JPH087731A - Resistance/temperature fuse for board - Google Patents

Abstract

PURPOSE:To keep the resistance value of a film constant even though the current impression is put on and off repeatedly by covering the film resistor formed on a board with the first glass layer, adjusting the resistance value with laser trimming, and then putting a covering of a second glass layer. CONSTITUTION:A low melting point metal piece 4 is connected between a pair of film electrodes 2, 2 formed on one surface of a ceramic base board 1, and flux 5 is applied to the metal piece 4. An electrode part 21 for a gap is furnished on the way of one of the film electrodes 2. and a film resistor 6 is connected to this electrode part 21. A resistance paste is screen printed on this film resistor 6 in such a way as straddling the electrode parts 21, 21 of the film electrodes 2, followed by a baking process so that a film resistor 60 is accomplished. The film resistor 60 is covered with the first glass layer 61. and the resistance value is adjusted to the specified value by means of laser, trimming. Then a covering of a second glass layer 62 is put, and a cut slit 63 in the trimming is filled with the glass material of the second glass layer 62. When the film resistance beated by an eddy current in the circuit, the metal piece 4 melts.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a substrate type resistance / temperature fuse in which a temperature fuse element (low melting point metal body) and a film resistor are provided on a ceramic substrate.

[0002]

2. Description of the Related Art In a substrate type resistance / temperature fuse,
A low melting point metal body and a film resistor are provided on a ceramic substrate, and these are over-coated with an insulating material.The film resistor is inserted in the circuit of the protected equipment, and the low melting point is applied to the input side of the circuit. When a metal body is inserted and the membrane resistance heats up due to an overcurrent in the circuit, the heat generated causes the low-melting metal body to melt and cut off the power supply to the circuit, preventing abnormal heat generation of protected equipment. ing.

In this case, the low melting point metal body is coated with a flux, and the low melting point metal melted by the heat generated from the film resistance coexists with the already melted flux. While dissolving the oxide of No. 1, while smoothing, the particles are divided into spheroids to ensure quick operation.

To form a film resistor in the above-mentioned substrate type resistance / temperature fuse, a film resistor is provided on a ceramic substrate by printing / baking a resistance paste, and this film resistor is mounted.
A predetermined resistance value is set by adjusting the resistance value by the trimming. In the above-mentioned substrate type resistance / temperature fuse, it is safe to coat a protective layer on the film resistance so that the resistance value of the film resistance does not change due to contact with the flux. A glass layer is usually used.

However, if a glass layer is formed on the film resistor after trimming the film resistor, that is, if a glass frit is applied and fired, the resistance value adjusted by trimming is changed by the heating during firing. Since there is some fear, the film resistor is covered with a glass layer before trimming, and then trimming is performed.

Conventionally, in a chip resistor, a film resistor is provided on a ceramic substrate by printing / baking a resistance paste, glass frit is applied / baked on the film resistor, and a resistance value is predetermined by laser trimming. It is known that the value is set, and then, the glass frit is applied and fired to carry out an overcoat (Japanese Patent Publication No. 64-4325).
JP-B-6-18121 and JP-A-59-8302).

[0007]

On the other hand, in the above-mentioned substrate type resistance / temperature fuse, since the low melting point metal body, which is the temperature fuse element, is provided, the over-heat resistance is reduced.
It is not possible to use the coating and firing of glass frit on the glass (the low-melting metal body is melted by the heating of the firing), and the temperature is sufficiently lower than the melting point of the low-melting metal body.
The overcoat is limited to those that can be baked, and usually an overcoat made by room temperature curing of an epoxy resin is used.

However, according to the results of experiments conducted by the inventors of the present invention with respect to such substrate type resistance / temperature fuses, if the on / off of voltage application is repeated, for example, the substrate type resistance / temperature fuse
If the temperature fuse is used as an inrush power supply limiting element of a switching power supply, a considerable resistance value fluctuation cannot be avoided.

