JP2015119125A - Chip resistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a chip resistor including an electrode structure that does not degrade even when being operated for a long period of time under high temperature of about 250 to 350°C.SOLUTION: Foundation internal electrodes 12, 13 are Ag-base thick film electrodes. In the chip resistor including an Au plating layer 20 on an outermost surface layer of an outer electrode, a metal intermediate plating layer 19 composed of a platinum group as a diffusion barrier against the Au plating layer 20 is provided. The intermediate plating layer 19 composed of a platinum group is preferably a palladium (Pd) plating layer.

Description

  The present invention relates to a chip resistor, and more particularly to a highly heat resistant electrode structure in which an electrode hardly deteriorates even when used in a high temperature environment.

  Many of the electrodes of chip resistors, which are becoming smaller and lighter, have a multilayer electrode structure. The base electrode layer of such a conventional resistor is mainly an Ag-based thick film electrode of Ag or Ag / Pd, and a Ni or Sn plating layer is formed as an external electrode on the upper layer (for example, Patent Documents). 1). This electrode is usually soldered to the circuit board by soldering, and the chip resistor is mounted on the circuit board.

  Recently, chip resistors mounted on automobiles and the like have been required to have higher heat resistance, and chip resistors that do not change in resistance value even under high temperature environments are required. In particular, a resistor used in the immediate vicinity of a SiC power module semiconductor is required to be usable even at an ambient temperature of 250 ° C., for example.

  In response to such a demand for high heat resistance, a chip resistor using Au having excellent heat resistance as the outermost layer of the electrode layer has been proposed as a measure for preventing oxidation of the electrode portion due to thermal stress (see Patent Document 2). Further, as an electrode that can be used in a high temperature environment, a chip resistor using Au as an outermost plating electrode has been proposed (see Patent Document 3).

JP 2007-194398 A JP 2002-064003 A JP-A-10-223402

  However, the electrode portion of the conventional chip resistor has an excellent oxidation stability in the outermost layer of the electrode of the chip resistor in the environmental test at the heat resistant temperature (about 150 ° C.) that has been required so far. Although it was able to prevent oxidation, it was not stable when exposed to high temperatures (approximately 250 to 350 ° C) for a long time, which is a recent need, and even if Au was the outermost layer of the electrode, the resistance value increased greatly. There is a problem of end. Further, there is a problem that the lower metal layer such as Ag or Ni is exposed by diffusion and an oxide film is formed, so that contact failure and resistance value change. That is, when the temperature reference of the heat resistance test is raised, the conventional metal layer structure lacks durability and it becomes difficult to sufficiently satisfy the high heat resistance.

  Furthermore, simultaneously with the demand for such a high heat resistance chip resistor, high heat resistance is also demanded on the substrate side on which electronic components such as a chip resistor are mounted. In particular, solder materials used at the time of bonding have been studied from an early stage because of their low heat resistance, and gold-germanium (melting point: about 350 ° C.) is one proposal for bonding electronic components and substrates in terms of high heat resistance. It is said that there is.

  The present invention has been made based on the above-mentioned circumstances, and a chip having an electrode made of a metal layer that does not greatly change the material of a conventional metal layer, for example, Ag for a base electrode layer on a ceramic substrate and Ni for an intermediate layer. An object of the present invention is to provide a chip resistor having an electrode layer having a high heat resistance in which an electrode is not easily deteriorated by a high temperature in a test in which the resistor is left in a high temperature environment of about 250 to 350 ° C. for a long time, and an arrangement structure thereof. And

  In the chip resistor of the present invention, the base internal electrode is an Ag-based thick film electrode, and the chip resistor having the Au plating layer as the outermost surface layer of the external electrode is an Ag diffusion barrier against the Au plating layer. An intermediate plating layer of metal is provided. The intermediate plating layer made of a platinum group metal is preferably a palladium (Pd) plating layer.

  According to the resistor, the intermediate layer effectively prevents the diffusion of Ag which is easily diffused from the underlying internal electrode, and prevents the intermediate layer from entering the Au plating layer. This suppresses the generation of Au / Ag-based intermetallic compounds, suppresses electrode deterioration even when used in a high temperature environment, and allows the chip resistor to be used for a long time in a high temperature environment.

It is sectional drawing of the chip resistor of one Example of this invention. It is sectional drawing of the chip resistor as a comparative example. It is a flowchart of the manufacturing process of the chip resistor shown in FIG.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 3. In addition, in each figure, the same code | symbol is attached | subjected and demonstrated to the same or equivalent member or element.

  FIG. 1 shows an electrode structure of a chip resistor according to an embodiment of the present invention, and FIG. 3 shows a manufacturing process thereof. This chip resistor is a thick film chip resistor, and a back electrode (Ag) 12 which is an internal electrode is formed on the back surface of an insulating substrate 11 made of alumina by screen printing, drying and baking, and is an internal electrode on the surface. The surface electrode (Ag) 13 is similarly formed by screen printing, drying and baking. And the resistor 14 is formed by screen printing, drying, and baking so that it may straddle between a pair of surface electrode (Ag) 13 provided in the both ends of the board | substrate 11. FIG.

  The resistor 14 is covered with a pre-glass 15, and is covered with a protective coat (glass) 16 after the trimming process. An end face electrode 17 made of a Ni—Cr thin film, which is an internal electrode, is formed on the end face of the substrate 11 by sputtering. The above configuration is the same as that of a normal chip resistor.

