Chip resistor and its manufacturing process

A chip resistor (1) includes a chip substrate (2) a mutually separated terminal electrodes (3, 4) formed on the upper surface of the substrate (2), and a meandering resistor film (5) formed between the two terminal electrodes (3, 4). Each of the terminal electrodes (3, 4) includes an inner edge (3a, 4a) extending diagonally from one side surface (2a) toward the other side surface (2b) of the chip substrate (2). Each of the inner edges (3a, 4a) has a portion closer to the resistor film (5) that is electrically connected to a narrow portion (7, 8) formed integral with the resistor film (5). The narrow portion extends outward from an end (5a, 5b) of the resistor film (5).

TECHNICAL FIELD

The present invention relates to a chip resistor and a method for manufacturing the same.

BACKGROUND ART

Conventionally various types of chip resistors have been proposed. For instance, the Patent Document 1 listed below discloses a chip resistor having a structure as shown inFIG. 9of the present application. The Patent Documents 2 and 3 disclose a chip resistor having a structure as shown inFIG. 11of the present application. It should be noted here that the chip resistor shown inFIG. 10of the present application is not presented as prior art, but as a comparative example only for better understanding of the present invention.

Specifically, the conventional chip resistor R1shown inFIG. 9of the present application includes a substrate A1, a resistor film A2and a pair of terminal electrodes A3connected to the resistor film A2. The substrate A1has a predetermined length L and a predetermined width W. The resistor film A2is formed with a trimming groove A4for resistance adjustment.

In the chip resistor R1, the single resistor film A2is provided between the paired terminal electrodes A3. With this arrangement, when a voltage is applied between the paired terminal electrodes A3, current flows only through the resistor film A2. Therefore, when the chip resistor R1is applied to a circuit for high power supply, the temperature of the resistor film A2may become excessively high. In such a case, the circuit may fail to operate properly.

This problem may be solved by employing the structure shown inFIG. 10, for example. Specifically, the chip resistor R2shown in the figure includes a substrate B1, a plurality of resistor films B2and a pair of terminal electrodes B3. The length L and the width W of the substrate B1are equal to those of the above-described substrate A1. Each of the terminal electrodes B3is formed on a longitudinally-extending side surface of the substrate B1. The resistor films B2are connected in parallel with each other with respect to the paired electrodes B3. In the chip resistor R2of this structure, the current flows as dispersed into the plurality of resistor films B2. Thus, although the size of the chip resistor R2is the same as that of the chip resistor A, the rated power of the chip resistor R2is large.

However, in the chip resistor R2, the effective length (length of the portion which functions as a resistor element) of each of the resistor films B2is shorter than that of the resistor film A2of the chip resistor R1. Therefore, when the chip resistor R2has the application of a surge voltage, its resistance tends to vary significantly (meaning that the resistor has a low surge resistance).

With reference toFIG. 11of the present application, the chip resistor disclosed in the Patent Document 2 or 3 will be described below. The chip resistor R3shown in the figure includes a substrate31, electrodes32and33formed on the substrate and a resistor element34. The left end37of the resistor element34is connected to a projection35of the electrode32, whereas the right end38of the resistor element34is connected to a projection36of the electrode33. The resistor element34extends in a meandering manner between the two electrodes32and33. With this arrangement, the current path in the resistor element34is longer than that of a resistor element extending straight between the two electrodes. Thus, the surge resistance of the chip resistor R3is enhanced.

Further, by connecting the opposite ends of the resistor element34to the projections35and36of the electrodes32and33, a sufficient distance is secured between the inner edge32aof the electrode32and the outer edge34aof the resistor film34(or between the inner edge33aof the electrode33and the outer edge34bof the resistor film34). Thus, in forming the resistor element34and the electrodes32and33on the substrate31by screen printing, the resistor element34and the electrodes32,33are prevented from becoming too close to or coming into contact with each other (if the resistor element and the electrodes are too close, discharge occurs between them).

However, the structure shown inFIG. 11has the following drawbacks.

As described above, the electrodes32and33(and the resistor element34) can be formed by screen printing. Specifically, a screen for printing formed with holes corresponding to the shape of the electrodes32and33is prepared. Then, the screen is placed on the upper surface of the substrate31. Then, material paste is applied from the upper surface side of the screen. Then, the material paste is loaded into the holes for electrode formation by using a squeegee. Finally, the screen is removed from the substrate31. In this way, the electrodes32and33are formed.

