JP2008192565A - Conductive paste and conductive coating film - Google Patents

Abstract

An object of the present invention is to provide a conductive paste and a conductive coating film capable of forming a sufficient gap between an element body and a coil in a multilayer inductor.
A conductive paste contains silver powder and an acrylic resin, and has a dynamic hardness of 9.8 to 20.6 measured when a residual solvent is 1.0% or less. If it does in this way, even if a pressure is simultaneously applied with respect to the electroconductive coating film in which an electroconductive paste is dried when pressing a green sheet laminated body, the density of an electroconductive coating film becomes difficult to become high. In addition, before and after pressing, the shrinkage rate during firing of the conductive coating film is maintained in a state larger than the shrinkage rate during firing of the green sheet.
[Selection figure] None

Description

  The present invention relates to a conductive paste and a conductive coating film.

Conventionally, magnetic body and magnetic green sheet having a specific surface area was set to 1.0m ² /g~10.0m ² / g of powder, conductor specific surface area of the powder is 0.5m ² /g~5.0m ² / G of conductive paste, and laminating and firing a plurality of magnetic green sheets coated so that the conductive paste has a predetermined shape. There is known a method of manufacturing a multilayer inductor in which a coil is disposed on a substrate (see, for example, Patent Document 1).
Japanese Patent No. 2983049

  By the way, in a multilayer inductor, when a magnetic element and a coil are in contact with each other, a decrease in inductance value or a DC superimposition characteristic is caused by the influence of a magnetic field (magnetic saturation phenomenon) generated when a direct current is passed through the coil. Deterioration will occur. In particular, in recent years, there has been a demand for further downsizing of the multilayer inductor, so that the thickness of the inner conductor constituting the coil is reduced, and the interval between the inner conductors adjacent to each other in the stacking direction of the multilayer inductor is reduced. As a result, the magnetic saturation phenomenon is more likely to occur.

  Therefore, in a multilayer inductor including a magnetic element body and a coil, it is preferable that most of the element body and the coil are not in contact with each other. Therefore, in the multilayer inductor described in Patent Document 1, by defining the specific surface area of the magnetic powder and the specific surface area of the conductive powder as described above, the conductive coating film formed by drying the conductive paste is used. The shrinkage rate at the time of firing is made larger than the shrinkage rate at the time of firing the magnetic green sheet so that a gap is provided between the element body and the coil.

  However, when manufacturing a multilayer inductor, a conductive green paste is applied to a magnetic green sheet so that the conductive paste has a predetermined shape and dried to form a conductive coating on the magnetic green sheet. After forming a green sheet laminated body by laminating a plurality, the green sheet laminated body is pressed (main press) at a predetermined pressure (for example, about 74 MPa), and the laminated magnetic green sheets are pressure-bonded. Therefore, when the green sheet laminate is pressed, pressure is also applied to the conductive coating film obtained by drying the conductive paste, and the density of the conductive coating film is increased. As a result, even if the specific surface area of the magnetic powder and the specific surface area of the conductive powder are defined as in Patent Document 1, the density of the conductive coating film increases, and thus the shrinkage during firing of the magnetic green sheet And the shrinkage ratio during firing of the conductive coating film are about the same, and the conductive coating film does not sinter (cannot shrink) during firing, so there is sufficient space between the element body and the coil. There is a problem that it is difficult to provide a simple gap.

  An object of the present invention is to provide a conductive paste and a conductive coating film capable of forming a sufficient gap between an element body and a coil in a multilayer inductor.

  The conductive paste according to the present invention is a conductive paste containing silver powder and an acrylic resin, and has a dynamic hardness measured in a cured state of 9.8 to 20.6.

  When manufacturing a multilayer inductor using a conductive paste having a dynamic hardness of 9.8 or more measured in a cured state, the conductive paste is brought into a cured state as the green sheet laminate is pressed. Even if pressure is applied to the coating film, the density of the conductive coating film tends to be difficult to increase. On the other hand, when manufacturing a multilayer inductor using a conductive paste having a dynamic hardness measured in the cured state of more than 20.6, the density of the conductive coating is high when the green sheet laminate is pressed. Although it is difficult to become, regardless of before and after pressing the green sheet laminate, the shrinkage rate when firing the conductive coating tends to be the same as or less than the shrinkage rate when firing the green sheet. is there. Therefore, in the conductive paste according to the present invention, by setting the dynamic hardness within the above range, the shrinkage rate during firing of the conductive coating film before and after pressing of the green sheet laminate is reduced when the green sheet is fired. Maintained at a rate greater than the rate. As a result, by using the conductive paste according to the present invention, it is possible to form a sufficient gap between the element body and the coil in the multilayer inductor. Note that the conductive paste is in a “cured state” when the conductive paste is in a dry state in which the residual solvent of the conductive paste is 1.0% or less, or the acrylic resin contained in the conductive paste is a photo-curable resin or a heat-resistant resin. In the case of a curable resin, it means a state in which a polymerization reaction is performed by light or heat.

