Conductive paste

Abstract

Provided is a conductive paste capable of greater suppression of blister generation. This conductive paste contains copper powder, glass powder, acrylic resin, and a solvent, wherein a shrinkage temperature T1 of the copper powder is 350°C or more, a thermal decomposition end temperature T2 of the acrylic resin in the conductive paste is 310°C-385°C, and the difference (T2−T3) between the thermal decomposition end temperature T2 and a thermal decomposition start temperature T3 of the acrylic resin in the conductive paste is 159°C or more. In other words, the difference (T2−T1) between the thermal decomposition end temperature T2 and the shrinkage temperature T1 is 35°C or less, and the difference (T2−T3) between the thermal decomposition end temperature T2 and the thermal decomposition start temperature T3 of the acrylic resin in the conductive paste is 159°C or more.

Description

Conductive paste

[0001] The present disclosure relates to a conductive paste.

[0002] Multilayer ceramic capacitors are expected to have a significant increase in demand in the communication and automotive fields, and various performances such as miniaturization with high capacitance, high reliability products, and multi-terminal products are required. In order to reduce the external dimensions of chip-type ceramic electronic components such as multilayer ceramic capacitors, thinning the external electrodes formed on the outer surface of the component body of the chip-type ceramic electronic component is considered as one of the effective means.

[0003] In order to obtain a highly dense external electrode with less defects and voids while thinning, it is necessary to atomize the copper powder and glass powder contained in the conductive paste. On the other hand, when using fine copper powder with a particle size of 1 μm or less as the copper powder contained in the conductive paste, the sintering of the copper powder is carried out at a lower temperature. Therefore, if the thermal decomposition of the binder resin contained in the conductive paste is insufficient, gas may be generated by the residual carbon derived from the binder resin during densification, and defects due to blisters may occur on the film.

[0004] In response to such problems, in Patent Document 1, by using an acrylic resin with a thermal decomposition start temperature of 150°C or higher and 250°C or lower as the binder of the conductive paste, the acrylic resin is thermally decomposed in a relatively low temperature range to suppress the generation of blisters.

[0005] Although Patent Document 1 suppresses the generation of blisters, in high-performance chip-type ceramic electronic components required in recent years, further suppression of blister generation is required.

[0006] Japanese Patent Application Laid-Open No. 2005-322751

[0007] An object of the present disclosure is to provide a conductive paste capable of suppressing the generation of blisters more effectively than conventional ones.

[0008] The conductive paste of this disclosure comprises copper powder, glass powder, an acrylic resin, and a solvent, wherein the shrinkage temperature T1 of the copper powder is 350°C or higher, the thermal decomposition completion temperature T2 of the acrylic resin in the conductive paste is 310°C or higher and 385°C or lower, and the difference (T2-T3) between the thermal decomposition completion temperature T2 and the thermal decomposition start temperature T3 of the acrylic resin in the conductive paste is 159°C or higher. In other words, the difference (T2-T1) between the thermal decomposition completion temperature T2 and the shrinkage temperature T1 is 35°C or lower, and the difference (T2-T3) between the thermal decomposition completion temperature T2 and the thermal decomposition start temperature T3 is 159°C or higher.

[0009] According to this disclosure, it is possible to provide a conductive paste that can suppress the generation of blisters more effectively than conventional methods.

[0010] 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.

[0011] The embodiments will be described in detail below with reference to the drawings.

