Multilayer resistor, and manufacturing method for multilayer resistor

Abstract

To increase the adhesion between an electrode and a resistance material including an insulating particle with a predetermined particle diameter.SOLUTION: A multilayer resistor is configured as a multilayer structure including a resistor having a plate shape and including a first flat surface and a second flat surface in a thickness direction, and a first electrode formed on the first flat surface and a second electrode formed on the second flat surface. This multilayer resistor includes a base electrode layer disposed on the first flat surface. The first electrode is formed in the base electrode layer. The resistor includes a metal body formed of an electroconductive metal material, and an insulating particle formed of an insulating material. The insulating particle includes a first insulating particle with a particle diameter of 5 μm or more.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a stacked resistor for sensing current and a method for making the same. [Background technology]

[0002] Patent Document 1 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 above-mentioned vertical resistor 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 specific resistance that is suitable for use in detecting large currents while maintaining a low height. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-035851 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the resistive material disclosed in Patent Document 1, 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.

[0006] 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. In other words, 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.

[0007] 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. [Means for solving the problem]

[0008] According to one embodiment of the present invention, a multilayer resistor is configured as a multilayer 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 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, and the insulating particles include first insulating particles having a particle size of 5 μm or more. Effect of the Invention

[0009] 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. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a perspective view showing the structure of the multilayer resistor according to this embodiment. [Diagram 2] FIG. 2 is a cross-sectional view of the multilayer resistor taken along line II-II in FIG. [Diagram 3] FIG. 3 is a schematic diagram illustrating a cross section of a resistor near its surface. [Figure 4] FIG. 4 is a schematic diagram illustrating a base electrode layer formed on the surface of the resistor. [Diagram 5] FIG. 5 is a schematic diagram illustrating a strike plating layer and a base electrode layer formed on the surface of a resistor. [Figure 6] FIG. 6 is a schematic diagram illustrating the strike plating layer, the base electrode layer, and the electrodes formed on the surface of the resistor. [Figure 7] FIG. 7 is a schematic diagram illustrating a circuit board as an example of mounting a resistor. [Figure 8] 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 resistance material by plating. [Figure 9] FIG. 9 is a diagram showing an SEM image of an arbitrary cross section of a resistive material. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] [Multilayer resistors] The structure of the multilayer resistor 1 of this embodiment will be described with reference to the drawings.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] The resistor 11 has a first plane 11A and a second plane 11B in the thickness direction. A base electrode layer 31 is disposed on the first plane 11A. The first electrode 21 is formed on the base electrode layer 31. A base electrode layer 32 is disposed on the second plane 11B. The second electrode 22 is formed on the base electrode layer 32.

[0016] 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.

[0017] 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 to be thin in order to realize miniaturization (particularly, low height).

[0018] Therefore, the resistivity (volume resistance) of resistor 11 according to this embodiment needs to be set to a value larger than the resistivity of an alloy alone used as a resistive material in a typical shunt resistor, which is about 50 μΩ·cm to 100 μΩ·cm.

[0019] <Resistor> In this embodiment, the resistive material 11a constituting the resistor 11 and realizing high resistivity is a resistive material 11a having a structure in which metal bodies are connected in a three-dimensional mesh shape around unmelted insulating particles.

[0020] The resistive material 11a in this embodiment is characterized in that it has a larger resistivity than the resistors of general shunt resistors because a current path is formed by three-dimensional mesh-like metal bodies formed between insulating particles.

[0021] Furthermore, the resistive material 11a in this embodiment has an advantage in that the use of insulating particles with a large particle size makes it easier for a three-dimensional mesh structure having a thin and long current path to be formed by the metal body between the insulating particles.

[0022] In this specification, the "grain size" refers to a value determined from a cross-sectional SEM image of the resistor 11 (resistance material 11a).

[0023] 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.

[0024] 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 mm. From the viewpoint of miniaturization, the length R of one side of the resistor 11 can be, for example, 3 to 6 mm. Note that FIG. 1 shows the structure of the resistor 1 having a quadrangular shape as an example. The planar shape of the resistor 1 can be a rectangle, a square, a polygon, a circle, or the like.

