JP2019102241A - Thick film conductive paste, and corner chip resistor manufactured by using the same - Google Patents

Abstract

To provide a thick film conducive paste hardly generating void in a sintered film.SOLUTION: There is provided a thick film conductive paste mainly containing three kinds of copper powders with a large diameter powder, a middle diameter powder, and a small diameter powder, the three kinds of copper powders are contained at 60 to 95 mass% at a mixed state in the thick film conductive paste, and blended with a percentage of the large diameter powder of 81 to 91 mass%, the middle diameter powder of 4.5 to 14 mass%, and the small diameter powder of 4.5 to 5.5 mass% based on total 100 mass% of the three kinds of copper powder, and preferably ratios of average particle diameter of the three kinds of copper powder is 0.4 to 0.5 for the middle diameter powder and 0.1 to 0.2 for the small diameter powder based on 1 for the large diameter powder.SELECTED DRAWING: None

Description

  The present invention relates to a thick film conductive paste as a material of a copper top electrode formed on both ends of a low resistance rectangular chip resistor, and a rectangular chip resistor manufactured using the same.

  In recent years, high-density mounting of electronic components has been required with the advancement of functionality and miniaturization of electronic devices, and a low resistance square chip thick film resistor having a substantially rectangular parallelepiped shape (hereinafter, square chip resistor or simply In chip resistors, applications of current detection and voltage control in electronic devices are increasing. The chip resistor has a structure in which a pair of upper surface electrodes and a resistor provided so as to partially cover the pair of upper surface electrodes are formed on an insulating substrate. In applications it is desirable to use low resistance materials to reduce power losses. Therefore, conventionally, a material in the form of a silver paste excellent in oxidation resistance has been used to form an electrode of a chip resistor by adding an organic vehicle to silver powder.

  However, silver powder is expensive and has the problem of being easily oxidized. In addition, silver may be diffused into the resistor in the firing process when manufacturing the chip resistor, and the resistance value and the temperature coefficient of resistance of the resistor may be easily changed. Therefore, copper powder and nickel powder are attracting attention as metal materials which are less expensive than silver powder and whose electrical resistance value is relatively close to that of silver, and copper powder in particular is attracting attention from the viewpoint of magnetism.

  For example, in Patent Document 1, a step of forming a first layer by printing and baking a conductive paste of copper powder containing a glass frit for giving adhesion to an insulating substrate on the surface of the insulating substrate, and Disclosed is a method for forming a copper electrode having a multilayer structure with low specific resistance, comprising the steps of: printing and firing a conductive paste of copper powder containing no glass frit on one layer; and forming a second layer There is. However, in the copper electrode of the multilayer structure produced in this manner, the molten glass frit is not filled between the copper particles of the second layer formed from the conductive paste of the copper powder not containing glass, so that the copper particles are not filled. It has been a problem that the air gap remains as it is. In addition, when the conductive paste contains glass frit, there is a problem that it is difficult to reduce the resistance value.

  On the other hand, Patent Document 2 discloses a conductive paste containing no glass frit, specifically, metal particles having an average particle diameter in the range of 0.2 to 30 μm and an average particle diameter in the range of 1 to 200 nm. A technique for forming a fired film free of voids by combining the metal nanoparticles of

JP, 2016-18814, A JP, 2013-247060, A

  However, in the technique of Patent Document 2, when firing at a high temperature around 900 ° C., the firing rate of metal nanoparticles is faster than that of metal particles, which may cause a problem that many voids are generated in the sintered film. The Further, in the case of two large and small types of metal particles described in Patent Document 2, the metal nanoparticles filling the voids between the metal particles are too small, which may cause uneven distribution of the respective particles. The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a thick film conductive paste in which voids are not easily generated in a sintered film even when firing is performed at a firing temperature of 900 to 1000 ° C.

  As a result of repeated studies to achieve the above object, the inventors of the present invention can significantly reduce the gaps between copper particles formed by using three kinds of copper powders having different average particle sizes. As a result, it has been found that generation of voids in a sintered film after sintering can be suppressed without using molten glass, and the present invention has been completed.

  That is, the thick film conductive paste according to the present invention is a thick film conductive paste mainly composed of three kinds of copper powder consisting of large diameter powder, medium diameter powder and small diameter powder and an organic vehicle, and the above three types of copper The powder is contained in an amount of 60 to 95% by mass in the thick film conductive paste in a mixed state, and 81 to 91% by mass of large diameter powder and medium diameter powder with respect to a total of 100% by mass of the three types of copper powder. It is characterized by being mix | blended in the ratio of 4.5-14 mass% and small diameter powder 4.5-5.5 mass%.

