Laminated resistor and method for manufacturing laminated resistor

Abstract

The laminated resistor has a plate-shaped resistor body 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, and the resistor body 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 diameter of 5 [mu] m or more, and when the laminated resistor is mounted on a printed circuit board, the end surface of the resistor body is exposed, and the second electrode is connected via solder.

Description

Multilayer Resistors and Their Manufacturing Method Technical Field

[0001] This invention relates to a stacked resistor for detecting current and a method for manufacturing the stacked resistor. Background Technology

[0002] JP2020-035851A discloses a resistor having a resistive body in the shape of a disc and 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, allowing current to flow longitudinally.

[0003] The aforementioned vertical resistor achieves high resistivity for high current sensing applications while maintaining a low profile by using a resistive material composed of a resistive material with a structure in which insulating particles are surrounded by a three-dimensional mesh of metal. Summary of the Invention

[0004] In the resistive material disclosed in JP2020-035851A, the resistive element and the electrode form a plate-like laminated structure. The resistive element and the electrode are each formed relatively thinly. Therefore, when the resistive element and an electrode are mounted on a printed circuit board using solder, solder wetting and diffusion to the electrode end face and the resistive element end face are likely to occur.

[0005] When solder that has wetted and diffused along the end face of one electrode and resistor reaches another electrode, it may cause a short circuit, resulting in product defects.

[0006] Therefore, the purpose of this invention is to prevent solder from wetting and spreading into a resistive body made of a high resistivity material, wherein the resistive body is low-profile and can be used for high current detection applications.

[0007] According to one aspect of the present invention, a stacked resistor is provided, comprising a plate-shaped resistive body 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, wherein the resistive body comprises a metal body made of a conductive metal material and insulating particles made of an insulating material, the insulating particles comprising first insulating particles with a particle size of 5 μm or more, and the stacked resistor is configured such that, when mounted onto a printed circuit board, the end face of the resistive body is exposed, and the second electrode is connected to the printed circuit board via solder.

[0008] According to one aspect of the present invention, it is possible to prevent solder from wetting and diffusing into a resistive body made of a high resistivity material, wherein the resistive body is low-profile and can be used for high current detection applications. Attached Figure Description

[0009] Figure 1 is a perspective view showing the structure of the stacked resistor in this embodiment.

[0010] Figure 2 is a cross-sectional view of the stacked resistor along line II-II in Figure 1.

[0011] Figure 3 is a schematic diagram showing an enlarged view of the cross section near the boundary between the resistive element and the first electrode.

[0012] Figure 4 is a schematic diagram showing an enlarged view of the cross-section near the end face of the resistor (region S shown in Figure 2).

[0013] Figure 5 is a schematic diagram illustrating a circuit board used as an example of resistor mounting.

[0014] Figure 6 is a schematic diagram illustrating the resistors mounted on the circuit board.

[0015] Figure 7 is a perspective view illustrating the resistor as a first variation of this embodiment.

[0016] Figure 8 is a perspective view illustrating a resistor as a second variation of this embodiment.

[0017] Figure 9 is an explanatory diagram illustrating a plating apparatus for forming a flash plating layer, a base electrode layer, a first electrode, and a second electrode on a resistive material by plating process.

[0018] Figure 10 is a schematic diagram illustrating a resistor mounted on a circuit board as a comparative example. Detailed Implementation

[0019] [Layered Resistors]

[0020] Referring to the accompanying drawings, the structure of the stacked resistor 1 of this embodiment will be described.

[0021] Resistor 1 is a resistor used for sensing current, and is called a current sensing resistor or shunt resistor. Resistor 1 is, for example, mounted in a power module for high current sensing applications.

[0022] Figure 1 is a perspective view showing the structure of the stacked resistor 1 (hereinafter referred to as resistor 1) in this embodiment, and Figure 2 is a cross-sectional view of resistor 1 along line II-II in Figure 1.

[0023] In this embodiment, the resistor 1 includes a resistive body 11 formed in the shape of a plate and made of a resistive material, a first electrode 21, and a second electrode 22.

[0024] The resistive element 11 has a first plane 11A and a second plane 11B in the thickness direction. A first electrode 21 is formed on the first plane 11A. In addition, a second electrode 22 is formed on the second plane 11B.

[0025] That is, resistor 1 has a stacked structure consisting of a first electrode 21, a resistive element 11, and a second electrode 22 stacked sequentially.

[0026] In this embodiment, a current path is formed on the resistive element 11 of the resistor 1 along the thickness direction D shown in Figures 1 and 2. Therefore, the current path is shorter compared to that of a conventional shunt resistor. In order to achieve miniaturization (especially low profile) in the resistor 1, the thickness h of the resistive element 11 is formed to be relatively thin.