In the above-described process, however, in removing the screen from the substrate31, part of the material paste loaded in the holes may be removed from the substrate31together with the screen. In such a case, the projections35and36of the electrodes32and33cannot have a desired straight edge but have a round edge as indicated by the double-dashed lines α and β inFIG. 11. As a result, the distance L0between the two electrodes32and33is larger than the proper distance L, which causes the resistance of the chip resistor R3to deviate from the desired value.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a chip resistor capable of solving or alleviating the above-described problems.

According to a first aspect of the present invention, there is provided a chip resistor comprising: a chip substrate including an upper surface and a pair of side surfaces opposite to each other; a pair of terminal electrodes formed on the upper surface of the substrate to be spaced from each other; and a resistor film having a meandering shape and formed between the paired terminal electrodes. Each of the terminal electrodes includes an inner edge extending diagonally from one of the paired side surfaces toward the other one of the paired side surfaces of the chip substrate. A portion of the inner edge positioned close to the resistor film is electrically connected to a narrow portion formed integral with the resistor film, where the narrow portion extends outward from an end of the resistor film.

Preferably, the inner edges of the paired terminal electrodes may extend in parallel with each other.

According to a second aspect of the present invention, there is provided a method for manufacturing a chip resistor. The method comprises the steps of: forming a pair of terminal electrodes spaced from each other on an upper surface of a chip substrate; and forming a resistor film having a meandering shape between the paired terminal electrodes. In the terminal electrode formation step, each of the terminal electrodes is so formed to have an inner edge extending diagonally from one side surface of the chip substrate toward another side surface of the chip substrate. In the resistor film formation step, the resist or film is so formed to include a narrow portion extending integrally outward from an end thereof and electrically connected to a portion of the inner edge of a corresponding one of the terminal electrodes, where the portion mentioned above is close to the resistor film.

According to a third aspect of the present invention, there is provided a chip resistor comprising: a chip substrate including an upper surface and a pair of side surfaces opposite to each other; a pair of terminal electrodes for solder connection formed on the paired side surfaces; and a plurality of resistor films formed between the paired terminal electrodes. Each of the resistor films has a meandering shape extending from one of the paired terminal electrodes toward the other one of the paired terminal electrodes.

Preferably, the chip substrate may be in the form of an elongated rectangle, and each of the terminal electrodes may be formed respectively on an elongated side surface extending longitudinally of the chip substrate.

BEST MODE FOR CARRYING OUT THE INVENTION

FIGS. 1 and 2show a chip resistor1according to a first embodiment of the present invention. The chip resistor1includes a rectangular chip substrate2made of a ceramic material. A pair of terminal electrodes3and4are formed by screen printing at longitudinally opposite ends of upper surface of the chip substrate2. A resistor film5formed by screen printing is provided between the paired terminal electrodes3and4on the upper surface of the chip substrate2. The resistor film5is formed with a plurality of grooves6extending inward from a pair of longitudinally extending edges of the resistor film. The grooves6may be formed in the above-described screen printing process or by trimming after the screen printing. With the provision of the grooves6, the resistor film5extends in a meandering manner between an end5aand another end5bthereof in the longitudinal direction.

As shown inFIG. 1, the terminal electrodes3and4include inclined inner edges3aand4a, respectively. Specifically, the terminal electrode3has a trapezoidal shape, and the upper base (the side adjacent to the side surface2bof the substrate2) is shorter than the lower base (the side adjacent to the side surface2aof the substrate2). The left side of the trapezoid (the side adjacent to the side surface2cof the substrate2(seeFIG. 2)) extends perpendicularly to both the upper base and the lower base and in parallel with the side surface2cof the substrate2. The right side of the trapezoid, i.e., the inner edge3aof the terminal electrode3is not parallel with the side surface2cof the substrate2. As shown inFIG. 1, the inner edge3aextends “diagonally outward” from the side surface2atoward the side surface2bof the chip substrate2. (That is, the inner edge3ais so inclined as to extend away from the center of the substrate2as progressing from the side surface2atoward the side surface2bof the chip substrate2.) Similarly, the inner edge4aof the terminal electrode4extends diagonally outward from the side surface2atoward the side surface2bof the chip substrate2. The ends5aand5bof the resistor film5are respectively formed integral with narrow portions7and8extending outward. Each of the narrow portions7and8is laminated on and electrically connected to the inclined inner edge3a,4aof the corresponding terminal electrode3,4at a portion closer to the resistor film5, i.e., the portion adjacent to the longitudinal side surface2aof the chip substrate2.