[0025] Furthermore, resistive material 11a constituting resistor 11 is required to be a resistive material that can be designed to have a resistivity within the range of 200 μΩ·cm (microohm centimeters) to 300,000 μΩ·cm.

[0026] In this embodiment, the resistivity of resistor 11 is preferably set within a range of 200 μΩ·cm to 1500 μΩ·cm, so that even if the inter-electrode distance is designed to be short in response to a design requirement to reduce the height of the product, the resistance value required for resistor 1 as a large current detection resistor can be achieved.

[0027] FIG. 3 is a schematic diagram illustrating a cross section of resistor 11 near its surface.

[0028] The resistive material 11a constituting the resistor 11 includes metal bodies and insulating particles, which will be described below.

[0029] (metal body) A typical resistive material for a shunt resistor can be used as the metal body applicable to the resistive material 11a. From the viewpoint of ensuring the stability of the resistive characteristics, it is preferable to use 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 the temperature change is small.

[0030] 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, it is preferable to use nichrome from the viewpoint of ensuring the resistance value of the resistance material. Also, it is preferable to use Manganin (registered trademark) from the viewpoint of processability.

[0031] In this manner, 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.

[0032] Nichrome is a Ni-Cr based alloy or an alloy containing it as the main component, copper manganese is a Cu-Mn based alloy or an alloy containing it as the main component, and copper nickel is a Cu-Ni based alloy or an alloy containing it as the main component. Manganin (registered trademark) is a Cu-Mn-Ni based alloy or an alloy containing it as the main component, and Zeranin (registered trademark) is a Cu-Mn-Sn based alloy or an alloy containing it as the main component.

[0033] From the viewpoint of forming a good three-dimensional mesh structure, it is preferable to use particles having an aspect ratio of 1.0 to 2.0 as the metal powder before sintering when forming the resistance material 11a, and it is preferable for the metal body to be particles having a particle size of 0.5 μm to 20 μm.

[0034] The ratio of the metal bodies contained in the resistance material 11a is 30 vol% or more and 80 vol% or less. If the ratio of the metal bodies is less than 30 vol%, the resistance material 11a cannot secure a sufficient current path and does not function as a resistance material. On the other hand, if the ratio of the metal bodies exceeds 80 vol%, the resistivity of the resistance material 11a decreases to a value almost equal to the resistivity of the metal bodies alone.

[0035] (insulating particles) As insulating particles applicable to the resistance material 11a, ceramic materials having excellent heat resistance as well as insulating properties can be used. For example, from the viewpoint of suppressing the occurrence of cracks due to thermal stress, at least one ceramic material selected from the group consisting of aluminum oxide (Al2O3), aluminum nitride (AlN), silicon nitride (Si3N4), and zirconia (ZrO2) can be used. Hereinafter, aluminum oxide and aluminum nitride are referred to as alumina and aluminum nitride, respectively.

[0036] Among the above-mentioned ceramic materials, it is preferable to use alumina, which is widely used as an insulating material, from the viewpoint of heat dissipation and heat cycle durability. In addition, in applications requiring higher heat dissipation, it is preferable to select aluminum nitride, which has high thermal conductivity, and in applications requiring high heat cycle durability, it is preferable to select silicon nitride.

[0037] In order to form a good current path in the three-dimensional mesh structure of the metal body formed between the insulating particles, the insulating particles are preferably mainly approximately spherical. The insulating particles may contain ellipsoidal insulating particles within a range that does not impede the formation of the current path. The insulating particles may also contain a predetermined proportion of flaky particles.

[0038] 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 such that the sum of the cross sections of the first insulating particles in the cross section of resistor 11 is greater than the sum of the cross sections of the second insulating particles.

[0039] 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 obtained from a cross-sectional SEM image as described above.

