CHIP-TYPE CURRENT FUSE

The chip-type current fuse is configured to include a fuse element 5 formed between a first front electrode 3 and a second front electrode 4. The fuse element 5 includes: a first linear portion 5a that has an end connected to the first front electrode 3 and extends in a direction toward the second front electrode 4; a second linear portion 5b that has an end connected to the second front electrode 4 and extends in parallel to the first linear portion 5a in a direction toward the first front electrode 3; and an inclined linear portion 5c that links the first linear portion 5a and the second linear portion 5b to each other. The inclined linear portion 5c is connected at an acute angle to each of the first linear portion 5a and the second linear portion 5b.

TECHNICAL FIELD

The present invention relates to a surface mounting chip-type current fuse.

BACKGROUND ART

A chip-type current fuse mainly includes: an insulating substrate of a rectangular solid shape; a pair of front electrodes that are respectively formed on both longitudinal end portions of the front surface of the insulating substrate; a fuse element that is formed between the pair of front electrodes; a protective layer that covers the fuse element; a pair of back electrodes that are formed on both longitudinal end portions of the back face of the insulating substrate; a pair of end electrodes that are formed on both longitudinal end faces of the insulating substrate and each provides connection between the corresponding front electrode and the corresponding back electrode; and the like.

In the chip-type current fuse configured in this way, if a predetermined overcurrent flows between a pair of front electrodes, the current is concentrated on the fuse element, so that heat is produced. In turn, the fuse element is melted by the produced heat to thereby protect various types of electronic equipment connected to the chip-type current fuse.

Where the fuse element is formed between the pair of front electrodes in a linear fashion, a shorter distance between the front electrodes with reduction in size of the chip-type current fuse causes a reduced thermal capacity of the fuse element, which in turn results in a decrease in pulse resistance. To avoid this, conventionally, chip-type current fuses with pulse resistance increased by forming a fuse element in a folded shape are suggested as described in Patent Literature 1.

FIG. 6is a plan view of the chip-type current fuse described above in Patent Literature 1, in which the chip-type current fuse100includes a first front electrode102and a second front electrode103that are formed on both longitudinal end portions of an insulating substrate101of a rectangular solid shape, as well as a fuse element104that is formed between the first front electrode102and the second front electrode103. The fuse element104is made up of: a linear portion104ahorizontally extending from an upper portion of the first front electrode102to the vicinity of an upper portion of the second front electrode103; a linear portion104bextending at a right angle from the leading end of the linear portion104a; a linear portion104cextending in parallel to the linear portion104afrom the leading end of the linear portion104bto the vicinity of a central portion of the first front electrode102; a linear portion104dextending at a right angle from the leading end of the linear portion104c; and a linear portion104eextending in parallel to the linear portion104afrom the leading end of the linear portion104dto the vicinity of a lower portion of the second front electrode103, so that the fuse element104is formed in a shape such as being folded into a plurality of straight lines.

Because the chip-type current fuse100configured as described above has the fuse element104of a folded shape, the full length of the fuse element104is longer than that of a fuse element formed in a linear fashion. As a result, the thermal capacity of the fuse element104is increased to improve pulse resistance.

CITATION LIST

Patent Literature

Patent Literature 1: Japanese Published Unexamined Patent Application No. Hei 11-96885

SUMMARY OF INVENTION

Technical Problem

In the chip-type current fuse described in Patent Literature 1, the linear portion104aconnecting continuously to the first front electrode102and the linear portion104econnecting continuously to the second front electrode103are locations that allow heat to escape readily (thermal dissipation portion). Therefore, the heat produced in the fuse element104is concentrated on the linear portion104b, the linear portion104c, and the linear portion104dwhich are formed between the linear portions104a,104e. Thus, when a predetermined overcurrent flows between the first front electrode102and the second front electrode103, melting occurs in any location of the linear portions104b,104c,104d. However, because it is not determined which location(s) of the linear portions104b,104c, and104dmelts with the linear portions104b,104c, and104dlinked together in a crank shape, there is a problem of unstable timing when melting occurs.

The present invention has been made in view of such circumstances in the conventional art and it is an object thereof to provide a chip-type current fuse capable of stabilizing timing when a fuse element melts.