  The conductive paste according to the present invention is a conductive paste containing silver powder and an acrylic resin, the silver powder content is 79 wt% to 90 wt%, and the acrylic resin content is It is characterized by being 6.2 to 11.3 parts by weight with respect to 100 parts by weight of silver powder.

  By setting the silver content and the acrylic resin content in the conductive paste within the above ranges, the dynamic hardness measured when the residual solvent is 1.0% or less is 9.8 to 20.6. A conductive paste is obtained. As a result, by using the conductive paste according to the present invention, it is possible to form a sufficient gap between the element body and the coil in the multilayer inductor.

  On the other hand, the conductive coating film according to the present invention is characterized by containing silver and having a dynamic hardness of 9.8 to 20.6.

  The conductive coating film according to the present invention contains silver powder and an acrylic resin, the silver powder content is 79% by weight to 90% by weight, and the acrylic resin content is 100 parts by weight of the silver powder. In contrast, the conductive paste is applied in an amount of 6.2 to 11.3 parts by weight.

  According to the present invention, it is possible to provide a conductive paste and a conductive coating film capable of forming a sufficient gap between an element body and a coil in a multilayer inductor.

  Preferred embodiments of the present invention will be described with reference to the drawings. In the description, the same reference numerals are used for the same elements or elements having the same function, and a duplicate description is omitted.

  With reference to FIGS. 1-4, the structure of the multilayer inductor 1 manufactured using the electrically conductive paste which concerns on this embodiment is demonstrated. FIG. 1 is a perspective view showing a multilayer inductor manufactured using the conductive paste according to the present embodiment. FIG. 2 is an exploded perspective view for explaining the configuration of the element body. FIG. 3 is a cross-sectional view taken along the line III-III in FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 3 showing a part of the conductor pattern in an enlarged manner.

  As shown in FIGS. 1 and 2, the multilayer inductor 1 includes a substantially rectangular parallelepiped element body 10, a pair of external electrodes 12 and 14 formed on both side surfaces of the element body 10 in the longitudinal direction, Inside the body 10, linear (substantially I-shaped) conductor patterns B1 and B17 and substantially C-shaped conductor patterns B2 to B16 are each provided with a coil L that is electrically connected to each other.

  As shown in FIG. 2, the element body 10 is configured by laminating magnetic layers A1 to A20. The magnetic layers A1 to A20 function as an insulator having electrical insulation. The actual multilayer inductor 1 is integrated to such an extent that the boundaries between the nonmagnetic layers A1 to A20 cannot be visually recognized.

  A conductor pattern B1 is formed on the surface of the magnetic layer A3. One end of the conductor pattern B1 is drawn out to the side of the magnetic layer A3 where the external electrode 12 is formed, and its end is exposed at the end face of the magnetic layer A3. For this reason, the conductor pattern B1 is electrically connected to the external electrode 12. The other end of the conductor pattern B1 is electrically connected to a through-hole electrode C1 formed through the magnetic layer A3 in the thickness direction. For this reason, the conductor pattern B1 is electrically connected to the corresponding conductor pattern B2 through the through-hole electrode C1 in a stacked state.

  Conductor patterns B2 to B16 are formed on the surfaces of the magnetic layers A4 to A18, respectively. One end of each of the conductor patterns B2 to B16 includes a region electrically connected to the through-hole electrodes C1 to C15 in a stacked state. The other ends of the conductor patterns B2 to B16 are electrically connected to through-hole electrodes C2 to C16 formed through the magnetic layers A4 to A18 in the thickness direction, respectively. For this reason, the conductor patterns B2 to B16 are electrically connected to the corresponding conductor patterns B3 to B17 via the through-hole electrodes C2 to C15 in a stacked state.

  A conductor pattern B17 is formed on the surface of the magnetic layer A19. One end of the conductor pattern B17 includes a region electrically connected to the through-hole electrode C16 in a stacked state. The other end of the conductor pattern B17 is drawn to the side on which the external electrode 14 is formed of the magnetic layer A19, and its end is exposed on the end surface of the magnetic layer A19. For this reason, the conductor pattern B <b> 17 is electrically connected to the external electrode 14.