[0040] The average particle size of the insulating particles is more preferably 2 μm to 9 μm. 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, so that the density of the sintered body formed of the insulating particles and the metal body will decrease, resulting in unstable resistance characteristics.

[0041] Furthermore, when 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 the metal body to be formed between the insulating particles, resulting in unstable resistance characteristics. When 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 this case, it is preferable to set it to 15 μm or less.

[0042] From the above viewpoints, the average particle size of the insulating particles is set to the above range. Furthermore, 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 with a surface roughness Ra of 2 μm to 9 μm, expressed by the arithmetic mean roughness, is obtained on the resistive material 11a.

[0043] 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 sum of the areas 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.

[0044] If the proportion of the total area of ​​the first insulating particles in the cross-sectional area of ​​resistor 11 is 50% or more, resistor 11 will not be able to secure a sufficient current path of a three-dimensional mesh structure, and will no longer function as a resistive material.

[0045] On the other hand, if the proportion of the total area of ​​the first insulating particles in the cross-sectional area of ​​resistor 11 is less than 15%, the resistivity of resistive material 11a decreases to a value almost equal to the resistivity of the metal body alone.

[0046] In this embodiment, in a resistive material formed from a mixed insulating particle, in which 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 are mixed such that the average particle size of the insulating particles is 10 μm or less and there are more first insulating particles than 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.

[0047] In other words, when the mixing ratio of the metal body and the insulating particles is metal body:insulating particles=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 ​​resistor 11 will also be approximately the same.

[0048] <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.

[0049] In the resistive material 11a according to the present embodiment, as the particle size of the insulating particles increases, a current path with a thin and long three-dimensional mesh structure can be formed. However, as the particle size of the insulating particles increases, the effect of the unevenness caused by the insulating particles appearing on the surface of the resistive material 11a also increases, so that the adhesion between the first electrode 21 and the resistor 11 and the adhesion between the second electrode 22 and the resistor 11 tend to decrease. This is because the adhesion between the insulating particles used in the resistive material 11a according to the present embodiment and the general-purpose copper plating as an electrode material is extremely low.

[0050] Therefore, in this embodiment, the resistor 11 includes a base electrode layer 31 on the resistor 11 (first plane 11A) 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.

[0051] In this embodiment, a material having a high affinity with insulating particles can be selected for the base electrode layers 31 and 32. As a material constituting the base electrode layers 31 and 32, nickel (Ni), a nickel-chromium alloy, or the like having a high affinity with insulating particles can be used.

[0052] The base electrode layer 31 can be formed on the first plane 11A of the resistor element 11 by plating.

[0053] 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 the 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.

[0054] 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 to set strict formation accuracy when forming the first electrode 21, and improves adhesion of the first electrode 21.

[0055] 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.

[0056] 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.

[0057] 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 of the main plating process for forming the base electrode layer 31 by a process that is performed with a higher current and for a shorter time than the main plating process.

[0058] In this case, following the strike plating layer 311, the above-mentioned base electrode layer 31 is formed by plating.

[0059] 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.

[0060] 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 adhesion of the base electrode layer 31, and can prevent the base electrode layer 31 from swelling or peeling after plating.

[0061] 6, in this embodiment, the surface of resistor 11 is uneven due to insulating particles, but the presence of base electrode layer 31 allows resistor 11 to adhere to first electrode 21. Furthermore, the anchor effect of strike plating layer 311 formed at the bottom of the unevenness allows base electrode layer 31 and resistor 11 to adhere to each other.

[0062] 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 element 11.

[0063] <Electrode> 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 metal material having high conductivity. 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, it is preferable to use copper (Cu).

[0064] In order to realize a low-profile 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.

[0065] In this embodiment, in order to form a thin electrode with low resistivity, it is effective to form the electrode by a plating method. The plating method can obtain a resistance value equivalent to that of a single metal, so-called bulk metal, and can form the electrode itself thinner than a method in which a bulk metal body is bonded to a resistor body by welding or the like.

[0066] In this embodiment, as an example, from the viewpoint of good electrical conductivity and reducing the height 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.

