JPH0433230A - Chip type fuse - Google Patents

Abstract

PURPOSE:To safely cut off the short circuit current and give high circuit stability by providing narrow sections narrower in width than the other conductive sections on multiple conductive sections crossing the opposing directions of end electrodes of a corrugated conductor. CONSTITUTION:Multiple conductive sections 4a1 perpendicular to the opposing directions of end electrodes 3 and curved conductive sections 4b connecting the adjacent conductive sections 4a1 and curved into a circular arc shape are arranged in turn for a conductor 4 to form a nearly rectangular wave-form, and narrow sections 4a2 narrower in width than the other conductive sections are formed at the center sections of the conductive sections 4a2. A thinner electroless nickel/phosphorus film 5 is formed on the thin metal film of the conductor 4 thus formed. The thin metal film forming the conductor 4 is made of copper, copper-zinc alloy, silver and their mixture.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is applicable to printed circuit boards of electronic devices and hybrid I
This relates to a chip fuse that surface-mounts safety components of C.

<Prior Art> In recent years, as electronic devices have become lighter, thinner, shorter, and smaller, high-density surface-mounted circuit boards are increasingly being used. Among them, hybrid ICs, which are composed of semiconductor pair chips with built-in power supply circuits, are particularly densely mounted on small-area substrates and sealed with resin. As a safety measure for these devices, surface-mountable chip type fuses are used.

A conventional chip-type fuse is known in which a conductor made of a thin metal film is formed in a recess provided on the bottom surface of an insulating chip substrate, and this is electrically connected to both end surfaces of the chip substrate. Utility Model Publication No. 61-11881).

In addition, when time lag performance is required as a function of the fuse element, the conductor 44a is formed into a rectangular wave shape (Fig. 4(a)), and when fast-acting performance is required, the central part of the conductor 44b is is formed to be narrower than both sides (fourth
Figure (b)) etc. were carried out.

<Problems to be Solved by the Invention> However, when the shape of the conductor is a rectangular wave shape, as is well known, the current has a property of passing through the shortest path between the conductors, and the shape of the conductor is shown in Fig. 4 ( Given the rectangular wave shape shown in a),
A large amount of current flows through the corner 45 which is the shortest path, and this corner 4
Melting starts from No. 5, and the location and state in which the melting occurs varies depending on various conditions. Furthermore, since the electric field concentrates on adjacent corners 47 on the outer periphery of the conductor, abnormal discharge may occur between the corners 47 or between other mounted components in the vicinity. Ta.

Therefore, when the conductor has a rectangular wave shape and has time lag performance, when the power supply voltage becomes high such as 250 VAC, the fuse element (metallic thin film conductor) is partially melted and vaporized by the short circuit current, and the circuit is interrupted. In some cases, the insulation gap caused by the melting is narrow, and the back electromotive force generated by the 250V voltage applied across the gap or the inductance of the circuit is also added, and the discharge starts again, developing into a re-arc and damaging the entire electronic circuit. There is a risk of major fire damage spreading to the area. Especially the 3216 type (length 3.2
Currently, there are no small chip-type fuses such as the 9 (1.6 mm wide, 0.5 m thick) that can safely interrupt the circuit.

It is also known that chip-type fuses having a structure in which the fuse element is insulated in advance with a silicone resin film do not have sufficient arc extinguishing ability to absorb arc energy after blowing out in an AC 250V circuit. Furthermore, simply coating the fuse surface with silicone resin is insufficiently effective because the mechanical stress applied during the numerous handling steps required to manufacture and automatically mount the chip-type fuse weakens the adhesion between the fuse element and the silicone resin film. The drawback was that it was not as expected.

Furthermore, when a narrow pinched part is formed in the center of the conductor to provide quick breaking performance, if the pinched part 46 is concentrated in one part as shown in FIG. The resulting insulation gap is small, and AC250V (peak value 355Vp)
) circuit could not prevent re-arc. Furthermore, since excessive power is concentrated in a limited narrow portion, thermal deterioration, that is, carbonization, of the surrounding insulating material is promoted, which also leads to re-arcing. There are also other problems with inrush currents, such as changes in resistance due to partial heating.

