Multilayer resistor and method for manufacturing multilayer resistor

Abstract

This multilayer resistor is configured as a multilayer structure comprising: a resistor of a plate-form shape, the resistor having a first flat surface and a second flat surface in the thickness direction thereof; a first electrode that is formed on the first flat surface; and a second electrode that is formed on the second flat surface. The multilayer resistor comprises a base electrode layer that is disposed on the first flat surface, the first electrode is formed on the base electrode layer, the resistor is configured from a metal body that is composed of an electroconductive metal material and insulating particles that are composed of an insulating material, and the insulating particles include first insulating particles that have a particle diameter of 5 μm or greater.

Description

Multilayer resistor and method for manufacturing the same

[0001] The present invention relates to a multilayer resistor for sensing current and a method for manufacturing the same.

[0002] JP2020-035851A discloses a resistor having a disk-shaped resistive element having a first plane and a second plane in the thickness direction, a first electrode formed on the first plane, and a second electrode formed on the second plane. This resistor is a vertical resistor in which current flows vertically.

[0003] The vertical resistor described above uses a resistor made of a resistive material having a structure in which a three-dimensional mesh-like metal body surrounds insulating particles, thereby achieving a high resistivity that is suitable for use in detecting large currents despite its low profile.

[0004] In the resistive material disclosed in JP2020-035851A, it has been found that by increasing the particle size of the insulating particles, thin and long current paths are obtained in the three-dimensional mesh-like structure of the metal body formed between the insulating particles, thereby stabilizing the resistance characteristics.

[0005] However, when the particle size of the insulating particles contained in the resistive material is increased, the influence of the insulating particles becomes more apparent on the surface of the resistor. That is, it has become clear that the insulating particles form irregularities on the surface of the resistor, which reduces the adhesive strength between the resistor and the electrodes formed on the surface of the resistor.

[0006] Therefore, an object of the present invention is to increase the adhesive strength between a resistive material and an electrode in a resistive material containing insulating particles of a predetermined particle size.

[0007] According to one aspect of the present invention, a multilayer resistor is configured as a laminated structure including a plate-shaped resistive element having a first plane and a second plane in a thickness direction, a first electrode formed on the first plane, and a second electrode formed on the second plane. This multilayer resistor includes a base electrode layer disposed on the first plane, the first electrode being formed on the base electrode layer, the resistive element being composed of a metal body made of a conductive metal material and insulating particles made of an insulating material, the insulating particles including first insulating particles having a particle size of 5 μm or more.

[0008] According to one aspect of the present invention, in a resistive material containing insulating particles of a predetermined particle size, the adhesive strength between the resistive material and the electrodes can be increased.

[0009] FIG. 1 is a perspective view showing the structure of a multilayer resistor according to this embodiment. FIG. 2 is a cross-sectional view of the multilayer resistor taken along line II-II in FIG. 1. FIG. 3 is a schematic diagram illustrating a cross section of a resistor near its surface. FIG. 4 is a schematic diagram illustrating a base electrode layer formed on the surface of the resistor. FIG. 5 is a schematic diagram illustrating a strike plating layer and a base electrode layer formed on the surface of the resistor. FIG. 6 is a schematic diagram illustrating a strike plating layer, a base electrode layer, and electrodes formed on the surface of the resistor. FIG. 7 is a schematic diagram illustrating a circuit board as an example of a mounted resistor. FIG. 8 is an explanatory diagram illustrating a plating apparatus for forming a strike plating layer, a base electrode layer, a first electrode 21, and a second electrode 22 on a resistive material by plating. FIG. 9 is a diagram showing an SEM image of an arbitrary cross section of the resistive material.

[0010] [Multilayer Resistor] The structure of the multilayer resistor 1 of this embodiment will be described with reference to the drawings.

[0011] The resistor 1 is a resistor for detecting a current, and is called a current detection resistor or a shunt resistor. The resistor 1 is mounted in, for example, a power module and used for detecting a large current.

[0012] FIG. 1 is a perspective view showing the structure of a multilayer resistor 1 (hereinafter referred to as resistor 1) according to this embodiment, and FIG. 2 is a cross-sectional view of resistor 1 taken along line II-II in FIG.

[0013] In this embodiment, the resistor 1 is formed in a plate shape and includes a resistive element 11 made of a resistive material, a first electrode 21, a second electrode 22, and an underlying electrode layer 31 and an underlying electrode layer 32.

[0014] The resistor 11 has a first plane 11A and a second plane 11B in the thickness direction. An underlying electrode layer 31 is disposed on the first plane 11A. The first electrode 21 is formed on the underlying electrode layer 31. Furthermore, an underlying electrode layer 32 is disposed on the second plane 11B. The second electrode 22 is formed on the underlying electrode layer 32.

[0015] That is, the resistor 1 has a laminated structure in which a first electrode 21, a base electrode layer 31, a resistive element 11, a base electrode layer 32, and a second electrode 22 are laminated in this order.

[0016] In the resistor 1 according to this embodiment, a current path is formed in the thickness direction of the resistor 11. Therefore, the current path is shorter than the current path of a general shunt resistor. In the resistor 1, the thickness h of the resistor 11 is formed thin in order to achieve miniaturization (particularly, a low profile).