[0067] Copper and nickel have a good affinity with each other, so when nickel (Ni), a nickel-chromium alloy, or the like is used for the base electrode layers 31 and 32, high adhesion can be obtained between the copper-plated electrodes.

[0068] [Effects of multilayer resistors] The resistor 1 of this embodiment obtained as described above is configured as a laminated 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.

[0069] 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.

[0070] In such a resistor 1, an uneven surface is formed on the surface of the resistor 11 due to the 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.

[0071] In addition, since the second plane 11B is provided with an underlying electrode layer 32 and the second electrode 22 is formed on the underlying electrode layer 32, the adhesion between the resistor 11 and the second electrode 22 is enhanced by the underlying electrode layer 32 interposed between the resistor 11 and the second electrode 22.

[0072] 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.

[0073] This eliminates the need to set strict precision when forming the first electrode 21 on the first plane 11A. Also, it eliminates the need to set strict precision when forming the second electrode 22 on the second plane 11B.

[0074] 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.

[0075] In addition, such resistive material 11a has a tendency to have a reduced adhesive strength between resistor 11 and first electrode 21 and second electrode 22 because insulating particles form unevenness on the surface. In contrast, in resistor 1 according to this embodiment, base electrode layers 31, 32 and strike plating layer 311 are used in combination with resistor 11, thereby making it possible to increase adhesive strength between resistor 11 and first electrode 21 and second electrode 22.

[0076] In the resistor 1, the first insulating particles are more numerous than the second insulating particles. In other words, since there are many first insulating particles with a particle size of 5 μm or more, a three-dimensional mesh structure of thin and long metal bodies is easily formed between the first insulating particles. Therefore, the resistance characteristics can be stabilized.

[0077] Moreover, the resistor 1 according to this embodiment has a strike plating layer 311 formed in a pretreatment for forming the base electrode layers 31 and 32.

[0078] In the resistor 1 according to this embodiment, the strike plating layer 311 is formed on the resistor element 11, thereby increasing the metallic activity of the metal body on the surface of the resistor element 11. This increases the adhesion 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 finished.

[0079] 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.

[0080] The metal bodies in the resistive material 11a are formed in a three-dimensional mesh shape so as to surround the insulating particles, which makes it easier to form long, thin current paths inside the resistive material 11a, and therefore makes it easier to stabilize the resistance characteristics.

[0081] Furthermore, the current path of the three-dimensional mesh structure is less likely to be broken due to temperature changes or application of high voltage, and the influence on the resistivity of the entire resistance material 11a is suppressed. Therefore, the resistivity of the resistance material 11a can be made larger than the resistivity of the metal body alone, and the resistance characteristics of the resistance material 11a can be stabilized.

[0082] According to the present 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 the change in resistance value due to temperature change is small. Therefore, by using these alloys, it is easy to ensure the resistance value required for current detection and the increase in TCR can be suppressed.

[0083] 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, have a low thermal expansion coefficient, and are used as substrate materials. 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.

[0084] In addition, according to the present embodiment, the metal body of the resistance material 11a is formed into a three-dimensional mesh structure, so that the TCR can be stabilized and kept within the allowable range of 100 ppm or less. Therefore, it is possible to suppress the deterioration of detection accuracy when detecting a current using the resistor 1.

[0085] Furthermore, it is possible to design the resistivity of the resistive material 11a to be within the range of 200 μΩ·cm to 30,000 μΩ·cm, inclusive, which makes it possible to ensure a resistance value required for detecting a large current, even in the case of a so-called vertical resistor 1 having a short current path as shown in FIG.

[0086] In addition, according to the present embodiment, a conductive metal is used in powder form, and the metal powder is mixed with insulating particles and granulated. This makes it easy to interpose the metal body in the gaps between the insulating particles, and when sintered, it becomes easy to form a three-dimensional mesh-like metal body in the resistance material 11a.

[0087] Furthermore, according to this embodiment, many current paths are formed in the resistor 11 while avoiding the insulating particles. Therefore, the resistivity of the resistor 11 can be increased and the resistance characteristics of the resistor 11 can be stabilized.