[0027] In this embodiment, the specific resistance (volume resistance value) of the resistor 11 needs to be set to a value greater than that of the alloy monomer used as a resistive material in a common shunt resistor, which is 50 μΩ·cm to 100 μΩ·cm.

[0028] <Electrode>

[0029] The first electrode 21 and the second electrode 22 are electrodes used to allow current to flow along the thickness direction of the resistive body 11, and are formed using a highly conductive metallic material. In this embodiment, the first electrode 21 and the second electrode 22 are generally formed using a metallic material suitable for forming electrodes. As an example of such a metallic material, copper (Cu) is preferably used.

[0030] In this embodiment, forming the electrode using a plating method is effective in order to construct a thin electrode with low specific resistance. According to the plating method, a resistance value similar to that of a metallic element, i.e., a bulk metal, can be obtained, and the electrode itself can be formed thinner compared to methods such as welding that attach a bulk metal body to a resistive body.

[0031] In this embodiment, as an example, from the viewpoint of good conductivity and low resistor 1, copper is used as the metal material. By copper plating, the thickness T1 of the first electrode 21 and the thickness T2 of the second electrode 22 can both be 30μm~150μm.

[0032] In particular, in this embodiment, it is possible to design the thickness T2 of the second electrode 22 connected to the printed circuit board 101 (FIG. 5) to be thinner than the thickness T1 of the first electrode 21 located on the upper side of the resistor 11.

[0033] In other words, the thickness T2 of the second electrode 22 connected to the printed circuit board 101 (FIG. 5) can be made thin, so the thickness T1 of the first electrode 21 located on the upper side of the resistor body 11 can be formed thicker without changing the overall height of the resistor.

[0034] <Resistor>

[0035] In this embodiment, the resistive material 11a that constitutes the resistive body 11 and achieves high specific resistance is applied around the unmelted insulating particles. The resistive material 11a has a structure in which metal bodies are connected to form a three-dimensional network.

[0036] The resistive material 11a in this embodiment is characterized in that, since the current path is formed by a three-dimensional network of metal bodies formed between insulating particles, it has a larger specific resistance compared to the resistive body of a conventional shunt resistor.

[0037] Furthermore, the resistive material 11a in this embodiment has the following advantages: by using insulating particles with large particle size, a three-dimensional network structure with slender current paths can be easily formed between the insulating particles through the metal body.

[0038] In this specification, "particle size" refers to the value obtained from the cross-sectional SEM image of the resistive body 11 (resistive material 11a).

[0039] In this embodiment, the thickness h of the resistor 11 is required to be set to, for example, a few millimeters or less, so that the self-inductance of the resistor 1 is reduced. From the viewpoint of miniaturization, as an example, the thickness h of the resistor 11 is 0.2 mm.

[0040] In this embodiment, for wiring patterns and ease of mounting to power semiconductors, the length R of one side of the resistor 11 can be set to be greater 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, as an example, the length R of one side of the resistor 11 can be 3 to 6 millimeters. It should be noted that, as an example, Figure 1 shows the structure of a resistor 1 made into a quadrilateral shape. The top view shape of the resistor 1 can be made into a rectangle, square, polygon, circle, etc.

[0041] Furthermore, the resistive material 11a constituting the resistive body 11 is required to be a resistive material whose specific resistance can be designed in the range of 200 μΩ·cm to 300,000 μΩ·cm.

[0042] In this embodiment, the specific resistance of the resistor 11 is preferably set in the range of 200 μΩ·cm to 1500 μΩ·cm. Therefore, even if the electrode spacing is designed to be shorter to reduce the product height, the required resistance value for the resistor 1, which is used for high-current sensing, can still be achieved.

[0043] Figure 3 is a schematic diagram showing an enlarged view of the cross-section near the boundary between the resistor 11 and the first electrode 21. Figure 4 is a schematic diagram showing an enlarged view of the cross-section near the end face of the resistor 11 (region S shown in Figure 2).

[0044] The resistive material 11a constituting the resistive body 11 is composed of a metallic body and insulating particles as described below.

[0045] (Metallic body)

[0046] As the metal body that can be used for resistive material 11a, a common shunt resistor material can be used. From the viewpoint of ensuring the stability of resistance characteristics, a metal material suitable for detecting large currents is preferred, for example, an alloy in which the change in resistance value caused by the temperature change of resistive body 11 is small.

[0047] Specific examples include at least one alloy selected from resistive materials such as nickel-chromium alloys, Manganin (registered trademark), Zeranin (registered trademark), and copper-nickel. In particular, from the viewpoint of ensuring the resistance value of the resistive material, nickel-chromium alloys are preferred. Furthermore, from the viewpoint of processability, Manganin (registered trademark) is preferred.