  Here, as shown in FIG. 3 and FIG. 4, the conductor patterns B1 to B17 constituting the coil L are partly in contact with the element body 10 but are separated from the element body 10 in other parts. (FIGS. 3 and 4 show only a part of the conductor patterns B1 to B17). That is, in the multilayer inductor 1 according to the present embodiment, the gap S is provided between the element body 10 and the coil L (conductor patterns B1 to B17).

  Next, a method for manufacturing the multilayer inductor 1 having the above-described configuration will be described with reference to FIG. FIG. 5 is a diagram for explaining a method of manufacturing a multilayer inductor.

  First, a conductive paste that is a precursor of the conductor patterns B1 to B17 is prepared. Specifically, an organic vehicle is prepared in which the blending ratio of the acrylic resin as the organic binder and the solvent is, for example, 2: 8 (weight ratio). Subsequently, a predetermined amount of silver powder is added to the organic vehicle and kneaded with a three-roll mill to produce a conductive paste. As the solvent, for example, α-terpineol, tetralin, butyl carbitol, butyl carbitol acetate can be used.

  Here, the content of the acrylic resin in the produced conductive paste is 6.2 parts by weight to 11.3 parts by weight with respect to 100 parts by weight of the silver powder. When the content of the acrylic resin in the conductive paste is less than 6.2 parts by weight, the dynamic hardness described later does not become a desired value, and the density of the conductive coating film formed by drying the conductive paste is described later. It becomes high at the time of this press which tends to shrink the conductive coating film. On the other hand, when the content of the acrylic resin in the conductive paste exceeds 11.3 parts by weight, the content of the silver powder decreases, and the conductivity decreases when the conductive paste is made into the conductor patterns B1 to B17. There is a tendency to end up.

  Moreover, content of the silver powder in the produced electrically conductive paste is 79 to 90 weight%. Since the resistance values of the conductive patterns B1 to B17 are proportional to the content of the silver powder in the conductive paste, the resistance of the conductive patterns B1 to B17 when the content of the silver powder in the conductive paste is less than 79% by weight. The value tends to be too high. Therefore, in order to set the resistance values of the conductor patterns B1 to B17 formed using the conductive paste with a small silver powder content to a desired value, the conductor patterns B1 to B17 are thickened or the conductor pattern B1 is used. It is necessary to increase the width of ~ B17. As a result, a conductive paste having a silver powder content of less than 79% by weight is disadvantageous when designing a small multilayer inductor.

  On the other hand, when the content of the silver powder in the conductive paste exceeds 90% by weight, the content of the silver powder in the conductive paste tends to be excessive. Therefore, the viscosity of the conductive paste is increased, the printability (line property, surface roughness) during screen printing of the conductive paste is deteriorated, and the content of the organic binder in the conductive paste is reduced. Therefore, the dynamic hardness described later does not become a desired value, and a sufficient gap S is not formed between the element body 10 and the coil L. Note that the line property represents the degree of bleeding of the printed conductor pattern (the conductive paste is formed in a region where the conductor pattern is not scheduled to be formed). There is a possibility that an inductance characteristic cannot be obtained, and a gap is generated between adjacent magnetic layers in a region where bleeding occurs. The surface roughness means the degree of unevenness on the surface of the conductive coating film obtained by drying the conductive paste. When the surface roughness is deteriorated, the thickness of the conductive coating film is locally thin. May occur and the resistance value may increase, and if this deterioration is significant, there is a possibility of disconnection.

  Subsequently, a plurality of magnetic green sheets that are precursors of the magnetic layers A1 to A20 are prepared. Specifically, the magnetic green sheet includes ferrite (for example, Ni—Cu—Zn ferrite, Ni—Cu—Zn—Mg ferrite, Cu—Zn ferrite, Ni—Cu ferrite), glass ceramic, and the like. It is formed by applying a slurry made from a raw material on a PET film by a doctor blade method. The thickness of the magnetic green sheet is, for example, 10 μm to 50 μm.