[0088] [Manufacturing method of multilayer resistors] 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.

[0089] <Method of manufacturing resistor material> A method for producing the resistive material 11a in this embodiment will be described.

[0090] The manufacturing method of the resistive material 11a includes a mixing step of mixing a conductive metal powder (metal powder) and an insulating powder (insulator powder) having insulating properties, and a sintering step of sintering the mixed powder obtained by mixing while applying pressure by a uniaxial pressing method at a predetermined temperature.

[0091] 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, and the first insulating particles are mixed in greater amounts than the second insulating particles.

[0092] 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.

[0093] In the mixing process, the metal powder is weighed out so that the proportion of the metal powder is 30 vol% or more and 80 vol% or less by total volume, and the insulating powder is weighed out so that the proportion of the insulating powder is the remainder. The two powders are then mixed uniformly and granulated.

[0094] 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 easier it is to ensure a current path in the resulting resistor material 11a. For this reason, it is preferable to set the pressing pressure to be high.

[0095] Moreover, the firing temperature for sintering is lower than the melting point of the metal powder, and is preferably set to a temperature approximately 15% lower than the melting point of the metal powder.

[0096] In the manufacturing method of the resistive material 11a described above, the 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 allows the resistive material 11a to be obtained in which the metal bodies formed between the insulating particles are formed in a three-dimensional mesh shape. The resistive material 11a having such a structure can achieve high resistivity.

[0097] Next, 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.

[0098] In the slicing step, a wire saw is preferably used. In the slicing process using a wire saw, a roller around which the wire is wound is rotated to run the wire, and the wire is applied to the sintered body while a slurry containing an abrasive is interposed, to cut out thin plate-shaped pieces of the resistance material.

[0099] When the sintered body is cut by the wire, the metal bodies contained in the resistance material are cut by the wire saw, while some of the insulating particles are ejected from the cut surface by the wire and removed, while others remain on the cut surface.

[0100] Therefore, on the cut surface, insulating particles surrounded by metal bodies in a matrix are scattered, and irregularities corresponding to the particle size of the insulating particles are formed.

[0101] <Resistor manufacturing method> In the method for 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.

[0102] In this embodiment, the base electrode layers 31, 32 can be formed by plating on the surface 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, 32.

[0103] The obtained plate-like laminated structure can be diced, for example, with a dicing blade, to separate it into chip-like pieces of a predetermined size. Through the above steps, the resistor 1 can be manufactured.

[0104] [Implementation example] FIG. 7 is a schematic diagram illustrating a circuit board 100 as an example of mounting the resistor 1. As shown in FIG.

[0105] 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.

[0106] The circuit board 100 includes a printed circuit board 101 made of an insulating material. Current wiring 111 and 112 that constitute a circuit are formed on the printed circuit board 101. Current detection wiring 113 and 114 that are connected to an IC for current detection are also formed.

[0107] The resistor 1 is disposed at a predetermined position on the current wiring 111. A first electrode 21 of the resistor 1 is connected to the current wiring 111 by a brazing material or a conductive adhesive.

[0108] The second electrode 22 of the resistor 1 is connected to the other current wiring 112 by a lead wire 121 .

[0109] The second electrode 22 of the resistor 1 is connected to the current detection wiring 113 by a bonding wire 131. The current detection 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.

[0110] In the circuit board 100 as described above, the resistor 1 can detect a large current flowing through the circuit.

[0111] [Other embodiments] Although the present embodiment has been described above, the above embodiment merely shows one application example of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configuration of the above embodiment.

[0112] The resistor 1 in this embodiment may be in the shape of a plate, and may be in the shape of a disk, a square corner, or a rectangular corner.

[0113] 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 either the area or the size different from each other. Also, the first electrode 21 and the second electrode 22 may have a through hole.