[0017] Therefore, the resistivity (volume resistance value) of the resistor 11 according to this embodiment needs to be set to a value greater than the resistivity of the alloy alone used as the resistive material of a general shunt resistor, which is approximately 50 μΩ·cm to 100 μΩ·cm.

[0018] <Resistor> In this embodiment, the resistor 11 is made of a resistive material 11a that has a structure in which metal bodies are connected in a three-dimensional mesh pattern around unmelted insulating particles, and the resistive material 11a that achieves high resistivity is used.

[0019] The resistive material 11a in this embodiment is characterized by having a higher resistivity than the resistive material of a typical shunt resistor, since a current path is formed by a three-dimensional mesh-like metal body formed between insulating particles.

[0020] Furthermore, the resistive material 11a in this embodiment has the advantage that, by using insulating particles with large particle diameters, a three-dimensional mesh structure having thin and long current paths due to the metal body is easily formed between the insulating particles.

[0021] In this specification, the term "grain size" refers to a value determined from a cross-sectional SEM image of the resistor 11 (resistive material 11a).

[0022] In this embodiment, the thickness h of the resistor 11 is required to be set to, for example, several mm (millimeters) or less so as to reduce the self-inductance value of the resistor 1. From the viewpoint of reducing the height, the thickness h of the resistor 11 is, for example, 0.2 mm.

[0023] In this embodiment, in order to facilitate mounting on a wiring pattern or a power semiconductor, the length R of one side of the resistor 11 can be set to be larger than the thickness h of the resistor 11. The length R of one side of the resistor 11 is required to be several millimeters. From the viewpoint of miniaturization, the length R of one side of the resistor 11 can be set to, for example, 3 to 6 mm. Note that FIG. 1 shows the structure of a rectangular resistor 1 as an example. The planar shape of the resistor 1 can be rectangular, square, polygonal, circular, or the like.

[0024] Furthermore, the resistive material 11a constituting the resistor 11 is required to be a resistive material that can be designed to have a specific resistance within the range of 200 μΩ·cm (microohm centimeters) to 300,000 μΩ·cm.

[0025] In this embodiment, the resistivity of the resistor 11 is preferably set within the range of 200 μΩ·cm to 1500 μΩ·cm, so that even if the inter-electrode distance is shortened in response to a design requirement to reduce the height of the product, the resistance value required for the resistor 1 as a large current detection resistor can be achieved.

[0026] FIG. 3 is a schematic diagram illustrating a cross section of the resistor 11 near its surface.

[0027] The resistive material 11a constituting the resistor 11 includes metal particles and insulating particles, which will be described below.

[0028] (Metal Body) As a metal body applicable to the resistive material 11a, a resistive material of a general shunt resistor can be used. From the viewpoint of ensuring stability of the resistance characteristics, a metal material suitable for detecting a large current, for example, an alloy in which the rate of change in the resistance value of the resistive material 11 due to temperature change is small, is preferable.

[0029] Specific examples include at least one alloy selected from resistance materials such as nichrome, Manganin (registered trademark), Zeranin (registered trademark), and copper-nickel. In particular, from the viewpoint of ensuring the resistance value of the resistance material, it is preferable to use nichrome. Furthermore, from the viewpoint of workability, it is preferable to use Manganin (registered trademark).

[0030] In this way, depending on the resistance value of the resistive material and the workability, the metal body of the resistive material 11a can be formed using at least one selected from the group consisting of nichrome, copper manganese, and copper nickel.

[0031] Nichrome is a Ni-Cr alloy or an alloy containing it as a main component, copper manganese is a Cu-Mn alloy or an alloy containing it as a main component, copper nickel is a Cu-Ni alloy or an alloy containing it as a main component, Manganin (registered trademark) is a Cu-Mn-Ni alloy or an alloy containing it as a main component, and Zeranin (registered trademark) is a Cu-Mn-Sn alloy or an alloy containing it as a main component.

[0032] From the viewpoint of forming a good three-dimensional network structure, it is preferable to use particles with an aspect ratio of 1.0 to 2.0 as the metal powder before sintering when forming the resistance material 11a, and it is also preferable that the metal body be particles with a particle size of 0.5 μm to 20 μm.

[0033] Furthermore, the proportion of metal bodies contained in the resistance material 11a is 30 vol% or more and 80 vol% or less. If the proportion of metal bodies is less than 30 vol%, the resistance material 11a will not be able to secure a sufficient current path and will no longer function as a resistance material. On the other hand, if the proportion of metal bodies exceeds 80 vol%, the resistivity of the resistance material 11a will decrease to a value almost equal to the resistivity of the metal bodies alone.

[0034] (Insulating Particles) As insulating particles applicable to the resistance material 11a, ceramic materials having excellent heat resistance in addition to insulating properties can be used. For example, aluminum oxide (Al ２ O ３), aluminum nitride (AlN), silicon nitride (Si ３ N ４ ) and zirconia (ZrO ２ In the following, aluminum oxide and aluminum nitride will be referred to as alumina and aluminum nitride, respectively.

[0035] Among the above ceramic materials, alumina, which is widely used as an insulating material, is preferred from the viewpoints of heat dissipation and heat cycle durability. Furthermore, for applications requiring higher heat dissipation, it is preferred to select aluminum nitride, which has high thermal conductivity, and for applications requiring high heat cycle durability, it is preferred to select silicon nitride.