  Subsequently, through holes are respectively formed by laser processing or the like at predetermined positions (positions where the through hole electrodes C1 to C16 are to be formed) of the magnetic green sheets to be the magnetic layers A3 to A18. And the conductive paste which is the precursor of conductor pattern B1-B17 is each screen-printed in the predetermined position of each magnetic body green sheet used as magnetic body layer A3-A18. Then, the conductive paste is dried at a predetermined temperature (for example, about 100 ° C. to 150 ° C.) for a predetermined time (for example, about 1 hour to 2 hours) so that the residual solvent in the conductive paste is 1.0% or less. Then, a conductive coating film is formed. At this time, the conductive paste was as described above (the silver powder content was 79% by weight to 90% by weight, and the acrylic resin content was 6.2 parts by weight to 11 parts by weight with respect to 100 parts by weight of the silver powder. The dynamic hardness measured when the residual solvent of the conductive paste is 1.0% or less (the dynamic hardness of the conductive coating film) is 9. It shows 8 to 20.6.

  Subsequently, the magnetic green sheets to be the magnetic layers A1 to A20 are stacked in the order shown in FIG. 2 (see FIG. 5A), and pressure (for example, 74 MPa) is applied in the stacking direction. Crimping (main pressing) is performed so that no gap is generated between the magnetic green sheets (see FIG. 5B). Here, in this embodiment, each magnetic green sheet on which the conductive coating film is not formed, which becomes the magnetic layers A1, A2, and A20, is a green sheet for adjusting the dimensions of the manufactured multilayer inductor 1. It has become.

  Subsequently, after the green sheet laminate formed by laminating and pressing the magnetic green sheets is cut into chips, firing is performed at a predetermined temperature (for example, about 840 ° C. to 900 ° C.), and the element body 10 is obtained. Form. By firing in this way, each magnetic green sheet becomes the magnetic layers A1 to A20, and the conductive coating film becomes the conductor patterns B1 to B17 and the through-hole electrodes C1 to C16. The element body 10 has a length in the longitudinal direction after firing of 1.0 mm, a width of 0.5 mm, and a height of 0.5 mm, for example. Each conductor pattern B1 to B17 has a width of 80 μm and a thickness of 15 μm after firing, for example.

  Subsequently, external electrodes 12 and 14 are formed on the element body 10. Thereby, the multilayer inductor 1 is formed. The external electrodes 12 and 14 are applied with electrode paste mainly composed of silver, nickel or copper on both end faces in the longitudinal direction of the element body 10 and baked at a predetermined temperature (for example, about 680 ° C. to 900 ° C.). Further, it is formed by performing electroplating. For this electroplating, Cu, Ni, Sn, or the like can be used.

  By the way, in the conventional multilayer inductor, by defining the specific surface area of the magnetic powder and the specific surface area of the conductive powder, the shrinkage rate at the time of firing the conductive paste is more than the shrinkage rate at the time of firing the magnetic green sheet. The gap is increased to provide a gap between the element body and the coil.

  However, when manufacturing a multilayer inductor, a conductive green paste is applied to a magnetic green sheet so that the conductive paste has a predetermined shape and dried to form a conductive coating on the magnetic green sheet. After the green sheet laminate is formed by laminating a plurality of layers, the green sheet laminate is pressed (main press) at a predetermined pressure (for example, about 74 MPa), and the laminated magnetic green sheets are pressed together. Therefore, when the green sheet laminate is pressed, pressure is also applied to the conductive coating film obtained by drying the conductive paste, and the density of the conductive coating film is increased. As a result, even if the specific surface area of the magnetic powder and the specific surface area of the conductive powder are specified as in the above-described multilayer inductor, the density of the conductive coating film is increased, so that the magnetic green sheet is fired. The shrinkage ratio of the conductive film and the shrinkage ratio at the time of firing of the conductive coating film are about the same, and the conductive coating film cannot be completely sintered (cannot shrink) during firing. There is a problem that it is difficult to provide a sufficient gap.

  In addition, if the density of the conductive coating film becomes high as described above, the binder removal of the conductive coating film (the step of removing the organic binder from the conductive coating film) is not sufficiently performed, and the conductive coating film is formed. Carbon may remain. Thus, when baking is performed in a state where residual carbon is present in the conductive coating film, the residual carbon is vaporized and the conductive coating film expands and expands. Therefore, for example, as shown in FIG. 6, the conductor pattern B <b> 20 has a porous shape (sponge shape) having a large number of holes H, and the formation of voids is hindered between the element body and the coil. .

  On the other hand, in order to suppress an increase in the density of the conductive coating film due to the pressing of the green sheet laminate, a conductive paste containing conductive particles and resin particles has been conventionally known (for example, JP 2005-310694 A). No. publication). Since the resin particles contained in this conductive paste are solid, an increase in the density of the conductive coating film is suppressed even when pressure is applied to the conductive coating film during the pressing of the green sheet laminate. It is like that.