[0114] In addition, the method for forming the first electrode 21 and the second electrode 22 on both sides of the resistor 11 may be a vacuum deposition method, an ion plating method, a sputtering method, a vapor phase growth method, a cold spray method, or the like, in addition to a plating method. EXAMPLES

[0115] 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.

[0116] [Making resistors] <Mixing / granulation> (insulating powder) As insulating particles applied to the resistance material 11a, the alumina powder contained 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, and had an average particle size of 8 μm. Mixed insulating particles were prepared 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 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% or more and 50% or less. (metal body) Nichrome powder [powder having an average particle size of 4 μm produced by atomizing Evanome (registered trademark)] was used as the metal powder for producing the metal body of the resistance material 11a.

[0117] The mixed insulating particles and metal powder were mixed in a volume ratio of metal body:insulating particles=50:50, and mixed and granulated until both were uniformly mixed.

[0118] <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 machine (multipurpose high-temperature furnace Hi-Multi 5000: manufactured by Fuji Denpa Kogyo Co., Ltd.), the mixed powder in the carbon die was heated (hot pressed) to a specified temperature lower than the melting point of nichrome, and in this state, the mixed powder was sintered while being pressurized. The obtained specimen of the resistance material was a cylindrical sintered body with a diameter of 50 mm and a thickness of 200 mm.

[0119] The hot pressing conditions in the pressure and sintering process were as follows: Atmosphere: 20 Pa or less Press pressure: 20MPa~50MPa Sintering temperature: 1000℃~1200℃ ·Holding time: 10 to 30 minutes

[0120] The cylindrical sintered body of the resistance material obtained by the above steps was sliced ​​to 0.2 mm using a wire saw to obtain the resistance material 11a.

[0121] Next, a first electrode 21 and a second electrode 22 were formed on a first plane and a second plane of the resistor element 11 obtained by the slicing process.

[0122] FIG. 8 is an explanatory diagram illustrating a plating apparatus 200 for forming a strike plating layer 311, base electrode layers 31 and 32, a first electrode 21, and a second electrode 22 on a resistance material by plating.

[0123] 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.

[0124] The nickel for the strike plating layer 311 and the base electrode layers 31 and 32 was connected to an anode electrode. In addition, the resistor 11 was connected to a cathode electrode 203. In addition, after forming the strike plating layer 311 and the base electrode layers 31 and 32, the first electrode 21 and the second electrode 22 were formed using a plating solution for forming electrodes.

[0125] The following multiple test pieces were produced 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 resistance material 11a.

[0126] Example 1 The resistor 11 had no strike plating layer 311, and a 1 μm-thick nickel plating layer was formed as the base electrode layers 31, 32. Furthermore, a copper plating electrode having a thickness of 100 μm was formed. From the obtained laminated structure, a test piece having a size of 5 mm×5 mm square and a thickness of 0.4 mm was prepared to measure the adhesion of the copper plating electrode.

[0127] Example 2 The resistor 11 had no strike plating layer 311, and a 5 μm-thick nickel plating layer 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 produced.

[0128] Example 3 After a strike plating layer 311 having a thickness of 0.01 μm to 0.02 μm was formed on the resistor 11, a nickel plating layer having a thickness of 5 μm was formed as the base electrode layers 31 and 32. Furthermore, a copper plating electrode having a thickness of 100 μm was formed. A test piece of the same size as that of Example 1 was produced.

[0129] Comparative Example 1 An attempt was made to form a copper-plated electrode on resistor 11 without forming strike plating layer 311 and base electrode layers 31, 32. A test piece of the same size as in Example 1 was prepared.

[0130] [Evaluation method] <Observation of resistor> (Cross section of resistor) The cross section of the resistive material cut by the wire saw was analyzed by SEM, and the results are shown in Figure 9.

[0131] (Surface roughness measurement) 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).

[0132] <Adhesion measurement> The adhesion strength between the copper-plated electrode and the resistor 11 in the test piece obtained from the laminated structure was The measurements were made in accordance with the plating adhesion test method (JIS H 8504). The results are shown in Table 1.