[0036] In order to form a good current path in the three-dimensional mesh structure of the metal body formed between the insulating particles, it is preferable that the insulating particles are mainly approximately spherical. Oval-spherical insulating particles may be included within a range that does not interfere with the formation of the current path. Furthermore, the insulating particles may include a predetermined proportion of flaky particles.

[0037] In this embodiment, the insulating particles include first insulating particles having a particle size of 5 μm or more. The insulating particles may also include second insulating particles having a particle size of less than 5 μm. When the second insulating particles are included, they are preferably mixed so that the total cross-sectional area of ​​the first insulating particles in the cross section of resistor 11 is greater than the total cross-sectional area of ​​the second insulating particles.

[0038] In this embodiment, the insulating particles preferably have an average particle size of 10 μm or less. In this specification, the term "average particle size" refers to the number average particle size per unit cross section determined from a cross-sectional SEM image as described above.

[0039] The average particle size of the insulating particles is more preferably 2 μm or more and 9 μm or less. If the average particle size is less than 2 μm, the number of first insulating particles having a particle size of 5 μm or more will be relatively small, which will reduce the density of the sintered body formed of the insulating particles and the metal body, resulting in unstable resistance characteristics.

[0040] Furthermore, if the average particle size exceeds 9 μm, the number of first insulating particles having a particle size of 5 μm or more increases, making it difficult for a three-dimensional mesh structure of metal bodies to be formed between the insulating particles, resulting in unstable resistance characteristics. Note that, if high precision in the resistance characteristics is not required, the average particle size of the insulating particles can be set to a range exceeding 9 μm, but even in that case, it is preferable to set it to 15 μm or less.

[0041] From the above viewpoints, the average particle size of the insulating particles is set to the above range. In addition, by setting the average particle size of the insulating particles to the above range, the average particle size of the insulating particles is reflected in the surface roughness of the resistive material 11a, and an uneven surface of the resistive material 11a having a surface roughness Ra, expressed by the arithmetic mean roughness, of 2 μm to 9 μm is obtained.

[0042] In this embodiment, from the viewpoint of forming a good current path through the metal body in the resistor 11, the amounts of the metal body, the first insulating particles, and the second insulating particles are set so that the ratio of the total area of ​​the first insulating particles having a particle size of 5 μm or more to the total cross-sectional area of ​​the resistor 11 is 15% or more and 50% or less.

[0043] If the proportion of the total area of ​​the first insulating particles in the cross-sectional area of ​​the resistor 11 is 50% or more, the resistor 11 will not be able to secure a sufficient three-dimensional mesh structure current path, and will no longer function as a resistive material.

[0044] On the other hand, if the proportion of the total area of ​​the first insulating particles in the cross-sectional area of ​​the resistor 11 is less than 15%, the resistivity of the resistive material 11a will decrease to a value almost equal to the resistivity of the metal body alone.

[0045] In this embodiment, in a resistive material formed from a mixed insulating particle obtained by mixing first insulating particles having a particle size of 5 μm or more and second insulating particles having a particle size of less than 5 μm so that the average particle size of the insulating particles is 10 μm or less and the first insulating particles are more numerous than the second insulating particles, and a metal body, the area ratio of the insulating particles to the metal body in the cross section of the resistor can be treated as being approximately equal to the volume ratio of the insulating particles to the metal body in the mixture of the insulating particles and the metal body.

[0046] In other words, when the ratio of the metal body to the insulating particles is 50:50, the ratio of the sum of the areas of the metal bodies to the sum of the areas of the insulating particles in the entire cross-sectional area of ​​the resistor 11 will also be approximately the same.

[0047] <Base electrode layer> Fig. 4 is a schematic diagram illustrating the base electrode layer 31 formed on the surface of the resistor 11. Fig. 5 is a schematic diagram illustrating the strike plating layer 311 and the base electrode layer 31 formed on the surface of the resistor 11. Fig. 6 is a schematic diagram illustrating the strike plating layer 311, the base electrode layer 31, and the first electrode 21 formed on the surface of the resistor 11.

[0048] In the resistive material 11a according to this embodiment, as the particle size of the insulating particles increases, a thin and long three-dimensional mesh structure of current paths can be formed. However, as the particle size of the insulating particles increases, the influence of the unevenness caused by the insulating particles on the surface of the resistive material 11a also increases, which tends to decrease the adhesion between the first electrode 21 and the resistor 11 and between the second electrode 22 and the resistor 11. This is because the insulating particles used in the resistive material 11a according to this embodiment have extremely low adhesion to general-purpose copper plating as an electrode material.

[0049] Therefore, in this embodiment, the resistor 11 includes a base electrode layer 31 on the first plane 11A of the resistor 11 as shown in Fig. 4. Although not shown in Fig. 4, the resistor 11 includes a base electrode layer 32 on the second plane 11B of the resistor 11.

[0050] In this embodiment, a material having a high affinity with insulating particles can be selected for the base electrode layers 31, 32. Nickel (Ni), nickel-chromium alloys, and the like, which have a high affinity with insulating particles, can be used as materials for the base electrode layers 31, 32.

[0051] The base electrode layer 31 can be formed on the first plane 11A of the resistor 11 by plating.

[0052] The thickness of the base electrode layer 31 is preferably such that the first insulating particles are not exposed. More specifically, the thickness of the base electrode layer 31 is preferably 20% to 90% of the difference between the peak and bottom of the unevenness formed on the surface of the resistor 11 (hereinafter referred to as unevenness difference), and more preferably 50% of the unevenness difference.