  According to the present invention, it is possible to obtain a highly dense sintered film with few voids.

It is a perspective view which shows the manufacturing process of the square-shaped chip resistor produced using the thick film electrically conductive paste of embodiment of this invention. It is a SEM image of the sintered film surface produced using the thick film electrically conductive paste of the Example of this invention. It is a SEM image of the sintered film surface produced using the thick film electrically conductive paste of the comparative example of this invention.

  Hereinafter, an embodiment of a thick film conductive paste according to the present invention will be described in detail. The thick film conductive paste according to the embodiment of the present invention contains copper powder and an organic vehicle as main components, and, if necessary, an additive such as an antioxidant and a surfactant, and an organic substance for viscosity adjustment such as terpineol. It further contains a solvent. The organic vehicle comprises a binder resin and an organic solvent, and the organic solvent constituting the organic vehicle may be the same as the organic solvent for viscosity adjustment. The thick film conductive paste according to the embodiment of the present invention contains 60 to 95% by weight of copper powder and 0.9 to 15% by weight of an organic vehicle.

  In the thick film conductive paste according to the embodiment of the present invention, the copper powder is composed of three kinds of copper powders different in average particle diameter, that is, large diameter powder, medium diameter powder and small diameter powder, and these three types of copper powder are mixed Included in the state. The ratio of the average particle diameter of these three types of copper powders is preferably 0.4 to 0.5 for the medium-sized powder and 0.1 to 0.2 for the small-sized powder with respect to the large-sized powder 1. In this case, the average particle diameter of the large-diameter powder is preferably 2.0 to 5.0 μm, and more preferably 2.5 to 3.5 μm. This makes it possible to adjust the sintering speed at the time of firing at a high temperature of 900 to 1000 ° C. well. Here, the average particle diameter is the median diameter D50 of volume integration in the particle size distribution obtained by measurement by the laser diffraction scattering method.

  If the ratio of the average particle size of the medium-sized powder is less than 0.4 or exceeds 0.5, the difference between the particle size of the large-sized powder and the small-sized particle size becomes small. The balance of the particle size is bad and many gaps are generated between the particles. On the other hand, when the ratio of the average particle diameter of the small diameter powder is less than 0.1, the effect of adding the small diameter powder is hardly obtained, and conversely, when it exceeds 0.2, the gaps between the particles of the large diameter powder and the medium diameter powder It will be difficult to fill.

  The above three types of copper powder preferably have a sharp particle size distribution, whereby a denser sintered film can be formed. Such copper powder having a sharp particle size distribution can be obtained by classifying the powder produced by the atomization method or the wet synthesis method. Here, the atomizing method is a method of releasing metal in a molten state from a nozzle and dispersing it in a gas phase such as nitrogen gas or in a liquid phase such as silicon oil to obtain a powder metal, and at the time of powder formation A stable powder with relatively low reactivity can be obtained, for example, because a film is formed on the particle surface. On the other hand, the wet synthesis method is a method in which a reducing agent such as hydrazine is added to an aqueous solution containing, for example, metal ions to precipitate metal for recovery, and in general, the particle surface is more reactive than the above atomization method. Powder can be obtained. In the thick film conductive paste according to the embodiment of the present invention, at least the large diameter powder and the medium particle diameter are preferably generated by the atomizing method.

  The above three types of copper powder contained in the thick film conductive paste of the embodiment of the present invention have 81 to 91 mass% of large diameter powder and medium diameter powder with respect to a total of 100 mass% of these three types of copper powder. It is mix | blended in the ratio of 5-14 mass% and small diameter powder 4.5-5.5 mass%. Thereby, it is possible to form a dense sintered film with few voids after sintering. If the content of the above large diameter powder is less than 81% by mass, the resistance value of the sintered film after sintering may become high, and conversely, if it exceeds 91% by mass, the effect of adding medium diameter powder and small diameter powder is obtained. It becomes difficult to be If the content of the above medium-sized powder is less than 4.5% by mass, the gaps between the particles of the large-sized powder can not be sufficiently filled, and conversely, if it exceeds 14% by mass, the gaps between the particles may increase There is. If the content of the small diameter powder is less than 4.5% by mass, it is difficult to obtain the effect of adding the small diameter powder, and conversely, if it exceeds 5.5% by mass, the gaps between the particles may be increased.