  However, since the resin particles contained in the conductive paste are solid, the viscosity of the conductive paste is higher than when a fluid resin is used. Therefore, the printability of the conductive paste has deteriorated. At this time, although the printability can be improved by reducing the content of the conductive particles in the conductive paste, it has a great influence on the characteristics of the multilayer inductor manufactured using the conductive paste. Become. Furthermore, the resin particles contained in the conductive paste are covered with an insoluble material that is insoluble in a solvent in order to maintain the shape as a solid, and thus the production of the conductive paste has been costly. .

  On the other hand, in this embodiment, the dynamic hardness measured when the residual solvent is 1.0% or less (in the dry state which is one of the cured states) is 9.8 to 20.6. Conductive paste is used. When the multilayer inductor 1 is manufactured using a conductive paste having a dynamic hardness of 9.8 or more measured when the residual solvent is 1.0% or less, the conductive coating is applied along with pressing of the green sheet laminate. Even if pressure is applied to the film, the density of the conductive coating film tends to be difficult to increase. On the other hand, when manufacturing the multilayer inductor 1 using a conductive paste having a dynamic hardness measured when the residual solvent is 1.0% or less exceeds 20.6, when pressing the green sheet laminate, Although it is difficult to increase the density of the conductive coating film, the shrinkage rate during firing of the conductive coating film is approximately the same as the shrinkage rate during firing of the green sheet, regardless of before and after pressing the green sheet laminate. It tends to be less than that. Therefore, in the conductive paste according to the present embodiment, by setting the dynamic hardness measured when the residual solvent is 1.0% or less within the above range, the conductive coating is applied before and after pressing the green sheet laminate. The shrinkage rate at the time of firing the film is maintained in a state larger than the shrinkage rate at the time of firing the green sheet. As a result, by using the conductive paste according to the present embodiment, it is possible to form a sufficient gap S between the element body 10 and the coil L in the multilayer inductor 1 (see FIGS. 3 and 4). ). At this time, since the gap S is formed by the difference between the shrinkage ratio when the conductive coating film is fired and the shrinkage ratio when the green sheet is fired, a sufficient effect can be obtained for the miniaturized multilayer inductor 1. can get.

  Here, in this embodiment, since the density of the conductive coating film is difficult to increase as described above, the binder is sufficiently removed, and almost no carbon remains in the conductive coating film. Therefore, foam expansion of the conductive coating film is suppressed, and formation of a gap between the element body 10 and the coil L is not inhibited. Further, in this embodiment, since the shrinkage rate at the time of firing the conductive coating film is larger than the shrinkage rate at the time of firing the magnetic green sheet as described above, the element body 10 and the coil L During this period, almost no residual stress is generated, and silver in the conductive paste hardly diffuses into the magnetic green sheet.

  Moreover, in this embodiment, content of silver powder is 79 weight%-90 weight%, and content of acrylic resin is 6.2 weight part-11.3 weight with respect to 100 weight part of silver powder. The conductive paste is a part. Therefore, it is possible to obtain a conductive paste having a dynamic hardness of 9.8 to 20.6 measured when the residual solvent is 1.0% or less.

  Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments. For example, in the present embodiment, the multilayer inductor 1 is manufactured by a sheet lamination method in which magnetic green sheets are laminated and the green sheet laminate is pressed. However, printing lamination is not performed as in the sheet lamination method. The multilayer inductor 1 may be manufactured by a construction method.

  Moreover, in this embodiment, although the electrically conductive paste was heated and it was set as the dry state by which the residual solvent was 1.0% or less, although the hardening state of the electrically conductive paste was implement | achieved, it is not restricted to this. Specifically, a photo-curable resin is used as an acrylic resin, and silver powder is mixed with the resin to produce a conductive paste, and the conductive paste is irradiated with light (for example, ultraviolet rays) to polymerize the acrylic resin. It is good also as making it react and making an electrically conductive paste a hardening state. In addition, a thermosetting resin is used as the acrylic resin, and silver powder, a curing agent, and an organic solvent are mixed with the acrylic resin to prepare a conductive paste, and the conductive paste is heated to cause a polymerization reaction of the acrylic resin. The conductive paste may be in a cured state.