[0053] In the resistor 1 according to this embodiment, the base electrode layer 31 is formed so as to cover the entire surface of the first plane 11A, and the first electrode 21 is formed on the surface of the base electrode layer 31 formed on the first plane 11A. This eliminates the need for strict formation accuracy when forming the first electrode 21, and improves adhesion of the first electrode 21.

[0054] Like the base electrode layer 31, the base electrode layer 32 can also be formed on the second plane 11B of the resistor 11 by plating.

[0055] The resistor 1 according to this embodiment includes the base electrode layers 31 and 32, which enhances the adhesion between the surface of the resistor 11 and the first electrode 21 and second electrode 22.

[0056] 5, a strike plating layer 311 may be formed in at least a portion of the region between the base electrode layer 31 and the first plane 11A of the resistor 11. The strike plating layer 311 is formed as a pretreatment for the main plating process for forming the base electrode layer 31, by a process that is performed at a higher current and for a shorter time than the main plating process.

[0057] In this case, the strike plating layer 311 is followed by the above-described base electrode layer 31 formed by plating.

[0058] Nickel, titanium, silver, etc. can be used as a material for forming the strike plating layer 311. The thickness of the strike plating layer 311 can be set to 0.01 μm to 0.02 μm.

[0059] Forming the strike plating layer 311 can enhance the metallic activity of the metal body on the surface of the resistor 11. This can enhance the adhesive strength of the base electrode layer 31, and can prevent swelling and peeling of the base electrode layer 31 after plating.

[0060] 6, in this embodiment, the surface of the resistor 11 is uneven due to insulating particles, but the presence of the base electrode layer 31 allows the resistor 11 to adhere closely to the first electrode 21. Furthermore, the anchor effect of the strike plating layer 311 formed at the bottom of the unevenness allows the base electrode layer 31 and the resistor 11 to adhere closely to each other.

[0061] Like the base electrode layer 31, the base electrode layer 32 also has a strike plating layer and a base electrode layer on the second plane 11B of the resistor 11.

[0062] <Electrodes> The first electrode 21 and the second electrode 22 are electrodes for passing a current in the thickness direction of the resistor 11, and are formed using a highly conductive metal material. In this embodiment, the first electrode 21 and the second electrode 22 can generally be formed using a metal material capable of forming an electrode. As an example of such a metal material, copper (Cu) is preferably used.

[0063] In order to achieve a low profile of the resistor 1 , the thickness T of each of the first electrode 21 and the second electrode 22 is formed to be thinner than the thickness h of the resistor body 11 .

[0064] In this embodiment, forming an electrode by a plating method is effective for forming a thin electrode with low resistivity. The plating method can obtain a resistance value equivalent to that of a single metal, so-called bulk metal, and can form a thinner electrode than a method in which a bulk metal body is attached to a resistor body by welding or the like.

[0065] In this embodiment, as an example, from the viewpoint of good electrical conductivity and a low profile of the resistor 1, it is preferable to use copper as the metal material and form the first electrode 21 and the second electrode 22 to have a thickness T of 30 μm to 150 μm by copper plating.

[0066] Copper and nickel have a good affinity with each other, so when nickel (Ni), nickel-chromium alloys, etc. are used for the base electrode layers 31 and 32, high adhesion can be obtained between the copper-plated electrodes.

[0067] [Effects and Functions of the Multilayer Resistor] The resistor 1 according to this embodiment obtained as described above is configured as a multilayer structure having a plate-shaped resistive element 11 having a first plane 11A and a second plane 11B in the thickness direction, a first electrode 21 formed on the first plane 11A, and a second electrode 22 formed on the second plane 11B.

[0068] The resistor 1 includes a base electrode layer 31 disposed on a first plane 11A, and the first electrode 21 is formed on the base electrode layer 31. The resistor 11 includes a metal body made of a conductive metal material and insulating particles made of an insulating material. The insulating particles include first insulating particles having a particle size of 5 μm or more.

[0069] According to such a resistor 1, an uneven surface is formed on the surface of the resistor 11 by first insulating particles having a particle size of 5 μm or more. However, since the first plane 11A is provided with a base electrode layer 31 and the first electrode 21 is formed on the base electrode layer 31, the adhesion between the resistor 11 and the first electrode 21 is increased by the base electrode layer 31 interposed between the resistor 11 and the first electrode 21.

[0070] In addition, since the second plane 11B is provided with a base electrode layer 32 and the second electrode 22 is formed on the base electrode layer 32, the adhesion between the resistor 11 and the second electrode 22 is increased by the base electrode layer 32 interposed between the resistor 11 and the second electrode 22.

[0071] In the resistor 1, the base electrode layer 31 covers the entire first plane 11A, and the base electrode layer 32 covers the entire second plane 11B.

[0072] This eliminates the need to strictly set the formation accuracy when forming the first electrode 21 on the first plane 11A. Also, it eliminates the need to strictly set the formation accuracy when forming the second electrode 22 on the second plane 11B.

[0073] The insulating particles constituting the resistive material 11a include second insulating particles having a particle size of less than 5 μm, and the ratio of the total cross section of the first insulating particles to the cross section of the resistor 11 is 15% or more and 50% or less. Such a resistive material 11a provides a good current path.

