation If all of the above evaluation ranks are ○, it is classified as Excellent (◎); if both the blister evaluation and moisture resistance reliability evaluation are ○ and the adhesion strength evaluation is △, it is classified as Good (△); if both the blister evaluation and moisture resistance reliability evaluation are ○ and the adhesion strength evaluation is ×, or if at least one of the blister evaluation and moisture resistance reliability evaluation is △ and does not include ×, it is classified as Poor (×). If at least one of the blister evaluation and moisture resistance reliability evaluation is ×, it is classified as Poor (×).

[0058]

[0059]

[0060] As shown in Tables 1 and 2, in the above embodiments, the conductive paste contained surface-treated copper powder having a surface treatment layer, the sintering completion temperature T1 of the surface-treated copper powder was within a predetermined range, the difference (T1-T2) was within a predetermined range, and temperatures T3 and T2 had a predetermined relationship. As a result, the sintering temperature of the conductive paste was lowered while the blister evaluation was excellent or good, and furthermore, the humidity resistance reliability evaluation was excellent or good. On the other hand, in the above comparative example, at least one of the following conditions was not met: the conductive paste contained surface-treated copper powder having a surface treatment layer, the sintering completion temperature T1 of the surface-treated copper powder was within a predetermined range, the difference (T1-T2) was within a predetermined range, and temperatures T3 and T2 had a predetermined relationship. As a result, the sintering temperature of the conductive paste was lowered while suppressing blister formation and achieving good humidity resistance reliability.

[0061] Furthermore, for surface-treated copper powders with the same particle size, the difference (T1-T2) value increased in the order of BTA, lauric acid, and isostearic acid, while the difference (T2-T3) value decreased in the order of BTA, lauric acid, and isostearic acid. A smaller difference (T1-T2) value means that the sintering delay of the surface-treated copper powder can be achieved while maintaining a low sintering completion temperature. Conversely, a larger difference (T2-T3) value means that the sintering of the surface-treated copper powder does not inhibit the degreasing of the binder. From the above, the degreasing properties of the surface treatment layer of the copper powder improved in the order of isostearic acid, lauric acid, and BTA. In addition, surface-treated copper powder having a surface treatment layer that has at least one of the following properties: nonpolarity, a large number of unsaturated bonds (π electrons), and a small excluded volume due to steric repulsion, exhibits stronger interaction with the binder, resulting in stronger adhesion strength of the dried film of the conductive paste. Therefore, the adhesion strength increased in the order of isostearic acid, lauric acid, and BTA.

[0062] Furthermore, various modifications and transformations are possible, as follows:

[0063] <1> A conductive paste comprising a surface-treated copper powder having copper powder and a surface treatment layer covering the surface of the copper powder, a binder, and glass powder, wherein the sintering completion temperature T1 of the surface-treated copper powder is 700°C or less, the difference (T1-T2) between the sintering completion temperature T1 and the degreasing temperature T2 of the surface treatment layer is 100°C or more and 350°C or less, and the temperature T3 at which the weight reduction rate of the binder is maximum is lower than the temperature T2.

[0064] <2> The conductive paste according to <1>, wherein the particle size of the surface-treated copper powder is 1 μm or less.

[0065] <3> The conductive paste according to <1> or <2>, wherein the particle size of the surface-treated copper powder is 500 nm or less.

[0066] <4> The conductive paste according to any one of <1> to <3>, wherein the particle size of the glass powder is 1 μm or less.

[0067] <5> The conductive paste according to any one of <1> to <4>, wherein the surface treatment layer is composed of a nitrogen-containing heteroaromatic compound, a linear saturated or unsaturated aliphatic organic acid, or a linear saturated or unsaturated aliphatic organic acid salt.

[0068] <6> The conductive paste described in <5>, wherein the surface treatment layer is composed of a nitrogen-containing heteroaromatic compound.

[0069] <7> The conductive paste according to any one of <1> to <6>, wherein the difference between the temperature T2 and the temperature T3 (T2-T3) is 50°C or more.

[0070] <8> A method for manufacturing a multilayer ceramic capacitor, comprising: a film formation step of applying a conductive paste described in any one of <1> to <7> to the surface of a ceramic body on which internal electrodes are exposed, and drying the coating film to obtain a dried film; and a sintering step of heating the dried film to sinter it.

[0071] 1. Multilayer ceramic capacitor 2. External electrodes 2a. First external electrode 2b. Second external electrode 20. Dried conductive paste film 3. Ceramic body 31. Internal electrode 32. Dielectric ceramic layer

Claims

1. A conductive paste comprising a surface-treated copper powder having copper powder and a surface treatment layer covering the surface of the copper powder, a binder, and glass powder, wherein the sintering completion temperature T1 of the surface-treated copper powder is 700°C or lower, the difference (T1-T2) between the sintering completion temperature T1 and the degreasing temperature T2 of the surface treatment layer is 100°C or more and 350°C or less, and the temperature T3 at which the weight reduction rate of the binder is maximum is lower than the temperature T2.

2. The conductive paste according to claim 1, wherein the particle size of the surface-treated copper powder is 1 μm or less.

3. The conductive paste according to claim 1 or 2, wherein the particle size of the surface-treated copper powder is 500 nm or less.

4. The conductive paste according to any one of claims 1 to 3, wherein the particle size of the glass powder is 1 μm or less.

5. The conductive paste according to any one of claims 1 to 4, wherein the surface treatment layer is composed of a nitrogen-containing heteroaromatic compound, a linear saturated or unsaturated aliphatic organic acid, or a linear saturated or unsaturated aliphatic organic acid salt.

6. The conductive paste according to claim 5, wherein the surface treatment layer is composed of a nitrogen-containing heteroaromatic compound.

7. The conductive paste according to any one of claims 1 to 6, wherein the difference between the temperature T2 and the temperature T3 (T2-T3) is 50°C or more.

8. A method for manufacturing a multilayer ceramic capacitor, comprising: a film forming step of applying a conductive paste according to any one of claims 1 to 7 to the surface of a ceramic body in which the internal electrodes are exposed, and drying the coating film to obtain a dried film; and a sintering step of heating the dried film to sinter it.

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