JPS5823138A - Fuse circuit board - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fuse circuit board used, for example, in a harness circuit of an automobile.

In automobile harness circuits, it may be necessary to insert fuse elements at appropriate locations. However, in the case of the conventional pipe type fuse (1)? E: Wire breaks often occur not due to electrical causes, but due to mechanical causes such as vibration. In Utility Application No. 55-18999, the applicants have already disposed circuit elements on an insulating substrate and provided a thin film-like fusing portion made of the same material as the connecting end portion attached to the insulating substrate. proposed a circuit element-equipped board that is resistant to mechanical shock and also has a fuse function. However, in actual use, because this fusing part is made of the same material as the connecting end made of copper foil, in some cases, when an overcurrent flows and the fusing occurs, smoke is generated due to heat generation. In addition, it was discovered that there was a problem with fuse rating adjustment.

For this type of fuse circuit board, the connection ends are formed by etching an insulating substrate to which reliable metal foil, such as copper foil, is attached during connection, or by directly chemically plating the insulating substrate. It is conceivable to electrically connect the fuse material between the connecting ends later on. However, the method of attaching a wire or sheet fuse made of an alloy of tin and lead to a circuit board is complicated and requires screws.
It is unsuitable for the purpose of miniaturization due to its shape and capacity, and has the drawback of lacking stability at the connection part and being susceptible to destruction due to vibrations, thermal distortion due to cooling/heating cycles, etc. Another method is to attach a low melting point material as a fuse circuit part to an insulating board, mask a certain part with plating, and plate copper etc. up to the connection end.
Plated bamboo pipes cannot be made because the ionization tendency of low melting point materials and connection end materials such as copper and silver are opposite. When a fuse circuit is created using a thick film printing method, the low melting point metal particles do melt, but the fuse often does not blow. This is because the thick film ink is cured by surrounding the metal particles with a binder, and this binder prevents the molten metal from aggregating due to surface tension and from fusing as a result. For example, JP-A-50-5
The safety circuit using the thick film printing method disclosed in No. 3851 is a type in which the metal vaporizes at normal pressure and fuses, and the melting temperature is considerably high, and the conductor part is covered with an insulating film. , the amount of smoke generated due to thermal decomposition of the substrate and coating insulation film is extremely large.

An object of the present invention is to eliminate the above-mentioned drawbacks, and provide a fuse circuit board in which the fusible part acts as a fuse at a low temperature reliably against excessive current, is resistant to mechanical shock, and is easy to replace. Its contents include a pair of connecting ends formed on an insulating substrate, and a strip-shaped fusible body part made of a fuse material that connects the connecting ends via a circuit element. , at least the connecting end portion is characterized in that the lower layer is a fuse material that is continuous with the fusible portion, and the upper layer is covered with a protective metal foil or the like.

The present invention will be explained in detail based on illustrated embodiments.

In FIG. 1, numeral 10 is an insulating substrate made of synthetic resin that is approximately cross-shaped and has a short axis in the horizontal direction of the drawing and a long axis in the vertical direction, and both ends of the short axis are covered with metal foil on the back side. A conductive thin film layer such as the like is applied, forming a plug-in connection end 11, 12 for connection with a connection terminal or the like. As shown in FIG. 1(a), an electronic circuit element 16 such as a diode is fixed to the front side of the long axis portion of the insulating substrate 1o, with its longitudinal direction matching the direction of the long axis portion, and both ends of the electronic circuit element 16 are fixed. lead end 14 of
．． 15 is connected by solder or the like to a conductor portion 16.17 made of a conductive thin film layer made of the same material as the connecting end portion 11.12 attached to the back side, as shown in FIG. 1(b). The conductor portion 16 to which the lead end 14 is connected is integrally connected to the connection end portion 11, but the conductor portion 16 to which the lead end 15 is connected is integrally connected to the connection end portion 11.
7 is connected to the connecting end portion 12 via the fusible body portion 18 . This fusible body portion 18 is made of a low melting point fuse material made of, for example, an alloy of zinc or tin, which is thinned and adhered in the form of strips. Further, the length and width of the fusible body part 18 are set to predetermined dimensions so that it can be reliably fused at a low temperature against an overcurrent. As shown in FIG. 1(C), the fuse material is also provided in the lower layer of the connection end 11.12 and the conductor portion 16.17, and in these areas, a double layer with a conductive thin film layer is applied on top of the fuse material. It has a layered structure.

This fuse circuit board is used by being housed in housings 21 and 22, for example, as shown in FIG. That is, the housings 21 and 22 have a structure that allows them to be combined by fitting into each other, and have a cavity 23 in which a fuse circuit board can be accommodated inside the combination, and each housing 2L 22 has a Receiving terminals 24.25 for electrical connection with a pair of insertion connection ends 11.12 of the fuse circuit board are built in, and are led out to the outside by electric wires 26.27 connected to these, respectively.

FIG. 3 shows another embodiment of a fuse circuit board, in which a circuit element 13' is arranged on an insulating substrate 10' having a pair of rectangular leg-shaped insertion connection ends 11' and 12'. ing. A conductive thin film layer made of metal foil is provided on the fuse material at the connecting ends 11' and 12', and the conductor part 17' to which the lead end 15' of the circuit element 13' is fixed has a predetermined length and width. The connecting end 12' is connected to the connecting end 12' through a fusible portion 18' made of a thin film layer of fuse material. On the other hand, the lead end 14' is connected to the connection end 11 through the conductor part 16'.
'It is connected to the.

