JPH0656734B2 - Thermal fuse - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a thermal fuse that ensures a circuit breaking operation due to a temperature rise.

[Conventional technology]

The thermal fuse of the present invention is, for example, a resistance circuit board used in a ventilation control device for an automobile, and is attached to a flat resistance board that controls an air flow rate by changing a voltage applied to a fan motor. When the temperature rises beyond this, it melts and cuts the circuit to prevent damage to the device. The resistance substrate is an enamel substrate in which a enamel layer is fired on the surface of a core material such as a steel plate, and a thick film paste (Ag-Pd system or the like) having an appropriate electric resistance is printed and fired on the surface to form a circuit. A conductor is formed and used as a resistance substrate. The thermal fuse is equipped with plate solder or thread solder between the ends of the discontinuous part provided in the middle of this circuit conductor, or by applying a metal paste of a low melting point metal by screen printing and heating between the ends. Is formed.

[Problems to be solved by the invention]

However, since the thread solder is cut to an appropriate length, it is placed between the ends, and a trowel is applied to melt the solder on the ends to connect the ends, so the amount of solder used is large. In some cases, even if it melts when the temperature rises, it becomes one large liquid mass and the ends are still connected. Therefore, the circuit may not be cut off and may not function as a fuse that should operate at a predetermined temperature. Further, when the fuse is formed by screen printing or the like, the present applicant has applied for an invention in which the thickness of the fuse is 0.1 mm to 1.0 mm in order to improve such a point (Japanese Patent Application No. 63- 25211
No. 0). However, there are problems that the operating temperature varies depending on the shape of the end portions and the distance between the end portions, and even if the fuse is melted, the fuse is not separated and the circuit is not cut off. Also, when mounting the circuit board with tilting, many fuses will be accumulated on the lower end side,
At this time, the fuse that could not be sufficiently held could come into contact with the other end portion and the circuit could not be cut off. Furthermore, if the surface of the fuse is in an oxidized state,
There has been a problem that the fused fuses are not satisfactorily aggregated and the circuit is not reliably cut off.

[Means for Solving the Problems]

The present invention is as follows in order to solve the above problems.
That is, in the thermal fuse that electrically connects between the ends of the discontinuous portion of the circuit divided in the vertical or inclined direction, the lower end of the ends is wider and has a larger area than the upper end. It is a substrate-type thermal fuse used in a tilted or vertical state in which is expanded.

[Work]

When a thermal fuse that connects the ends of the discontinuous portion of the circuit divided vertically or in the inclined direction is heated to a temperature higher than the melting temperature of the fuse, it is melted and surface tension acts at the same time. Is held, the fuse is not left between the ends, and the circuit is surely cut off.

〔Example〕

Examples of the thermal fuse according to the present invention will be described below.

The substrate on which the thermal fuse is mounted is a porcelain enamel layer centered around a steel core material, and a conductor circuit is printed and fired on the surface of the enamel layer to form a resistance circuit. The conductor paste is made of Ag-Pd or the like and has an appropriate electric resistance value. The conductor paste is printed on the circuit board by screen printing or the like and then fired to form a circuit. The fuse is provided by setting at least one proper position divided on the circuit board in the vertical or inclined direction, and the fuse is provided on the notch for cutting the circuit conductor, and the end portion of the circuit conductor is straddled over the notch. Printing is performed so that the spaces are continuous. The fuse is, for example, lead, tin, silver, indium,
It is an alloy containing antimony, bismuth, etc., and its melting point is set to the allowable temperature of the electric equipment to which this circuit board is attached, such as an automobile blower. Specifically, the thickness t of the fuse is set to any value within the range of 0.1 mm to 1.0 mm, and the end of the circuit conductor in contact with the fuse has the same length and width. The length t is twice or more, and the distance between the end portions is also twice or more the value t. In addition, the circuit board is attached to the device in a non-horizontal form such as tilted or vertical, and after satisfying the above conditions, the lower end of both ends is wider than the upper one to make the area larger. Form. When the fuse is formed in this way, when the molten fuse drops downward, it can be held on the lower end portion, and the fuse does not remain between the end portions.
The circuit is reliably broken.