Referring toFIG. 2, indicated by the reference sign9is a cover coat covering the entirety of the resistor film5. Indicated by the reference signs10and11are terminal electrodes formed on the reverse surface of the chip substrate2. Indicated by the reference signs12and13are side surface terminal electrodes formed on the side surfaces2cand2dof the chip substrate2to electrically connect the terminal electrodes3and4on the upper surface side to the terminal electrodes10and11on the lower surface side.

In the above-described structure, as noted above, the inner edges3aand4aof the terminal electrodes3and4are inclined outwardly from the side surface2atoward the side surface2bof the chip substrate2. The narrow portions7and8extending integrally outward from the opposite ends5aand5bof the resistor film5are laminated on and electrically connected to portions of the inclined inner edge3aand4awhich are close to the resistor film5. With this arrangement, even when pattern misalignment between the resistor film5and the terminal electrodes3,4in the longitudinal direction of the resistor film5occurs in screen printing the terminal electrodes and the resistor film, a distance sufficient to allow the pattern misalignment is defined between the inner edges3a,4aof the terminal electrodes3,4and the ends5a,5bof the resistor film5.

The above-described shape of the terminal electrodes3and4can be provided just by inclining the inner edges3aand4aoutwardly. Thus, in forming the terminal electrodes3and4by screen printing, the inner edges3aand4aare properly formed into a shape extremely close to the predetermined shape. Thus, the effective length L of the resistor film5is prevented from varying, so that the resistance of the resistor film5is prevented from deviating from a desired value.

FIG. 3shows a chip resistor1′ according to a second embodiment of the present invention.

The chip resistor1′ includes a chip substrate2′ in the form of an elongated rectangle made of a ceramic material, terminal electrodes3′ and4′ formed by screen printing at longitudinally opposite ends of the upper surface of the chip substrate2′, and a resistor film5′ formed by screen printing between the paired terminal electrodes3′ and4′ on the upper surface of the chip substrate2′ to extend longitudinally of the chip substrate. The resistor film5′ is formed with a plurality of grooves6′ extending inward from the longitudinal edges thereof, which may be formed in the screen printing process or by trimming after the screen printing. With the provision of the grooves, the resistor film5extends in a meandering manner between an end5a′ and another end5b′ thereof in the longitudinal direction.

The terminal electrode3′ has an inner edge3a′ which is inclined outwardly from a longitudinal side surface2a′ toward a longitudinal side surface2b′ of the chip substrate2′. The terminal electrode4′ has an inner edge4a′ which is inclined outwardly from the side surface2b′ toward the side surface2a′ of the chip substrate2′.

The inclined inner edge3a′ of the terminal electrode3′ and the inclined inner edge4a′ of the terminal electrode4′ extend in parallel with or generally in parallel with each other.

The end5a′ of the resistor film5′ is formed with a narrow portion7′ extending integrally outward therefrom. The narrow portion is laminated on and electrically connected to the inclined inner edge3a′ of the terminal electrode3′ at a portion close to the resistor film5′, i.e., the portion adjacent to the longitudinal side surface2a′ of the chip substrate2′. Similarly, the end5b′ of the resistor film5′ is formed with a narrow portion8′ extending integrally outward therefrom. The narrow portion is laminated on and electrically connected to the inclined inner edge4a′ of the terminal electrode4′ at a portion close to the resistor film5′, i.e., the portion adjacent to the longitudinal side surface2b′ of the chip substrate2′.