Therefore, the inventors of the present invention conducted various experiments in order to investigate the cause, and found that discharge was generated in the cutting slit for trimming the film resistance every time the switch was turned on and off. It is observed that the resistance value fluctuates because the cutting slit for trimming is eroded by repeating this discharge, and as if the trimming progresses further, the resistance value of the membrane resistance fluctuates. It is estimated to be.

An object of the present invention is to provide a substrate type resistance / temperature fuse capable of keeping the resistance value of the film resistance adjusted by trimming sufficiently constant even when the power is repeatedly turned on and off. .

[0011]

A substrate type resistance / temperature fuse according to the present invention is provided with a low melting point metal body and a film resistor on a ceramic substrate, and the film resistor is used for printing a resistance paste. The film resistor formed by baking is provided by coating the first glass layer and then adjusting the resistance value by laser trimming, and the second glass layer is provided on this film resistor. It is preferable that the ceramic substrate is covered with a resin so as to cover the low melting point metal body, and the first glass layer and the second glass layer are made of the same material.

The structure of the present invention will be described below with reference to the drawings. 1A is a plan explanatory view of an example of the substrate type resistance / temperature fuse according to the present invention, and FIG.
The cross-sectional views along line (a) of FIG.
In FIG. 1A and FIG. 1B, 1 is a ceramic substrate. Reference numerals 2 and 2 are a pair of membrane electrodes provided on one surface of the ceramic substrate 1, and 3 and 3 are lead wires connected to the respective membrane electrodes 2 and 2. Reference numeral 4 is a low-melting metal body connected to the tip between the membrane electrodes, and 5 is a flux applied on the low-melting metal body 4, and a part of this flux is applied to the low-melting metal body 4 and the substrate 1.
It can be invaded between and. Reference numeral 21 is a gap electrode portion provided in the middle of one of the membrane electrodes, and 6 is a membrane resistance connected to the gap electrode portion 21.

In the membrane resistor 6, as shown in FIG. 2, a resistance paste is screen-printed across the gap electrode portions 21 and 21 of the membrane electrode, and is fired to burn the membrane resistor 6. A body 60 is provided, a first glass layer 61 is coated on the film resistor 60 by coating and baking glass frit, and then the resistance value is adjusted by laser trimming to set a predetermined resistance value. After that, the second glass layer 62 is covered by coating and baking glass frit, and the trimming cutting slit 63 is filled with the glass of the second glass layer 62.

Different glass frits can be used for the first glass layer 61 and the second glass layer 62, but both glasses are integrated, a frit coating device is commonly used, and frit mixture management is performed in a single manner. It is preferable to use the same glass frit in terms of chemical conversion.

1 (a) and 1 (b), 7 is an overcoat of an insulating resin, and an epoxy resin liquid is applied dropwise to the insulating resin and cured at room temperature. Is preferred.

The board type resistance / temperature fuse is used by inserting a film resistor into the circuit of the protected equipment and inserting a low melting point metal body into the input side of the circuit,
When the film resistance generates heat due to the overcurrent of the circuit, the heat generated causes the low melting point metal body to melt and operate.

FIG. 3A is a plan view of another example of the substrate type resistance / temperature fuse according to the present invention, FIG. 3B is a bottom view of the same, and FIG. 3A is a sectional view taken along the line of FIG. 3A, and FIG. 3D is a sectional view taken along the line II of FIG. (A) of FIG.
3 (d), 1 is a ceramic substrate. Reference numerals 2a and 2a denote a pair of membrane electrodes provided on one surface of the ceramic substrate, and include a lead wire attachment portion 201 and a low melting point metal body attachment portion 202. 3a and 3a are each membrane electrode 2
It is a lead wire connected to a and 2a. 4 is the membrane electrode 2a,
A low melting point metal body connected by welding or welding between 2a,
5 is a flux applied to the low melting point metal body 4.

2b and 2b are on the other surface of the ceramic substrate 1,
There are two pairs of symmetrically provided membrane electrodes, and strip-shaped membrane electrodes 204 each having a lead wire attachment portion 203 at one end are arranged so that the lead wire attachment portions 203 are located at both left and right ends of the ceramic substrate 1. It is provided.