  The binder resin constituting the organic vehicle contained in the thick film conductive paste of the embodiment of the present invention is not particularly limited, and ethyl cellulose, methacrylate and the like similar to those used in conventional thick film conductive paste can be used. . The content of the binder resin contained in the organic vehicle is preferably 2% by mass or less with respect to the thick film conductive paste. Further, the organic solvent constituting the above organic vehicle is also not particularly limited, and one similar to those used for conventional thick film conductive pastes such as terpineol and butyl carbitol can be used in a general compounding amount . The content of the organic solvent contained in the organic vehicle is not particularly limited, and the blending ratio with the binder resin may be appropriately adjusted so as to obtain a viscosity of a paste suitable for screen printing described later. Further, as the additive, in addition to the above-mentioned antioxidant and the like, a dispersant having an effect of improving the dispersibility of the conductive powder and preventing separation and sedimentation during storage can be used as needed. The organic solvent can also be added alone at the end to adjust the viscosity of the paste.

  Next, a method of manufacturing a square chip resistor using the thick film conductive paste of the embodiment of the present invention described above with reference to FIG. 1 will be described. In general, in the manufacture of chip resistors, a plurality of chip resistors should be simultaneously formed on a single substrate, cut into pieces, and manufactured into chip resistors in individual finishing steps. However, in the following description, a method of manufacturing a chip resistor will be described focusing on only one chip resistor for the sake of simplicity.

  First, the thick film conductive paste of the embodiment of the present invention is printed by the screen printing method or the like on the upper surface of a plate-like substrate 1 made of an insulating material such as alumina, and then dried and fired to form FIG. A pair of top electrodes 2 as shown is formed. Next, a resistive paste is printed by screen printing or the like so as to at least partially overlap the upper surface of each of the pair of upper surface electrodes 2, then this is dried and fired to pair the upper surface electrodes 2 with each other. The resistor 3 to be connected is formed. As the above-mentioned resistance paste material, although those used for general thick film resistors etc. can be used, organic resins such as ethyl cellulose and solvents such as terpineol can be used for ruthenium oxide powder and glass powder. It is desirable to use a paste obtained by kneading the above into a paste.

  Next, after the precoat layer 4 is formed on the resistor 3 formed in the above, laser light is applied to the resistor 3 from above the precoat layer 4 to adjust the resistance value of the resistor 3. Do trimming. As a result, as shown in FIG. 1 (b), a cut portion 5 in which the resistor 3 and the precoat layer 4 are cut at the same time is formed. Next, as shown in FIG. 1C, the overcoat layer 6 is formed on the surface of the precoat layer 4.

  In the actual chip resistor manufacturing process, a plurality of pairs of the upper electrode 2 and the resistor 3 are formed in a matrix on the upper surface of the plate-like substrate before cutting. In each chip resistor, generally, a pair of back surface electrodes is also formed on the back surface side of the plate-like substrate 1. In each chip resistor after being cut off, sputtering or curing of the conductive resin paste is performed on both end faces on the side where the pair of top electrodes 2 and the pair of back electrodes are formed almost from end to end. A pair of end face electrodes are formed. Further, a plating film is formed on the pair of end face electrodes by a general wet plating method. Thereby, a square chip resistor can be manufactured.

(Test 1)
Prepare three types of copper powder with an average particle size of 0.3 μm, 1.2 μm, and 2.5 μm, measure these copper powders in various proportions, and use a 3-roll mill (with an organic vehicle) It mixed using Buhler Co., Ltd. make, SDY-300). The organic vehicle used contained 10% by mass of ethylcellulose as a binder resin, and was prepared in advance so that the remainder was a terpineol solution as an organic solvent. Thus, samples of the thick film conductive pastes of Examples 1 to 6 and Comparative Examples 1 to 7 were produced. Next, a thick film conductive paste of each sample was printed on an alumina substrate so as to form a rectangular pattern using a screen printer, and dried at 120 ° C. for 10 minutes using a box dryer to form a dried film. . The obtained dried film was fired in a belt furnace at a maximum temperature of 950 ° C. in a nitrogen atmosphere with an oxygen concentration of 30 volume ppm.