[0048] In this way, depending on the resistance value and processability of the resistive material, the metallic body of the resistive material 11a can be formed using at least one selected from the group consisting of nickel-chromium alloy, copper-manganese, and copper-nickel.

[0049] Nickel-chromium alloys are Ni-Cr based alloys or alloys with Ni as the main component; copper-manganese alloys are Cu-Mn based alloys or alloys with Cu as the main component; and copper-nickel alloys are Cu-Ni based alloys or alloys with Cu as the main component. It should be noted that Manganin (registered trademark) is a Cu-Mn-Ni based alloy or alloy with Cu as the main component, and Zeranin (registered trademark) is a Cu-Mn-Sn based alloy or alloy with Zeranin as the main component.

[0050] From the viewpoint of forming a good three-dimensional network structure, the metal powder used before sintering when forming the resistive material 11a is preferably composed of particles with an aspect ratio of 1.0 or higher and 2.0 or lower. Furthermore, the metal body is preferably composed of particles with a particle size of 0.5 μm or higher and 20 μm or lower.

[0051] Furthermore, the proportion of metallic body contained in the resistive material 11a is 30 vol% or more and 80 vol% or less. When the proportion of metallic body is less than 30 vol%, sufficient current path cannot be ensured in the resistive material 11a, and it does not function as a resistive material. On the other hand, when the proportion of metallic body exceeds 80 vol%, the resistivity of the resistive material 11a decreases to a value almost the same as that of the resistivity of the metallic element.

[0052] (Insulating particles)

[0053] As insulating particles that can be used in resistive material 11a, ceramic materials that also exhibit excellent heat resistance in addition to their insulating properties can be used. For example, from the viewpoint of suppressing cracking caused by thermal stress, at least one ceramic material selected from the group consisting of alumina (Al2O3), aluminum nitride (AlN), silicon nitride (Si3N4), and zirconium oxide (ZrO2) can be cited. Hereinafter, alumina and aluminum nitride will be referred to as alumina and aluminum nitride, respectively.

[0054] Among the aforementioned ceramic materials, alumina, which is widely used as an insulating material, is preferred from the viewpoint of heat dissipation and thermal cycling durability. Furthermore, for applications requiring even higher heat dissipation, aluminum nitride, with its high thermal conductivity, is preferred; and for applications requiring high thermal cycling durability, silicon nitride is preferred.

[0055] In the three-dimensional network structure of the metallic body formed between insulating particles, from the viewpoint of forming good current paths, the insulating particles are preferably mainly approximately spherical. Ellipsoidal insulating particles may also be included within a range that does not impede the formation of current paths. Furthermore, sheet-like particles may be included in the insulating particles in a prescribed proportion.

[0056] In this embodiment, the insulating particles include first insulating particles with a particle size of 5 μm or more. Furthermore, the insulating particles may also include second insulating particles with a particle size of less than 5 μm. When second insulating particles are included, it is preferable to mix them in such a manner that the sum of the cross-sections of the first insulating particles in the cross-section of the resistor 11 is greater than the sum of the cross-sections of the second insulating particles.

[0057] In this embodiment, the average particle size of the insulating particles is preferably less than 10 μm. It should be noted that, in this specification, "average particle size" refers to the average number of particles per unit cross-section, as determined by the cross-sectional SEM image as described above.

[0058] The average particle size of the insulating particles is preferably 2 μm or more and 9 μm or less. When the average particle size is less than 2 μm, the number of first insulating particles with a particle size of 5 μm or more becomes relatively small, thus reducing the density of the sintered body formed by the insulating particles and the metal body, and making the electrical resistance characteristics unstable.

[0059] Furthermore, when the average particle size exceeds 9 μm, the number of first insulating particles with a particle size of 5 μm or larger increases. Therefore, it is not easy for the insulating particles to form a three-dimensional network structure from the metallic body, and the resistance characteristics become unstable. It should be noted that when high-precision resistance characteristics are 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.

[0060] Based on the above viewpoint, the average particle size of the insulating particles is made to be within the aforementioned range. Furthermore, by making the average particle size of the insulating particles within the aforementioned range, the average particle size of the insulating particles is reflected by the surface roughness of the resistive material 11a, and in the resistive material 11a, a surface with an uneven surface characterized by a surface roughness Ra of 2 μm to 9 μm, as represented by the arithmetic mean roughness, is obtained.

[0061] In this embodiment, from the viewpoint that a good current path can be formed on the resistor 11 by the metal body, the proportions of the metal body, the first insulating particle and the second insulating particle are set such that the total area of ​​the first insulating particles with a particle size of 5 μm or more is 15% or more and 50% or less relative to the total cross-sectional area of ​​the resistor 11.

[0062] When the total area of ​​the first insulating particles in the cross-sectional area of ​​the resistor 11 is more than 50%, the current path of the three-dimensional network structure in the resistor 11 cannot be guaranteed, and it does not have the function of a resistive material.