[0133] [result] <Cross section of resistor> FIG. 9 is a SEM image of an arbitrary cross section of the resistive material 11a, and is an image of the surface of the resistive material 11a enlarged 1000 times. The resistive material 11a observed with the SEM was obtained from a mixture of 50% nichrome and 50% alumina by volume. In the resistive material thus produced, 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%.

[0134] 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 be said to be a resistor capable of forming a good current path.

[0135] <Surface roughness of resistor> The surface roughness Ra of the resistor 11 was 2 μm to 9 μm. The maximum difference between the projections and recesses was 9 μm.

[0136] <Adhesion strength measurement results> The results of the evaluation test of the adhesion between the copper-plated electrodes and the resistive material in the laminate structures of Examples 1 to 3 and Comparative Example 1 are shown in Table 1.

[0137] [Table 1]

[0138] According to the measurement results of the surface roughness of resistor 11, the surface roughness Ra was 2 to 9. Furthermore, the maximum unevenness difference formed on the surface of resistor 11 by the insulating particles was 9 μm.

[0139] In other words, in the laminate structure of Comparative Example 1, in which a copper-plated electrode was 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 electrode to resistor 11 was close to zero.

[0140] 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, the resistive material 11a including 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.

[0141] On the other hand, in the laminated structure of Example 1, the adhesion strength of the copper-plated electrode to the resistor 11 was 5 MPa.

[0142] 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 a copper-plated electrode on the surface of the resistive material 11a where a copper-plated electrode could not be formed in the Comparative Example.

[0143] This shows that the base electrode layers 31 and 32 contribute to increasing the adhesive strength between the resistor 11 and the copper-plated electrode.

[0144] In Example 2, the adhesion was 25 MPa by forming a 5 μm thick base electrode layer. Since the unevenness on the surface of the resistive material 11a was 9 μm, it was found that the adhesion 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 is 55% of the unevenness of the surface of the resistive material 11a, which is 9 μm.

[0145] That is, the base electrode layers 31 and 32 have an appropriate thickness for increasing adhesion, and it is preferable that the thickness of the base electrode layers 31 and 32 is set to about 50% of the surface unevenness difference.

[0146] 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 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 in combination with the base electrode layers 31 and 32.

[0147] 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 ​​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 resistor 11 and first electrode 21 and second electrode 22.

[0148] In contrast, it has been found that by using the base electrode layers 31, 32 and further the strike plating layer 311 in the resistor 11, the adhesion between the resistor 11 and the first electrode 21 and the second electrode 22 can be increased even if the surface of the resistor 11 is uneven. [Explanation of symbols]

[0149] 1 resistor 11 Resistor 11a resistance material 11A 1st plane 11B 2nd plane 21 1st electrode 22 2nd 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 equipment 201 Plating bath 202 Anode electrode 203 Cathode Electrode 311 Strike plating layer

Claims

1. A multilayer resistor having a laminated structure including a plate-shaped resistor 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, a base electrode layer disposed on the first plane; the first electrode is formed on the base electrode layer, the resistor is composed of 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. Multilayer resistor.

2. 2. The multilayer resistor according to claim 1, The base electrode layer covers the entire first plane. Multilayer resistor.

3. 2. The multilayer resistor according to claim 1, The insulating particles include second insulating particles having a particle size of less than 5 μm; a ratio of the total cross section of the first insulating particles to the cross section of the resistor is 15% or more and 50% or less; Multilayer resistor.

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

5. 2. The multilayer resistor according to claim 1, a strike plating layer is provided in at least a portion of the region between the base electrode layer and the first plane of the resistor; Multilayer resistor.

6. A method for manufacturing a multilayer resistor having a laminated structure including a resistor 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, comprising: the resistor having the first plane and the second plane is made of insulating particles including first insulating particles made of an insulating material and having a particle size of 5 μm or more, and a metal body made of a metal material having electrical conductivity; forming a base electrode layer on the first plane of the resistor; forming the first electrode on the base electrode layer; A method for manufacturing multilayer resistors.

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