A reference numeral 6 extends between each pair of membrane electrodes 2b, 2b,
It is a film resistance provided on the other surface of the ceramic substrate 1. As shown in FIG. 2, each pair of film electrodes 204, 2 of the resistance paste.
Forming each film resistor 60 by printing and firing across 04, and applying the glass frit and firing the first glass layer 6
Formation of 1 (as shown in (b) of FIG. 3), it may be generally covered over both the left and right membrane resistors, or may be coated on each of the membrane resistors], 1st Rays from the glass layer side
Setting of a predetermined resistance value by adjusting the resistance value of each film resistor by the trimming, application of the glass frit on the first glass layer 61 after trimming, and firing of the second glass layer 6
2 [similarly to the first glass layer 61, it may be covered over both the left and right film resistors, or may be covered over the individual film resistors].

In FIG. 3 (a) to FIG. 3 (d),
Reference numeral 3b is a lead wire connected to each of the membrane electrodes 2b by welding or welding. A resin overcoat 7 is provided on both sides of the ceramic substrate 1 so as to cover the low melting point metal body 4 and the film resistor 6, and is coated with an epoxy resin solution by a dipping method and cured at room temperature. Preference is given to using.

In the substrate type resistance / temperature fuse shown in FIGS. 3 (a) to 3 (d), one membrane resistance is provided in a portion where the circuit is present and the other is provided in the electric circuit to be protected. Are used by inserting and connecting the membrane resistance of each of the other to the other part of the same circuit, and inserting and connecting the low melting point metal body to the input end of the same circuit. When the body heats up, the generated heat melts the low melting point metal body to cut off the power supply to the circuit.

In each of the above substrate type resistance / temperature fuses, conductive particles (eg, Ag-Pd based metal, Ag-Pt based metal, Ag based metal, etc.) are used to form the membrane electrodes 2, 2a and 2b. A method of screen-printing a conductive paste formed by mixing a Cu-based metal) and a glass frit and firing the conductive paste can be used. For forming the film resistor 60, resistor particles (eg ruthenium oxide) are used. , Lanthanide boride (LaB ₆ ),
A method of screen-printing a resistance paste formed by mixing doped tin oxide] and a glass frit and firing the same can be used.

In the above, the low melting point metal body 4 is made of tin,
It is preferable to use a eutectic alloy of two or more kinds such as lead, indium, bismuth, and cadmium at a predetermined temperature. The flux 5 may be rosin as a main component and an activator (organic chloride, organic bromide, etc.) added thereto.

In the above, the ceramic substrate 1 is required to have excellent thermal conductivity, and alumina is usually used, but SIC, AIN, etc. can also be used. In the above-mentioned substrate type resistance / temperature fuse, the film resistor coated with the first glass layer is trimmed, the second glass layer is coated, and then the low-melting metal body is welded between the film electrodes, by contact bonding or the like. Manufactured in the connecting work sequence. Further, the second glass layer covers the entire surface of the first glass layer, but it is not always necessary to cover the entire surface of the first glass layer as long as the cutting slit for trimming can be filled with glass. .

In the above, the surface of the resin overcoat (usually black) has a predetermined indication such as rating (usually, black).
(White, yellow, orange) is printed.

[0026]

The cutting slit cut from the first glass layer into the film resistor by laser trimming is filled with the glass of the second glass layer, and the cutting edge of the film resistance is covered with the glass. Even if the power is turned on and off repeatedly, it is possible to sufficiently prevent the discharge at the trimming cutting slit.

Further, the first glass layer acts as a thermal resistance against the conduction of the heat of firing of the second glass layer to the film resistor, so that the film resistor is sufficiently heated and deformed when the second glass layer is fired. Can be prevented.

Therefore, the resistance value of the film resistance set by trimming can be kept sufficiently constant by well eliminating the discharge erosion and the heat deformation of the film resistor, and the operation can be performed by the fluctuation of the resistance value of the substrate type resistance / temperature fuse. You can eliminate defects. This is
It is clear from the comparison between the example and the comparative example described below.