[0063] On the other hand, when the total area of ​​the first insulating particles in the cross-sectional area of ​​the resistive body 11 is less than 15%, the resistivity of the resistive material 11a is reduced to a value that is approximately the same as the resistivity of a metallic element.

[0064] In this embodiment, it is possible to make the area ratio of insulating particles to metal body in the cross section of the resistive material formed by the mixed insulating particles and metal body approximately the same as the volume ratio of insulating particles to metal body in the mixture of the insulating particles and metal body. The mixed insulating particles are formed by mixing first insulating particles with a particle size of 5 μm or more and second insulating particles with a particle size of less than 5 μm in such a way 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.

[0065] That is, when the ratio of metal body to insulating particles is metal body: insulating particles = 50:50, the ratio of the total area of ​​the metal body to the total area of ​​the insulating particles in the cross-sectional area of ​​the resistor 11 is also approximately the same.

[0066] [The effect of stacked resistors]

[0067] In the resistor 1 of this embodiment, the end faces of the first electrode 21 and the second electrode 22 are smoother than the end face of the resistive body 11. Therefore, the end faces of the first electrode 21 and the second electrode 22 are easily wetted by solder.

[0068] In contrast, as shown in Figure 4, the resistive material 11a constituting the resistive body 11 is in a state where insulating particles are scattered and surrounded by a matrix-like metallic body. Therefore, protrusions corresponding to the particle size of the insulating particles are formed on the end face of the resistive body 11. Furthermore, the metallic body constituting the resistive material 11a is exposed and in contact with the atmosphere, making it prone to becoming inert.

[0069] Therefore, by including first insulating particles with a particle size of 5 μm or more as insulating particles, a protrusion formed by the insulating particles can be obtained on the end face of the resistor 11 to suppress the wetting and diffusion of the solder. At this time, the average particle size of the insulating particles is preferably 10 μm or less (surface roughness Ra = 5~9 μm).

[0070] Furthermore, by using an alloy that is insulating and not easily wetted by solder as insulating particles, the effect of preventing solder wetting and diffusion can be further improved.

[0071] [Manufacturing method of multilayer resistors]

[0072] Next, the method for manufacturing resistor 1 will be described. The method for manufacturing resistor 1 includes a method for manufacturing resistive material and a method for manufacturing a resistor using the obtained resistive material.

[0073] <Manufacturing Methods of Resistive Materials>

[0074] The manufacturing method of the resistive material 11a in this embodiment will be described.

[0075] The manufacturing method of the resistive material 11a includes: a mixing step of mixing conductive metal powder (metal powder) and insulating powder (insulator powder); and a sintering step of sintering the mixed powder under pressure at a specified temperature by a uniaxial pressure method.

[0076] In this embodiment, the insulating powder is a mixture of first insulating particles with an average particle size of 10 μm or less and a particle size of 5 μm or more, and second insulating particles with a particle size of less than 5 μm. Furthermore, the mixture is prepared such that the number of first insulating particles is greater than the number of second insulating particles.

[0077] As the metal powder, a powder of a metal with a melting point lower than that of the insulating powder is used. Granulation is preferably carried out in a manner that makes the particle size of the metal powder equal to or smaller than that of the insulating powder.

[0078] In the mixing process, the metal powder is weighed in such a way that the proportion of metal powder is more than 30 vol% and less than 80 vol% of the total volume, and the insulating powder is weighed in such a way that the proportion of insulating powder is the remainder. The two powders are then mixed evenly and granulated.

[0079] In the sintering process, for example, the container for mixing the powder is brought to a vacuum state, and the powder is pressurized. The higher the pressing pressure, the more easily the current path is ensured in the resulting resistive material 11a. Therefore, it is preferable to set a high pressing pressure.

[0080] Furthermore, the sintering temperature used for sintering is a temperature lower than the melting point of the metal powder, preferably set to a temperature about 15% lower than the melting point of the metal powder.

[0081] In the above-described method for manufacturing the resistive material 11a, a mixture of insulating powder and metal powder is heated to a predetermined temperature lower than the melting point of the metal powder, and then sintered under pressure. This results in a resistive material 11a in which the metallic bodies formed between the insulating particles are arranged in a three-dimensional network. The resistive material 11a with this structure achieves a high resistivity.

[0082] Next, the sintered body (bulk body) of the resistive material obtained through the above process is sliced ​​and processed to a specified thickness to obtain resistive material 11a.

[0083] In the slicing process, a wire saw is preferred. In the slicing process using a wire saw, the wire is advanced by rotating a roller with the wire wound on it, and a slurry containing abrasive is present between the wire and the sintered body, so as to cut out thin sheet-shaped resistor material sheets.