[0074] Furthermore, such resistive material 11a has a tendency to have unevenness formed on the surface due to insulating particles, which reduces the adhesive strength between the resistor 11 and the first electrode 21 and the second electrode 22. In contrast, in the resistor 1 according to this embodiment, the resistor 11 is provided with the base electrode layers 31, 32 and the strike plating layer 311 in combination, thereby increasing the adhesive strength between the resistor 11 and the first electrode 21 and the second electrode 22.

[0075] In the resistor 1, the first insulating particles are more numerous than the second insulating particles. That is, since there are many first insulating particles with a particle size of 5 μm or more, a three-dimensional network structure of thin and long metal bodies is easily formed between the first insulating particles. Therefore, the resistance characteristics can be stabilized.

[0076] The resistor 1 according to this embodiment also has a strike plating layer 311 formed in a pretreatment for forming the base electrode layers 31 and 32 .

[0077] In the resistor 1 according to this embodiment, the strike plating layer 311 is formed on the resistor element 11, thereby enhancing the metallic activity of the metal body on the surface of the resistor element 11. This enhances the adhesive strength of the base electrode layer 31 formed by the main plating process performed after the strike plating, and prevents swelling and peeling of the plating layer after the plating is completed.

[0078] In addition, the anchor effect of the strike plating layer 311 formed at the bottom portion of the unevenness caused by insulating particles formed on the surface of the resistor 11 can improve the effect of increasing the adhesion between the first electrode 21 and the resistor 11.

[0079] The metal bodies in the resistive material 11a are formed in a three-dimensional mesh shape so as to surround the insulating particles, which facilitates the formation of thin and long current paths within the resistive material 11a, thereby facilitating the stabilization of the resistive characteristics.

[0080] Furthermore, the current path of the three-dimensional mesh structure is less likely to be broken by temperature changes or application of high voltage, and the influence on the resistivity of the entire resistive material 11 a is reduced. Therefore, the resistivity of the resistive material 11 a can be made larger than the resistivity of the metal body alone, and the resistance characteristics of the resistive material 11 a can be stabilized.

[0081] Furthermore, according to this embodiment, the conductive metal body of the resistance material 11a is formed using at least one metal powder selected from the group consisting of nichrome, copper-manganese, and copper-nickel. These metal powders are alloys used for current detection, and have small changes in resistance due to temperature changes. Therefore, by using these alloys, it is easy to ensure the resistance value required for current detection and to suppress an increase in TCR.

[0082] Furthermore, according to this embodiment, the insulating particles are formed using at least one insulating powder selected from the group consisting of alumina, aluminum nitride, silicon nitride, and zirconia. These insulating powders are ceramic materials with low thermal expansion coefficients and are used as substrate materials. Therefore, by using these insulating powders, the thermal stress of the resistor 11 made of the resistance material 11a can be made closer to the thermal stress of the substrate. Therefore, the occurrence of cracks due to heat cycles between the resistor 11 and the substrate can be suppressed.

[0083] Furthermore, according to this embodiment, by forming the metal bodies of the resistive material 11a into a three-dimensional mesh structure, the TCR can be stabilized and kept within the allowable range of 100 ppm or less, thereby preventing a decrease in detection accuracy when detecting a current using the resistor 1.

[0084] Furthermore, it is possible to design the resistivity of the resistive material 11a to be in the range of 200 μΩ cm to 30,000 μΩ cm, which makes it possible to ensure a resistance value particularly necessary for detecting large currents, even in the case of a so-called vertical resistor 1 having a short current path as shown in FIG.

[0085] Furthermore, in this embodiment, a conductive metal is used in powder form, and the metal powder is mixed with insulating particles and granulated, which makes it easy to interpose metal bodies in the gaps between the insulating particles, and thus makes it easy to form a three-dimensional mesh-like metal body in the resistance material 11a when sintered.

[0086] Furthermore, according to this embodiment, a large number of current paths are formed in the resistor 11 while avoiding the insulating particles, thereby making it possible to increase the resistivity of the resistor 11 and stabilize the resistance characteristics of the resistor 11.

[0087] [Method for Manufacturing Multilayer Resistor] Next, a method for manufacturing the resistor 1 will be described below. The method for manufacturing the resistor 1 includes a method for manufacturing a resistive material and a method for manufacturing a resistor using the obtained resistive material.

[0088] <Method for Manufacturing Resistance Material> A method for manufacturing the resistance material 11a in this embodiment will be described.

[0089] The manufacturing method of the resistive material 11a includes a mixing step of mixing a conductive metal powder (metal powder) with an insulating powder (insulator powder) and a sintering step of sintering the mixed powder obtained by mixing while applying pressure by a uniaxial pressing method at a predetermined temperature.

[0090] In this embodiment, the insulating powder is a mixture of first insulating particles having an average particle size of 10 μm or less and second insulating particles having a particle size of less than 5 μm, with the first insulating particles being more numerous than the second insulating particles.

[0091] The metal powder used is a powder of a metal having a melting point lower than that of the insulating powder. The metal powder is preferably granulated so that the particle size of the metal powder is equal to or smaller than that of the insulating powder.