  The surface of the obtained fired film was photographed at 500 × using a scanning electron microscope SEM, and the number of voids present in arbitrarily selected 100 μm in the vertical and horizontal directions in the SEM image was counted. The results are shown in the following Table 1 together with the components constituting the thick film conductive paste of each sample and the content thereof with respect to 100% by mass of the thick film conductive paste. When the total content of the copper powder and the organic vehicle is less than 100% by mass, the balance consists of the organic solvent. Moreover, the SEM image of Example 2 as a representative of a present Example, and the SEM image of the comparative example 4 as a representative of a comparative example are respectively shown to FIG.

  From the results of Table 1 above, the sintered films formed using the thick film conductive pastes of Comparative Examples 1 to 6 as the material are formed using the thick film conductive pastes of Examples 1 to 6 that satisfy the requirements of the present invention as the material It can be seen that more voids are generated than the sintered film. The reason is that in the thick film conductive pastes of Comparative Examples 1 to 6, since the content of any one of the copper powders of each particle diameter is out of the range of the present invention, the mixing ratio of the three types of copper powder It is considered that a large amount of voids are generated due to the presence of many gaps between the particles. In addition, since the thick film conductive paste of Comparative Example 7 is a thick film conductive paste of two types of copper powder without medium-sized powder, a sintered film is composed of only large-sized powder and small-sized powder, It is considered that the small-diameter powder is sintered faster than the large-diameter powder at the time of sintering, and the void generated thereby becomes a starting point.

  On the other hand, in the thick film conductive pastes of Examples 1 to 6 satisfying the requirements of the present invention, since three types of copper powders different in average particle diameter are blended in a well-balanced manner, Although generation of voids is observed, it can be seen that a more dense fired film with less voids is formed as compared to the thick film conductive pastes of Comparative Examples 1 to 7 described above.

(Test 2)
Examples 7 and 8 and Examples 7 and 8 in the same manner as in Test 1 except that the total content of copper powder in the thick film conductive paste was changed, but using the same compounding amount of each copper powder as Example 2 in Test 1 Samples of the thick film conductive pastes of Comparative Examples 8 and 9 were prepared and fired under the same conditions as in Test 1. The surface of the obtained fired film was observed using a scanning electron microscope SEM in the same manner as in Test 1, and the number of voids was counted. The results are shown in the following Table 2 together with the components constituting the thick film conductive paste of each sample and the content thereof with respect to 100% by mass of the thick film conductive paste.

  From the results in Table 2 above, the sintered film formed using the thick film conductive paste of Comparative Example 8 as the material is more than the sintered film formed using the thick film conductive paste of the example satisfying the requirements of the present invention as the material. It can be seen that many voids are generated. The reason is that the thick film conductive paste of Comparative Example 8 has a relatively low total content of copper powder, so the amount of solvent is relatively increased, and the solvent and binder resin are sufficiently removed during drying and baking. It is thought that there is no room for it and it has become a void. Further, in the thick film conductive paste of Comparative Example 9, the content of the organic solvent was too small because the amount of the copper powder was too large, and the flowability of the paste was not sufficiently obtained, and it was not possible to print smoothly. As a result, the number of voids could not be properly measured, so the evaluation result was “−”. It can be seen that, in the thick film conductive pastes of Examples 7 and 8 satisfying the requirements of the present invention, a dense fired film is formed as in Examples 1 to 6 of Test 1 above.

(Test 3)
The thickness of Examples 9 and 10 was the same as in Test 1 except that the content of each of the copper powders was the same as in Example 2 in Test 1 except that the content of the organic vehicle in the thick film conductive paste was reduced. A sample of film conductive paste was prepared and fired under the same conditions as in Test 1. Moreover, in Examples 11 and 12, the material of the same blending amount of each copper powder as in Example 2 is used except that the content of the organic vehicle is increased and the total content of the copper powder is reduced to 80% by mass. A sample of a thick film conductive paste was prepared in the same manner as in Test 1, and fired under the same conditions as in Test 1. The surface of the obtained fired film was observed using a scanning electron microscope SEM in the same manner as in Test 1, and the number of voids was counted. The results are shown in the following Table 3 together with the components constituting the thick film conductive paste of each sample and the content thereof with respect to 100% by mass of the thick film conductive paste.