  Hereinafter, although this invention is demonstrated more concretely based on Examples 1-6 and Comparative Examples 1-2 and FIGS. 7-9, this invention is not limited to a following example. In addition, FIG. 7 is a table | surface which shows each implementation conditions, a measurement result, and an evaluation result of Examples 1-6 and Comparative Examples 1-2. FIG. 8 is a diagram showing the porosity, impedance, and number of breaks in printing in Examples 1 to 4 and 6 and Comparative Examples 1 and 2. FIG. 9 is a diagram showing the correlation between the porosity and the impedance in Examples 1 to 4 and 6 and Comparative Examples 1 and 2.

(Example 1)
First, resin A: a copolymer containing methyl methacrylate and resin B: polymethyl methacrylate were mixed to obtain an acrylic resin. And the organic vehicle which adjusted the compounding ratio of this acrylic resin and a solvent ((alpha) -terpineol) so that it might be set to 2: 8 (weight ratio) is produced, and a particle size is 0.5 micrometer-5.0 micrometers in this organic vehicle. A conductive paste was prepared by adding the silver powder and kneading with a three-roll mill.

  Here, the content of the acrylic resin in the produced conductive paste is 6.6 parts by weight (2.1 parts by weight of resin A and 4.5 parts by weight of resin B) with respect to 100 parts by weight of silver powder. I did it. Further, the content of silver powder in the produced conductive paste was set to 83.4% by weight.

(Examples 2 to 6)
The content of acrylic resin in the conductive paste is 7.4 parts by weight (2.4 parts by weight of resin A and 5.0 parts by weight of resin B), 6.2 parts by weight, respectively, with respect to 100 parts by weight of silver powder. (5.5 parts by weight of resin A, 0.7 parts by weight of resin B), 8.3 parts by weight (2.7 parts by weight of resin A, 5.6 parts by weight of resin B), 11.3 parts by weight (11.3 parts by weight of resin A only), 6.6 parts by weight (4.5 parts by weight of resin A and 2.1 parts by weight of resin B), and the silver powder in the conductive paste The same procedure as in Example 1 was conducted except that the contents were 82.2 wt%, 90.0 wt%, 80.5 wt%, 79.0 wt%, and 85.0 wt%, respectively. The conductive paste of Examples 2-6 was produced.

(Comparative Examples 1-2)
The content of acrylic resin in the conductive paste is 7.5 parts by weight (7.5 parts by weight of resin A alone) and 8.3 parts by weight (6.7% by weight of resin A), respectively, with respect to 100 parts by weight of silver powder. And 1.6 parts by weight of resin B), and the content of the silver powder in the conductive paste was 79.0% by weight and 85.0% by weight, respectively. In the same manner as in Example 1, conductive pastes of Comparative Examples 1 and 2 were produced.

(Measurement of dynamic hardness)
Using the applicator with a gap of 250 μm, the conductive pastes of Examples 1 to 6 and Comparative Examples 1 and 2 were applied on a PET film. This conductive paste was dried together with a PET film at 110 ° C. for 2 hours, so that the residual solvent in the conductive paste was 1.0%. And by the test method prescribed | regulated in ISO145757-1, dynamic hardness which is one of the material parameters prescribed | regulated in the appendix A of ISO145777-1 is used for Examples 1-6 and Comparative Examples 1-2 after drying. Each of the conductive pastes was measured.

Here, the dynamic hardness can be obtained by measuring how much the indenter has entered the sample. Specifically, when the test load P (mN) and the penetration amount of the indenter into the sample (indentation depth) D (μm), the dynamic hardness DH is DH = αP / D ²
(Α is a constant, and α = 3.8585 when a triangular pyramid indenter is used)
Is defined as In Examples, dynamic hardness was measured under the following measurement conditions using a dynamic ultra-micro hardness meter (model DUH-210S: manufactured by Shimadzu Corporation). The measurement results are shown in FIG.
Working indenter: Triangular pyramid indenter (115 °)
Test load: 30mN
Load speed: 6.6 mN / sec
Test mode: "Load-unload" test Holding time: 10 seconds

(Measurement of density of conductive coating)
Using the applicator with a gap of 250 μm, the conductive pastes of Examples 1 to 6 and Comparative Examples 1 and 2 were applied on a PET film. This conductive paste was dried together with a PET film at 110 ° C. for 2 hours, and the residual solvent in the conductive paste was adjusted to 1.0% to form a conductive coating film. Then, each of the conductive pastes (conductive coating films) of Examples 1 to 6 and Comparative Examples 1 and 2 after drying was punched out with a φ25 mm mold, and the weight and volume of each test piece were measured. The density of each conductive coating film before this press was measured. In addition, after pressing each test piece with a pressure of 74 MPa (assuming the main press of the green sheet laminate), the weight and volume of each test piece are measured again, and the density of each conductive coating film after the press is determined. It was measured. The measurement results are shown in FIG.