[0012] The inventors have diligently conducted research on conductive pastes as follows:

[0013] Patent Document 1 focuses on the thermal decomposition properties of the resin alone. However, when the raw materials constituting a conductive paste are made into a paste, the thermal decomposition properties of the resin change due to the interaction between the metal and the resin, and the interaction between the oxide and the resin. Therefore, we believe that considering the thermal decomposition properties of the resin when it is made into a paste is more practical. That is, we focused not on the thermal decomposition properties of the acrylic resin alone, but on the thermal decomposition properties of the acrylic resin in the conductive paste, or in other words, the thermal decomposition properties of the acrylic resin affected by the interaction between copper powder and the acrylic resin, or the interaction between glass powder and the acrylic resin. Furthermore, while Patent Document 1 focuses on the thermal decomposition onset temperature as a measure of the thermal decomposition properties of the resin, we believe that even if the thermal decomposition onset temperature is low, if the thermal decomposition termination temperature is high, desorbed gases may be generated during the densification process, leading to the formation of blisters. We also believe that if the thermal decomposition of the resin proceeds rapidly in a certain temperature range, the pressure of the desorbed gases due to the rapid generation of decomposition gases may lead to the formation of blisters.

[0014] Based on the above considerations, we investigated and found that by controlling the shrinkage temperature T1 of the copper powder, the thermal decomposition completion temperature T2 of the acrylic resin in the conductive paste, and the thermal decomposition start temperature T3 of the acrylic resin in the conductive paste to satisfy a predetermined relationship, the generation of blisters can be suppressed compared to conventional pastes when the conductive paste is applied and sintered. Based on this finding, we have completed this disclosure.

[0015] The conductive paste of the embodiment comprises copper powder, glass powder, acrylic resin, and a solvent, wherein the shrinkage temperature T1 of the copper powder is 350°C or higher, the thermal decomposition completion temperature T2 of the acrylic resin in the conductive paste is 310°C or higher and 385°C or lower, and the difference (T2-T3) between the thermal decomposition completion temperature T2 and the thermal decomposition start temperature T3 of the acrylic resin in the conductive paste is 159°C or higher. In other words, the difference (T2-T1) between the thermal decomposition completion temperature T2 and the shrinkage temperature T1 is 35°C or lower, and the difference (T2-T3) between the thermal decomposition completion temperature T2 and the thermal decomposition start temperature T3 is 159°C or higher.

[0016] The conductive paste contains copper powder, glass powder, acrylic resin, and a solvent. The acrylic resin acts as a binder for the conductive paste.

[0017] The conductive paste has at least one of configuration (A) or configuration (B).

[0018] Configuration (A) is a configuration in which the shrinkage temperature T1 of the copper powder is 350°C or higher, and the thermal decomposition completion temperature T2 of the acrylic resin in the conductive paste (hereinafter also simply referred to as the thermal decomposition completion temperature T2 of the acrylic resin) is 310°C or higher and 385°C or lower. Configuration (B) is a configuration in which the difference (T2-T1) between the thermal decomposition completion temperature T2 of the acrylic resin in the conductive paste and the shrinkage temperature T1 of the copper powder is -400°C or higher and 35°C or lower.

[0019] Furthermore, the conductive paste has a configuration (C). Configuration (C) is that the difference (T2-T3) between the thermal decomposition completion temperature T2 of the acrylic resin and the thermal decomposition start temperature T3 of the acrylic resin in the conductive paste (hereinafter also simply referred to as the thermal decomposition start temperature T3 of the acrylic resin) is 159°C or higher. The thermal decomposition completion temperature T2 of the acrylic resin is higher than the thermal decomposition start temperature T3 of the acrylic resin.

[0020] The shrinkage temperature T1 of the copper powder contained in the conductive paste is higher than the thermal decomposition onset temperature T3 of the acrylic resin, and is between 350°C and 800°C. Furthermore, from the viewpoint of lowering the sintering temperature of the conductive paste, the shrinkage temperature T1 of the copper powder is preferably 700°C or lower, and more preferably 600°C or lower.

[0021] The shrinkage temperature T1 of the copper powder is obtained from thermomechanical analysis (TMA). First, copper powder is filled into a cylindrical body, and a punch is pressed in from the top of the housing, and the copper powder is pressurized with 10 kg for 1 minute to obtain a cylindrical compact of 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 powder molded product is sandwiched between two plates and positioned so that its long axis is vertical, and TMA measurement is performed. In the TMA measurement, a load of 98 mN is applied in the long axis direction, and the temperature is increased from room temperature to 1000°C at a rate of 10°C / min under a nitrogen atmosphere with a nitrogen gas flow rate of 200 ml / min. The temperature at which the differential value of the shrinkage rate (dTMA) is maximized is defined as T1.