In these fuse circuit boards, when an excessive flow exceeding the rating flows, the fusible body portion 18,18' made of the fuse material generates heat and melts due to its resistance value, thereby preventing the circuit elements 16,16' and other articles from catching fire. As will be described later, the amount of heat generated by this fusible portion 18, 18' can be made extremely small by appropriately selecting its material, dimensions, etc. Moreover, since it melts instantaneously at a low temperature, there is no thermal influence on other circuit elements, etc. Not at all. Furthermore, since a protective conductive thin film layer is provided on the fuse material at the connection ends 11.11', 12.12', etc., the electrical connection characteristics between the fuse material and the conductive thin film layer are It is in good condition and will not be damaged when inserted or removed.

In manufacturing this fuse circuit board, for example, a base material such as paper or glass cloth impregnated with a thermosetting resin and a metal foil as a fuse material are cured under heat and pressure to produce a metal foil laminated board. Next, an etching resist is applied to areas other than the predetermined circuits that will become conductive parts such as connection ends, conductor parts, and fusible parts, and after etching and peeling off the resist, the predetermined circuits are formed.
There is a method of forming a conductive thin film layer on the connection end portion and the conductor portion using a silk screen method or the like. Further, the formation of a predetermined circuit which becomes a conductive part using the fuse material can also be carried out by applying a methishresist to areas other than the predetermined circuit and chemical plating.

For the fusible part, we set the conditions that it would not melt at 12 volts and 2 amperes, and that it would melt within 1 minute at 3 amperes, and that the amount of smoke emitted until melting would be small and that it would not catch fire. , the melting point of the metal material is 250 to 500°C, the cross-sectional area of the strips of the fusible part is o,
oos~0.05ij, width is 1.51! Dimensions within I are required. If the melting point of the metal material exceeds 500° C., the amount of smoke emitted before melting increases significantly, which is not preferable. or,
If the melting point is lower than 250℃, the melting point will be too low, and the workability of soldering when fixing circuit elements will deteriorate, and the length of the fusible part will be considerably reduced! , 2, and the resistance of this part must be increased, otherwise the circuit other than the fusible part will melt. As the metal to be mixed for the purpose of the present invention, zinc is particularly preferred, and alloys of zinc, tin, lead, etc. can also be used. On the other hand, even if these metal foils with relatively low melting points are used, if the value in the circuit exceeds 1.511, the fusible portion will melt, but it will not be sufficiently isolated, so it has been confirmed that it is difficult to use it for safety circuits. ing. The narrower and thicker the width of the strip, the more reliable the fusing becomes, and it is particularly preferably within 0.8 mm.
The minimum width is limited to about 0.21 m1 due to printing technology constraints. The amount of heat generated by the fusible portion depends on its length and cross-sectional area, but if the cross-sectional area is smaller than o, oos-, it will be fused with a very small current and will be impractical. Moreover, if it is larger than 0.05, it will not melt unless the length is made very large and the amount of heat generated is increased, and the amount of heat that escapes also increases, making it unsuitable for small fuse circuit boards.

Although the above-mentioned fusible portion has been considerably improved, the insulating substrate is thermally affected by heat generation during melting, and it is difficult to completely eliminate smoke and gas generation. To prevent the generation of smoke and gas, for example, Evokin resin, polyester,
It is effective to form a film on the soluble portion using a polymeric material made of a thermosetting resin such as polyurethane. This eliminates the generation of gas and smoke, and if a polymeric material with particularly poor thermal conductivity is used, the amount of heat that escapes is reduced, so the time for fusing is shortened slightly and the time becomes constant.

Furthermore, this polymer material coating also prevents water from adhering to the fuse material and preventing sulfur dioxide gas from coming into contact with it, and has the advantage of maintaining long-term durability.

As described above, the fuse circuit board according to the present invention has a fusible part made of a fuse material on an insulating substrate, and the other conductive parts have a two-layer structure of a conductive thin film layer and a fuse material. It has the advantage of being able to reliably fuse at low temperatures due to overcurrent, being easy to manufacture, and being resistant to mechanical shock.

[Brief explanation of the drawing]

Figure 1 shows an embodiment of the fuse circuit board according to the present invention, in which (a) is a plan view, (b) is a back view, and (C) is a view taken along line C-C in (1)). 2 is a longitudinal sectional view showing the fuse circuit board accommodated in the housing, and FIG. 3 is a plan view of another embodiment of the fuse circuit board. Code 10.10' is an insulating substrate, 11.11', 12.1
2' is an insertion connection end, 16.16' is a circuit element, 18.
18' is a soluble portion. Connection 10 (G) tb) (C)

Claims (1)

[Claims] 1. A device comprising: a pair of connecting ends formed on an insulating substrate; and a strip-shaped fusible portion made of a fuse material that connects the connecting ends via a circuit element; 1. A fuse circuit board characterized in that at least a connecting end portion has a lower layer of fuse material continuous with the fusible portion, and an upper layer thereof is covered with a protective metal foil or the like. 2. The fuse circuit board according to claim 1, wherein the fusible portion is coated with a polymeric material. 3. As the fuse material, a material with a melting point of 250 to 50°C is used, and the cross-sectional area of the fusible part is 0.005 to 0.05.
The fuse circuit board according to claim gS1, wherein -1 width is within 1.5 width.