[0084] When the sintered body is cut by a steel wire, the metallic components contained in the resistive material are cut by the wire saw. In contrast, some of the insulating particles are ejected and removed from the cut surface by the steel wire, while others remain on the cut surface.

[0085] Therefore, the cut surface has a state in which insulating particles exist sporadically, surrounded by a matrix-like metal body, and the unevenness corresponds to the particle size of the insulating particles.

[0086] Metal layers serving as the first electrode 21 and the second electrode 22 are formed on the surface of a thin sheet of resistive material by plating. That is, the first electrode 21 is formed on the surface of the thin sheet of resistive material, which is the first plane 11A, and the second electrode 22 is formed on the surface of the second plane 11B.

[0087] Using, for example, a dicing blade, the obtained plate-like stacked structure can be cut to separate chip-like wafers of a specified size. By using the dicing blade, the wafers can be separated into wafers with residual unevenness formed by insulating particles on the end faces. Through the above processes, resistor 1 can be manufactured.

[0088] [Example of mounting to a circuit board]

[0089] Figure 5 is a schematic diagram illustrating an example of a circuit board 100 in which resistor 1 is mounted. Figure 6 is a schematic diagram showing an enlarged view of the main part of resistor 1 in circuit board 100.

[0090] The circuit board 100 shown in Figure 5 is, for example, a power supply module that performs high voltage and high current processing, and the resistor 1 is used as a current sensing resistor to detect high current.

[0091] The circuit board 100 is a printed circuit board 101 made of insulating material. Current wiring 111 and 112 constituting a circuit are formed on the printed circuit board 101. In addition, current sensing wiring 113 and 114 for connecting to an IC are formed.

[0092] As shown in Figure 6, resistor 1 is mounted to a designated location on current wiring 111 by soldering. An example of soldering resistor 1 will be described.

[0093] First, solder paste 30 is printed at a designated location on the current wiring 111. Then, with the second electrode 22 of the resistor 1 mounted on top of the solder paste 30 on the current wiring 111, the solder paste 30 is melted and cured under specified mounting conditions.

[0094] Thus, a solder fillet 31 is formed between the second electrode 22 and the current wiring 111, and the resistor 1 is mounted on the printed circuit board 101.

[0095] The first electrode 21 of resistor 1 is connected to another current wiring 112 via lead 121.

[0096] The first electrode 21 of resistor 1 is connected to the current sensing wiring 113 via wire bonding 131. In addition, the current wiring 111 and the current sensing wiring 114, which are connected to the second electrode 22 of resistor 1, are connected via wire bonding 132.

[0097] In the circuit board 100 described above, resistor 1 is capable of detecting large currents flowing into the circuit.

[0098] [The effect of mounting multilayer resistors onto a circuit board]

[0099] As described above, in the resistor 1 of this embodiment, although the solder fillet 31 rises along the end face of the second electrode 22, it does not reach the end face of the resistor body 11.

[0100] This is because the insulating particles contained in the resistive material 11a are exposed on the end face of the resistor 11, and a protrusion composed of insulating particles is formed. Therefore, even if there are differences in the amount of solder paste applied or the size of the connection part on the current wiring 111, the increase of the solder fillet can be suppressed.

[0101] Therefore, it is possible to prevent the solder fillet from rising to the end face of the first electrode 21 formed on the upper side of the resistor 11. As a result, it is possible to prevent short circuit of the resistor 1.

[0102] Furthermore, in a stacked resistor, such as resistor 1 in this embodiment, in which electrodes are formed on the surface of the resistive body by plating, when the electrodes and current sensing wiring are connected by wire bonding, sufficient durability for wire bonding may not be obtained because the electrodes are thin.

[0103] Therefore, due to the thinness of the electrode, the potential distribution on the electrode becomes larger. Thus, even a misalignment error occurring only at the wire bonding connection point can affect the accuracy of current detection. However, forming a thicker electrode to meet the durability requirements of wire bonding increases the height of resistor 1, which is detrimental to miniaturization.

[0104] In contrast, in the resistor 1 of this embodiment, since no solder wetting and diffusion occurs on the resistor body 11, the thickness of the second electrode 22 connected to the current wiring 111 by solder can be reduced on the printed circuit board 101 side.

[0105] Therefore, the thickness of the first electrode 21 can be increased without changing the overall height of the resistor 1. Furthermore, since the thickness of the first electrode 21 can be increased, the potential distribution inside the first electrode 21 can be mitigated, thereby improving the durability during wire bonding.

[0106] In the resistor 1 of this embodiment, as an example, the thickness T2 of the second electrode 22 on the printed circuit board 101 side can be set to 30 μm, and the thickness T1 of the upper first electrode 21 can be set to 170 μm. As a result, the same current detection accuracy as when using a 100 μm thick electrode can be ensured, and the durability of the wire bonding of the upper first electrode 21 can be improved.