[0022] The thermal decomposition completion temperature T2 of the acrylic resin in the conductive paste is different from the thermal decomposition completion temperature of the acrylic resin not contained in the conductive paste, i.e., the thermal decomposition completion temperature of the acrylic resin before it is added to the conductive paste. Furthermore, the thermal decomposition start temperature T3 of the acrylic resin in the conductive paste is different from the thermal decomposition start temperature of the acrylic resin not contained in the conductive paste, i.e., the thermal decomposition start temperature of the acrylic resin before it is added to the conductive paste.

[0023] The thermal decomposition completion temperature T2 and thermal decomposition start temperature T3 of the acrylic resin are obtained by thermogravimetric differential thermal analysis (TG-DTA). Using a thermogravimetric differential thermal analyzer, the dry film of the conductive paste powder (an amount equivalent to 1.5 mg of acrylic resin) is measured under a nitrogen atmosphere with a nitrogen gas flow rate of 300 ml / min, and the temperature is raised from room temperature to 800°C at a heating rate of 10°C / min. The temperature at which the dry film loses 95% of its weight is defined as the thermal decomposition completion temperature T2, and the temperature at which the dry film loses 5% of its weight is defined as the thermal decomposition start temperature T3. The dry film of the conductive paste is obtained by drying a 100 μm thick coating film, which is obtained by applying the conductive paste, at 100°C for 15 minutes.

[0024] As stated above, the thermal decomposition termination temperature T2 of the acrylic resin in conductive paste is not the thermal decomposition termination temperature of the acrylic resin alone. Therefore, the target of analysis for the thermal decomposition termination temperature T2 of the acrylic resin in conductive paste is the acrylic resin in the conductive paste (dried film of conductive paste), not the acrylic resin alone. Similarly, the thermal decomposition start temperature T3 of the acrylic resin in conductive paste is not the thermal decomposition start temperature of the acrylic resin alone. Therefore, the target of analysis for the thermal decomposition start temperature T3 of the acrylic resin in conductive paste is the acrylic resin in the conductive paste (dried film of conductive paste), not the acrylic resin alone.

[0025] Having at least one of the above configuration (A) or above configuration (B), and also having above configuration (C), allows the thermal decomposition of the acrylic resin during the baking of the conductive paste to proceed sufficiently and slowly, thereby suppressing the occurrence of blisters. In particular, when the copper powder is in the form of fine powder, it is possible to suppress blisters that occur when the sintering of the fine copper powder proceeds before the gas generated by the decomposition of residual carbon due to insufficient thermal decomposition of the acrylic resin is sufficiently discharged, causing the internal pressure of the trapped gas to increase and foam. Furthermore, it is possible to suppress blisters that occur due to the pressure of desorbed gas caused by the rapid decomposition of the acrylic resin before the sintering of the copper powder.

[0026] Furthermore, the 50% weight cumulative particle size (hereinafter simply referred to as D50) of copper powder measured by laser diffraction scattering particle size distribution analysis is preferably 1.00 μm or less, more preferably 0.80 μm or less, and even more preferably 0.40 μm or less. When the D50 of copper powder is 1.00 μm or less, the occurrence of blisters can be sufficiently suppressed even if the copper powder is fine powder when it is used to bake the conductive paste onto the external electrode, and the density can be improved while thinning the film, that is, defects can be reduced and voids can be reduced. Alternatively, for example, the D50 of copper powder is 0.050 μm or more.

[0027] Furthermore, it is preferable that the multiple copper particles constituting the copper powder are spherical.