Solution to Problem

To achieve the object, an aspect of the present invention provides a chip-type current fuse that includes: an insulating substrate of a rectangular solid shape; a first front electrode and a second front electrode that are formed on both longitudinal end portions of a front face of the insulating substrate; a first back electrode and a second back electrode that are formed on both longitudinal end portions of a back face of the insulating substrate; a first end electrode that is formed on one of longitudinal end faces of the insulating substrate to connect the first front electrode and the first back electrode to each other; a second end electrode that is formed on the other longitudinal end face of the insulating substrate to connect the second front electrode and the second back electrode to each other; and a fuse element that is formed between the first front electrode and the second front electrode. The fuse element includes: a first linear portion that has an end connected to the first front electrode and extends in a direction toward the second front electrode; a second linear portion that has an end connected to the second front electrode and extends in parallel to the first linear portion in a direction toward the first front electrode; and an inclined linear portion that links the first linear portion and the second linear portion to each other. The inclined linear portion is connected at an acute angle to each of the first linear portion and the second linear portion.

In the chip-type current fuse configured as described above, the first linear portion connected to the first front electrode and the second linear portion connected to the second front electrode serve as locations that allows heat to escape readily, and the inclined linear portion formed between the first linear portion and the second linear portion is connected at an acute angle to each of the both linear portions. As a result, the heat produced in the fuse element is concentrated on the vicinity of the center of the inclined linear portion, so that the vicinity of the center of the inclined linear portion can be melted at stable timing.

In the chip-type current fuse of the above configuration, the fuse element has a point symmetric shape which is symmetric about a point at the center of the inclined linear portion, specifically, a Z shape in planar view with both ends of the inclined linear portion connecting continuously to the first linear portion and the second linear portion, respectively. Because of this, melting stably will occur in the vicinity of the center of the inclined linear portion.

Further, in the chip-type current fuse of the above configuration, the distance from the center of the inclined linear portion to the first back electrode and the second back electrode is set to be longer than the distance from the center of the inclined linear portion to the first front electrode and the second front electrode. Because of this, the heat produced in the fuse element is hard to be dissipated from the first back electrode and the second back electrode located on the underside of the insulating substrate. Therefore, the vicinity of the center of the inclined linear portion can be melted stably.

Further, the chip-type current fuse of the above configuration, when an area between the first front electrode and the second front electrode is defined as an element formation region, the first back electrode and the second back electrode are formed on the outside of a back face region on which the element formation region is projected. Thus, the vicinity of the center of the inclined linear portion can be melted stably.

Advantageous Effects of Invention

In the chip-type current fuse according to the present invention, the inclined linear portion formed between the first linear portion and the second linear portion is connected at an acute angle to each of the linear portions. This enables stabilization of timing when the fuse element melts.

DESCRIPTION OF EMBODIMENT

Embodiments according to the invention will now be described with reference to the accompanying drawings.FIG. 1is a plan view of a chip-type current fuse according to example embodiments of the present invention.FIG. 2is a sectional view taken along line II-II ofFIG. 1.

As illustrated inFIGS. 1 and 2, the chip-type current fuse according to the example embodiments mainly includes: an insulating substrate1of a rectangular solid shape; a thermal storage layer2that is formed on a region of the front face of the insulating substrate1other than both longitudinal end portions thereof; a first front electrode3and a second front electrode4that are formed on the both longitudinal end portions of the front face of the insulating substrate1to overlap partially the thermal storage layer2; a fuse element5that is formed on the thermal storage layer2to provide continuity between the first front electrode3and the second front electrode4; an inner protective layer6that covers the fuse element5; a protective layer7that covers parts of the first front electrode3and the second front electrodes4and the entire inner protective layer6; a first back electrode8and a second back electrode9that are formed on both longitudinal end portions of the back face of the insulating substrate1; a first end electrode10that is formed on one of longitudinal end faces of the insulating substrate1to connect the first front electrode3and the first back electrode8to each other; and a second end electrode11that is formed on the other longitudinal end face of the insulating substrate1to connect the second front electrode4and the second back electrode9to each other.

The insulating substrate1is one of multiple insulating substrates obtained by dividing a large substrate, which will be described later, along crisscross division grooves. The large substrate is a ceramic substrate made primarily of alumina.

The thermal storage layer2is made by coating (e.g., screen printing) and firing of glass paste or by coating (e.g., spin coat) and curing of resin such as polyimide resin and/or the like, and is formed in a rectangular shape to cover a central portion of the front face of the insulating substrate1.

For the first front electrode3, the second front electrode4and the fuse element5, a metal thin film (e.g., Cu, Ag, Au, Al and/or the like) which is meltable as a fuse is sputtered or evaporated onto the entire front face of the insulating substrate1, and the resultant is patterned using photolithography. The first front electrode3and the second front electrode4are formed in a rectangular shape on the both longitudinal end portions of the insulating substrate1, and the fuse element5is formed in a Z shape in planar view, between the first front electrode3and the second front electrode4. Incidentally, the detailed configuration of the fuse element5will described later.