[0092] In the mixing process, the metal powder is weighed so that the proportion of the metal powder is 30 vol% or more and 80 vol% or less in total volume ratio, and the insulating powder is weighed so that the proportion of the insulating powder is the remainder, and the two powders are mixed uniformly and granulated.

[0093] In the sintering process, for example, the container for the mixed powder is evacuated and the mixed powder is pressurized. The higher the pressing pressure, the more likely it is that a current path will be secured in the resulting resistance material 11a. Therefore, it is preferable to set the pressing pressure higher.

[0094] The firing temperature for sintering is lower than the melting point of the metal powder, and is preferably set to a temperature about 15% lower than the melting point of the metal powder.

[0095] In the manufacturing method of the resistive material 11a described above, a mixed powder of insulating powder and metal powder is heated to a predetermined temperature lower than the melting point of the metal powder and sintered under pressure. This results in the resistive material 11a in which metal particles formed between insulating particles form a three-dimensional network. The resistive material 11a having such a structure can achieve high resistivity.

[0096] Subsequently, the sintered body (bulk body) of the resistance material obtained by the above process is sliced ​​to a predetermined thickness to obtain the resistance material 11a.

[0097] In the slicing step, it is preferable to use a wire saw. In the slicing process using a wire saw, a roller around which the wire is wound is rotated to make the wire travel, and the wire is brought into contact with the sintered compact while an abrasive-containing slurry is interposed, thereby cutting out thin plate-shaped pieces of the resistance material.

[0098] When the sintered body is cut with a wire, the metal particles contained in the resistance material are cut with the wire saw, while some insulating particles are ejected and removed from the cut surface by the wire, while others remain on the cut surface.

[0099] Therefore, the cut surface has insulating particles surrounded by a matrix of metal bodies scattered thereon, and also has irregularities corresponding to the particle size of the insulating particles.

[0100] <Method of Manufacturing Resistor> In the method of manufacturing the resistor 1, base electrode layers 31 and 32 are formed on the first plane 11A and the second plane 11B of the resistor element 11 obtained by slicing. Then, the first electrode 21 is formed on the surface of the obtained base electrode layer 31, and the second electrode 22 is formed on the surface of the base electrode layer 32.

[0101] In this embodiment, the base electrode layers 31 and 32 can be formed by plating on the surfaces of the resistor 11. Furthermore, the first electrode 21 and the second electrode 22 can be formed by plating on the surfaces of the base electrode layers 31 and 32.

[0102] The obtained plate-like laminated structure can be diced, for example, using a dicing blade, to separate it into chip-like pieces of a predetermined size. Through the above steps, the resistor 1 can be manufactured.

[0103] [Mounting Example] FIG. 7 is a schematic diagram illustrating a circuit board 100 as a mounting example of the resistor 1. As shown in FIG.

[0104] The circuit board 100 shown in FIG. 7 is, for example, a power module that processes high voltage and large current, and the resistor 1 functions as a current detection resistor that can detect large currents.

[0105] The circuit board 100 includes a printed circuit board 101 made of an insulating material. Current wirings 111 and 112 that constitute a circuit are formed on the printed circuit board 101. Current detection wirings 113 and 114 that are connected to a current detection IC are also formed on the printed circuit board 101.

[0106] The resistor 1 is disposed at a predetermined position on the current wiring 111. The first electrode 21 of the resistor 1 is connected to the current wiring 111 by a brazing material or a conductive adhesive.

[0107] The second electrode 22 of the resistor 1 is connected to the other current wiring 112 by a lead wire 121 .

[0108] The second electrode 22 of the resistor 1 is connected to the current detection wiring 113 by a bonding wire 131. The current wiring 111 to which the first electrode 21 of the resistor 1 is connected is connected to the current detection wiring 114 by a bonding wire 132.

[0109] In the circuit board 100 as described above, the resistor 1 can detect a large current flowing through the circuit.

[0110] [Other Embodiments] The present embodiment has been described above, but the above embodiment merely shows one application example of the present invention, and is not intended to limit the technical scope of the present invention to the specific configuration of the above embodiment.

[0111] The resistor 1 in this embodiment may be in the shape of a plate, such as a disk, a square, or a rectangular shape.

[0112] For example, in the above embodiment, the first electrode 21 and the second electrode 22 of the resistor 1 are shown to have the same area and size, but the first electrode 21 and the second electrode 22 may be formed to have different areas and sizes. Also, the first electrode 21 and the second electrode 22 may have through holes formed therein.

[0113] In addition, as a method for forming the first electrode 21 and the second electrode 22 on both sides of the resistor 11, in addition to plating, vacuum deposition, ion plating, sputtering, vapor phase growth, cold spray, or the like may also be used.

[0114] A test specimen based on the resistor 1 according to the embodiment of the present invention was fabricated, and various measurements were performed to evaluate the resistor 1. A method for fabricating the test specimen and its evaluation will be described below.

[0115] [Resistor Fabrication] <Mixing and Granulation> (Insulating Powder) The insulating particles used in the resistive material 11a were alumina powder containing first insulating particles having a particle size of 5 μm or more and second insulating particles having a particle size of less than 5 μm, with an average particle size of 8 μm. Mixed insulating particles were prepared by mixing the first insulating particles having a particle size of 5 μm or more and the second insulating particles having a particle size of less than 5 μm so that the ratio of the total area of ​​the first insulating particles having a particle size of 5 μm or more to the total cross-sectional area at any position of the obtained resistor 11 was 15% to 50%. (Metal Body) Nichrome powder [powder with an average particle size of 4 μm produced by an atomization method using Evanome (registered trademark)] was used as the metal powder for fabricating the metal body in the resistive material 11a.