[0028] Furthermore, the 50% weight cumulative particle size of the glass powder contained in the conductive paste, as measured by laser diffraction scattering particle size distribution analysis, is preferably 1.00 μm or less, more preferably 0.90 μm or less, even more preferably 0.70 μm or less, and particularly preferably 0.30 μm or less. When the D50 of the glass powder is 1.00 μm or less, the external electrode obtained by baking the conductive paste can be made thinner while improving its density, that is, reducing defects and voids. Alternatively, for example, the D50 of the glass powder is 0.050 μm or more.

[0029] Furthermore, the glass powder is preferably a B-Si-Ba type glass.

[0030] Furthermore, the weight-average molecular weight of the acrylic resin is preferably 50,000 or more and 1,000,000 or less.

[0031] Furthermore, it is preferable that the content of acrylic resin in the conductive paste is 5% by weight or more and 15% by weight or less. Also, it is preferable that the ratio of copper powder and glass powder to non-volatile components other than the solvent ((volume of copper powder and volume of glass powder) / (volume of non-volatile components other than the solvent)) is 50% or more and 70% or less.

[0032] Furthermore, the solvent contained in the conductive paste includes, for example, at least one of terpineol, dihydroterpineol, dihydroterpinyl acetate, propylene glycol phenyl ether, benzyl alcohol, texanol, and butyl carbitol acetate. The solvent type can be analyzed by measuring the generated gas using gas chromatography-mass spectrometry. Gas chromatography-mass spectrometry can be performed, for example, using an Agilent Technologies, Inc. mass spectrometer 7890A / 5975C (heated at 500°C).

[0033] Furthermore, if blister formation can be suppressed, the conductive paste may contain various additives, such as coating properties improvers, in addition to the copper powder, glass powder, acrylic resin, and solvent mentioned above.

[0034] Because conductive paste can suppress the generation of blisters as described above, it is suitable for use as a paste for forming external electrodes of chip-type ceramic electronic components.

[0035] Next, a method for manufacturing a multilayer ceramic capacitor using the conductive paste of the embodiment will be described.

[0036] 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.

[0037] 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. Further, 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.

[0038] The manufacturing method of the multilayer ceramic capacitor has a film forming step and a sintering step.

[0039] In the film forming step, as shown in FIG. 4, a coating film formed by applying the conductive paste of the above embodiment on the surface of the ceramic body 3 where the internal electrode 31 is exposed is dried to obtain a dried film 20 of the conductive paste.

[0040] In the sintering step performed after the film forming step, the dried film 20 is heated and sintered. The heating temperature of the dried film 20 in the sintering step is not less than the shrinkage temperature T1 of the copper powder. By sintering the dried film 20, as shown in FIGS. 1 to 3, an external electrode 2 covering the surface of the ceramic body 3 is formed. Thus, the multilayer ceramic capacitor 1 can be manufactured. In the manufacture of the multilayer ceramic capacitor, since the above conductive paste is used, the generation of blisters in the external electrode 2 is suppressed in the obtained multilayer ceramic capacitor.

[0041] According to the embodiment described above, by controlling the shrinkage temperature T1 of the copper powder, the thermal decomposition end temperature T2 of the acrylic resin in the conductive paste, and the thermal decomposition start temperature T3 of the acrylic resin in the conductive paste so as to satisfy a predetermined relationship, when the conductive paste is applied and sintered, the generation of blisters can be suppressed more than in the prior art.

[0042] Although the embodiment has been described above, the present invention is not limited to the above embodiment, includes all aspects included in the concept of the present disclosure and the scope of the claims, and can be variously modified within the scope of the present disclosure.

[0043] Next, examples and comparative examples will be described, but the present disclosure is not limited to these examples.

[0044] (Examples 1 to 4, Comparative Examples 1 to 2) Copper powder having D50 shown in Table 1, glass powder having D50 shown in Table 1, an acrylic resin having a weight average molecular weight shown in Table 1, and a solvent were blended so as to be 50% by weight, 5% by weight, 5% by weight, and 40% by weight, respectively. After premixing with a planetary mixer, they were dispersed with a three-roll mill to obtain a conductive paste having a shrinkage temperature T1, a thermal decomposition end temperature T2, and a thermal decomposition start temperature T3 shown in Table 1.