  As for the external electrode, an Ni plating layer 18 is formed on the upper surfaces of the internal electrodes 12, 13, and 17, an intermediate plating layer 19 of a platinum group metal is formed on the upper surface, and an Au plating layer 20 is further formed on the upper surface. doing. In this embodiment, a palladium (Pd) plating layer is employed as the intermediate plating layer 19.

  The Ni plating layer 18 plays a role of electrical conduction between the front electrode 13 and the back electrode 12 and has a certain barrier effect against Ag diffusion described later in this embodiment. Although Ni also has the property of diffusing into other metals, it was clear from the test results that the amount of diffusion was smaller than that of Ag.

  The intermediate plating layer 19 made of platinum group metal is a plating layer of palladium (Pd) alone in this embodiment. Ag diffusion from the base Ag-based thick film electrode and diffusion of Ni from the base Ni plating layer. It acts as a barrier against The platinum group metal is ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), platinum (Pt), etc., and is close to gold (Au). Similar to gold (Au), it is difficult to be attacked by acids and bases. However, among these, osmium (Os) has the property of being easily sublimated at about 400 ° C. and is easily oxidized, so it has elements that are unsuitable for use in plating. Shall be excluded.

  The outermost Au layer functions to prevent oxidation of the electrode of the chip resistor that operates at a high temperature, and at the same time, it satisfactorily bonds to a substrate wiring layer such as a solder material or a wiring pad during mounting.

  As a result, the electrode structure is Au / Pd / Ni / Ag from the upper layer, and each metal layer of Pd and Ni is interposed as an intermediate layer, so that even if operated at a high temperature of 250-350 ° C., the Au layer on the surface layer A chip in which Ag does not diffuse from an Ag-based thick film electrode, an intermetallic compound with Ag or the like is not generated in the Au layer, the connectivity between electrode layers in the chip resistor is ensured, and resistance value fluctuations are suppressed. A resistor can be obtained.

  That is, the conventional general chip resistor has an electrode structure of Sn / Ni / Ag from the upper layer as described above. In this case, it is apparent that Sn has a melting point of about 230 ° C. and cannot be operated at a high temperature of 250 to 350 ° C. Therefore, as a comparative example, as shown in FIG. 2, it is conceivable to simply replace the Sn plating layer with an Au plating layer 20 having a high melting point and good solderability. The electrode structure in this case is Au / Ni / Ag from the upper layer.

  However, in the test results of the present inventors, the chip resistor provided with the Au plating layer of the above structure on the outermost layer is excellent in short-time high heat resistance, but when 250 hours have passed in the 350 ° C. high temperature standing test, It has been found that Ni and Ag diffuse to the outside of the Au plating layer, and a portion of the Ni plating layer is exposed and an oxide film is formed thereon, thereby causing a phenomenon that is not suitable for soldering.

  As a result of analysis, this phenomenon is caused by the fact that Ag of the underlying Ag-based thick film electrode 12 passes through the Ni plating layer 18 and enters the Au plating layer 20 to form an intermetallic compound of Ag and Au. it is conceivable that. Then, it is considered that this problem can be solved if a diffusion barrier for the Au plating layer can be provided so that Ag of the underlying internal electrode does not enter the Au plating layer. Therefore, by providing a metal intermediate layer made of a platinum group such as Pd having characteristics similar to those of Au, it works so that Ag of the underlying internal electrode is captured by the layer, and reaches the outermost Au layer. It acts as a diffusion barrier against the Au plating layer. By obtaining a structure that can clear the high heat resistance leaving test, it is considered that this example is a chip resistor that can be satisfactorily bonded to a bonding material such as a high heat resistance solder material or a pad during mounting.

  Therefore, the electrode structure of the present invention has been devised. By laminating a Ni-plated layer, a Pd-plated layer, and an Au-plated layer on a base Ag-based thick film electrode, the Pd-plated layer is made of Ag and Ni. It functions as a diffusion barrier and prevents Ag and Ni from entering the Au layer 20. Therefore, in the Au layer 20, an intermetallic compound that damages the electrode is not generated, and even when operated for a long time in a high temperature environment, the electrode does not deteriorate, and therefore, an electrode structure in which the resistance value does not change is obtained.

  In the above embodiment, the example in which the Ag electrode is used as the base internal electrode has been described. However, an Ag—Pd-based electrode may be used. Moreover, although the example which forms the end surface electrode 17 by sputtering of Ni-Cr was demonstrated, you may use an Ag or Ag-Pd type thick film electrode.

  Although one embodiment of the present invention has been described so far, it is needless to say that the present invention is not limited to the above-described embodiment, and may be implemented in various forms within the scope of the technical idea.

  The present invention can be suitably used for a chip resistor used in a high temperature environment.

11 Insulating substrate 12 Internal electrode / Back electrode
13 internal electrode / surface electrode 14 resistor 15 pre-glass 16 protective coat (glass)
17 Internal electrode / End face electrode (Ni-Cr)
18 Ni plating layer 19 Intermediate plating layer (platinum group)
20 Au plating layer

Claims (4)

  The base internal electrode is an Ag-based thick film electrode, and in the chip resistor having the Au plating layer as the outermost layer of the external electrode, an intermediate plating layer made of a platinum group metal is provided as a diffusion barrier to the Au plating layer. Chip resistor characterized by.   2. The chip resistor according to claim 1, wherein the platinum group metal is ruthenium (Ru), rhodium (Rh), palladium (Pd), iridium (Ir), or platinum (Pt).   The chip resistor according to claim 1, wherein the intermediate plating layer of a metal made of a platinum group is formed on the Ni plating layer.   2. The chip resistor according to claim 1, wherein the intermediate plating layer made of a platinum group metal is a palladium (Pd) plating layer.

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