[0107] Furthermore, the insulating particles constituting the resistive material 11a include second insulating particles with a particle size of less than 5 μm, and the total cross-sectional area of ​​the first insulating particles on the cross-section of the resistive body 11 is 15% or more and less than 50%. Such a resistive material 11a can achieve a good current path.

[0108] In resistor 1, there are more first insulating particles than second insulating particles. That is, because there are more first insulating particles with a particle size of 5μm or larger, it is easier to form a three-dimensional network structure of slender metallic bodies between the first insulating particles. Therefore, the resistance characteristics can be stabilized.

[0109] The metallic body in the resistive material 11a forms a three-dimensional network surrounding the insulating particles. This facilitates the formation of elongated current paths within the resistive material 11a, thus easily stabilizing its resistance characteristics.

[0110] Furthermore, the current path of the three-dimensional network structure is not easily interrupted by temperature changes or the application of high voltage, thus preventing any impact on the overall resistivity of the resistive material 11a. Therefore, the resistivity of the resistive material 11a can be made greater than that of a metallic element, and the resistive characteristics of the resistive material 11a can be stabilized.

[0111] Furthermore, according to this embodiment, at least one metal powder selected from the group consisting of nickel-chromium alloy, copper-manganese, and copper-nickel is used to form a conductive metallic body in the resistive material 11a. These metal powders are alloys used for current detection, and their resistance values ​​change little due to temperature variations. Therefore, by using these alloys, the resistance value required for current detection can be easily ensured, and the increase in TCR can be suppressed.

[0112] Furthermore, according to this embodiment, insulating particles are formed using at least one insulating powder selected from the group consisting of alumina, aluminum nitride, silicon nitride, and zirconium oxide. These insulating powders are ceramic materials with low coefficients of thermal expansion and are used as substrate materials. Therefore, by using these insulating powders, the thermal stress of the resistor 11 made of resistive material 11a can be made close to the thermal stress of the substrate. Thus, cracking due to thermal cycling between the resistor 11 and the substrate can be suppressed.

[0113] Furthermore, according to this embodiment, by forming a three-dimensional network structure in the metal body of the resistive material 11a, the TCR can be stabilized and kept below 100 ppm within an acceptable range. Therefore, the decrease in detection accuracy when using resistor 1 to detect current can be suppressed.

[0114] Furthermore, the resistivity of the resistive material 11a can be designed to be in the range of 200 μΩ·cm or more and 30,000 μΩ·cm or less. Thus, even the so-called vertical resistor 1 with a short current path as shown in FIG1 can, in particular, ensure the resistance value required for high current detection.

[0115] Furthermore, according to this embodiment, a conductive metal is used in powder form, and the metal powder is mixed with insulating particles and granulated. This makes it easy for metal bodies to exist between the insulating particles, thus facilitating the formation of a three-dimensional network of metal bodies within the resistive material 11a during sintering.

[0116] Furthermore, according to this embodiment, multiple current paths are formed in the resistor 11, avoiding insulating particles. Therefore, the specific resistance of the resistor 11 can be increased, while the resistance characteristics of the resistor 11 can be stabilized.

[0117] [Example of a resistor variation]

[0118] <Variation Example 1>

[0119] Figure 7 is a perspective view illustrating resistor 2, which is a first variation of this embodiment.

[0120] In the resistor 2 of this embodiment, since the resistive element 11 does not experience solder wetting and diffusion, the thickness of the second electrode 22 connected to the current wiring 111 via solder can be reduced on the printed circuit board 101 side. Therefore, the thickness of the first electrode 310 can be increased. Thus, the design flexibility of the resistor can be improved.

[0121] In the first modified example, by thickening the first electrode 310, the first electrode 310 can be cut into a first part 311 and a second part 312 through the slit 313 formed along the length direction of the resistor 2.

[0122] According to the resistor 2 having the electrode shape shown in FIG. 7, when mounted on a circuit board, the first portion 311 of the first electrode 310 and the current detection wiring can be connected by wire bonding. Since the first portion 311 is cut off from the second portion 312, the current measurement point can be set to a position away from the mainstream current flowing through the resistor 11. Therefore, the accuracy of current detection can be improved.

[0123] <Variation Example 2>

[0124] Figure 8 is a perspective view illustrating the resistor 3 as a second variation of this embodiment.

[0125] In resistor 3, which is illustrated as a second variation, the first electrode 410 is thickened and is cut into a first part 411 and a second part 412 by an L-shaped slit 413.

[0126] When resistor 3 is mounted on a circuit board, the first portion 411 of the first electrode 410 can be connected to the current detection wiring via wire bonding. This allows the current measurement point to be positioned away from the main current flowing through the resistor 11. Therefore, the accuracy of current detection can be improved.