The present invention was made in order to solve the above-mentioned drawbacks, and in a circuit with a power supply voltage of 250 VAC or less, it normally acts as a resistor with little change in resistance value, and in the event of an abnormality such as a short circuit, it can safely cut off the short circuit current. The purpose is to provide a chip-type fuse that exhibits high circuit stability.

<Means for Solving the Problems> The present invention has been made in view of the above-mentioned objects, and the gist thereof is lI! The chip substrate has a peripheral chip substrate, a pair of end surface electrodes formed on opposing both sides of the chip substrate, and a wavy conductor formed on the top surface of the chip substrate to electrically connect the pair of end surface electrodes. In chip type fuses,
The chip-type fuse is provided with a plurality of conductive parts of the wave-shaped conductor that cross the direction in which the end face electrodes are opposed to each other, and provided with narrow portions having a narrower width than other conductors.

Further, the conductor may form the waveform by alternately arranging conductive portions provided with the narrow portions and curved conductive portions curved in an arc shape.

Furthermore, the metal thin film forming the conductor is formed from copper, copper-zinc alloy, silver, or a mixture thereof, and an electroless nickel-phosphorous film is formed on the metal thin film of the conductor to coat the surface. It may be covered.

Note that the waveform includes all other waveforms such as a sine wave, a rectangular wave, and a trapezoidal wave.

Effects> If an overcurrent flows during a short circuit or the like, the conductor is reliably fused at the plurality of pinched portions. Further, the fusing of the plurality of narrow portions acts to obtain a desired insulation gap between the end face electrodes. .

<Example> First, a chip type fuse according to the present invention will be explained based on the accompanying drawings.

Chip type fuse 1 is +! 1! Edge chip substrate 2 (
Length 3. 2++wnt @1.6mm, thickness 0.5a
m), a pair of end face electrodes 3 formed on opposite sides of the chip substrate 2, and a conductor 4 made of a metal thin film that electrically connects the pair of end face electrodes 3.

The metal thin film forming the conductor 4 is formed by sputtering or vacuum deposition, which is known as a dry method, and then a film formed by electroless plating or electroplating, which is known as an immersion method, is superimposed thereon. Copper, copper-zinc alloy, silver, mixtures thereof, etc. can be used as the material. A conductor 4, which will become a fuse element, is formed on the metal thin film by patterning it using conventional photoetching.

The shape of the conductor 4 is such that a plurality of conductive parts 4a perpendicular to the facing direction of the end electrode 3 and an adjacent conductive part 4a1
Curved conductive portions 4b connected to each other and curved in an arc shape are arranged alternately to form a substantially rectangular waveform. Further, a narrow portion 4a having a narrower width than other conductive portions is formed in the center of the conductive portion 4a□.

Further, on the formed metal thin film of the conductor 4, an even thinner electroless nickel/phosphorous film 5 is formed.

Next, the end face electrode 3 is formed by a known method. First, plating base electrodes 6 are formed on opposing sides of the chip substrate 2, thick copper plating is applied to the electrical connections between the plating base electrodes 6 and the conductor 4 to form copper electrodes 7, and finally the copper electrodes 7 on top,
During surface mounting, solder plating with good solder wettability is performed to form plated electrodes 8, which serve as end surface electrodes 3. Instead of the solder plating, copper plating may be followed by thin nickel plating, and gold displacement plating may be performed on the conductor 4 as well.

When an overcurrent flows through the chip-type fuse l formed as described above, the conductor 4 is instantly and reliably fused at each of the pinched portions 4a2 to cut off the current. In addition, when this melting occurs,
Due to the presence of a plurality of pinched portions 4a2 in the conductor 4 and the waveform formation of the conductor 4, it exhibits a kind of time lag performance, and an insulating gap that can sufficiently prevent re-arcing is created between the electrodes 3 on both end faces. You can definitely get it. At this time, the curved conductive portion 4a1 of the conductor 4 is attached to the curved conductive portion 4a1 shown in FIG.
Since there is no corner 45 as shown in a), the current flows in a substantially negative direction over the entire width of the curved conductive portion 4a1, so that partial melting at this location is reduced.

Further, the chip type fuse can be formed into an end surface electrode 3 by providing side through holes 9 on both opposing sides of the chip base Fi, 2 as shown in FIGS. 2(a) and 2(b).