The inner protective layer6is made by drying and firing a coating (e.g., screen printing) of inner protective materials (e.g., glass paste, silicone resin and/or the like), and is formed in a rectangular shape to cover parts of the first front electrode3and the second front electrode4and the entire fuse element5.

The protective layer7is made by heating and curing a coating (e.g., screen printing) of epoxy-based resin paste, and is formed in a rectangular shape to cover parts of the first front electrode3and the second front electrode4and the entire inner protective layer6.

The first back electrode8and the second back electrode9are made by drying and firing a coating (e.g., screen printing) of Ag based paste made primarily of silver, and are formed in a rectangular shape on both longitudinal end portions of the back face of the insulating substrate1. The first front electrode3and the first back electrode8are formed in positions corresponding to each other, and the second front electrode4and the second back electrode9are also formed in positions corresponding to each other. The first back electrode8and the second back electrode9are formed to be smaller in area than the first front electrode3and the second front electrode4. Therefore, when an element formation region is defined between the first front electrode3and the second front electrode4which are formed on the front face of the insulating substrate1, the first back electrode8and the second back electrode9are placed on the outside of a back face region on which the element formation region is projected.

The first end electrode10and the second end electrode11are made by sputtering or evaporating end electrode materials (e.g., a Ni/Cr2 layer, a NiCr alloy, a Ni/Ti2 layer, a NiTi alloy) onto both longitudinal end faces of the insulating substrate1. The first end electrode10and the second end electrode11are correspondingly formed to provide continuity between the first front electrode3and the first back electrode8and to provide continuity between the second front electrode4and the second back electrode9. Although not shown, the surfaces of the first end electrode10and the second end electrode11are covered with external electrodes which have double-layer structure formed of a Ni plated layer and a Sn plated layer.

FIG. 3is an explanatory diagram of the fuse element5described earlier. As illustrated inFIG. 3, the fuse element5is made up of a first linear portion5a, a second linear portion5b, and an inclined linear portion5c. The first linear portion5ahas an end connected to an upper portion of the first front electrode3inFIG. 3, and extends in parallel to the longitudinal direction of the insulating substrate1in a direction toward the second front electrode4. The second linear portion5bhas an end connected to a lower portion of the second front electrode4inFIG. 3, and extends in parallel to the first linear portion5ain a direction toward the first front electrode3. The inclined linear portion5clinks the first linear portion5aand the second linear portion5bto each other. The inclined linear portion5cis connected at an acute angle to each of the first linear portion5aand the second linear portion5b. Here, the first linear portion5aand the second linear portion5bare set to be identical in horizontal length, and the fuse element5has a point symmetric shape which is symmetric about a point at the center O of the inclined linear portion5c, specifically, in a Z shape in planar view.

A process of manufacturing the chip-type current fuse according to the example embodiment will be described below with reference toFIGS. 4 and 5.FIGS. 4A to 4Fare superficial plan views of a large substrate used in the manufacturing process.FIGS. 5A to 5Frespectively show sectional views of an equivalent of a chip taken along the longitudinal central portion inFIGS. 4A to 4F.

Initially, a large substrate from which multiple insulating substrates1are obtained is prepared. Primary division grooves and secondary division grooves are previously formed in a grid shape in the large substrate, and each of individual squares defined by the primary and secondary division grooves results in a single chip region. Although a large substrate20A corresponding to a single chip region is illustrated as a representative inFIGS. 4 and 5, in actuality, each of process steps as described below is collectively performed on the large substrate corresponding to a large number of chip regions.

Specifically, after the front face of the large substrate20A is coated (e.g., screen printed) with glass paste, the resultant is dried and fired to thereby form the thermal storage layer2of a rectangular shape in a central portion of the front face of the large substrate20A as illustrated inFIG. 4AandFIG. 5A.

Then, after the back face of the large substrate20A is coated (e.g., screen printed) with Ag based paste, the resultant is dried and fired to thereby form the first back electrodes8and the second back electrodes9on the opposite sides of a predetermined space from each other on the back face of the large substrate20A as illustrated inFIG. 4BandFIG. 5B.

Then, a metal thin film such as of Cu, Ag and/or the like is deposited on the entire front face of the large substrate20A by sputtering (or evaporating), which is then patterned using photolithography to thereby form integrally the first front electrodes3and the second front electrodes4on the opposite sides of a predetermined space from each other, as well as the fuse elements5each running between the first front electrode3and the second front electrode4, as illustrated inFIG. 4CandFIG. 5C. Each fuse element5is formed in a Z shape in planar view on the thermal storage layer2, and has: the first linear portion5athat has an end connected to the first front electrode3and extends in parallel to the longitudinal direction of the insulating substrate1in a direction toward the second front electrode4; the second linear portion5bthat has an end connected to the second front electrode4and extends in a direction toward the first front electrode3; and the inclined linear portion5cthat links the first linear portion5aand the second linear portion5bto each other. The inclined linear portion5cis connected at an acute angle to each of the first linear portion5aand the second linear portion5b. The shortest distance from the center of the inclined linear portion5cto the back front electrode8and the second back electrode9is set to be longer than the shortest distance from the center of the inclined linear portion5cto the first front electrode3and the second front electrode4.