[0116] The mixed insulating particles and metal powder were mixed in a volume ratio of metal body:insulating particles=50:50, and the mixture was mixed and granulated until both were uniformly mixed.

[0117] <Pressing and Sintering> Next, the granulated mixed powder was placed in a carbon die with a diameter of 50 mm. Then, using a hot press (multipurpose high-temperature furnace Hi-Multi 5000: manufactured by Fuji Radio Kogyo Co., Ltd.), the mixed powder in the carbon die was heated (hot pressed) to a predetermined temperature lower than the melting point of nichrome, and in this state, the mixed powder was sintered while being pressed. The obtained resistive material specimen was a cylindrical sintered body with a diameter of 50 mm and a thickness of 200 mm.

[0118] The hot pressing conditions in the pressing and sintering process were as follows: Atmosphere: 20 Pa or less Pressing pressure: 20 MPa to 50 MPa Sintering temperature: 1000°C to 1200°C Holding time: 10 minutes to 30 minutes

[0119] The cylindrical sintered body of the resistive material obtained by the above steps was sliced ​​to 0.2 mm using a wire saw to obtain the resistive material 11a.

[0120] Next, a first electrode 21 and a second electrode 22 were formed on the first and second planes of the resistor 11 obtained by slicing.

[0121] FIG. 8 is an explanatory diagram illustrating a plating apparatus 200 for forming a strike plating layer 311, base electrode layers 31, 32, first electrode 21, and second electrode 22 on a resistance material by plating.

[0122] The plating apparatus 200 includes a plating bath 201 in which a plating solution is stored, an anode electrode 202, and a cathode electrode 203.

[0123] The nickel for the strike plating layer 311 and the base electrode layers 31 and 32 was connected to the anode electrode. The resistor 11 was connected to the cathode electrode 203. After the strike plating layer 311 and the base electrode layers 31 and 32 were formed, the first electrode 21 and the second electrode 22 were formed using a plating solution for electrode formation.

[0124] The following multiple test pieces were fabricated by the plating apparatus 200 using the same plating solution for the base electrode layer and the same plating solution for electrode formation for the same resistive material 11a.

[0125] Example 1 A resistor 11 was formed without a strike plating layer 311, and had 1 μm-thick nickel plating layers formed as base electrode layers 31, 32. Furthermore, copper-plated electrodes having a thickness of 100 μm were formed. A test piece measuring 5 mm×5 mm square and 0.4 mm thick was prepared from the resulting laminated structure to measure the adhesion of the copper-plated electrodes.

[0126] Example 2 The resistor 11 was provided with no strike plating layer 311 and had 5 μm-thick nickel plating layers formed as the base electrode layers 31 and 32. Furthermore, copper plating electrodes with a thickness of 100 μm were formed. A test piece of the same size as in Example 1 was prepared.

[0127] (Example 3) After forming a strike plating layer 311 having a thickness of 0.01 μm to 0.02 μm on the resistor 11, a nickel plating layer having a thickness of 5 μm was formed as the base electrode layers 31, 32. Furthermore, a copper plating electrode having a thickness of 100 μm was formed. A test piece of the same size as in Example 1 was prepared.

[0128] Comparative Example 1 An attempt was made to form a copper-plated electrode on the resistor 11 without forming the strike plating layer 311 and the base electrode layers 31 and 32. A test piece of the same size as in Example 1 was prepared.

[0129] [Evaluation Method] <Observation of Resistor> (Cross Section of Resistor) The cross section of the resistor material obtained by cutting with a wire saw was analyzed with an SEM. The results are shown in FIG.

[0130] (Measurement of Surface Roughness) The surface roughness of the cross section of the obtained resistive material was measured using a shape analysis laser microscope (VK-X150, manufactured by Keyence Corporation).

[0131] <Measurement of Adhesion Strength> The adhesion strength between the copper-plated electrodes and resistor 11 of the test pieces obtained from the laminated structure was measured in accordance with the plating adhesion test method (JIS H 8504). The measurement results are shown in Table 1.

[0132] [Results] <Cross-section of resistor> Figure 9 shows an SEM image of an arbitrary cross-section of the resistive material 11a, magnified 1000 times. The resistive material 11a observed under SEM was obtained from a mixture of 50% nichrome and 50% alumina by volume. In the resistive material thus prepared, the ratio of the total area of ​​alumina particles with a particle size of 5 μm or more per unit cross-sectional area was 30.0%, and the ratio of the total area of ​​alumina particles with a particle size of less than 5 μm was 13.3%.

[0133] Therefore, the ratio of the total area of ​​the first insulating particles having a particle size of 5 μm or more was 30.0%, which is within the range of 15% to 50%. This means that the obtained resistor can form a good current path.

[0134] <Surface Roughness of Resistor> The surface roughness Ra of the resistor 11 was 2 μm to 9 μm. The maximum difference in unevenness was 9 μm.

[0135] <Measurement Results of Adhesion Strength> Table 1 shows the results of the evaluation test of adhesion strength between the copper-plated electrodes and the resistance material in the laminate structures of Examples 1 to 3 and Comparative Example 1.