[0127] [Other Implementation Methods]

[0128] The above description illustrates this embodiment, but it is only an example of the application of the present invention and is not intended to limit the scope of the present invention to the specific configuration of the above embodiment.

[0129] In this embodiment, resistor 1 can be plate-shaped, and can be circular, square, or rectangular.

[0130] 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 either the area or size of the first electrode 21 and the second electrode 22 may be different. Furthermore, through-holes may be formed on the first electrode 21 and the second electrode 22.

[0131] In addition, as a method for forming the first electrode 21 and the second electrode 22 on both sides of the resistor 11, besides plating, vacuum evaporation, ion plating, sputtering, vapor deposition or cold spraying can also be used.

[0132] In the resistive material 11a of this embodiment, as the particle size of the insulating particles increases, a slender three-dimensional network structure of current paths can be formed. However, as the particle size of the insulating particles increases, the impact of the unevenness formed by the insulating particles on the surface of the resistive material 11a also increases. Therefore, there is a tendency for the adhesion between the first electrode 21 and the resistive body 11 and the adhesion between the second electrode 22 and the resistive body 11 to decrease. In this case, a base electrode layer may also be provided on the resistive body 11 (first plane 11A). Furthermore, a base electrode layer may also be provided on the second plane 11B of the resistive body 11.

[0133] Materials with high affinity for insulating particles can be used as the base electrode layer. For example, nickel (Ni) and nickel-chromium alloys, which have high affinity for insulating particles, can be used as materials constituting the base electrode layer.

[0134] Furthermore, a flash plating layer can be formed between the base electrode layer and the resistor 11. Nickel, titanium, silver, etc., can be used as materials for forming the flash plating layer.

[0135] By forming a base electrode layer and a flash plating layer, the metallic activity of the metal body on the surface of the resistor 11 can be improved. This enhances the adhesion of the base electrode layer and prevents expansion and peeling of the plated base electrode layer.

[0136] Example

[0137] A test sample of resistor 1 according to an embodiment of the present invention was prepared, various measurements were performed, and resistor 1 was evaluated. The method for preparing the test sample and its evaluation will be described below.

[0138] [Fabrication of Resistors]

[0139] <Mixing and Granulation>

[0140] (Insulating powder)

[0141] As insulating particles used in resistive material 11a, alumina powder contains first insulating particles with a particle size of 5 μm or more and second insulating particles with a particle size of less than 5 μm, with an average particle size of 8 μm.

[0142] Mixed insulating particles are prepared by mixing first insulating particles with a particle size of 5 μm or more and second insulating particles with a particle size of less than 5 μm, such that the total area of ​​the first insulating particles with a particle size of 5 μm or more is 15% or more and less than 50% of the total cross-sectional area at any position of the obtained resistor 11.

[0143] (Metallic body)

[0144] As the metal powder used to make the metal body in the resistive material 11a, a nickel-chromium alloy powder [a powder with an average particle size of 4 μm generated by EVANOHM (registered trademark) through atomization] is used.

[0145] The above-mentioned mixed insulating particles and metal powder are mixed at a volume ratio of metal to insulating particles of 50:50 until they are uniformly mixed, and then granulated.

[0146] <Pressure Sintering>

[0147] Next, the granulated mixed powder was loaded into a carbon mold with a diameter of 50 mm. Then, using a hot press (High Multi 5000 high-temperature furnace: manufactured by Fuji Denpa Kogyo Co., Ltd.), the mixed powder in the carbon mold was heated to a specified temperature lower than the melting point of the nickel-chromium alloy, and sintered under pressure in this state. The resulting resistive material test sample was a cylindrical sintered body with a diameter of 50 mm and a thickness of 200 mm.

[0148] The conditions for the hot press in the pressure sintering process are as follows.

[0149] • Atmosphere: Below 20 Pa

[0150] • Compressed pressure: 20MPa~50MPa

[0151] Sintering temperature: 1000℃~1200℃

[0152] • Duration: 10-30 minutes

[0153] The cylindrical sintered body of the resistive material obtained through the above process is sliced ​​into 0.2 mm pieces using a wire saw to obtain resistive material 11a.

[0154] [Resistor Manufacturing]

[0155] Next, a first electrode 21 and a second electrode 22 are formed on the first and second planes of the resistive body 11 obtained by slicing.

[0156] Figure 9 is an explanatory diagram illustrating a plating apparatus 200 for forming a first electrode 21 and a second electrode 22 on a resistive material by plating process.

[0157] The plating apparatus 200 includes a plating bath 201 containing plating solution, an anode electrode 202, and a cathode electrode 203.