Then, after the front face of the large substrate20A is screen printed with glass paste, the resultant is dried and fired to thereby form the inner protective layers6so that each inner protective layer6covers parts of the first front electrode3and the second front electrode4and the entire fuse element5, as illustrated inFIG. 4DandFIG. 5D. In this way, the fuse element5is sandwiched between the thermal storage layer2and the inner protective layer6.

Then, after the front face of the large substrate20A is coated (e.g., screen printed) with epoxy-based resin paste, the resultant is heated and cured, to thereby form the protective layers7so that each protective layer7covers parts of the first front electrode3and the second front electrode4and the entire inner protective layer6, as illustrated inFIG. 4EandFIG. 5E.

Then, after the large substrate20A is primarily divided along the primary division grooves into strip-shaped substrates20B, end electrode materials are sputtered or evaporated (e.g., a Ni/Cr2 layer, a NiCr alloy, a Ni/Ti2 layer, a NiTi alloy) onto divided faces of each strip-shaped substrate20B to thereby form the first end electrodes10and the second end electrodes11on both ends of the strip-shaped substrate20B, as illustrated inFIG. 4FandFIG. 5F. Each first end electrode10provides continuity between the corresponding first front electrode3and the corresponding first back electrode8and each second end electrode11provides continuity between the corresponding second front electrode4and the corresponding second back electrode9.

And then, after the strip-shaped substrate20B is secondarily divided along the secondary division grooves into multiple chip substrates, electrolytic plating is added to each chip substrate to form a layer of Ni—Sn plating. Thereby, an external electrode (not shown) is formed to cover each of the surfaces of the first end electrode10and the second end electrode11. In this manner, the chip-type current fuse illustrated inFIGS. 1, 2is completed.

As described above, the chip-type current fuse according to the example embodiment is configured to include the fuse element5formed between the first front electrode3and the second front electrode4, the fuse element5including: the first linear portion5athat has an end connected to the first front electrode3and extends in parallel to the longitudinal direction of the insulating substrate1in a direction toward the second front electrode4; the second linear portion5bthat has an end connected to the second front electrode4and extends in parallel to the first linear portion5ain a direction toward the first front electrode3; and the incline linear portion5cthat links the first linear portion5aand the second linear portion5bto each other, and the inclined linear portion5cis connected at an acute angle to each of the first linear portion5aand the second linear portion5b. Therefore, the first linear portion5aconnected to the first front electrode3and the second linear portion5bconnected to the second front electrode4serve as locations that allows heat to escape readily (thermal dissipation portion), and the inclined linear portion5cformed between the first linear portion5aand the second linear portion5bis connected at an acute angle to each of the linear portions5a,5b. As a result, the heat produced in the fuse element5is concentrated on the vicinity of the center of the inclined linear portion5c, so that the vicinity of the center of the inclined linear portion5ccan be melted at stable timing.

Also, in the chip-type current fuse according to the example embodiment, because the fuse element5has a point symmetric shape which is symmetric about a point at the center O of the inclined linear portion5c(a Z shape in planar view), melting will stably occur in the vicinity of the center of the inclined linear portion5c. Furthermore, the shortest distance from the center of the inclined linear portion5cto the back front electrode8and the second back electrode9is set to be longer than the shortest distance from the center of the inclined linear portion5cto the first front electrode3and the second front electrode4. Because of this, the heat produced in the fuse element5is hard to be dissipated from the first and second back electrodes8,9located on the underside of the insulating substrate1, and therefore the vicinity of the center of the inclined linear portion5ccan be melted stably. Further, if an element formation region is defined between the first front electrode3and the second front electrode4which are formed on the front face of the insulating substrate1, the first back electrode8and the second back electrode9are placed on the outside of a back face region on which the element formation region is projected. In this respect, the vicinity of the center of the inclined linear portion5ccan also be melted stably.

It should be understood that although the first linear portion5a, the second linear portion5b, and the inclined linear portion5cof the fuse element5are approximately equal in length to each other in the above example embodiment, the relative length of each linear portion5a,5b,5cis not limited to the above example embodiment and, for example, the length of the inclined linear portion5cmay be sufficiently shorter than the first linear portion5aand the second linear portion5b.

LIST OF REFERENCE SIGNS