With this arrangement, as in the first embodiment, even when some pattern misalignment between the resistor film5′ and the terminal electrodes3′,4′ in the longitudinal direction of the resistor film5′ occurs in screen printing of the terminal electrodes and the resistor film, a distance sufficient to allow the pattern misalignment can be provided between the inner edges3a′,4a′ of the terminal electrodes3′,4, and the ends5a′,5b′ of the resistor film5owing to the outward inclination of the inner edges3a′,4a′ of the terminal electrodes3′,4′.

The above-described shape of the terminal electrodes3′ and4′ can be provided just by inclining the inner edges3a′ and4a′ outwardly. In forming the terminal electrodes3′ and4′ by screen printing, the inner edges3a′ and4a′ are properly formed into a shape extremely close to the predetermined shape. Thus, the effective length L′ of the resistor film5′ is prevented from varying.

As noted above, the inclined inner edge3a′ of the terminal electrode3′ and the inclined inner edge4a′ of the terminal electrode4′ extend in parallel with or generally in parallel with each other. Thus, even when pattern misalignment between the resistor film5′ and the terminal electrodes3′,4′ in a direction perpendicular to the longitudinal direction of the resistor film5′ occurs in screen printing the terminal electrodes and the resistor film, the effective length L′ of the resistor film5′ does not vary. Thus, the resistance of the resistor film5′ is reliably prevented from varying.

FIGS. 4-6show a chip resistor101according to a third embodiment of the present invention.

The chip resistor101includes an insulating substrate102made of a heat-resistant insulating material such as a ceramic material. The insulating substrate102is in the form of an elongated rectangle having a length L and a width W.

Terminal electrodes103for solder connection are provided on a pair of longitudinally-extending side surfaces102′ of the insulating substrate102to extend along the side surfaces102′.

A plurality of resistor films104(three resistor films in the example shown in the figure) are provided between the terminal electrodes103on the upper surface of the insulating substrate102. The resistor films are arranged, in parallel with each other and spaced from each other in the longitudinal direction of the insulating substrate102. Each of the resistor films104has opposite ends electrically connected to the terminal electrodes103.

Each of the resistor films104is alternately formed with a plurality of grooves105(two in the figure) extending inward from the longitudinal edge104′ of the resistor film and a plurality of grooves106(two in the figure) extending inward from the other longitudinal edge104″ of the resistor film. Thus, the resistor film has a meandering shape.

A cover coat covering the entirety of the resistor films104is provided on the upper surface of the insulating substrate102.

The meandering shape of each of the resistor films104may be provided by forming the grooves105and106in screen printing the resistor film104or by forming part or entirety of the grooves105and106by trimming by e.g. laser beam irradiation after the screen printing.

In the above-described structure, the power applied to the terminal electrodes103is dispersed into each of the resistor films104. Thus, the chip resistor is applicable to large electric power. Since each of the resistor films104has a meandering shape, the current path is long. Thus, the rate of change of the resistance in the case where a surge voltage is applied is small. Thus, the surge resistance is enhanced.

FIGS. 7 and 8show the results of experiments carried out to compare the performance of the chip resistor101according to the present invention, the conventional chip resistor R1shown inFIG. 9and the chip resistor R2shown inFIG. 10as a comparative example, all of which had an elongated rectangular shape of a same size (with a same length L and a same width W).

Specifically,FIG. 7shows the relationship between the power (P) applied to the terminal electrodes and the temperature rise (ΔT) at the surface of the resistor film. As indicated by the single-dashed line C, the temperature rise at the conventional chip resistor R1is relatively large. On the other hand, as indicated by the solid line D, the temperature rise at the chip resistor101according to the present invention (and the chip resistor R2as the comparative example) is considerably small.

FIG. 8shows the results of electrostatic breakdown test (evaluation of surge resistance). In the figure, the abscissa indicates the resistance (R) of the chip resistor, whereas the ordinate indicates the rate of change (RC) of the resistance. As indicated by the single-dashed line E, the resistance change of the chip resistor R2as a comparative example is considerably large. On the other hand, as indicated by the solid line F, the resistance change of the chip resistor101according to the present invention is considerably small.

In this embodiment, each of the longitudinal side surfaces102′ of the insulating substrate102is formed with at least one recess108, and the terminal electrode103is formed also on the inner surface of the recess108. With this arrangement, in soldering the chip resistor onto e.g. a printed board109, the soldering strength can be enhanced by forming a solder fillet bulging into the recess108.