[0136]

[0137] According to the measurement results of the surface roughness of the resistor 11, the surface roughness Ra was 2 to 9. Furthermore, the maximum difference in unevenness formed on the surface of the resistor 11 by the insulating particles was 9 μm.

[0138] That is, in the laminate structure of Comparative Example 1 in which copper-plated electrodes were formed on the surface of resistor 11 having a surface roughness Ra = 9 without forming base electrode layers 31, 32, the adhesion of the copper-plated electrodes to resistor 11 was close to zero.

[0139] Therefore, it can be considered that a copper-plated electrode cannot be substantially formed on the surface of a resistive material 11a obtained by mixing alumina powder having an average particle size of 8 μm and nichrome powder having an average particle size of 4 μm in a volume ratio of 50:50, which contains first insulating particles having a particle size of 5 μm or more and second insulating particles having a particle size of less than 5 μm.

[0140] On the other hand, in the laminated structure of Example 1, the adhesive strength of the copper-plated electrode to the resistor 11 was 5 MPa.

[0141] Therefore, it became clear that by forming 1 μm base electrode layers 31, 32 on the surface of the same resistive material 11a as in Comparative Example 1, it became possible to form copper-plated electrodes on the surface of the resistive material 11a, where copper-plated electrodes could not be formed in the Comparative Example.

[0142] This indicates that the base electrode layers 31 and 32 contribute to increasing the adhesive strength between the resistor 11 and the copper-plated electrode.

[0143] In Example 2, the adhesion strength was 25 MPa by forming a 5 μm thick base electrode layer. Since the difference in surface roughness of the resistive material 11a was 9 μm, it was found that the adhesion strength between the resistor 11 and the copper-plated electrode was further increased by forming the base electrode layers 31 and 32 with a thickness that was 55% of the 9 μm difference in surface roughness of the resistive material 11a.

[0144] That is, the base electrode layers 31 and 32 have an appropriate thickness for increasing the adhesive strength, and it is preferable that the thickness of the base electrode layers 31 and 32 be about 50% of the difference in surface irregularities.

[0145] In addition, in Example 3, a strike plating layer 311 of 0.01 μm to 0.02 μm was formed on the surface of the resistive material 11a, and then a base electrode layer of 5 μm in thickness was formed, resulting in an adhesion strength of 30 MPa. This indicates that even higher adhesion strength can be obtained by using the strike plating layer 311 and the base electrode layers 31 and 32 in combination.

[0146] According to this embodiment, a resistive material in which the ratio of the total area of ​​first insulating particles having a particle size of 5 μm or more to the total cross-sectional area of ​​the resistor 11 is 15% or more and 50% or less provides a good current path, but the insulating particles form unevenness on the surface, which may lead to a decrease in the adhesion between the resistor 11 and the first electrode 21 and the second electrode 22.

[0147] In contrast, it has been found that by using the base electrode layers 31, 32 and also the strike plating layer 311 on the resistor 11, it is possible to increase the adhesion between the resistor 11 and the first electrode 21 and the second electrode 22 even if unevenness is formed on the surface of the resistor 11.

[0148] This application claims priority based on Japanese Patent Application No. 2023-181279, filed with the Japan Patent Office on October 20, 2023, the entire contents of which are incorporated herein by reference.

[0149] REFERENCE SIGNS LIST 1 resistor 11 resistive element 11a resistive material 11A first plane 11B second plane 21 first electrode 22 second electrode 31, 32 base electrode layer 100 circuit board 101 printed circuit board 111, 112 current wiring 113, 114 current detection wiring 121 lead wire 131, 132 wire bonding 200 plating device 201 plating bath 202 anode electrode 203 cathode electrode 311 strike plating layer

Claims

1. A multilayer resistor configured as a laminated structure having a plate-shaped resistive element having a first plane and a second plane in the thickness direction, a first electrode formed on the first plane, and a second electrode formed on the second plane, the multilayer resistor further comprising an underlying electrode layer disposed on the first plane, the first electrode being formed on the underlying electrode layer, the resistive element being composed of a metal body made of a conductive metallic material and insulating particles made of an insulating material, the insulating particles including first insulating particles having a particle size of 5 μm or more.

2. A multilayer resistor according to claim 1, wherein the base electrode layer covers the entire surface of the first plane.

3. A multilayer resistor as claimed in claim 1, wherein the insulating particles include second insulating particles having a particle size of less than 5 μm, and the proportion of the total cross section of the first insulating particles in the cross section of the resistor is 15% or more and 50% or less.

4. A multilayer resistor according to claim 3, wherein the sum of the areas of the first insulating particles in a cross section of the resistor is greater than the sum of the areas of the second insulating particles.

5. A multilayer resistor according to claim 1, comprising a strike plating layer in at least a portion of the region between said base electrode layer and said first flat surface of said resistor body.

6. A method for manufacturing a multilayer resistor configured as a laminated structure having a resistor having a first plane and a second plane in the thickness direction, a first electrode formed on the first plane, and a second electrode formed on the second plane, comprising the steps of: constructing the resistor having the first plane and the second plane from insulating particles made of an insulating material, the insulating particles including first insulating particles having a particle size of 5 μm or more, and a metal body made of a conductive metal material; forming a base electrode layer on the first plane of the resistor; and forming the first electrode on the base electrode layer.

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