(Measurement of shrinkage rate of conductive paste)
Using the applicator with a gap of 250 μm, the conductive pastes of Examples 1 to 6 and Comparative Examples 1 and 2 were applied on a PET film. This conductive paste was dried together with a PET film at 110 ° C. for 2 hours, and the residual solvent in the conductive paste was adjusted to 1.0% to form a conductive coating film. Then, after drying, the conductive pastes (conductive coating films) of Examples 1 to 6 and Comparative Examples 1 and 2 were each punched out with a φ25 mm mold into test pieces (diameter d ₁ = 25 mm), and then each test. The piece was fired at 900 ° C. for 1 hour. Then, by measuring the diameter d ₂ of each specimen after firing, by obtaining the ratio of the diameter of the before and after firing the test piece (d 2 _{/ d 1),} to measure the shrinkage of the conductive coating film.

In addition, the conductive pastes (conductive coating films) of Examples 1 to 6 and Comparative Examples 1 and 2 after being dried under the above conditions are each punched out with a φ25 mm mold to form test pieces (diameter d ₁ = 25 mm). Each test piece was pressed at a pressure of 74 MPa (assuming the main press of the green sheet laminate), then each test piece was fired at 900 ° C. for 1 hour, and the ratio of the diameters of the test pieces before and after firing (d ₂ / By determining d ₁ ), the shrinkage ratio of the conductive coating film after the press was measured. The measurement results are shown in FIG.

(Measurement of viscosity of conductive paste)
Using the Brookfield viscometer, the viscosities of the conductive pastes of Examples 1 to 6 and Comparative Examples 1 and 2 were measured. The measurement results are shown in FIG.

(Measurement of porosity in multilayer inductors)
First, 8 parts by weight of butyral resin as an organic binder and 3.5 parts by weight of a phthalate ester plasticizer are added to 100 parts by weight of a Ni—Cu—Zn ferrite magnetic material, and toluene is added as a solvent. What added 30 weight part of weight parts and 2-methyl- 1-propanol was thrown into the ball mill, and it dispersed for 24 hours, and obtained the slurry. And this slurry was apply | coated on PET film by the doctor blade method, and multiple magnetic body green sheets were prepared. Furthermore, using the prepared magnetic green sheets and the conductive pastes of Examples 1 to 6 and Comparative Examples 1 and 2, multilayer inductors were manufactured according to the above-described multilayer inductor manufacturing method.

Subsequently, by cutting the multilayer inductor manufactured using each of the conductive pastes of Examples 1 to 6 and Comparative Examples 1 and 2 at a predetermined cross section and observing with an electron microscope, one of the element bodies is obtained. The total length L1 of the portion surrounding the conductor pattern and the total length L2 of the portion where the element body and the one conductor pattern are in contact were measured. Based on L1 and L2 obtained in this way, the porosity of each multilayer inductor is calculated as follows: Porosity = 1−L2 / L1
It was calculated by the formula defined as The result is shown in FIG.

(Evaluation results)
From the measurement results for each of the above items, each of the conductive pastes of Examples 1 to 5 has a small increase in density before and after this press, and the shrinkage rate during firing after this press is magnetic green. It was larger than the shrinkage rate (slightly less than 20%) during firing of the sheet. In addition, each of the conductive pastes of Examples 1 to 5 has a viscosity that can be applied to the magnetic green sheet without any problem, and does not cause poor adhesion with the magnetic green sheet during lamination. It was. And in the multilayer inductor manufactured using each electrically conductive paste of Examples 1-5, the big porosity which exceeds 50% was obtained in all. As mentioned above, as an evaluation result of the electrically conductive paste of Examples 1-5, it was "(circle): favorable".

  Further, in the conductive paste of Example 6, the increase in density was small before and after the press, and the shrinkage rate after firing after the press was slightly higher than the shrinkage rate (less than 20%) of the magnetic green sheet. . In addition, the conductive paste of Example 6 has a viscosity that can be applied to the magnetic green sheet without any problem, and adhesion failure with the magnetic green sheet did not occur during lamination. In the multilayer inductor manufactured using the conductive paste of Example 6, a slightly high porosity of 43% was obtained. From the above, the evaluation result of the conductive paste of Example 6 was “Δ: Somewhat good”.