After mounting the chip-type fuse 1 on the circuit board, applying a silicone resin coating and epoxy resin sealing treatment prevents arcing due to metal vapor generated at the fused portion of the conductor 4, and Demonstrates highly reliable circuit breaking performance.

A fusing test using alternating current was conducted using three types of chip-type fuses shown below.

<Test method> Chip type fuses A and B serve as test sample 36.

After soldering 34 to the test circuit board 30 and attaching the drawer door 31, the upper surface of the test circuit board 30 is covered with silicone resin 35. Thereafter, it is inserted into the center of the test case 32, and epoxy resin 33 is cast around it. In this state, test voltages of 200V, 250V, and 300V are applied between the extraction leads 31, and the number of chip-type fuses that break down abnormally is determined.

<Test object> A...Chip-type fuse according to the present invention shown in FIG. 1 above.

B: A chip-type fuse in which the narrow portion 4a2 is not formed in the conductive portion 4a1 in the above A, and the conductor 4 is formed with the widths of the conductive portion 4a and the curved conductive portion 4b all being constant.

C: A chip type fuse in which the conductor 4 is formed into the rectangular wave shape shown in FIG. 4(a).

Main resistance values (A, B, C)---1,1+0.1Ω Test results> The test results are shown in Table 1.

Table 1 Number of abnormally broken pieces in the fusing test (test quantity: 200 pieces) The situation after the fusing test with the chip type fuse A is between the both end face electrodes around the narrow part 4a2 provided in parallel in the direction of the both end face electrodes 3. A wide insulation gap is formed,
Along with the synergistic effect of the arc-extinguishing effect of silicone resin,
Both arc discharge voltages are increased. On the other hand, in the case of a chip-type fuse B that does not have the narrow part 4a2 or a chip-type fuse C that is a conventional product, the discharge location is not specified, and the conductor 4 also has an angular shape (see C), so re-arcing occurs. The voltage also became low, causing abnormal breakdown due to re-arcing, and it was confirmed that it was not functioning adequately as a circuit breaker element.

As mentioned above, the chip type fuse A is a hybrid I which is coated with silicone resin in a circuit of AC300v or less.
It is a highly reliable element as a fuse used in C circuits, is extremely useful as a safety component, and can be mass-produced with common specifications such as square chip resistors.

<Effects of the Invention> The chip-type fuse according to the present invention has a plurality of conductive portions that electrically connect a pair of end surface electrodes, that is, a plurality of conductive portions that cross with respect to the opposing direction of the end surface electrodes. A configuration was adopted in which a narrow portion is provided that is narrower than other conductors. Therefore, when an overcurrent flows, the conductor is reliably cut off by the plurality of small parts, so a desired insulation gap can be obtained between the end electrodes, and high circuit safety is achieved. be.

[Brief explanation of drawings]

FIG. 1(a) is a plan view showing a chip-type fuse according to the present invention, FIG. 1(b) is a sectional view taken along the line 1-IJi in FIG. 1(a), and FIG. 2(a) is another embodiment. 2 (b)
) are cross-sectional views taken along line nn in Figures 2(a) and (7), and Figure 3(a).
Figure 3(b) is a side view showing the test condition, Figure 3(a) is
FIGS. 4(a) and 4(b) are plan views showing a conventional chip type fuse. 1... Chip type fuse, 2... Chip substrate, 3... End surface electrode, 4... Conductor, 4ai... Conductive part, 4a,...
Pincer part, 4b... curved conductive part. ! /Figure tσノ(b) Figure (b)

Claims (1)

[Scope of Claims] 1) An insulating chip substrate, a pair of end surface electrodes formed on opposite sides of the chip substrate, and an electrical connection between the pair of end surface electrodes formed on the top surface of the chip substrate. In a chip type fuse having a waveform conductor, a plurality of conductive portions of the waveform conductor that cross the direction in which the end face electrodes face each other are provided with narrow portions having a width narrower than other conductors. A chip type fuse characterized by being provided with. 2) The chip type according to claim 1, wherein the conductor is formed by alternately arranging conductive parts provided with the narrow portions and curved conductive parts curved in an arc shape to form the waveform. fuse. 3) The metal thin film forming the conductor is formed from copper, copper-zinc alloy, silver, or a mixture thereof, and an electroless nickel-phosphorus film is formed on the metal thin film of the conductor,
The chip type fuse according to claim 1, characterized in that the surface is coated.