  From the results of Table 3 above, a sintered film formed using the thick film conductive pastes of Examples 9 and 12 out of the requirements of the content of the preferred organic vehicle is an example satisfying the requirements of the content of the preferred organic vehicle It can be seen that the number of voids is slightly larger than that of the sintered film formed using the thick film conductive pastes of 10 and 11 as materials. Although the thick film conductive paste of Example 9 does not increase the generation amount of voids significantly, the adhesion with the substrate may be poor. As in the thick film conductive paste of Example 12, when the amount of the organic vehicle is too large, voids may increase depending on the timing of the removal of the organic vehicle. On the other hand, in the thick film conductive pastes of Examples 10 and 11, it is understood that a dense fired film is formed as in Examples 1 to 6 of Test 1 above.

(Test 4)
The ratio of each particle size to the large particle size copper powder used for the thick film conductive paste is changed, and the medium particle size is 0.8 μm, 1.0 μm, 1.25 μm, 1.3 μm copper powder, and the small particle size is used. Samples of thick film conductive pastes of Examples 13 to 20 were prepared under the same conditions as Example 2 of Test 1 except that 0.2 μm, 0.25 μm, 0.5 μm, and 0.6 μm copper powder were used as And the same conditions as in Test 1. The surface of the obtained fired film was observed using a scanning electron microscope SEM in the same manner as in Test 1, and the number of voids was counted. The results are shown in the following Table 4 together with the components constituting the thick film conductive paste of each sample and the content thereof with respect to 100% by mass of the thick film conductive paste.

  From the results of Table 4 above, the sintered films formed using the thick film conductive pastes of Examples 13, 16, 17 and 20 which deviate from the requirements of the preferred copper powder diameter ratio, satisfy the requirements of the preferred copper powder diameter ratio It can be seen that the number of voids is slightly larger than that of the sintered film formed using the thick film conductive paste of Examples 14, 15, 18, and 19 as a material. The reason for this is that the balance of the preferred copper powder size is broken in Examples 13, 16, 17, and 20, and therefore, it is considered that the void is increased because the copper powder interval can not be sufficiently narrowed. On the other hand, it can be seen that, in the thick film conductive pastes of Examples 14, 15, 18, and 19, similar to Examples 1 to 6 of Test 1, a dense fired film is formed.

(Test 5)
The particle size of the large particle size copper powder which is the basis of the thick film conductive paste is changed, and the medium particle size and the particle size of the small particle size are also changed accordingly, and the large particle size is 5.0 μm, 3.5 μm, Using 2.0 μm copper powder, using 2.5 μm, 1.6 μm, 0.9 μm copper powder as medium particle size, using 0.5 μm, 0.4 μm, 0.3 μm copper powder as small particle size The samples of the thick film conductive pastes of Examples 21 to 25 were prepared under the same conditions as in Test 1 except that the content of each copper powder was also changed, and was fired under the same conditions as in Test 1. The surface of the obtained fired film was observed using a scanning electron microscope SEM in the same manner as in Test 1, and the number of voids was counted. The results are shown in the following Table 5 together with the components constituting the thick film conductive paste of each sample and the content thereof with respect to 100% by mass of the thick film conductive paste.

  From the results in Table 5 above, even if the diameter of the copper powder is changed, a dense fired film is formed in the same manner as in Examples 1 to 6 of Test 1 above by maintaining the preferable copper powder diameter ratio of the present invention I understand that

Reference Signs List 1 plate-like substrate 2 pair of top electrodes 3 resistor 4 precoat layer 5 cut portion 6 overcoat layer

Claims (4)

  A thick film conductive paste mainly composed of three kinds of copper powder consisting of large diameter powder, medium diameter powder and small diameter powder and an organic vehicle, wherein the three types of copper powder are mixed in a mixed state with the thick film conductive paste 60 to 95% by mass, and 81 to 91% by mass of large diameter powder, 4.5 to 14% by mass of medium diameter powder, and small diameter powder with respect to a total of 100% by mass of the three types of copper powder A thick film conductive paste characterized in that it is blended in a ratio of 4.5 to 5.5% by mass.   The organic vehicle contains a binder resin and an organic solvent, and the organic vehicle is contained in an amount of 0.9 to 15% by mass with respect to 100% by mass of the thick film conductive paste. Thick film conductive paste as described.   The ratio of the average particle diameter of the three types of copper powder is characterized in that the medium diameter powder is 0.4 to 0.5 and the small diameter powder is 0.1 to 0.2 with respect to the large diameter powder 1. The thick film conductive paste according to claim 1 or 2.   A square chip resistor having an upper surface electrode formed of the thick film conductive paste according to any one of claims 1 to 3.