  Further, in the conductive paste of Comparative Example 1, the density increase was very large before and after the press, and the shrinkage rate after firing after the press was about the same as the shrinkage rate (less than 20%) of the magnetic green sheet. . Further, in the conductive paste of Comparative Example 1, no adhesion failure with the magnetic green sheet occurred during lamination, but the viscosity was high enough to cause a problem when applied to the magnetic green sheet. . In the multilayer inductor manufactured using the conductive paste of Comparative Example 1, the porosity was as small as 28%. From the above, the evaluation result of the conductive paste of Comparative Example 1 was “x: defective”.

  In the conductive paste of Comparative Example 2, the increase in density was small before and after the press, but the shrinkage rate after firing after the press was slightly smaller than the shrinkage rate (less than 20%) of the magnetic green sheet. Met. The conductive paste of Comparative Example 2 had a viscosity that could be applied without any problem to the magnetic green sheet, but poor adhesion to the magnetic green sheet occurred during lamination. In the multilayer inductor manufactured using the conductive paste of Comparative Example 2, the porosity was as small as 20%. From the above, the evaluation result of the conductive paste of Comparative Example 2 was “x: defective”.

  Here, the impedance of each multilayer inductor manufactured using each of the conductive pastes of Examples 1 to 4 and 6 and Comparative Examples 1 to 2 was also measured. The measurement results are shown in FIG. FIG. 9 shows the relationship between the porosity and impedance of each multilayer inductor manufactured using each of the conductive pastes of Examples 1 to 4 and 6 and Comparative Examples 1 and 2.

  As shown in FIG. 9, the impedance increases as the porosity increases, and it is understood that sufficiently large impedance is obtained in Examples 1 to 4 and 6 in which the porosity exceeds 20%. . Therefore, it was confirmed that the multilayer inductors manufactured using the conductive pastes of Examples 1 to 4 and 6 have good characteristics.

  A number of thin patterns having a line width of 50 μm were screen-printed using the conductive pastes of Examples 1 to 4 and 6 and Comparative Examples 1 and 2. At this time, the number of print breaks was counted. The result is shown in FIG.

  As shown in FIG. 8, even when any of the conductive pastes of Examples 1 to 4 and 6 and Comparative Examples 1 to 2 were used, printing breakage did not occur in 10,000 pieces. Therefore, it was confirmed that it was possible to screen-print a pattern with a narrow line width without any problem using any of the conductive pastes of Examples 1 to 4 and 6 and Comparative Examples 1 and 2.

It is a perspective view which shows the multilayer inductor manufactured using the electrically conductive paste which concerns on this embodiment. It is a disassembled perspective view for demonstrating the structure of an element | base_body. FIG. 3 is a cross-sectional view taken along the line III-III in FIG. 2 showing a part of the conductor pattern in an enlarged manner. FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 3 showing a part of the conductor pattern in an enlarged manner. It is a figure for demonstrating the manufacturing method of a multilayer inductor. It is a figure which expands and shows a part of conductor pattern with which the multilayer inductor manufactured using the conventional electrically conductive paste is provided. It is a table | surface which shows each implementation condition, the measurement result, and evaluation result of Examples 1-6 and Comparative Examples 1-2. It is a figure which shows the porosity, the impedance in Examples 1-4, 6 and Comparative Examples 1-2, and the number of generation | occurrence | production of the break of printing. It is a figure which shows the correlation of the porosity and impedance in Examples 1-4, 6 and Comparative Examples 1-2.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Multilayer inductor, 10 ... Element body, 12.14 ... External electrode, A1-A20 ... Magnetic body layer, B1-B18 ... Conductor pattern, C1-C16 ... Through-hole electrode, H ... Hole, S ... Air gap.

Claims (4)

A conductive paste containing silver powder and acrylic resin,
A conductive paste having a dynamic hardness of 9.8 to 20.6 measured in a cured state. A conductive paste containing silver powder and acrylic resin,
The silver powder content is 79% by weight to 90% by weight, and the acrylic resin content is 6.2 parts by weight to 11.3 parts by weight with respect to 100 parts by weight of the silver powder. Characteristic conductive paste.   A conductive coating film comprising silver and having a dynamic hardness of 9.8 to 20.6.   A silver powder and an acrylic resin, wherein the silver powder content is 79 wt% to 90 wt%, and the acrylic resin content is 6.2 wt parts to 100 wt parts of the silver powder; 11. A conductive coating film obtained by applying a conductive paste of 11.3 parts by weight.

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