[0045] [Measurement and Evaluation] The following measurements and evaluations were performed on the conductive pastes obtained in the above examples and comparative examples. The results are shown in Table 1.

[0046] [1] D50 of copper powder and D50 of glass powder The copper powder used in the conductive paste was photographed with a SEM, and the average value D50 of 500 particle diameters was obtained using image analysis software, and this value was defined as the D50 of the copper powder. Similarly, the glass powder used in the conductive paste was photographed with a SEM, and the average value D50 of 500 particle diameters was obtained using image analysis software, and this value was defined as the D50 of the glass powder.

[0047] [2] Shrinkage temperature T1 of copper powder Copper powder was filled into a cylindrical cylinder, a punch was pushed in from the upper part of the housing, and the copper powder was pressurized at 10 kg for 1 minute to obtain a compression molded product of a cylindrical copper powder having 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 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. In the TMA measurement, while applying a load of 98 mN in the long axis direction, the temperature was raised from room temperature to 1000 °C at 10 °C / min under a nitrogen gas flow rate of 200 ml / min in a nitrogen atmosphere, and the temperature at which the differential value of the shrinkage rate (dTMA) became maximum was defined as T1.

[0048] [3] Thermal decomposition completion temperature T2 of acrylic resin in conductive paste A thermogravimetric differential thermal analyzer (TG-DTA8211, manufactured by Rigaku Corporation) was used to measure the thermal decomposition completion temperature T2. The dry film of the conductive paste was measured using powder (an amount equivalent to 1.5 mg of acrylic resin), with a nitrogen gas flow rate of 300 ml / min, under a nitrogen atmosphere, and heated from room temperature to 800°C at a heating rate of 10°C / min. The temperature at which the dry film lost 95% of its weight was defined as the thermal decomposition completion temperature T2. The dry film of the conductive paste was obtained by drying a 100 μm thick coating film, which was obtained by applying the conductive paste, at 100°C for 15 minutes.

[0049] [4] Thermal decomposition start temperature T3 of acrylic resin in conductive paste A thermogravimetric differential thermal analyzer (TG-DTA8211, manufactured by Rigaku Corporation) was used to measure the thermal decomposition start temperature T3. The dry film of the conductive paste was measured using powder (an amount equivalent to 1.5 mg of acrylic resin), with a nitrogen gas flow rate of 300 ml / min, under a nitrogen atmosphere, and heated from room temperature to 800°C at a heating rate of 10°C / min. The temperature at which the dry film lost 5% of its weight was defined as the thermal decomposition start temperature T3. The dry film of the conductive paste was obtained by drying a 100 μm thick coating film, which was obtained by applying the conductive paste, at 100°C for 15 minutes.

[0050] [5] Blister Evaluation A conductive paste was applied by dipping to the surface of a ceramic substrate with planar dimensions of 0.6 mm × 0.3 mm where the internal electrodes were exposed. The resulting coating was dried to form a dried conductive paste film. Subsequently, the dried film was heated at 720°C and sintered to form the external electrodes. In this way, multilayer ceramic capacitors were obtained. The 100 obtained multilayer ceramic capacitors were visually inspected 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 good (○). If blistering was observed in one or more multilayer ceramic capacitors, it was judged as poor (×).

[0051]

[0052] As shown in Table 1, in the above example, the shrinkage temperature T1 of the copper powder, the thermal decomposition completion temperature T2 of the acrylic resin in the conductive paste, and the thermal decomposition start temperature T3 of the acrylic resin in the conductive paste satisfied the predetermined relationship, resulting in a good blister evaluation. On the other hand, in the above comparative example, the shrinkage temperature T1 of the copper powder, the thermal decomposition completion temperature T2 of the acrylic resin in the conductive paste, and the thermal decomposition start temperature T3 of the acrylic resin in the conductive paste did not satisfy the predetermined relationship, resulting in a poor blister evaluation.