[0029]

【Example】

[Embodiment] A substrate-type resistance / temperature fuse having the configuration described in FIGS. 3 (A) to 3 (D) and FIG. The ceramic substrate has a thickness of 0.6 mm, a length of 9 mm, and a width of 14 m.
First, all the membrane electrodes were formed with a thickness of 25 μm by printing and baking with silver paste.

Further, the film resistor is provided with a resistance paste (a mixture of ruthenium oxide powder and glass frit) having a thickness of 20 μm.
m by printing and baking (baking temperature 900 ° C.), and the first glass layer has a low melting point glass frit thickness of 40 μm.
It is provided by applying and baking m (baking temperature 500 ° C).
Trimming the resistance value of both film resistors to 1000Ω
Adjusted to. After this trimming, the second glass layer was formed by applying and baking a low melting point glass frit with a thickness of 40 μm (baking temperature 500 ° C.).

Next, a copper lead wire having a diameter of 0.6 mm was connected to each membrane electrode. Furthermore, diameter 0.5mm, liquidus temperature 9
A low melting point metal wire at 6 ° C. was connected, and a flux containing rosin as a main component was applied onto the low melting point fusible alloy wire. Finally, epoxy resin liquid (viscosity 200
00 cps to 50000 cps) is applied by the dipping method,
Cured at room temperature.

Comparative Example The same as the example except that the coating of the second glass layer was omitted.

For each of these example products and comparative example products (the number of each sample is 50), one film resistance and one low melting point metal body are connected in series, and 500 V is 30 μm.
When the resistance value of each film resistance was measured after 100 cycles had elapsed by repeatedly applying electricity for 2 seconds on and 10 seconds off, all of the examples showed a resistance value variation of within ± 5%. On the other hand, in the comparative examples, the resistance value variation is ± 10% or more,
When the ceramic substrate was peeled off, the second glass layer was exposed, and the trimming trace was observed with a magnifying glass, traces of discharge were found.

[0034]

In the substrate type resistance / temperature fuse according to the present invention, the cutting slit of the first glass layer coating film resistor whose resistance value is adjusted by laser trimming is used as the glass of the second glass layer. Since it is filled with, the discharge at the cutting slit can be well prevented, and the fluctuation of the resistance value during use can be sufficiently avoided. In this case, the overcoat is performed with resin,
Since the coating of the second glass layer is limited only to the film resistance,
The discharge can be prevented without adversely affecting the low melting point metal body.

[Brief description of drawings]

1 (a) is a plan explanatory view showing an example of a substrate type resistance / temperature fuse according to the present invention, and FIG. 1 (b) is FIG.
It is a sectional view taken along line (a) of FIG.

FIG. 2 is a cross-sectional explanatory view showing a structure of a film resistor used in the present invention.

3 (a) is a plan view of another example of the substrate resistance / temperature fuse according to the present invention, FIG. 3 (b) is a bottom view of the same, and FIG. 3 (c). Is the line in (a) of FIG.
3C is a sectional view, and FIG. 3D is a sectional view taken along line II in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ceramic substrate 2 Membrane electrode 2a Membrane electrode 2b Membrane electrode 3 Lead wire 3a Lead wire 3b Lead wire 4 Low melting point metal body 5 Flux layer 6 Membrane resistance 60 Membrane resistor 61 First glass layer 62 Second Glass layer 63 Cutting slit for trimming 7 Overcoat of resin

Claims (2)

[Claims] 1. A low melting point metal body and a film resistor are provided on a ceramic substrate, and the film resistor is formed by printing and baking a resistance paste, and then covering the film resistor with a first glass layer. A second glass layer is provided on the film resistor by adjusting the resistance value by laser trimming, and the ceramic substrate is coated with a resin so as to cover the film resistor and the low melting point metal body. Substrate type resistance / temperature fuse characterized by
Z. 2. The substrate type resistance / temperature fuse according to claim 1, wherein the first glass layer and the second glass layer are made of the same material.