[0158] Using a plating solution for forming electrodes, a first electrode 21 and a second electrode 22 are formed on the surface of the resistor 11. After the electrodes are formed, a 5mm × 5mm square, 0.4mm thick chip-shaped test piece of the resistor 1 is made using a cutting tool.

[0159] <Example>

[0160] An electrode with a thickness of 30 μm is formed on one surface of the resistor 11. In addition, an electrode with a thickness of 170 μm is formed on the other surface.

[0161] <Comparative Example>

[0162] Similar to the embodiments, an electrode with a thickness of 30 μm was formed on one surface of the resistive element in the comparative example. Furthermore, an electrode with a thickness of 170 μm was formed on the other surface.

[0163] <Installation Requirements>

[0164] In the laminates of the obtained embodiments and comparative examples, the surface with an electrode having a thickness of 30 μm was connected to a predetermined copper pattern formed on a printed circuit board by soldering during reflow soldering in a nitrogen atmosphere.

[0165] [Evaluation Method]

[0166] <Surface roughness of resistive element>

[0167] The surface roughness of the resistive element was determined by shape analysis laser microscopy.

[0168] <Results of Solder Wetting and Spreadability Tests>

[0169] Using a magnifying glass, visually inspect the solder wetting and spreading properties of the installed product from an oblique angle.

[0170] [result]

[0171] <Surface roughness of resistive element>

[0172] The surface roughness Ra of the resistive element in the embodiment is 8 μm. On the other hand, the surface roughness Ra of the resistive element in the comparative example is less than 2 μm.

[0173] <Results of Solder Wetting and Spreadability Tests>

[0174] Figure 10 is a schematic diagram illustrating a resistor 4, which is a comparative example, mounted on a printed circuit board 101.

[0175] As shown in Figure 10, in the resistor 4 of the comparative example, a solder fillet 223 is formed between the second electrode 222 and the current wiring 111, and the resistor 4 is mounted on the printed circuit board 101. In the resistor body 211 of the resistor 4 of the comparative example, no protrusion formed of insulating particles is formed on its end face.

[0176] Therefore, depending on the amount of solder paste applied and the size of the connection part on the current wiring 111, the solder fillet 223 rises to the end face of the resistor 211 and the end face of the first electrode 221, resulting in a short circuit between the first electrode 221 and the second electrode 222.

[0177] In contrast, it can be seen that the test piece in the embodiment can obtain good electrical properties without the wetting and diffusion of solder.

[0178] Therefore, it can be seen that in a resistor containing insulating particles with a first insulating particle size of 5 μm or more, the surface roughness Ra of the end face of the resistor is 5 μm or more. After soldering, the end face of the resistor is still exposed and no solder wetting and diffusion will occur.

[0179] This application claims priority based on Japanese Patent Application No. 2023-181260, filed with the Japan Patent Office on October 20, 2023, the entire contents of which are incorporated herein by reference.

[0180] Explanation of reference numerals in the attached figures

[0181] 1: Resistor; 11: Resistor element; 11a: Resistor material; 11A: First plane; 11B: Second plane; 21: First electrode; 22: Second electrode; 30: Solder fillet; 100: Circuit board; 101: Printed circuit board; 111, 112: Current wiring; 113, 114: Current detection wiring; 121: Lead; 131, 132: Wire bonding; 200: Plating apparatus; 201: Plating bath; 202: Anode electrode; 203: Cathode electrode; 221: First electrode; 222: Second electrode; 223: Solder fillet.

Claims

1. A stacked resistor comprising a plate-shaped resistive body 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 resistive body comprising a metal body made of a conductive metal material and insulating particles made of an insulating material, the insulating particles comprising first insulating particles with a particle size of 5 μm or more, the stacked resistor being configured such that, when mounted onto a printed circuit board, the end face of the resistive body is exposed, and the second electrode is connected to the printed circuit board via solder.

2. The stacked resistor according to claim 1, wherein, The thickness of the second electrode connected to the printed substrate is thinner than the thickness of the first electrode.

3. The stacked resistor according to claim 1, wherein, The insulating particles include second insulating particles with a particle size of less than 5 μm, and the proportion of the total cross-section of the first insulating particles on the cross-section of the resistor is more than 15% and less than 50%.

4. The stacked resistor according to claim 3, wherein, The sum of the areas of the first insulating particles on the cross-section of the resistive element is greater than the sum of the areas of the second insulating particles.

5. A method for manufacturing a multilayer resistor, the multilayer resistor comprising a plate-shaped resistive body 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, wherein the resistive body having the first plane and the second plane is formed using insulating particles made of insulating material containing first insulating particles with a particle size of 5 μm or more and a metal body made of conductive metal material, the first electrode and the second electrode are formed on the resistive body by plating to form a multilayer, and the multilayer is cut to form a chip-shaped resistor.

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