[0053] Table 1 shows that when the shrinkage temperature T1 of the copper powder is 350°C or higher, and the thermal decomposition completion temperature T2 of the acrylic resin in the conductive paste is 310°C or higher and 385°C or lower, or when the difference between the thermal decomposition completion temperature T2 of the acrylic resin in the conductive paste and the shrinkage temperature T1 of the copper powder (T2-T1) is -400°C or higher and 35°C or lower, blistering caused by foaming due to increased internal pressure of trapped gas proceeds before the gas generated by the decomposition of residual carbon due to insufficient thermal decomposition of the acrylic resin is sufficiently discharged. In addition, it was found that when the difference between the thermal decomposition completion temperature T2 of the acrylic resin in the conductive paste and the thermal decomposition start temperature T3 of the acrylic resin in the conductive paste (T2-T3) is 159°C or higher, blistering caused by the pressure of desorbed gas resulting from the rapid decomposition of the acrylic resin before the sintering of the copper powder can also be suppressed. By combining these conditions, blistering can be suppressed more effectively.

[0054] Furthermore, various modifications and transformations are possible, as follows:

[0055] <1> A conductive paste comprising copper powder, glass powder, acrylic resin, and a solvent, wherein the shrinkage temperature T1 of the copper powder is 350°C or higher, the thermal decomposition completion temperature T2 of the acrylic resin in the conductive paste is 310°C or higher and 385°C or lower, and the difference (T2-T3) between the thermal decomposition completion temperature T2 and the thermal decomposition start temperature T3 of the acrylic resin in the conductive paste is 159°C or higher.

[0056] <2> The conductive paste according to <1>, wherein the 50% weight cumulative particle size of the copper powder measured by laser diffraction scattering particle size distribution analysis is 1.00 μm or less.

[0057] <3> The conductive paste according to <1> or <2>, wherein the 50% weight cumulative particle size of the glass powder measured by laser diffraction scattering particle size distribution analysis is 1.00 μm or less.

[0058] <4> A conductive paste comprising copper powder, glass powder, acrylic resin, and a solvent, wherein the difference between the thermal decomposition completion temperature T2 of the acrylic resin in the conductive paste and the shrinkage temperature T1 of the copper powder (T2-T1) is -400°C or more and 35°C or less, and the difference between the thermal decomposition completion temperature T2 and the thermal decomposition start temperature T3 of the acrylic resin in the conductive paste (T2-T3) is 159°C or more.

[0059] 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 copper powder, glass powder, acrylic resin, and a solvent, wherein the shrinkage temperature T1 of the copper powder is 350°C or higher, the thermal decomposition completion temperature T2 of the acrylic resin in the conductive paste is 310°C or higher and 385°C or lower, and the difference (T2-T3) between the thermal decomposition completion temperature T2 and the thermal decomposition start temperature T3 of the acrylic resin in the conductive paste is 159°C or higher.

2. The conductive paste according to claim 1, wherein the 50% weight cumulative particle size of the copper powder measured by laser diffraction scattering particle size distribution analysis is 1.00 μm or less.

3. The conductive paste according to claim 1 or 2, wherein the 50% weight cumulative particle size of the glass powder measured by laser diffraction scattering particle size distribution analysis is 1.00 μm or less.

4. A conductive paste comprising copper powder, glass powder, acrylic resin, and a solvent, wherein the difference between the thermal decomposition completion temperature T2 of the acrylic resin in the conductive paste and the shrinkage temperature T1 of the copper powder (T2-T1) is 35°C or less, and the difference between the thermal decomposition completion temperature T2 and the thermal decomposition start temperature T3 of the acrylic resin in the conductive paste (T2-T3) is 159°C or more.

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