When the cream solder is used, the flux contained in the cream solder remains on the surface after the fuse is formed. Therefore, it is preferably left as it is without being removed by washing. By doing so, oxidation of the surface of the fuse is prevented, and the fuse is likely to be separated and aggregated at both ends during melting. Therefore, good operating characteristics can be obtained even when the fuse surface is used for a long time in an atmosphere where the surface of the fuse is easily oxidized. Although the end portion may be the conductor itself made of Ag-Pd or the like, it is desirable to form the end portion with a material having good solder wettability such as Ag or Cu when a conductor having poor solder wettability is used. .

Next, the result of the experiment conducted on the above example will be described.

(Example 1) A was placed on the enamel substrate 6 which was inclined as shown in FIG.
The g-Pd thick film conductor 8 is formed by printing and firing with a width of 1.0 mm, and a gap with an interval of at least 1.0 mm is provided therein.
A first fuse base 3 made of Ag having a length (L1) and a width (W1) of 2.0 mm is formed at one of the ends of the gap, and a gap (G) from the first fuse base 3 is 1. Width (W2) 1.0 mm, length (L2) 1.
A 0 mm second fuse base 5 is formed. Cream solder (Sn—Pb eutectic solder melting temperature 183 ° C.) was applied on the first fuse base 3 and the second fuse base 5 by using a metal mask having a thickness of 0.15 mm. Printing was performed so as to cover the fuse base 5, and after printing, this was heated and melted to form a fuse 2 having a thickness of 0.1 mm. Flux on the surface generated by heating is not washed, but attached. Such fuses 2 were produced at 100 locations, one on each of 100 circuit boards, and an operation test was conducted. In the experiment, the entire circuit board was heated at a rate of 10 ° C./min while the circuit board was inclined at 45 ° with the first fuse base 3 side facing downward. Then, 183 ℃
Part of the fuses 2 started to be melted at the point of reaching, and all the fuses 2 were melted within 5 seconds after the melting was started. Then, the melted fuse 2 was mainly accumulated on the lower first fuse base 3 and did not remain between the first fuse base 3 and the second fuse base 5, and it was confirmed that the circuit was reliably cut off.

FIG. 2 shows a comparative example in which the width of the ends of the circuit is the same for both the upper and lower ends, and the area of the solder-attached parts at the lower ends is the same as that of the upper part. Due to the small area underneath, molten solder cannot be held at the lower end during operation, resulting in an incomplete circuit break.

As described above, according to the fuse of the present invention, the thermal fuse is provided between the ends of the discontinuous portions of the vertically divided circuit on the vertically or inclined enameled substrate, Since the lower end of the fuse is wider than the upper end and has a larger area, when the ambient temperature rises above the allowable temperature of the device and the fuse melts, the fused fuse that tries to flow downward is lowered. Since it is possible to hold a larger amount at the ends of the fuse, the fused fuse is easily separated and aggregated at both ends,
The circuit is surely cut off.

[Brief description of drawings]

FIG. 1 shows an embodiment of a fuse according to the present invention A ...
A vertical plan view and a vertical side view before operation, B ... A vertical plan view and a vertical side view at the time of operation are shown. FIG. 2 shows a comparative example of a fuse in the case where the soldering ends of the upper and lower circuits have the same width and area. A ... Vertical plan view and vertical side view before operation, B ... Vertical plan view during operation and A vertical side view is shown. In the drawing, 2 ... Fuse, 3 ... First fuse base, 5 ... Second fuse base, 6 ... Enameled substrate, 8 ... Conductor.

Front Page Continuation (72) Inventor Kenichi Uruga 1-5-1, Kiba, Koto-ku, Tokyo Fujikura Electric Line Co., Ltd. In-house (56) Reference JP-A-2-100221 (JP, A) JP-A-1-80743 (JP, A) JP-A-2-288124 (JP, A)

Claims (1)

[Claims] 1. A thermal fuse for electrically connecting between ends of a discontinuous portion of a circuit divided in a vertical or inclined direction, wherein a lower end of the ends is wider than an upper end. A substrate-type thermal fuse that is used in a tilted or vertical state with an expanded area.